Abstract:The aim of the present study is to evaluate the transverse strength, modulus of elasticity, surface roughness, hardness, and water sorption/solubility of nanoparticle zirconium oxide (nano-ZrO 2 ) added to heat-cured poly(methyl methacrylate) (PMMA) after thermocycling. The specimens were divided into four groups according to the ratio of nano-ZrO 2 addition to heat-cured PMMA; group 1: 5% nano-ZrO 2 ; group 2: 10% nano-ZrO 2 ; group 3: 20% nano-ZrO 2 , and group 4 (control): PMMA without nano-ZrO 2 . A statistically significant decrease in transverse strength was observed by all additional rates of nanoZrO 2 compared with group 4 (control; P < 0.025). When hardness results were evaluated, groups 1 and 2 showed statistically higher values compared with groups 3 and 4 (P < 0.025). The surface roughness of group 3 was statistically higher than the other groups (P < 0.025), but it was within the clinically acceptable limits. As the nano-ZrO 2 addition rate increased, water sorption/solubility values of the specimens also increased. Although nano-ZrO 2 addition had an adverse effect on some mechanical and physical properties of heat-cured PMMA, it increased hardness values, implying that the addition of nano-ZrO 2 would contribute positively to some mechanical properties of PMMA denture base material when nano-ZrO 2 was homogeneously distributed in PMMA.

We evaluated the effects of three different surface treatments and two different bonding procedures on shear bond strength of resin composites to different computer-aided design/manufacturing (CAD/CAM) ceramics with or without thermocycling. The test specimens were prepared from three different CAD/CAM ceramics (Group A, IPS e.max CAD; Group B, IPS e.max ZirCAD; Group C, Vita Suprinity). They were divided into eight subgroups according to the surface treatment and bonding procedures. After resin composite was applied to the surfaces of all test specimens, they were stored in distilled water for 24 h at 37C. Next, half of the test specimens were subjected to a thermocycling procedure, and the other half were stored in distilled water at 37°C throughout thermocycling. The shear bond strength was performed using a universal testing machine. Statistical analysis revealed that the ceramic types (P > 0.0031) and thermocycling (P > 0.0021) did not, but the surface treatment technique did significantly affect the shear bond strength values (P < 0.05; except group C). Higher bond strength values were observed with HF etching in Groups A and C compared with the other tested surface treatments.

PURPOSEThe purpose of this study was to investigate the effect of various surface treatments (ST) on the shear bond strength of resin composite to three bilayer dental ceramics made by CAD/CAM and two veneering ceramics.MATERIALS AND METHODSThree different bilayer dental ceramics and two different veneering ceramics were used (Group A: IPS e.max CAD+IPS e.max Ceram; Group B: IPS e.max ZirCAD+IPS e.max Ceram, Group C: Vita Suprinity+Vita VM11; Group D: IPS e.max Ceram; Group E: Vita VM11). All groups were divided into eight subgroups according to the ST. Then, all test specimens were repaired with a nano hybrid resin composite. Half of the test specimens were subjected to thermocycling procedure and the other half was stored in distilled water at 37℃. Shear bond strength tests for all test specimens were carried out with a universal testing machine.RESULTSThere were statistically significant differences among the tested surface treatments within the all tested fracture types (P<.005). HF etching showed higher bond strength values in Groups A, C, D, and E than the other tested ST. However, bonding durability of all the surface-treated groups were similar after thermocycling (P>.00125).CONCLUSIONThis study revealed that HF etching for glass ceramics and sandblasting for zirconia ceramics were adequate for repair of all ceramic restorations. The effect of ceramic type exposed on the fracture area was not significant on the repair bond strength of resin composites to different ceramic types.

The present study aims to investigate the mechanical properties of base materials [polymethyl methacrylate (PMMA)/polyether ether ketone (PEEK)] fabricated with computeraided design/computer-aided manufacturing (CAD/CAM) and heatpolymerized conventional base materials. Material and Methods: Two different base polymers milled with CAD/CAM (Yamahachi PMMA Disk and Juvora Dental Disk PEEK) and heat-polymerized acrylic resin (Meliodent PMMA) were used in this study. A total of 120 specimens were prepared with 10 specimens in each subgroup of the test materials. Half of the test specimens were stored in distilled water, while the other half were subjected to a thermal cycle. After the thermal cycle, the flexural strength, elasticity module, and, surface hardness of all test specimens was evaluated. The Mann-Whitney U and Kruskal-Wallis tests were used in the analysis of the data. Results: According to the findings of flexural strength and elasticity module of the test specimens, the highest to lowest value ranking was as follows: CAD/CAM PEEK>CAD/CAM PMMA>heat-polymerized PMMA. In the PMMA group produced with CAD/CAM, surface hardness values were significantly higher in the thermocycle applied test specimens compared to those stored in distilled water (p<0.001). Conclusion: CAD/CAM PMMA and PEEK materials were compared with the heat-polymerized test specimens found to show better mechanical properties.

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