Effect of solvent/disinfectant ethanol on the micro-surface structure and properties of multiphase denture base polymers

Prolonged post-washing in ethanol decreases bond strength of additively manufactured crown materials

OBJECTIVES

This study aimed to investigate the effect of post-washing duration and crown thickness on the bond strength between additively manufactured crown materials and dental cement in vitro.

METHODS

Rectangular-shaped specimens of two thicknesses (1.5 and 2.0 mm) were additively manufactured from permanent VarseoSmile Crown (VC) and long-term temporary NextDent (ND) materials. The specimens were post-washed (n = 160) in ethanol for 5 min, 10 min, 1 h, and 8 h then cemented with dual-cure resin cement. Twenty PMMA (TC) were milled as a control. A chevron-notch test was performed to measure the maximum load until failure (N). Interfacial bond strength (J/m2) was calculated and statistically analysed. The mode of failure was analysed by scanning electron microscopy (SEM).

RESULTS

There was a significant difference in the bond strength between all groups (p < 0.01). VC at 1.5mm thickness post-washed for 10 min showed the highest mean bond strength (1.77 ±0.96 J/m2) while VC at 2.0mm thickness post-washed for 8 h showed the lowest (0.22 ±0.10 J/m2). Exposure to ethanol for 8 h resulted in lower bond strength. Within the type of material, there were no differences in bond strength between the thicknesses when post-washed for the same duration.

CONCLUSIONS

Prolonged post-washing of AM crown materials can significantly decrease the bond strength to resin cement. There were no differences between the permanent and long-term temporary AM materials. When post-washed for 5 min, AM materials observed comparable or higher bond strength values compared to PMMA.

CLINICAL SIGNIFICANCE

The output of this research serves as a guide for dental practitioners, emphasising the importance of adhering to correct post-washing procedures for optimal bond strength of additively manufactured crown materials.

Effects of disinfectants on physical properties of denture base resins: A systematic review and meta-analysis

STATEMENT OF PROBLEM

The disinfection of removable dental prostheses and orthodontic appliances is essential to preventing transmission of pathogens. However, whether different disinfection solutions and durations affect the physical properties of denture base resins is unclear.

PURPOSE

The purpose of this systematic review and meta-analysis was to statistically analyze the influence of disinfectants on the physical properties of denture base resins.

MATERIAL AND METHODS

A systematic search in Medline, Embase, PubMed, and Cochrane Library databases was conducted to evaluate the effects of chemical disinfection on the physical properties of denture base resins such as surface morphology, roughness, hardness, and flexural strength. Of 1909 studies, 44 studies were included in the systematic review and 41 in the meta-analysis. Heterogeneity was analyzed by using I2 statistics. The influence of different disinfection solutions and durations on the physical properties was further analyzed, and the risk of bias evaluated. Statistical analyses were performed by using the RevMan 5.4 software program with the standardized mean differences (SMDs) and 95% confidence intervals (CIs).

RESULTS

Of the 44 included studies, 40 studies were assessed as having a low risk of bias, and 4 had an unclear risk of bias. Meta-analysis results showed that compared with the control, disinfection could not significantly affect surface roughness and hardness within 60 minutes of immersion in disinfectant solutions or flexural strength within 30 minutes (roughness: P=.79, I2=0%; flexural strength: P=.08, I2=0%; hardness: P=.05, I2=19%). In addition, the physical properties were not significantly affected when glutaraldehyde, chlorhexidine, and peracetic acid were repeatedly used for more than 30 minutes.

CONCLUSIONS

Most of the disinfectants did not reduce the physical properties of denture base resin within 30 minutes of immersion. Glutaraldehyde, chlorhexidine, and peracetic acid are recommended if longer immersion or repeated disinfection is required.

Effects of washing agents on the mechanical and biocompatibility properties of water-washable 3D printing crown and bridge resin

Three-dimensional (3D) printing, otherwise known as additive manufacturing in a non-technical context, is becoming increasingly popular in the field of dentistry. As an essential step in the 3D printing process, postwashing with organic solvents can damage the printed resin polymer and possibly pose a risk to human health. The development of water-washable dental resins means that water can be used as a washing agent. However, the effects of washing agents and washing times on the mechanical and biocompatibility properties of water-washable resins remain unclear. This study investigated the impact of different washing agents (water, detergent, and alcohol) and washing time points (5, 10, 20, and 30 min) on the flexural strength, Vickers hardness, surface characterization, degree of conversion, biocompatibility, and monomer elution of 3D printed samples. Using water for long-term washing better preserved the mechanical properties, caused a smooth surface, and improved the degree of conversion, with 20 min of washing with water achieving the same biological performance as organic solvents. Water is an applicable agent option for washing the 3D printing water-washable temporary crown and bridge resin in the postwashing process. This advancement facilitates the development of other water-washable intraoral resins and the optimization of clinical standard washing guidelines.

Influence of Post-Processing on the Degree of Conversion and Mechanical Properties of 3D-Printed Polyurethane Aligners

BACKGROUND

This study explores how different post-processing methods affect the mechanical properties and degree of conversion of 3d-printed polyurethane aligners made from Tera Harz TC-85 resin.

METHODS

Using Fourier-transform infrared (FTIR) spectroscopy, the degree of conversion of liquid resin and post-processed materials was analyzed. This investigation focused on the effects of various post-curing environments (nitrogen vs. air) and rinsing protocols (centrifuge, ethanol, isopropanol, and isopropanol + water). The assessed mechanical properties were flexural modulus and hardness.

RESULTS

The degree of conversion showed no significant variance across different groups, though the polymerization environment influenced the results, accounting for 24.0% of the variance. The flexural modulus varied considerably, depending on both the rinsing protocol and the polymerization environment. The standard protocol (centrifugation followed by nitrogen polymerization) exhibited the highest flexural modulus of 1881.22 MPa. Hardness testing revealed significant differences, with isopropanol treatments showing increased resistance to wear in comparison to the centrifuge and ethanol rinse treatments.

CONCLUSIONS

This study conclusively demonstrates the adverse effects of oxygen on the polymerization process, underscoring the critical need for an oxygen-free environment to optimize material properties. Notably, the ethanol rinse followed by nitrogen polymerization protocol emerged as a viable alternative to the conventional centrifuge plus nitrogen method.

Effect of different disinfection protocols on the surface properties of CAD-CAM denture base materials

STATEMENT OF PROBLEM

Which disinfection protocol provides optimal water contact angle and microhardness for computer-aided design and computer-aided manufacturing (CAD-CAM) polymethyl methacrylate (PMMA) materials is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of different disinfection protocols (1% sodium hypochlorite, denture cleanser gel, and effervescent tablet) on the water contact angle and microhardness of different CAD-CAM PMMA denture base materials by comparing them with a heat-polymerized PMMA.

MATERIAL AND METHODS

Disk-shaped specimens (Ø10×2 mm) were fabricated from 3 different CAD-CAM PMMAs-AvaDent (AV), Merz M-PM (M-PM), and Polident (Poli)-and a heat-polymerized PMMA (Vynacron) (CV) (n=21). Three disinfection protocols (1% sodium hypochlorite [HC], denture cleanser gel [GEL], an effervescent tablet [TAB]) were applied to simulate 180 days of cleansing. The water contact angle and microhardness of specimens were measured before and after disinfection and compared by using a 2-way ANOVA (α=.05).

RESULTS

For water contact angle, material (P=.010) and disinfection protocol (P=.002) had a significant effect. The material (P<.001), disinfection protocol (P=.001), and their interaction (P<.001) significantly affected the microhardness after disinfection. When the condition after disinfection was compared with that before disinfection, the water contact angle increased significantly in all material-disinfection protocol pairs (P≤.025), and microhardness increased significantly in all material-disinfection protocol pairs (P≤.040), except for GEL- (P=.689) or TAB-applied (P=.307) AV, HC-applied M-PM (P=.219), and TAB-applied Poli (P=.159).

CONCLUSIONS

The material and disinfection protocol affected the water contact angle of all tested PMMAs after disinfection, resulting in more hydrophobic surfaces for heat-polymerized or CAD-CAM PMMAs. The microhardness of heat-polymerized PMMA was less than that of all CAD-CAM PMMAs after disinfection, regardless of the protocol.

Effects of washing solution temperature on the biocompatibility and mechanical properties of 3D-Printed dental resin material

The use of digital manufacturing, particularly additive manufacturing using three-dimensional (3D) printing, is expanding in the field of dentistry. 3D-printed resin appliances must undergo an essential process, post-washing, to remove residual monomers; however, the effect of the washing solution temperature on the biocompatibility and mechanical properties remains unclear. Therefore, we processed 3D-printed resin samples under different post-washing temperatures (without temperature control (N/T), 30 °C, 40 °C, and 50 °C) for different durations (5, 10, 15, 30, and 60 min) and evaluated the degree of conversion rate, cell viability, flexural strength, and Vickers hardness. Increasing the washing solution temperature significantly improved the degree of conversion rate and cell viability. Conversely, increasing the solution temperature and time decreased the flexural strength and microhardness. This study confirmed that the washing temperature and time influence the mechanical and biological properties of the 3D-printed resin. Washing 3D-printed resin at 30 °C for 30 min was most efficient to maintain optimal biocompatibility and minimize changes of mechanical properties.

Disinfection and Isotonic Drinks' Influence on Hardness and Color Stability of Ethylene-Vinyl-Acetate Copolymer Mouthguards Used in Martial Arts: An In Vitro Study

This in vitro study aimed to evaluate the hardness and color change of an ethylene-vinyl-acetate copolymer (EVA) material for mouthguards after exposition to different cleaning agent solutions and isotonic drinks. Four hundred samples were prepared and divided into four equinumerous groups (n = 100), in which there were 25 samples from each color of EVA (red, green, blue and white). The hardness, using the digital durometer, and the color coordinates (CIE L*a*b*), using the digital colorimeter, were measured before the first exposition and after 3 months of exposition to spray disinfection and incubation in the oral cavity temperature, or immersion in isotonic drinks. The values of Shore A hardness (HA) and color change (ΔE-calculated by Euclidean distance) were statistically analyzed using the Kolmogorov-Smirnov test, multiple comparison ANOVA/Kruskal-Wallis and appropriate post-hoc tests. Statistically significant changes in color and hardness between the tested groups were demonstrated after the use of agents predestined for disinfecting the surface of mouthguards on the tested samples. There were no statistically significant differences in color and hardness between the groups immersed in isotonic sport drinks potentially consumed by competitors practicing combat sports using mouthguards. Despite the changes in color and hardness after the use of disinfectants, the deviations were minor and limited to specific colors of the EVA plates. The intake of isotonic drinks practically did not change either the color or the hardness of the samples, regardless of the tested color of the EVA plates.

Color Stability of Zinc Oxide Poly(methyl methacrylate) Nanocomposite-A New Biomaterial for Denture Bases

(1) Background: The purpose of this in vitro study was to evaluate the color change and stability of a zinc oxide nanoparticle-poly(methyl methacrylate) (ZnO NP-PMMA) nanocomposite for denture base material after immersion in different dietary and cleaning agent solutions. (2) Methods: One hundred samples were prepared and divided into four equinumerous groups depending on the weight content of ZnO NPs. The color coordinates (CIE L*a*b*) were measured using a digital colorimeter, ColorReader (Datacolor AG Europe, Rotkreuz, Switzerland), before and after immersion of the specimens in five different solutions (distilled water, coffee, red wine, black tea, denture cleaning tablet solution) for 6 months. The color changes (ΔE) were calculated using Euclidean distance and analyzed by the Shapiro-Wilk test and the ANOVA/Kruskal-Wallis multiple comparison and adequate post hoc tests. (3) Results: All tested materials showed significant color changes after their exposure to all solutions. Color changes were greatest in the case of red wine and progressed with the duration of the study. (4) Conclusions: The modification of PMMA with ZnO nanoparticles is acceptable in aesthetic terms in 2.5% and 5% weight content; however, color changes are more noticeable with higher nanoparticle content and must be discussed with the patient prior to possible use.

Effect of interfacial surface treatment on bond strength of particulate-filled composite to short fiber-reinforced composite

Objective

The aim was to investigate the effect of different interfacial surface treatments on the shear bond strength (SBS) between a short fiber-reinforced flowable composite (SFRC) and a particulate-filled flowable composite (PFC). In addition, SBS between two successive layers of similar materials was evaluated.

Materials and methods

One-hundred and forty-four specimens were prepared having either SFRC (everX Flow) as a substructure composite and PFC (G-aenial Flo X) as a surface composite or having one of the two materials as both substructure and surface layer. Eight groups of specimens were created (n = 18/per group) according to the interfacial surface protocol used. Group 1: no treatment; Group 2: ethanol one wipe; Group 3: ethanol three wipes; Group 4: phosphoric acid etching + bonding agent; Group 5: hydrofluoric acid etching + bonding agent; and Group 6: grinding + phosphoric acid etching. Group 7: only PFC layers and Group 8 (control) only SFRC layers without any surface treatment. After one-day storage (37 °C), SBS between surface and substructure composite layers was measured in a universal testing machine, and failure modes were visually analyzed. SEM was used to examine the bonding surface of the SFRC composite after surface treatment. SBS values were statistically analyzed with a one-way analysis of variance (ANOVA) followed by the Tukey HSD test (α = .05).

Results

The SBS between successive SFRC layers (Group 8) was statistically (p < .05) the highest (43.7 MPa) among tested groups. Surface roughening by grinding followed by phosphoric acid etching (Group 6) resulted in a higher SBS (28.8 MPa) than the remaining surface treatments.

Conclusion

Flowable composite with glass fibers (everX Flow) showed higher interlayer SBS compared to PFC flowable composite. Interfacial surface roughness increases the bonding of PFC to the substructure of SFRC.

Evaluation of microhardness in two types of denture bases after using sodium hypochlorite and NatureDent disinfecting agents

Background. Chemical agents, in combination with mechanical methods, play an important role in reducing microbial plaque on denture surfaces. However, these methods might change the mechanical behavior of acrylic resins, including microhardness and surface roughness. This in vitro study investigated the effect of two disinfectants, i.e., water and sodium hypochlorite, on the microhardness of conventional heat-cured and TiO₂ nanoparticle-reinforced acrylic resins. Methods. Sixty acrylic resin specimens were divided into two groups, and the samples in each group were randomly assigned to three subgroups (n=10). Heat-cured specimens and 1 wt% TiO₂ acrylic resin were prepared and immersed in three solutions: water, a solution prepared with NatureDent pills, and 1% sodium hypochlorite for 30, 60, and 90 days. Microhardness tests were performed on each sample at each immersion stage. The data were analyzed using descriptive statistical methods, three-way and one-way ANOVA, repeated-measures t test, and Tukey HSD tests using SPSS 17. P values<0.05 were considered significant. Results. All three independent parameters, including resin, solution, and time, significantly affected microhardness (P<0.05). The microhardness of both specimen types, i.e., conventional heat-cured and TiO₂ nanoparticle-reinforced acrylic resins, immersed for 30, 60, and 90 days, was the highest and lowest in water and hypochlorite solutions, respectively. Regarding 90 days, the microhardness values of conventional heat-cured and TiO₂ nanoparticle-reinforced acrylic resins were 17.050±0.094 and 19.953±0.053 in water, 15.675±0.069 and 18.965±0.037 in hypochlorite, and 16.713±0.122 and 19.39±20.113 in NatureDent solutions, respectively. Conclusion. Disinfecting two types of acrylic resin specimens decreased their microhardness as a function of immersion time for up to 90 days in the three solutions. However, the magnitude of hardness lost was less for TiO₂ nanoparticles-reinforced acrylic resin.

Effects of the Washing Time and Washing Solution on the Biocompatibility and Mechanical Properties of 3D Printed Dental Resin Materials

Three-dimensional (3D) printing technology is highly regarded in the field of dentistry. Three-dimensional printed resin restorations must undergo a washing process to remove residual resin on the surface after they have been manufactured. However, the effect of the use of different washing solutions and washing times on the biocompatibility of the resulting resin restorations is unclear. Therefore, we prepared 3D-printed denture teeth and crown and bridge resin, and then washed them with two washing solutions (isopropyl alcohol and tripropylene glycol monomethyl ether) using different time points (3, 5, 10, 15, 30, 60, and 90 min). After this, the cell viability, cytotoxicity, and status of human gingival fibroblasts were evaluated using confocal laser scanning. We also analyzed the flexural strength, flexural modulus, and surface SEM imaging. Increasing the washing time increased the cell viability and decreased the cytotoxicity (p < 0.001). Confocal laser scanning showed distinct differences in the morphology and number of fibroblasts. Increasing the washing time did not significantly affect the flexural strength and surface, but the flexural modulus of the 90 min washing group was 1.01 ± 0.21 GPa (mean ± standard deviation), which was lower than that of all the other groups and decreased as the washing time increased. This study confirmed that the washing time affected the biocompatibility and mechanical properties of 3D printed dental resins.

The Influence of Decontamination Procedures on the Surface of Two Polymeric Liners Used in Prosthodontics

Polymeric liners are materials commonly used in prosthodontics to reshape denture surfaces contacting the soft tissues of the oral cavity. The aim of the study was to determine the impact of different cleaning methods on two polymeric materials used in prosthodontics as non-adhesive permanent liners. The material for the research consisted of samples made from Mollosil Plus (Detax, Ettlingen, Germany)-direct polysiloxan liner; and Plastitanium (Pressing Dental, San Marino, Republic of San Marino)-an injection-molded liner. A total of 198 samples were made, 99 of each assessed material. They were exposed to different cleaning methods-a toothbrush, a toothbrush and soap, a toothbrush and toothpaste (BlendaMed, Procter&Gamble, Cincinnati, OH, USA), a toothpaste and denture cleaning paste (Protefix Hygiene Denture Paste, Queisser Pharma, Germany), denture cleansing tablets (Protefix Hygiene Cleaning Tablets, Queisse Pharma, Germany), and a disinfecting spray (Aftermat, Port Jefferson Station, New York City, NY, USA)-for 1 min, 5 min, 10 min, and 15 min. The image acquisition was performed with scanning electron microscopy and samples were analyzed for the homogeneity of their surfaces-the presence of holes, grooves, precipitate, and small and large separating pieces of the material marking departures from this homogeneity. For each type of damage, one point was given. Continuous data from two groups were compared with Mann-Whitney U testing. Due to a small sample size and distribution of variables other than normal, to compare more than two groups, Kruskal-Wallis testing with post hoc analysis (Dunn test with Bonferroni correction) was used. Categorical data were compared with the chi-square test and the Fisher's exact test. The Mollosil Plus material should be decontaminated with the use of a toothbrush or toothbrush with soap, while Plastitanium material should be disinfected. Plastitanium samples are more susceptible to damage during the decontamination procedures than Mollosil Plus.

Interfacial Adhesion of a Semi-Interpenetrating Polymer Network-Based Fiber-Reinforced Composite with a High and Low-Gradient Poly(methyl methacrylate) Resin Surface

The research aimed to determine the tensile bond strength (TBS) between polymerized intact and ground fiber-reinforced composite (FRC) surfaces. FRC prepregs (a reinforcing fiber pre-impregnated with a semi-interpenetrating polymer network (semi-IPN) resin system; everStick C&B) were divided into two groups: intact FRCs (with a highly PMMA-enriched surface) and ground FRCs (with a low PMMA gradient). Each FRC group was treated with: StickRESIN and G-Multi PRIMER. These groups were further divided into four subgroups based on the application time of the treatment agents: 0.5, 1, 2, and 5 min. Next, a resin luting cement was applied to the FRC substrates on the top of the photo-polymerized treating agent. Thereafter, weight loss, surface microhardness, and TBS were evaluated. Three-factor analysis of variance (p ≤ 0.05) revealed significant differences in the TBS among the FRC groups. The highest TBS was recorded for the intact FRC surface treated with G-Multi PRIMER for 2 min (13.0 ± 1.2 MPa). The monomers and solvents of G-Multi PRIMER showed a time-dependent relationship between treatment time and TBS. They could diffuse into the FRC surface that has a higher PMMA gradient, further resulting in a high TBS between the FRC and resin luting cement.

Repairability of a 3D printed denture base polymer: Effects of surface treatment and artificial aging on the shear bond strength

OBJECTIVES

The present study aimed to evaluate the repairability of a 3D printed denture base material. The effects of surface treatments and artificial aging on the shear bond strength (SBS) were investigated.

METHODS

A total of 224 specimens were printed by digital light processing technology (Rapid Shape D30II) using a 3D printing denture base material (FREEPRINT denture). To evaluate the repairability, the SBS and failure modes were measured after surface treatment and artificial aging. Specifically, half of the specimens were further performed with thermocycling (5-55 °C, 5000 cycles) for artificial aging. The aged and non-aged specimens were further divided into four subgroups (n = 28) to simulate a denture base repair with one of the following treatments: control (without surface treatment), monomer (applying methylmethacrylate for 120 s), P600 (grinding with P600 silicon carbide paper) and sandblasting (blasted with 125 μm aluminum oxide with 2 bar), respectively. Surface roughness was measured (n = 6) and surface topography was observed by scanning electron microscopy (n = 2). A test rod was built on the sample surface using the same 3D printing material. Afterward, all specimens further underwent thermocycling (5-55 °C, 10,000 cycles).

RESULTS

For non-aged groups, no significant differences in SBS could be found (p < 0.05), and bondings failed cohesively in the denture base material. Regarding the aged control and monomer group, adhesive failures at the interface were primarily observed, and SBS values were statistically lower than those of the other groups (p < 0.05).

CONCLUSIONS

The 3D printed denture base material exhibited favorable repairability. For the realignment surface, the SBS at the bonding interface is satisfying and additional surface treatments could be not necessary. In contrast, the aged surface could significantly decrease the SBS; hence subtractive surface treatments are highly recommended.

Assessment of surface roughness changes on orthodontic acrylic resins by all-in-one spray disinfectant solutions

Background. The disinfection of orthodontic acrylic resins might change the physical and mechanical properties of these materials. We aimed to investigate the impact of four different commercially available disinfectants on the surface roughness of acrylic resins used for orthodontic appliances.

Methods. Four disinfectant solutions (BirexSE, Opti-Cide3, COEfect MinuteSpray, and CaviCide Spray) were used to disinfect orthodontic acrylic resins using the spraying method. The resins were subjected to repeated disinfection protocols. Distilled water, also applied via spraying method, was used as a control. Surface roughness was scrutinized to examine the extent of surface topography changes by stylus profilometry. Data normality was evaluated via the Shapiro–Wilk test, followed by the Wilcoxon Signed-Rank test for non-parametric data or paired Student’s t-test for parametric data to compare intra-group differences in roughness before and after the use of the disinfectant solutions.

Results. Some of the disinfectants (BirexSE and CaviCide) resulted in significant changes in surface roughness values before and after the disinfection compared to the controls (P<0.05). The groups that were in contact with distilled water, Opti-Cide, and Coeffect did not exhibit significant differences in surface roughness before and after the intervention (P>0.05). However, from a clinical perspective, the resulting variations in surface roughness (<%0.15) induced by these solutions might not reflect clinically significant differences.

Conclusion. The use of disinfectant solutions is unlikely to harm the surface of orthodontic acrylic resins. Oral care providers need to be attentive to the interpretation and implementation of clinically significant changes in their evidence-based approach regarding potential material damages by disinfection sprays.

Effects of polishing on surface roughness and hardness of glass-fiber-reinforced polypropylene

Removable partial dentures (RPDs) with resin-clasp retentive parts, which are known as non-metal-clasp dentures (NMCDs), have been used as alternatives for conventional RPDs with metal clasp, in case of aesthetic prosthodontic treatments. In this study, a profilometer and dynamic micro-indentation tests were used to investigate the effects of polishing on the surface properties such as surface roughness (Ra), dynamic hardness, and elastic modulus of high-rigidity glass-fiber-reinforced thermoplastics (GFRTPs) composed of E-glass fibers and polypropylene for NMCDs. The Ra values of the GFRTPs after polishing were significantly lower than those before polishing. The values were close to the Ra threshold level of 0.2, which corresponds to an acceptable surface smoothness for denture base materials. Polishing did not significantly change the dynamic hardnesses and elastic moduli of the GFRTPs. The fiber loading did not greatly affect the micromechanical properties of the GFRTPs because the glass-fiber reinforcement is embedded in the polypropylene matrix.