Data on the three?dimensional (3?D) morphology of normal faces and
facial deformities as well as objective techniques for evaluating postoperative
changes are currently unavailable. With the advent of stereophotography and
cone?beam CT (CBCT), it is possible to acquire 3?D images of soft and hard
tissues of the maxillofacial complex. A series of studies were conducted aimed
at 1) establishing 3?D facial anthropometric norms for Hong Kong young
adults, 2) determining 3?D facial anthropometric features in skeletal Class II
and III deformities, 3) characterizing the oropharyngeal space in Class II and III
skeletal deformities, 4) exploring clinical applications of 3?D colour maps, 5)
establishing a non?invasive technique for estimating serial volume changes
and 6) creating virtual craniofacial models by fusing 3?D photographs and
CBCT images.
Study 1: A stereophotographic system was used to capture 3?D images of 103
Hong Kong Chinese young adults with normal balanced faces. An
anthropometric analysis protocol with linear, angular and proportional
measurements was developed to establish a normative database and quantify
dysmorphology. The Hong Kong Chinese norms were distinct from Caucasians,
especially with regard to ocular and nasal measurements. Facial height and
nasolabial measurements differed significantly between Hong Kong males and
females.
Study 2: Anthropometric analyses of 3?D facial images from 41 skeletal Class II
and 43 Class III subjects were performed. The Class II subjects had increased
lower facial height compared with Class III, who had longer total facial heights
and narrower faces. While Class II deformity primarily resulted from
mandibular deficiency with a normal maxilla, Class III presented as combined
midfacial hypoplasia and mandibular hyperplasia.
Study 3: Anthropometric characteristics of the oropharygeal space in skeletal
Class II and III were evaluated using 62 CBCT scans. The retroglossal (RG) and
retropalatal (RP) volumes and average cross sectional areas were significantly
larger in Class III than Class II skeletal deformity. The RP compartment was
larger but less uniform than the RG compartment in both Classes.
Study 4: 3?D photographs or CBCT images acquired at two different time
points were superimposed using a common unaffected area. 3?D colour maps
were generated depicting distance differences between superimposed images
in a graphical format. These maps were used as an objective tool for
treatment planning and assessing outcomes after orthognathic surgery,
bimaxillary distraction and facial trauma.
Study 5: 3?D photogrammetry was employed for planning soft tissue
expansion (STE) and transplantation of a vascularised scapular flap in
hemifacial microsomia. This technique facilitated the identification of extent
and degree of tissue deficiency, selection of the appropriate tissue expander,
monitoring volumetric changes during STE and estimation of the free flap
dimensions.
Study 6: 3?D facial photographs and CBCT scans of 29 subjects were merged
to create virtual craniofacial models with natural surface texture. Accuracy
was assessed with 3?D colour maps and Root Mean Square (RMS) error. The
CBCT and 3?D photographic data were integrated while minimizing average
RMS error to 0.441mm. These virtual composite craniofacial models
permitted concurrent 3?D assessment of bone and soft tissue. / published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/210236 |
| Date | January 2011 |
| Creators | Jayaratne, Yasas Shri Nalaka |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Rights | Creative Commons: Attribution 3.0 Hong Kong License, The author retains all proprietary rights, (such as patent rights) and the right to use in future works. |
| Relation | HKU Theses Online (HKUTO) |
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