title: Reporting numeric values of complete crowns. Part 2: Retention and resistance theories.
abstract: BACKGROUND
  Determining the retention and resistance of a tooth preparation for a complete crown has only existed in theory, and these theories have never been measured on tooth preparations performed in vivo.
  
  
  OBJECTIVE
  The purpose of this study was to measure the theoretical retention and resistance of clinically produced complete crown preparations by using an objective measuring method.
  
  
  METHODS
  Stone dies from 236 complete crown preparations were collected from dental laboratories. The dies were scanned and analyzed with the coordinate geometry method. Cross-sectional images were captured, and the surface area was measured with a cone frustum and right truncated pyramid formula. Two different theories of resistance form, the "on" or "off" theory (limiting taper) and the linear model (resistance length), were calculated for premolar and molar preparations.
  
  
  RESULTS
  The mean surface areas ranged from 33.97 mm(2) to 105.44 mm(2) for the cone frustum formula and 41.75 mm(2) to 117.50 mm(2) for the right truncated pyramid formula. The facial side of maxillary premolars exhibited the highest percentage of resistance form with the limiting taper, at 58%, and the mesial side of the mandibular molars exhibited the lowest percentage of resistance form, at 6%.
  
  
  CONCLUSIONS
  The objective method used in this study provides a way for retention and resistance theories to be tested and for further clinical implications to be investigated.
authors: Doctoral student, Sir John Walsh Research Institute, Faculty of Dentistry, University of Otago, Dunedin, New Zealand. Electronic address: janine.tiu@gmail.com.
authors: Janine
authors: J
authors: Tiu
authors: Senior lecturer and Prosthodontist, Department of Oral Rehabilitation, Sir John Walsh Research Institute, Faculty of Dentistry, University of Otago, Dunedin, New Zealand.
authors: Basil
authors: B
authors: Al-Amleh
authors: Associate Professor, Department of Oral Rehabilitation, Sir John Walsh Research Institute, Faculty of Dentistry, University of Otago, Dunedin, New Zealand.
authors: J Neil
authors: JN
authors: Waddell
authors: Professor, Department of Oral Sciences, Sir John Walsh Research Institute, Faculty of Dentistry, University of Otago, Dunedin, New Zealand.
authors: Warwick J
authors: WJ
authors: Duncan
mesh_terms: D001641:Bicuspid / Q000033:anatomy & histology; D017076:Computer-Aided Design; D003442:Crowns / Q000706:statistics & numerical data*; D003481:Cuspid / Q000033:anatomy & histology; D000044:Dental Abutments; D003776:Dental Porcelain / Q000737:chemistry; D017268:Dental Prosthesis Retention / Q000706:statistics & numerical data*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007180:Incisor / Q000033:anatomy & histology; D007754:Laboratories, Dental; D003765:Models, Dental; D008963:Molar / Q000033:anatomy & histology; D061848:Optical Imaging / Q000379:methods; D012984:Software; D013314:Stress, Mechanical; D013499:Surface Properties; D019231:Tooth Preparation, Prosthodontic / Q000706:statistics & numerical data*
chemical_list: C508050:IPS e.max Press; C493120:lithia disilicate; D003776:Dental Porcelain