title: The retention of complete crowns prepared with three different tapers and luted with four different cements.
abstract: BACKGROUND
  The role of adhesive properties of cements on the retentive strength of crowns with different degrees of taper is not clear.
  
  
  OBJECTIVE
  This study evaluated the retention of full crowns prepared with 3 different tapers and cemented with 2 conventional and 2 adhesive resin cements.
  
  
  METHODS
  One hundred twenty sound human molar teeth were assigned randomly to 1 of 12 groups, (n=10). The groups represented the 4 cements: zinc phosphate (Fleck's), a conventional glass ionomer (Ketac-Cem); 2 adhesive resin cements (C&B Metabond and Panavia); and 3 tapers of 6-degrees, 12-degrees, and 24-degrees within each cement. Crowns were cast with a high noble alloy. The 6-degree taper was considered the control within each cement group. Retention was measured (MPa) by separating the metal crowns from the prepared teeth under tension on a universal testing machine. Analysis of variance was used to test the main effects on the retentive strength of full crowns, namely cements, tapers, and failure modes. The Fisher's multiple comparison test was used to evaluate the source of the differences. The chi(2) analyses were used to examine the relationships between failure types, cements, and tapers. All statistical tests were conducted at alpha=.05.
  
  
  RESULTS
  There was a significant difference in the main effect cement (P<.0001) and taper (P=.0002). The mean retentive strength values of both Fleck's and Ketac-Cem were significantly lower than the mean retentive strength values of both C&B Metabond and Panavia (P<.0001). The retention of crowns prepared with 6-degree taper was not significant from the 12-degree taper (P=.0666). The difference in retention was significant between the 6-degree taper and the 24-degree taper (P<.0001) and between 12-degree taper and 24-degree taper (P=.0178). The types of failure were adhesive in the cement (65%), cohesive in the tooth (31%), and assembly failure (fracture of embedding resin) (4%). The type of failure was dependent on the degree of taper (P<.0001) and on the type of cement (P<.0042).
  
  
  CONCLUSIONS
  Within the limitations of this study, the retentive values of the adhesive resins at 24-degree taper were 20% higher than the retentive values of the conventional cements at 6-degree taper. The use of resin luting agents yielded retention values that were double the values of zinc phosphate or conventional glass ionomer cement.
authors.affiliation: School of Dentistry, University of Minnesota, Minneapolis, USA. zidano@umn.edu
authors.forename: Omar
authors.initials: O
authors.lastname: Zidan
authors.forename: Gary C
authors.initials: GC
authors.lastname: Ferguson
mesh_terms: D000704:Analysis of Variance; D016009:Chi-Square Distribution; D003442:Crowns; D003722:Dental Alloys / Q000737:chemistry; D001840:Dental Bonding; D003738:Dental Cements / Q000737:chemistry*; D017267:Dental Prosthesis Design; D017268:Dental Prosthesis Retention; D019232:Dental Restoration Failure; D005899:Glass Ionomer Cements / Q000737:chemistry; D006801:Humans; D019279:Resin Cements / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength; D015036:Zinc Phosphate Cement / Q000737:chemistry
chemical_list: D003722:Dental Alloys; D003738:Dental Cements; D005899:Glass Ionomer Cements; D019279:Resin Cements; D015036:Zinc Phosphate Cement