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 cm(3) (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.     

A new method for the computer-aided evaluation of three-dimensional changes in gypsum materials.

OBJECTIVES: The quantitative evaluation of the time- or process-dependent three-dimensional stability of dental materials is a common question in dentistry. An investigation procedure has been developed based on a CAD-surface model of a prepared upper canine, as well as a high-precision physical copy (metal master die). The specific aim of this study was to test this method's reliability. Additionally, the ability of the developed procedure to determine the three-dimensional stability of resin-reinforced gypsum master casts over time was investigated. METHODS: Ten duplicate dies of improved dental stone (esthetic-rock, dentona, Germany) were manufactured, and digitized 1, 3, 7, 28 and 56 days after pouring. A three-coordinate optical measuring device was used for the data acquisition. The three-dimensional accuracy of stone dies was determined by comparing the digitized data of the stone dies made from the metal master die to its CAD-surface model (Surfacer) Version 9.0. Imageware Inc., Ann Arbor Michigan, USA). To assess the procedure, test surfaces were created from the digitized data and compared with a reference. RESULTS: The mean deviation between the digitized point cloud and the test surface was less than 3 microm. During the 56 day examination period no significant three-dimensional changes in dimensional stability were found. SIGNIFICANCE: The procedure for the quantitative three-dimensional evaluation was shown to be suitable. Best-fit registration enabled a reliable alignment of the point cloud to the CAD-surface model. Alteration of three-dimensional accuracy over 6 weeks was insignificant and without clinical relevance.     

Visualizing three-dimensional facial soft tissue changes following orthognathic surgery

Laser scanning can be used to visualize the face in three dimensions. These scans can then be processed to enable assessment of facial changes. The aim of this single-centre, prospective, longitudinal, cohort study was to investigate whether four different visualization methods correctly represented facial changes occurring as a result of orthognathic surgery. Twenty-six consecutive orthognathic patients (13 female mandibular advancement and 13 male bimaxillary Class III) were included as well as a control group of 12 non-growing adults (6 males and 6 females). Pre- and post-operative facial laser scans were superimposed and four different visualization methods applied: correspondences with sensitivity to movement, normals, radial, and closest point. A group of 10 'blinded' observers determined the surgical procedure (if any) that had been performed by applying a specific colour scale to each facial image. The sensitivities and specificities for each visualization method applied to each subject group were determined. The intraobserver repeatability was investigated using Cohen's kappa (k). The radial method was found to be superior for identifying mandibular advancement patients (sensitivity/specificity 58.5/92.4 per cent), the normals method for visualization of bimaxillary Class III cases (26.2/99.6 per cent), while the control group was best represented using the closest point (60.0/80.8 per cent). Overall, intraobserver repeatability was good (k = 0.61). A good level of repeatability was demonstrated in the separate subject groups (mandibular advancement 0.70, bimaxillary Class III 0.70, and controls 0.62). There was no significant difference in the abilities of the four visualization methods to represent facial changes. Each method allowed correct identification of different proportions of the subject groups.     

A comparison of craniofacial morphology in patients with and without facial asymmetry--a three-dimensional analysis with computed tomography

This study intended to evaluate the morphological characteristics of the cranial base and maxillomandibular structures of facial asymmetry in adult patients, so as to determine whether mandibular asymmetry is a result of primary mandibular deformity or if it is influenced by cranial base deformity. Forty-two adult patients with dentofacial deformity were placed into two groups according to the deviation of the chin: Asymmetry group (n = 24) and Non-asymmetry group (n = 18). They were compared with three-dimensional (3D) CT reformatted images using a 3D visualization and analyzing program. The differences between the two groups, the correlation between the cranial base and maxillomandibular asymmetry were evaluated statistically. The degree of cranial base asymmetry in the Asymmetry group was not statistically different from the Non-asymmetry group. The asymmetric condyle position was found to be associated with skull base characteristics. The 3D position of the condyle and cranial base, however, was not closely related with mandibular asymmetry. The results showed that the cranial measurement variables were not the dominant factors that determined the degree of facial asymmetry. It seems that the mandibular skeletal factors itself, functional or intrinsic asymmetric growth potential, compensate or aggravate the influence of cranial asymmetry during the growth period.     

Co-ordinate grids for three-dimensional facial measurements

Alternative methods for recording the shape of the facial soft tissue integument in three dimensions are discussed. The requirements for and problems associated with head positioning are indicated, and a technique is described by which head positioning errors can be overcome. The results of three-dimensional analysis of a sample of human subjects are described, with particular reference to the method of analysis and orientation planes selected. Finally, possible clinical uses for three-dimensional recording are suggested.     

三维面部影像在面部软组织不对称研究中的进展

面部美学是口腔医学关注的重点内容,而面部软组织对称性是影响面部美学的重要因素,近年来随着三维面部扫描技术及相关软件的发展,使得客观准确地评价面部软组织不对称性成为可能,相较于CBCT技术而言,该法更为便捷且无需担心辐射对患者的影响,因此在临床应用中有比较大的潜力。本文回顾了近年来利用三维面部影像分析面部不对称性的相关研究,梳理了该领域的发展方向以及具体的应用领域。     

三维面部影像在面部软组织不对称研究中的进展

面部美学是口腔医学关注的重点内容,而面部软组织对称性是影响面部美学的重要因素,近年来随着三维面部扫描技术及相关软件的发展,使得客观准确地评价面部软组织不对称性成为可能,相较于CBCT技术而言,该法更为便捷且无需担心辐射对患者的影响,因此在临床应用中有比较大的潜力。本文回顾了近年来利用三维面部影像分析面部不对称性的相关研究,梳理了该领域的发展方向以及具体的应用领域。     

Long-term changes in soft tissue height on the facial surface of dental implants

The success of osseous healing around dental implants has allowed for an increased emphasis on soft tissue healing and esthetic results. However, there is limited information profiling the long-term healing of the soft tissues following prosthesis placement. The purpose of this study was to assess the long-term changes in the position of the facial soft tissue margins following restoration of a one-stage implant system. One hundred and six one-stage ITI implants were evaluated in 39 patients. Implants were placed in maxillary and mandibular anterior regions. Clinical assessment of the soft tissues on the midfacial aspect of the implants was performed over a 2-year period, at 3 and 6 month intervals, following placement of the final restoration. A total of 63 implants were placed as multiple units in the mandible, 23 as single units in the maxilla, and 20 as multiple units in the maxilla. There were no implant failures over this time period. Overall, on the facial aspect of 61% of the 106 implants there was 1 mm or more of soft tissue recession, whereas 19% of the implants showed 1 mm or more of gain in soft tissue height. There was a significantly (P < 0.01) greater number of implants showing a gain in soft tissue levels in the mandibular implants compared with the maxillary implants. Of the 39 patients assessed, 24 showed a loss and five showed a gain of 1 mm or more of the soft tissue levels around the implants. Overall, there was a significant decrease in the mean levels of tissue height of 0.6 mm within the first 6 months, with relatively little change afterward. However, in evaluating only patients showing a loss in tissue height around one or more implants, the mean loss in tissue height was 1.6 mm after 24 months. These results suggest that the potential for significant changes in soft tissue levels after completion of restorative therapy need to be considered for implant therapy in esthetic areas.     

The relationship between the changes in three-dimensional facial morphology and mandibular movement after orthognathic surgery

PurposeThe purpose of this study was to investigate the relationship between changes in three-dimensional (3D) facial morphology and mandibular movement after orthognathic surgery. We hypothesized that facial morphology changes after orthognathic surgery exert effects on 3D mandibular movement.Materials and methodsWe conducted a prospective follow-up study of patients who had undergone orthognathic surgical procedures. Three-dimensional facial morphological values were measured from facial CT images before and three months after orthognathic surgery. Three-dimensional maximum mandibular opening (MMO) values of four points (bilateral condylions, infradentale, and pogonion) were also measured using a mandibular movement tracking and simulation system. The predictor variables were changes in morphological parameters divided into two groups (deviated side (DS) or contralateral side (CS) groups), and the outcome variables were changes in the MMO at four points.ResultsWe evaluated 21 subjects who had undergone orthognathic surgical procedures. Alterations in the TFH (total facial height), LFH (lower facial height), CS MBL (mandibular body length), and DS RL (ramus length) were negatively correlated with changes in bilateral condylar movement. The UFH, DS MBL and CS ML (mandibular length) showed correlations with infradentale movement. The CS ML, DS ML, MBL, UFH, and SNB were correlated with pogonion movement.ConclusionThe height of the face is most likely to affect post-operative mandibular movement, and is negatively correlated with movement changes in the condyles, infradentale and pogonion. The changes in CS morphological parameters are more correlated with mandibular movement changes than the DS. The changes in CS MBL and bilateral RL were negatively correlated with condylar movement changes, while the bilateral MBL and CS ML were positively correlated with changes in infradentale and pogonion.     

A mathematical model for the computation of the forces exerted by the facial orthopedic mask.

This study presents a model for the computation of the forces exerted on the chin and on the forehead by the facial orthopedic mask in skeletal Class III malocclusions. Cephalometric data as well as geometry of the mask are taken into account to simulate in quantitative terms the entire approach. A computer program has been implemented to validate the model on a group of patients. Despite the approximations about the mechanical characteristics of the appliance and of the constraints (rigid body, ideal constraints) and despite the unavoidable errors in the estimation of the geometric parameters (dimensions and angles), it is shown that the computation of the forces (in orientation and in magnitude) at the forehead and at the chin is possible. Some practical applications of the model are presented.     

A method for three-dimensional measurement by cineradiography

Summary The purpose of this study was to devise a method for three-dimensional (3-D) measurement of the craniofacial complex by means of cineradiography, and to assess the errors of this method. A perspective transformation method was applied to biplane cineradiography in combination with the correction of geometric distortion of cineradiographic images by the quadratic transformation. As an aid in determining the errors, landmarks on a dry skull surrounded by geometric reference points were imaged by both conventional and cineradiography in the two planes. Distance error dD (differences between calculated distances from reconstructed 3-D coordinates and measured distances by slide caliper) and displacement error dP (differences between reconstructed 3-D coordinates and those calculated from distances measured by slide caliper) by conventional, cineradiographic, and a combined method of the two were compared. These results indicate that the accuracy of the perspective transformation method by conventional, cineradiographic and the combined method would result in 0.3 mm, 0.4 mm, 0.7 mm respectively in space.     

Development of three-dimensional facial expression models using morphing methods for fabricating facial prostheses

Purpose

It is essential to fabricate a best-fit three-dimensional (3D) facial prosthesis model capable of facial expressions. In order for the facial prosthesis to remain in position, especially around marginal areas subject to movement, a new method of making 3D facial expression models using time-series data allowing changes in facial expression by morphing technique was developed.

Evaluation of facial soft tissue asymmetric changes in Class III patients after orthognathic surgery using three-dimensional stereophotogrammetry

The aim of this study was to investigate changes in facial soft tissue asymmetry over time after orthognathic surgery in Class III patients using three-dimensional stereophotogrammetry. The study included 101 patients with a skeletal Class III malocclusion (72 female, 29 male; age range 19–53 years, mean age 28.6 years) who underwent orthognathic surgery. The minimum follow-up was 12 months. Three-dimensional photographs were acquired using the 3dMDtrio stereophotogrammetry system, and 21 anthropometric landmark positions were evaluated at three time points: before surgery (T0), 6 months (T1) and 12 months (T2) after surgery. Facial asymmetry was assessed and classified as follows: 0–2 mm, mild; 2–5 mm, moderate;> 5 mm, severe. The average distance for whole face asymmetry differed between T0 (median 0.76 mm) and T1 (median 0.70 mm); however, there was no statistically significant difference at any time point. The chin volume asymmetry score differed significantly between T0 (median 1.11 mm) and T1 and T2 (median 1.08 mm for both; P < 0.001 and P = 0.001, respectively), but not between T1 and T2 (P = 0.061). The study findings indicate that the asymmetry of the facial soft tissues has the potential to return after 6 months, without reaching the baseline.     

A comparison of two- and three-dimensional incisor angles

Two- and three-dimensional incisor angulations are compared in 40 patients using lateral radiographs and direct dental cast measurement using the Reflex Metrograph coupled to a computer. The two-dimensional upper and lower incisor angulations to the occlusal plane were also compared by the two methods. It was found that: The two-dimensional radiographic and three-dimensional dental cast inter-incisor angulation showed a significant difference at a probability level 0.01 greater than p greater than 0.001. The two-dimensional radiographic and two-dimensional dental cast upper left and right incisor angulations to the functional occlusal plane showed a significant difference at a probability level of 0.01 greater than p greater than 0.001. The significant differences can be attributed to the measurement of the incisor crown angulation in the dental cast measurement and the incisor tip and apex assessment in the radiographic technique. The system of dental cast measurement arguably provides a more realistic and reliable assessment of incisal angles than conventional radiographic measurement techniques.     

A method for three-dimensional image reformation for quantitative cephalometric analysis

Recognition and treatment of craniofacial deformities require an understanding of complex skeletal structures in three planes of space. Traditional imaging techniques rely on biplanar radiographs which provide only two-dimensional data. The introduction of three-dimensional image display (3DIR) has provided a method of object analysis in three planes of space, obviating the need for mental reconstruction, and yielding more spatial information than was previously available. This study was undertaken to investigate the quantitative value of three-dimensional images compared with cephalometric techniques in assessing a craniofacial deformity. Metallic marker references were placed on a deformed skull. Measurements taken from cephalograms and three-dimensional images were compared with corresponding digitized and manual measurements taken from the skull. Three-dimensional image reformation provided a more accurate representation of the deformity than the cephalometric methods. Because all structural relationships are preserved in the CT data matrix, measurements are inherently accurate and reproducible. 3DIR offers dynamic advantages over cephalometric methods because data can be manipulated interactively. Further investigation is needed to study the importance of head position and to develop patient selection criteria, scan protocols, and surgical treatment planning algorithms.