Effects of prosthesis design and impression techniques on human cortical bone strain around oral implants under load.

Purpose: The purpose of this study was to evaluate the effects of two different prosthetic designs (screw-retained versus cement-retained) and two impression techniques (open versus closed tray) on bone-level strains around implants.

Materials And Methods: Two Ø 4.1 mm x 10 mm Straumann implants were placed in the bilateral fibulas of six fresh cadavers; bone segments were removed en bloc. Twelve implant-level and six abutment-level (18 total) working casts were made to fabricate fixed partial dentures, resulting in three test groups: Group 1: closed-tray technique/implant-level model/screw-retained prostheses; Group 2: closed-tray technique/abutment-level model/cement-retained prostheses; Group 3: open-tray technique/implant-level model/screw-retained prostheses. Linear strain-gauges were bonded to the cortical bone between implants and the lateral wall of the fibula in close proximity to the implant necks in each bone fragment. Strain-gauge signals were digitized by a data acquisition system and corresponding software at a sample rate of 10 KHz, simultaneously monitored from the computer during application of an external static load of 150 N on the middle of the pontic, using a loading frame.

Results: The approximal and lateral strains were extremely similar in both prosthetic groups (p>0.05). Within-group comparisons for the indirect impression technique showed that approximal and lateral strains in screw- and cement-retained prostheses were similar (p>0.05). Neither the prostheses design nor the impression technique had any discernable effect on bone-level strain.

Conclusion: Strains on the cortical bone around two implant supported, 3-unit screw- or cement-retained fixed prostheses, fabricated either by direct or indirect impression techniques on Straumann dental implants, are similar under a 150 N static load.