title: Effect of CNC-milling on the marginal and internal fit of dental ceramics: a pilot study.
abstract: OBJECTIVE
  Machined restorations have been investigated for their preciseness before, while detailed information on the milling-step itself are lacking. Therefore, the aim of this laboratory study was to quantify the effect of a novel milling-procedure on the marginal and internal fit of ceramic restorations.
  
  
  METHODS
  An acrylic model of a lower left first molar was prepared to receive a ceramic partial crown and was duplicated by one step dual viscosity impressions. Gypsum casts were formed and laser-scanned to realize virtual datasets, before restorations were designed, exported (PRE) and machined from lithium disilicate blanks. Crowns were digitized by a structure-light-scanner to obtain post-milling-data (POST). PRE and POST were virtually superimposed on the reference tooth and subjected to computer-aided-inspection. Visual fit-discrepancies were displayed with colors, while root mean square deviations (RMSD) and degrees of similarity (DS) were computed and analysed by t-tests for paired samples (n=5, α=0.05).
  
  
  RESULTS
  The milling procedure resulted in a small increase of the marginal and internal fit discrepancies (RMSD mean: 3μm and 6μm, respectively). RMSD differences were not statistically significant (p=0.495 and p=0.160 for marginal and internal fit, respectively). These results were supported by the DS data.
  
  
  CONCLUSIONS
  The products of digital dental workflows are prone to imprecisions. However, the present findings suggest that differences between computer-aided designed and actually milled restorations are small, especially when compared to typical fit discrepancies observed clinically. Imprecisions introduced by digital design or production processes are small.
authors.affiliation: Policlinic of Prosthetic Dentistry and Material Science, Centre for Dental Medicine, Jena University Hospital, 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: Geoffrey A
authors.initials: GA
authors.lastname: Thompson
authors.forename: Georg
authors.initials: G
authors.lastname: Cachovan
authors.forename: Arthur F
authors.initials: AF
authors.lastname: Hefti
authors.forename: Arndt
authors.initials: A
authors.lastname: Guentsch
mesh_terms: D002133:Calcium Sulfate / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry; D017076:Computer-Aided Design; D003442:Crowns / Q000592:standards*; D003761:Dental Impression Technique; D018772:Dental Marginal Adaptation; D003764:Dental Materials / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D003765:Models, Dental; D008963:Molar / Q000033:anatomy & histology; D010865:Pilot Projects; D013499:Surface Properties; D019231:Tooth Preparation, Prosthodontic / Q000379:methods; D014584:User-Computer Interface
chemical_list: D003764:Dental Materials; C493120:lithia disilicate; D003776:Dental Porcelain; C023506:Glass ceramics; D002133:Calcium Sulfate
keywords: CAD/CAM; Dental ceramics; Internal fit; Marginal fit; Three-dimensional analysis