title: Gap comparison between single crown and three-unit bridge zirconia substructures.
abstract: OBJECTIVE
  To compare marginal and internal gaps of zirconia substructure of single crowns with those of three-unit fixed dental prostheses.
  
  
  METHODS
  Standardized Co-Cr alloy simulated second premolar and second molar abutments were fabricated and subsequently duplicated into type-III dental stone for working casts. After that, all zirconia substructures were made using Lava™ system. Marginal and internal gaps were measured in 2 planes (mesial-distal plane and buccal-palatal plane) at 5 locations: marginal opening (MO), chamfer area (CA), axial wall (AW), cusp tip (CT) and mid-occlusal (OA) using Replica technique.
  
  
  RESULTS
  There were significant differences between gaps at all locations. The mean ± SD of marginal gap in premolar was 43.6 ± 0.4 µm and 46.5 ± 0.5 µm for single crown and 3-unit bridge substructure respectively. For molar substructure the mean ± SD of marginal gap was 48.5 ± 0.4 µm and 52.6 ± 0.4 µm for single crown and 3-unit bridge respectively. The largest gaps were found at the occlusal area, which was 150.5 ± 0.5 µm and 154.5 ± 0.4 µm for single and 3-unit bridge premolar substructures respectively and 146.5 ± 0.4 µm and 211.5 ± 0.4 µm for single and 3-unit bridge molar substructure respectively.
  
  
  CONCLUSIONS
  Independent-samples t-test showed significant differences of gap in zirconia substructure between single crowns and three-unit bridge (P<.001). Therefore, the span length has the effect on the fit of zirconia substructure that is fabricated using CAD/CAM technique especially at the occlusal area.
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Mahidol University, Bangkok, Thailand.
authors.forename: Chuchai
authors.initials: C
authors.lastname: Anunmana
authors.affiliation: Dental Division, Queen Sirikit Naval Hospital, Chonburi, Thailand.
authors.forename: Masnisa
authors.initials: M
authors.lastname: Charoenchitt
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Mahidol University, Bangkok, Thailand.
authors.forename: Chanavut
authors.initials: C
authors.lastname: Asvanund
keywords: 3-unit bridge; CAD/CAM; Ceramics; Marginal fit; Zirconia