title: Machinability of CAD-CAM materials.
abstract: BACKGROUND
  Although new materials are available for computer-aided design and computer-aided manufacturing (CAD-CAM) fabrication, limited information is available regarding their machinability. The depth of penetration of a milling tool into a material during a timed milling cycle may indicate its machinability.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to compare the tool penetration rate for 2 polymer-containing CAD-CAM materials (Lava Ultimate and Enamic) and 2 ceramic-based CAD-CAM materials (e.max CAD and Celtra Duo).
  
  
  METHODS
  The materials were sectioned into 4-mm-thick specimens (n=5/material) and polished with 320-grit SiC paper. Each specimen was loaded into a custom milling apparatus. The apparatus pushed the specimens against a milling tool (E4D Tapered 2016000) rotating at 40 000 RPM with a constant force of 0.98 N. After a 6-minute timed milling cycle, the length of each milling cut was measured with image analysis software under a digital light microscope. Representative specimens and milling tools were examined with scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy.
  
  
  RESULTS
  The penetration rate of Lava Ultimate (3.21 ±0.46 mm/min) and Enamic (2.53 ±0.57 mm/min) was significantly greater than that of e.max CAD (1.12 ±0.32 mm/min) or Celtra Duo (0.80 ±0.21 mm/min) materials. SEM observations showed little tool damage, regardless of material type. Residual material was found on the tools used with polymer-containing materials, and wear of the embedding medium was seen on the tools used with the ceramic-based materials. Edge chipping was noted on cuts made in the ceramic-based materials.
  
  
  CONCLUSIONS
  Lava Ultimate and Enamic have greater machinability and less edge chipping than e.max CAD and Celtra Duo.
authors.affiliation: Assistant Professor, Division of Prosthodontics, Department Restorative Sciences, University of Alabama at Birmingham, Birmingham, Ala.
authors.forename: Ramakiran
authors.initials: R
authors.lastname: Chavali
authors.affiliation: Graduate student, Department of Biomaterials, Clinical and Community Sciences, University of Alabama at Birmingham, Birmingham, Ala.
authors.forename: Amir H
authors.initials: AH
authors.lastname: Nejat
authors.affiliation: Assistant Professor, Department of Biomaterials, Clinical and Community Sciences, University of Alabama at Birmingham, Birmingham, Ala. Electronic address: nlawson@uab.edu.
authors.forename: Nathaniel C
authors.initials: NC
authors.lastname: Lawson
mesh_terms: D017076:Computer-Aided Design; D003764:Dental Materials; D017267:Dental Prosthesis Design / Q000379:methods*; D008422:Materials Testing
chemical_list: D003764:Dental Materials