title: Marginal and internal fit of pressed lithium disilicate partial crowns in vitro: a three-dimensional analysis of accuracy and reproducibility.
abstract: OBJECTIVE
  The objective of this in vitro study was to visualize and to quantify the marginal and internal fit of heat-pressed ceramic restorations by a novel three-dimensional procedure. Accuracy and reproducibility of the employed measuring method were determined.
  
  
  METHODS
  An acrylic model of a lower left first molar was prepared to receive a partial crown and duplicated by single step dual viscosity impressions. Corresponding working casts were formed from Type IV die stone and indirect restorations were fabricated from heat-pressable lithium disilicate ceramics (IPS e.max Press, Ivoclar Vivadent AG, Schaan, Liechtenstein). The acrylic tooth model and the ceramic partial crowns were digitized by a structure light scanner with a measurement-uncertainty of 4 μm and subjected to computer-aided quality inspection. Visual discrepancies in marginal and internal fit were displayed with colors. For quantitative analysis, mean quadratic deviations (RMS) were computed and analyzed by Student's t-test (n=5, α=0.05).
  
  
  RESULTS
  Mean RMS-values for accuracy (reproducibility) ranged from 34 (14) μm for internal areas to 78 (23) μm for marginal surfaces. Differences in accuracy (p=0.003) and reproducibility (p<0.001) were statistically significant. In general, areas with sharp internal line angles such as occlusal ridges and the preparation finish line exhibited oversized dimensions, whereas areas with rounded and soft internal line angles were undersized.
  
  
  CONCLUSIONS
  The viability of a computer-aided and three-dimensional approach for assessing marginal and internal fit of indirect restorations was demonstrated. Thereby, the obtained results track complex form changes as they occur during laboratory processing.
authors.affiliation: Jena University Hospital-Friedrich Schiller University Jena, Policlinic of Prosthetic Dentistry and Material Science, Jena, Germany. oliver.schaefer@med.uni-jena.de
authors.forename: Oliver
authors.initials: O
authors.lastname: Schaefer
authors.forename: David C
authors.initials: DC
authors.lastname: Watts
authors.forename: Bernd W
authors.initials: BW
authors.lastname: Sigusch
authors.forename: Harald
authors.initials: H
authors.lastname: Kuepper
authors.forename: Arndt
authors.initials: A
authors.lastname: Guentsch
mesh_terms: D017076:Computer-Aided Design; D003442:Crowns; D018772:Dental Marginal Adaptation; D003776:Dental Porcelain; D017267:Dental Prosthesis Design; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D003765:Models, Dental; D008963:Molar; D017755:Prosthesis Fitting; D015203:Reproducibility of Results
chemical_list: C493120:lithia disilicate; D003776:Dental Porcelain