In this study, dentin bond fatigue resistance and interfacial science characteristics of universal adhesives through etch-and-rinse and self-etch modes were investigated. Resin composite was bonded to human dentin with four universal adhesives, namely, Adhese Universal, All-Bond Universal, G-Premio Bond, and Scotchbond Universal Adhesive. The initial bond strengths, bond fatigue strengths, and interfacial science characteristics of the universal adhesives with dentin through etch-and-rinse and self-etch modes were determined. Bond fatigue resistance (initial bond strength and bond fatigue strength) of universal adhesives in etch-and-rinse mode showed no significant difference in contrast to that in self-etch mode and was material-dependent regardless of the etching mode. Although phosphoric acid conditioning of dentin did not have a strong impact on the bond fatigue resistance, surface free energy and parameters of dentin were significantly decreased by etching and by application of universal adhesives regardless of etching mode. Changes in γ S and γ S h for when universal adhesive was applied to etched and ground dentin were significantly different depending on the adhesive. The results suggest that bonding performance of universal adhesives was effective in both etching modes; however, bonding mechanisms may be different for each. Keywords; light-curing of dental adhesives, dental debonding, dental etching, dental restoration failure, dental stress analysis Materials and Methods Study materials Four universal adhesives were used in this study: (i) Adhese Universal (AU, Ivoclar Vivadent, Schaan, Liechtenstein), (ii) All-Bond Universal (AB, Bisco, Schaumburg, IL, USA), (iii) G-Premio Bond (GB, GC, Tokyo, Japan), and (iv) Scotchbond Universal Adhesive (SU, 3M Oral Care). Ultra-Etch (Ultradent, South Jordan, UT, USA) was used as a 35% phosphoric acid pre-etching agent and Z100 Restorative (3M Oral Care) as the resin composite employed to make specimens. Table 1 lists the tested materials and their lot numbers and components. Specimen preparation This study used de-identified extracted human molar teeth. To comply with research ethics, the protocol was reviewed and approved by the Ethics Committee for Human Studies of NU (#2015-06) and Biomedical Institutional Review Board at CU (#760765-1). Preparation of the teeth was done in the manner described in the study by Nagura et al. [18], except that a flat dentin surface, rather than enamel surface, was prepared. Specimens with and without etching were prepared for each adhesive, giving a total of eight experimental groups for each of the procedures performed (Table 2). Initial bond strength testing Initial bond strength testing was carried out as described by Nagura et al. [18]. Bond fatigue strength testing Bond fatigue strength testing was carried out as described by Nagura et al. [18].

We used optical coherence tomography to examine the effect of a coating material containing surface reaction-type pre-reacted glass-ionomer (S-PRG) filler on primary enamel demineralization in 18 extracted human primary teeth. The pulp was removed, and each tooth was ultrasonically cleaned with distilled water. Six teeth were treated with 0.1-M lactic acid buffer solution (De group). In the second group (n = 6), a thin film of coating material was applied before demineralization (PRG group). A third group (Control group; n = 6) was maintained in artificial saliva. Using optical coherence tomography, we measured peak signal intensity (dB) and width at 1/e (µm) at predetermined locations on the enamel surface and calculated integrated values. All data were analyzed with ANOVA and the Tukey-Kramer test (α = 0.05). Although changes in integrated values differed between groups, there was a small but significant increase in the Control group and a small but significant decrease in the De group. In the PRG group, integrated values were significantly higher at 7 days after the start of the experiment and significantly increased thereafter. Our findings indicate that a coating material containing S-PRG fillers may prevent primary enamel demineralization.

In this study, we investigated the effect of light irradiation and primer/adhesive application on the polymerization reaction and elastic modulus (E) of self-adhesive resin cement (SAC) through ultrasonic velocity (V) measurements. The V values of longitudinal and shear waves were determined based on the transit time through the specimens and specimen thicknesses, and were used to calculate the E values. Analysis of variance and Tukey tests revealed that V increased rapidly, reaching a plateau at 2,700-2,900 m/s, when the SACs were light-irradiated. However, the increasing rate of V was retarded for the non-irradiated SACs. In addition, when the primer/adhesive was applied, higher E values were obtained after 24 h. Finally, the polymerization behavior of the SACs was affected by light irradiation and primer application, and the use of prime/adhesive might improve mechanical properties. In clinical situations, use of primer/adhesive is recommended for getting proper adhesion.