McCance, Andrew Murray; (1992) A three dimensional analysis of soft tissue and bone changes following orthognathic surgery. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Introduction: This report investigates the ability of surgeons to achieve predicted surgical movements in five different groups of patients, and analyses both the predictions and the changes in two dimensions using scale space analyses (Campos 1991). The report then progresses to the three dimensional analysis of the bone, the soft tissues and the ratio of soft tissue to bone following surgery, using a colour coded techniques (Fright and Linney, 1991) to illustrate the changes. The average soft tissue scans from each group of patients were averaged and compared to a control group at the preoperative, three months and 1 year postoperative stages (Fright, 1991) Data Acquisition: Bone measurements were recorded from lateral skull radiographs preoperatively and 48 hrs postoperatively, and CT scans preoperatively and 1 year postoperatively. Soft tissue measurements from an optical scanner, preoperatively, three months and 1 year postoperatively. Patients 1) Control group: 30 females and 30 males 2) Skeletal class 2 patients: 15 Females and 2 Males 3) Skeletal class 3 patients: 9 Females and 7 Males 4) Cleft Palate Patients a) Unilateral cleft lip and palate: I 6 Females: 2 left and 4 right sided clefts 7 Males: 3 left and 4 right sided clefts b) Bilateral cleft lip and palate: 5 Males and 1 Female c) Clefts of the Hard and Soft palate: 5 Females. Results: Prediction: There was a surprisingly poor match between the predicted and achieved movements in both the horizontal and vertical direction in all patient groups. The scale space analysis provided an efficient method of illustrating profile changes. Soft tissue movements There were definite patterns of change and relapse in the patient groups. The relapse being most marked in the cleft palate patients. Bone movements and soft tissue to bone ratios Definite patterns of movement for the maxilla and the mandible became apparent for both the bone and soft tissue to bone ratio of movement in each group. For maxillary impactions in the skeletal 2 group there was a 1:1 ratio of movement of the soft tissue to bone in the midline increasing to 1.25:1 in the canine region and 1.5:1 in the paranasal region. Conclusions: There is a need to develop a technique to aid the the surgeons in carrying out planned surgical movements. The colour coded method was shown to be a simple, efficient and easily understandable way of analysing surgical change. Diagnosis of surgical requirements was aided by the ability to objectively compare the individual to a control group. The prediction of surgical change should be greatly aided by adapting the current database to include the distinct patterns of movement in the bone and ratio of movements of the soft tissues to the bone.

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