title: Stresses within porcelain veneers and the composite lute using different preparation designs.
abstract: OBJECTIVE
  The purpose of this study was to investigate compressive and tensile stresses in porcelain and composite at the labial marginal region of porcelain veneer restorations using chamfer, shoulder, or knife-edge labial margin designs with labial window or incisal overlap incisal preparation designs.
  
  
  METHODS
  Porcelain veneer models were constructed and loaded with (1) a 200-N, 45 degrees palatal load to simulate functional loading, and (2) a horizontal labial loading of 200 N to mimic trauma. Maximum tensile and compressive stresses were recorded within the labial marginal region of both porcelain and composite lute.
  
  
  RESULTS
  Under the 45 degrees palatal load, stresses within the palatal marginal porcelain were chiefly compressive, and stresses for the knife-edge designs as much as 42% less than for shoulder designs. Incisal overlap preparations were generally associated with less compressive stress within both porcelain and composite than the window preparation. When a labial load was applied, tensile stresses were as much as 25 times greater for the chamfer and shoulder designs compared with the knife-edge design. Labial loading also resulted in an increase in tensile stresses within the composite lute, and stresses were again lowest within the knife-edge margin design.
  
  
  CONCLUSIONS
  Under the limitations of this study, using the incisal overlap preparation, porcelain veneers with knife-edge labial margins could better sustain occlusal loading without fracture. J Prosthodont 2001;10:16-21.
authors.affiliation: Department of Adult Oral Health, St. Bartholomew's and the Royal London School of Medicine and Dentistry, Queen Mary and Westfield College, Whitechapel, London E1 2AD, England. k.g.seymour@mds.qmw.ac.uk
authors.forename: K G
authors.initials: KG
authors.lastname: Seymour
authors.forename: G P
authors.initials: GP
authors.lastname: Cherukara
authors.forename: D Y
authors.initials: DY
authors.lastname: Samarawickrama
mesh_terms: D001732:Bite Force; D003188:Composite Resins / Q000737:chemistry*; D003198:Computer Simulation; D003738:Dental Cements / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry*; D019232:Dental Restoration Failure; D003801:Dental Veneers; D004548:Elasticity; D020342:Finite Element Analysis; D006801:Humans; D007180:Incisor; D008954:Models, Biological; D019279:Resin Cements / Q000737:chemistry*; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength; D018677:Tooth Injuries / Q000503:physiopathology; D019246:Tooth Preparation / Q000379:methods*
chemical_list: D003188:Composite Resins; D003738:Dental Cements; D019279:Resin Cements; D003776:Dental Porcelain