Are we achieving less maxillary clockwise rotation than we anticipate? A retrospective study on the accuracy of 3D planned orthognathic surgery.

Introduction: In orthognathic surgery planning, there is often an aim to give the maxilla a clockwise rotation, especially in cases with significant overjet, to avoid excessive protrusion of the pogonion. In our 3D planning approach, 3D-printed intermediate wafers are utilized. For a planned maxillary clockwise rotation, these wafers are slightly thicker at the back to achieve the intended posterior maxillary intrusion. We suspect that in reality, less posterior intrusion is achieved than planned due to technical reasons. The current study investigated this hypothesis by retrospectively comparing the actual performed maxillary clockwise rotation (MCR) with the planned MCR.

Materials and Methods: Fifty-three patients (22 male, 31 female; aged 13 to 56 years) who underwent bimaxillary surgery with clockwise maxillary rotation between January 2023 and October 2023 were included. Using a 3D virtual assessment tool, postoperative computed tomography scans were compared with preoperative 3D virtual planning. The difference in maxillary pitch was analyzed. The postoperative maxillary pitch, roll, yaw, and up-down movement were reentered into the preoperative 3D virtual planning to calculate the actual movement of the maxilla determined by the maxillary points on the virtually planned osteotomy line (A and D posterior and B and C anterior, right and left, respectively). The difference in maxillary movement was then analyzed.

Results: On average, the postoperative measured pitch deviated by 1.2° (ranging from 5.7° to -3.3°) from the planned pitch (P < 0.0001), consistently resulting in a reduction of the pitch. Additionally, the postoperative deficiency in pitch increased with larger movements. Posterior maxillary points A and D showed decreased intrusion by an average of 1.2mm compared to anteriorly situated points B and C (0.9mm) (p<0.0001).

Conclusion: These results confirm the hypothesis that, during the execution of the 3D planning, typically less MCR is achieved than planned. While minor discrepancies between the actual movement performed and the preoperative 3D planning are expected, the consistent deviation in the same direction, namely decreased pitch in MCR, suggests the rationale for considering a standard overcorrection in planning this movement.