title: Precision of fit and retention force of cast non-precious-crowns on standard titanium implant-abutment with different design and height.
abstract: OBJECTIVE
  The cost-effectiveness of cast nonprecious frameworks has increased their prevalence in cemented implant crowns. The purpose of this study was to assess the effect of the design and height of the retentive component of a standard titanium implant abutment on the fit, possible horizontal rotation and retention forces of cast nonprecious alloy crowns prior to cementation.
  
  
  METHODS
  Two abutment designs were examined: Type A with a 6° taper and 8 antirotation planes (Straumann Tissue-Level RN) and Type B with a 7.5° taper and 1 antirotation plane (SICace implant). Both types were analyzed using 60 crowns: 20 with a full abutment height (6 mm), 20 with a medium abutment height (4 mm), and 20 with a minimal (2.5 mm) abutment height. The marginal and internal fit and the degree of possible rotation were evaluated by using polyvinylsiloxane impressions under a light microscope (magnification of ×50). To measure the retention force, a custom force-measuring device was employed.
  
  
  METHODS
  one-sided Wilcoxon rank-sum tests with Bonferroni-Holm corrections, Fisher's exact tests, and Spearman's rank correlation coefficient.
  
  
  RESULTS
  Type A exhibited increased marginal gaps (primary end-point: 55 ± 20 μm vs. 138 ± 59 μm, P < 0.001) but less rotation (P < 0.001) than Type B. The internal fit was also better for Type A than for Type B (P < 0.001). The retention force of Type A (2.49 ± 3.2 N) was higher (P = 0.019) than that of Type B (1.27 ± 0.84 N). Reduction in abutment height did not affect the variables observed.
  
  
  CONCLUSIONS
  Less-tapered abutments with more antirotation planes provide an increase in the retention force, which confines the horizontal rotation but widens the marginal gaps of the crowns. Thus, casting of nonprecious crowns with Type A abutments may result in clinically unfavorable marginal gaps.
authors.affiliation: Department of Prosthodontics, University of Bern, Bern, Switzerland; Department of Prosthodontics, Preclinical Education and Dental Material Science, University of Bonn, Bonn, Germany.
authors.forename: Norbert
authors.initials: N
authors.lastname: Enkling
authors.forename: Takayuki
authors.initials: T
authors.lastname: Ueda
authors.forename: Hadi
authors.initials: H
authors.lastname: Gholami
authors.forename: Stefan
authors.initials: S
authors.lastname: Bayer
authors.forename: Joannis
authors.initials: J
authors.lastname: Katsoulis
authors.forename: Regina
authors.initials: R
authors.lastname: Mericske-Stern
mesh_terms: D002484:Cementation; D003442:Crowns; D000044:Dental Abutments; D003722:Dental Alloys; D017267:Dental Prosthesis Design; D017268:Dental Prosthesis Retention; D019094:Dental Prosthesis, Implant-Supported; D006801:Humans; D066298:In Vitro Techniques; D017755:Prosthesis Fitting / Q000379:methods*; D012399:Rotation; D013499:Surface Properties; D014025:Titanium
chemical_list: D003722:Dental Alloys; D014025:Titanium
keywords: cast implant crowns; degree of rotation; internal fit; marginal fit; non precious alloy; retention force