Page 144 - Craniomaxillofacial Implant Surgery - Jeroen P.J. Dings
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Chapter 8
errors showed significant submillimeter overestimation of the bony dimensions with both the CBCT and MDCT imaging modalities. The different contrast settings resulted in an average measurement bias of 0.39 to 0.53 mm for CBCT and 0.57 to 0.59 mm for MDCT. This influence on measurement accuracy was only statistically significant for CBCT images (p<0.0015) and for inter-observer variation on MDCT imaging (p<0.029). Within the limitations of this study, it was demonstrated that linear measurements on cross-sectional images from 3D-virtual models for preoperative planning of CMF implants showed a consistent submillimeter overestimation.
In Chapter 3, an analysis of the accuracy of skin-supported surgical templates ‘with and without’ bone fixation is described. The study comprised 10 fresh frozen cadaver heads. After acquiring MDCT and CBCT scans, and subsequent virtual implant planning in the orbital, nasal and mastoid region, surgical templates were designed. In these templates, cylindrical openings were created to allow the application of guide sleeves and, thereby, enabling flapless implant placement. For each anatomical region surgical templates ‘with and without’ multiple fixations pins were produced. The accuracy of implant placement was determined three-dimensionally (3D-) by matching the virtually planned implant positions with the postoperative achieved implant positions. In total, 136 Brånemark MK III TiU® (Nobel Biocare, Kloten, Switzerland.) implants were installed; 57 in the orbital region, 19 nasal implants and 60 auricular implants. Overall, applying fixation pins showed statistical significant larger ‘mean deviations’ at the implant shoulder (range, 3.0 to 4.4 mm) (p=0.025), angle (range, 6.9 to 9.2 degrees) (p=0.018), and depth (range, -1.2 to -0.4 mm) (p=0.001) in comparison to the use of non-fixated surgical templates (‘mean deviations’ at implant shoulder (range, 1.8 to 3.2 mm), angle (range, 4.7 to 7.1 mm) and depth (range, -0.2 to 0.6 mm), respectively). Mean implant deviations were shown to be highest for auricular implants with the exception of angular deviations. Surgical templates without fixation pins only showed a non-significant difference in angular deviation with regard to the various anatomical regions. No statistically significant difference was found for depth of implants being placed with the bone-fixated surgical templates. The reported unacceptable high deviations can presumably be explained by a suboptimal positioning of the skin- supported surgical template due to resilience of the skin. The larger ‘mean implant deviation’, associated with the use of surgical guides in combination with the fixation pins, are likely the result of suboptimal fixation of the template as a result of unfavorable movement during the fixation procedure. The eccentric location of the auricular region in the surgical template is supposed to have worsened this inaccuracy.































































































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