Inaccuracies on Virtual Planned Orthognathic Cases: A Retrospective Evaluation

The new era of orthognathic surgery came with the use of virtual planning to substitute traditional model surgery. Although many advantages are offered, orthognathic surgery is still dependent of many details to provide accurate results. The aim of this study is to identify cases in which obtained results were apart from the planned movements. A retrospective cohort of bimaxillary orthognathic surgery cases, in which virtual planning was accomplished, performed by the Department of Oral and Maxillofacial Surgery at the University of Illinois at Chicago were evaluated. Inaccurate movements, evaluated by pre and immediate post-operative computed tomography scans using Dolphin Imaging, were the ones in which the mean difference between predicted movement and the obtained movement at the upper incisor tip landmarks were above 2mm on at least one of the axis (X, Y or Z). This study was performed under the principles of the Declaration of Helsinki and ethical approval by the University of Illinois Institutional Review Board (IRB no. 2015-0184) was obtained prior the beginning of the study. Descriptive and statistical (2x2 contingency table using Fisher´s exact test, considering significance for p<0.05) evaluation included the gender, type of deformity, mean and standard deviation values of the inaccurate movement. Among 50 patients that presented computed tomography scans according to the proposed methodology, 22 cases (44%) revealed discrepancies between predicted and obtained movements at the upper incisor tip landmark: 15 cases presented inaccurate movement on one axis, 5 cases on two axes and 2 cases on three axes. Discrepant movements were seen in 11 instances both for the lateral and sagittal movements while in 9 instances for vertical movements. Out of 12 Class II cases, discrepant movements were seen 7 (52%) times on lateral movements, 4 (33%) on vertical movements and 5 (41%) on sagittal movements whereas among 38 class III cases, discrepant movements were seen 4 (10%) times on lateral movements, 5 (13%) on vertical movements and 6 (15%) on sagittal movements; statistical evaluation was significant for lateral movements but not for vertical and sagittal movements (p=0.02, p=0.19 and p=0.1, respectively). Out of 34 female patients, discrepant movements were seen 7 (20%) times on lateral movements, 6 (17%) on vertical movements and 7 (20%) on sagittal movements whereas among 16 male patients, discrepant movements were seen 4 (25%) times on lateral movements, 3 (18%) on vertical movements and 4 (25%) on sagittal movements; statistical evaluation was not significant for lateral, vertical or sagittal movements (p=0.72, p=1 and p=0.72, respectively). Lateral movements displayed mean value of discrepancy between planned and obtained movements of negative 1.48mm, with standard deviation of 2.68mm, being the highest value 2.9mm0 and the lowest number negative 3.90mm; vertical movements displayed mean value of discrepancy between planned and obtained movements of 2.94mm, with standard deviation of 0.80mm, being the highest value 4.68mm and the lowest number 2.10mm; sagittal movements displayed mean value of discrepancy between planned and obtained movements of negative 2.08mm, with standard deviation of 2.39mm, being the highest value 5.50mm and the lowest number negative 2.70mm. Class II patients seem more vulnerable to inaccurate results, regardless of their gender. Variables such as the variability on perioperative mandibular position, ability to orientate the skull on virtual planning, intraoperative vertical controls might seem points of observation on a prospective basis.

 

References

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