title: A Comparison of the Marginal and Internal Fit of Cobalt- Chromium Copings Fabricated by Two Different CAD/CAM Systems (CAD/ Milling, CAD/ Ceramill Sintron).
abstract: BACKGROUND
  Marginal fitness is the most important criteria for evaluation of the clinical acceptability of a cast restoration. Marginal gap which is due to cement solubility and plaque retention is potentially detrimental to both tooth and periodontal tissues.
  
  
  OBJECTIVE
  Thisin vitrostudy aimed to evaluate the marginal and internal fit of cobalt- chromium (Co-Cr) copings fabricated by two different CAD/CAM systems: (CAD/ milling and CAD/ Ceramill Sintron).
  
  
  METHODS
  We prepared one machined standard stainless steel master model with following dimensions: 7 mm height, 5mm diameter, 90˚ shoulder marginal finish line with 1 mm width, 10˚ convergence angle and anti-rotational surface on the buccal aspect of the die. There were 10 copings produced from hard presintered Co-Cr blocks according to CAD/ Milling technique and ten copings from soft non- presintered Co-Cr blocks according to CAD/ Ceramill Sintron technique. Marginal and internal accuracies of copings were documented by the replica technique. Replicas were examined at ten reference points under a digital microscope (230X). The Student's t-test was used for statistical analysis.p< 0.001 was considered significant.
  
  
  RESULTS
  Statistically significant differences existed between the groups (p< 0.001). The CAD/milling group (hard copings) had a mean marginal discrepancy (MD) of 104 µm, axial discrepancy (AD) of 23 µm and occlusal discrepancy of 130 µm. For CAD/ Ceramill Sintron group, these values were 195 µm (MD), 46 µm (AD), and 232 µm (OD). Internal total discrepancy (ITD) for the CAD/milling group was 77 µm, whereas for the CAD/Ceramill Sintron group was 143 µm.
  
  
  CONCLUSIONS
  Hard presintered Co-Cr copings had significantly higher marginal and internal accuracies compared to the soft non-presintered copings.
authors.affiliation: Dept. of Prosthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Mahroo
authors.initials: M
authors.lastname: Vojdani
authors.affiliation: Dept. of Prosthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Kianoosh
authors.initials: K
authors.lastname: Torabi
authors.affiliation: Postgraduate Student in Prosthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Berivan
authors.initials: B
authors.lastname: Atashkar
authors.affiliation: Postgraduate Student in Prosthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
authors.forename: Hossein
authors.initials: H
authors.lastname: Heidari
authors.affiliation: Dept. of Prosthodontics, School of Dentistry, Azad University of Medical Sciences, Tehran, Iran.
authors.forename: Mahshid
authors.initials: M
authors.lastname: Torabi Ardakani
keywords:  Base Metal Alloy;  CAD/CAM ;  Ceramill Sintron ; Marginal and Internal fit 