Soncul, Murat; (2002) Evaluation of facial soft tissue changes and surgical outcome of orthognathic surgery. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The prediction of soft tissue changes and surgical outcome are main concerns in orthognathic surgery carried out to resolve functional and aesthetic problems. This study programme validated and used the optical surface scanner for assessment of facial appearance for orthognathic surgery treatment planning and postoperative review. The reproducibility of head position for the scans was tested using a headrest, a spirit level and a vertical beam of laser light. The results were analysed using thin-plate splines, a novel morphometric analysis and a useful tool for clinical research. The error due to variation in head position was insignificant. This study found the optical surface scanner an accurate, non-invasive, and user-friendly tool. It was comparable to cephalography with additional advantages of a 3D system. The presentation of Caucasoid facial patterns in the media determines people's notions of beauty. In line with the homogenisation of culture throughout the world, the panel in this study, although formed of racially different individuals, shared a common base for the assessment and judgement of beauty. Caucasian facial features were perceived more familiar, standard, and beautiful. The best-ranked Afro-Caribbean and Oriental subjects in this study had facial features similar to Caucasians. Facial symmetry, alar base and vermilion border were strong markers for facial beauty according to this study. The chin was coincident and the mid-face was anterior to the facial plane in the most beautiful faces. Other features for a beautiful face indicated by this study included shorter lips, upper incisor exposure of 4-5 mm, equal facial thirds in the vertical height, equal alar base width and intercanthal distance, and equal interlimbus distance and commissural width. The ratios of the soft tissue changes after correction of Class II and Class III skeletal deformities were quantified and analysed (n=102) using the optical surface scanner and thin-plate splines morphometric analysis for accurate surgical planning. The ratio of soft to hard tissue movement decreased further lateral to the facial midline and on suspended tissues like the lips compared to tissues firmly attached to the underlying structures like subnasale and pogonion. The soft to hard tissue change ratio was 1:1 on the pogonion but decreased gradually on the labiomental groove (90%) and subcomissural regions (50%). The subnasale projected 80% of the skeletal movement, but the effect on subalar and supracomissural tissues on the upper lip decreased down to 35%. The nasal tip was least affected by 30% despite an 80% change on paranasal regions. The interaction of one lip with the other, and with the incisors affected the lips as well as the skeletal movement. The upper lip vermilion projected up to 75% of the surgical change and the upper vermilion width increased from 7.2±2.3 mm to 8.7±2.1 mm which was statistically significant (p<0.05), but the mean lower lip vermilion width increased from 9.9±2.4 mm to 10.4±2.2 mm which was not significant (p>0.05). The prediction of soft tissue changes after orthognathic surgery can be difficult because these changes depend on various factors including: muscle attachments, proximity of the soft tissues to the underlying bone, the geometrical shape of the bones, soft tissue elasticity, thickness, surgical technique and the magnitude of surgical movement. However, this study highlighted the regions of the face significantly affected by the osteotomy movements. The role of the occlusal wafer and training elastics in postoperative proprioception was evaluated. The patients (n=100) were randomly divided into three groups; a) training elastics and occlusal wafer, b) elastics but no wafer and, c) no elastics and no wafer, for the first 2 postoperative weeks. The findings indicated that routine use of occlusal wafers and training elastics did not lead to a significant difference in the postoperative occlusion. The theoretical value of providing proprioceptive guidance was concluded to be more comforting for the surgeon than the patient. However, it is believed to provide a visible means of clinical assessment. Results of this investigation would contribute significantly in diagnosis, treatment planning and postoperative management of orthognathic surgery patients.

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