title: The analysis of restoration survival data in split-mouth designs.
abstract: OBJECTIVE
  To report methodological difficulties with restoration survival data in controlled clinical trials on Class II amalgam restorations using a split-mouth design. The advantages and disadvantages of different ways of handling these data are described.
  
  
  METHODS
  Three statistical methods (Kaplan-Meier estimation, logistic regression with random component and Friedman's statistic) are compared using data from a controlled clinical trial in which cavosurface angle (regular or non-standard) and cavity wall finish (applied or not applied) determine four treatment modalities of New True Dentalloy restorations.
  
  
  RESULTS
  In this study logistic regression with a random component yields the best interpretable results. Cavity wall finish in combination with a regular cavosurface angle is indicated as the worst and cavity wall finish in combination with a non-standard cavosurface angle as the best treatment when the criterion is replacement or not within 15 years.
  
  
  CONCLUSIONS
  The dependency between restorations within a patient needs to be taken into account. Logistic regression with a random component may be a valuable alternative to very advanced statistical survival modelling when restricting the research question to replacement within a certain time interval is not a major problem.
authors.affiliation: Department of Paediatric Dentistry, Academic Centre for Dentistry Amsterdam, The Netherlands. H.Tobi@acta.nl
authors.forename: H
authors.initials: H
authors.lastname: Tobi
authors.forename: C M
authors.initials: CM
authors.lastname: Kreulen
authors.forename: R J
authors.initials: RJ
authors.lastname: Gruythuysen
authors.forename: W E
authors.initials: WE
authors.lastname: van Amerongen
mesh_terms: D003722:Dental Alloys / Q000737:chemistry; D003723:Dental Amalgam / Q000737:chemistry; D003737:Dental Cavity Preparation / Q000145:classification / Q000706:statistics & numerical data; D003793:Dental Restoration, Permanent / Q000145:classification / Q000706:statistics & numerical data*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D016015:Logistic Models; D008297:Male; D015233:Models, Statistical; D016032:Randomized Controlled Trials as Topic / Q000706:statistics & numerical data; D012107:Research Design / Q000706:statistics & numerical data*; D019233:Retreatment; D013499:Surface Properties
chemical_list: D003722:Dental Alloys; C031359:New True Dentalloy; D003723:Dental Amalgam