title: Trueness of milled prostheses according to number of ball-end mill burs.
abstract: BACKGROUND
  Making a computer-aided design/computer-aided manufacturing (CAD/CAM) prosthesis with a milling machine often requires 2 (2- and 1-mm diameter) or 3 (2-, 1-, and 0.6-mm diameter) burs; however, using 3 burs can reduce time effectiveness and increase cost. Studies evaluating the trueness of prostheses made with 2 and 3 burs are lacking.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to evaluate the 3-dimensional trueness of crown prostheses made using 2 and 3 ball-end mill burs in the milling process.
  
  
  METHODS
  The abutment die of the maxillary right first molar for ceramic crowns was designed with computer-aided design software. After the crown prosthesis design was completed, polyurethane blocks were milled using 2 and 3 burs with a 5-axis milling machine. The outer and inner surfaces of the milled crown prostheses were scanned with a dental scanner. The inner part was separated into a marginal part and an internal part using 3-dimensional evaluation software. The 3-dimensional trueness of the prostheses milled with 2 or 3 burs was compared.
  
  
  RESULTS
  No significant differences in trueness were found for the inner or internal parts of the prosthesis (P>.05). However, the outer and marginal parts of the prosthesis did show significant differences in trueness (P<.05).
  
  
  CONCLUSIONS
  Milling the marginal part of the inner prosthesis was better with 2 burs, whereas milling the outer part was better with 3 burs.
authors.affiliation: Doctoral student, Department of Dental Laboratory Science and Engineering, College of Health Science, Korea University, Seoul, South Korea.
authors.forename: Chong-Myeong
authors.initials: CM
authors.lastname: Kim
authors.affiliation: Doctoral student, Department of Dental Laboratory Science and Engineering, College of Health Science, Korea University, Seoul, South Korea.
authors.forename: So-Ri
authors.initials: SR
authors.lastname: Kim
authors.affiliation: Professor, Department of Dental Laboratory Science and Engineering, College of Health Science, Korea University, Seoul, South Korea.
authors.forename: Ji-Hwan
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Associate Professor, Department of Dental Laboratory Science and Engineering, College of Health Science and Department of Public Health Sciences, Graduate School and BK21+ Program in Public Health Sciences, Korea University, Seoul, South Korea.
authors.forename: Hae-Young
authors.initials: HY
authors.lastname: Kim
authors.affiliation: Professor, Department of Dental Laboratory Science and Engineering, College of Health Science, Korea University, Seoul, South Korea. Electronic address: kuc2842@korea.ac.kr.
authors.forename: Woong-Chul
authors.initials: WC
authors.lastname: Kim
mesh_terms: D002516:Ceramics; D017076:Computer-Aided Design; D003442:Crowns; D003762:Dental Instruments; D018772:Dental Marginal Adaptation; D017267:Dental Prosthesis Design; D006801:Humans; D008963:Molar; D012984:Software