Background: Polymethyl methacrylate (PMMA) is widely used for the fabrication of removable prostheses. Recently, zirconium oxide nanoparticles (nano-ZrO₂) have been added to improve some properties of PMMA, but their effect on the optical properties and tensile strength are neglected. Objective: The aim of this study was to investigate the effect of nano-ZrO₂ addition on the translucency and tensile strength of the PMMA denture base material. Materials and methods: Eighty specimens (40 dumbbell-shaped and 40 discs) were prepared out of heat-polymerized acrylic resin and divided into four groups per test (n=10). The control group for each test included unreinforced acrylic, while the test groups were reinforced with 2.5, 5, and 7.5 wt% nano-ZrO₂. Acrylic resin was mixed according to manufacturer’s instructions, packed, and processed by conventional method. After polymerization, all specimens were finished, polished, and stored in distilled water at 37°C for 48±2 hours. Tensile strength (MPa) was evaluated using the universal testing machine while the specimens’ translucency was examined using a spectrophotometer. Statistical analysis was carried out by SPSS using the paired sample t-test (p≤0.05). A scanning electron microscope was used to analyze the morphological changes and topography of the fractured surfaces. Results: This study showed that the mean tensile strength of the PMMA in the test groups of 2.5%NZ, 5%NZ, and 7.5%NZ was significantly higher than the control group. The tensile strength increased significantly after nano-ZrO₂ addition, and the maximum increase seen was in the 7.5%NZ group. The translucency values of the experimental groups were significantly lower than those of the control group. Within the reinforced groups, the 2.5%NZ group had significantly higher translucency values when compared to the 5%NZ and 7.5%NZ groups. Conclusion: The addition of nano-ZrO₂ increased the tensile strength of the denture base acrylic. The increase was directly proportional to the nano-ZrO₂ concentration. The translucency of the PMMA was reduced as the nano-ZrO₂ increased. Clinical significance: Based on the results of the current study, the tensile strength was improved with different percentages of nano-ZrO₂ additions. However, translucency was adversely affected. Therefore, it is important to determine the appropriate amount of reinforcing nano-ZrO₂ that will create a balance between achieved properties – mechanical and optical.

This study is aimed at evaluating the hybrid reinforcement effects of zirconium oxide nanoparticles (nano-ZrO₂) and glass fibers (GFs) at different ratios on the flexural and impact strengths of a polymethylmethacrylate (PMMA) denture base. A total of 160 specimens were fabricated from heat-polymerized acrylic resins using the water bath technique. For the control group, the specimens did not receive any additions; for the test group, different concentrations of nano-ZrO₂/GFs at 5% of the PMMA polymer were added. The concentrations of nano-ZrO₂/GFs were as follows: 5%–0%, 4%–1%, 3%–2%, 2.5%–2.5%, 2%–3%, 1%–4%, and 0%–5%. The flexural strength was measured using the three-point bending test. The impact strength was measured using the Charpy impact test. Results were tabulated and analyzed using one-way analysis of variance (ANOVA) and the Tukey–Kramer multiple comparison test (p≤0.05). The flexural and impact strengths of PMMA-nano-ZrO₂ + GF composites were significantly improved when compared with those of pure PMMA (p<0.05). The maximum flexural strength (94.05 ± 6.95 MPa) and impact strength (3.89 ± 0.46 kJ/m²) were obtained with PMMA (2.5%)/nano-ZrO₂ + 2.5% GF mixtures and could be used for removable prosthesis fabrication.

Titanium dioxide nanoparticles (TiO₂NP) have gained interest in the dental field because of their multiple uses in addition to their antimicrobial effect. One of the applications in dentistry involves the incorporation into poly methyl methacrylate (PMMA) resin. However, there is a lack of evidence on their effects on the behavior of the resulting nanocomposite. Therefore, the present review aims to screen literatures for data related to PMMA/TiO₂nanocomposite to figure out the properties of TiO₂nanoparticles, methods of addition, interaction with PMMA resin matrix, and finally the addition effects on the properties of introduced nanocomposite and evidence on its clinical performance. Regardless of the latest research progress of PMMA/TiO₂nanocomposite, the questionable properties of final nanocomposite and the lack of long-term clinical evidence addressing their performance restrict their wide clinical use. A conclusive connection between nanoparticle size or addition method and nanocomposite properties could not be established.

Precise fit of a crown and accurate reproduction of the digital design are paramount for successful treatment outcomes and preservation of clinician and technician time. The study aimed to compare the internal fit, marginal adaptation, precision, and trueness of 3D-printed zirconia crowns compared to their milled counterpart. A total of 20 monolithic 3 mol% yttria stabilized-zirconia crowns (n = 10) were made using computer-assisted design (CAD) followed by additive (3D-printed) and subtractive (milled) manufacturing. Digital scanning of the master die with and without a fit checker followed by image superimposition, and analysis was performed to evaluate internal and marginal adaptation in four areas (occlusal, axial, marginal, and overall). ISO 12836:2015 standard was followed for precision and trueness evaluation. Statistical analysis was achieved using a t-test at α = 0.05. Internal fit and marginal adaptation revealed no significant difference between the two test groups (p > 0.05). The significant difference in trueness (p < 0.05) was found between the two groups in three areas (occlusal, axial, and internal). The best and worst trueness values were seen with 3D-printed crowns at occlusal (8.77 ± 0.89 µm) and Intaglio (23.90 ± 1.60 µm), respectively. The overall precision was statistically better (p < 0.05) in the 3D-printed crowns (9.59 ± 0.75 µm) than the milled (17.31 ± 3.39 µm). 3D-printed and milled zirconia crowns were comparable to each other in terms of internal fit and marginal adaptation. The trueness of the occlusal and axial surfaces of 3D-printed crowns was better, whereas the trueness of fitting surface of milled crowns was better. 3D-printed crowns provided a higher level of precision than milled crowns. Although the internal and marginal fit of both production techniques were comparable, 3D printing of zirconia produced more precise crowns.