title: Effect of modifying the screw access channels of zirconia implant abutment on the cement flow pattern and retention of zirconia restorations.
abstract: BACKGROUND
  The effect of managing the screw access channels of zirconia implant abutments in the esthetic zone has not been extensively evaluated.
  
  
  OBJECTIVE
  The purpose of this study was to determine the effect of an insert placed within the screw access channel of an anterior zirconia implant abutment on the amount of cement retained within the restoration-abutment system and on the dislodging force.
  
  
  METHODS
  Thirty-six paired zirconia abutments and restorations were fabricated by computer-aided design and computer-aided manufacturing and were divided into 3 groups: open abutment, with the screw access channel unfilled; closed abutment, with the screw access channel sealed; and insert abutment, with a thin, tubular metal insert projection continuous with the screw head and placed into the abutment screw access channel. The restorations were cemented to the abutments with preweighed eugenol-free zinc oxide cement (TempBond NE). Excess cement was removed, and the weight of the cement that remained in the restoration-abutment system was measured. Vertical tensile dislodging forces were recorded at a crosshead speed of 5 mm/min after incubation in a 37°C water bath for 24 hours. The specimens were examined for the cement flow pattern into the screw access channel after dislodgement. Data were analyzed with ANOVA, followed by multiple comparisons by using the Tukey honestly significant difference test (α = .05).
  
  
  RESULTS
  The mean (standard deviation) of retentive force values ranged from 108.1 ± 29.9 N to 148.3 ± 21.0 N. The retentive force values differed significantly between the insert abutment and both the open abutment (P < .05) and closed abutment groups (P < .01). Distinct patterns of cement failure were noted. The weight of the cement that remained in the system differed significantly, with both open abutment and insert abutment being greater than closed abutment (P < .05).
  
  
  CONCLUSIONS
  Modifying the internal configuration of the screw access channel of an esthetic zirconia implant abutment with a metal insert significantly affected both the cement retained within the abutment itself and the retention capabilities of the zirconia restoration cemented with TempBond NE cement.
authors.affiliation: Private practice, Bellevue, Washington; Affiliate Faculty, Department of Restorative Dentistry, University of Washington, Seattle, Wash. Electronic address: cpkw@uw.edu.
authors.forename: Chandur
authors.initials: C
authors.lastname: Wadhwani
authors.affiliation: Professor, Department of Restorative Dentistry, University of Washington, Seattle, Wash.
authors.forename: Kwok-Hung
authors.initials: KH
authors.lastname: Chung
mesh_terms: D002484:Cementation / Q000379:methods; D017076:Computer-Aided Design; D000044:Dental Abutments; D003738:Dental Cements / Q000737:chemistry*; D059605:Dental Implant-Abutment Design; D003764:Dental Materials / Q000737:chemistry*; D017268:Dental Prosthesis Retention; D019094:Dental Prosthesis, Implant-Supported; D003799:Dental Stress Analysis / Q000295:instrumentation; D006801:Humans; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry; D015034:Zinc Oxide / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003738:Dental Cements; D003764:Dental Materials; C474196:Tempbond NE; D014867:Water; D015040:Zirconium; C028541:zirconium oxide; D015034:Zinc Oxide