title: Fabrication of crown restoration retrofitting to existing clasps using CAD/CAM: fitness accuracy and retentive force.
abstract: OBJECTIVE
  A crown restoration engaged by a clasp as an abutment tooth for a removable partial denture (RPD) occasionally might be removed and eliminated due to secondary caries or apical lesions. However, if the RPD is clinically acceptable without any problems and refabricating the RPD is not recommended, the new crown must be made to retrofit to the existing clasp of the RPD. This in vitro study evaluated the conventional and CAD/CAM procedures for retrofitting crown restorations to the existing clasps by measuring the fitness accuracy and the retentive forces.
  
  
  METHODS
  The crown restoration on #44 was fabricated with CP titanium and zirconium on the plaster model with #45 and #46 teeth missing to retrofit to the existing clasp using conventional thin coping and CAD/CAM procedures. The gap distance between the clasp (tip, shoulder, and rest regions) and the fabricated crown was measured using silicone impression material. The retentive force of the clasp was also measured, using an autograph at a crosshead speed of 50mm/min. The obtained data were analyzed by one-way ANOVA/Tukey's multiple comparison test (α=0.05).
  
  
  RESULTS
  The CAD/CAM procedure caused significantly smaller gap distances in all of the clasp regions, as compared to the conventional procedure (p<0.05). The retentive force of the CAD/CAM crown was significantly higher than for the conventional one (p<0.05).
  
  
  CONCLUSIONS
  When a crown restoration must be remade to retrofit an existing clasp, CAD/CAM fabrication can be recommended so that both appropriate fitness and retentive force are obtained.
authors: Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine, Yokohama, Japan. Electronic address: ozawa-daisuke@tsurumi-u.ac.jp.
authors: Daisuke
authors: D
authors: Ozawa
authors: Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine, Yokohama, Japan.
authors: Yasunori
authors: Y
authors: Suzuki
authors: Dental Technician Institute, Tsurumi University School of Dental Medicine, Yokohama, Japan.
authors: Noboru
authors: N
authors: Kawamura
authors: Department of Removable Prosthodontics, Tsurumi University School of Dental Medicine, Yokohama, Japan.
authors: Chikahiro
authors: C
authors: Ohkubo
mesh_terms: D003442:Crowns; D000044:Dental Abutments; D016734:Dental Clasps; D017267:Dental Prosthesis Design / Q000379:methods*; D003793:Dental Restoration, Permanent / Q000379:methods*; D003832:Denture, Partial, Removable; D003765:Models, Dental
keywords: Abutment teeth; CAD/CAM; Digital dentistry; Removable prosthodontics