Effects of cleansing methods on 3-D surface roughness, gloss and color of a polyamide denture base material

Investigation of color and physicomechanical properties of peek and pekk after storage in a different medium

The aim of this study is to assess color stability, solubility, and water sorption on polyether ether ketone (PEEK) and polyether ketone ketone (PEKK) after immersion in different storage conditions. Material and Methods Ninety disc-shaped specimens (8 × 2) were obtained from CAD/CAM blocks [PEEK (n = 45) and PEKK (n = 45)]. Before immersion, baseline color value data were recorded with a spectrophotometer. The specimens were soaked in three solutions red wine, coffee, and distilled water at 37 °C for 28 days. Following immersion, color values were remeasured, and color-change values (ΔE) were calculated. Water sorption and solubility were assessed by mass gain or loss after storage in water for 28 days. The Kruskal-Wallis and the Mann-Whitney U test were used for analysis (P = 0.05). Results ΔE00 between PEEK and PEKK was significantly different statistically (P < 0.001). PEEK presented higher water sorption than PEKK (P = 0.005). The difference in solubility between PEEK and PEKK was not statistically significant (P = 0.163). The materials and storage medium types had a statistically significant impact (P = 0.100). In terms of staining potential, the solutions tested in this experiment were ranked as: coffee > red wine > distilled water. The results of this study demonstrated that PEKK was more successful in polymer-containing CAD/CAM materials as it exhibited less color change and water absorption.

Color stability, surface, and physicochemical properties of three-dimensional printed denture base resin reinforced with different nanofillers

Various materials have been introduced for the three-dimensional (3D) printing of dentures. In this study, the color stability and surface and physicochemical properties of 3D-printed denture base resins with four types of nanofiller particles were evaluated. Al2O3, ZnO, CeZr, and SiO2 nanofillers were added to a 3D printable denture base-resin matrix and subjected to digital light processing. The specimens were immersed in Coke, coffee, black tea, or distilled water for 6 days. For the assessment of color differences, 6 samples were analyzed using a spectrophotometer. In a separate investigation, surface properties of 10 samples were examined, while a different set of 6 samples was used to analyze water sorption and solubility. All experimental groups exhibited higher color stability in Coke than the control group. However, the groups containing ZnO and CeZr had lower color stability in coffee and black tea than the control group. Moreover, they had agglomerated nanofillers and lower gloss than the control group. Compared with that of the control group, the contact angle of the CeZr group and microhardness of the ZnO group were not significantly different. Water sorption was higher in the Al2O3 group, whereas the solubility of the experimental and control groups was not statistically significant. The results demonstrated the significant effect of ZnO and CeZr nanofillers on the color stability of the dentures when exposed to discoloring beverages. These results will facilitate the development of fillers that enhance the resistance of 3D printed denture base resins to discoloration in the oral environment.

Different Polymers for the Base of Removable Dentures? Part II: A Narrative Review of the Dynamics of Microbial Plaque Formation on Dentures

This review focuses on the current disparities and gaps in research on the characteristics of the oral ecosystem of denture wearers, making a unique contribution to the literature on this topic. We aimed to synthesize the literature on the state of current knowledge concerning the biological behavior of the different polymers used in prosthetics. Whichever polymer is used in the composition of the prosthetic base (poly methyl methacrylate acrylic (PMMA), polyamide (PA), or polyether ether ketone (PEEK)), the simple presence of a removable prosthesis in the oral cavity can disturb the balance of the oral microbiota. This phenomenon is aggravated by poor oral hygiene, resulting in an increased microbial load coupled with the reduced salivation that is associated with older patients. In 15-70% of patients, this imbalance leads to the appearance of inflammation under the prosthesis (denture stomatitis, DS). DS is dependent on the equilibrium-as well as on the reciprocal, fragile, and constantly dynamic conditions-between the host and the microbiome in the oral cavity. Several local and general parameters contribute to this balance. Locally, the formation of microbial plaque on dentures (DMP) depends on the phenomena of adhesion, aggregation, and accumulation of microorganisms. To limit DMP, apart from oral and lifestyle hygiene, the prosthesis must be polished and regularly immersed in a disinfectant bath. It can also be covered with an insulating coating. In the long term, relining and maintenance of the prosthesis must also be established to control microbial proliferation. On the other hand, several general conditions specific to the host (aging; heredity; allergies; diseases such as diabetes mellitus or cardiovascular, respiratory, or digestive diseases; and immunodeficiencies) can make the management of DS difficult. Thus, the second part of this review addresses the complexity of the management of DMP depending on the polymer used. The methodology followed in this review comprised the formulation of a search strategy, definition of the inclusion and exclusion criteria, and selection of studies for analysis. The PubMed database was searched independently for pertinent studies. A total of 213 titles were retrieved from the electronic databases, and after applying the exclusion criteria, we selected 84 articles on the possible microbial interactions between the prosthesis and the oral environment, with a particular emphasis on Candida albicans.

Mechanical and chemical characterization of contemporary occlusal splint materials fabricated with different methods: a systematic review

OBJECTIVE

To systematically review studies on various occlusal splint materials and describe their mechanical and chemical properties.

METHODS

MEDLINE (PubMed), Scopus, and Web of Science searches were conducted for in vitro studies focusing on occlusal splint materials. Two reviewers performed an assessment of the identified studies and data abstraction independently, and this was complimented by an additional hand search. The articles were limited to those in the English language that were published between January 1st, 2012, and December 1st, 2022.

RESULTS

The initial search yielded 405 search results of which 274 were selected for full-text review following abstract evaluation. 250 articles that did not meet the inclusion criteria were excluded, and the remaining 25 articles (with 1 article identified from the reference lists of included articles) providing mechanical and chemical values were used in this review. Poly methyl methacrylate (PMMA) -based occlusal splint materials showed the highest values in terms of hardness, wear resistance, flexural strength, flexural modulus, e-modulus, and fracture toughness. The material group with the highest water sorption and water solubility was 3D printed (PR) splint materials. In addition, the lowest degree of double bond conversion was also observed in this group of materials.

CONCLUSIONS

The outcome of this review suggests that mechanically and chemically acceptable properties can be attained with PMMA-based occlusal splint materials using both conventional and digital production methods. PR splint materials should not be considered as the primary choice for long-term treatments due to their low mechanical and chemical properties.

CLINICAL RELEVANCE

This review provides clinical recommendations for selecting the appropriate material and fabrication method for occlusal splints while taking the patients' needs and the materials´ mechanical and chemical properties into account.

Comparison of surface characteristics of denture base resin materials with two surface treatment protocols and simulated brushing

PURPOSE

To investigate the effects of 4 denture base materials, 2 surface treatment protocols, and simulated brushing (SB) on the surface hardness, surface roughness, surface gloss, and the surface loss of denture base materials.

MATERIALS AND METHODS

Four denture base resin material groups (compression-molded, injection-molded, 3D-printed, and milled) with two different surface treatment protocols (polished and glazed) were utilized in this study. A total of 80 samples (n = 10) were evaluated for surface hardness (Vickers) before SB. SB was performed for each sample (custom-built V8 cross brushing machine, 50,000 reciprocal strokes). Surface roughness (Ra) was measured before and after SB with a non-contact optical profilometer. Surface gloss was performed using a glossmeter to determine changes in surface reflectivity of the specimens before and after SB. Surface loss (wear resistance) was measured after SB using optical profilometry. The effects of material, surface treatment, and SB on all surface characteristics were examined with two-way and three-way analysis of variance models (ANOVA) (α = 0.05).

RESULTS

The polished compression-molded group had significantly higher surface hardness than all other groups. The protective glaze coating significantly increased the surface hardness for all groups (P < 0.001). SB increased the surface roughness of all groups regardless of surface treatments (P < 0.001). The increase in surface roughness after SB was significantly higher with polished surface treatment than with a glazed surface treatment in all groups (P < 0.001). Surface gloss was significantly higher with the glazed surface treatment than with the polished surface treatment for all denture base materials (P < 0.001). After SB, milled denture base material showed the highest, and 3D-printed material showed the second highest surface gloss compared to the other groups (P < 0.001), regardless of surface treatment. In all materials tested, surface glaze significantly decreased surface loss (P < 0.001). With the glaze surface treatment, compression-molded denture base material had significantly less surface loss (more surface gain) than other materials, while with the polished surface treatment, 3D-printed denture base material had the least surface loss when compared with other groups.

CONCLUSIONS

A single layer of nano-filled, light-polymerizing protective glaze coating has displayed potential for enhancing the longevity of denture base materials, as evidenced by increased hardness and wear resistance. Following simulated brushing, the milled denture material exhibited the highest surface gloss and lowest surface roughness among all groups, regardless of the surface treatment protocol. This indicates that milled denture base material possesses favorable surface properties and may serve as a viable alternative to traditional denture base materials.

Effect of denture cleansers on color stability and surface properties of denture base material containing titanium dioxide nanoparticles

PURPOSE

To investigate the effect of different denture cleansers on color stability, surface roughness, and hardness of polymethylmethacrylate (PMMA) infused with titanium dioxide nanoparticles (TiO2 NPs) at concentrations of 1% and 2% by weight on each.

MATERIALS AND METHODS

In this in vitro study, 90 disc-shaped specimens (10×10×2 mm) were divided into 3 main groups: the non-containing nanoparticle group (0wt% concentration), 1wt% concentration, and 2wt% concentration TiO2 NPs groups. Each group was further assorted into 3 subgroups (n = 10): immersed in distilled water, oxygenating tablet (Corega), and 0.5% sodium hypochlorite. Color change, surface roughness, and hardness values were assessed after 90 and 180 days of storage. Color changes (∆E) were measured with a spectrophotometer (VITA, Easy Shade V, Germany) and assessed using the CIE L*a*b* colorimetric system and the American National Bureau of Standards (NBS = 0.92×∆E). The surface roughness and surface hardness values were measured using a profilometer device and Vickers hardness tester, respectively. First, ANOVA-repeated measurements were performed, followed by the Tukey test. The significance level in this study was considered 0.05.

RESULTS

At all concentrations, there were significant differences in the mean color changes of samples immersed in cleansers compared to distilled water (p < 0.01). Moreover, hypochlorite caused a significant increase compared to Corega at 0wt% concentration after 90 days and at 1wt% concentration after 90 and 180 days. Evaluations also showed that the mean NBS values in all cleanser groups were in the range of appreciable change, except the water group. In addition, only hypochlorite changed the color higher than the clinically acceptable range (∆E >3.7). The mean roughness of samples immersed in hypochlorite at 0wt% concentration was significantly higher than the samples containing TiO2 NPs (p = 0.006). No significant difference was observed in surface roughness of samples containing different concentrations of TiO2 NPs immersed in different cleansers; however, hypochlorite increased the surface roughness of samples without TiO2 NPs compared to samples containing TiO2 NPs after 180 days. The immersion time in cleansers had a significant influence on the surface roughness and hardness while having no effect on the color.

CONCLUSION

In general, the cleansers had a significant effect on color change in all groups compared to distilled water. The adverse effect of hypochlorite was more than Corega. The cleansers in the samples containing TiO2 NPs did not make a significant difference in surface roughness in comparison with the distilled water groups. Surface hardness of the samples was not affected in a steady pattern by the cleansers.

Effect of Effervescent Denture Cleansers on 3D Surface Roughness of Conventional Heat Polymerized, Subtractively, and Additively Manufactured Denture Base Resins: An In Vitro Study

PURPOSE

To compare the change in surface roughness of denture bases fabricated using three different techniques (additive manufacturing, subtractive manufacturing, and conventional heat-polymerizing) when immersed in two commonly available denture cleansers.

MATERIALS AND METHODS

One hundred and seventeen disc-shaped denture base specimens (39/group), were fabricated by subtractive manufacturing (Wieland), additive manufacturing (NextDent Denture 3D+), and conventional heat-polymerizing (Meliodent) techniques, following the manufacturers' instructions. Specimens were randomly divided into 3 groups and immersed in two effervescent denture cleansing solutions and distilled water to simulate 180 days of denture cleansing. A 3D optical noncontact surface profilometer was used to record the surface roughness of the tested denture base materials before and after immersion. Two-way ANOVA, followed by Bonferroni post hoc test, was used to assess the effects of denture cleansers on surface roughness of tested denture base resins.

RESULTS

When immersed in Fixodent and Fittydent effervescent denture cleansing solutions, the highest change in absolute surface roughness (∆Sa, in μm) was observed in additively manufactured denture base material (0.181 ±0.018 and 0.079 ±0.008), followed by heat-polymerized denture base material (0.149 ±0.012 and 0.059 ± 0.011), while subtractively manufactured denture base material showed the least change (0.110 ±0.026 and 0.038 ±0.007), respectively. There was a difference in the extent of change in surface roughness between the denture cleansers. The change in surface roughness was much higher with the Fixodent denture cleanser as compared to the Fittydent denture cleanser.

CONCLUSION

Subtractively manufactured denture base resin displayed the lowest change while additively manufactured denture base resin displayed the highest change in surface roughness in both denture cleansers, but the extent of change in surface roughness was variable.

Poly (Methyl Methacrylate)-Containing Silver-Phosphate Glass Exhibits Potent Antimicrobial Activity without Deteriorating the Mechanical and Biological Properties of Dental Prostheses

Poly (methyl methacrylate) (PMMA) is a commonly used denture material with poor antimicrobial effects. This study investigated the antimicrobial effects of PMMA-containing silver-phosphate glass. We fabricated a novel material comprising PMMA-containing silver-phosphate glass. Then, microhardness, flexural strength, and gloss unit were analyzed. Antimicrobial activity against Streptococcus mutans and Candida albicans was investigated. Colony-forming units were counted, and antimicrobial rates were measured. Biocompatibility tests were performed using a colorimetric MTT assay for evaluating cell metabolic activity. The microhardness, flexural strength, and gloss unit of the experimental groups (with silver-phosphate glass) were not significantly different from those of the control group (no silver-phosphate glass) (P > 0.05), which showed clinically valid values. With increasing proportions of silver-phosphate glass, the antimicrobial activity against the two microorganisms increased (P < 0.05). Furthermore, S. mutans showed more than 50% antimicrobial activity in 4%, 6%, and 8% experimental groups, C. albicans showed more than 50% antimicrobial activity in 6% and 8% groups, and a statistically significant difference in antimicrobial activity was observed compared to the control (P < 0.05). The cell viability of the experimental groups was not significantly different from that of the control group (P > 0.05). Both control and experimental groups showed approximately 100% cell viability. These results suggest that silver-phosphate glass is a promising antimicrobial material in dentistry.

Influence of Propolis Extract (Caffeic Acid Phenethyl Ester) Addition on the Candida albicans Adhesion and Surface Properties of Autopolymerized Acrylic Resin

Background. Denture stomatitis has been linked to the adhesion and proliferation of Candida albicans (C. albicans) on denture bases, which is a common and recurrent problem in denture wearers. The current study aimed to evaluate the effect of incorporating caffeic acid phenethyl ester (CAPE) into autopolymerized polymethyl methacrylate (PMMA) acrylic resin on C. albicans adhesion, surface roughness, and hardness as well as the correlation between tested properties. Methods. Autopolymerized acrylic resin discs (N = 100, 50/C. albicans adhesion; 50/C. albicans surface roughness and hardness test) were fabricated in dimensions 15 × 2.5 mm, samples were categorized into 5 groups (n = 10) based on CAPE concentrations; unmodified (control), 2.5, 5, 10 and 15% wt of acrylic powder. Specimens were stored in distilled water for 48 h at 37°C. C. albicans adhesion was evaluated via direct culture method. Profilometer and Vickers hardness tester were used for surface roughness and hardness measurement. Post hoc Tukey’s HSD with ANOVA test was performed to compare the difference of means amongst groups. $P$ values were statistically significant at ≤0.05. Results. The addition of 2.5% of CAPE to PMMA has significantly reduced C. albicans counts in comparison to higher CAPE concentrations ( $p<0.001$ ). As for surface roughness, it was noticed that it increased with increased CAPE concentrations ( $p<0.0001$ ). While surface hardness decreased as CAPE concentrations increased ( $p<0.0001$ ). All tested properties showed a significant difference amongst groups for C. albicans colony count and surface parameters. Conclusion. The addition of 2.5% of CAPE to PMMA acrylic resin significantly decreased C. albicans count compared to higher CAPE concentrations. CAPE can be used as an adjunct in the prevention of DS by incorporating in the PMMA acrylic resin.

Effect of Different Solutions on the Colour Stability of Nanoparticles or Fibre Reinforced PMMA

This study aimed to evaluate the colour stability of polymethyl methacrylate (PMMA) denture base reinforced with ZrO2 nanoparticles, E-glass fibres, and TiO2 nanoparticles at various concentrations over 180-day storage in Steradent™ (STD) denture cleaner or coffee (CF). A total of 130 disc-shaped specimens were fabricated at various filler concentrations and divided into four main groups to measure the colour changes. Groups Z, T, and E consisted of PMMA reinforced with ZrO2 nanoparticles, TiO2 nanoparticles, or E-glass fibre, respectively, while Group C consisted of PMMA specimens without filler served as the control group (n = 10). The three reinforced groups were further subdivided according to the filler content (n = 10) added to the PMMA (1.5%, 3.0%, 5.0%, and 7.0% wt.%). Half of the specimens were stored in STD, while the other half was stored in CF for 180 days. A Minolta Chroma Meter was used to measure the colour changes (ΔE) at 7, 30, 90 and then 180 days. The results were assessed using two-way repeated-measures analysis of variance (RM-ANOVA) along with Bonferroni post hoc tests at a p ≤ 0.05 significance level. Significant different colour changes (ΔΕ) were observed between all tested groups and across different time points. TiO2-reinforced PMMA in coffee showed the lowest colour stability, while the E-glass fibre-reinforced PMMA in STD/CF showed the highest colour stability. Furthermore, coffee appeared to have the greatest impact on the CF change in comparison to the STD/CF. The results indicated that the filler type and concentration, type of solution, and length of storage all affected the colour stability of the tested specimens.

Novel polymethyl methacrylate modified with metal methacrylate monomers: biological, physicomechanical, and optical properties

This study sought to evaluate the physical and antimicrobial properties of a thermopolymerizable acrylic resin (PMMA) modified with metallic methacrylate monomers -zirconia (ZM), tin (TM), and di-n-butyl (DNTMB) methacrylates. Color stability was evaluated before and after immersion of samples in a staining solution by a digital spectrophotometer. The mechanical brushing test was evaluated by the roughness test. The flexural strength test used a mechanical testing machine. Human keratinocytes were used to assess cell viability and the biofilm formation assay was carried out for 5 days, in a microcosms model after one year of specimen storage. For statistical analysis, the method chosen was based on adherence to the normal distribution model and equality of variances (p < 0.05). The addition of DNTMB to PMMA promoted great antimicrobial action, acceptable cytocompatibility, without hampering the physical-mechanical properties of the commercial material. Therefore, the modified PMMA proved to be a promisor alternative to conventional resins.This study sought to evaluate the physical and antimicrobial properties of a thermopolymerizable acrylic resin (PMMA) modified with metallic methacrylate monomers -zirconia (ZM), tin (TM), and di-n-butyldimethacrylate-tin (DNTMB) methacrylates. Color stability was evaluated before and after immersion of samples in a staining solution using a digital spectrophotometer. The mechanical brushing test was evaluated by the roughness test. The flexural strength test used a mechanical testing machine. Human keratinocytes were used to assess cell viability and the biofilm formation assay was carried out for 5 days in a microcosm model after one year of specimen storage. For statistical analysis, the method chosen was based on adherence to the normal distribution model and equality of variances (p < 0.05). The addition of DNTMB to PMMA promoted great antimicrobial action, acceptable cytocompatibility, without hampering the physical-mechanical properties of the commercial material. Therefore, the modified PMMA proved to be a promising alternative to conventional denture base resins for dental use.

Optical Properties and Color Stability of Dental PEEK Related to Artificial Ageing and Staining

Considering that the processes of PEEK discoloration caused by either intrinsic or extrinsic factors require elucidation, the aim of this study was to investigate the long-term effect of the combined action of ageing and immersing solutions on the optical properties and color stability of PEEK material, related to surface processing (polishing or glazing). (2) Methods: This study aims to determine the influence of different ageing and staining protocols on optical properties, color changes, and surface roughness of a reinforced PEEK material (bioHPP, Bredent, Senden, Germany). For ageing, specimens were submitted to 5000 cycles in a 55 °C bath and a 5 °C bath filled with distilled water. For staining, thermal cycling was performed in a hot coffee bath (55 °C) and a bath filled with distilled water (37 °C) and in a cold juice bath (5 °C) and a bath filled with distilled water (37 °C). Translucency (TP) and opalescence (OP) parameters were determined, the total color change value (ΔΕ*) was calculated, specimens’ surface roughness was analyzed, and statistical analyses were performed. (3) Results: The mean TP values of the studied samples were in the interval of 1.25–3.60, which is lower than those reported for natural teeth or other aesthetic restoration materials. The OP values of PEEK were registered in the range of 0.27–0.75, being also lower than those of natural teeth or other aesthetic restoration materials. OP has a very strong positive relationship with TP. The mean registered Ra values for all subgroups were below 0.13 µm. Artificial ageing and staining in hot coffee proved to increase the roughness values. (4) Conclusions: The glazing of PEEK has a favorable effect on surface roughness and opalescence, irrespective of the artificial ageing or staining protocols. Artificial ageing damages the color stability and roughness of PEEK, regardless of surface processing, and decreases the translucency and opalescence of glazed surfaces. Immersion in hot coffee leads to perceivable discolorations.

An In-Vitro Study to Evaluate the Effect of Denture Cleansing Agents on Color Stability of Denture Bases Fabricated Using CAD/CAM Milling, 3D-Printing and Conventional Techniques

The current literature lacks substantial information about the effect of denture cleansers on the color stability of denture bases formed using Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM) additive and CAD/CAM subtractive manufacturing techniques. This study aimed to assess the effect of two commercially available denture cleansers on the color stability of denture base resins fabricated using four different techniques. Forty-five disc-shaped specimens were fabricated using each technique. Initial color readings were recorded. Specimens were randomly divided into three subgroups (n = 15): a control group (distilled water) and two denture cleanser groups. They were immersed in these solutions, simulating 180 days of use. Final color readings were recorded. The color difference was calculated, and the data were statistically analyzed. For all the specimens, significant color changes were observed after immersion in denture cleanser solutions. The extent of color change varied according to the type of denture cleanser used. When placed in the denture cleanser solutions, the CAD/CAM subtractive group showed the maximum color change (−1.10 and −0.72), while the CAD/CAM additive (3D printing) groups showed the least color change (−0.48 and −0.54). Clinicians should choose appropriate denture cleansers for newly introduced denture base resins to minimize the changes in the color of the dentures.

In Vitro Assessment of Artificial Aging on the Antifungal Activity of PMMA Denture Base Material Modified with ZrO2 Nanoparticles

The antifungal effect of zirconium dioxide nanoparticles (ZrO₂NPs) incorporated into denture base material has been inadequately investigated; additionally, to the authors' knowledge, no studies have assessed the influence of artificial aging on the antifungal activity of these particles. Methodology. Heat-polymerized acrylic resin disks were fabricated and divided into four groups (0%, 1%, 2.5%, and 5% ZrO₂NPs by weight). Antifungal activity was assessed using the direct culture and disk diffusion methods. Surface roughness and contact angles were measured using a profilometer and a goniometer, respectively. The artificial aging procedure was performed by repeating all tests at 7, 14, and 30 days following 2 rounds of thermocycling. Data were analyzed using ANOVA and Tukey's post-hoc test (p < 0.05). Results. The addition of ZrO₂NPs significantly decreased the adhesion of Candida albicans with and without artificial aging procedures (p < 0.001), while the disk diffusion methods did not reveal inhibition zones. ZrO₂NP-modified specimens displayed significantly higher surface roughness compared to specimens in the control group (p < 0.05) and showed the same behaviors with artificial aging procedures. The contact angle was significantly decreased in all modified groups in comparison to the control group (p < 0.05). Conclusion. The addition of ZrO₂NPs to polymethylmethacrylate denture base material reduced the adhesion of Candida albicans with a long-term antifungal effect. With the addition of ZrO₂NPs, contact angles were decreased and surface roughness was increased; 1% was the most appropriate concentration. Clinical significance. The addition of ZrO₂NPs to denture base material confers a long-term antifungal effect and could be used as a possible method for preventing and treating denture stomatitis.

Effect of Staining Solutions on Color Stability, Gloss and Surface Roughness of Removable Partial Dental Prosthetic Polymers

PURPOSE

To assess the effect of commonly used solutions on color stability, gloss, and surface roughness of removable partial dental prostheses polymers.

MATERIALS AND METHODS

Discs (n = 112) were made of a poly(etheretherketone) (PEEK) polymer, a polyamide, an acetal resin and a heat-cured poly(methylmethacrylate) PMMA acrylic resin polished according to manufacturers' instructions. Seven specimens of each material were immersed in coffee, red wine, coca cola and distilled water for 30 days at 37^ο C. Changes of color (ΔΕ*) and color coordinates L*α*b* after immersion were calculated with a colorimeter. Changes in the values of gloss and surface roughness parameters (Sa, Sz, Str, Sdr, Sci, Svi) were also measured. Two-way ANOVA and pairwise comparisons were used to evaluate the effect of material and staining solution on parameter value alterations (α = 0.05).

RESULTS

The two-way ANOVA revealed that the interaction between material and staining solution significantly affected color changes after immersion [F(9,96) = 44.67, p < 0.001]. PEEK presented the lowest color change (ΔΕ* = 3.83 ± 2) while polyamide had the highest color change overall (ΔΕ* = 14.59 ± 8.65) (p < 0.001). Coffee caused the highest color (ΔΕ* = 13.08 ± 6.98) and gloss changes (ΔG = -6.36 ± 19.2 GU) among different solutions (p < 0.001). PEEK showed the highest alteration of gloss (ΔG = -11.31 ± 15.49 GU), with significant difference with the other three materials (p < 0.001). Insignificant interaction of material and immersing solution was found for surface roughness parameters (p > 0.05).

CONCLUSIONS

Among the materials tested, PEEK seemed to be the most stable material when subjected to common, everyday staining solutions. Therefore, PEEK could be a viable solution for an RPDP framework fabrication, expanding the material list of prosthetic options. Further research and clinical trials are required to confirm the above statement.

Comparison of hardness and polishability of various occlusal splint materials

OBJECTIVES

To measure polishability of occlusal splint materials manufactured by various methods.

METHODS

Seven occlusal splint materials manufactured by four different methods - Heat cured (Vertex Rapid simplified Clear), CAD-milled (Ceramill a-splint), Vacuum-formed (Proform splint) and 3D-printed (Freeprint Ortho, KeySplint Soft, DentaClear and FreePrint Splint 2.0) were tested for gloss, roughness, and surface hardness and elastic modulus. For all groups, the tests were repeated with the materials polished with three different polishing burs, pumice and high shine. All polishing procedures were standardised by applying the force of 1 N for 1 min at the set speed. 3D printed materials were further tested with additional specimens manufactured at different printing angles of 0°, 45° and 90°. Data was statistically analysed using ANOVA (SPSS Version 26) and MatLab (R2020a). Polished surfaces of each specimen were analysed under scanning electron microscope.

RESULTS

Vacuum-formed materials showed the highest polishability (80.61 ± 0.98 GU) with no statistical significance to heat-cured or CAD-milled (p = 1.00). Pumice and high shine polish significantly improved the gloss for all groups. The mean gloss and surface roughness for all 3D-printed materials ranged from 75.24 ± 25.05 GU to 0.18 ± 0.21 GU and 2.73 ± 3.18 μm to 0.06 ± 0.01 μm, which was significantly lower (p < 0.001) than heat-cured, CAD-milled and vacuum-formed materials. The highest hardness (0.40 ± 0.009 GPa), elastic modulus (6.06 ± 1.49 GPa) and gloss were found when materials were 3D-printed at 45°, with the lowest surface roughness.

CONCLUSION

Statistically significant differences in polishability were found among the different occlusal splint materials. The polishability and surface hardness of 3D-printed occlusal splint materials was influenced by the print angle. The 0° 3D-printed occlusal splint materials produced the highest gloss and the lowest surface roughness pre-polished, indicating that no polishing is required. While the 3D-printed occlusal splint materials at 45^oand 90° required polishing with burs, pumice and high shine to reduce the surface roughness, there were layering structures created during printing.

Effect of Cleansers on the Colour Stability of Zirconia Impregnated PMMA Bio-Nanocomposite

Exposure of denture base acrylic resins to the oral environment and storage media for extended periods of time results in colour change due to changes in the properties of the material. The purpose of this in vitro study was to assess the colour stability of high-impact heat-polymerized denture base acrylic resin (HI PMMA) impregnated with zirconia nanoparticles after storage in distilled water (DW) and denture cleaners such as Steradent (STD) and Milton (MIL) for 180 days. Ninety specimens of PMMA + Zirconia nanocomposite with varying nanoparticle concentrations (1.5 wt.%, 3.0 wt.%, 5.0 wt.%, 7.0 wt.% and 10 wt.%) were prepared with a diameter and thickness of 25 ± 1.0 mm × 2 ± 0.1 mm and divided into six groups, while each group was further divided into three subgroups: storage in DW (control), STD and MIL. Colour changes were measured with a Minolta Chroma Meter (Minolta, Osaka, Japan), and assessed using the CIE L*a*b* colorimetric system. Data were statistically analysed for colour change with Friedman's Two-way and Kruskal-Wallis tests at a pre-set alpha value level of 0.05. The colour change (ΔΕ) exhibiting significant differences were found among all groups immersed in denture cleaners, and all values increased with time. According to the National Bureau of Standards, the control group displayed the lowest colour change value (ΔΕ = 1.22), and the highest value was for 10 wt.% ZrO₂ while stored in MIL (ΔΕ = 6.07). The values of colour change for storage in water ranged from 0.49 (control) to 1.82 (10 wt.% ZrO₂). The colour change value for the composite group containing 3 wt.% zirconia was clinically acceptable. However, high concentrations of denture cleaners should be avoided, and the shortest cleaning time is recommended to improve the clinical life of the nanocomposite denture base.

Color changes of polyetheretherketone (PEEK) and polyoxymethelene (POM) denture resins on single and combined staining/cleansing action by CIELab and CIEDE2000 formulas

PURPOSE

The purpose of study was to investigate the long-term effect of staining and/or cleansing solutions on the color stability of two non-metal removable partial denture materials.

METHODS

One hundred disks (25×3mm) of polyoxymethylene (POM) and polyetheretherketone (PEEK) were immersed in water, wine, coffee, cleanser and combo bath, simulating normal daily use. Color parameters in the CIELAB system was measured every 30 cycles up to 240 using a contact colorimeter and color differences estimated using ΔE_ab and ΔE₀₀ formulas. Two-way repeated measures ANOVAs and regression analyses were performed at α=0.05.

RESULTS

Regression analysis indicated a strong R² between color changes and number of cycles, for both materials. Tests of within-subjects effects for the ΔE_ab revealed significant differences among cycles and between the materials in the wine and coffee baths (p<0.001). Significant materialXcycles interactions were also recorded with all staining baths. ΔE₀₀ values were lower than ΔE_ab up to 63.6%. Tests within and between-subjects effects for the ΔE₀₀ gave similar but not the same with ΔE_ab results.

CONCLUSIONS

ΔE₀₀ found to correlate well with ΔE_ab. Long term exposure of both materials showed a progressive discoloration in all except control baths. POM discolored more than PEEK in coffee, and combo baths but not in cleanser. Discoloration was smaller in combo bath (where a cleanser was also used) indicating the effectiveness of a cleanser to prevent long term discoloration of both materials.

An in vitro study to evaluate and compare the surface roughness in heat-cured denture-based resin and injection-molded resin system as affected by two commercially available denture cleansers

Background:

Denture hygiene is of utmost importance to maintain the dentures as well as the underlying tissues in appropriate health. Various denture cleansers as well as denture-based materials have evolved in the market; however, the effect of denture cleansers on different types of denture-based materials has not been very well documented.

Aim:

The purpose of this in vitro study was to evaluate and compare the surface roughness in heat-cured denture-based resin and injection-molded resin system as affected by two commercially available denture cleansers for a period of 15, 30, and 45 days.

Methodology:

A standardized metal die was fabricated to make 120 denture-based resin discs of uniform dimensions. The samples of heat-cured denture-based resin and injection-molded thermoplastic denture-based resin were immersed in the two denture cleansing solutions for a period of 15, 30, and 45 days, respectively. The surface roughness was evaluated by surface profilometer TR200. The data were subjected to statistical analysis and the comparison of quantitative data was done using unpaired t-test and repeated-measures ANOVA test.

Results:

The surface roughness values (Ra) of heat cured denture base resin samples when immersed in two denture cleansers were 0.22 μm at 0 days, 0.27 and 0.29 μm at 15 days, 0.29 and 0.31 μm at 30 days, 0.30 and 0.31 μm at 45 days whereas for injection moulded samples surface roughness values were 1.31 & 1.27 μm at 0 days, 1.46 & 1.66 μm at 15 days, 1.50 & 1.69 μm at 30 days, and 1.50 & 1.69 μm at 45 days.

Conclusion:

The surface roughness (Ra) increased significantly in injection-molded polyamide denture-based resin samples when immersed in both the denture cleansers. Whereas, heat-cured denture-based resin samples did not reveal any significant surface changes at the various time intervals. Hence, the use of denture cleansers is questionable in thermoplastic resins.

Long-term microwaving of denture base materials: effects on dimensional, color and translucency stability

While the combined effect of microwave irradiation with cleansing solutions on denture base materials has been investigated, the effects of only using microwave irradiation and, more importantly, in a long-term basis, was not studied yet.

Evaluation of a Realistic Cleansing Protocol for Preventing Discoloration of Denture Resins

PURPOSE

To evaluate the efficacy of a realistic staining/cleansing protocol for long-term prevention of discoloration of denture base resins.

MATERIALS AND METHODS

Sixty discs (20 × 2.5 mm) of auto- and heat-polymerizing denture acrylic resins were fabricated following manufacturer's instructions, polished on one side and stored in water (37°C) for 24 hours before they were assigned randomly into 6 groups (3 for each material, n = 10) to receive 220 cycles of three immersion protocols. Group A was immersed in the following baths: (1) filtered coffee at 45°C for 2 minutes, (2) tap water at 24°C for 20 seconds, (3) as bath 1, (4) as bath 2, (5) Corega Extradent cleansing solution at 45°C for 3 minutes, and (6) water at 24°C for 20 seconds. Group B was immersed in the four first baths of group A (without cleansing action) and group C in bath 1 for the cumulative action of 20 cycles (80 minutes in 45°C coffee) and bath 2 for 40 seconds. A noncontact optical interferometric profilometer was used for qualitative evaluation of the specimens and a contact colorimeter to estimate color change values (ΔΕ*ab) at baseline and every 20 cycles in the baths for a total of 220 cycles. Data were statistically analyzed using a 2-way-repeated measures ANOVA with Bonferoni multiple comparisons and trend analysis at α = 0.05 level of significance.

RESULTS

Data indicated changes in color from 1.7 to 14.2 ΔΕ*ab units. The highest values were related to the number of cycles and group B immersion protocol. Significant differences were found among immersion protocols (p < 0.001) and immersion cycles (p < 0.001) with a significant interaction between protocols and cycles (p < 0.001) but not between denture resins (p = 0.991).

CONCLUSION

The evaluated protocol A was found effective in preventing color changes in both denture resins even after a long period of action. Protocol C had a much lower staining effect on both resins than protocol B and behaved similarly to protocol A until 140 to 160 cycles. Therefore, it is probably not appropriate for use in short-term color stability experiments.

The Influence of Thermocycling on the Flexural Strength of a Polyamide Denture Base Material

Objective

The aim of the present study was to evaluate the influence of thermocycling on the flexural strength of a polyamide base denture material.

Materials and methods

A polyamide denture base material (Valplast) was tested, whereas a PMMA material (Vertex) was used as a control. Thirty specimens of each material were fabricated for flexural strength testing according to ISO 1567. They were prepared and stored in water at 37°C for 48 hours. The specimens of each material were divided into three equal groups (n=10). Flexural strength testing was performed immediately after water storage and after thermocycling (5°C / 55°C, 2 c/min) for 3000 and 5000 cycles. A three point flexural test was performed on a universal testing machine at a crosshead speed of 5 mm/min. The final flexural strength was calculated using the formula: F_S = 3 PL/2 bd². A two-way ANOVA with post-hoc analysis using Tukey's procedure was applied at .05 level of statistical significance.

Results

A statistically significant reduction in flexural strength was recorded after thermocycling at 3000 cycles for PMMA and at 5000 cycles for both materials. The flexural strength of PMMA was significantly higher compared to polyamide for all the conditions tested (p<0.05).

Conclusion

Thermocycling had a significant adverse effect on the flexural strength of polyamide and PMMA denture base materials.

In Vitro Evaluation of the Inhibitory Activity of Thymoquinone in Combatting Candida albicans in Denture Stomatitis Prevention

Candida albicans adhesion and proliferation on denture bases may lead to denture stomatitis, which is a common and recurrent problem in denture wearers. The goal of this study was to assess the inhibitory effect of thymoquinone incorporated in the polymethyl methacrylate denture base material against Candida albicans. Eighty acrylic resin specimens were fabricated and divided into eight groups (n = 10) according to thymoquinone concentrations of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, and 5% of acrylic powder. Two methods were used to evaluate the effect of thymoquinone on Candida albicans: the slide count and the serial dilution test. A multivariate analysis of variance (MANOVA) and the post-hoc Tukey’s Honestly Significant Difference (HSD) test were performed to compare the difference of means between the observations taken at various intervals with baseline. The p value was statistically significant at ≤0.05. According to the slide count and the serial dilution test, the mean number of adhered Candida albicans in the control group was 5436.9 ± 266 and 4691.4 ± 176.8; however, this number dramatically decreased to 0 ± 0 and 32.4 ± 1.7 in group 8 (concentration 5%). These results suggest that the incorporation of thymoquinone into the acrylic resin denture base material might be effective in preventing Candida albicans adhesion.

Impact of Denture Cleansing Solution Immersion on Some Properties of Different Denture Base Materials: An In Vitro Study

PURPOSE

To evaluate the effect of several denture cleansing solutions on the color stability, surface roughness, and flexural strength of three denture base materials.

MATERIALS AND METHODS

Twenty-seven specimens were prepared using heat-polymerized (HP) denture base material, 27 using autopolymerized (AP) denture base material, and 27 using visible-light-polymerized (VLP) denture base, creating a total of 81 specimens. The specimens were randomly divided into three groups (n = 27): the distilled water group (DWG), Corega group (CG), and Renew group (RG). Color changes (ΔE), surface roughness (Ra, nm), and flexural strength (MPa) of each specimen were measured using a spectrophotometer, an optical profilometer, and a universal testing machine, respectively. The results were statistically analyzed using a one-way ANOVA and a post hoc Tukey's test (α = 0.05).

RESULTS

The only statistically significant color change detected was in the VLP resin treated with Corega and Renew. There was a significant increase in the surface roughness of all denture resin groups after immersion in Corega. Immersion in Renew significantly increased surface roughness only in the HP and AP specimens. The only significant reduction in flexural strength was detected in the HP resin after immersion in Corega (p < 0.05).

CONCLUSIONS

Within the limitations of this study, it can be concluded that Corega has a significantly greater negative impact than distilled water on the flexural strength of HP resin base materials. Renew significantly increased the surface roughness of AP and HP, while Corega increased the surface roughness of all resin materials.