title: Three-dimensional fit of lithium disilicate partial crowns in vitro.
abstract: OBJECTIVE
  A novel three-dimensional scanning technique was used to investigate the effects a one-step and a two-step impression methods can have on the three-dimensional fit of ceramic partial crowns.
  
  
  METHODS
  An acrylic model of a mandibular first molar was prepared to receive a partial coverage all-ceramic crown (mesio-occlusal-distal inlay preparation with reduction of all cusps and rounded shoulder finish line of buccal wall). Type IV plaster replicates were cast based on one-step single viscosity (OS/SV), one-step dual viscosity (OS/DV), and two-step dual viscosity (TS/DV) impressions. Five partial crowns were fabricated per impression method using hot-pressed lithium disilicate ceramics. Then, preparation and restorations were digitized using a non-contact, white-light scanner featuring self-calibrating optics (overall measurement uncertainty of <5μm). Data were entered into quality inspection software which superimposed the records (best-fit-algorithm), calculated fit-discrepancies for every pixel, and colour-coded the results to aid visualization. Furthermore, mean quadratic deviations (RMS) were computed and analyzed statistically with a 1-way ANOVA. Scheffé's procedure was applied for multiple comparisons (α=0.05).
  
  
  RESULTS
  Mean RMS-values for marginal (internal) surfaces were: OS/SV 70 (20)μm, OS/DV 78 (34)μm, and TS/DV 107 (52)μm. Differences among impression techniques were statistically significant at p=0.006 (0.001). Qualitatively, occlusal ridges and preparation finish lines were over contoured, whereas inner occlusal boxes and the proximal-occlusal isthmus were under contoured.
  
  
  CONCLUSIONS
  OS/SV and OS/DV impressions resulted in statistically significantly smaller marginal and internal discrepancies than the two-step technique.
  
  
  CONCLUSIONS
  Marginal and internal fit of hot-pressed lithium disilicate partial crowns depended on the employed impression technique. One-step impressions are preferred over two-step techniques in many day-to-day clinical situations, especially for the fabrication of partial coverage crown restorations.
authors.affiliation: Policlinic of Prosthetic Dentistry and Material Science, Centre for Dental Medicine, Jena University Hospital, An der Alten Post 4, 07743 Jena, Germany. oliver.schaefer@med.uni-jena.de
authors.forename: Oliver
authors.initials: O
authors.lastname: Schaefer
authors.forename: Harald
authors.initials: H
authors.lastname: Kuepper
authors.forename: Bernd W
authors.initials: BW
authors.lastname: Sigusch
authors.forename: Geoffrey A
authors.initials: GA
authors.lastname: Thompson
authors.forename: Arthur F
authors.initials: AF
authors.lastname: Hefti
authors.forename: Arndt
authors.initials: A
authors.lastname: Guentsch
mesh_terms: D000704:Analysis of Variance; D017076:Computer-Aided Design; D003442:Crowns; D003761:Dental Impression Technique; D018772:Dental Marginal Adaptation; D003776:Dental Porcelain; D017267:Dental Prosthesis Design; D006801:Humans; D021621:Imaging, Three-Dimensional; D003765:Models, Dental; D017755:Prosthesis Fitting; D018709:Statistics, Nonparametric; D019231:Tooth Preparation, Prosthodontic; D014783:Viscosity
chemical_list: C493120:lithia disilicate; D003776:Dental Porcelain