title: Computer-aided evaluation of preparations for CAD/CAM-fabricated all-ceramic crowns.
abstract: OBJECTIVE
  The aim of this study was the evaluation of preparations from general dental practitioners for zirconia crowns and their correlation with clinical recommendations using a digital approach.
  
  
  METHODS
  Seventy-five datasets of left first upper molars (FDI 16) prepared for single zirconia crowns by general dental practitioners were analyzed using a computer-aided design software (LAVA(TM) Design; 3M ESPE, Seefeld, Germany) and a 3D-inspection software (COMETinspect®plus version 4.5; Steinbichler Optotechnik, Neubeuern, Germany). Evaluated parameters were convergence angle, undercuts, interocclusal reduction, abutment height, and design of preparation margin.
  
  
  RESULTS
  The mean convergence angle was determined to be 26.7°. The convergence angle in the mesiobuccal to distopalatal dimension was significantly the highest (31.7°), and the abutment height showed a mean value of 4.1 mm. Convergence angle and abutment height showed a negative correlation. Seventy-three percent of the evaluated locations revealed a margin design conforming to ceramic restorations. In over 30 % of the cases, the interocclusal reduction was insufficient. Generally, no preparation fulfilled all recommendations. Five (6.66 %) of the preparations fulfilled four criteria, 16 (21.33 %) preparations fulfilled three criteria, 31 (41.33 %) fulfilled two criteria, 17 (22.66 %) preparations fulfilled one criterion, and 6 (8 %) fulfilled no criterion.
  
  
  CONCLUSIONS
  Within the limitations of this study, most general dental practitioners seem to have difficulties fulfilling all clinical recommendations given for the preparation of zirconia crowns. The presented digital approach seems to be a useful method to evaluate the preparation geometry.
  
  
  CONCLUSIONS
  The correct preparation geometry represents an important prerequisite for the success of all-ceramic full crowns. As preparations clearly need to be improved, the approach presented could be the basis of a future tool to increase preparation quality in practice and education by direct objective feedback.
authors.affiliation: Department of Prosthodontics, Dental School, Ludwig-Maximilians University Munich, Goethestraße 70, Munich, Germany. jan_frederik.gueth@med.uni-muenchen.de
authors.forename: Jan-Frederik
authors.initials: JF
authors.lastname: Güth
authors.forename: Jan
authors.initials: J
authors.lastname: Wallbach
authors.forename: Michael
authors.initials: M
authors.lastname: Stimmelmayr
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Gernet
authors.forename: Florian
authors.initials: F
authors.lastname: Beuer
authors.forename: Daniel
authors.initials: D
authors.lastname: Edelhoff
mesh_terms: D017076:Computer-Aided Design; D003442:Crowns; D003776:Dental Porcelain; D017267:Dental Prosthesis Design; D005069:Evaluation Studies as Topic; D005792:General Practice, Dental; D005858:Germany; D006801:Humans; D008422:Materials Testing; D008437:Maxilla; D008963:Molar; D009716:Numerical Analysis, Computer-Assisted; D012984:Software; D018709:Statistics, Nonparametric; D019231:Tooth Preparation, Prosthodontic; D015040:Zirconium
chemical_list: D003776:Dental Porcelain; D015040:Zirconium; C028541:zirconium oxide