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Background  The outcome of the evaluation of impression techniques accuracy may improve the selection criteria for an ideal technique. The aim was to evaluate the accuracy of the open and closed tray techniques for implant impressions, in a partially edentulous maxilla, replaced with a three-unit fixed partial denture, as well as to assess the effect of implants parallelism on accuracy.    Material and methods  This is an experimental in vitro study to evaluate impressions accuracy of a simulated area restored with an implant retained FPD, using the open and closed tray implant impression techniques. The effect of implant position angulation, parallelism, and implant systems (Straumann, SIC Invent, Osstem) was also evaluated. Three custom-made acrylic resin test models were prepared with two parallel and two non-parallel implants, on either side of a maxillary arch. One hundred and ninety-two impressions were made using monophase VPS impression material. Their master casts were obtained and evaluated for the horizontal and vertical discrepancy. The casts were scanned using a model scanner. The distances between the two reference points were measured.    Results  The Straumann and SIC Invent implants showed no statistically significant differences (Mann-Whitney  U  test), regarding accuracy for both the open and closed tray impression techniques ( P  = 0.667 and  P  = 0.472). There were no significant differences for the parallel and non-parallel implants ( P  = 0.323 and  P  = 0.814), respectively, while the Osstem system showed statistically significant differences for both the open and closed tray impression techniques ( P  = 0.035) and between the parallel and non-parallel implants ( P  = 0.045). For the vertical discrepancies, significant differences were detected (chi-square test) between the open and closed tray impression techniques ( P  = 0.037).    Conclusions  Within the limitations of this study, there were generally no significant differences between open and closed, although better results were obtained for the open tray techniques. On the use of the non-parallel implants, the open tray technique provided a better result than the closed tray technique.

Implant impression accuracy of parallel and non-parallel implants: a comparative in-vitro analysis of open and closed tray techniques