Variables Affecting the Accuracy of Implant Master Casts: An In Vitro Pilot Study

Impression and master cast accuracy have been identified as being the major determinants of superstructure fit in implant-supported restorations. The goal of this in vitro investigation was to determine the effects of different transfer components, impression materials, disinfection, storage time, and stone type on master cast accuracy. Following impression making from a reference model with two internal-hex bone-level implants and master cast fabrication (eight experimental groups; n = 5), a bar-type measurement device equipped with a strain gauge was fixed on all master casts while strain development was recorded. Statistical analysis was performed applying ANOVA and paired t-tests with the level of significance set at α = 0.05. The transfer components with plastic sleeves caused maximum misfit strain which was significantly greater as compared to click (P = 0.02) and open tray transfer components (P = 0.00). No significant effect on master cast accuracy was recorded for the parameters impression material, impression disinfection, and storage of impressions or casts. Lower strain development was observed in casts poured in type 3 stone as compared to casts poured in type 4 stone (P = 0.01). For the bone-level implant system considered here, the great levels of accuracy could be achieved using pick-up impressions with either click or open tray impression components. 1. Introduction Due to the ankylotic fixation of dental implants in alveolar bone which is considerably more rigid than the periodontal ligament in natural teeth, restorations splinting several implants require a passive fit [1, 2]. If this cannot be achieved, static implant loading will occur thereby increasing the risk for technical complications such as loosening of restorative screws and biologic complications such as bone loss [3]. In this context, it has been clarified that every step in the restorative process contributes to the amount of misfit present in a specific restoration [4]. Although the term “passive fit” has never been defined, most authors agree that the amount of misfit stress evoked by a certain restoration can only be minimized, for example, by using CAD/CAM technology [5], but no procedure described so far is capable of producing a totally passive fit [6]. While it has been claimed based on an in vivo pilot study that static implant loads may induce bone adaptation thereby reducing the restorations’ amount of misfit, reliable insight in bone response to static loading is missing so far [7]. The restorative team should therefore still strive to optimize fit at the