The purpose of this study was to evaluate how ultrasonic cleaning of silica-coated zirconia surfaces would influence the latter&prim;s bond strength to resin luting material. Forty zirconia specimens were divided into four groups: one air abrasion group and three silica-coated groups. Silica-coated specimens were cleaned with distilled water using an ultrasonic cleaner after tribochemical silica coating and then divided into three groups according to cleaning durations: 1 minute, 5 minutes, or without cleaning. Following which, resin luting material was polymerized against the specimens. After storage in water for 24 hours, the specimens were subjected to shear bond strength test. Shear bond strength of silica-coated group without cleaning was significantly higher than the other three groups, but there were no statistically significant differences among the three latter groups. SEM images suggested visible differences among the treatment methods. With EDXS analysis, it was revealed that ultrasonic cleaning decreased the silica content on the treated surfaces. Therefore, results showed that ultrasonic cleaning of tribochemically silica-coated zirconia surfaces decreased the adhesion efficacy to resin luting material.

Plasma irradiation on surface of heat-cured acrylic resin prior to processing self-curing acrylic resin is likely to effectively increase the adhesive strength between these materials for short-term period. However, long-term reliability of adhesive strength between these materials has not been clarified yet. In the present study, these materials were stored in water for a long period (100 days), and the effect on their shear bond strength was investigated. Forty-four test specimens with flat bonding test surface were made with heat-cured acrylic resin. They were divided into four groups according to treatment procedures for bonding surface: plasma treatment, adhesive primer application, adhesive primer application after plasma treatment, and no treatment (for control). Self-curing acrylic resin was processed against all bonding surfaces. After storage in water for 100 days, shear bond strength values between heat-cured and self-cured acrylic resins were measured. Specimens in plasma treatment group exhibited higher shear bond strength value than those in control, although the difference was not significant.

To evaluate the flexural and bonding properties, marginal adaptation, and polymerization shrinkage in flowable composite restorations and their relationships, four new generation flowable composites, one conventional, and one bulk-fill flowable composite were used in this study. Flexural properties of the composites and shear bond strength to enamel and dentin for flowable restorations were measured immediately and 24 h after polymerization. Marginal adaptation, polymerization shrinkage, and stress were also investigated immediately after polymerization. The flexural properties, and bond strength of the flowable composites to enamel and dentin were much lower immediately after polymerization than at 24 h, regardless of the type of the composite. Polymerization shrinkage and stress varied depending on the material, and bulk-fill flowable composite showed much lower values than the others. The marginal adaptation and polymerization shrinkage of the composites appeared to have a much stronger correlation with a shear bond strength to dentin than to enamel. The weak mechanical properties and bond strengths of flowable composites in the early stage after polymerization must be taken into account when using them in the clinic. In addition, clinicians should be aware that polymerization shrinkage of flowable composites can still lead to the formation of gaps and failure of adaptation to the cavity regardless of the type of composite.