Different Polymers for the Base of Removable Dentures? Part I: A Narrative Review of Mechanical and Physical Properties

Gingival margin interfacial microleakage, staining, and push-out strengths of gingival colored composite resins in denture bases

STATEMENT OF PROBLEM

Staining at the gingival margin could impact denture longevity, but the behavior of gingival colored composite resins (GCCs) in this area remains unclear.

PURPOSE

This in vitro study evaluated surface staining, microleakage, and push-out bond strength at the gingival margin of artificial teeth, comparing two consistencies of GCCs with two resin base materials.

MATERIAL AND METHODS

Specimens included artificial teeth (Ivostar; Ivoclar AG) and two acrylic resin base materials: conventional (Ondacryl; Clássico) and high-impact (Diamond D; Keystone Industries) (n=300). Specimens were divided in three groups: control (acrylic resin) and experimental groups, receiving one of the two GCCs consistencies: paste (SR Nexco; Ivoclar AG) or flowable (Gradia Plus Gum; GC Europe)). Initial artificial aging treatment in distilled water (5 days at 55º C) was performed and the specimens were then immersed in 5% methylene blue dye or coffee for 7 days at 37º C. Staining was visually assessed, and the specimens were sectioned for dye infiltration analysis at the gingival margin using a stereomicroscope. Bond strength was measured with the push-out test in the gingival colored composite resin specimens. Data were analyzed using 2-way and 3-way ANOVA with Bonferroni post hoc test and Kruskal-Wallis test with Dunn post hoc test (α=.05).

RESULTS

A significantly higher surface staining and microleakage was observed in experimental groups compared to the control (acrylic resin) (P<.001). Surface staining revealed that paste consistency GCC was more susceptible to discoloration in coffee, while flowable GCC was more affected by methylene blue. Lower microleakage values were observed in the control (acrylic resin) groups (0.11 ±0.13 mm for the conventional base and 0.08 ±0.11 mm for the high-impact base) in comparison with the experimental groups (P<.05). The flowable GCC showed the highest microleakage with methylene blue (0.98 ±0.21 mm for the conventional base and 0.91 ±0.31 mm for the high-impact base), significantly greater than the paste consistency for both base materials (0.53 ±0.22 mm for the conventional base and 0.66 ±0.34 mm for the high-impact base; P<.001). For coffee immersion, both GCC consistencies displayed similar microleakage values (P>.05). Push-out bond strength was comparable between paste and flowable GCCs (P>.05).

CONCLUSIONS

Microleakage at the gingival margin was significantly greater when GCC was applied, regardless of the consistency. However, the GCC consistency seems to not affect push-out bond strength. Further clinical studies are needed to better understand the impact of these findings on prosthesis longevity.

Investigation of the mechanical properties of lavender-reinforced heat-activated polymethyl methacrylate denture base resin

STATEMENT OF PROBLEM

The antimicrobial efficacy of lavender has been well evidenced. However, investigations into its impact on the mechanical properties of denture resins are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the flexural strength, impact strength, surface characteristics, roughness, elastic modulus, and yield strength of lavender-reinforced, heat-activated polymethyl methacrylate denture base resin.

MATERIAL AND METHODS

A total of 200 specimens were categorized into 5 groups based on 0, 0.5, 1.0, 1.5, and 2.0 wt% of dry lavender extract incorporated into heat-activated polymethyl methacrylate denture base resin powder. Unmodified resin served as the control group. Flexural strength, elastic moduli, and yield strength were determined with a universal testing machine, impact strength with an Izod impact tester, surface characteristics with scanning electron microscopy, and roughness with a profilometer. The data were statistically analyzed with 1-way ANOVA followed by Tukey post hoc tests for pairwise comparison within the groups (α=.05).

RESULTS

Compared with the control group, all the mechanical properties significantly improved with the addition of lavender (P<.001). The highest flexural, yield, and impact strengths and elastic modulus values were in the 2% group. Elevated surface roughness in 0.5, 1.0 and 1.5 wt% and a decline in roughness at 2 wt% were noted when compared with the control group.

CONCLUSIONS

The addition of lavender enhanced the flexural strength, yield strength, impact strength, elastic moduli, and decreased surface roughness when added at 2 wt%.

Water Absorption of Underwater Products by Additive Manufacturing

Rapid prototyping techniques offer significant advantages in terms of fabrication speed, accessibility, and low cost. This study explores the use of low-cost stereolithographic resins to produce prototypes intended for underwater conditions. The objective is to evaluate the feasibility of different low-cost resin brands by identifying their water absorption percentage and their response in terms of appearance and deformation after prolonged exposure to an underwater environment. Through three different tests, the suitability of the resins and possible coatings is evaluated, allowing for obtaining data not disclosed by commercial manufacturers and indicating that there are low-cost brands that offer water absorption levels suitable for underwater use. The coefficients for water absorption at saturation begin at 3.3% in saltwater and increase for chlorinated water. Additionally, significant insights are gained regarding the use of coatings. It is found that coatings commonly applied to filament-printed prototypes are generally less suitable for parts produced through stereolithography intended for underwater applications. The most effective strategy is to avoid using coatings altogether.

Microbial Adhesion to Different Thermoplastic Denture Base Materials in Kennedy Class I Partially Edentulous Patients

Introduction Since the polished and fitting surface of the denture base may promote the colonization of microorganisms, it is essential to know how the different types of denture bases prevent or encourage the adhesion of microorganisms. This study aimed to compare the microbial adhesion to the polished and fitting surfaces of thermoplastic nylon, thermoplastic acetal, and thermoplastic acrylic denture bases in Kennedy Class Ⅰ, partially edentulous patients. Materials and methods Thirteen patients were included in the study. The group consisted of eight males (61.54%) and five females (38.46%), with an age range of 41-50 years (mean age 46.1 years). Three types (groups) of removable partial dentures will be made for each patient using different thermoplastic denture base materials: thermoplastic nylon; thermoplastic acetal; and thermoplastic acrylic. The polished and fitting surfaces of the denture bases were swabbed after a one-month follow-up period. Microbial adhesion was evaluated by counting the microorganisms' colony-forming units (CFU) in the collected specimens. The data were collected and statistically analyzed. Results The study revealed no statistically significant difference in microbial adhesion to both polished and fitting surfaces between all types of studied thermoplastic denture base materials. However, the results showed that for the polished surface, the microbial adhesion median of thermoplastic acrylic denture base (40.5 CC x 102/ml) was higher than that of thermoplastic acetal (29.0 CC x 102/ml) and thermoplastic nylon (16.0 CC x 102/ml). Regarding the fitting surface, the microbial adhesion median of thermoplastic acrylic (51.0 CC x 102/ml) is higher than that of thermoplastic acetal (41.0 CC x 102/ml) and thermoplastic nylon (23.0 CC x 102/ml). Conclusion The thermoplastic nylon denture base materials showed less microbial adhesion among the studied thermoplastic materials, so it may be recommended to be used as a denture base material for individuals at high risk of denture stomatitis.

Effect of Adding Different Concentrations of Silver Nanoparticles on Flexural Strength and Microhardness of Different Denture Base Materials

AIM

This study aimed to evaluate the effect of adding different concentrations of silver nanoparticles (AgNPs) on the flexural strength and microhardness of various denture base materials.

MATERIALS AND METHODS

For this study, a total of 60 specimens were used and divided into equal groups. The first group consisted of heat-cured acrylic resin (Vertex-Germany), while the second group consisted of thermoplastic resin (Breflex 2nd edition, Germany). The samples were created using a split brass mold with dimensions of 65 × 10 × 2.5 mm, in accordance with the specifications of the American Dental Association (specifically No. 12 for flexural and microhardness). Following this, the samples were divided into three groups (A, B, and C) based on different concentrations of AgNPs (0, 2, and 5%). The flexural and microhardness of the samples were assessed using a universal testing machine and the Vickers hardness test, respectively. The data were gathered, organized, and analyzed using statistical methods.

RESULTS

The flexural strength findings showed a significant difference between the two groups. Also, there was a considerable decrease in the average value of the acrylic group as the concentrations of AgNPs rose, while the flexural strength of the thermoplastic group notably improved. Regarding microhardness, the results showed a significant difference between the two groups. It showed that the mean value of both groups increased with increasing concentrations of AgNPs.

CONCLUSION

Within the limitations of laboratory testing conditions of this study, it was discovered that AgNPs negatively impact the flexural strength of acrylic resins. Furthermore, an increase in the concentration of AgNPs was found to be directly related to the flexural strength of thermoplastic resin and the microhardness of both groups.

CLINICAL SIGNIFICANCE

The concentration of AgNPs has a significant impact on certain mechanical properties of denture base materials, but it is important to consider their potential toxicity. How to cite this article: El-Hussein IG. Effect of Adding Different Concentrations of Silver Nanoparticles on Flexural Strength and Microhardness of Different Denture Base Materials. J Contemp Dent Pract 2024;25(5):417-423.

Comparative Analysis of the Mechanical Properties and Biocompatibility between CAD/CAM and Conventional Polymers Applied in Prosthetic Dentistry

Modern media often portray CAD/CAM technology as widely utilized in the fabrication of dental prosthetics. This study presents a comparative analysis of the mechanical properties and biocompatibility of CAD/CAM (Computer-Aided Design/Computer-Aided Manufacturing) polymers and conventional polymers commonly utilized in prosthetic dentistry. With the increasing adoption of CAD/CAM technology in dental laboratories and practices, understanding the differences in material properties is crucial for informed decision-making in prosthodontic treatment planning. Through a narrative review of the literature and empirical data, this study evaluates the mechanical strength, durability, esthetics, and biocompatibility of CAD/CAM polymers in comparison to traditional polymers. Furthermore, it examines the implications of these findings on the clinical outcomes and long-term success of prosthetic restorations. The results provide valuable insights into the advantages and limitations of CAD/CAM polymers, informing clinicians and researchers about their suitability for various dental prosthetic applications. This study underscores the considerable advantages of CAD/CAM polymers over conventional ones in terms of mechanical properties, biocompatibility, and esthetics for prosthetic dentistry. CAD/CAM technology offers improved mechanical strength and durability, potentially enhancing the long-term performance of dental prosthetics, while the biocompatibility of these polymers makes them suitable for a broad patient demographic, reducing the risk of adverse reactions. The practical implications of these findings for dental technicians and dentists are significant, as understanding these material differences enables tailored treatment planning to meet individual patient needs and preferences. Integration of CAD/CAM technology into dental practices can lead to more predictable outcomes and heightened patient satisfaction with prosthetic restorations.