title: Influence of preparation design and existing condition of tooth structure on load to failure of ceramic laminate veneers.
abstract: BACKGROUND
  Although investigators have evaluated the effect of ceramic veneer preparation design, limited information is available regarding preparation design in association with the condition of existing tooth structure.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to evaluate the effect of preparation design and the amount of existing tooth structure on the fracture resistance of pressable ceramic laminate veneers.
  
  
  METHODS
  Thirty-two extracted human maxillary central incisors were allocated into 4 groups (n=8) to test for 2 variables: (1) the preparation design (a 2 mm incisal reduction shoulder finish line with or without palatal chamfer) and (2) the existing amount of tooth structure (non-worn tooth or worn tooth). Measurement of the remaining enamel thickness on the inciso-occlusal surface was made after the tooth was prepared. All prepared teeth were restored with pressable ceramic (IPS Empress) veneers, and the veneers were luted with resin cement (Rely-X Veneer). These luted specimens were loaded to failure in a universal testing machine, in the compression mode, with a crosshead speed of 0.05 mm/min. The data were analyzed using a 2-way ANOVA and Tukey's HSD multiple comparison test (α=.05)
  
  
  RESULTS
  Preparation design and the amount of existing tooth structure had a significant effect on the load to failure value (P<.001); however, the interaction between preparation design and existing amount of tooth structure was not significant (P=.702). Mean (SD) load to failure values were as follows: a preparation design with a palatal chamfer margin with a non-worn tooth (166.67 N (28.89)) revealed a significantly higher failure load than the group with a shoulder finish line alone (131.84 N (18.88)) (P<.01). The preparation design with a palatal chamfer margin for worn teeth (119.56 N (23.88)) revealed a significantly higher failure load than a shoulder finish line design alone (90.56 N (9.32)) (P<.05). The preparation design with a shoulder finish line for worn teeth had a significantly lower failure load than those on non-worn teeth (P<.003).
  
  
  CONCLUSIONS
  Preparation design and the amount of existing tooth structure had a significant effect on load to failure for ceramic veneers. This study revealed that using a palatal chamfer margin design significantly increased the load to failure compared to a shoulder finish line.
authors.affiliation: Department of Restorative Dentistry, School of Dentistry, University of Washington, Everett, USA. km29schmidt@msn.com
authors.forename: Kyle K
authors.initials: KK
authors.lastname: Schmidt
authors.forename: Yada
authors.initials: Y
authors.lastname: Chiayabutr
authors.forename: Keith M
authors.initials: KM
authors.lastname: Phillips
authors.forename: John C
authors.initials: JC
authors.lastname: Kois
mesh_terms: D000704:Analysis of Variance; D019245:Compressive Strength; D003776:Dental Porcelain; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D003801:Dental Veneers; D006801:Humans; D007180:Incisor / Q000473:pathology; D018709:Statistics, Nonparametric; D019231:Tooth Preparation, Prosthodontic / Q000379:methods*; D057085:Tooth Wear / Q000473:pathology*
chemical_list: D003776:Dental Porcelain