title: The effect of engaging the screw access channel of an implant abutment with a cement-retained restoration.
abstract: OBJECTIVE
  Factors affecting the retention of fixed prostheses to natural abutments are well understood. In contrast, little is known concerning the factors influencing the retention of fixed prostheses cemented to implant abutments. The purpose of this study was to investigate the effect that extending a casting into the screw access channel of an implant abutment has on the retention when cemented using Temp Bond.
  
  
  METHODS
  Replace Select Straight abutments received set modifications (buccal wall removal at 15 degrees , 22 degrees , and 30 degrees ) using a milling machine; controls were unmodified. Two castings were fabricated for each of the modified abutments, one with and one without an extension into the screw access channel. Following cementation with Temp Bond under standardized conditions, the castings were removed from the abutments using an Instron machine, and the peak removal force was recorded.
  
  
  RESULTS
  Extending the casting into the screw access channel significantly (p < 0.001) increased the peak load of removal. Significant differences (p < 0.05) were found between no modification and 30 degrees modification, 15 degrees and 30 degrees modification, and 22 degrees and 30 degrees modification in the groups when the casting extended into the abutment. In the group where the casting did not extend into the abutment, all groups were significantly different (p < 0.001) with the exception of 22 degrees and 30 degrees modification.
  
  
  CONCLUSIONS
  The increased load required to remove a casting that extends into the screw access channel of an implant abutment may compensate for loss in retention, which occurs through unfavorable modification of the abutment.
authors.affiliation: Unit of Prosthodontics, UCL Eastman Dental Institute, University College London, UK.
authors.forename: Supritha
authors.initials: S
authors.lastname: Naik
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Tredwin
authors.forename: Michael
authors.initials: M
authors.lastname: Nesbit
authors.forename: Derrick J
authors.initials: DJ
authors.lastname: Setchell
authors.forename: David R
authors.initials: DR
authors.lastname: Moles
mesh_terms: D002484:Cementation / Q000379:methods*; D000044:Dental Abutments; D003734:Dental Casting Investment / Q000737:chemistry; D003735:Dental Casting Technique; D015921:Dental Implants; D017267:Dental Prosthesis Design; D017268:Dental Prosthesis Retention; D003794:Dental Restoration, Temporary; D003799:Dental Stress Analysis / Q000295:instrumentation; D005054:Eugenol / Q000737:chemistry; D006047:Gold Alloys / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength; D015034:Zinc Oxide / Q000737:chemistry; D015035:Zinc Oxide-Eugenol Cement / Q000737:chemistry
chemical_list: D003734:Dental Casting Investment; D015921:Dental Implants; D006047:Gold Alloys; D015035:Zinc Oxide-Eugenol Cement; D005054:Eugenol; C076899:Temp-Bond; D015034:Zinc Oxide