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Three-dimensional assessment of facial deformities and their surgical outcomes

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


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


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
Date January 2011
CreatorsJayaratne, Yasas Shri Nalaka
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
Source SetsHong Kong University Theses
Detected LanguageEnglish
RightsCreative 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.
RelationHKU Theses Online (HKUTO)

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