Three-dimensional volumetric changes in the upper airway after maxillomandibular advancement in obstructive sleep apnoea patients and the impact on quality of life.

Obstructive sleep apnoea (OSA) is a sleep-related breathing disorder, characterized by repetitive airway obstructions, causing disruptive snoring and daytime sleepiness. Maxillomandibular advancement (MMA), which enlarges the upper airway, is a therapeutic surgical approach. However, no study has performed an upper airway sub-region analysis using validated three-dimensional (3D) anatomical and technical limits on cone beam computed tomography (CBCT). Hence, this prospective, observational trial was performed to evaluate 3D volumetric changes in the upper airway according to validated 3D cephalometric landmarks, before and after MMA, for all patients with a polysomnography diagnosis of OSA (apnoea-hypopnoea index (AHI) ≥5). The secondary objective was to evaluate the impact of MMA on the AHI and in a subjective manner with the Epworth Sleepiness Scale (ESS) and OSA questionnaire. Eleven consecutive OSA patients were included. A significant volume increase in the oropharynx (P=0.002) and hypopharynx (P=0.02) was observed, in contrast to a non-significant volume reduction in the nasopharynx (P >0.05). The median AHI (P=0.03) and ESS score (P=0.004) decreased significantly as a result of surgery. In conclusion, MMA significantly enlarges the airway volume of the oropharynx and hypopharynx and is associated with improved quality of life.

Virtual occlusion in planning orthognathic surgical procedures.

Accurate preoperative planning is mandatory for orthognathic surgery. One of the most important aims of this planning process is obtaining good postoperative dental occlusion. Recently, 3D image-based planning systems have been introduced that enable a surgeon to define different osteotomy planes preoperatively and to assess the result of moving different bone fragments in a 3D virtual environment, even for soft tissue simulation of the face. Although the use of these systems is becoming more accepted in orthognathic surgery, few solutions have been proposed for determining optimal occlusion in the 3D planning process. In this study, a 3D virtual occlusion tool is presented that calculates a realistic interaction between upper and lower dentitions. It enables the surgeon to obtain an optimal and physically possible occlusion easily. A validation study, including 11 patient data sets, demonstrates that the differences between manually and virtually defined occlusions are small, therefore the presented system can be used in clinical practice.

The accuracy of matching three-dimensional photographs with skin surfaces derived from cone-beam computed tomography.

The state-of-the-art diagnostic tools in oral and maxillofacial surgery and preoperative orthodontic treatment are mainly two-dimensional, and consequently reveal limitations in describing the three-dimensional (3D) structures of a patient's face. New 3D imaging techniques, such as 3D stereophotogrammetry (3D photograph) and cone-beam computed tomography (CBCT), have been introduced. Image fusion, i.e. registration of a 3D photograph upon a CBCT, results in an accurate and photorealistic digital 3D data set of a patient's face. The purpose of this study was to determine the accuracy of three different matching procedures. For 15 individuals the textured skin surface (3D photograph) and untextured skin surface (CBCT) were matched by two observers using three different methods to determine the accuracy of registration. The registration error was computed as the difference (mm) between all points of both surfaces. The registration errors were relatively large at the lateral neck, mouth and around the eyes. After exclusion of artefact regions from the matching process, 90% of the error was within+/-1.5 mm. The remaining error was probably caused by differences in head positioning, different facial expressions and artefacts during image acquisition. In conclusion, the 3D data set provides an accurate and photorealistic digital 3D representation of a patient's face.

Predicting soft tissue deformations for a maxillofacial surgery planning system: from computational strategies to a complete clinical validation.

In the field of maxillofacial surgery, there is a huge demand from surgeons to be able to pre-operatively predict the new facial outlook after surgery. Besides the big interest for the surgeon during the planning, it is also an essential tool to improve the communication between the surgeon and his patient. In this work, we compare the usage of four different computational strategies to predict this new facial outlook. These four strategies are: a linear Finite Element Model (FEM), a non-linear Finite Element Model (NFEM), a Mass Spring Model (MSM) and a novel Mass Tensor Model (MTM). For true validation of these four models we acquired a data set of 10 patients who underwent maxillofacial surgery, including pre-operative and post-operative CT data. For all patient data we compared in a quantitative validation the predicted facial outlook, obtained with one of the four computational models, with post-operative image data. During this quantitative validation distance measurements between corresponding points of the predicted and the actual post-operative facial skin surface, are quantified and visualised in 3D. Our results show that the MTM and linear FEM predictions achieve the highest accuracy. For these models the average median distance measures only 0.60 mm and even the average 90% percentile stays below 1.5 mm. Furthermore, the MTM turned out to be the fastest model, with an average simulation time of only 10 s. Besides this quantitative validation, a qualitative validation study was carried out by eight maxillofacial surgeons, who scored the visualised predicted facial appearance by means of pre-defined statements. This study confirmed the positive results of the quantitative study, so we can conclude that fast and accurate predictions of the post-operative facial outcome are possible. Therefore, the usage of a maxillofacial soft tissue prediction system is relevant and suitable for daily clinical practice.

[Dentomaxillary and -facial problems in cleidocranial dysplasia]. / Dentomaxillaire en -faciale problemen bij cleidocraniale dysplasie.

A 14-year old boy with cleidocranial dysplasia was referred because of an almost complete presence of the deciduous dentition. Diagnostics by means of a panoramic radiograph, lateral headfilm, CT scan and 3D computer images of the dentomaxillary complex showed 7 supernumerary permanent teeth: 13', 11', 21', 23', 28', 35' and 45'. A combined orthodontic-surgical treatment was started. The supernumary teeth were removed surgically and the impacted teeth are exposed. The closed eruption technique was used to extrude these teeth orthodontically.

Large-scale in-vivo Caucasian facial soft tissue thickness database for craniofacial reconstruction.

A large-scale study of facial soft tissue depths of Caucasian adults was conducted. Over a 2-years period, 967 Caucasian subjects of both sexes, varying age and varying body mass index (BMI) were studied. A user-friendly and mobile ultrasound-based system was used to measure, in about 20min per subject, the soft tissue thickness at 52 facial landmarks including most of the landmarks used in previous studies. This system was previously validated on repeatability and accuracy [S. De Greef, P. Claes, W. Mollemans, M. Loubele, D. Vandermeulen, P. Suetens, G. Willems, Semi-automated ultrasound facial soft tissue depth registration: method and validation. J. Forensic Sci. 50 (2005)]. The data of 510 women and 457 men were analyzed in order to update facial soft tissue depth charts of the contemporary Caucasian adult. Tables with the average thickness values for each landmark as well as the standard deviation and range, tabulated according to gender, age and BMI are reported. In addition, for each landmark and for both sexes separately, a multiple linear regression of thickness versus age and BMI is calculated. The lateral asymmetry of the face was analysed on an initial subset of 588 subjects showing negligible differences and thus warranting the unilateral measurements of the remaining subjects. The new dataset was statistically compared to three datasets for the Caucasian adults: the traditional datasets of Rhine and Moore [J.S. Rhine, C.E. Moore, Tables of facial tissue thickness of American Caucasoids in forensic anthropology. Maxwell Museum Technical series 1 (1984)] and Helmer [R. Helmer, Schädelidentifizierung durch elektronische bildmischung, Kriminalistik Verlag GmbH, Heidelberg, 1984] together with the most recent in vivo study by Manhein et al. [M.H. Manhein, G.A. Listi, R.E. Barsley, R. Musselman, N.E. Barrow, D.H. Ubelbaker, In vivo facial tissue depth measurements for children and adults. J. Forensic Sci. 45 (2000) 48-60]. The large-scale database presented in this paper offers a denser sampling of the facial soft tissue depths of a more representative subset of the actual Caucasian population over the different age and body posture subcategories. This database can be used as an updated chart for manual and computer-based craniofacial approximation and allows more refined analyses of the possible factors affecting facial soft tissue depth.