Computer Guided Implant Surgery Accuracy is Affected by Cortical Bone Thickness, in-Vitro Study.

Computer guided implant surgery is considered as a relatively accurate method for implant placement, but yet, there are certain discrepancies between virtual planning and final outcome.

Aim: to evaluate the effect of cortical bone density on the accuracy of guided implant placement outcome in an in-vitro study.

18 dental implants (Cortex Dynamix®, diameter 3.8mm, length 11.5mm), were placed, using a surgical guide, in nine models, which simulate trabecular bone. In each model 21 sites were surrounded by thin acrylic structure, while 16 sites were surrounded by thick acrylic structure. All implants were pre-planned using 3Shape Implant Studio® program and were inserted according to guided surgery protocol. After placement of the implants, we used 3Shape TRIOS 3® intra-oral scanner, while the mounting device served as a scan body. By using SOLIDWORKS Desktop 3D CAD® we virtually placed the implant in the model according to the scan body location and superimposed it using 3Shape Implant Studio® program with the virtually pre-planned model. Horizontal and vertical discrepancies and axial divergence were measured.

Mean horizontal discrepancy in the apical area was 0.46± 0.45mm (0.03-0.99mm) and 0.24±0.23mm (0.02-1.05mm) in the cervical area. The mean vertical discrepancy in the apical area was 0.45± 0.34mm (0.02mm-1.69mm) and 0.44±0.39mm (0.02-1.22mm) in the cervical area. The mean axial divergence was 1.5±1.27 degrees (0-3.65 degrees). When comparing the thick cortex group to the thin cortex group, the mean horizontal discrepancies were 0.28±0.26mm and 0.63±0.33mm respectively (P=0.02). The mean vertical discrepancies in the thick cortex group and the thin cortex group, were 0.12±0.09mm and 0.8±0.39mm respectively (P<0.0001). In the axial comparison, we found 0.8±0.91degrees divergence in the thick cortex and 2.19±1.23 degrees in the thin cortex, (P=0.01).

cortical bone thickness may affect guided implant placement accuracy. In soft bone, accuracy will decrease in both vertical and horizontal axis.