Microtensile bond strength between crown and root dentin and two adhesive systems

Abstract

Since bonding agent effectiveness is usually evaluated on coronal substrates, available knowledge for judging the effectiveness of bonds to root dentin is insufficient. The objective of this study was to evaluate the bond strength of 2 adhesive systems to crown, cervical finish line, and post space dentin. Twenty bovine maxillary incisors were used in this study. Teeth were sectioned along the cemento-enamel junction using a low-speed diamond blade to separate the crowns and roots. Then the crowns and roots were each divided into 2 groups, according to the 2 adhesive systems tested (n=10). The facial enamel surfaces of the crowns were abraded with 600-grit silicon carbide paper to expose flat, midcoronal dentin surfaces. Drills and a diamond rotary cutting instrument were used in a low-speed handpiece to prepare post spaces in the root canals. The same diamond rotary instrument was used to prepare horizontally flat surfaces in the cervical areas, similar to the horizontal aspect of a shoulder finish line. Composite resin was placed incrementally into the post spaces, over the flat cervical shoulder areas, and on the coronal dentin. Bonded beam specimens (0.5 mm(2) of cross-sectional area) derived from crown, cervical finish line, and post space dentin, were prepared for microtensile bond testing and tested in tension. Data were analyzed using 2-way ANOVA and Tukey post hoc test (alpha=.05). Failure patterns of tested specimens were analyzed using scanning electron microscopy. The mean tensile bond strength values (SD) (MPa) were: Single Bond-crown: 29.8 (4.0); Single Bond-finish line: 18.7 (4.3); Single Bond-post space: 17.0 (4.8); Clearfil SE Bond-crown: 30.1 (6.4); Clearfil SE Bond-finish line: 30.4 (5.3); and Clearfil SE Bond-post space: 17.0 (4.2). Bond strengths to post space dentin were lower than those to coronal dentin for both adhesives (P<.001). However, no significant difference was observed between coronal and finish line dentin for Clearfil SE Bond. Bond strength was reduced when adhesives were used in bonding to post space dentin. Cervical finish line sites bonded using Clearfil SE Bond adhesive yielded bond strength similar to that of coronal dentin sites.