title: Cumulative effects of successive restorative procedures on anterior crown flexure: intact versus veneered incisors.
abstract: OBJECTIVE
  When successive restorative procedures (e.g., porcelain veneers, interdental resin composite restorations, and endodontic treatment) are carried out on the same tooth, significant effects on crown flexure can be expected.
  
  
  METHODS
  Dentin-bonded porcelain veneers (experimental group) were assessed in vitro using functional and cyclic thermal loads. They were compared to natural teeth (control group) with respect to 2 parameters: coronal flexure (investigated using experimental strain gauges) and morphology of the tooth-restoration interface (scanning electron microscopic evaluation). For both veneered and natural teeth, crown deformation was recorded at 5 sequential experimental steps: intact tooth (baseline), Class III cavities, Class III resin composite restorations, endodontic treatment, and endodontic restoration (without posts).
  
  
  RESULTS
  No significant differences in crown flexure were found between natural and veneered incisors when compared across experimental steps. The main effect for experimental steps was highly significant. When averaged across all specimens (natural and veneered teeth), the endodontic treatment step resulted in the highest crown flexure (1.55x the baseline value). The unrestored Class III cavities and the endodontic restoration were next highest (1.30x and 1.28x the baseline value, respectively). The lowest crown flexures were found after restoration of the Class III cavities (1.13x the baseline value). No measurable microleakage or gaps were detected at the ceramic-resin, resin-enamel, or resin-dentin interfaces (Optibond FL, Kerr).
  
  
  CONCLUSIONS
  Each subsequent reduction in 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 seemed to minimally affect crown flexure. Porcelain veneers showed perfect biomimetic behavior, because cumulated restoration procedures had the same effect on natural and veneered incisors.
authors.affiliation: Minnesota Dental Research Center for Biomaterials and Biomechanics, Department of Oral Science, School of Dentistry, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: P
authors.initials: P
authors.lastname: Magne
authors.forename: W H
authors.initials: WH
authors.lastname: Douglas
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry; D003737:Dental Cavity Preparation / Q000145:classification; D003743:Dental Enamel / Q000502:physiology / Q000648:ultrastructure; D003763:Dental Leakage / Q000145:classification; D018772:Dental Marginal Adaptation; D003776:Dental Porcelain / Q000737:chemistry; D003793:Dental Restoration, Permanent / Q000145:classification / Q000379:methods*; D003801:Dental Veneers; D003804:Dentin / Q000502:physiology / Q000648:ultrastructure; D017220:Dentin-Bonding Agents / Q000737:chemistry; D004548:Elasticity; D006801:Humans; D007180:Incisor / Q000502:physiology* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D012390:Root Canal Therapy; D013314:Stress, Mechanical; D013499:Surface Properties; D019228:Tooth Crown / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D003188:Composite Resins; D017220:Dentin-Bonding Agents; D003776:Dental Porcelain