Prediction of the nose and mouth using cone-beam computed tomography in Thai adults

Abstract

The nose and mouth are parts of the face that enhance facial recognition and are, undoubtedly, important for facial approximation. Moreover, these features have been reported to show ethnic differences. Many prediction methods for the nose and mouth have been proposed. Their studies were mainly based on White subjects whereas Asian subjects used in their studies were limit. Most of previous studies focused on only some landmarks on the nose and mouth. The prediction variables used in the previous methods were, usually, based on craniometrics, angles, landmarks on the face such as the eye position or landmarks on the teeth. Unfortunately, teeth are vulnerable to lose from the socket in skeletal remains, and the position of the eyeball is still controversial. The main purposes of this study were to formulate prediction equations for the coordinates of landmarks on the nose and mouth. The prediction guidelines for the nose and mouth widths and soft tissue thickness at the midline of the face were also investigated in this study. The study protocol was based on 3-D images of the face and skull reconstructed from cone-beam computed tomography scans of 108 Thai subjects seated in and upright position. The coordinates of bone landmarks were used to formulate regression equations for coordinates of the landmarks on the nose and mouth. The infraorbital foramen and canine were used to formulate prediction guidelines for the nose and mouth widths. Horizontal and vertical distances between skull landmarks and the skin surface were used to assess the soft tissue thickness. The results showed that regression equations for coordinates of soft tissue landmarks of the nose and mouth can be applied with the mean differences of the predicted and actual values ranged between -0.6 mm and 2.1 mm for midline landmarks, and between -1.0 mm and 1.6 mm for bilateral landmarks. Nose and mouth widths can be predicted using the calculated ratios between the bone tissue width to the soft tissue width, or using the average distances between them. The extents of variability to the mean of the ratios or average distances were good (Coefficient of variation of less than 0.08). For soft tissue thickness, sex and BMI were mostly influence the thickness. The study showed that there were progressive nasal tip and lip thickness changes relative to age. Therefore, care should be taken when applying facial approximation in the base of the nose and lip regions. In conclusion, the results of this study should be beneficial for facial approximation of the nose and mouth in a Thai population.