title: Effect of implant abutment modification on the extrusion of excess cement at the crown-abutment margin for cement-retained implant restorations.
abstract: OBJECTIVE
  To compare the effect of implant abutment modification on the amount of cement extruded at the crown-abutment margin and to evaluate the vertical discrepancy after cementation.
  
  
  METHODS
  Access openings of titanium abutments were modified with an opening (open) and placement of two vent holes 3 mm from the occlusal edge and 180 degrees apart (internal vent). Access openings were filled with resin material (closed) and used as controls. Each abutment was secured to an implant analog. Eugenol-free zinc oxide cement (TempBond NE) was selected to cement the cast crowns (n = 9) onto test abutments. The amount of cement extruded out of the margin was calculated, and vertical seating discrepancies were determined with a linear transducer device before and after cementation. Differences among groups were analyzed statistically.
  
  
  RESULTS
  The mean amount of extruded cement ranged from 36% to 90% of the total cement placed within the crowns. The order, from least to greatest amount of excess cement extrusion at the margins, was internal vent, open, and closed; significant differences were observed between test groups. The net vertical discrepancies of tested specimens ranged from -7 μm to +6 μm (mean, 0 μm). No statistically significant differences in vertical discrepancy were found between the groups.
  
  
  CONCLUSIONS
  Venting the hollow abutment resulted in the least amount of cement extrusion when compared to closing off the screw access channel or leaving it open. Within the limitations of this study, it may be concluded that the use of two, 0.75-mm radius vent holes placed 3 mm apical to the occlusal area of the abutment and 180 degrees apart will limit the amount of cement extruded into the gingival sulcus of implant-retained crowns.
authors.affiliation: Department of Restorative Dentistry, University of Washington, Seattle, USA. cpkw@uw.edu
authors.forename: Chandur
authors.initials: C
authors.lastname: Wadhwani
authors.forename: Alfonso
authors.initials: A
authors.lastname: Piñeyro
authors.forename: Timothy
authors.initials: T
authors.lastname: Hess
authors.forename: Hai
authors.initials: H
authors.lastname: Zhang
authors.forename: Kwok-Hung
authors.initials: KH
authors.lastname: Chung
mesh_terms: D002484:Cementation / Q000379:methods*; D003442:Crowns; D000044:Dental Abutments; D003738:Dental Cements; D059605:Dental Implant-Abutment Design; D015921:Dental Implants; D019094:Dental Prosthesis, Implant-Supported; D003793:Dental Restoration, Permanent / Q000295:instrumentation / Q000379:methods; D003794:Dental Restoration, Temporary / Q000295:instrumentation / Q000379:methods; D006801:Humans; D014716:Vertical Dimension
chemical_list: D003738:Dental Cements; D015921:Dental Implants