Effects of core characters and veneering technique on biaxial flexural strength in porcelain fused to metal and porcelain veneered zirconia

PURPOSE: The purpose of this study was to assess the impact of the core materials, thickness and fabrication methods of veneering porcelain on prosthesis fracture in the porcelain fused to metal and the porcelain veneered zirconia. MATERIALS AND METHODS: Forty nickel-chrome alloy cores and 40 zirconia cores were made. Half of each core group was 0.5 mm-in thickness and the other half was 1.0 mm-in thickness. Thus, there were four groups with 20 cores/group. Each group was divided into two subgroups with two different veneering methods (conventional powder/liquid layering technique and the heat-pressing technique). Tensile strength was measured using the biaxial flexural strength test based on the ISO standard 6872:2008 and Weibull analysis was conducted. Factors influencing fracture strength were analyzed through three-way ANOVA (alpha< or =.05) and the influence of core thickness and veneering method in each core materials was assessed using two-way ANOVA (alpha< or =.05). RESULTS: The biaxial flexural strength test showed that the fabrication method of veneering porcelain has the largest impact on the fracture strength followed by the core thickness and the core material. In the metal groups, both the core thickness and the fabrication method of the veneering porcelain significantly influenced on the fracture strength, while only the fabrication method affected the fracture strength in the zirconia groups. CONCLUSION: The fabrication method is more influential to the strength of a prosthesis compared to the core character determined by material and thickness of the core.

Evaluation of shear bond strength between dual cure resin cement and zirconia ceramic after thermocycling treatment

PURPOSE: This study was performed to evaluate shear bond strength (SBS) between three dual-cured resin cements and silica coated zirconia, before and after thermocycling treatment. MATERIALS AND METHODS: Sixty specimens were cut in 15 x 2.75 mm discs using zirconia. After air blasting of 50 microm alumina, samples were prepared by tribochemical silica coating with Rocatec(TM) plus. The specimens were divided into three groups according to the dual-cure resin cement used: (1) Calibra silane+Calibra(R), (2) Monobond S+Multilink(R) N and (3) ESPN sil+RelyX(TM) Unicem Clicker. After the resin cement was bonded to the zirconia using a Teflon mold, photopolymerization was carried out. Only 10 specimens in each group were thermocycled 6,000 times. Depending on thermocycling treatment, each group was divided into two subgroups (n=10) and SBS was measured by applying force at the speed of 1 mm/min using a universal testing machine. To find out the differences in SBS according to the types of cements and thermocycling using the SPSS, two-way ANOVA was conducted and post-hoc analysis was performed by Turkey's test. RESULTS: In non-thermal aged groups, SBS of Multilink group (M1) was higher than that of Calibra (C1) and Unicem (U1) group (P<.05). Moreover, even after thermocycling treatment, SBS of Multilink group (M2) was higher than the other groups (C2 and U2). All three cements showed lower SBS after the thermocycling than before the treatments. But Multilink and Unicem had a significant difference (P<.05). CONCLUSION: In this experiment, Multilink showed the highest SBS before and after thermocycling. Also, bond strengths of all three cements decreased after thermocycling.

Surface roughness and Candida albicans adhesion to flexible denture base according to various polishing methods / 대한치과보철학회지

PURPOSE: The purpose of this study was to compare the effect of 3 chairside polishing methods and laboratory polishing methods on surface roughness and C. albicans adhesion of polyamide denture base. MATERIALS AND METHODS: Using contact profilometer, the surface of polyamide specimens (25x15x2 mm) was studied after conventional polishing without finishing and after chiarside polishing with 2 chiarside polishing kits and chairside-pumice polishing following finishing with tungsten carbide bur. To evaluate the adhesion of C. albicans, C. albicans suspension was overlayed on the test specimen. And the specimens were incubated for 2 hours. Imprint culture method was achieved and counted the colony on the agar plate. Polished polyamide were evaluated using a scanning electron microscope. The statistics were conducted using one-way ANOVA and in case of difference, Scheffe test and Tamhane's T2 test were used. RESULTS: Surface roughness (Ra) of surfaces polished with 2 chairside polishing kits had higher than conventional polishing and pumice polishing. The highest roughness value was 0.32 +/- 0.10 microm, and the lowest was 0.02 +/- 0.00 microm. The adhesion of C. albicans on the specimens polished with chairside polishing group and pumice polishing group were increased than conventional polishing group (P.01).