title: Dynamometric assessment of the mechanical resistance of porcelain veneers related to tooth preparation: a comparison between two techniques.
abstract: BACKGROUND
  There is little agreement regarding a palatal extension of the preparation for porcelain veneers, as it represents a more invasive technique than a preparation limited to the facial surface of a tooth.
  
  
  OBJECTIVE
  The purpose of this study was to detect the stress in maxillary anterior teeth restored with porcelain veneers and compare the resistance to fracture of porcelain veneers prepared using different preparation designs.
  
  
  METHODS
  Forty-five maxillary anterior teeth were restored with porcelain veneers and divided into 9 groups as follows: Ca, canines with no preparation; Ca-Ch, canines with palatal chamfer preparation; Ca-W, canines with window preparation; LI, lateral incisors with no preparation; LI-Ch, lateral incisors with palatal chamfer preparation; LI-W, lateral incisors with window preparation; CI, central incisors with no preparation; CI-Ch, central incisors with palatal chamfer preparation; CI-W, central incisors with window preparation. Shear-flexural fracture tests were performed. The fractured specimens were subjected to scanning electron microscope (SEM) analysis. Data were statistically analyzed with univariate analysis of variance and the Tukey post hoc test for multiple comparisons (alpha=.05).
  
  
  RESULTS
  The following mean fracture load values (N) were recorded: Ca, 395 +/- 6; Ca-Ch, 310 +/- 8; Ca-W, 322 +/- 8; LI, 309 +/- 8; LI-Ch, 242 +/- 6; LI-W, 225 +/- 8; CI, 298 +/- 8; CI-Ch, 255 +/- 8; CI-W, 221 +/- 6. The SEM analysis showed that both adhesive and cohesive fractures were primarily concentrated at the cervical region. Statistical analysis showed that both the type of tooth and the design of the preparation significantly influenced the resistance to fracture of the restored teeth (P<.001).
  
  
  CONCLUSIONS
  The chamfer preparation is recommended for central incisors, whereas the window preparation showed better results for canines. Both preparations can be adopted in the restoration of lateral incisors.
authors: Department of Fixed Prosthodontics, University of Federico II of Naples, Italy. zarone@unina.it
authors: Fernando
authors: F
authors: Zarone
authors: Ettore
authors: E
authors: Epifania
authors: Giuliana
authors: G
authors: Leone
authors: Roberto
authors: R
authors: Sorrentino
authors: Marco
authors: M
authors: Ferrari