Accuracy of Implant Impressions with Different Impression Coping Types and Shapes

Abstract

Accurate recording of implant location is required so that definitive restorations are properly supported and do not place additional stresses on the implants. Movement of impression copings inside the impression material using an open-tray or close-tray impression technique during clinical and laboratory phases may cause inaccuracy in transferring the three-dimensional spatial orientation of implants intraorally to the definitive cast. Consequently, the restoration may require corrective procedures. This in vitro study compared the accuracy of two different impression techniques with two different impression coping shapes using polyether impression material to obtain precise definitive casts. Two reference acrylic resin models (Technovits 4000, Heraeus Kulzer GmbH & Co., Wehrheim, Germany) with five internal connection implants having different shapes of impression copings (Implantium [Dentium, Seoul, South Korea] and Replace Select [Nobel Biocare AB, Göteborg, Sweden]) were fabricated. Twenty medium-consistency polyether impressions of these models were made with square and conical impression copings of each system using open-tray and close-tray techniques. Matching implant replicas were screwed into the impression copings in the impressions. Impressions were poured with type IV stone, and the positional accuracy of the implant replica heads in x-, y-, and z-axes (represented in [Δr]) and also rotational displacement (ΔΘ) were evaluated using a coordinate measuring machine (Mistral, DEA Brown&Sharpe, Grugliasco, Italy). These measurements (linear and rotational displacements) were compared with the measurements calculated on the reference resin models that served as control, and data were analyzed with a two-way analysis of variance at α = 0.05. Less inaccuracy occurred in less retentive shape impression copings (Replace Select) compared with the more retentive one (Implantium) (p(r) < .001 and p(Θ) < .001), but there was no significant difference between direct and indirect impression techniques (p(r) and p(Θ) > .05). The impression coping shape had more impact on impression inaccuracy than impression technique did. Understanding of the magnitude and variability of distortion when employing certain impression-making methods and impression coping shapes helps the clinician to select a better implant component and impression technique.