Page 54 - Craniomaxillofacial Implant Surgery - Jeroen P.J. Dings

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Chapter 3
For the evaluation of the surgical results in comparison with the pre-operative planned virtual positions all cadavers were rescanned after implant insertion. Postoperative CBCT and MDCT scans were acquired using the same settings as for the preoperative scans. These scans were superimposed to the preoperative scans that were used for the virtual implant planning using voxel-based registration. To obtain the postoperative tip and shoulder coordinates of the implants, the surgically installed implants were segmented from the postoperative scan for visualization purposes. 3D-image models of the virtually planned implants with equal length and diameter from the planning were aligned with these segmented implants followed by calculation of the 3D-deviations of the variables ‘implant tip’, ‘implant shoulder’, ‘angulation’ and ‘depth’.
2.2. Statistical analysis
Linear mixed models were used to analyse the influence of the implant variables on the deviations between planned and post-operative implant positions. In this model a random patient intercept was used, with the influence of implant characteristics as a fixed factor. Backwards step-wise regression was used for comparison between surgical templates with and without bone fixation pins. Differences were considered statistically significant with a P-value of <0.05. The statistical analysis was performed using SAS® version 9.4 (SAS Institute Inc., Cary, NC, USA).
RESULTS
A total of 136 Branemark MK III TiU implants with regular platform (∅ 3.75 mm) were placed in 10 cadaver heads (Table 1): 57 implants in the orbital region, 19 nasal implants and 60 auricular implants. Due to an impacted cuspid tooth one nasal implant could not be planned. Three orbital implants could not be planned due to bony defects in the orbital region. Bone fixation pins were used in 5 cadaver heads on 25 surgical templates. No statistically significant differences were shown between different lengths of implants and between implants placed at the left or right side of the cadaver head.