title: Marginal and internal fit of pressed ceramic crowns made from conventional and computer-aided design and computer-aided manufacturing wax patterns: An in vitro comparison.
abstract: BACKGROUND
  To our knowledge, no studies have evaluated the influence of the wax fabrication technique on the internal adaptation and marginal accuracy of pressed ceramic single crowns.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to compare the marginal and internal ﬁt of a lithium disilicate crown fabricated either from conventional waxing or from a subtractive milled wax pattern.
  
  
  METHODS
  Ten silicone impressions were made for a maxillary canine prepared to receive a complete crown. Two pressed lithium disilicate glass ceramic copings were made on the die poured from each impression. The first was from a conventional wax pattern and the second from milled wax blocks. The replica technique was used to measure the fit by scanning electron microscope at ×80 magnification. Collected data were analyzed with the paired Student t test for the marginal and wall fit. For the occlusal fit, the difference in scores did not follow a normal distribution, and the Wilcoxon signed ranks test was used (α=.05).
  
  
  RESULTS
  The mean values +SD were 170.3 ±50.7 μm for the marginal fit and 130.3 ±21.6 μm for the internal fit with the conventional technique. For the computer-aided design and computer-aided manufacturing (CAD-CAM) technique, they were 105.1 ±39.6 μm and 98.1 ±26.1 μm. Statistical significance was found for the marginal and internal fit (P<.05). The occlusal fit median and interval interquartile scores were 305.0 μm (269.9 to 334.4) for conventional fabrication and 199.0 μm (141.5 to 269.9) for subtractive manufacturing. The differences were not statistically significant (P>.05).
  
  
  CONCLUSIONS
  The subtractive CAD-CAM waxing technique resulted in the improved fit of a pressed lithium disilicate crown by decreasing the marginal discrepancies and internal adaptation.
authors.affiliation: Assistant Professor, Prosthodontics Department, Lebanese University School of Dentistry, Hadath, Lebanon. Electronic address: drloubna1@hotmail.com.
authors.forename: Loubna
authors.initials: L
authors.lastname: Shamseddine
authors.affiliation: Clinical instructor, Prosthodontics Department, Lebanese University School of Dentistry, Hadath, Lebanon.
authors.forename: Rola
authors.initials: R
authors.lastname: Mortada
authors.affiliation: Professor, Prosthodontics Department, Lebanese University School of Dentistry, Hadath, Lebanon.
authors.forename: Khaldoun
authors.initials: K
authors.lastname: Rifai
authors.affiliation: Professor, Prosthodontics Department, Lebanese University, School of Dentistry, Hadath, Lebanon.
authors.forename: Jose Johann
authors.initials: JJ
authors.lastname: Chidiac
mesh_terms: D002516:Ceramics; D017076:Computer-Aided Design; D003442:Crowns; D003735:Dental Casting Technique; D003761:Dental Impression Technique; D018772:Dental Marginal Adaptation; D003776:Dental Porcelain; D017267:Dental Prosthesis Design; D006801:Humans; D066298:In Vitro Techniques; D007283:Inlay Casting Wax
chemical_list: C493120:lithia disilicate; D003776:Dental Porcelain; D007283:Inlay Casting Wax; C023506:Glass ceramics