Ashraf Ayoub

Current Products and Practices: Applications of 3D imaging in orthodontics: Part II

Part I of this paper describes the background, general concepts, available techniques and the clinical applications of recording external craniofacial morphology in three dimensions. Part II explores the different 3D techniques of imaging the dental arches, and their possible uses in orthodontic diagnosis and treatment.Part I of this paper describes the background, general concepts, available techniques and the clinical applications of recording external craniofacial morphology in three dimensions. Part II explores the different 3D techniques of imaging the dental arches, and their possible uses in orthodontic diagnosis and treatment.Part I of this paper describes the background, general concepts, available techniques and the clinical applications of recording external craniofacial morphology in three dimensions. Part II explores the different 3D techniques of imaging the dental arches, and their possible uses in orthodontic diagnosis and treatment.

Validation of a Vision-Based, Three-Dimensional Facial Imaging System

Objective The aim of this study was to assess the accuracy of a newly developed three-dimensional (3D) imaging system in recording facial morphology. Methods Twenty-one infants with cleft lip each had a full-face alginate impression taken at the time of primary lip repair, and a stone cast was constructed from each impression. Five anthropometric points were marked on each cast. Each cast was digitized, and the 3D co-ordinates of the five points were obtained using a co-ordinate measuring machine (CMM, Ferranti) of documented accuracy (9.53 μm). Each cast was scanned in four positions using a computerized stereophotogrammetry (C3D) system. The five points were located on the 3D images, and their 3D co-ordinates were extracted by three operators. The co-ordinate systems produced by C3D were aligned, via translation and rotation, to match the CMM co-ordinate system using partial ordinary procrustes analysis. The displacements of the adjusted C3D co-ordinates from the reference co-ordinates were then measured. Three different types of errors were identified: operator, system, and registration errors. Results Operator error was within 0.2 mm of the true co-ordinates of the landmarks. C3D was accurate within 0.4 mm. The average displacement of points over the 21 casts at four positions for the three operators was 0.79 mm (median 0.68). Conclusions The presented 3D imaging system is reliable in recording facial deformity and could be utilized in recording cleft deformities and measuring the changes following surgery

Methods of assessment of cleft-related facial deformity: A review

Objective To review the stimulus media, measurements and scoring system, raters characteristics, and facial region used in assessment of the appearance of cleft-related deformity. Methods A review of the literature was conducted using MedLine from January 1966 to June 2003. Key orthodontic journals and The Cleft Palate–Craniofacial Journal were hand searched as well. Results Most studies used a static two-dimensional means of assessment. Direct clinical assessment, three-dimensional media, or both have been used to a lesser extent. Only one study utilized all three assessment media. Three studies, however, attempted to compare the direct clinical assessment with that obtained using two-dimensional media. Most of the studies demonstrated that appearance of the cleft-related deformity could be measured by a variety of judges. The reliability and validity of the three different media as methods of assessment have received limited attention. The facial area assessed has varied from the full face, nasolabial area, or specific features of the lip or nose. Conclusions Wide variation exists in the study design related to assessment of cleft-related deformity. An internationally agreed objective method of assessment for this facial deformity is required. A three-dimensional, rather than a two-dimensional, means of assessment should be adopted.

A vision-based three-dimensional capture system for maxillofacial assessment and surgical planning

We describe a vision-based three-dimensional facial data capture system designed for the planning of maxillofacial operations. We describe the system requirements and outline the methods used to develop a complete three-dimensional facial capture system. Our approach is based upon imaging the face using two stereo-pair sets of cameras. Scale-space-based stereo-matching is then used to recover correspondences between each of the captured stereo-pairs. Photogrammetric routines based on adjustment of bundles are used off-line to calibrate the system by imaging a single object that references all cameras to the same co-ordinate frame. This calibration scheme allows us to convert stereo correspondences to world points for each pair of cameras without the need for any subsequent fusion of data. Initial results show that we are able to capture key facial landmarks to within 0.5 mm.

Current Products and Practices

Part I of this paper describes the background, general concepts, available techniques and the clinical applications of recording external craniofacial morphology in three dimensions. Part II explores the different 3D techniques of imaging the dental arches, and their possible uses in orthodontic diagnosis and treatment.Part I of this paper describes the background, general concepts, available techniques and the clinical applications of recording external craniofacial morphology in three dimensions. Part II explores the different 3D techniques of imaging the dental arches, and their possible uses in orthodontic diagnosis and treatment.Part I of this paper describes the background, general concepts, available techniques and the clinical applications of recording external craniofacial morphology in three dimensions. Part II explores the different 3D techniques of imaging the dental arches, and their possible uses in orthodontic diagnosis and treatment.

How accurate is model planning for orthognathic surgery

The purpose of this study was to evaluate the accuracy of model surgery prediction after orthognathic surgery and to identify possible errors associated with the prediction process. The study included 46 patients who had undergone orthognathic surgical procedures; 22 in Group A who had had a Le Fort I osteotomy; and 24 in Group B who had had a Le Fort I osteotomy and mandibular setback surgery. The immediate postoperative and preoperative lateral cephalograms were analysed to calculate surgical changes; these were compared with those obtained from model surgery prediction and a statistical analysis was undertaken. The maxilla was more under-advanced and over-impacted anteriorly than predicted by model surgery. The amount of mandibular setback was more than that predicted by model surgery. None of the differences between prediction planning and actual surgical changes was statistically significant at p<0.05. Inaccuracy with the face bow recording, the intermediate wafer, and auto-rotation of the mandible in the supine or anaesthetized patient would appear to be the principal reasons for errors. Inaccuracies are associated with the transfer of prediction planning to model surgery planning and prediction, which should be eliminated to improve the accuracy and predictability of orthognathic surgery.

An appraisal of three methods of rating facial deformity in patients with repaired complete unilateral cleft lip and palate.

OBJECTIVES To evaluate the reliability of clinical assessment, two-dimensional color transparencies and three-dimensional imaging for evaluating the residual facial deformity in patients with repaired complete unilateral cleft lip and palate (UCLP) and compare the ratings of facial deformity made by health care professionals with those made by lay assessors. PATIENTS AND PARTICIPANTS Thirty-one randomly selected subjects aged 10 to 30 years with repaired complete UCLP. Five professionals and five laypersons evaluated each subjects residual cleft-related facial deformity using clinical assessment, two-dimensional color transparencies, and three-dimensional images. MAIN OUTCOME MEASURES The facial deformity of the full face, lip, nose, and midface were scored using a 5-point ordinal scale on two occasions with a 1-month interval. Intra- and interexaminer agreements were calculated from weighted kappa statistics. Bootstrap permutation tests were used to detect any differences in agreement. RESULTS Assessment of facial deformity showed good reproducibility across the three assessment media (kappa = 0.42 to 0.83, SE 0.08). Clinical assessment among lay assessors, however, was poor to moderate (kappa = 0.16 to 0.58, SE 0.07). For all assessors, there was no difference in the two nonclinical media relative to the standard clinical assessment for assessments of the full face (p =.377). For assessments of the lip or nose, transparency scores were in greater agreement with the clinical scores than were the three-dimensional assessment scores (p =.017 and.011, respectively). For rating the midface, the three-dimensional scores were in greater agreement with the clinical scores than were the color transparencies scores (p =.047). CONCLUSIONS In comparison with lay assessors, clinical assessment among professionals was more reproducible. This was not so for nonclinical media. The equivalence of using the color transparencies and three-dimensional media relative to the clinical assessment depends on the region of the face being considered.

Are Facial Expressions Reproducible

OBJECTIVES To determine the extent of reproducibility of five facial expressions. DESIGN Thirty healthy Caucasian volunteers (15 males, 15 females) aged 21 to 30 years had 20 landmarks highlighted on the face with a fine eyeliner pencil. Subjects were asked to perform a sequence of five facial expressions that were captured by a three-dimensional camera system. Each expression was repeated after 15 minutes to investigate intrasession expression reproducibility. To investigate intersession expression reproducibility, each subject returned 2 weeks after the first session. A single operator identified 3-dimensional coordinate values of each landmark. A partial ordinary procrustes analysis was used to adjust for differences in head posture between similar expressions. Statistical analysis was undertaken using analysis of variance (linear mixed effects model). RESULTS Intrasession expression reproducibility was least between cheek puffs (1.12 mm) and greatest between rest positions (0.74 mm). The reproducibility of individual landmarks was expression specific. Except for the lip purse, the reproducibility of facial expressions was not statistically different within each of the two sessions. Rest position was most reproducible, followed by lip purse, maximal smile, natural smile, and cheek puff. Subjects did not perform expressions with the same degree of symmetry on each occasion. Female subjects demonstrated significantly better reproducibility with regard to the maximal smile than males (p =.036). CONCLUSIONS Under standardized conditions, intrasession expression reproducibility was high. Variation in expression reproducibility between sessions was minimal. The extent of reproducibility is expression specific. Differences in expression reproducibility exist between males and females.

A New Three-Dimensional Method of Assessing Facial Volumetric Changes After Orthognathic Treatment

Objective To validate a new method of facial volumetric assessment that is dependent on the use of stereophotogrammetric models and a software-based Facial Analysis Tool. Design The method was validated in vitro with three-dimensional (3D) models of a lifelike plastic female dummy head and in vivo with a male-subject head. Methods Thirty facial silicone explants were added in the nasal and perioral regions of each head, and their volumes were obtained by three different algorithms. These were compared with the actual values obtained by a “water displacement” method. Results The least mean error was found with the “tetrahedron formation” method followed by the “projection” method and the “back-plane construction” method. The error with the tetrahedron formation method was 0.071 cm3 (95% confidence interval [CI]: −0.074 to 0.2161 cm3) with the in vitro models and 0.314 cm3 (95% CI: −0.080 to 0.708 cm3) with the in vivo models. The increased volumetric assessment error observed in vivo was attributed to the registration procedure and possible changes in facial expression. Conclusions These results encourage the use of this method in the 3D assessment of orthognathic surgical outcome, provided a standardized facial expression is used for image acquisition.

Facial characterization of infants with cleft lip and palate using a three-dimensional capture technique.

Objective To characterize the soft tissue features of infants with unilateral cleft lip (UCL) and unilateral complete cleft lip and palate (UCLP) prior to primary surgery and compare with noncleft controls. Design Prospective controlled capture of the facial morphology of infants using a noninvasive three-dimensional stereophotogrammetry method. Participants 23 children with presurgical cleft: 11 UCL (M = 6, F = 5); 12 UCLP (M = 9, F = 3), and 21 noncleft controls (M = 7, F = 14) were imaged at approximately 3 months of age (range 10 to 16 weeks). Main Outcome Measure Accurate, repeatable quantification of facial soft tissues in infants with clefts prior to surgery. Results Significant differences (p < .05) were found between the UCLP group and UCL and control groups in anatomical and soft nose width, cleft-side alar wing length, and nasal tip horizontal displacement. Both cleft groups were significantly different from controls and from each other in cleft-side nostril dimensions, alar wing angulation, columella angle, and alar base to corner of mouth dimension; alar base width; and soft tissue defect in nose and the lip and philtrum length bordering the cleft. Significant differences between clefts and controls were identified in the nostril and philtrum on the noncleft side. Conclusions The use of children with UCL as controls for UCLP studies is inappropriate. This technique overcame the limitations of direct measurement of infant faces to aid the surgeon in the planning and subsequent re-evaluation of surgical rationale.