Comparison of initial Implant stability placed using bi-cortical fixation, indirect sinus lift and uni-cortical fixation

Abstract

Purpose: This study aim was to determine if self-threading dental implants placed using stopper drills so to bi-cortically engage both the alveolar crest and sinus floor (bi-cortical fixation) achieved comparable primary and/or secondary stabilities to that of short implants only engaging alveolar crest cortical bone (uni-cortical fixation) or implants engaging both crest and sinus floor but via greenstick fracture and grafting (indirect sinus lift).Material and Methods: Thirty-eight patients exhibiting 7 - 11 mm of bone coronal to the sinus floor as confirmed by pre-operative CBCT were recruited. Forty-five implants were randomly assigned to one of the placement techniques. No patient received more than two implants, which were placed in opposite sides of the maxilla while using different surgical techniques. An Osstell ISQ was employed immediately after implant placement to measure stability 6 times in a buccal/lingual dimension. Secondary stability was measured at 2nd stage surgery after a 3- to 6-month healing period. Results: The greatest primary implant stability was achieved via indirect sinus lift. However, no statistical significant difference was found among the three surgical techniques (P = 0.13; bi-cortical fixation: 71.4 [SE 2.1], uni-cortical fixation: 69.6 [2.1], indirect sinus lift: 75.9 [2.3]). The three techniques had similar secondary stability (P = 1.0; respectively 79.9 [1.2], 80.0 [1.2], 80.0 [1.3]). Baseline residual ridge height measured on CBCT was similar (P = 0.1; respectively 8.8 mm, 9.9 mm, 9.4 mm) but implant diameter and length placed in the maxilla differed (P = 0.03/P < 0.001; respectively 4.7/11.4 mm, 4.3/8.1 mm, 4.7/11.8 mm). Primary implant stability was significantly correlated to CBCT bone density (r = 0.37). Conclusion: Primary and secondary implant stabilities of bi-cortical fixation did not differ significantly from those of uni-cortical fixation and indirect sinus lift. However, use of the bi-cortical fixation technique is warranted since it is simpler and more economical than the indirect sinus lift plus allows for longer implants than the unicortical fixation while yielding similar secondary implant stability.