Page 58 - Craniomaxillofacial Implant Surgery - Jeroen P.J. Dings

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Chapter 3
on the level of bone-implant contact was not separately determined. Furthermore, since maxillofacial prostheses frequently indicate the use of individualized framework using angled or customized implant abutments an improper position of an extra-oral implant can mostly be restored40,41.
Reported deviations can be explained by the resilience of the skin, since accuracy is mainly dependent on precise and stable positioning and inherent support of the surgical template42,43. Resiliency is likely to be negatively influenced by the reduced quality and altered thickness of the soft tissue of fresh frozen cadavers who were defrosted several times. In an effort to minimize positional discrepancies, bone-fixation pins were used in this study. Disadvantageously, placing of fixation pins can introduce an extra error by bringing the surgical template out of balance28. As Neugebauer et al pointed out, fixation is not necessarily carried out in the same position as during virtual planning16. Our results are consistent with the results of Verhamme et al10 showing that bone-fixation pins do not offer more accurate transfer from planning to placement of maxillary implants. However, in our study statistically significant greater differences were found in deviation of the shoulder, angle, and depth with regard to implants being placed with the use of bone fixated surgical templates. Larger deviations of auricular implants in our study are hypothesized to be influenced by the eccentric location of the guide sleeves in the surgical templates for auricular implants. Manual pressure may cause tilting of the template and henceforth unfavorable rotation and translation during implant surgery. All auricular implants were planned on cross-sectional images derived from MDCT data. Widmann et al and Primo et al demonstrated no clinical relevant difference in accuracy for 3D-printed surgical templates using CBCT or MDCT imaging modalities44,45.
Unintentional deformation of surgical templates during printing or per-operative bending might have occurred since the templates and extending arms covered a large surface21. To minimize dimensional changes an overall thickness of 3.0 mm of surgical templates was planned31. Furthermore, possible dimensional printing errors were assessed through laser surface scanning in this study and showed no relevant dissimilarities.
Mean angular deviations in this study were also likely to be influenced with the position of the drill within the guide sleeves. Van Assche et al31 described a maximum angular deviation of 4.71 degrees for a maximal inclination of the drill. Large deviations for nasal