Effect of dentin conditioning time on nanoleakage.

OBJECTIVES: To study the nanoleakage pattern in the dentin hybrid layer by using different dentin adhesives. The null hypotheses tested in this study were: 1) dentin conditioning time does not affect nanoleakage within the hybrid layer; 2) the type of dentin adhesive used does not affect nanoleakage. METHODS: Standardized Class V cavities were prepared in 30 intact human molars on the buccal and lingual surfaces. The specimens were randomly assigned to 2 total-etch dentin adhesives (OptiBond SOLO Plus [OPS, Kerr] and One-Step [ONS, BISCO Inc]) and 2 self-etch dentin adhesives (Clearfil SE Bond [CSE, Kuraray] and Adper Prompt L-Pop [APL, 3M ESPE]). The specimens were etched or conditioned for 15 seconds, 30 seconds or 60 seconds. Upon restoration of the Class V cavities with the proprietary resin composite, the specimens were isolated with nail polish except for a 2.0-mm rim around the restoration, and they were immersed in 50 wt% ammoniacal silver nitrate solution (pH=9.5) for 24 hours followed by 8 hours of immersion in photo-developing solution to reduce the silver ions to metallic silver. The specimens were fixed, dehydrated and processed for FESEM and TEM. Silver penetration was measured along the cervical wall, and data were analyzed with Kruskal-Wallis non-parametric tests at a significance level of 95%. RESULTS: There were no statistically significant differences among the experimental groups for the factor "conditioning time" (p>0.926). There were significant differences for the variable "dentin adhesive" (p<0.0001). The least amount of nanoleakage within the hybrid layer occurred with CSE, while ONS resulted in the greatest penetration of silver ions. The adhesives OPS and APL ranked in the intermediary subset. Under TEM, all adhesives resulted in some degree of nanoleakage within the hybrid layer. Both spotted/reticular and water-tree nanoleakage patterns were observed. SIGNIFICANCE: Longer conditioning times did not increase nanoleakage within the hybrid layer. Nanoleakage varied with the type of adhesive used.

Enamel bond strengths of pairs of adhesives from the same manufacturer.

Most manufacturers of dental adhesives have both a total-etch adhesive and a simplified self-etching adhesive available on the market. This study measured the enamel microtensile bond strengths of five pairs of enamel adhesives as a function of enamel roughness. The proximal surfaces of 25 extracted mandibular molars were sectioned with a diamond saw to obtain 50 enamel rectangles with an area of 8x4 mm2. The enamel rectangles were divided in two equal parts via a groove to obtain 4x4 mm2 squared bonding surfaces. One half was roughened with a coarse diamond bur under water for five seconds, while the other half was kept intact. The enamel surfaces were randomly assigned to 10 enamel adhesives grouped into five pairs. Each pair included one self-etch adhesive and one total-etch adhesive from the same manufacturer: Adper Prompt and Adper Single Bond (PLP and SB, 3M ESPE); AdheSE and Excite (ADH and EXC, Ivoclar Vivadent); OptiBond Solo Plus SE and OptiBond Solo Plus (OPTSE and OPT, Kerr); Tyrian SPE/One-Step Plus and One-Step (TYR and OST, BISCO, Inc); Xeno III and Prime&Bond NT (XEN and PBNT, Dentsply). The adhesives were applied according to the manufacturers' instructions. Buildups were constructed with Filtek Z250 (3M ESPE). The specimens were sectioned in sticks with a cross section of 0.8+/-0.2 mm2 and tested to failure in tension at a crosshead speed of 1 mm/minute. Two-way ANOVA followed by Duncan's post-hoc test at p<0.05 was computed. The highest mean bond strengths were obtained with total-etch adhesives. For "roughened enamel," three pairs of materials had statistically different means in which the total-etch adhesive resulted in statistically higher bond strengths (MPa) than the corresponding self-etch adhesive: EXC (36.6) > ADH (23.0) at p<0.026; OPT (34.5) > OPTSE (25.3) at p<0.028; PBNT (36.6) > XEN (19.5) at p<0.0001. For "intact enamel," four pairs of materials resulted in statistically different means: SB (31.7) > PLP (20.9) at p<0.049; EXC (37.9) > ADH (16.3) at p<0.0001; OST (30.1) > TYR (18.0); PBNT (43.8) > XEN (16.0) at p<0.0001. When the same adhesive was compared on intact vs roughened enamel, all the self-etch materials resulted in lower bond strengths on intact enamel, but this difference was only significant for TYR (p<0.042) and ADH (p<0.050). For total-etch materials, only OPT resulted in statistically lower bond strengths when applied on intact enamel p<0.011).