title: A 3-dimensional accuracy analysis of chairside CAD/CAM milling processes.
abstract: BACKGROUND
  Milling is a central and important aspect of computer-aided design and computer-aided manufacturing (CAD/CAM) technology. High milling accuracy reduces the time needed to adapt the workpiece and provides restorations with better longevity and esthetic appeal. The influence of different milling processes on the accuracy of milled restorations has not yet been reviewed.
  
  
  OBJECTIVE
  The purpose of this study was to investigate the influence of different milling processes on the accuracy of ceramic restorations.
  
  
  METHODS
  Four groups of partial crowns were milled (each n = 17): Three groups in a 4-axial milling unit: (1) 1-step mode and Step Bur 12S (12S), (2) 1-step mode and Step Bur 12 (1Step), (3) 2-step mode and Step Bur 12 (2Step), and (4) one group in a 5-axial milling unit (5axis). The milled occlusal and inner surfaces were scanned and superimposed over the digital data sets of calculated restorations with specialized difference analysis software. The trueness of each restoration and each group was measured. One-way ANOVA with a post hoc Tukey test was used to compare the data (α = .05).
  
  
  RESULTS
  The highest trueness for the inner surface was achieved in group 5axis (trueness, 41 ± 15 μm, P<.05). The 4-axial milling unit exhibited trueness at settings ranging from 61 μm (2Step) to 96 μm (12S). For the occlusal surface, the highest trueness was achieved with group 5axis (trueness, 42 ± 10 μm). The 4-axial milling unit exhibited trueness at settings ranging from 55 μm (1Step) to 76 μm (12S).
  
  
  CONCLUSIONS
  Restorations milled with a 5-axial milling unit have a higher trueness than those milled with a 4-axial milling unit. A rotary cutting instrument with a smaller diameter results in a more accurate milling process. The 2-step mode is not significantly better than the 1-step mode.
authors.affiliation: Research Assistant, Division for Computerized Restorative Dentistry, Center of Dental Medicine, University of Zürich, Zürich, Switzerland. Electronic address: gabriel.bosch@zzm.uzh.ch.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Bosch
authors.affiliation: Research Assistant, Division for Computerized Restorative Dentistry, Center of Dental Medicine, University of Zürich, Zürich, Switzerland.
authors.forename: Andreas
authors.initials: A
authors.lastname: Ender
authors.affiliation: Head of Division, Division for Computerized Restorative Dentistry, Center of Dental Medicine, University of Zürich, Zürich, Switzerland.
authors.forename: Albert
authors.initials: A
authors.lastname: Mehl
mesh_terms: D002516:Ceramics / Q000592:standards*; D017076:Computer-Aided Design / Q000295:instrumentation / Q000706:statistics & numerical data*; D003442:Crowns / Q000706:statistics & numerical data; D003764:Dental Materials / Q000592:standards*; D017267:Dental Prosthesis Design / Q000706:statistics & numerical data; D003793:Dental Restoration, Permanent / Q000706:statistics & numerical data*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000706:statistics & numerical data*; D007284:Inlays / Q000706:statistics & numerical data; D066330:Printing, Three-Dimensional; D013499:Surface Properties; D013674:Technology, Dental / Q000706:statistics & numerical data
chemical_list: D003764:Dental Materials