Objective: The acrylic resin layer of a composite denture tooth is removed when there is inadequate space for tooth arrangement. A composite denture tooth without a resin layer is frequently removed from the denture base. This study evaluated the bonding strengths of denture base resin to composite denture teeth without the acrylic resin layer using two commercial primers. Methods: Square specimens (10 x 10 x 3 mm) of both the acrylic resin layer and the composite resin layer of composite denture teeth (Duracross, Nishin, Japan) were prepared by the manufacturer. After the bonding surfaces of the specimens were abraded with #2000 emery paper, only the surfaces of the composite resin specimens were primed with Composit Primer (CP; GC, Japan) and Cera Resin Bond (CB; Shofu, Japan). Heat-cured resin (Acron, GC) was packed in a conical form (4.8 mm diam.) and polymerized to bond the specimens. As controls, specimens with an unprimed acrylic resin layer (AR) and with a composite resin layer (CR) were fabricated. The bond strengths (MPa) of the one-week aged (37 °C) specimens were measured by shear testing. The results (n=5) were analyzed by ANOVA/Tukey's test (a=0.05). Results: The bonding strengths [Mean (SD)] were: AR [25.13 (3.55)]; CR [15.14 (3.89)]; CP [18.20 (3.02)]; CB [17.40 (4.49)]. All of the composite resin specimens (CR, CP, CB) exhibited significantly lower bonding strengths than did AR (P<0.05). Although the two primed composites (CP and CB) tended to have greater bond strengths than the non-primed composite (CR), there were no significant differences (P>0.05). Conclusions: Even when primers were used on the composite resin layer of the composite denture teeth, better bonding strengths could not be achieved compared to that for the acrylic resin layer without a primer.

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