The evaluation of stress patterns in porcelain laminate veneers with different restoration designs and loading angles induced by functional loads: A three-dimensional finite element analysis study.

BACKGROUND: Fractures in porcelain laminate veneers (PLVs) are a significant clinical problem. Preparation designs can affect stress distribution, which leads to fractures in PLVs. Therefore, identification of the most favorable preparation design in terms of stress distribution is required. OBJECTIVE: The purpose of this study is to examine the functional stress patterns of PLVs with featheredge, incisal bevel, and overlapped preparation designs under 0°, 60°, and 120° functional loads using finite element analysis. MATERIALS AND METHODS: Porcelain veneers with three different preparation designs (incisal overlap, incisal bevel, and featheredge) were modeled. A cement layer of 100 µm of luting composite resin was assumed, and a thickness of 0.5 mm of porcelain veneers was used. All models were loaded at 0°, 60°, and 120° to the long axis of the tooth to determine the stresses that may occur during mastication under different load angulations. A total force of 200 N was applied from the incisal edge of the models. RESULTS: Maximum stresses were recorded in the incisal overlapped design (53.3 MPa) under 120° of functional load. Minimum stresses were recorded in the incisal bevel preparation design (22.37 MPa) under 0° of functional load. CONCLUSION: Both the preparation design and load angle affected the stress distribution on the PLVs. The incisal bevel preparation design provided a more appropriate geometry for stress distribution compared with the other techniques. Lateral forces produced more stress on the tooth and laminate material than vertical forces.

Bond strength of resin composite to light activated bleached enamel.

OBJECTIVES: This study evaluated the microtensile bond strength (µTBS) of a resin composite bonded to bleached enamel as a function of bleaching conditions. MATERIALS AND METHODS: The whiteness hydrogen peroxide (HP) bleaching agent containing 35% HP was applied to the central incisors' facial enamel surface and irradiated as follows: No treatment (G1; control); no light (G2); light-emitting diode, the 40s (G3); diode laser, the 20s (G4); and neodymium:yttrium aluminum garnet laser, 20s (G5). A Variolink II resin composite structure was then built up incrementally on the surface. The teeth were sectioned into three 1.2 mm × 1.2 mm wide "I"-shaped sections. The specimens were then subjected to microtensile testing at a crosshead speed of 1 mm/min. Data were analyzed using one-way ANOVA (α =0.05) followed by the Tukey Honestly Significant Difference post-hoc test. The fractured surfaces were observed with a stereomicroscope at × 100 magnification. RESULTS: One-way ANOVA revealed no statistical differences among the groups (P > 0.05). No differences appeared between the groups bonded 14 days after bleaching (P > 0.05). Mean µTBS values (MPa) were as follows: 22.05 ± 5.01 (G1); 19.6 ± 5.6 (G2); 19.3 ± 5.4 (G3); 20.08 ± 2.08 (G4); and 18.1 ± 4.8 (G5). Many adhesive failures occurred at the bleached and irradiated enamel surfaces. CONCLUSION: The various irradiation treatments following the application of the whiteness HP bleaching agent to enamel did not significantly reduce the µTBS within a 14-day period.

Effect of provisional restorations on the final bond strengths of porcelain laminate veneers.

The purpose of this in vitro study was to evaluate the effect of the different provisional restorations cementation techniques on the final bond strengths of porcelain laminate veneers (PLVs). Thirty-six extracted human central incisors were sectioned 2 mm below the cemento-enamel junction, and crown parts were embedded into self-cure acrylic resin. Standardized PLV preparations were carried out on labial surfaces of the teeth. Then the teeth were randomly divided into three groups of 12 each. In group 1, provisional restorations were cemented with eugenol-free cement. In group 2, prepared teeth surfaces were first coated with a desensitizing agent then provisional restorations were cemented with resin cement. In group 3, provisional restorations were not fabricated to serve as control. After specimens were stored in distilled water for 2 weeks, provisional restorations were removed and final IPS Empress 2 ceramic veneers were bonded with a dual-curing resin. Two microtensile samples from each tooth measuring 1.2 x 1.2 x 5 mm were prepared. These sections were subjected to microtensile testing and failure values were recorded. The data were analysed by one-way anova and Tukey HSD tests. The PLVs, placed on the tooth surface that had received a dentine desensitizer and provisional restorations luted with resin cement (group 2), showed the lowest bond strength in all test groups. But no statistically significant differences were found between the bond strength of PLVs in control group (no provisional restorations) and group 1 (provisional restorations cemented with eugenol-free cement before final cementations). Scanning electron microscopic (SEM) examination of this study also showed that the bonding to enamel surface was better in control group and group 1 than group 2.

Microleakage of different cementation techniques in Class V ceramic inlays.

Microleakage between the restorative materials and the cavity walls of teeth remains a problem. The purpose of this study was to evaluate the microleakage around Class V ceramic inlay restoration using three different cementation techniques. Class V preparations were made on the buccal surfaces of 45 freshly extracted premolar teeth. The teeth were randomly divided into three groups of 15. In the first group, dentine bonding agent (DBA) (Clearfil Liner Bond 2V) was applied immediately after the tooth preparation (D-DBA). In the second group, DBA was applied to the prepared cavities while luting ceramic inlays (I-DBA). In the third group, DBA was not applied at either stage (No-DBA). Impressions were made and ceramic inlays (Ceramco II) fabricated and cemented in the Class V cavities. The restorations were stored in water at room temperature for 24 h. All restorations were thermocycled and then subjected to a dye penetration test. After sectioning, leakage at cavity/restoration interface was scored. Statistical analysis was performed using Kruskal-Wallis, Mann-Whitney U and Wilcoxon's signed tests. Results showed no significant difference among three different cementation techniques (P > 0.05). Microleakage at the dentine margins was greater than that at the enamel margins (P < 0.05).

Influence of different light sources on microtensile bond strength and gap formation of resin cement under porcelain inlay restorations.

Clinical success with ceramic inlays/onlays has been assisted by the ability to develop a reliable bond of composite resin to dental tissues. The purpose of this study was to test the efficiency of two different light sources on microtensile bond strength and the gap formation of resin cement under class II porcelain inlay restorations. Standardized mesio-occlusal cavities were prepared in 30 freshly extracted, intact human premolar teeth. Then impressions were made and ceramic inlays were fabricated. In the cementation process, the resin cement/inlay combinations were exposed to two different photopolymerization units. The polymerizations through 15 specimens were performed with a conventional halogen light source for 60 s, and the other specimens were cured by a plasma arc light for 9 s. After the cementation process, two 1.2 x 1.2 mm wide 'I' shape sections per tooth were produced with a sectioning machine and sections were subjected to microtensile testing after 24 h or 1 week. Gap formation of specimens cured by different photopolymerization units were evaluated with scanning electron microscopy (SEM). Statistically significant differences were found between the microtensile bond strength of inlays exposed to conventional light and plasma arc curing unit (P < 0.001). Plasma arc curing units make it possible to polymerize composite in much shorter times than conventional curing unit. However, the samples polymerized with conventional halogen light produced better microtensile bond strength than the plasma arc unit.

The effect of dentin desensitizers on thermal changes in the pulp chamber during fabrication of provisional restorations.

The purpose of this study was to evaluate the effect of two dentin desensitizers on the pulp chamber temperature increase during fabrication of provisional restorations by a direct method. Sixty intact extracted mandibular third molars were prepared for a metal-ceramic complete crown. Then the teeth were randomly divided into three groups of 20 each. Group 1, no dentin desensitizer was used as the control group; group 2, a resin-based dentin desensitizer was selected; and group 3, the prepared teeth surfaces were coated with polyurethane cyanoacrylate adhesive. Each of the three groups was further divided into two polymerizing systems (autopolymerizing and a photopolymerizing) of 10 each. After insertion of the resin-filled matrix, the temperature change in the pulpal chamber was recorded with thermocouple connected to a data logger. anova indicated no significant differences for all combinations of desensitizing agents and curing methods (P > 0.05). When light cured composite or chemical curing acrylics were used to make temporary crowns, the presence of desensitizing agent did not reduce the temperature transmitted from the provisional material; the residual temperature rise transmitted was of such a magnitude as to cause concern regarding possible thermal injury to pulp.

The efficiency of different light sources to polymerize resin cement beneath porcelain laminate veneers.

Plasma arc light units for curing resin composites have been introduced with the claim of relatively short curing times. The purpose of this study was to evaluate the efficiency of two different light sources to polymerize dual curing resin cement beneath porcelain laminate veneers. Twenty extracted healthy human maxillary centrals were used. Teeth were sectioned 2 mm below the cemento-enamel junction and crown parts were embedded into self-cure acrylic resin, labial surface facing up. Cavity preparation was carried out on labial surfaces. These teeth were divided into two groups of 10 each. The resin cement/veneer combination was exposed to two different photo polymerization units. A conventional halogen light (Hilux 350, Express Dental Products) and a plasma arc light (Power PAC, ADT) were used to polymerize resin cement. Ten specimens were polymerized conventionally (40 s) and the other specimens by plasma arc curing (PAC) (6 s). Two samples from each tooth measuring 1.2 x 1.2 x 5 mm were prepared. These sections were subjected to microshear testing and failure values were recorded. Statistically significant differences were found between the bond strength of veneers exposed to conventional light and PAC unit (P < 0.001). Samples polymerized with halogen light showed better bond strength. The results of this study suggest that the curing efficiency of PAC through ceramic was lower compared with conventional polymerization for the exposure durations tested in this study.