Cumulative effects of successive restorative procedures on anterior crown flexure: Intact versus veneered incisors

Objective: When successive restorative procedures (eg, porcelain veneers, i nterdental resin composite restorations, and endodontic treatment) are carr ied out on the same tooth, significant effects on crown flexure can be expe cted. Method and materials: Dentin-bonded porcelain veneers (experimental g roup) were assessed in vitro using functional and cyclic thermal loads. The y were compared to natural teeth (control group) with respect to 2 paramete rs: coronal flexure (investigated using experimental strain gauges) and mor phology of the tooth-restoration interface (scanning electron microscopic e valuation). For both veneered and natural teeth, crown deformation was reco rded at 5 sequential experimental steps: intact tooth (baseline), Class III cavities, Class III resin composite restorations, endodontic treatment, an d endodontic restoration (without posts). Results: No significant differenc es in crown flexure were found between natural and veneered incisors when c ompared across experimental steps. The main effect for experimental steps w as highly significant. When averaged across all specimens (natural and vene ered teeth), the endodontic treatment step resulted in the highest crown fl exure (1.55x the baseline value). The unrestored Class III cavities and the endodontic restoration were next highest (1.30x and 1.28x the baseline val ue, respectively). The lowest crown flexures were found after restoration o f the Class III cavities (1.13x the baseline value). No measurable microlea kage or gaps were detected at the ceramic-resin, resin-enamel, or resin-den tin interfaces (Optibond FL, Kerr), Conclusion: Each subsequent reduction i n tooth structure resulted in a substantial increase in crown flexibility, even after restoration. Endodontic procedures were responsible for most of the loss in crown stiffness. Extensive proximal cutting and restorations se emed to minimally affect crown flexure. Porcelain veneers showed perfect bi omimetic behavior, because cumulated restoration procedures had the same ef fect on natural and veneered incisors.