Effect of dentin primer application on regional bond strength to cervical wedge-shaped cavity walls

The purpose of this study was to examine the effect of multiple applications of self-etching primer on regional tensile bond strength (microTBS) to artificial wedge-shaped cavities (i.e., occlusal vs gingival wall). Eighteen extracted noncarious human molars were used to measure microTBS, and four additional teeth were used for scanning electron microscopy (SEM) of the interface. Wedge-shaped defects were prepared in the buccal cervical dentin. The teeth were mounted on their distal surface, simulating the supine position of the teeth during dental treatment. The teeth were divided into two groups according to the bonding systems [Clearfil Liner Bond II (LB) or Imperva Fluoro Bond (FB)], and again divided into two subgroups for bonding. One group (Group S) was treated once with the primer according to the manufacturer's instructions. For the other group (Group M), the primer was applied several times for the period recommended by the manufacturer. The adhesive bonding resins were then applied to the cavity walls, and restored with a low-viscosity resin composite (Protect Liner F), and stored in 37 degrees C water for 24 hours. The resin-bonded teeth were serially sliced parallel to the long axis of the tooth. The adhesive interface of each slice was trimmed alternately at the occlusal or gingival wall, and a microtensile testing method was used to compare resin bond strength to each wall. With both adhesive systems and primer application methods, tensile bond strength to the gingival wall was significantly lower than to the occlusal wall (P < 0.05). Tensile bond strength of LB to each cavity wall of a wedge-shaped defect increased significantly by multiple primer application (P < 0.05); however, bond strengths of FB were not significantly different after multiple primer applications.