title: Torque resistance of impression copings after direct implant impression: An in vitro evaluation of impression materials with and without adhesive.
abstract: BACKGROUND
  No data are available on the ability of an impression coping to resist the manual placement of an abutment replica (implant analog) during prosthodontic laboratory procedures after a direct (pick-up) impression.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to evaluate the torque resistance of impression copings after a direct impression, that is, the amount of rotational torque sufficient to induce irreversible displacement of impression copings in the impression material bulk once the impression has been made.
  
  
  METHODS
  A reference model with 5 abutment replicas was constructed. Five impression copings were screwed onto the abutment replicas, and standardized impressions were made. A controlled twisting force was applied to each impression coping. A torque tester recorded the torque variation. Three elastomeric impression materials were tested. ANOVA and the Tukey test (α=.05) were performed using an average of 30 measurements per impression material, with and without adhesive.
  
  
  RESULTS
  ANOVA and the Tukey test results showed that the adhesive, cohesive, and mechanical bonds between the impression coping and the impression material depended greatly on the type of material and that the average rupture threshold of these bonds was statistically significantly different in pairwise comparisons (P<.05). The curve analysis showed that when the impression materials are used with adhesives, the deformation of the interface is irreversible beyond 5 Ncm of torque.
  
  
  CONCLUSIONS
  The polyether impression material is the direct impression material that showed the highest breakdown threshold for adhesive bonding when used without an adhesive. The use of an adhesive on impression copings leads to irreversible deformation of the interface at torque stresses well below the adhesive bond threshold of the same materials used without an adhesive.
authors.affiliation: Professor, Department of Prosthodontics, University of Auvergne Clermont Ferrand I, Clinical Research Laboratory in Prosthetic Dentistry, CHU Clermont-Ferrand, Dental Services, Clermont-Ferrand, France. Electronic address: pascal.auroy@mac.com.
authors.forename: Pascal
authors.initials: P
authors.lastname: Auroy
authors.affiliation: Professor, Department of Prosthodontics, University of Auvergne Clermont Ferrand I, Center of Research (CROC EA4847) Dental Clinic, Clermont-Ferrand, France, CHU Clermont-Ferrand, Dental Services, Clermont-Ferrand, France.
authors.forename: Emanuel
authors.initials: E
authors.lastname: Nicolas
authors.affiliation: Assistant Professor, Department of Prosthodontics, Rennes I University, Faculty of Dentistry, Rennes, France, CHU Rennes, Pôle d'Odontologie, Rennes, France.
authors.forename: Yvan
authors.initials: Y
authors.lastname: Bedouin
mesh_terms: D003738:Dental Cements / Q000627:therapeutic use*; D003760:Dental Impression Materials; D003761:Dental Impression Technique; D006801:Humans; D066298:In Vitro Techniques; D011476:Prosthodontics; D019415:Torque
chemical_list: D003738:Dental Cements; D003760:Dental Impression Materials