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

Efficacy of denture cleansers on Candida albicans adhesion and their effects on the properties of conventional, milled CAD/CAM, and 3D-printed denture bases

OBJECTIVES

Evaluate the efficacy of denture cleaners on the adhesion of Candida albicans and their effects on the surface, optical, and mechanical properties of resins for conventional, milled, and 3D-printed denture bases.

MATERIALS AND METHODS

A total of 240 resin samples were made, 120 for testing Candida albicans adhesion, optical stabilities (ΔE00), roughness (Ra), hydrophilicity (°), surface free energy (Owens-Wendt) and 120 samples for testing Candida albicans adhesion, surface microhardness (Knoop), flexural strength and modulus of elasticity in a three-point test, in which they were divided into 3 groups of denture resin (n = 40) and subdivided into 5 cleaners of dentures (n = 8). Data were evaluated by two-way ANOVA and Tukey's test for multiple comparisons (α = 0.05).

RESULTS

Denture cleaners with an alkaline solution and dilute acid composition were those that showed the greatest effectiveness in reducing Candida albicans (P < 0.001), however 1% NaOCl significantly affected the properties of the resins (P < 0.05). Denture 3D-printed showed that the surface microhardness was significantly lower for all cleansers (P < 0.05).

CONCLUSIONS

Listerine demonstrated superior efficacy in reducing Candida albicans with minimal effect on denture properties, whereas 1% NaOCl had a significant negative impact on the properties. The mechanical properties were significantly lower in 3D-printed resin than in other resins for all denture cleansers.

CLINICAL RELEVANCE

Denture base materials are being sold to adapt to the CAD/CAM system, increasing the number of users of dentures manufactured with this system. Despite this, there is little investigation into denture cleaners regarding the adhesion capacity of microorganisms and the optical, surface and mechanical properties of dentures, thus requiring further investigation.

Effects of simulated long-term exposure to bottled, neutral pH electrolyzed oxidizing water on the properties of denture base resins

STATEMENT OF PROBLEM

Denture stomatitis can pose serious health risks, especially to older people. Chemical denture cleaning agents must be effective, yet not adversely affect the longevity of removable dentures. Ready-to-use (RTU) neutral pH electrolyzed oxidizing water (EOW) is an effective biocide against Candida albicans biofilms on denture resins, but the effects of daily disinfection with EOW on the physical and mechanical properties of resins have not been established.

PURPOSE

The purpose of this in vitro study was to investigate the effects of simulated long-term exposure to RTU EOW on the color, surface characteristics, and flexural strength of denture base resins.

MATERIAL AND METHODS

Heat-polymerized (HP), 3D printed (3D) and computer-aided design and computer-aided manufacture (CAD-CAM)-milled (CC) denture resin specimens (square: 20×20×3.3 mm; beam: 64×10×3.3 mm) were immersed in tap water (TW), RTU EOW (Neutral Anolyte ANK; Envirolyte; EOW), or a commercial denture cleaning tablet solution (Polident 3-Minute; Glaxo SmithKline; PD), mimicking a 5-minute once daily disinfection routine performed up to 3.0 years. Color and surface roughness were recorded (n=3, squares), and changes in color (∆E00) and surface roughness (∆Ra) were calculated. Flexural strength (n=12, beams) and surface hardness (n=18, beams) were measured with a universal testing machine. The fractured surfaces of specimens were examined by scanning electron microscopy and energy dispersive spectroscopy. Data were assessed by performing the Shapiro-Wilk or D'Agostino and Pearson normality tests. Two-way ANOVA or the Kruskal-Wallis test with a post hoc Tukey HSD or Dunn multiple comparisons (α=.05) was used for statistical analyses.

RESULTS

No significant changes were found in either color or surface roughness for HP, 3D, and CC resins after 1.5-year and 3.0-year immersion in any of the agents (P>.05). The surface hardness of 3D resins reduced by 14% with TW and by 23% with EOW and PD at 3.0 years. The flexural strengths of all 3 resins were unaffected by 3.0-year immersion (P>.05).

CONCLUSIONS

Simulated long-term immersion disinfection with RTU neutral pH EOW did not adversely affect the physical and mechanical properties of HP or CC denture resins.

Effects of various disinfectants on surface roughness and color stability of thermoset and 3D-printed acrylic resin

Denture cleansers are extensively utilized to inhibit the colonization of various Candida species. Currently, additive technology in denture fabrication has become more prevalent. This study aims to assess the impact of disinfectants on the surface roughness and color stability of distinct denture bases. Disc-shaped samples (N=66) were exposed to three different disinfectants: 0.5% sodium hypochlorite, 1% hydrogen peroxide, and 2% chlorhexidine. The samples underwent evaluation via spectrophotometry and profilometry, respectively. Data analysis was conducted utilizing analysis of variance (ANOVA) (p < 0.05). Within the heat-cured group, sodium hypochlorite resulted in the most notable change in surface roughness (0.2 μm), while chlorhexidine exhibited the least impact (0.001 μm), showing a significant difference (p <0.008). The color change (ΔE) for 3D-printed samples immersed in all disinfectants was higher compared to heat-cured samples. Among the heat-cured samples, chlorhexidine induced the highest ΔE (2.76), while sodium hypochlorite resulted in the lowest (ΔE = 1.44), and this difference was statistically significant (p <0.008). Chlorhexidine caused the most significant color alteration among the solutions, while sodium hypochlorite induced the most considerable changes in surface roughness.

Effect of denture cleansers on the physical and mechanical properties of CAD-CAM milled and 3D printed denture base materials: An in vitro study

STATEMENT OF PROBLEM

Studies on the impact of denture cleansers on the physical and mechanical properties of denture bases designed and constructed by using computer software programs are lacking.

PURPOSE

The purpose of this in vitro study was to test the effect of a peroxide denture cleanser on the hardness, fracture toughness, water sorption, and solubility of denture base materials manufactured by 3D printing and computer-aided design and computer-aided manufacturing (CAD-CAM) milling.

MATERIAL AND METHODS

The hardness, fracture toughness, water solubility, and sorption of CAD-CAM milled and 3D printed groups (n=40) were evaluated before and after exposure to a denture cleanser. Hardness (n=10) was analyzed with a Vickers hardness testing machine, and fracture toughness (n=20) with the 3-point bend test. After the fracture of specimens, a scanning electron microscope at ×300 was used for fractographic analysis. Water sorption and solubility (n=10) were evaluated before and after immersion in denture cleanser for 6 days to simulate 180 days of immersion. Two-way repeated ANOVA and 2-way ANOVA were used to test normally distributed data, whereas the Mann Whitney U test and Wilcoxon signed ranks test were used for data that were not normally distributed (α<.05).

RESULTS

The Vickers hardness and fracture toughness of both materials decreased after immersion in denture cleansers, with a higher decrease in values for the 3D printed group (P<.001). The denture cleanser had no effect on the water sorption and solubility of either group.

CONCLUSIONS

Milled specimens had higher hardness values and fracture toughness before and after immersion in the denture cleanser. Denture cleansers resulted in the reduced hardness and fracture toughness of both groups, but the percentage change in the milled group was lower. Denture cleansers had no effect on water sorption or solubility.

Effect of denture cleansers on color stability and surface roughness of denture bases fabricated from three different techniques: Conventional heat-polymerizing, CAD/CAM additive, and CAD/CAM subtractive manufacturing

PURPOSE

Denture base materials are commonly exposed to different denture cleansers which can affect their essential properties. This study aimed to assess the effect of denture cleansers on color stability and surface roughness of poly methyl methacrylate (PMMA) denture bases fabricated from different techniques: Conventional heat-polymerizing, CAD/CAM additive and CAD/CAM subtractive.

MATERIALS AND METHODS

In this in vitro study, 24 disc-shaped specimens were fabricated by the mentioned methods for each group. The initial color and surface roughness of specimens were recorded. The specimens were randomly divided into three subgroups (n = 8): a control subgroup (distilled water), and two experimental subgroups of bioactive oxygen tablet (Corega) and 1% sodium hypochlorite solution. Then they were immersed in the solutions simulating 180 days of clinical use. Color change (∆E) was measured by a spectrophotometer according to the CIE L*a*b* color space and the American National Bureau of Standards (NBS = 0.92 × ∆E). Final surface roughness was recorded by a profilometer and its change was calculated. The Kruskal-Wallis test followed by the Wilcoxon signed rank test were used for statistical analyses (α = .05).

RESULTS

The conventional and CAD/CAM subtractive groups showed an increase in surface roughness following immersion in hypochlorite solution (p < .05). After immersion in the solutions, the highest surface roughness was noted in the conventional group, and the lowest in the CAD/CAM additive group. The CAD/CAM additive group experienced a significant color change in hypochlorite solution (p < .05) and showed the highest color change while the CAD/CAM subtractive group showed the lowest color change in all denture cleanser solutions.

CONCLUSION

Although the CAD/CAM additive denture base resins had the lowest surface roughness after exposure to denture cleanser solutions, they showed significant color change, which should be taken into account. Using hypochlorite as a denture cleanser should be cautioned due to its negative effects on the surface roughness and color stability of denture base materials.

Impact of different chemical denture cleansers on the properties of digitally fabricated denture base resin materials

PURPOSE

To compare the impact of three different chemical denture cleansers (CDCs) (Corega, chlorhexidine, and hydrogen peroxide) on the surface roughness, microhardness, and color stability of 3D-printed, computer-aided design and computer-aided manufacturing (CAD-CAM) milled, and heat-polymerized denture base material (DBM).

MATERIALS AND METHODS

A total of 420 disc-shaped specimens (10 ± 0.1 × 2 ±0.1 mm) were fabricated using three different construction techniques: three-dimensional (3D) printing (n = 140), CAD-CAM milling (n = 140), and heat-polymerization (n = 140). Sixty specimens (20 of each DBM) were used for baseline (pre-immersion) measurements (T1 ) for the tested surface properties (hardness [n = 10/material] and roughness [n = 10/material]). The remaining 360 specimens (n = 120/material) were investigated for surface roughness, microhardness, and color change after immersion for 1 year (T2 ) in distilled water or CDCs (n = 30/solution and n = 10/test). The data were analyzed using two-way ANOVA, one-way ANOVA followed by post-hoc Tukey's test at a significance level of less than 0.05.

RESULTS

Significant differences were observed in the effects of the tested CDCs on the surface roughness, micro-hardness, and color stability of varying DBM specimens (p < 0.05). Corega showed the highest surface roughness and color change in all DBMs while H2 O2 resulted in the lowest microhardness for all DBMs. The lowest changes in all tested properties were seen with distilled water followed by chlorhexidine. A significant effect of type of cleanser, denture base material, and the interaction between the two was seen on all measured properties (p < 0.05).

CONCLUSIONS

The tested CDCs significantly affected the surface properties of all DBMs but at varying degrees. Corega produced the highest negative effect on roughness and color change while H2 O2 dramatically affected the microhardness. Prolonged use of CDCs should be cautiously followed.

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.

Effect of Denture Disinfectants on the Mechanical Performance of 3D-Printed Denture Base Materials

Denture care and maintenance are necessary for both denture longevity and underlying tissue health. However, the effects of disinfectants on the strength of 3D-printed denture base resins are unclear. Herein, distilled water (DW), effervescent tablet, and sodium hypochlorite (NaOCl) immersion solutions were used to investigate the flexural properties and hardness of two 3D-printed resins (NextDent and FormLabs) compared with a heat-polymerized resin. The flexural strength and elastic modulus were investigated using the three-point bending test and Vickers hardness test before (baseline) immersion and 180 days after immersion. The data were analyzed using ANOVA and Tukey's post hoc test (α = 0.05), and further verified by using electron microscopy and infrared spectroscopy. The flexural strength of all the materials decreased after solution immersion (p < 0.001). The effervescent tablet and NaOCl immersion reduced the flexural strength (p < 0.001), with the lowest values recorded with the NaOCl immersion. The elastic modulus did not significantly differ between the baseline and after the DW immersion (p > 0.05), but significantly decreased after the effervescent tablet and NaOCl immersion (p < 0.001). The hardness significantly decreased after immersion in all the solutions (p < 0.001). The immersion of the heat-polymerized and 3D-printed resins in the DW and disinfectant solutions decreased the flexural properties and hardness.

Effects of Smokeless Tobacco on Color Stability and Surface Roughness of 3D-Printed, CAD/CAM-Milled, and Conventional Denture Base Materials: An In Vitro Study

Tobacco consumption in its different forms can affect the optical and surface properties of dental materials that are used in the oral cavity. Thus, the present study was conducted to evaluate the effects of two commercially available smokeless tobacco products on the color stability and surface roughness of denture base resins that were fabricated using three different techniques (CAD/CAM milling, 3D printing, and conventional heat polymerization). A total of 126 denture base resin specimens were fabricated using the three different manufacturing techniques (n = 42 each). Specimens from each group were further subdivided into three subgroups (n = 14 each) and immersed in three different immersion media (a khaini suspension, a tabbaq suspension, and artificial saliva). The differences in color and surface roughness were assessed according to data that were collected and statistically analyzed using SPSS version 24.0. The tabbaq smokeless tobacco was found to cause greatest changes in color and surface roughness; the effect was observed to be highest in the 3D-printed specimens followed by the conventional heat-polymerized and CAD/CAM milled specimens. The mean changes in color and surface roughness were the highest for the tabbaq smokeless tobacco followed by the khaini smokeless tobacco and the artificial saliva. Statistically significant (p-value < 0.05) differences were observed among all techniques and suspensions. We concluded that the mean changes in color and surface roughness were significantly higher for the 3D-printed dentures compared to the conventional heat-polymerized and CAD/CAM-milled dentures. Thus, the results of the present study strengthened the concept that tobacco in any form can lead to changes in the color and surface roughness of denture base materials.

3D Printing of Dental Prostheses: Current and Emerging Applications

Revolutionary fabrication technologies such as three-dimensional (3D) printing to develop dental structures are expected to replace traditional methods due to their ability to establish constructs with the required mechanical properties and detailed structures. Three-dimensional printing, as an additive manufacturing approach, has the potential to rapidly fabricate complex dental prostheses by employing a bottom-up strategy in a layer-by-layer fashion. This new technology allows dentists to extend their degree of freedom in selecting, creating, and performing the required treatments. Three-dimensional printing has been narrowly employed in the fabrication of various kinds of prostheses and implants. There is still an on-demand production procedure that offers a reasonable method with superior efficiency to engineer multifaceted dental constructs. This review article aims to cover the most recent applications of 3D printing techniques in the manufacturing of dental prosthetics. More specifically, after describing various 3D printing techniques and their advantages/disadvantages, the applications of 3D printing in dental prostheses are elaborated in various examples in the literature. Different 3D printing techniques have the capability to use different materials, including thermoplastic polymers, ceramics, and metals with distinctive suitability for dental applications, which are discussed in this article. The relevant limitations and challenges that currently limit the efficacy of 3D printing in this field are also reviewed. This review article has employed five major scientific databases, including Google Scholar, PubMed, ScienceDirect, Web of Science, and Scopus, with appropriate keywords to find the most relevant literature in the subject of dental prostheses 3D printing.

Physical and Mechanical Properties of 3D-Printed Provisional Crowns and Fixed Dental Prosthesis Resins Compared to CAD/CAM Milled and Conventional Provisional Resins: A Systematic Review and Meta-Analysis

Newly introduced provisional crowns and fixed dental prostheses (FDP) materials should exhibit good physical and mechanical properties necessary to serve the purpose of their fabrication. The aim of this systematic literature review and meta-analysis is to evaluate the articles comparing the physical and mechanical properties of 3D-printed provisional crown and FDP resin materials with CAD/CAM (Computer-Aided Designing/Computer-Aided Manufacturing) milled and conventional provisional resins. Indexed English literature up to April 2022 was systematically searched for articles using the following electronic databases: MEDLINE-PubMed, Web of Science (core collection), Scopus, and the Cochrane library. This systematic review was structured based on the guidelines given by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The focused PICO/PECO (Participant, Intervention/exposure, Comparison, Outcome) question was: ‘Do 3D-printed (P) provisional crowns and FDPs (I) have similar physical and mechanical properties (O) when compared to CAD/CAM milled and other conventionally fabricated ones (C)’. Out of eight hundred and ninety-six titles, which were recognized after a primary search, twenty-five articles were included in the qualitative analysis, and their quality analysis was performed using the modified CONSORT scale. Due to the heterogeneity of the studies, only twelve articles were included for quantitative analysis. Within the limitations of this study, it can be concluded that 3D-printed provisional crown and FDP resin materials have superior mechanical properties but inferior physical properties compared to CAD/CAM milled and other conventionally fabricated ones. Three-dimensionally printed provisional crowns and FDP materials can be used as an alternative to conventional and CAD/CAM milled long-term provisional materials.

Comparison between Conventional PMMA and 3D Printed Resins for Denture Bases: A Narrative Review

The aim of the current paper is to review the available literature reporting on comparative studies of heat-cured resins and three-dimensionally printed biomaterials for denture bases in terms of their composition, properties, fabrication techniques and clinical performance. The methodology included applying a search strategy, defining inclusion and exclusion criteria, selecting studies to summarize the results. Searches of PubMed, Scopus, and Embase databases were performed independently by three reviewers to gather literature published between 2018 and 2021. A total of 135 titles were obtained from the electronic databases, and the application of exclusion criteria resulted in the identification of 42 articles pertaining to conventional and 3D printed technology for removable dentures. The main disadvantages of the heat-cured resins for removable dentures are that they require lots of special equipment, skilled personnel and time. Emerging technologies, such as 3D printed dentures, have the potential to alleviate these problems allowing for faster patient rehabilitation. With the development of digital dentistry, it is becoming increasingly necessary to use 3D printed resin materials for the manufacturing of removable dentures. However, further research is required on the existing and developing materials to allow for advancement and increase its application in removable prosthodontics.