Page 126 - Craniomaxillofacial Implant Surgery - Jeroen P.J. Dings

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Chapter 7
is the risk of malrotation caused by surgical debridement and the intrinsic elasticity of the supporting soft tissues18,19. Furthermore, no direct reference to the quality and quantity of the underlying bone is provided20.
A total of 136 CMF implants were template-guided installed in 10 cadaver heads, following the Nobel Guide® surgical protocol. Preoperatively, CBCT and MDCT scans were acquired to perform a virtual implant planning. Postoperatively, CBCT and MDCT scans were made for validation purposes. To prevent movement artefacts the cadaver skulls were stabilized in an upright position for the CBCT scan and in a supine position for the MDCT scan, as per a real clinical situation. The hypothesis was that surgical templates allow proper implant placement and the use of bone-fixated pins would improve precision. Accuracy was determined as a difference less than the clinically considered threshold of 1.0 millimeter between virtually planned implant and actual position [3]. This accuracy was analyzed by measuring the Euclidean distance between the planned and post-operative position of the implant at the tip and shoulder of the implants. The depth and the angular deviation of the central axis was also calculated. Results did not corroborate the hypothesis of this study. The linear and angular deviations found in the current study, when comparing actual CMF implant positions versus the preoperatively planned implant positions, were clinically unacceptable encompassing 1.8 to 4.4 millimeter at the implant shoulder and tip. The angular deviation ranged from 4.7 to 9.2 degrees. Surprisingly, the use of bone-fixated pins even worsened accuracy. This lack of added value of pins was also described in intra- oral implantology21.
Results of Chapter 3 indicate that accuracy of guided surgery is based on cumulative errors. Therefore, in case of CMF implants, guided surgery using surgical templates is insufficient for clinical application. It is difficult to judge if the main factor contributing to the final error was the fit of the surgical template or operation errors. The latter was not controlled in this study, since the analysis of deviation was made post-surgery. The influence of possible dimensional printing errors were assessed through laser surface scanning in this study and showed no relevant dissimilarities.
The success of a surgical template is mainly dependent on its fit, meaning its direct soft tissue contact. Therefore, the results of this study should be interpreted cautiously, as it is difficult to make direct comparisons between studies due to both study design (in vitro versus in vivo versus ex vivo studies, type of support, single versus multiple