Three-dimensional finite element analysis of anterior two-unit cantilever resin-bonded fixed dental prostheses

The aim of this study was to evaluate the influence of different framework materials on biomechanical behaviour of anterior two-unit cantilever resin-bonded fixed dental prostheses (RBFDPs). A three-dimensional finite element model of a two-unit cantilever RBFDP replacing amaxillary lateral incisorwas created. Five frameworkmaterialswere evaluated: direct fibre-reinforced composite (FRC-Z250), indirect fibre-reinforced composite (FRC-ES), gold alloy (M), glass ceramic (GC), and zirconia (ZI). Finite element analysis was performed and stress distribution was evaluated. A similar stress pattern, with stress concentrations in the connector area, was observed in RBFDPs for all materials.Maximal principal stress showed a decreasing order: ZI >M>GC> FRC-ES > FRCZ250. The maximum displacement of RBFDPs was higher for FRC-Z250 and FRC-ES than for M, GC, and ZI. FE analysis depicted differences in location of the maximum stress at the luting cement interface between materials. For FRC-Z250 and FRC-ES, the maximum stress was located in the upper part of the proximal area of the retainer, whereas, for M, GC, and ZI, the maximum stress was located at the cervical outline of the retainer. The present study revealed differences in biomechanical behaviour between all RBFDPs.The general observation was that a RBFDP made of FRC provided a more favourable stress distribution

Rebond strength of bonded lingual wire retainers

There is no consensus in the literature concerning the rebonding procedure for orthodontic retainers. The aim of this in vitro study was to evaluate the bond and rebond strength of retainers bonded to enamel surfaces with and without composite remnants. The retainers were bonded with Excite and Tetric Flow on three different surfaces: clean enamel, enamel where the composite had been removed by a tungsten carbide bur, and with cured composite remnants roughened by a tungsten carbide bur. The bond strength was determined by means of a cantilever-tensile bond strength test using a repeated crossover design. Each tooth was rebonded twice and tested three times (N = 114). The surface was examined by scanning electron microscopy (SEM), electron backscatter diffraction and micro X-ray fluorescence (EDAX), and scored using the adhesive remnant index (ARI). Two-way analysis of variance of the mean bond strengths did not show significant differences between the three different enamel surface treatments. However, the specimens with cured composite remnants showed a higher standard deviation. This was confirmed by Weibull analyses. The ARI score showed that 96.5 per cent of bond fractures occurred at the retainer-resin interface. In contrast to the ARI score obtained in this study, the clinical ARI scores also showed failures at the resin-enamel interface. Based on these results, it is recommended that for rebonding the bond site is controlled, and the enamel surfaces are free of old composites remnants

Effect of polyvinyl siloxane impression material on the polymerization of composite resin

Statement of problem: Polyvinyl siloxane impression material has been widely used as a lingual matrix for rebuilding missing tooth structure with composite resin. The composite resin is light polymerized in contact with the polyvinyl siloxane impression material. However, polyvinyl siloxane impression material has been shown to interact with other dental materials. Purpose: The purpose of this study was to assess the effect of polyvinyl siloxane impression materials on the polymerization of composite resins by assessing the Vickers microhardness and degree of conversion of polyvinyl siloxane. Material and methods: The composite resins were light polymerized in contact with 3 polyvinyl siloxane impression materials (Flexitime Easy Putty; President Light Body; Xantopren L Blue) (n=8) and in contact with a matrix strip as the control group (n=8). Vickers microhardness and degree of conversion on contact surfaces were measured to evaluate the polymerization of composite resins. The depth of the effect was assessed by Vickers microhardness on section surfaces and observed with scanning electron microscopy. The results were analyzed by 1-way analysis of variance and the post hoc Tukey honest significant differences test (α=.05). Results: The Vickers microhardness and degree of conversion values on the contact surfaces of the experiment groups were significantly lower than those of the control group (P.05). The scanning electron microscope observation showed that an approximately 10-μm deep unpolymerized layer was found in the experimental group. Conclusions: Polyvinyl siloxane impression materials have an inhibitory effect on the polymerization of the composite resins, but just limited to within approximately 10 μm from the surface in contact with the impression material

Influence of filler existence on microleakage of a self-etch adhesive system

Aim: This study evaluated the effect of filler existence in self-etch adhesive resin on the marginal leakage of a class V restoration. Materials and Methods: Class V cavities were prepared and restored with a resin composite on the buccal surfaces of 48 premolars lined with unfilled or filled adhesives (n = 24). After thermo cycling, teeth in each group were divided to two subgroups (n = 12), specimens of the first subgroup were incubated for 24 h in distilled water at 37°C, and for the second group three months in the same condition. Specimens were placed in 50% silver nitrate for 24 h at 37°C, and then were cut buccolingually 1 mm thick. Dye penetration was measured using a stereomicroscope and scaled from 0 to 5 in a blind method. SEM images were made to evaluate the dentin-adhesive interfaces. Collected data were analyzed using the nonparametric Kruskal-Wallis and Mann-Whitney U-tests at a significant level of P<0.05. Results: There was no significant difference between microleakage of filled and unfilled adhesive at 24 h and 3 months (P<0.05). There was a significant difference in cervical microleakage between 24 h and 3 months, which was independ on filler load of the adhesive (P<0.001). In contrast, there was no significant difference in occlusal microleakage between 24 h and 3 months and the cervical microleakage was significantly higher than occlusal microleakage after 3 months. SEM images reveald that unfilled adhesive infiltrate slightly better than filled adhesive. Conclusion: The application of filler particles in a self etch adhesive system had no influence on marginal leakage at both the enamel and dentin margins. While the unfilled adhesive infiltrate better than the filled adhesive, its long term performance is not promising