Flapless Implant Surgery Using an Image-Guided System. A 1- to 4-Year Retrospective Multicenter Comparative Clinical Study: Influence of Flapless Procedure on Survival Rate

Purpose: The aim of this retrospective multicenter clinical study was to compare the survival rate of dental implants placed with two different surgical procedures: (1) a flapless surgical procedure using an image-guided system (IGS flapless protocol) and (2) the conventional technique (open flap without IGS) with a computed tomography scan. Materials and Methods: Between 2001 and 2004, 552 implants were placed in 169 patients by six practitioners who used both protocols to restore completely and partially edentulous arches: 271 of them were placed with the IGS flapless protocol (test group) and 281 with the conventional procedure (control group). Each implant was categorized as "survival" or "failure" after 1 to 4 years of follow-up after prosthesis implantation. A preoperative classification was used to evaluate the anatomic features of each case. There was initially no possible comparison between these two groups because of the indication bias relative to the retrospective clinical study data characteristics. After a classic logistic regression analysis, propensity scores were used to reduce this bias: prognosis variables were included in a regression logistic model to define the probability for each implant to be treated with the IGS flapless protocol. Implants showing the same probability were categorized into three classes. The implants were then compared with each other within the same class. Results: After the follow-up period, the cumulative survival rate was 98.57% in the control group and 96.30% in the test group. Whatever the statistical method used, no statistical differences between the two protocols were shown. Transmucosal implant placement showed a survival rate of 97%. Even though the initial conditions were less favorable, the survival rate in the test group was comparable with the standard protocol group. Conclusion: Passing an implant through the gum does not interfere with osseointegration. The IGS flapless procedure makes it possible to use the flapless procedure, even though anatomic conditions were initially unfavorable.