SEM characterization of the resin-dentine interface produced in vivo

Objectives: A freeze-fracture technique with critical-point drying has been shown to preserve the structure of collagen in demineralized primed dentine in vitro (Titley K et al. Am J Dent 1994; 7: 22–26). This study utilized the technique to examine the attachment to dentine produced in vivo by All-Bond 2 (AB2), Scotchbond Multi-Purpose (SBMP) and Prisma Universal Bond 3 (PUB3). Methods: Eighteen medium-depth restorations were placed in buccal and/or lingual surfaces of premolar teeth (n = 7) scheduled for extraction for orthodontic purposes. After extraction, the restored teeth were split transversely by freeze-fracture, critical-point dried and examined under SEM. Results: AB2 and SBMP produced significant gap-free attachment to dentine showing similar microscopic structural features. Resin interdiffusion with collagen fibrils of the intertubular matrix was clearly seen. Microspaces, observed at the periphery of the widened tubules and among the interdiffused collagen fibrils, suggested incomplete resin penetration. Fractures occurring parallel with the interface frequently showed detachment in the deepest layers of the hybrid zone. Adhesive gaps were seen at the resin-dentine interface, indicating some clinical technique failure. The PUB3 attachment was generally incomplete, with separation between the primed dentinal surface and the composite restoration. Where present, the bonded interface showed no evidence of true hybridization. Conclusion: Dentine conditioning, as a separate step, prior to priming, appears to be an important factor in successful resin-dentine attachment. Critical-point drying revealed variations in the degree of resin interdiffusion with intertubular collagen, suggesting potential sites for bond failure.