Comparison of mechanical and dynamic mechanical behaviors of different dental resins polymerized by different polymerization techniques

Purpose: The aim of the present investigation was to evaluate the effect of autoclave polymerization method on the mechanical and dynamic mechanical properties of different polymethylmethacrylate denture base materials.Materials and Methods: Three different denture materials were used during the study, two of them were heat polymerizable denture base material (Meliodent and Paladent) and one was microwave polymerizable denture base material (Acron MC). Duncan test was used for the statistical analysis. Statistical analyses were completed using a two‑way analysis of variance. Statistical analysis of test results was carried out with a 95% confidence level.Results: Tensile strength was increased with autoclave polymerization regardless of the denture base material type. Paladent specimens with autoclave polymerization (30 min at 60°C and 10 min at 130°C) have the highest average impact strength value. Acron MC specimens have the highest average flexural strength and modulus. Flexural strength improved with autoclave polymerization for both of 10 and 20 min polymerizations for each of Meliodent and Paladent specimens.Conclusions: Autoclave polymerization provided higher polymerization temperatures compared with the conventional heat polymerization. Autoclave‑polymerized acrylic resin specimens showed higher tensile strength values; however, this was not the case for the impact test results. Flexural strength of specimens was improved with autoclave polymerization. Glass transition temperature was increased with autoclave polymerization.Keywords: Autoclave, dental polymers, denture base resin, mechanical propertie

Effect of cavity design on the fracture resistance of zirconia onlay ceramics

Objective: The purpose of this study was to evaluate the fracture resistance and failure modes of onlay restorations prepared with different preparation designs.Materials and Methods: A total of 42 extracted, mandibular first molars (36, 46) were used and divided into six groups according to preparation design, as follows 1A: Anatomic preparation of cusps/rounded shoulder margin/occlusal groove; 1B: Flat preparation of cusps/rounded shoulder margin/occlusal groove; 2A: Anatomical preparation of cusps/occlusal groove; 2B: Flat preparation of cusps/occlusal groove; 3A: Complete anatomical reduction of cusps/rounded shoulder margin; 3B: Complete flat reduction of cusps/rounded shoulder margingroups; intact tooth: No preparation. Onlays were constructed with 0.5‑mm copings of Zirconia ceramic. The copings were veneered with porcelain (IPS e. max Ceram). All samples were subjected to fracture resistance testing. Data were analyzed with Kruskal–Wallis and Bonferroni‑Dunn tests.Results: Fracture resistance varied significantly according to preparation design. Among the anatomic occlusal preparation designs, fracture resistance was significantly lower in Group 3 when compared to Groups 1 and 2 (P < 0.05). Among the flat occlusal preparation designs, fracture resistance was significantly higher in Group 1 when compared to Groups 2 and 3 (P < 0.05).Conclusion: Preparation design affected the fracture resistance of onlay restorations. Cavities with flat occlusal preparation designs, a groove and shoulder margins (1B) resulted in the highest fracture resistance, whereas teeth prepared with a complete reduction of cusps and shoulder margins (3A) had the lowest fracture resistance.Keywords: Fracture resistance, onlay restoration, preparation design, zirconi

The Effects of Disinfectant Solutions on the Viscoelastic Properties of Acrylic Resins

Scopu

Effect of green gold nanoparticles synthesized with plant on the flexural strength of heat-polymerized acrylic resin

Purpose: The aim of this study was to investigate the effect of gold nanoparticle on the flexural strength of polymethyl methacrylate (PMMA).Materials and Methods: PMMA specimens (65 mm × 10 mm × 3.3 mm) containing different sizes (45 nm, 55 nm, and 65 nm) and concentrations (0.05% and 0.2%) of gold nanoparticles were prepared, along with a control group containing no added nanoparticles. Flexural strength of all specimens was measured, and one‑way ANOVA and Tukey–Kramer post hoc multiple comparisons tests were performed to identify statistical differences between groups.Results: The addition of gold nanoparticles increased the flexural strength of acrylic resin. Significantly greater increases were obtained with lower concentrations (0.05%) when compared to higher concentrations (0.20%).Conclusion: Differences in concentrations of gold nanoparticles added to PMMA have significantly different effects on PMMA flexural strength, whereas differences in sizes of gold nanoparticles added to PMMA do not significantly affect its flexural strength. Accordingly, adding gold nanoparticles to PMMA may enhance the mechanical properties of denture bases used in clinical practice.Keywords: Flexural strength, gold, nanoparticles, polymethyl methacrylat