The Effect of Fractional CO2 Laser Irradiation on Shear Bond Strength of Resin Cement to Feldspathic Porcelain

Introduction: This study investigated the effect of fractional CO2 laser on shear bond strength (SBS) of resin cement to feldspathic porcelain.Methods: Sixty blocks of unglazed feldspathic porcelain were randomly divided into 5 groups of 12 by treatment. Group 1 and 2 underwent etching with 9.6% hydrofluoric acid (HF) and air abrasion with alumina particles, respectively. In groups 3 and 4, a fractional CO2 laser was applied for 10 seconds using 20 W/10 mJ (group 3) or 15 W/20 mJ (group 4). The specimens in group 5 were first treated by fractional CO2 laser (15 W/20 mJ) and then etched by HF acid. After silane application, a resin cement (Clearfil SA) was poured into plastic molds over the porcelain surface and light cured. SBS was assessed by a universal testing machine and the type of bond failure was determined.Results: Analysis of variance (ANOVA) indicated a significant difference in SBS among the study groups (P < 0.001). Pairwise comparison demonstrated that the application of fractional CO2 laser followed by HF acid yielded SBS that was significantly greater than that of the other groups (P < 0.05). The SBS of both laser groups (groups 3 and 4) were comparable to each other and significantly lower than the other groups (P < 0.05). No significant difference was found in the distribution of failure modes among the groups (P = 0.522)Conclusion: The application of fractional CO2 laser followed by HF acid treatment can improve SBS of resin cement to feldspathic porcelain and could be recommended when demanding extra retention

The Effect of Lithium Disilicate Ceramic Thickness and Translucency on Shear Bond Strength of Light-cured Resin Cement

Introduction: To achieve acceptable clinical performance, a ceramic veneer must be bonded to enamel by well-polymerized resin cement. Among different factors, thickness and translucency of the ceramic may affect the resin cement polymerization. Thus, the current study evaluated the effect of the thickness and translucency of lithium disilicate ceramic on light-cured resin cement bond strength to enamel. Methods: In this laboratory study, 208 sound bovine incisors were equally divided into 16 groups (n = 13). The lithium disilicate ceramic cubes in four thicknesses (0.4, 0.6, 0.8 and 1 mm) with four translucencies (high and medium opaque, high and low translucent) were fabricated and bonded to prepared enamel surfaces using a light-cured translucent resin cement according to manufacturer recommendations. After 5000 cycles of thermocycling, the bonded specimens were placed in a universal testing machine and loaded to the point of fracture. To determine the mode of failure, each sample was observed under a stereomicroscope. Data were recorded and analyzed by Shapiro-Wilk test and two-way analysis of variance (ANOVA). Results: The ceramic thickness and translucency could not significantly affect shear bond strength (SBS) of resin cement to enamel (p = 0.17 and p = 0.097, respectively).  The Adhesive and ceramic cohesive failures were reported as the maximum and minimum mode of failure, respectively. Conclusion: The SBS of the light-cured resin cement bonding to enamel and lithium disilicate ceramic was not affected by the translucency of ceramics having a thickness of less than 1 mm

Microleakage Evaluation of Class II Composite Resin Restorations with Different Thicknesses of Resin-Modified Glass Ionomer

Background and Aim: One of the weaknesses of Class II composite resin restorations is gingival microleakage which contributes to postoperative sensitivity and secondary caries. The aim was to evaluate the microleakage in Class II composite resin restorations with different thicknesses of resin-modified glass ionomer (RMGI). Materials and Methods: In this in-vitro study, standardized Class II slot cavities were prepared on the proximal surfaces of 90 molars. In group 1, total-etch adhesive and composite resin were applied using the incremental technique. In group 2, total-etch adhesive and composite were applied using the bulk technique. In group 3, 1 mm of RMGI was applied over the gingival floor, which was covered with increments of composite. In group 4, 1 mm of RMGI was placed on the gingival floor and covered with composite using the bulk technique. In group 5, 2 mm of RMGI was applied over the gingival floor, followed by an incremental composite placement. In group 6, 2 mm of RMGI was placed on the gingival floor, and the cavity was filled using the bulk technique. After thermocycling and staining with methylene blue, the samples were sectioned, and the extent of dye penetration was examined under a stereomicroscope. Data were analyzed using Kruskal-Wallis test and logistic regression (α=0.05). Results: The lowest and highest dye penetrations were observed in the first, second, and fifth groups, respectively. The RMGI thickness did not influence the microleakage scores significantly in either composite placement techniques (P=0.828). Conclusion: None of the restorative techniques completely eliminated microleakage of Class II composite resin restorations

Effect of Bleaching and Thermocycling on Resin-Enamel Bond Strength

The aim of this study was to evaluate the effect of bleaching and thermocycling on microshear bond strength of bonded resin composites to enamel. Enamel slices were prepared from ninety-six intact human premolars and resin composite cylinders were bonded by using Adper Single Bond 2 + Filtek Z350 or Filtek silorane adhesive and resin composite. Each essential group was randomly subdivided to two subgroups: control and bleaching. In bleaching group, 35% hydrogen peroxide was applied on samples. Thermocycling procedure was conducted between 5°C and 55°C, for 3.000 cycles on the half of each subgroup specimen. Then microshear bond strength was tested. Methacrylate-based resin composite had higher bond strength than silorane-based one. The meyhacrylate-based group without bleaching along with thermocycling showed the most bond strength, while bleaching with 35% carbamide peroxide on silorane-based group without thermocycling showed the least microshear bond strength. Bleaching caused a significant degradation on shear bond strength of silorane-based resin composites that bonded using self-etch adhesive resin systems

An Innovative Rigid Tray Technique as a New Alternative Matrix System for Buildup of Severely Damaged Endodontically Treated Teeth (A Case Report)

Direct restoration of severely damaged endodontically treated teeth (ETT) using available and conventional and current matrix systems is sometimes impractical and in some clinical cases is impossible. The aim of this paper is to introduce and describe a new matrix system based on Rigid Tray Technique (RTT) for dealing with such difficult clinical cases

Do Different Tooth Bleaching–Remineralizing Regimens Affect the Bleaching Effectiveness and Enamel Microhardness In Vitro?

Objective. Tooth bleaching may negatively affect the enamel surface properties, such as reduction in hardness values, and remineralizing agents can reverse these effects. This study evaluated the effect of remineralizing agents before, during, and after the bleaching process on enamel’s whitening effectiveness and microhardness. Methods and Materials. The initial color of 104 bovine incisors after immersion in tea solution was recorded, and then, the teeth were randomly divided into eight groups (n = 13). Group 1 (NC) was considered the control with no treatment, and Group 2 (B) was bleached with 40% hydrogen peroxide gel. The 3% fluorohydroxyapatite (FHA) and 2% sodium fluoride (NaF) were applied before (FHA/B, NaF/B), during (FHA + B, NaF + B) and after (B/FHA, B/NaF) the bleaching process in other groups. The final color and microhardness in three depths of 20–30, 50–60, and 100–120 µm were measured. Data were analyzed using Shapiro–Wilk, one-way ANOVA, Tukey, Games Howell, repeated measurement, and LSD tests. Results. The FHA + B presented the lowest ΔE, significantly lower than other groups, except B/FHA. The ΔE in B/FHA was significantly lower than B/NaF. The bleaching significantly reduced the enamel hardness in three depths. The highest microhardness values were reported for B/NaF and NaF + B, which have no noticeable difference with NC, while FHA/B showed the lowest hardness in three depths, which was significantly lower than NC. Conclusion. The application of NaF before, during, and after the bleaching improved the microhardness of bleached enamel as the unbleached one with no adverse effect on whitening effectiveness