Strain analysis in posterior implant-supported fixed dental prostheses – cemented compared to screwed: An in vitro study

Background. Research on the etiology of excessive strain at the implant neck, which may be associated with technical and biological complications, is still lacking. Objectives. This in vitro study aimed to compare strain development at the implant neck between cement-retained and screw-retained implant-supported fixed restorations, as well as among 3 prosthesis designs, using strain gauge analysis. Material and methods. Six prosthetic configurations were fabricated and divided according to their retention mechanism: single crowns – cement-retained and screw-retained (SC-c and SC-s, respectively); splinted restorations – cement-retained and screw-retained (SP-c and SP-s, respectively); and simple three-unit bridges – cement-retained and screw-retained (SB-c and SB-s, respectively). Two strain gauges were attached to the implant necks. A vertical load of 200 N was applied simultaneously at 3 identical loading points on each restoration. Strain measurements were analyzed statistically using ANOVA and Scheffé’s post hoc contrast analysis. Results. Cement-retained restorations transferred significantly less cervical strain to the implant neck than screw-retained restorations in all 3 prosthetic configurations tested (p < 0.001; SC-c < SC-s; SP-c < SP-s; and SB-c < SB-s). Single crowns transferred significantly less strain to the implant neck than the other restoration designs in both cement-retained and screw-retained groups (p < 0.001; SC-c < SP-c and SB-c; SC-s < SP-s and SB-s). Conclusions. The use of cement-retained implant-supported fixed prostheses results in less strain development at the implant neck when subjected to high occlusal loads as compared to screw-retained prostheses. Splinting the adjacent implant-supported restorations does not necessarily reduce strain at the implant neck.