Influence of intraoral conditions on the accuracy of digital and conventional implant impression techniques for two-implant-supported fixed dental prostheses

Purpose: To compare the trueness and precision of different impression techniques for two-implant-supported fixed dental prostheses between extraoral and intraoral conditions at different locations.Methods: Six volunteers participated in this study. A resin block with two parallel analogs was fabricated as an implant site simulator (ISS). The ISS was bonded to a molded ethylene vinyl acetate sheet to create a reference model. For each participant, four reference models were prepared based on the locations of the ISSs: maxillary posterior/anterior region (MaxP/MaxA) and mandibular posterior/anterior region (ManP/ManA). Five impressions were taken extraorally using the open-tray (conventional implant impression technique, CIT) and intraoral scanning (digital implant impression technique, DIT) techniques. The reference models were positioned in the participants' mouths, and impressions were obtained intraorally using the CIT and DIT. The interanalog distance (d) and angulation (theta) were measured to calculate trueness (Delta d, Delta theta) and precision (dP, theta P). Two-way ANOVA and t tests were performed (alpha=0.05).Results: For the DIT, under intraoral conditions, the Delta d and Delta theta in MaxP and Delta theta in ManP were significantly higher than those under extraoral conditions. For the CIT, under intraoral conditions, the Delta d and Delta theta in ManA and ManP and Delta theta in MaxP were significantly lower than those under extraoral conditions. No significant differences in the dP and theta P of either DIT or CIT were observed between the two conditions.Conclusions: Intraoral conditions affected the trueness of DIT and CIT in different regions but had no influence on precision.