The relationship between the changes in three-dimensional facial morphology and mandibular movement after orthognathic surgery

Abstract

Purpose

The purpose of this study was to investigate the relationship between changes in three-dimensional (3D) facial morphology and mandibular movement after orthognathic surgery. We hypothesized that facial morphology changes after orthognathic surgery exert effects on 3D mandibular movement.

Materials and methods

We conducted a prospective follow-up study of patients who had undergone orthognathic surgical procedures. Three-dimensional facial morphological values were measured from facial CT images before and three months after orthognathic surgery. Three-dimensional maximum mandibular opening (MMO) values of four points (bilateral condylions, infradentale, and pogonion) were also measured using a mandibular movement tracking and simulation system. The predictor variables were changes in morphological parameters divided into two groups (deviated side (DS) or contralateral side (CS) groups), and the outcome variables were changes in the MMO at four points.

Results

We evaluated 21 subjects who had undergone orthognathic surgical procedures. Alterations in the TFH (total facial height), LFH (lower facial height), CS MBL (mandibular body length), and DS RL (ramus length) were negatively correlated with changes in bilateral condylar movement. The UFH, DS MBL and CS ML (mandibular length) showed correlations with infradentale movement. The CS ML, DS ML, MBL, UFH, and SNB were correlated with pogonion movement.

Conclusion

The height of the face is most likely to affect post-operative mandibular movement, and is negatively correlated with movement changes in the condyles, infradentale and pogonion. The changes in CS morphological parameters are more correlated with mandibular movement changes than the DS. The changes in CS MBL and bilateral RL were negatively correlated with condylar movement changes, while the bilateral MBL and CS ML were positively correlated with changes in infradentale and pogonion.

Introduction

Orthognathic surgery is widely performed to improve facial aesthetics and masticatory function, including mandibular movement, thus enhancing quality of life (Jan and Johanne, 2012). Some studies have examined the functional or morphological changes that can occur after orthognathic surgery, assessing parameters such as mechanical advantages, bite force, soft tissue, and range of mandibular movement (Kouta et al., 2012; Popat et al., 2012; Sforza et al., 2010; Song et al., 1997; Throckmorton and Ellis, 2001; Throckmorton et al., 2000, 1980; Verze et al., 2011; Yang et al., 2005; Zarrinkelk et al., 1996, 1995). Mandibular movement generally decreases after orthognathic surgery (Aragon et al., 1985; Boyd et al., 1991; Storum and Bell, 1984; Ueki et al., 2008). On the other hand, in their long-term follow-up study, Pepersack and Chausse reported no decrease in maximum mouth opening (Pepersack and Chausse, 1978). Zimmer et al. (1992) reported differences in the patterns of changes in mandibular movement according to different orthognathic surgical procedures. Other studies have explored the relationship between changes in mandibular movement and morphology after surgery (Aragon et al., 1985; Ueki et al., 2005). A positive correlation was found between changes in the condylar long axis angle and in the incisal path and lateral movement range (Ueki et al., 2005). The amount of surgically created mandibular setback was also correlated with the maximal interincisal opening (Aragon et al., 1985). No study has assessed the relationship between changes in three-dimensional (3D) facial morphology and 3D mandibular movement after orthognathic surgery.

Some studies have investigated the relationship between mandibular movement and facial morphology (Farella et al., 2005; Fukui et al., 2002; Ingervall, 1971). A correlation between the mandibular movement range and the facial morphology of the ramus inclination and mandibular length was reported (Ingervall, 1971). Fukui et al. (2002) reported positive correlations between maximum mouth opening and various facial morphology parameters, including ramus inclination, gonial angle, and maxillary length. In addition to these findings, patients with facial asymmetry exhibited an asymmetrical condylar path angle (Mimura and Deguchi, 1994), and condylar path asymmetry was associated with facial asymmetry parameters (Pirttiniemi et al., 1990). In a previous study, we analyzed the relationship between the range of mandibular movement and facial morphology, as measured in 3D (Kim et al., 2010a). The mandibular movement was correlated with facial morphology features such as SNA, ramus length, mandibular length, and mandibular body length. The 3D morphology value could predict the variation in mandibular movement to a certain extent (Kim et al., 2010a). The asymmetry in movement between the condyles increased as the mandibular deviation increased (Kim et al., 2010a). Therefore, the 3D facial morphology changes that are introduced by orthognathic surgery can affect 3D mandibular movement, and a relationship may exist between the extent of changes in facial morphology and mandibular movement, as measured in 3D.

The purpose of this study was to investigate the relationship between 3D mandibular morphological and movement changes after orthognathic surgery. We hypothesized that the facial morphology changes that follow orthognathic surgery exert effects on the 3D mandibular movement. Three-dimensional mandibular movement and facial morphology changes were acquired pre- and post-operatively from patients who had undergone orthognathic surgeries. We then analyzed the relationship between the changes in 3D facial morphology and mandibular movement.