title: Determination of the minimum number of marginal gap measurements required for practical in-vitro testing.
abstract: BACKGROUND
  Gap measurements along margins are frequently used to assess the quality of single crowns. However, the number of gap measurements required for clinically relevant results in laboratory studies is not known.
  
  
  OBJECTIVE
  This study estimated the minimum number of gap measurements on margins of single crowns to produce relevant results for gap analysis.
  
  
  METHODS
  Ten all-ceramic crowns were fabricated on a master steel die. Gaps along crown margins were investigated in a scanning electron microscope on the master steel die without cementation and on replica dies after conventional cementation. Measurements were made in 100 microm steps according to 3 gap definitions. The initial number of measurements per crown (n = 230) was reduced to smaller subsets using both systematic and random approaches to determine the impact on the quality of results.
  
  
  RESULTS
  On the data of gap definition 1, reduction from 230 to about 50 measurements caused less than +/-5 microm variability for arithmetic means. Analysis of standard errors showed slowly increasing values smaller than 3 microm, both indicating no relevant impact on the quality of results. Smaller data sizes yielded accelerated increase of standard errors and divergent variabilities of mean. The minimum of 50 measurements did not depend on gap definition or on cementation condition.
  
  
  CONCLUSIONS
  Fifty measurements are required for clinically relevant information about gap size regardless of whether the measurement sites are selected in a systematic or random manner, which is far more than what current in vitro studies use.
authors.affiliation: Dental Clinic, Department of Prosthodontics, University of Tübingen, Tübingen, Germany. martin_groten@med.uni_tuebingen.de
authors.forename: M
authors.initials: M
authors.lastname: Groten
authors.forename: D
authors.initials: D
authors.lastname: Axmann
authors.forename: L
authors.initials: L
authors.lastname: Pröbster
authors.forename: H
authors.initials: H
authors.lastname: Weber
mesh_terms: D000537:Aluminum Oxide; D003442:Crowns / Q000706:statistics & numerical data; D018772:Dental Marginal Adaptation; D003776:Dental Porcelain; D003779:Denture Design / Q000379:methods* / Q000706:statistics & numerical data; D006801:Humans; D007180:Incisor; D008437:Maxilla; D008855:Microscopy, Electron, Scanning; D017755:Prosthesis Fitting / Q000379:methods / Q000706:statistics & numerical data; D013997:Time Factors
chemical_list: C078572:Celay; D003776:Dental Porcelain; C070870:In-Ceram; D000537:Aluminum Oxide