title: Qualitative computer aided evaluation of dental impressions in vivo.
abstract: OBJECTIVE
  Clinical investigations dealing with the precision of different impression techniques are rare. Objective of the present study was to develop and evaluate a procedure for the qualitative analysis of the three-dimensional impression precision based on an established in-vitro procedure. The zero hypothesis to be tested was that the precision of impressions does not differ depending on the impression technique used (single-step, monophase and two-step-techniques) and on clinical variables.
  
  
  METHODS
  Digital surface data of patient's teeth prepared for crowns were gathered from standardized manufactured master casts after impressions with three different techniques were taken in a randomized order. Data-sets were analyzed for each patient in comparison with the one-step impression chosen as the reference. The qualitative analysis was limited to data-points within the 99.5%-range. Based on the color-coded representation areas with maximum deviations were determined (preparation margin and the mantle and occlusal surface). To qualitatively analyze the precision of the impression techniques, the hypothesis was tested in linear models for repeated measures factors (p < 0.05).
  
  
  RESULTS
  For the positive 99.5% deviations no variables with significant influence were determined in the statistical analysis. In contrast, the impression technique and the position of the preparation margin significantly influenced the negative 99.5% deviations.
  
  
  CONCLUSIONS
  The influence of clinical parameter on the deviations between impression techniques can be determined reliably using the 99.5 percentile of the deviations. An analysis regarding the areas with maximum deviations showed high clinical relevance. The preparation margin was pointed out as the weak spot of impression taking.
authors.affiliation: Department of Prosthetic Dentistry, Dresden University of Technology, University Hospital Carl Gustav Carus, Dental School, Fetscherstrasse 74, 01307 Dresden, Germany. ralph.luthardt@uniklinikum-dresden.de
authors.forename: Ralph G
authors.initials: RG
authors.lastname: Luthardt
authors.forename: Rainer
authors.initials: R
authors.lastname: Koch
authors.forename: Heike
authors.initials: H
authors.lastname: Rudolph
authors.forename: Michael H
authors.initials: MH
authors.lastname: Walter
mesh_terms: D017076:Computer-Aided Design; D003442:Crowns; D003761:Dental Impression Technique / Q000295:instrumentation / Q000706:statistics & numerical data*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional; D003765:Models, Dental; D015203:Reproducibility of Results; D013499:Surface Properties; D014070:Tooth / Q000033:anatomy & histology; D019231:Tooth Preparation, Prosthodontic