Analysis of the Adhesive Interface of a Self-Adhesive Resin Cement

Objective: The purpose of this investigation was to provide deeper insights into the adhesion mechanism of the self-adhesive resin cement RelyX™ Unicem (RXU) to tooth substance.

Methods: Composite blocks (Paradigm MZ100) were cemented with RXU Aplicap (both 3M ESPE) to human dentin (ground with 600 grit wet SiC paper followed by rinsing with water-spray and gentle air-drying) under standardized pressure (20g/mm²) simulating the clinical situation. The specimens were cured (light and self cured according to manufacturer's instructions), stored for 24h at 36°C, 100% rel. hum. and 3d in water, sectioned, etched (HCl 32%, 30s) and subsequently treated with NaOCl (³4% active chlorine, 120s) and dried in ethanol. The interface RXU-dentin was investigated by FE-SEM (LEO 1530VP, Zeiss) and elemental analysis by EDX (energy dispersive x-ray spectroscopy, INCA 300, Oxford).

Results: RXU was shown to penetrate the smear layer forming an intimate contact to dentin including the formation of resin tags. Resin tags could not be dissolved demonstrating an efficient polymerization of RXU in contact with the dentin smear layer and in the tubuli. Elemental analysis confirmed the microscopic observations detecting RXU specifically at the dentin surface and in tubuli.

Conclusion: The self-adhesive resin cement RXU penetrates the dentin smear layer and forms resin tags. The unique initiator chemistry leads to efficient polymerization of RXU under these special interface conditions. This contributes to the good adhesive performance observed for RelyX Unicem to dentin.