The difference between registered natural head position and estimated natural head position in three dimensions

A Preliminary Study of a Novel Reference Plane of the Head: Comparing With the True Horizontal Plane

A new reference plane of the head, based on soft tissue landmarks and suitable for clinical analysis and soft tissue measurements, is needed. We recently discovered a novel reference plane, that is, the COs plane, which was formed by bilateral Lateral Canthus and bilateral Otobasion Superius and might be horizontal at the natural head position (NHP). In this study, we investigated the angles between the COs plane and the true horizontal (TrH) plane while sitting and standing, aiming to explore whether the new plane could be used as a substitution for the reference plane in clinical practice. Briefly, 26 volunteers were enrolled. Their sitting and standing NHP were recorded using the 3dMDface system. In the pitch axis, the mean angle of COs/TrH was 0.29 degrees and 0.41 degrees for sitting and standing positions, respectively, showing no statistical difference ( P >0.05). However, in the roll axis, the mean angle of COs/TrH for sitting position and standing positions was 1.08 and 1.33 degrees ( P <0.05), which was considered to be the result of habitual canting of the head. Moreover, there were no significant differences between the sitting and standing NHP, considering the COs/TrH angles ( P >0.05). To sum up, we concluded that the COs plane could be used as a reliable reference plane in certain soft tissue analysis and clinical applications.

Recording Natural Head Position Using Cone Beam Computerized Tomography

The purpose of this study was to develop a technique to record the natural head position (NHP) of a subject using the scout images of cone beam computerized tomography (CBCT) scans. The first step was to align a hanging mirror with the vertical (XY) plane of the CBCT field-of-view (FOV) volume. Then, two scout CBCT images, at frontal and at sagittal planes, were taken when the subject exhibited a NHP. A normal CBCT scan on the subject was then taken separately. These scout images were used to correct the orientation of the normal CBCT scan. A phantom head was used for validation and performance analysis of the proposed method. It was found that the orientation detection error was within 0.88°. This enables easy and economic NHP recording for CBCT without additional hardware.

Different Modalities to Record and Transfer Natural Head Position to Virtual Planning in Orthognathic Surgery: Case Reports of Asymmetric Patients

Aim

To describe different modalities to record and transfer natural head position (NHP) to 3D facial imaging by using the virtual surgical planning software in three facial asymmetry patients.

Case Reports

Three patients with facial asymmetries (A, B, and C) were evaluated by means of dental and facial analysis, photographs, cone-beam computed tomography (CBCT) and digitized dental arches. Before starting the VSP workflow with Dolphin Imaging, NHP was recorded by three modalities and transferred to three-dimensional (3D) facial images as follows: (a) facial photographs taken with digital camera and the estimated NHP was transferred to 3D images by comparing lines and planes from both images; (b) cross-line level laser was used to place radiopaque markers on the face skin for recording the estimated NHP, which was transferred to 3D images by alignment of planes and markers in the software; and (c) photographs of the face were processed to generate facial surface mesh by using the Agisoft PhotoScan software, which maintained the same position of the estimated NHP in 3D for aligning the images of the soft tissue with the facial surface mesh by using superimposition. All the three patients underwent bi-maxillary orthognathic surgery.

Conclusion

There are different modalities using simple and available technologies in the clinical routine, but whose reproducibility, reliability and validation could not be assessed nor compared to each other. There was no trend for better predictability, feasibility and efficiency because the postoperative outcomes were adequate regarding the patients' satisfaction and facial symmetry.

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

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.