Research Paper
Orthognathic Surgery
Variation between natural head orientation and Frankfort horizontal planes in orthognathic surgery patients: 187 consecutive cases

https://doi.org/10.1016/j.ijom.2021.02.011Get rights and content

Abstract

The purpose of this study was to assess the relationship between the Frankfort horizontal (FH) and natural head orientation (NHO), their correlation between patients’ malocclusion, and the impact of counterclockwise rotation (CCW) on the FH-NHO angle variation after orthognathic surgery. An evaluation of 187 consecutive patients was performed at the Maxillofacial Institute (Teknon Medical Center, Barcelona). FH-NHO° was measured pre- and postoperatively at 1 and 12 months, after three-dimensional (3D) superimposition using a software (Dolphin®). Patients were classified as follows: 3.2%, 48.7% and 48.1%, class I, II and III, respectively. Baseline FH-NHO° was significantly positive for patients with dentofacial deformities (2.73° ± 4.19 (2.12–3.33°, P < 0.001). The impact of orthognathic surgery in FH-NHO° was greater in class II when compared with class III patients, with a variation of 2.04° ± 4.79 (P < 0.001) and −1.20° ± 3.03 (P < 0.001), respectively. FH-NHO° increased when CCW rotational movements were performed (P = 0.006). The results of this study suggest that pre- and postoperative NHO differs from FH in orthognathic patients. The angle between FH and NHO is significantly larger in class III than in class II patients at baseline, which converges after orthognathic surgery when CCW rotation is performed. Therefore, NHO should be used as the real horizontal plane when planning for orthognathic surgery.

Section snippets

Materials and methods

To address the research purpose, the investigators designed and implemented a retrospective cohort study. The study population consisted of consecutive patients with dentofacial deformities who underwent orthognathic surgery (either mono- or bimaxilar) at the Maxillofacial Institute (Teknon Medical Centre in Barcelona, Spain) during 2019. Clinical data and three-dimensional (3D) radiological images were obtained from the Institute's database. Each patient provided written informed consent to

Results

A sample of 187 consecutive patients who underwent orthognathic surgery were included in the study. The sample comprised 124 women (66.3%) and 63 men (33.7%), with a mean age of 33.9 ± 11.2 years (range 15–67). Patients were classified as dental class I (3.2%), class II (48.7%) or class III (48.1%) according to Angle's malocclusion classification.18 All of the selected patients underwent bimaxillary (80%) or monomaxillary (20%) surgery, of whom 55.9% and 43% received a CCW and clockwise rotation

Discussion

The head positioning of the CBCT is essential for the virtual planning of orthognathic surgery. The results of the present study show that FH is not equivalent to NHO and that a positive angle between FH-NHO exists (2.73° ± 4.19, P < 0.001, t-test). This implies that FH is located superior to the NHO plane in most cases, which is in agreement with the published literature.5 However, when grouping patients according to dental class, class II patients showed a smaller FH-NHO angle (1.35° ± 4.29),

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Competing interests

There are no competing interests.

Ethical approval

This study was approved by the Teknon Medical Hospital Institutional review board (IRB) (Barcelona, Spain) (Ref.2019/60-CMF-TEK).

Patient consent

Patient written informed consent was provided to access the CBCT database.

Acknowledgements

The authors would like to extend special thanks to Steven Huang and David Neagu for providing help during research recording data, as well as to all the staff members at the Institute of Maxillofacial Surgery, Teknon Medical Centre (Barcelona), for their administrative and clinical support.

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