title: Fit of pressed crowns fabricated from two CAD-CAM wax pattern process plans: A comparative in vitro study.
abstract: BACKGROUND
  Subtractive and additive computer-aided design and computer-aided manufacturing (CAD-CAM) wax pattern processing are 2 methods of fabricating a pressed ceramic crown. Whether a subtractive milled wax pattern or a pattern from the micro-stereolithography additive process produces lithium disilicate crowns with better marginal and internal ﬁt is unclear.
  
  
  METHODS
  Ten silicone impressions were made for a prepared canine tooth. Each die received 2 lithium disilicate (IPS e.max) copings, 1 from milled wax blocks and 1 from additive wax. The replica technique was used to measure the fit by scanning electron microscopy at ×80 magnification. Collected data were analyzed using the paired Student t test for the marginal and internal fit. For the occlusal fit, the difference in scores did not follow a normal distribution, and the Wilcoxon signed rank test was used (α=.05).
  
  
  RESULTS
  The mean marginal, axial, and occlusal fit showed no significant differences when the 2 CAD-CAM manufacturing processes were compared (P>.05). For the marginal fit, the mean (±SD) values were 105.1 μm ±39.6 with the milled process and 126.2 μm ±25.2 for the additive process. The mean values were 98.1 μm ±26.1 for the axial fit in the milled process and 106.8 μm ±21.2 in the additive process. For the occlusal fit, median values (interquartile interval) were 199.0 μm (141.5 to 269.9) for subtractive manufacturing and 257.2 μm (171.6 to 266.0) for micro-SLA manufacturing.
  
  
  CONCLUSIONS
  No significant difference was found between the fit of the 2 techniques. The mean values of axial and occlusal median values were 10 and 5 to 6 times greater than machine's nominal values.
authors.affiliation: Assistant Professor, Prosthodontics Department, Lebanese University School of Dentistry, Beirut, 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, Beirut, Lebanon.
authors.forename: Rola
authors.initials: R
authors.lastname: Mortada
authors.affiliation: Professor, Prosthodontics Department, Lebanese University School of Dentistry, Beirut, Lebanon.
authors.forename: Khaldoun
authors.initials: K
authors.lastname: Rifai
authors.affiliation: Professor, Prosthodontics Department, Lebanese University School of Dentistry, Beirut, Lebanon.
authors.forename: Jose Johann
authors.initials: JJ
authors.lastname: Chidiac
mesh_terms: D002516:Ceramics; D017076:Computer-Aided Design; D003442:Crowns; D003481:Cuspid; D003735:Dental Casting Technique; D003760:Dental Impression Materials / Q000737:chemistry; D003761:Dental Impression Technique / Q000295:instrumentation; D018772:Dental Marginal Adaptation; D003776:Dental Porcelain / Q000737:chemistry; D017267:Dental Prosthesis Design / Q000379:methods*; D006801:Humans; D066298:In Vitro Techniques; D008437:Maxilla; D012984:Software; D013499:Surface Properties
chemical_list: D003760:Dental Impression Materials; C493120:lithia disilicate; D003776:Dental Porcelain