Accuracy of implant placement using precision surgical guides with varying occlusogingival heights: an in vitro study.

STATEMENT OF PROBLEM Surgical guides may interfere with effective use of surgical instrumentation during implant placement in the posterior segments where interocclusal distance may be limited. PURPOSE The purpose of this study was to measure and compare the accuracy of posterior implant placement using 3 precision surgical guides with varying occlusogingival heights, and to evaluate the difference in accuracy of implant placement through precision guides as compared to freehand placement. MATERIAL AND METHODS Three groups of surgical guides were fabricated with occlusogingival heights of 4, 6, and 8 mm, respectively. A jig was fabricated to allow for accurate positioning in bone substitute blocks. Ninety implants were placed in the mandibular first molar site on a manikin. Thirty implants (Astra Tech AB) were placed for each group, with 15 through the guide and 15 freehand. Distances between a reference implant and each placed implant were measured at both implant and abutment levels using a coordinate measuring machine. Apex position and angular discrepancy were calculated using the coordinates of the centers of the implant platform and of the occlusal aspect of the abutment. Data was assessed using 2-way ANOVA (alpha=.05). RESULTS Two-way ANOVA demonstrated that guide height did not significantly affect the accuracy of the implant position. The distance from the reference point to the point of measurement was significantly smaller for placement through the guide compared to freehand placement at both implant (P<.001) and abutment levels (P<.001). The angular discrepancy was also significantly smaller for placement through the guide (P<.001). CONCLUSIONS Precision surgical guides with 4-mm occlusogingival height allow placement as accurate as precision guides with 8-mm height. Placement through the guide reproduced the target position more accurately than freehand insertion.