RESUMO
OBJECTIVE: The aim of this study was to determine the effect of trenched zirconia bar on the von Mises stress distribution of IPS -Empress II core ceramics. MATERIALS AND METHODS: The three-dimensional model including a three-unit bridge from the second premolar to the second molar was designed. The model was reinforced with zirconia bar (ZB), zirconia bar with vertical trench (VZB) and zirconia bar with horizontal trench (HZB) (cross sections of these bars were circular). The model without zirconia bar was designed as the control. The bridges were loaded by 200 N and 500 N on the occlusal surface at the middle of the pontic component and von Mises stresses were evaluated along a defined path. RESULTS: IN THE CONNECTOR AREA, VON MISES STRESS IN MPA WERE APPROXIMATELY IDENTICAL IN THE SPECIMENS WITH ZB (AT MOLAR CONNECTOR (MC): 4.75 and at premolar connector (PC): 6.40) and without ZB (MC: 5.50, PC: 6.68), and considerable differences were not recognized. Whereas, Von-Mises stress (MPa) in the specimens with horizontal trenched Zirconia bar (HZB) (MC: 3.91, PC: 2.44) and Vertical trenched Zirconia bar (VZB) (MC: 2.53, PC: 2.56) was decreased considerably. CONCLUSION: Embeded trenched zirconia bar could reinforce IPS-Empress II at the connector area which is a main failure region in all ceramic fixed partial dentures.
RESUMO
OBJECTIVE: This study evaluated the effect of saliva contamination during bonding procedures without removing saliva on shear dentin bond strength of three adhesive generations when rubber dam isolation is not feasible. MATERIALS AND METHODS: Flat superficial dentin surfaces of seventy-two extracted human molars were randomly divided into three groups (A: Scotch Bond MP Plus (SBMP), B: Single Bond (SB), C: Prompt L-Pop) according to the applied adhesives and twelve subgroups (n=6) according to the following saliva contamination applied in different bonding steps. The specimens were contaminated with saliva after etching (A1 and B1), after primer application (A2), after adhesive application before polymerization (A3, B2 and C1), and after adhesive polymerization (A4, B3 and C2). Three subgroups were not contaminated as controls (A5, B4 and C3). Resin composite was placed on dentin subsequently followed by thermocycling. Shear test was performed by Universal testing machine at 0.5 mm/min crosshead speed. The collected data were statically analyzed using one and two-way ANOVA and Tukey HSD. RESULTS: In contrast to SBMP and SB, the mean shear bond strength of Promote L-Pop was not significantly different between contaminated and uncontaminated subgroups. Mean shear bond strengths of SBMP subgroups contaminated after adhesive polymerization or uncontaminated were significantly higher compared to the other two groups (p<0.05). CONCLUSION: Unlike Promote L-Pop, saliva contamination could reduce shear bond strength of the total-etch adhesives. Furthermore, the step of bonding procedures and the type of adhesive seems to be effective on the bond strength of adhesive contaminated with saliva.
