Thesis (M. Orth.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 178-189).

published_or_final_version / Dentistry / Master / Master of Orthodontics

published_or_final_version / Dentistry / Master / Master of Orthodontics

published_or_final_version / Dentistry / Master / Master of Orthodontics

Purpose: To define initial hard and soft tissue convexity necessary for profiles to consistently improve after mandibular advancement and to assess if pre-surgical lower incisor inclination (IMPA) affects profile change. Methods: 20 general public, 20 orthodontists, and 20 oral surgeons used a Likert scale to rate attractiveness of before and after treatment profiles of mandibular advancement patients. Spearman’s correlation tested for relationships between amount of profile change and varying ANB, profile angle and pre-surgical IMPA. Wilcoxon test compared extraction and non-extraction profile changes. Results: There was a tendency for inverse correlations between profile change and profile angle, but was not statistically significant any of the 3 groups. There was a tendency for positive correlations between profile change and ANB, but was considered significant only for orthodontists. Orthodontists, oral surgeons and the general public found profiles consistently improved when profile angles were ≤159º, ≤158º and ≤157º, respectively. Orthodontists and oral surgeons found profiles consistently improved when ANB angles were ≥5.5º and ≥6.5º, respectively. Profile worsening increases 2.6 to 5.0 times when profile angles exceeded thresholds, and 4.5 to 7.9 times when ANB angles were less than thresholds. No difference in IMPA or profile change in extraction and non-extraction groups. Conclusion: Extractions are not predictive of a greater surgical profile change. Pre-treatment profile angles <160º and ANB >6º are necessary for consistent improvements after surgery.

Purpose: To define initial hard and soft tissue convexity necessary for profiles to consistently improve after mandibular advancement and to assess if pre-surgical lower incisor inclination (IMPA) affects profile change. Methods: 20 general public, 20 orthodontists, and 20 oral surgeons used a Likert scale to rate attractiveness of before and after treatment profiles of mandibular advancement patients. Spearman’s correlation tested for relationships between amount of profile change and varying ANB, profile angle and pre-surgical IMPA. Wilcoxon test compared extraction and non-extraction profile changes. Results: There was a tendency for inverse correlations between profile change and profile angle, but was not statistically significant any of the 3 groups. There was a tendency for positive correlations between profile change and ANB, but was considered significant only for orthodontists. Orthodontists, oral surgeons and the general public found profiles consistently improved when profile angles were ≤159º, ≤158º and ≤157º, respectively. Orthodontists and oral surgeons found profiles consistently improved when ANB angles were ≥5.5º and ≥6.5º, respectively. Profile worsening increases 2.6 to 5.0 times when profile angles exceeded thresholds, and 4.5 to 7.9 times when ANB angles were less than thresholds. No difference in IMPA or profile change in extraction and non-extraction groups. Conclusion: Extractions are not predictive of a greater surgical profile change. Pre-treatment profile angles <160º and ANB >6º are necessary for consistent improvements after surgery.

Master of Science / Most studies of condylar movement are based on the movement of an arbitrary condylar point. As the condyle is a 3-dimensional body which undergoes complex rotations and translations in function, the movement of one point in the vicinity of the condyle may not accurately represent condylar movement. The aims of this investigation were to determine in human subjects, during open-close and excursive jaw movements, the movement patterns of arbitrary and anatomical condylar points; and whether the trajectory of a single selected point can accurately reflect the movement of the condyle. In 44 subjects, condylar point movements were recorded with an opto-electronic tracking system (JAWS3D), which recoded the position of three light-emitting diodes attached to each dental arch. The primary point, selected to represent movement of the condyle, was 15 mm medial to the palpated lateral condylar pole, parallel to the Frankfort horizontal plane. Additionally, four points were selected along orthogonal axes in the sagittal plane, and four in the horizontal plane: each was 5 mm from the primary point. In two subjects, the mandibular condyles were imaged by computerised tomography (CT) and the lateral and medial poles, most superior, anterior and posterior points of their condyles were selected. The trajectories of each point were compared for each subject for the mandibular movements listed above. Variability in both path form and dimension was noted between the subjects for all mandibular movements. For example, in an open-close mandibular movement the condylar point translation varied in the antero-posterior direction between 1.8-22.8 mm, and in the supero-inferior direction between 4.5-12.1 mm. For each subject, the pathway of each point was different in form and dimension from that subject’s other condylar points for the open-close, and ipsilateral lateral mandibular movements. For the open-close movement, in only four of the 44 subjects were the arbitrary point traces similar in form within a subject; and the tracings of each subject’s condylar points showed, on average, a 3.2 mm difference in maximal horizontal (i.e. antero-posterior) translation and 2.9 mm in maximal vertical (i.e. supereo-inferior) translation. For contralateral lateral mandibular movements, the path form and dimension in the sagittal plane of the condylar points were similar within a subject; however the lateral component showed variability in path length for the different points within a subject. The pathways of the condylar points for a protrusive movement displayed the most similarity within a subject, with an average of 0.4 mm variation in maximal horizontal or vertical displacement between each subject’s arbitrary condylar points’ tracings. The anatomical condylar points of the two subjects showed variability between and within each subject. For these two subjects the trajectories of the arbitrary condylar points moved in directions similar to the anatomical points of all movements except for the ipsilateral lateral mandibular movement, where in one subject, the arbitrary condylar points moved posteriorly, inferiorly and laterally whereas the anatomical points moved anteriorly, inferiorly and laterally. There is much variability in both form and dimension for mandibular condylar movement between human subjects. There is also considerable variability within subjects in the form and dimension of condylar point movement, whether arbitrary or anatomical, depending on the point selected. By inference therefore, a single condylar point cannot accurately reflect the movement of the mandibular condyle, except perhaps for a protrusive mandibular movement. Multiple mandibular points are therefore required to describe the motion of the condyle. In an ipsilateral lateral mandibular movement, for example, an arbitrary point may move in a completely different direction to the mandibular condyle, and so anatomically derived condylar points should be utilised to assess accurately condylar movement.

Thesis (Ph. D.)--University of Hong Kong, 2008. / Also available in print.

Thesis (M.Orth.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 178-189). Also available in print.

Thesis (M. Orth.)--University of Hong Kong, 2005.