Comparison of surface roughness of oral hard materials to the threshold surface roughness for bacterial plaque retention: a review of the literature

Polishing of 4Y- and 5Y- zirconia: effects on roughness, color and gloss

OBJECTIVES

To investigate the effects of polishing systems on the roughness, gloss and color of two zirconia materials as a function of the rotational speed and number of polishing movements.

MATERIALS AND METHODS

Specimens (n = 8/group) from 4Y-TZP and 5Y-TZP were milled, diamond grinded and polished. The intraoral polishing varied in the number of polishing steps, the grain size and the matrix. Different number of polishing movements and rotation speed were used. Roughness (ISO25178-2:2021), gloss (ISO2813:2014) and color stability (ISO/CIE 11664-4:2019) were determined.

STATISTICS

Shapiro-Wilk, one-way analysis, Bonferroni, Pearson, variance analysis/intermediate sub-effects (α = 0.05).

RESULTS

Roughness Sa varied between 2.45 ± 0.93 µm and 6.47 ± 0.26 µm (4Y-TZP) and 2.31 ± 0.19 µm and 6.54 ± 0.22 µm (5Y-TZP). Maximum roughness Sz ranged from 32.92 ± 12.59 µm to 99.32 ± 19.87 µm (4Y-TZP) and 31.45 ± 3.02 µm to 90.75 ± 12.59 µm (5Y-TZP). Different gloss from 28.9 ± 4. 23 to 102.39 ± 18.63 GU (4Y-TZP) and 33.19 ± 3.68 to 101.28 ± 10.00 GU (5Y-TZP) was found. ΔE results ranged from 0.39 ± 0.34 to 6.30 ± 1.22 (4Y-TZP) and 0.87 ± 0.71 to 7.50 ± 1.67 (5Y-TZP). Significant (p ≥ 0.095) intermediate sub-effects were found.

CONCLUSIONS

Polishing led to a reduction in roughness, an increase in gloss and a significant change in color. Polishing had a stronger effect on 5Y-TZP.

CLINICAL RELEVANCE

The correct use of the polisher type (stages, binder) and its specific application (rotational speed, movements) can improve roughness, gloss and color variations.

Physical properties, microbial adhesion, and biocompatibility of additively manufactured ceramic-reinforced resin: Effect of zwitterionic polymer content

STATEMENT OF PROBLEM

Studies focusing on the effect of zwitterionic polymer content on the physical and biological properties of additively manufactured (AM) ceramic-reinforced resin for dental applications are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of different concentrations of 2-methacryloyloxyethyl phosphorylcholine (MPC) on the surface properties, mechanical properties, microbial adhesion, and cellular responses of ceramic-reinforced resins.

MATERIAL AND METHODS

Four different groups of AM resins filled with 60 wt% silicate-based composites and varying concentrations of MPC were prepared: 0 wt% (CRN), 1.1 wt% (CRM1), 2.2 wt% (CRM2), and 3.3 wt% (CRM3). Test specimens were fabricated from the resins using digital light processing and were tested for surface roughness (Sa and Ra), flexural strength and modulus, Vickers hardness (HV), and contact angle. The adhesion of oral microbes (Streptococcus mutans and Streptococcus gordonii), cytotoxicity, and cell viability of tested resins were also assessed. One-way analyses of variances and post hoc analyses using the Bonferroni correction and Tukey HSD tests were conducted to detect statistical differences among the groups (α=.05).

RESULTS

CRM2 exhibited significantly lower Ra (P=.020) and Sa (P=.013) values than CRM3, as well as greater flexural strength (P=.002) and modulus (P=.049), HV (P<.001), and contact angle (P=.015). CRM3 showed significantly lower flexural strength and modulus, HV, and contact angle than CRN (all P<.001). Both CRM2 and CRM3 exhibited significantly reduced adhesion of S. gordonii and S. mutans compared with CRN (all P<.001). Regardless of MPC content, the tested resins demonstrated biocompatibility and showed no signs of cytotoxicity.

CONCLUSIONS

Incorporating low-concentration MPC into AM ceramic-reinforced resins significantly changed the surface properties, mechanical properties, microbial adhesion, and biocompatibility. CRM2 provided an optimal balance between structural integrity and bacterial-repellent activity while maintaining biocompatibility.

Textured Intaglio Micropores Improve the Properties of 3D-Printed Zirconia Crowns

Monolithic zirconia crowns fabricated using computer-aided design and computer-aided manufacturing (CAD-CAM) via subtractive manufacturing (SM) exhibit limited bonding properties compared with other ceramics. Traditional methods such as air abrasion can improve bonding but may negatively affect the mechanical stability of zirconia. Nanoparticle jetting (NPJ), an emerging 3-dimensional-printing technology for zirconia restorations, offers the potential to create intricate structures, such as porous surfaces, with high precision. This study aimed to demonstrate that NPJ-manufactured monolithic zirconia crowns with an intaglio porous design can enhance bonding properties while maintaining mechanical strength. Standard NPJ zirconia crowns and commercially available SM zirconia crowns (SZC) were used as control groups. The surface roughness, fracture load, 2-body wear, and shear bond strength (SBS) were evaluated. The NPJ intaglio porous crowns (NIPC) with an intaglio porous design exhibited satisfactory and comparable fracture strength to SZC (within 1-mm occlusal thickness). Although the NIPC retained a relatively high original surface roughness, it demonstrated similar occlusal surface roughness, 2-body wear, and aging resistance to SZC after thorough polishing. Furthermore, the NIPC showed significantly superior intaglio surface roughness and SBS compared with conventionally air-abraded zirconia. Overall, this study successfully demonstrated the potential of NIPC as a viable restorative option, offering robust bonding and reliable mechanical properties.

Metrics for prosthetic cervical margin integrity assessment after dental CAD/CAM milling: a critical analysis from engineering viewpoint

Dental prostheses have significantly evolved due to advances in Computer Aided Design and Manufacturing (CAD/CAM) technology. CAD/CAM systems provide a variety of biomaterials like ceramics, Polymer-Infiltrated Ceramic Network (PICN), and composites, which are preferred for their mechanical and aesthetic properties. However, ceramics, despite their popularity, are brittle and prone to chipping during the machining process, impacting the prosthesis's clinical functions, aesthetics, biological integrity, and mechanical performance. Chipping, especially at thin cervical margin, can cause visible defects, poor sealing, and bacterial growth, reducing prosthesis lifespan. Milling factors influence cervical margin integrity. Chipping assessment involves understanding biomaterial mechanical and machinability characteristics regarding dimensional characterization of milled prosthesis shape. Thus, different type of metrics, based on biomaterial properties or dimensional measurement can be used to assess chipping phenomenon for milled dental ceramics. These metrics are both, based on experimental studies found in literature, and proposed by this paper authors to fill the existing lacks. The brittleness index, based on the ratio between hardness and fracture toughness, predicts susceptibility to chipping after milling. Unidirectional dimensional metrics like the Chipping Factor and weighted Chipping Factor characterize the chipping ratio of the cervical margin. Advanced 2D and 3D metrics, including chip projected area, total weighted chip projected area, and Surface Aspect Ratio, offer more detailed assessments. 3D analysis involves comparing scanned files with CAD models to compute chipped volumes. The aim of this paper is to propose a critical analysis from an engineering viewpoint on metrics used to assess cervical margin integrity for milled dental prosthesis.

Effect of implant abutment surface treatments on bacterial biofilm composition and structure

Background

For the long-term success of dental implants, implant abutment surface should promote the attachment of oral epithelial cells and reduce bacterial adhesion. Titanium nitride (TiN) coatings show antimicrobial properties. Nevertheless, there is a lack of clinical trials that assess the biofilm formation on TiN abutments in the context of clinical practice. Thus, the objective of this study was to evaluate the effect of different abutment surfaces (machined, TiN and TiN oxidized) on bacterial biofilm composition and structure.

Materials and methods

Implant abutments were connected to the dental implants. Bacterial communities were sampled at 1 and 60 days later. The relationship between surface, periodontal indices and bacterial community dynamics was assessed using 16S rRNA metagenomics. A total of 17 patients were involved in this study (14 included in final analyses: 15 machined, 16 TiN and 14 TiN oxidized abutments).

Results

No significant differences between surfaces were found considering taxa abundance, most alpha diversity metrics or community structure. Time showed a significant effect on diversity and also on the abundance of several bacterial taxa.

Conclusions

These results indicate that the effect of the three tested abutment surfaces on biofilm structure and composition was negligible, whereas patient and time exert strong influences on bacterial biofilm formation at different scales.

Nanocomposites soft and hard denture liners containing ZrO2 nanoparticles: An in vitro evaluation of surface roughness and Candida albicans adhesion

PURPOSE

To investigate the impact of zirconium dioxide nanoparticles (nano-ZrO2) addition to hard and soft liners on the surface roughness and Candida albicans adhesion.

MATERIALS AND METHODS

Nano-ZrO2 was added to hard and soft chairside reline material in two concentrations (2% wt. and 4% wt.) while an unmodified group of each liner acted as a control, (n = 10). Disc-shaped (10 × 1.3 mm) specimens of hard denture reline (N = 60) and soft denture reline (N = 60) materials were prepared (30/test). A noncontact profilometer was used for surface roughness measurement. A colony-forming unit (CFU/mL) was used to evaluate Candida albicans adhesion. Data was analyzed using ANOVA and a post hoc Tukey's test (α = 0.05).

RESULTS

No significant change in surface roughness was observed with nano-ZrO2 addition; however, the control groups showed the highest value while 2% nano-ZrO2 showed the lowest value. In comparison to the control groups, nano-ZrO2 addition to the hard and soft liners significantly reduced Candida albicans adhesion (p < 0.001), regardless of the concentration.

CONCLUSION

Incorporating nano-ZrO2 into hard and soft liner had no effect on surface roughness while its addition reduced Candida albicans adhesion. Using chairside soft and hard liners containing nano-ZrO2 is recommended to reduce the incidence of denture stomatitis (DS) among denture wearers.

The effect of cigarette smoking and heated tobacco products on different denture materials; an in vitro study

PURPOSE

This study compares the effect of conventional cigarette smoke versus heated tobacco on the discoloration, surface roughness, and bacterial colonization of different oral prosthesis materials.

MATERIALS AND METHODS

A total of one hundred and twenty disc-shaped samples made of four different denture base materials were prepared to represent different denture bases to assess the surface roughness and biofilm formation; group (CA): conventional heat-cured acrylic resin (Acrostone, Egypt), group (FA): flexible acrylic resin (Valplast International Corp, USA), group (TA): heat-cured acrylic resin reinforced with titanium nanoparticles (TA nanoparticles, Nanogate, Egypt), and group (PA): 3D printed acrylic resin (Nexdent, The Netherlands). Another sixty samples of artificial and 3D printed teeth were used to assess the color change: conventional ready-made acrylic resin teeth (Acrostone, Egypt) and 3D-printed acrylic resin teeth (Nexdent, The Netherlands). Each group was further divided according to the smoking method into three subgroups (n = 10): the no-smoking exposure group (C), the conventional smoking exposure group (CS), and the heated tobacco exposure group (HT). A custom-made smoking device was used to perform the experiment. Six hundred cigarettes/heets representing 30 days of medium smoking behavior (20 cigarettes/day) were used. The surface roughness of the disc-shaped samples was measured before and after the experiment using the JITAI8101 surface roughness tester (Beijing Jitai Tech Detection Device Co., Ltd, China), and the color parameters were assessed before and after the experiment using VITA Easyshade Advance 4.01 (VITA shade, VITA made, VITA).

RESULTS

The results showed that both conventional cigarette smoking and heated tobacco increased the surface roughness of the denture base disc samples. This change was statistically significant in all sample groups. Bacterial accumulation was also increased in all four denture base sample groups, with the heated tobacco causing greater bacterial accumulation than conventional cigarette smoke. Regarding the color change, conventional smoking caused a more significant color change than heated tobacco for both types of teeth used.

CONCLUSION

Both conventional smoke and heated tobacco affect dental materials adversely. Conventional cigarette smoking caused greater surface roughness and discoloration of the samples, while heated tobacco resulted in greater bacterial accumulation of study materials.

CLINICAL IMPLICATIONS

Increase dentists' and patients' awareness of the effects of different types of smoke.

Assessing the Effect of Toothpastes on Enamel Surface Roughness Using a Custom-Designed and Fabricated Toothbrush Simulator Device for Evaluation

The primary objective of this study is to emphasize the importance of maintaining optimal oral health through regular toothbrushing practices. To achieve this objective, a custom-designed electromechanical toothbrush simulator device was developed. This innovative tool enables researchers to investigate the impact of abrasive-based whitening toothpastes on enamel surface roughness compared to brushing without toothpaste. The device design is composed of multiple systems, including mechanical, motorization, and toothpaste irrigation components. The device incorporates various components, including mechanical, motorization, and toothpaste irrigation systems. Specifically, the mechanical aspect comprises fabricated metal parts, 3D printed elements, and a load cell for measuring brushing force. The motorization section integrates a microcontroller and a stepper motor, allowing for the adjustment of brushing cycles and speed. Furthermore, the toothpaste irrigation system employs a pump with adjustable speed, along with a toothpaste canister and a waste receptacle. By providing a controlled environment for evaluating the effects of different toothpaste formulations on enamel integrity, this simulator device contributes significantly to advancements in oral care research and product development.

Impact of air-polishing with erythritol on exposed root dentin: A randomized clinical trial

INTRODUCTION

The effects of air-polishing on exposed root dentin surfaces are largely unknown, as there are only few studies which show heterogeneous results. Thus, this study was to investigate roughness changes of exposed dentin surfaces after air-polishing and the influence of subsequent polishing with cup and paste.

METHODS

Totally 54 teeth with exposed root dentin surfaces were treated using a split-mouth design by either air-polishing with erythritol and a rubber cup with polishing paste on the test side, or rubber cup and paste alone. Teeth were finally cleaned using a sonic tooth brush. Impressions were taken at relevant time points and replicated using epoxy resin. The resulting casts were profilometrically analysed to obtain the average surface roughness (sRa) and maximum peak-to-valley height (sRz), which are given as the mean ± standard deviation in μm.

RESULTS

After air-polishing, in comparison to the baseline, there was a slight but significant increase in sRa (0.168 ± 0.143, p < 0.001), but sRz did not change (-0.471 ± 4.857, p = 0.936). Subsequent polishing with cup and paste and cleaning with a sonic toothbrush did not reduce the surface roughness (sonic toothbrush-air-polishing, sRa -0.044 ± 0.081, p = 0.218; sRz -0.551 ± 3.563, p = 0.903).

CONCLUSION

The use of erythritol led to a slight increase in the roughness of the dentin surface, which was not reduced by polishing with a cup and paste. Polishing paste did not seem to conceal surface irregularities.

Surface properties and biofilm formation on resins for subtractively and additively manufactured fixed dental prostheses aged in artificial saliva: Effect of material type and surface finishing

STATEMENT OF PROBLEM

Additive manufacturing (AM) and subtractive manufacturing (SM) have been widely used for fabricating resin-based fixed dental prostheses. However, studies on the effects of material type (AM or SM resin) and surface finishing (polishing or glazing) on the surface properties and biofilm formation are lacking.

PURPOSE

The purpose of this in vitro study was to investigate the effects of material type and surface finishing on the surface roughness, wettability, protein adsorption, and microbial adhesion of the AM and SM resins marketed for fixed restorations under artificial saliva-aged conditions.

MATERIAL AND METHODS

Disk-shaped specimens (∅10×2 mm) were fabricated using 3 types of resins: AM composite resin with fillers (AMC), AM resin without fillers (AMU), and SM composite resin with fillers (SMC). Each resin group was divided into 2 subgroups based on surface finishing: polished (P) and glazed (G). Therefore, 3 polished surface groups (AMCP, AMUP, and SMCP) and 3 glazed surface groups (AMCG, AMUG, and SMCG) were prepared. Specimens were then categorized according to aging condition in artificial saliva. Surface roughness (Ra and Sa), contact angle, surface free energy (SFE), protein adsorption, and microbial adhesion were measured. The data were analyzed using a nonparametric factorial analysis of variances and post hoc tests with Bonferroni correction (α=.05).

RESULTS

When nonaged, significant interactions between material type and surface finishing were detected for Ra, contact angle, SFE, protein adsorption, and microbial adhesion (P≤.008). AMCP showed higher Ra and microbial adhesion than AMUP and SMCP, and higher contact angle and protein adsorption than SMCP (P<.001). AMCG had lower SFE than AMUG (P=.005) and higher bacterial adhesion than SMCG (P<.001). AMC had higher Sa than AMU and SMC (P≤.006). When aged, significant interactions between material type and surface finishing were detected for Ra, Sa, protein adsorption, and microbial adhesion (P≤.026). The contact angle and SFE were significantly affected only by the material type (P≤.001), as AMC exhibited higher wettability than SMC (P≤.004). AMCP had higher Ra and microbial adhesion than AMUP and SMCP (P≤.003). AMCP had higher Sa and protein adsorption than SMCP (P≤.004). AMCG showed lower Ra and higher protein adsorption than AMUG (P≤.001).

CONCLUSIONS

Both material type and surface finishing significantly affected surface properties and biofilm formation. AMCP exhibited higher surface roughness, protein adsorption, and microbial adhesion compared with SMCP. Glazing may reduce the differences in surface-biofilm interactions between AMC and SMC.

Mechanical properties of a polylactic 3D-printed interim crown after thermocycling

Polylactic acid (PLA) has garnered attention for use in interim dental restorations due to its biocompatibility, biodegradability, low cost, ease of fabrication, and moderate strength. However, its performance under intraoral conditions, particularly under heat and moisture, remains underexplored. This study evaluated the mechanical properties of PLA interim crowns compared with those of polymethylmethacrylate (PMMA) and bisphenol crowns under simulated intraoral conditions with thermocycling. Three CAD/CAM polymers-PMMA (milling), PLA (fused deposition), and bisphenol (stereolithography)-were tested for fracture resistance, hardness, and surface roughness. For fracture strength, 25 crowns from each group were cemented onto dies. The Shore D hardness and surface roughness were measured on round discs before and after 10,000 thermocycles (5°C/55°C). The surface topography was assessed via scanning electron microscopy. PMMA exhibited the highest fracture strength (2787.93 N), followed by bisphenol (2165.47 N) and PLA (2088.78 N), with no significant difference between the latter two. PMMA and bisphenol showed vertical fractures and cracks, whereas PLA showed crown tearing or die deformation. Bisphenol had the highest Shore D hardness, followed by PMMA and PLA, with no significant changes after thermocycling. The surface roughness (Ra) was lowest for bisphenol and similar between PMMA and PLA. The roughness (Rz) increased from bisphenol to PMMA to PLA. The roughness of the PMMA remained unchanged after thermocycling, whereas the Ra but not the Rz of the PLA increased. Bisphenol showed a significant increase in both Ra and Rz (p<0.0001). In conclusion, PLA interim crowns demonstrated mechanical properties comparable to those of conventional PMMA and bisphenol crowns after thermocycling.

Comparison of the Performance Parameters of BioHPP® and Biocetal® Used in the Production of Prosthetic Restorations in Dentistry-Part II: Physicochemical and Microbiological Tests: An In Vitro Study

The natural aging process of the human organism leads to both physiological and pathological changes, including tooth loss. This requires dental prosthetic interventions aimed at restoring patients' quality of life. The use of such prostheses necessitates selection of sufficiently strong, aesthetic and biocompatible materials, which also offer ease of shaping. The market for materials used in prosthetic applications offers a wide array of options; however, selection of the most suitable material for specific clinical scenarios can be challenging for dental professionals. This paper continues the comprehensive investigation of the physiochemical and mechanical/functional properties of two commonly used prosthetic-Biocetal and BioHPP-offering a comparative analysis of their characteristics to provide valuable insights for dentists and prosthodontists. The study focuses on in vitro analyses of physiochemical parameters, including density, water sorption, contact angle, and surface roughness. The structure of the materials was examined via scanning electron microscopy. Additionally, microbiological studies were performed using strains of Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa and Candida albicans. Statistical analysis was performed using Shapiro-Wilk test, Q-Q plot analysis, Grubbs test, and Student's T-test (p < 0.05). The findings indicate that BioHPP demonstrates superior physiochemical and microbiological properties. However, Biocetal exhibit better surface characteristics. Despite its high performance, BioHPP presents certain drawbacks, which may influence dentists' material choice in specific clinical cases, particularly for certain prosthetic restorations.

The Efficacy of 3 Bleaching Methods on Stained Polymer-Based CAD/CAM Materials

INTRODUCTION AND AIMS

This study aimed to investigate the efficacy of 3 bleaching methods on stained polymer-based CAD/CAM blocks in terms of surface roughness, hardness stability, discolouration reduction and susceptibility to re-staining following bleaching.

METHODS

Two-mm-thick slabs (N = 128) were prepared from CeraSmart (CS), Grandio Blocs (GB), Vita Enamic (VE), and direct resin composite GrandioSO (RC). Coffee-stained specimens (n = 8) were subdivided into bleaching (BL) groups: in-office bleaching (OB), home bleaching (HB), whitening mouthwash (MW), and a control group with 14-day storage in water (CL). Measurements of roughness (Ra), Vickers hardness (HV), and colour parameters (ΔE00, ΔL*, Δb*) were taken before and after BL. Then, all the bleached specimens were re-stained to determine their stain susceptibility. Repeated measures of ANOVA, Pearson's χ2 test, and multiple post hoc tests were performed (α = 0.05).

RESULTS

HB was more effective in whitening in terms of achieving minimal residual colour (-0.87 to 0.7) and greater resistance to re-staining (0.41 to 0.89). MW resulted in an increased lightness (ΔL*) of all materials (1.96 - 2.30). However, MW increased the roughness of VE (0.8 µm) and RC (0.4 µm), compared to their baseline measurements (0.057 µm and 0.087 µm, respectively, p = 0.003). All the BL treatments resulted in a greater hardness reduction (14.4% to 18.1%) in the RC than in the other materials.

CONCLUSION

The investigated polymer-based materials and modes of bleaching treatment influenced the bleaching efficacy. For CAD/CAM blocks, in-office bleaching and whitening mouthwash reduced the discolouration but adversely affected their roughness and hardness compared to home bleaching. Home bleaching proved to be the least susceptible to re-staining.

CLINICAL RELEVANCE

Knowing how a specific bleaching product affects the colour, roughness and hardness and consequent susceptibility to staining of 4 studied polymer-based materials that represent pre-existing restorations would impact the consideration of bleaching treatment.

Surface Roughness and Color Stability of Conventional and Bulk-Fill Resin Composite with S-PRG Fillers After Coffee Exposure: An in-vitro Study

Objective

This study aimed to evaluate the in vitro effects of coffee exposure on the color and roughness of conventional and bulk-fill resin composites, with and without surface pre-reacted glass-ionomer (S-PRG) filler.

Methodology

Forty-eight cylindrical samples (Ø6 mm × 2 mm) were prepared and categorized as follows (n = 12 per group): conventional nano-hybrid (Tetric N-Ceram, Ivoclar); nano-hybrid with S-PRG filler (Beautifil II, Shofu); bulk-fill (Tetric N-Ceram Bulk Fill, Ivoclar); and bulk-fill with S-PRG filler (Beautifil Bulk Restorative, Shofu). The samples were assessed for surface roughness (Ra, μm), color coordinates (CIE Lab), and overall color change (ΔEab, ΔE00). Measurements were taken at baseline and after 7 days of coffee immersion (pH = 4.95). Data were analyzed using generalized linear models, Kruskal-Wallis, Dunn, and paired Wilcoxon tests (α = 0.05).

Results

After the coffee exposure, all resin composites exhibited a significant decrease in L* (towards black), an increase in a* (towards red), an increase in b* (towards yellow), and a higher Vita color score (p < 0.05). Tetric N-Ceram demonstrated the lowest roughness values post-exposure; however, a significant increase in roughness over time was observed only for Tetric N-Ceram Bulk Fill (p < 0.05). For ΔEab, Beautifil Bulk Restorative and Tetric N-Ceram showed higher values compared to Beautifil II. For ΔE00, a significant difference was noted between Beautifil Bulk Restorative and Beautifil II (p < 0.05).

Conclusion

Resin composites with S-PRG fillers exhibited similar pigmentation dynamics to conventional composite but showed greater surface roughness after exposure to coffee. Considering the S-PRG materials, the bulk-fill version is more susceptible to staining.

Effect of post-processing on the surface, optical, mechanical, and dimensional properties of 3D-printed orthodontic clear retainers

OBJECTIVES

To address the high surface roughness and poor optical properties of three-dimensional (3D) printed orthodontic clear retainers, an alternative post-processing protocol was investigated with the goal of achieving improved surface, optical, and mechanical properties while preserving dimensional accuracy.

MATERIALS AND METHODS

Samples were prepared from two biocompatible methacrylate-based 3D-printing resins (Formlabs Dental LT Clear V2, NextDent OrthoFlex) and one thermoplastic material (Duran). For the 3D-printed resins, one group was post-processed by rinsing in isopropyl alcohol, while another group was centrifuged before post-curing in glycerine. Three different testing conditions were used: dry, wet (24-h water immersion), and aged (thermocycling for 10,000 cycles). Surface characteristics were evaluated qualitatively and quantitatively. Optical properties were assessed for transparency and colour stability, while mechanical properties were elicited from tensile and microhardness tests. Water sorption and solubility were calculated. Samples mounted on a dental model were scanned by micro-computed tomography to measure thickness and gap width.

RESULTS

3D-printed samples post-processed by centrifugation showed significantly decreased surface roughness and improved visible light transmission, colour stability, tensile strength, and hardness. The centrifuged samples showed significantly increased thickness, while designing an offset equal to this thickness improved the adaptation.

CONCLUSIONS

Post-processing by centrifugation produces surface coating that enhances the surface and optical properties of the 3D-printed orthodontic retainers, while curing in an oxygen-free environment improves their mechanical properties. Design modifications may be necessary for this protocol to ensure proper adaptation to the dentition.

CLINICAL RELEVANCE

Proper design and post-processing protocols are necessary to achieve the desired properties of orthodontic clear retainers.

Effect of Staining and External Bleaching on the Color Stability and Surface Roughness of Universal-Shade Resin-Based Composite

Aim

This study evaluated the color stability and surface roughness of two universal-shade compared to two nanohybrid composites after staining and external bleaching with 40% hydrogen peroxide.

Methods

Two universal shade resin-based composites and two nanohybrid composites were tested. Twenty disc-shaped specimens from each material were fabricated and divided into two subgroups: one group was stained and bleached (staining group) and the other received bleaching treatment only (control group). The staining group was stained with coffee solution for 24 h. Subsequently, each sample of all four materials was bleached using an in-office bleaching gel using 40% hydrogen peroxide. Color measurements were performed using a spectrophotometer to obtain the International Commission on Illumination parameters, L*; a*; and b* for each of the following periods: baseline, after bleaching, and two weeks after bleaching for the control group. The staining group was examined at baseline, after staining, after bleaching, and two weeks after bleaching. Surface roughness (Ra) of all the materials after each treatment step were also recorded. The data was statistically analyzed using SPSS 26.0 statistical software. Changes were considered statistically significant at P = 0.05.

Results

Descriptive statistics (means and standard deviations) were used to describe color measurements and surface-roughness values. Two-analysis of variance and one-way analysis of variance were used to compare the mean values of surface roughness, L*a*b*and ΔE00 values. Statistically significant differences and clinically acceptable ΔE00 were observed between all materials during the different stages in color measurements, whereas the surface roughness was significantly different for each study material and treatment mode.

Conclusion

Staining with coffee solution and external bleaching produced acceptable color changes for all materials tested. Staining and bleaching increased the surface roughness values of the tested resin-based composites.

Determination of streptococcus mutans retention in acidic and neutral pH artificial saliva environment of all-ceramic materials with different surface treatment

BACKGROUND

Although surface finishing processes are effective against Streptococcus mutans biofilm, the mechanism of action of saliva with different acidity values ​​has not been studied in detail. This study aims to produce four different all-ceramic materials in a single session with CAD/CAM devices and apply two different surface finishing processes, glazing and polishing, and then determine the retention of Streptococcus mutants on the surfaces of the materials in saliva with varying levels of acidity.

METHODS

Zirconia-reinforced lithium silicate (Vita Suprinity, Vita Zahnfabrik, Bad Saöckingen, Germany), monochromatic feldspar (Vitablocs Mark 2, Vita Zahnfabrik, Bad Saöckingen, Germany), leucite glass ceramic (IPS Empress CAD, Ivoclar Vivadent, Liechtenstein), and monolithic zirconia (Incoris TZI (Cerec) Sirona, Germany) were used in the study. The surface roughness values ​​of all samples were measured with a profilometer before the application of S. mutans biofilm. A modified Fusayama artificial saliva model was prepared to reflect the oral environment. S. mutans bacterial biofilm growth rate was determined for each group with tetrazolium dye (MTT) assay and the colony-forming unit (CFU/mL). Scanning electron microscopy was used to compare the efficacy of all-ceramic materials against bacterial biofilm.

RESULTS

The surface treatment applied with polishing rubber (Ra 0.18-0.33) resulted in a slightly less rough surface than the glaze (Ra 0.32-0.35) treatment. S. mutans showed less retention in ceramic samples treated with the pH 5 saliva compared to the pH 7 ones. When this group's percentage growth rates, colony-forming units, and scanning electron microscopy images colored with ImageJ were examined, the Glaze application reduced growth (65.02 - 91.38%) and colony formation (6.1 × 1010 - 7.8 × 1010) in all samples except for Vita Suprinity compared to the Polishing Rubber application (p < 0.05).

CONCLUSION

The pH of the salivary, the surface roughness, and the chemical content of the ceramic samples may directly affect the S. mutans biofilm formations. The Polishing Rubber of the surface treatment type should only be suggested for Vita Suprinity, whereas the Glaze of the surface treatment type should be proposed for Vita Block Mark II and InCoris TZI in an acidic salivary environment. A surface treatment method other than Glaze and Polishing Rubber should be preferred for IPS Empress CAD.

Evaluation of one versus two glaze firings on the color stability and mechanical properties of an extrinsically characterized monolithic CAD-CAM lithium disilicate glass ceramic

PURPOSE

To evaluate the effects of 1 versus 2 glaze firings on the color and mechanical properties of an extrinsically characterized lithium disilicate ceramic after thermal cycling, brushing, or both.

MATERIALS AND METHODS

Eighty specimens were divided into 2 groups: 1 glaze firing (GL1) and 2 glaze firings (GL2). Each group was subdivided into 4 groups (n = 10), according to the experimental conditions: thermal-cycling, brushing, thermal-cycling + brushing, and immersion in distilled water (control). Color variation, surface roughness, and Vickers microhardness were analyzed before each designated experiment and after the simulated periods of 2.5, 5, and 10 years. Three-way mixed ANOVA was used for all outcomes, followed by 1-way ANOVA, repeated measures 1-way ANOVA, Bonferroni post hoc test, and t-test to check for statistical differences (α = 0.05).

RESULTS

Thermal cycling generated greater color changes in the GL1 group at 2.5 and 5 years (p < 0.001; p = 0.013). Brushing generated color changes in GL1 at 5 years (p = 0.003) and in GL2 at 10 years (p = 0.017). Regarding surface roughness, the GL1 group suffered alterations in thermal cycling + brushing at 5 years. In the control group, the GL1 group exhibited higher roughness values than GL2 (p < 0.05). Most of the groups experienced an increase in microhardness at 2.5 years (p < 0.05). In the GL1 group, thermal-cycling increased the microhardness at 5 years (p = 0.006); at 5 and 10 years, the GL1 group had a higher microhardness than the GL2 in thermal-cycling + brushing (p < 0.05).

CONCLUSION

Ceramics with 1 glaze firing showed greater color, roughness, and microhardness changes compared to those submitted to 2 firings.

Effect of toothbrushing on surface roughness and gloss of CAD-CAM versus conventional interim materials with different surface treatments

STATEMENT OF PROBLEM

Characterizing interim restorations promotes esthetics. However, studies on the effects of characterization materials on the surface roughness and gloss of interim materials after toothbrushing are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the surface roughness and gloss of 5 different interim materials with different surface treatments after 1 year of simulated toothbrushing.

MATERIAL AND METHODS

Cuboid specimens (10×12×2 mm) were fabricated from each interim material: autopolymerized polymethyl methacrylate (UNIFAST Trad), autopolymerized bis-acryl composite resin (Protemp 4), light-activated composite resin (REVOTEK LC), milled polymethyl methacrylate block (DD provi P HI), and 3-dimensionally printed methacrylate oligomer (Nextdent C&B MFH). Each material was divided into 3 groups based on surface treatment (n=10): polishing, application of Lite Art and Resin Glaze, and application of OPTIGLAZE color. The specimens were subjected to 5000 and 10000 cycles of toothbrushing. The surface roughness and gloss were measured and separately analyzed by using 3-way repeated measures ANOVA (α=.05).

RESULTS

Significant interactions of the surface roughness and gloss among interim materials, surface treatments, and toothbrushing durations were found (P<.001). After 5000 and 10000 cycles, each polished material showed no significant difference in surface roughness compared with baseline: Protemp 4 (P>.999), REVOTEK LC (P>.999, P=.922), and Nextdent C&B MFH (P>.999), except for UNIFAST Trad and DD provi P HI (P<.001). Coating with Lite Art and Resin Glaze, as well as OPTIGLAZE color, significantly reduced surface roughness after both 5000 and 10000 cycles for all materials (application of Lite Art and Resin Glaze with UNIFAST TRAD (P<.001), Protemp 4 (P<.001), REVOTEK LC (P<.001), DD provi P HI (P<.001), and Nextdent C&B MFH (P<.001, P=.002), and application of OPTIGLAZE color with UNIFAST TRAD (P<.001), Protemp 4 (P<.001), REVOTEK LC (P<.001, P=.002), DD provi P HI (P<.001), and Nextdent C&B MFH (P<.001, P=.008)). Specimens with these treatments also exhibited significantly better gloss compared with the polished specimens (P<.001).

CONCLUSIONS

After 5000 to 10000 cycles of toothbrushing, Protemp 4, REVOTEK LC, and Nextdent C&B MFH, interim materials containing fillers, exhibited smoother surfaces compared with UNIFAST Trad and DD provi P HI, interim materials without fillers. Coating of all materials reduced surface roughness and increased gloss. After 5000 to 10000 cycles of toothbrushing, the surface roughness of each material remained stable; while the gloss decreased slightly, it remained within clinically acceptable levels.

Surface Roughness and Color Stability of Newly Developed Resin Composites With Color Adjustment Potential After Immersion in Staining Solutions

The aim of this this study was to evaluate the surface roughness and color stability of resin composites (RCs) with color adjustment potential (CAP): Omnichroma (OM), (Tokuyama Dental, Tokyo, Japan); Neo Spectra ST (NS) (Dentsply Sirona, York, PA,USA); and Charisma Diamond One (CD) (Kulzer, Hanau, Germany), compared to a conventional RC, Filtek Z350XT (FZ) (3M ESPE, St. Paul, MN,USA), after immersion in three staining solutions, cola, coffee, and black tea, with distilled water as a control. Forty specimens (8 mm diameter x 2 mm thickness) were prepared for each RC material and divided into subgroups (n=10/group) based on the immersion solution. Surface roughness was measured at baseline and after 21 days of immersion using a non-contact optical profilometer. Color change (ΔE00) was evaluated at baseline, 1, 7, and 21 days with a spectrophotometer. The results showed that FZ demonstrated the lowest surface roughness (0.14), significantly differing from that of the other RCs with CAP (p<0.05), while no significant differences in surface roughness were observed between RCs with CAP (p>0.05). There were no significant changes in surface roughness before and after immersion in various solutions. The results for color change (ΔE00) were statistically significant. Neo Spectra ST showed the lowest tendency for color change, while Filtek Z350XT displayed a moderate potential, and Omnichroma and Charisma Diamond One showed the highest potential for color change.

Comparison of physical, mechanical, and optical properties between thermoplastic materials and 3-dimensional printing resins for orthodontic clear retainers

INTRODUCTION

This study investigated the physical, mechanical, and optical properties of 3-dimensional (3D) printing resins compared with thermoplastic materials to evaluate their suitability for the fabrication of orthodontic clear retainers.

METHODS

Samples were prepared from thermoplastic sheets (Duran [Scheu-Dental GmbH, Iserlohn, Germany] and Zendura [Bay Materials LLC, Fremont, Calif]) and biocompatible 3D-printing resins (Dental LT Clear V2 [Formlabs Inc, Somerville, Mass] and OrthoFlex [Nextdent BV, Soesterberg, The Netherlands]) according to the manufacturer's instructions. The materials were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, and water sorption tests. Mechanical properties were assessed by tensile tests and hardness under 3 different conditions: dry, wet (24-hour water immersion), and aged (thermocyled for 10,000 cycles). Surface characteristics were qualitatively and quantitatively evaluated by scanning electron microscopy and 3D confocal imaging, respectively. Optical properties were assessed by ultraviolet-visible spectroscopy and color stability tests by immersion into various staining solutions.

RESULTS

The mechanical properties of the 3D-printing resins were more markedly altered in different testing conditions (dry, wet, and aged) than in thermoplastic materials. The surface roughness, transparency, and color stability of 3D-printing resins are significantly inferior, especially NextDent OrthoFlex.

CONCLUSIONS

The evaluated 3D-printing resins are more brittle and less ductile compared with the thermoplastic materials. The 3D-printing resins also do not meet the clinical thresholds of surface roughness and optical properties for the fabrication of orthodontic clear retainers. Further postprocessing of the 3D-printing resins may be required to improve these properties.

Structure and composition of early biofilms formed on dental implants are complex, diverse, subject-specific and dynamic

Biofilm-associated peri-implant infections pose a major problem in modern medicine. The understanding of biofilm development is hampered by biofilm complexity and the lack of robust clinical models. This study comprehensively characterized the dynamics of early biofilm formation in the transmucosal passage of implant abutments in 12 patients. Biofilm structures and compositions were complex, diverse, subject-specific and dynamic. A total of 371 different bacterial species were detected. 100 phylogenetically diverse unnamed species and 35 taxonomically diverse disease-associated species comprised an average 4.3% and 3.1% of the community, respectively, but reached up to 12.7% and 21.7% in some samples. Oral taxa formed numerous positive associations and clusters and were characterized by a high potential for metabolic interactions. The subspecies diversity was highly patient-specific and species-dependent, with 1427 ASVs identified in total. The unprecedented depth of early biofilm characterization in this study will support the development of individualized preventive and early diagnostic strategies.

Roughness profile and surface roughness after toothbrushing and degree of conversion of bulk-fill resins

The aim of this study was to assess roughness profile and surface roughness after simulated toothbrushing cycles, as well as the degree of conversion (DC) of bulk-fill resin composites at different depths. Forty nine composite discs were made from three low-viscosity bulk-fill resins (Filtek Bulk-Fill Flowable/3M Oral Care - FBF, Beautifil-Bulk Flowable/Shofu Inc. - BBF and Surefill SDR Flow/Dentsply Caulk - SDR), three high-viscosity bulk-fill resin composites (Filtek Bulk-Fill Restorative/3M Oral Care - FBR, Beautifil-Bulk Restorative/Shofu Inc. - BBR and Tetric EvoCeram Bulk Fill/Ivoclar Vivadent - TEB) and one conventional composite (Filtek Supreme Ultra/3M Oral Care - FSU) (n=7), using addition silicon molds (2 mm thick x 10 mm diameter). The roughness profile (Rv) and surface roughness (Sa) were analyzed after 30,000 brushing cycles using confocal laser scanning microscopy. Five samples (4 mm thick x 2 mm diameter) were produced per resin composite and light-cured for 20 seconds using a LED-curing unit. After 24 hours at 37oC, DC of samples was evaluated at four depths, using a confocal Raman microscope. The data were analyzed by ANOVA and Tukey post hoc multiple-comparison tests (α = 0.05). The Rv values of FSU were lower than those obtained for BBR and BBF. The toothbrushing significantly decreased the Sa for all composites. The DC was significantly reduced at 4 mm depth. Toothbrushing changed composite surface of all materials, especially for BBR and BBF. Composites were not able to maintain the DC values shown at the top compared with those at the bottom (4 mm depth).

In Vitro Evaluation of the Effectiveness and pH Variation of Dental Bleaching Gels and Their Effect on Enamel Surface Roughness

Objectives: Potential adverse effects and pH-related effectiveness of bleaching agents have raised some concerns. The aim of this study was to compare three bleaching agents containing hydrogen peroxide (HP) and carbamide peroxide (CP) in terms of whitening effectiveness, pH variation, and changes in enamel surface roughness. Methods: After controlled staining with a black tea solution, 42 human enamel specimens underwent bleaching treatment using the following agents: HP 40%; HP 35%; CP 16%. Color changes were evaluated according to the CIEDE2000 system. Gel pH was measured before and after each application. Surface roughness (Sa) was assessed through optical 3D profilometry before and after bleaching treatment. Results: The whitening effectiveness was similar for HP 40% and HP 35% while CP 16% had significantly lower results. HP 40% showed a remarkable pH acidification (-0.41), while HP 35% and CP 16% showed a mild increase in pH values (+0.26 and +0.03, respectively), and the differences between HP 40% and HP 35% and between HP 35% and CP 16% were statistically significant. Sa slightly decreased in all groups after bleaching, with no significant differences among them and a significant difference in HP 40% before and after treatment. Conclusions: Similar bleaching results were achieved regardless of pH and HP concentration for HP-based agents, while a lower bleaching effect was observed for the less concentrated CP-based agent, as anticipated. Higher HP and greater tendency to pH instability induced more pronounced modifications of surface roughness. This in vitro study suggests that bleaching gels with neutral and stable pH ensure good bleaching effectiveness and are less likely to cause enamel surface changes.

TiO2 nanotubes incorporated into a glaze-coating ceramic: surface roughness, color, and antibiofilm activity

This study evaluated the surface roughness, color change, and antibacterial effect of a ceramic glaze enhanced with TiO2 nanotubes (n-TiO2). n-TiO2 (0, 2, 2.5, and 5 wt%) was added to a ceramic glaze powder, applied to the surface of forty feldspathic ceramic specimens, and sintered. The surface roughness average (Ra) before glaze application (T0) and after glaze crystallization (T1) was measured using a profilometer. The colorimetric alteration was determined by CIEDE2000 (ΔE00) and CIELab (ΔEab), and the whiteness index for dentistry (ΔWID). The antibacterial effect against S. mutans and S. sanguinis was evaluated (CFU/mL). Data were analyzed by two-way repeated-measures ANOVA, followed by the Bonferroni test (α = 0.05). No differences in ΔEab and ΔE00 were observed among groups (p > 0.05), and ΔWID was only affected by 5% n-TiO2. All groups surpassed the perception thresholds of 1.8 (ΔE00) and 2.3 (ΔEab). At T0, no Ra differences were detected among groups (p > 0.05). In T1, Ra decreased (p < 005) compared to T0, but 5% n-TiO2 increased roughness compared to the control group (without n-TiO2). The incorporation of n-TiO2 into the glaze powder did not impair bacteria adhesion, and no differences in biofilm formation were found among the concentrations (p < 0.05). The ceramic covered with a glaze containing 5% n-TiO2 caused minimal interference in the color and roughness with no effect on biofilm formation.

Comparison of Mechanical and Surface Properties between Conventional and CAD/CAM Provisional Restorations

OBJECTIVE

 This study compared the flexural strength, surface hardness, and surface roughness of conventional, milled, and three-dimensional (3D)-printed provisional restorations.

MATERIALS AND METHODS

 Bar-shaped polymethyl methacrylate (PMMA) specimens (25 × 2 × 2 mm3) and disc-shaped specimens (9 × 2 mm2) were fabricated using three different techniques (n = 10/group): conventional (SR Ivocron C&B, Ivoclar Vivadent, Schaan, Liechtenstein), milling (Aidite Temp PMMA Blocks, Aidite, Qinhuangdao, China), and 3D printing (Asiga DentaTOOTH, Asiga, Sydney, Australia). Flexural strength was evaluated using a universal testing machine until fracture occurred. Vickers hardness and surface roughness tests were performed on the disc-shaped specimens using a micro-Vickers hardness tester and atomic force microscopy, respectively.

STATISTICAL ANALYSIS

 Data were statistically analyzed using one-way ANOVA. The post hoc Tukey's honest significant difference was conducted to compare the differences value between groups (p < 0.05).

RESULTS

 The milled computer-aided design/computer-aided manufacturing (CAD/CAM) provisional restorative material exhibited a significantly higher flexural strength (125.16 ± 6.83 MPa) compared with both the traditional (109.74 ± 14.14 MPa) and 3D-printed (71.09 ± 9.09 MPa) materials (p < 0.05). The conventional material had a higher Vickers hardness (19.27 ± 0.41 kgf/mm2) compared with the milled (18.53 ± 0.32 kgf/mm2) and 3D-printed (17.80 ± 1.85 kgf/mm2) materials, though the difference was statistically significant only between the conventional and 3D-printed groups. The surface roughness of the milled CAD/CAM material (8.80 ± 2.70 nm) was significantly lower than that of the 3D-printed material (24.27 ± 9.82 nm) (p < 0.05).

CONCLUSION

 The provisional restorations fabricated using milled PMMA technology provide adequate flexural strength, surface hardness, and low surface roughness, offering a viable alternative for creating provisional restorations.

Surface characteristics and bacterial adhesion on single-shade composite resins: A comparative in vitro study of one-step versus multi-step polishing techniques

This study evaluated the effects of two polishing systems, OptraGloss (G; one-step) and OptiDisc (D; multi-step), on surface roughness (SR), contact angle (CA), surface free energy (SFE), and bacterial adhesion on three single-shade composite resins: Omnichroma (O), ZenChroma (Z), and Charisma Diamond One (C). Data for SR, CA, SFE, and adhesion of Streptococcus mutans (S. mutans) and Streptococcus mitis (S. mitis) were analyzed using one-way ANOVA, Tukey post-hoc tests, and Pearson correlation (α=0.05). Multi-step polishing groups (OD, ZD, and CD) exhibited significantly lower SR (0.18, 0.18, and 0.29 µm, respectively) compared to OG (0.46 µm), ZG (0.30 µm), and CG (0.44 µm) (p<0.05). The highest CA was observed in ZG (91.6º). S. mitis adhesion was greater than S. mutans in all groups except OG. A significant correlation was observed between SR and the adhesion of S. mutans (r=0.693, p<0.001). Polishing systems applied to single-shade composite resins did not impact the SFE but affected SR, and bacterial adhesion.

Effect of chairside polishing systems on the surface roughness of different CAD-CAM denture base materials

STATEMENT OF PROBLEM

Adjusting and polishing a denture base affects surface roughness and, consequently, microbial adhesion. Since various computer-aided design and computer-aided manufacturing (CAD-CAM) denture base materials are available, the efficiency of chairside polishing systems to achieve a proper surface roughness should be investigated.

PURPOSE

The purpose of this in vitro study was to compare the surface roughness of milled and 3-dimensional (3D) printed denture base materials with that of heat-polymerized acrylic resin after the use of 2 different chairside polishing systems.

MATERIAL AND METHODS

Heat-polymerized (control), milled, and 3D printed denture base materials were tested. Laboratory polished and unpolished denture bases served as positive and negative controls. Specimens were divided into 2 chairside silicone polishing systems (AcryPoint system and Exa technique). Surface roughness was measured before and after polishing. Surface morphology of the unpolished and polished specimens was observed via scanning electron microscopy. The surface hardness of unpolished specimens was measured using a Vickers hardness tester. Stress-strain behavior of the silicone matrix and abrasive filler size of each polisher was assessed. The effects of denture base materials and polishing systems on surface roughness and hardness were evaluated using 1-way, 2-way, and repeated measures analyses of variance (ANOVA) (α=.05), along with Weibull proportional hazards regression to assess the likelihood of achieving clinically acceptable surface roughness. The Spearman correlation assessed the relationship between the hardness of unpolished denture bases and final surface roughness.

RESULTS

The surface roughness of all denture bases decreased with increased polishing duration, reaching a plateau after 60 seconds. For the heat-polymerized and milled dentures, the Exa technique consistently yielded lower roughness than the AcryPoint system (P<.001). Conversely, both polishing systems produced comparable surface roughness on the 3D printed denture base. The Vickers hardness of the unpolished milled denture was significantly higher than of the others (P=.010). The stress-strain behavior of the polisher matrix revealed distinct characteristics between coarse or medium and fine polishers within each polishing system. The abrasive filler size of the AcryPoint coarse polisher was relatively larger than that of the Exa technique.

CONCLUSIONS

Regardless of polishing protocols, the 3D printed denture base exhibited the highest surface roughness, followed by heat-polymerized and milled denture bases. The surface roughness of the polished denture was not related with the material hardness. For heat-polymerized and milled dentures, a chairside silicone polishing system can be used to attain a level of surface roughness similar to that of laboratory polishing, depending on the properties of the chairside silicone polishing system.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available upon request from the corresponding author.

Preserving Integrity: Investigating the Influence of Disinfecting Agents on Polymethylmethacrylate Dental Prosthesis Surface Characteristics in Children

Introduction

In children, polymethylmethacrylate (PMMA) is a commonly used material for fabrication of dental prostheses, such as obturators, removable space maintainers, habit-breaking appliances, removable orthodontic appliances, and removable partial and complete dentures. Regular cleaning of such prostheses is vital for maintaining the health of the oral tissues as well as the longevity of the prosthesis. The chemical method of disinfection, using different chemical cleansers, is commonly used for cleaning a dental prosthesis. Some of these disinfecting agents have been reported to alter the physical and mechanical properties of PMMA.

Aim

The aim of the study was to analyze the effect of two commonly used disinfecting agents on the surface roughness and surface hardness of two PMMA-based materials processed using different curing cycles.

Materials and methods

PMMA samples were made using short and long curing cycles. The surface roughness and hardness of the samples before and after immersion in the two disinfecting agents were recorded. A profilometer was used to measure surface roughness, whereas hardness was measured using the Vickers hardness tester.

Results

Both disinfecting agents increased the surface roughness and decreased the hardness of the PMMA samples. The effect was more profound in samples made using the short curing cycle.

Conclusion

It is important to select the appropriate disinfecting agents and follow the manufacturers' instructions to ensure that the other properties of the prosthesis are not affected.

How to cite this article

Kumar S, Saran R. Preserving Integrity: Investigating the Influence of Disinfecting Agents on Polymethylmethacrylate Dental Prosthesis Surface Characteristics in Children. Int J Clin Pediatr Dent 2024;17(12):1404-1408.

Chemical analysis and performance evaluation of ClearCorrect® aligners as received and after intraoral use: Implications for durability, aesthetics, and patient safety

BACKGROUND

Orthodontic treatment with transparent aligners is popular with patients. Any alteration of the plastic material, as subjected to the oral environment, could influence the treatment's durability, the aligner's aesthetic appearance, and the patient's safety.

PURPOSE

This study concerns the physicochemical properties of ClearCorrect® aligners before and after intraoral use, focusing on transparency, surface topography, leachable, polymer glass transition temperature, and viscoelastic properties.

METHODS

Aligners were collected after two weeks of intraoral use. Unused samples were obtained from the manufacturers. Transparency was measured by UV-visible spectroscopy. Chemical modifications were studied using infrared and Raman spectroscopies. Thermal degradation, glass transition (Tg), and storage modulus (E') were characterized by thermal analysis (DSC, TGA, DMA). Surface morphology and roughness were studied thanks to SEM and AFM. Aligners were immersed in water-based solutions to identify and quantify organic leachable by HPLC chromatography and trace elements by atomic absorption spectroscopy.

RESULTS

ClearCorrect® aligners have a three-layer structure (outer PETG/inner PU layers). Slight chemical alterations occurred after aging. There was also no significant evolution in Tg and thermal degradation temperatures and only a minimal evolution of E'. Surface and transparency alterations occurred. A difference in organic compound and trace element release levels between new and used aligners was evidenced, suggesting an intraoral release during use.

SIGNIFICANCE

Intra-oral aging mainly impacts the aligner transparency and surface. The leachable study suggests significant ingestion of organic and non-organic compounds by the patient: investigations are needed to assess the impact of the long-term use of trays on patient health.

Effect of daily immersion of different beverages on the surface roughness and color stability of 3D-printed denture base resins

PURPOSE

To measure the effect of daily immersion in varying beverages (distilled water, tea, carbonated beverage, and orange juice) on surface roughness and color stability of 3D-printed denture base resins.

MATERIALS AND METHODS

160 acrylic resin discs (15 × 2.5 mm) were made from heat-polymerized (HP), and 3D-printed resins (FormLabs, ASIGA, and NextDent). Resin discs (N = 40) were immersed in different solutions (distilled water, tea, carbonated beverage, or orange juice; (n = 10/group)). Surface roughness (Ra, µm) was measured initially (T0), 6 months post immersion (T1), and 12 months post immersion (T2) using a non-contact profilometer. Color change (∆E00) was calculated using CIEL2000 at T1 and T2 using a spectrophotometer. The data were analyzed using Mann-Whitney U test and Kruskal-Wallis test in addition to general linear modeling (α = 0.05).

RESULTS

Significant differences in surface roughness (Ra) were found between the baseline and immersion in distilled water, carbonated beverage, and orange juice (p < 0.05). HP resin showed increased roughness with all immersion solutions compared to T0 with the highest value seen at T1 with tea. ASIGA resin had the highest mean Ra of 1.78 (0.43) after carbonated beverage immersion, while FormLabs resin had the lowest mean Ra of 0.88 (0.06) after distilled water immersion. Tea immersion did not significantly affect Ra among the resins (p > 0.05). Noticeable color changes were observed after immersion in tea, carbonated beverage, and orange juice. All resins exceeded perceptibility and acceptability thresholds at T1 and T2. The combined effect of time and resin on color change was statistically significant (p < 0.001), while the combined effects of time/immersion solution, immersion solution/resin, and immersion solution/resin/time were not.

CONCLUSION

Carbonated beverage, tea, and orange juice increase the surface roughness of 3D-printed resins. Tea, carbonated beverage, and orange juice resulted in noticeable color changes of HP and 3D-printed denture base resins and this change was time-dependent.

Influence of thermal-cycling or staining medium on the surface properties and color stability of conventional, milled, and 3D-printed base materials

The study of denture base resin fabricated by digital technology with surface properties or color stability remains limited. In this study, thermal cycling and staining media (distilled water, artificial saliva, green tea, and Coca-Cola) immersion were used to simulate the intraoral environment to assess the surface properties and color stability of CAD/CAM (milled) and 3D-printed base resin materials, the conventionally polymerized base served as the control group. After thermal cycling, all groups showed increased surface roughness, contact angle (i.e. hydrophilicity) and color difference (∆E), the 3D-printed group had the most significant increase among the 3 groups (P<0.001). While there were no significant difference (or the difference is very small) between the conventional and milled groups. After 7 and 30 days of immersion in four staining media, the ∆E values remained highest in the 3D-printed group (∆E ≥ 3.34) (P<0.001), exceeding the clinically acceptable threshold (∆E = 2.7) at 30 days. Additionally, all groups showed significantly higher ∆E values after 30 days compared to 7 days (P<0.05). The 3D-printed group exhibited a rougher surface, poorer hydrophilicity, and reduced color stability compared to the conventional or milled groups, indicating that further improvements are needed before clinical application.

A comparative study of strength and surface properties of permanent 3D-printed resins with CAD-CAM milled fixed dental prostheses

PURPOSE

To compare the strength, surface roughness, and hardness of newly introduced permanent three-dimensional (3D)-printed resin in comparison with computer-aided design and computer-aided manufacturing (CAD-CAM) milled materials.

MATERIALS AND METHODS

Three 3D-printed resins (NextDent C&B, Formlabs Permanent Crown, and VarseoSmile Crown plus) and two CAD-CAM milled (IPS e.max ZirCAD LT and VITA Enamic) resins were used to fabricate discs specimens. A total of 200 disc specimens were fabricated according to manufacturer recommendations. Within each group, half of the specimens were subjected to thermal cycling (5°C-55°C, the 30 s, 5000 cycles). Aged and nonaged specimens were evaluated for biaxial flexural strength (BFS), surface roughness, and hardness. Results were statistically analyzed using analysis of variance (ANOVA) and t-tests (α = 0.05).

RESULTS

Significant differences (p < 0.05) were observed in the BFS, surface roughness, and hardness between the 3D-printed and milled groups, before and after thermal aging. Overall, the CAD-CAM milled ceramic group had superior strength, surface roughness, and hardness when compared to all other groups (p < 0.001), except for surface roughness after thermal aging, which was similar in all groups (p = 0.063). Within each group, there was no significant difference (p > 0.05) in surface roughness after thermal aging. BFS values of 3D-printed materials were statistically similar. In terms of surface roughness, Formlabs specimens displayed the highest value before and after thermal cycling, when compared to other 3D-printed materials. Regarding hardness, the VarseoSmile Crown plus group demonstrated the highest values compared to other 3D-printed materials, before and after thermal cycling.

CONCLUSION

Permanent 3D-printed resins have lower strength than CAD-CAM milled materials. 3D-printed permanent resin materials exhibited high roughness and comparable hardness to CAD-CAM materials. Thermal aging negatively affected the properties of 3D-printed permanent crowns. Owing to the low strength of 3D-printed permanent resins, they may not be recommended for clinical practice until further improvements in flexural strength are made to meet clinical standards.

Surface Roughness on Cementoenamel Junction After Rubber-Dam Clamp Application

OBJECTIVE

To investigate the surface roughness on cementoenamel junction after application of various rubber-dam retraction clamps for different durations.

MATERIALS AND METHODS

Fifty-four extracted human molar teeth were used. Various retraction clamps were placed on the cementoenamel junction. There are three main examination groups in the study. Group 1 (n = 6) included a polymer clamp (SoftClamp, Kerr Hawe, Switzerland), Group 2 (n = 6) included a metal clamp with a flat edge (Black Line RDCM7X, Hu-Friedy Group, USA), and Group 3 (n = 6) included a metal clamp with a serrated edge (Fiesta Color Coded, Coltene, USA). All clamps were applied for 30 min, 1, and 2 h. Surface roughness measurements were performed using a profilometer before and after the clamp application and surface morphology was assessed through the SEM images. One-way ANOVA was used to compare three or more groups. Percentage changes were evaluated using the Kruskal-Wallis test, followed by Dunn's test for post hoc analyses. The deemed significance was set at p < 0.05.

RESULTS

Between the initial and the final roughness measurements, after 30 min of clamp application, only Group 3 showed significant increases in roughness (p = 0.001). After 1 and 2 h of clamp application, there were significant increases in roughness for all groups. No significant differences in percentage changes for all groups in 30 min and 2 h of application (p = 0.220 and p = 0.091, respectively). However, Group 1 presented significantly lower surface roughness in percentage after the 1 h of application (p = 0.040). No significant differences in the percentage changes in roughness were observed within the groups for 30 min, 1, and 2 h applications (p = 0.220, p = 0.884, and p = 0.755 for Groups 1, 2, and 3, respectively). In SEM analysis, deep point microstructure defects were seen as the clamp application time increased.

CONCLUSIONS

Rubber-dam clamp application may cause damage to the cementoenamel junction area. However, the level of damage is clamp-type-dependent. Slight scratch-type damages were observed on teeth with plastic clamps, while metal clamps generally caused cracks. The increase in the duration of the same rubber-dam clamp application was not considered an effective factor regarding the damage.

CLINICAL SIGNIFICANCE

During rubber-dam isolation, clamp type and duration of the application may cause damage to the tooth surface or progress an existing defect. Examining the teeth before selecting the clamp might be beneficial for minimizing dental tissue damage.

Effect of different polishing systems on surface roughness and gloss values of single-shade resin composites

BACKGROUND

The aim of this study was to evaluate variations in the surface roughness and gloss of different single-shade resin composites after polishing with a range of systems.

METHODS

In total, 120 specimens were prepared from three different types of single-shade resin composites (supra-nanospherical-Omnichroma, nanohybrid-Charisma Diamond One, and microhybrid- Essentia Universal). The specimens were placed in distilled water and stored at 37 °C for 24 h. Each resin composite (n = 40) was divided into four groups (n = 10) according to the finishing/polishing (F/P) system: Mylar strip (control), Sof-Lex (multi-step), Twist Dia (two-step), and OneGloss (one-step). Surface roughness and gloss were measured. Surface characteristics were evaluated by atomic force microscopy (AFM) and a scanning electron microscope (SEM). A two-way analysis of variance (ANOVA) and Tukey's honestly significant difference test were used for statistical analysis (p < 0.05).

RESULTS

Among all the composites, both the highest surface roughness and lowest gloss values were obtained in the groups treated with the OneGloss polishing system (p < 0.05). Compared with all the composites, Omnichroma had the lowest surface roughness and highest gloss values (except Twist Dia) both unpolished and after polishing with all the F/P systems (p < 0.05). All composites treated with the Twist Dia F/P system had similar gloss values. The results of the AFM and SEM analyses were consistent with the surface roughness measurements.

CONCLUSIONS

The gloss values of both the microhybrid and nanohybrid composites after F/P using the two-step system was superior to that of the traditional multistep system. The surface of the supra-nanofilled resin-based composite was smoother than that of both the microhybrid and nanohybrid composites.

Anodized SLM Ti6Al4V surfaces: influence of surface characteristics on NTs growth and resulted surfaces properties

TiO2 nanotubes (NTs) obtained via electrochemical anodization (EA) on conventionally machined titanium surfaces are reported to be promising for achieving mucointegration in dental implant therapy. Dental abutments, manufactured by selective laser melting (SLM), combined with thermal post-treatment, present a promising alternative to conventionally machined titanium. Based on an original protocol, this study aims to investigate how the characteristic microstructure of the α + β phases in post-heated SLM Ti6Al4V can influence the growth of NTs and the resulting physical and chemical surface properties. Ti6Al4V-SLM discs were fabricated, heat post-treated and mechanically polished. The samples were then subjected to EA under different voltage conditions (10, 20 and 30 V). The specimens' surfaces were characterized at the same location, before NTs formation by electron backscatter diffraction (EBSD), and after by scanning electron microscopy (SEM). Then, roughness and wettability were studied to determine how EA affects surface properties compared to conventionally machined and polished titanium surfaces without NTs (reference). Surface reactivity was evaluated through chemical analysis and collagen binding capacities. The self-organized TiO2 layer was developed on the α phase only and the β phase was preferentially dissolved. The characteristic dimensions of the nanotubes (diameter, length and wall thickness), measured by SEM image analysis, increased proportionally with the rise in voltage but were not affected by the crystallographic orientation of the underlying α grain. Micro-roughness was the same for nanotubular and reference surfaces. Wettability was improved, as was surface reactivity towards collagen, which may contribute to improved bioactivity of titanium surfaces in dentistry.

The effect of various denture cleansers on the physical and mechanical properties of CAD/CAM and heat-polymerized denture base materials: an in vitro study

OBJECTIVES

To investigate the effects of denture cleansers on the various properties of CAD/CAM and heat-polymerized polymethyl methacrylate (PMMA).

MATERIALS AND METHODS

Two different brands of heat-polymerized and two of milled PMMA were fabricated (n = 50), in total 200. Each group was randomly divided into five subgroups (n = 10): control groups (D1) kept in distilled water, cleaning tablets (D2, D3), neutral (D4) and acidic electrolyzed acid water (EAW) (D5). Surface roughness, hardness and flexural strength values were evaluated. Data were statistically analyzed with two-way ANOVA and Tukey post hoc test for comparison (p<0.05).

RESULTS

The milled group showed significantly lower surface roughness, greater surface hardness, and higher flexural strength values than heat polymerized denture bases (p<0.05). The denture cleansers had no significant effect on the surface roughness values of the milled specimens (p>0.05), whereas the specimens in the heat-polymerized groups and treated with D5 showed greater surface roughness values compared with the other cleaning agents (p > 0.05). The denture cleansers had no significant effect on surface hardness and flexural strength of heat polymerize groups (p > 0.05). However, D2, D3 and D5 cleaning agent decreased the hardness values of the milled group (p<0.05) and D5 cleaning agent decreased the flexural strength of the milled group (p<0.05).

CONCLUSIONS

It was observed that the applied denture cleansers affected the surface roughness, surface hardness, and flexural strength values of both denture bases but within a clinically acceptable value.

CLINICAL RELEVANCE

CAD/CAM denture bases showed significantly higher physical and mechanical properties than to heat-polymerized base materials. Although the applied neutral EAW cleaners give desired results for denture bases, clinical studies are needed for biological compatibility.

Scanning electron microscopy evaluation of enamel surfaces using different air-polishing powders in the orthodontic setting: an in vitro study

PURPOSE

The aim of this in vitro study was to quantify and compare changes of the enamel surface caused by periodical use of different air-polishing powders during multibracket therapy.

METHODS

Bovine high-gloss polished enamel specimens were air-polished using an AIR-FLOW® Master Piezon with maximum powder and water settings. Each specimen was blasted with sodium bicarbonate (AIR-FLOW® Powder Classic, Electro Medical Systems, Munich, Germany) and erythritol (AIR-FLOW® Powder Plus, Electro Medical Systems). Blasting duration was adapted to the powders' cleaning efficacy and corresponded to 25 air-polishing treatments in a patient with braces. A spindle apparatus ensured uniform guidance at a distance of 4 mm and a 90° angle. Qualitative and quantitative assessments were performed with the use of low vacuum scanning electron microscopy. Following external filtering and image processing, arithmetical square height (Sa) and root mean square height (Sq) were determined.

RESULTS

Both prophy powders caused a significant increase in enamel roughness. Surfaces blasted with sodium bicarbonate (Sa = 64.35 ± 36.65 nm; Sq = 80.14 ± 44.80 nm) showed significantly (p < 0.001) higher roughness than samples treated with erythritol (Sa = 24.40 ± 7.42 nm; Sq = 30.86 ± 9.30 nm). The observed defects in enamel structure caused by sodium bicarbonate extended across prism boundaries. Prism structure remained intact after air-polishing with erythritol.

CONCLUSION

Both applied air-polishing powders led to surface alterations. Despite shorter treatment times, sodium bicarbonate was significantly more abrasive than erythritol. Clinicians must compromise between saving time and abrasively removing healthy enamel.

Physicochemical Properties and Bacterial Adhesion of Conventional and 3D Printed Complete Denture PMMA Materials: An In Vitro Study - Part I

AIM

To evaluate and compare the surface morphology, wettability, roughness, and bacterial adhesion properties of polymethyl methacrylate (PMMA) materials fabricated by conventional methods and 3D printing for complete denture applications.

MATERIALS AND METHODS

Two PMMA materials were investigated: Conventionally processed (ProBase Hot) and 3D-printed (3DP) (V-Print Dentbase). Surface morphology (n = 3) was analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Surface roughness (n = 10) was measured using an optical profilometer. Wettability was assessed through contact angle measurements (n = 6) at 10, 30, and 60 seconds. Bacterial adhesion (n = 9) and biofilm formation (n = 3) were evaluated using Escherichia coli (E. coli) as a model organism, with quantitative bacterial counts and SEM analysis of bacterial morphology. Data were statistically analyzed.

RESULTS

Scanning electron microscopy analysis revealed nanoparticles on the surface of 3DP samples, while EDX detected silicon in these samples, absent in conventional PMMA. 3D-printed surfaces exhibited significantly lower roughness (1.05 ± 0.32 µm) compared to conventional surfaces (20.46 ± 6.71 µm) (p < 0.001). Contact angle measurements showed that 3DP surfaces were more hydrophilic (64-68°) than conventional surfaces (100°) (p < 0.05). Bacterial adhesion studies demonstrated more adherent bacteria on 3DP surfaces (92.5 ± 30.8) compared to the conventional surfaces (57.6 ± 12.5), but biofilm formation was observed only on conventional surfaces.

CONCLUSION

3D-printed PMMA exhibited distinct surface characteristics compared to conventionally processed PMMA, including the presence of silicon nanoparticles, lower surface roughness, and higher hydrophilicity. While 3DP surfaces showed higher initial bacterial adherence, in contrast, they appeared to inhibit biofilm formation, which highlights the complex nature of bacterial interactions with these materials.

CLINICAL SIGNIFICANCE

Further clinical studies are needed to validate the results of this investigation and generate clinical translational data. How to cite this article: Khoury P, Kharouf N, Etienne O, et al. Physicochemical Properties and Bacterial Adhesion of Conventional and 3D Printed Complete Denture PMMA Materials: An In Vitro Study - Part I. J Contemp Dent Pract 2024;25(11):1001-1008.

Improving accuracy and efficiency of the machined PEEK denture based on NSGA-II integrated GABP neural network

OBJECTIVES

The polymer polyetheretherketone (PEEK) is gradually being used in dental restorations because of its excellent mechanical properties, chemical resistance, fatigue resistance, thermal stability, radiation translucency and good biocompatibility. To process PEEK dentures with lower surface roughness as quickly as possible, the non-dominated sorting genetic algorithm-II (NSGA-II) integrated genetic algorithm back propagation (GABP) neural network was proposed, which can adjust the combination of process parameters for milling PEEK dentures.

METHODS

The PEEK machining was conducted using a four-axis dental milling machine at different process parameters. The surface roughness of PEEK dentures was characterized using surface roughness profiler and scanning electron microscopy (SEM). The optimum machining performance of milling PEEK dentures was investigated using a multi-objective optimization model named as NSGA-II integrated GABP neural network algorithm. The surface roughness (Ra) and material removal rate (MRR) were used as optimization objectives.

RESULTS

The multi-objective optimization model effectively improved surface roughness and machining efficiency for milling PEEK dentures. The validation experiments showed that the surface roughness of all PEEK dentures was less than 0.2μm, which was within the range of surface roughness set in this paper. The GABP surface roughness prediction model had an average error of 6 %. For the same surface roughness value, the optimized milling parameters all had a greater material removal rate.

SIGNIFICANCE

The research results can improve current PEEK denture CAD/CAM technology by providing appropriate milling parameters using NSGA-II integrated GABP algorithm.

Effects of different curing methods on the color stability of composite resins

Objectives

The aim of this study was to compare the effects of different polymerization strategies and the effectiveness of finishing and polishing procedures of composite resins on color stability.

Materials and Methods

The samples were divided into 4 main groups according to the polymerization strategy, and all groups except the control group received surface treatment. Each group was subsequently divided into 3 subgroups respectively: Kuraray Clearfil Majesty ES-2 Classic, Premium and Universal. Approximately 24 hours after preparation of the samples, they were immersed for 7 days in a coffee solution. A first color measurement was performed after the preparation of the samples, the second measurement was performed after 7 days in the coffee solution. All measurements were carried out using a dental spectrophotometer to assess the CIE L* a* b* color parameters.

Results

There was a statistically significant difference between ΔE values for different procedures (p = 0.003); in particular, the differences were found only between the groups that received surface treatment and the control group. In addition, a statistically significant difference was observed between the values of ΔE for different composites in the different procedure groups.

Conclusions

Spectrophotometric analysis showed that the additional photopolymerization and oxygen inhibition procedures did not yield better results in relation to color stability. In addition, finishing and polishing provided better color stability compared to not performing these procedures.

Bacterial Adhesion and In Situ Biodegradation of Preheated Resin Composite Used as a Luting Agent for Indirect Restorations

OBJECTIVE

To evaluate surface roughness and bacterial adhesion after in situ biodegradation of the cementation interface of indirect restorations cemented with preheated resin composite.

METHODS AND MATERIALS

Resin composite blocks (Z250XT/3M ESPE) were cemented to bovine enamel (7 × 2.5 × 2 mm) using preheated microhybrid resin composites: (1) Filtek Z100 (3M ESPE) (Z100); (2) Gradia Direct X (GC America) (GDX); and (3) Light-cured resin cement RelyX Veneer (3M ESPE) (RXV) (n=21). The resin composites were preheated on a heating device (HotSet, Technolife) at 69°C for 30 minutes. Disk-shaped specimens (7 × 1.5 mm) were made for biodegradation analysis with the luting agents (n=25). The in situ phase consisted of 20 volunteers' using an intraoral palatal device for 7 days. Each device had six cylindrical wells for the blocks and the disk-shaped specimens. Biodegradation was evaluated through surface roughness (Ra), scanning electron microscopy (SEM) micromorphological analysis, and colony-forming unit (CFU) count. The film thickness of the luting agents was also measured under stereomicroscopy.

RESULTS

Increased surface roughness was observed after the cariogenic challenge without differences between the luting agents. Higher variation and surface flaws suggestive of particulate detachment were observed for Z100. No differences were observed in CFU counts.

CONCLUSIONS

All materials underwent surface biodegradation, and the surface roughness of the resin cements was similar to or lower than that of the preheated resin composites. The resin composites' film thickness was thicker than that of the resin cement. Clinicians should be aware of these factors when choosing the use of preheated resin composite since it can lead to reduced longevity of the cementation interface and, therefore, restorations.

Effects of Finishing on Surface Roughness of Four Different Glass-Ionomer Cements and One Alkasite: In Vitro Investigation over Time Using Aging Simulation

In 2017, Europe implemented a ban on amalgam restorations for children aged <15 years and for pregnant/breastfeeding women, highlighting the need for alternative filling materials exhibiting less surface roughness and enhanced longevity. This in vitro study aimed to examine the surface roughness variations of five amalgam-replacement materials across three time points and using six finishing methods: (1) no finishing (control), (2) Arkansas burs, (3) diamond burs, (4) tungsten carbide burs, (5) SofLex discs in descending grit size, and (6) coarse SofLex discs combined with silicone polishing. We prepared 960 samples. Each material group, i.e., Cention Forte (CNF), DeltaFil (DLF), Ketac Universal (KTU), IonoStar Molar (ISM), and Equia Forte HT (EQF), comprised 60 samples (n = 10 per finishing method) created using standardized 3D-printed metal molds. Surface roughness (Sa) was measured immediately after finishing, after 30 days of storage in distilled water, and after thermocycling (5000 cycles) using a non-contact profilometer. The results indicate that conventional and hybrid glass-ionomer cements have smoother surfaces than high-viscosity GICs. The DLF and CNF groups exhibited stable outcomes. These findings underscore the importance of selecting appropriate finishing methods based on the restorative material to minimize surface roughness.

Characterization of 3D printed composite for final dental restorations

OBJECTIVES

This study evaluated the mechanical, optical, microstructural, surface, and adhesive behavior of a 3D printing resin comparing it with a machinable resin composite.

MATERIALS AND METHODS

Specimens of different sizes and shapes were either printed (Vitality, Smart Dent) or machinable (Grandio Blocs, Voco GmbH) resin composites with similar composition were prepared. Surface and mechanical characterization were performed with Knoop hardness, flexural strength (three-point-bending), and elastic modulus tests. The wear of the tested materials was evaluated against steatite antagonists. The optical properties stability (color change, ΔE00, and translucency, TP00) were observed after staining in red wine. In addition, the bond strength of the resin composites to two resin cement protocols were investigated with microshear bond strength tests at baseline and after thermocycling. Scanning electron microscope (SEM) coupled with Energy-Dispersive X-ray Spectroscopy (EDS) was used for microstructural and chemical characterization. Statistical analyses were performed with t- and ANOVA tests.

RESULTS

Hardness values (132.76 (16.32) KH- Machinable and 35.87 (2.78) KH - Printed), flexural strength (172.17 (26.99) MPa - Machinable and 88.69 (8.39) MPa - Printed), color and translucency change (1.86 (0.31)/0.06 - Machinable and 3.73 (0.36)/9,16- Printed), and wear depth (24.97 mm (3.60)- Machinable and 7.16 mm (2.84) - Printed) were statistically different. Average Regarding bond strength, mean values (MPa) for non-aged and aged groups were respectively 21.76 (6.64) / 31.9 (12.66) for Bifix cement (Voco GmbH, Cuxhaven, Germany) and 26.75 (5.14) / 24.36 (6.85) for Variolink cement (Ivoclar Vivadent, Schaan, Liechtenstein) in Printed and 17.79 (3.89) / 9.01 (3.36) ) for Bifix cement and 22.09 (6.55) / 11.01 (3.77) for Variolink cement in Machinable materials. The material and aging factors did affect bond strength but the cement factor did not (p = 0.202). No statistical differences were observed for mean roughness (Ra) between materials. The better dispersion and larger size of the inorganic particles in the Machinable resin were contrasted with the clustered smaller particles of printed resin, under SEM.

CONCLUSIONS

The mechanical properties and color stability of the machinable resin were superior to those of the printed resin, probably due to the greater amount and dispersion of inorganic particles in the Mach resin, but bond strength after aging was stronger and more stable in the printed resin.

CLINICAL RELEVANCE

3D-printed resin composites with similar compositions to machinable resin composites do not necessarily exhibit the same properties, which can impact clinical performance. Understanding these differences can assist manufacturers in improving their materials and help clinicians distinguish between materials appropriate for provisional and final restorations.

The effect of whitening toothpastes on the surface properties and color stability of different ceramic materials

OBJECTIVES

This study aimed to evaluate the effect of whitening toothpastes on the surface roughness and colour change of CAD-CAM materials.

MATERIALS AND METHODS

A total of 96 samples (2 × 10 × 12 mm3) were prepared from Cerasmart (CS) and Celtra Duo blocks. Celtra Duo samples were divided into two groups. One group was fired with glaze paste (CDG) and the other was not treated (CD). All groups were then divided into 4 subgroups (n = 8). The groups were brushed with conventional (Colgate™ Max Fresh), silica (Opalescence™), charcoal (Curaprox™ Black in White) and blue covarine (Signal™ White Now) toothpastes for 30,000 brushing cycles. The initial and final surface roughness values were measured with contact profilometer and a dental spectrophotometer used for obtaining colour values. One sample from each brushed group was analyzed using a scanning electron microscope. Data was analyzed with Kruskal-Wallis and Mann-Whitney tests (p = 0.05).

RESULTS

The surface roughness of CS samples brushed with Opalescence™ and Curaprox™ was significantly higher than CD and CDG. Surface roughness change values of CS samples brushed with Curaprox™ were significantly higher than the CD and CDG. Curaprox™ brushed samples showed significant difference in colour change values for all materials.

CONCLUSIONS

Brushing increases the surface roughness of CAD-CAM ceramic materials. The roughness of resin-based materials is higher than zirconia-reinforced lithium silicates. Silica-contained toothpastes may cause discoloration of nanoceramic and zirconia-reinforced glass ceramic restorations.

CLINICAL RELEVANCE

It should be clinically considered that whitening toothpastes may cause roughness in ceramic materials and change the desired color.

Effect of Artificial Saliva Modification on Corrosion Resistance of Metal Oxide Coatings on Co-Cr-Mo Dental Alloy

Surface modifications not only improve the corrosion resistance of Co-Cr-Mo dental alloys (Bego Wirobond® C) but also ensure their long-term performance and reliability in dental applications. This paper describes the preparation of single-layer TiO2-ZrO2 sol-gel coatings on the Co-Cr-Mo dental alloy using the method of dip-coating. The TiO2-ZrO2 sol-gel coatings were sintered at 300 and 500 °C. SEM analysis shows that sintering at 300 °C produces a uniform, slightly dense structure without micro-cracks, while sintering at 500 °C results in a denser structure with micro-cracks due to higher stress and shrinkage. EDS confirms that sintering temperature affects the elemental composition of the coating, with higher temperatures causing the volatilization or diffusion of Ti and Zr. Roughness measurements indicate that the Ra value increases with the sintering temperature, meeting dental application requirements. Electrochemical measurements by open-circuit potential, EIS, and cyclic potentiodynamic curves demonstrate that sintering temperature and saliva composition affect corrosion resistance, with NaF and mouthwashes (Listerine Total Care Teeth Protection® and Meridol®) generally increasing charge transfer resistance and double-layer capacitance. The ceramic TiO2-ZrO2 coatings significantly reduce pitting corrosion susceptibility at physiological and acidic pH, with the 500 °C sintered coating showing better protective properties. These findings highlight the potential of TiO2-ZrO2 coatings in enhancing the performance of Co-Cr-Mo dental alloys.

Can wheel polishers improve surface properties and color stability of monochromatic resin composites?

BACKGROUND

To overcome the color layering procedure, monochromatic resin composites have been introduced. However, little is known about their polishability, gloss and color stability. This study aimed to investigate the surface roughness, gloss, and color change of monochromatic resin composites polished with wheel systems after being immersed in coffee.

MATERIALS AND METHODS

Omnichroma, Zenchroma, Essentia Universal, Charisma Diamond One and NeoSpectra ST were used to obtain 120-disc samples of 8 × 2 mm. Only one side of the sample was polished with Twist Dia (TWD) or Nova Twist (NOV). The samples were examined for surface roughness, gloss, and color (ΔE and ΔE00) before and after 7 days of immersion in coffee and subsequent repolishing. The discs were examined via SEM. Surface roughness and gloss values were analyzed using ANOVA, Tukey and Pearson correlation tests. ΔE and ΔE00 values were evaluated using T tests, multivariate ANOVA, and Dunnett's post-hoc tests.

RESULTS

For TWD groups, the smoothest material was Omnichroma (p < 0.05), while for NOV groups, it was Omnichroma and Zenchroma. Omnichroma was the glossiest, while Charisma Diamond One was the least glossy. In TWD groups, Charisma Diamond One and Essentia Universal were the most discolored, while Zenchroma and Omnichroma were the least. For NOV groups, Essentia Universal and Charisma Diamond One were the most discolored, while NeoSpectra ST, Omnichroma and Zenchroma were the least. After repolishing, Charisma Diamond One did not reach the level of ΔE < 2, while the other groups showed values below. Color evaluation with the CIELab and CIEDE2000 systems revealed similar results for the TWD groups after post-staining.

CONCLUSIONS

Smooth and glossy surfaces could be achieved with the wheel system regardless of the composite resin. Repolishing after discoloration ensures that the color recovery is below the acceptable limit. Color evaluations with CIELab and CIEDE2000 yielded similar results.

Influence of light-polymerizing units and zirconia on the physical, chemical and biological properties of self-adhesive resin cements

BACKGROUND

Self-adhesive resin cements (SARCs) are widely used for fixed prostheses, but incomplete cleaning near the gingival margin can cause inflammation. However, the factors influencing cement properties and the biological response of gingival fibroblasts to cement eluates are not well understood. This study examines the impact of two light-polymerizing units (LPUs) on the physical and chemical properties of two SARCs under simulated clinical conditions, as well as the subsequent response of human gingival fibroblasts (hGFs) to these eluates.

METHODS

Dental cement discs of SARCs were polymerized using Kerr DemiPlus and 3 M Elipar DeepCure-S LED LPUs with or without a 2-mm thick zirconia screen. Physical properties (microhardness, surface roughness, residual monomers) were evaluated. hGFs' cell viability, wound healing potency, and gene expression were assessed.

RESULTS

Both Maxcem and RelyX exhibited reduced microhardness and increased surface roughness when polymerized through zirconia or with DemiPlus LPU. Higher residual monomers (HEMA and GDMA in Maxcem; TEGDMA in RelyX) concentration was observed with DemiPlus and zirconia polymerization. Maxcem polymerized with DemiPlus exhibited lower cell viability, impaired healing, and altered gene expression in hGFs compared to those polymerized with Elipar LPU. Gene expression changes included downregulated NRF2 and HO-1 and upregulated CCR-3.

CONCLUSIONS

Light-polymerizing Maxcem through zirconia with DemiPlus LPU compromised SARCs' properties, leading to higher residual monomers and negatively impacting hGFs' viability, healing, and gene expression. Careful material selection and polymerization techniques are crucial to minimize adverse effects on surrounding tissues.

CLINICAL SIGNIFICANCE

Clinicians should exercise caution when using LPUs and SARCs, especially when polymerizing through zirconia. This will help optimize the physical and chemical properties of SARCs and minimize potential adverse effects on the surrounding gingival soft tissues.

Polishing systems for modern aesthetic dental materials: a narrative review

Objectives To review the current literature surrounding chairside polishing systems for resin composites, zirconia and lithium disilicate restorations.Methods A literature search was undertaken and databases were hand-searched for the most relevant articles.Discussion The current marketplace contains a wide variety of polishing systems, each with different abrasive compounds and number of steps. Current efforts are aimed at reducing the number of steps required for polishing to improve clinical effectiveness. Reduced step systems showed some comparable results to the more traditional multi-step protocols, but the most effective results were achieved with the use of polishing paste as an additional step.Conclusions Based on the current available literature, the use of material-specific polishing systems is effective for chairside polishing of direct and indirect restorative materials. However, it is important to emphasise that, for optimum outcomes, it is essential to follow manufacturers' recommendations for each step, with particular considerations of the handpiece speed, time spent per step and use of adjunct water coolant.

Effect of Two Different Intraoral Polishing Systems on Surface Roughness, Color Stability, and Bacterial Accumulation of Zirconia-Reinforced Lithium Silicate Ceramic

OBJECTIVE

 The aim of this study was to investigate the effects of two intraoral polishing methods on zirconia-reinforced lithium silicate ceramic after ultrasonic scaling.

MATERIALS AND METHODS

 Thirty disc-shaped samples of zirconia-reinforced lithium silicate were constructed. Freshly extracted bovine teeth were collected and cleaned then the discs were cemented into a cavity prepared onto their labial surface. The samples were divided into three groups (10 samples per group); S: Scaling only, SE: Scaling followed by polishing using Eve Diapro lithium disilicate polishers, SD: Scaling followed by polishing using Diatech ShapeGuard ceramic polishing plus kit. The surface roughness was evaluated after scaling and polishing the samples. For color stability, the samples were stored for 12 days at 37°C in an incubator to simulate 1-year consumption of coffee. L*a*b* color parameters were assessed using VITA Easyshade Advance 4.0 before and after the staining procedure and the color difference was measured. Finally, bacterial accumulation was evaluated by incubating the samples with a suspension of Streptococcus mutans ( S. mutans), after that the S. mutans colonies were counted to obtain the values of colony-forming units (CFU). The final overall roughness, change in color and bacterial count were compared between all groups using one-way ANOVA and Tukey's post-hoc analysis. The Pearson correlation coefficient was used to determine the correlation between continuous variables. The cutoff for significance was chosen at p ≤ 0.05.

RESULTS

 Scaling induced surface roughness of the zirconia-reinforced lithium silicate ceramic was significantly decreased after using both intraoral polishing systems and this was accompanied by a significant decrease in color change and bacterial count.

CONCLUSION

 Intraoral polishing techniques can reduce the roughness of the surface of zirconia reinforced lithium silicate restorations induced due to scaling and subsequently reduce the stainability and bacterial accumulation.