The Influence of Implant Angulation on Accuracy of Dental Casts

Objectives:Impression making is a critical stage in the construction of implant prostheses. This study sought to test the null hypothesis that implant angulation had no influence on the accuracy of dental casts obtained from impressions made with selected elastomeric impression materials via a simulated closed tray impression technique. Methods: This in vitro study used a suitably modified dental articulator to permit accurate implant angulations of 0, 10, 20 and 30 degrees together with simulation of the pick-up impression technique using polyether or polyvinylsiloxane (PVS) impression materials in custom impression trays. Linear distances between impression copings on master casts and 180 die stone intaglios made from elastomeric impressions of the master casts were measured using an electronic calliper and then compared. Results: Data from the measurements was entered into SPSS. Analysis demonstrated that intraoperator reliability for the measurements made was excellent with alpha 0.99. Significant differences (p<0.05)were noted between the distances measured on the master casts and their intaglios obtained from impressions made in polyether or PVS. Dimensional differences between the master casts and intaglios increased with increasing implant angulation. Conclusion: Implant angulation has a significant influence on the accuracy of dental casts obtained by a simulated closed tray impression technique. This may have implications for the choice of impression technique in cases which involve the restoration of implants at differing angulations.