Innovation in prediction planning for anterior open bite correction

This study applies recent advances in 3D virtual imaging for application in the prediction planning of dentofacial deformities. Stereo-photogrammetry has been used to create virtual and physical models, which are creatively combined in planning the surgical correction of anterior open bite. The application of these novel methods is demonstrated through the surgical correction of a case

PRELIMINARY FINDINGS OF A POTENZIATED PIEZOSURGERGICAL DEVICE AT THE RABBIT SKULL

The number of available ultrasonic osteotomes has remarkably increased. In vitro and in vivo studies have revealed differences between conventional osteotomes, such as rotating or sawing devices, and ultrasound-supported osteotomes (Piezosurgery®) regarding the micromorphology and roughness values of osteotomized bone surfaces. Objective: the present study compares the micro-morphologies and roughness values of osteotomized bone surfaces after the application of rotating and sawing devices, Piezosurgery Medical® and Piezosurgery Medical New Generation Powerful Handpiece. Methods: Fresh, standard-sized bony samples were taken from a rabbit skull using the following osteotomes: rotating and sawing devices, Piezosurgery Medical® and a Piezosurgery Medical New Generation Powerful Handpiece. The required duration of time for each osteotomy was recorded. Micromorphologies and roughness values to characterize the bone surfaces following the different osteotomy methods were described. The prepared surfaces were examined via light microscopy, environmental surface electron microscopy (ESEM), transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM) and atomic force microscopy. The selective cutting of mineralized tissues while preserving adjacent soft tissue (dura mater and nervous tissue) was studied. Bone necrosis of the osteotomy sites and the vitality of the osteocytes near the sectional plane were investigated, as well as the proportion of apoptosis or cell degeneration. Results and Conclusions: The potential positive effects on bone healing and reossification associated with different devices were evaluated and the comparative analysis among the different devices used was performed, in order to determine the best osteotomes to be employed during cranio-facial surgery

3D soft-tissue, 2D hard-tissue and psychosocial chantes following orthognathic surgery

A 3D imaging system (C3D®), based on the principles of stereophotogrammetry, has been developed for use in the assessment of facial changes following orthognathic surgery. Patients’ perception of their facial appearance before and after orthognathic surgery has been evaluated using standardised questionnaires, but few studies have tried to link this perception with the underlying two-dimensional cephalometric data. Comparisons between patients’ subjective opinions and 3D objective assessment of facial morphology have not been performed. Aims: (1) To test the reliability of the 3D imaging system; (2) to determine the effect of orthognathic surgery on the 3D soft-tissue morphology; (3) to assess skeletal changes following orthognathic surgery; (4) to evaluate soft-tissue to hard-tissue displacement ratios; (5) to ascertain the impact of orthognathic surgery on patients’ perception of their facial appearance and their psychosocial characteristics, (6) to explore the dentofacial deformity, sex and age on the psychosocial characteristics; (7) to evaluate the extent of compatibility between the cephalometric and the three-dimensional measurements and (8) to determine if the magnitude of facial soft-tissue changes affects the perception of facial changes at six months following surgery. Results and Conclusions: C3D imaging system was proved to be accurate with high reproducibility. The reproducibility of landmark identification on 3D models was high for 24 out of the 34 anthropometric landmarks (SD£0.5 mm). One volumetric algorithm in the Facial Analysis Tool had an acceptable accuracy for the assessment of volumetric changes following orthognathic surgery (mean error=0.314 cm3). The error of cephalometric method was low and the simulation of mandibular closure proved to be reproducible. 2D soft-tissue measurements were compatible with 3D measurements in terms of distances, but angular measurements showed significant differences (p<0.05)

Three dimensional study to quantify the relationship between facial hard and soft tissue movement as a result of orthognathic surgery

Introduction Prediction of soft tissue changes following orthognathic surgery has been frequently attempted in the past decades. It has gradually progressed from the classic “cut and paste” of photographs to the computer assisted 2D surgical prediction planning; and finally, comprehensive 3D surgical planning was introduced to help surgeons and patients to decide on the magnitude and direction of surgical movements as well as the type of surgery to be considered for the correction of facial dysmorphology. A wealth of experience was gained and numerous published literature is available which has augmented the knowledge of facial soft tissue behaviour and helped to improve the ability to closely simulate facial changes following orthognathic surgery. This was particularly noticed following the introduction of the three dimensional imaging into the medical research and clinical applications. Several approaches have been considered to mathematically predict soft tissue changes in three dimensions, following orthognathic surgery. The most common are the Finite element model and Mass tensor Model. These were developed into software packages which are currently used in clinical practice. In general, these methods produce an acceptable level of prediction accuracy of soft tissue changes following orthognathic surgery. Studies, however, have shown a limited prediction accuracy at specific regions of the face, in particular the areas around the lips. Aims The aim of this project is to conduct a comprehensive assessment of hard and soft tissue changes following orthognathic surgery and introduce a new method for prediction of facial soft tissue changes.   Methodology The study was carried out on the pre- and post-operative CBCT images of 100 patients who received their orthognathic surgery treatment at Glasgow dental hospital and school, Glasgow, UK. Three groups of patients were included in the analysis; patients who underwent Le Fort I maxillary advancement surgery; bilateral sagittal split mandibular advancement surgery or bimaxillary advancement surgery. A generic facial mesh was used to standardise the information obtained from individual patient’s facial image and Principal component analysis (PCA) was applied to interpolate the correlations between the skeletal surgical displacement and the resultant soft tissue changes. The identified relationship between hard tissue and soft tissue was then applied on a new set of preoperative 3D facial images and the predicted results were compared to the actual surgical changes measured from their post-operative 3D facial images. A set of validation studies was conducted. To include: • Comparison between voxel based registration and surface registration to analyse changes following orthognathic surgery. The results showed there was no statistically significant difference between the two methods. Voxel based registration, however, showed more reliability as it preserved the link between the soft tissue and skeletal structures of the face during the image registration process. Accordingly, voxel based registration was the method of choice for superimposition of the pre- and post-operative images. The result of this study was published in a refereed journal. • Direct DICOM slice landmarking; a novel technique to quantify the direction and magnitude of skeletal surgical movements. This method represents a new approach to quantify maxillary and mandibular surgical displacement in three dimensions. The technique includes measuring the distance of corresponding landmarks digitized directly on DICOM image slices in relation to three dimensional reference planes. The accuracy of the measurements was assessed against a set of “gold standard” measurements extracted from simulated model surgery. The results confirmed the accuracy of the method within 0.34mm. Therefore, the method was applied in this study. The results of this validation were published in a peer refereed journal. • The use of a generic mesh to assess soft tissue changes using stereophotogrammetry. The generic facial mesh played a major role in the soft tissue dense correspondence analysis. The conformed generic mesh represented the geometrical information of the individual’s facial mesh on which it was conformed (elastically deformed). Therefore, the accuracy of generic mesh conformation is essential to guarantee an accurate replica of the individual facial characteristics. The results showed an acceptable overall mean error of the conformation of generic mesh 1 mm. The results of this study were accepted for publication in peer refereed scientific journal. Skeletal tissue analysis was performed using the validated “Direct DICOM slices landmarking method” while soft tissue analysis was performed using Dense correspondence analysis. The analysis of soft tissue was novel and produced a comprehensive description of facial changes in response to orthognathic surgery. The results were accepted for publication in a refereed scientific Journal. The main soft tissue changes associated with Le Fort I were advancement at the midface region combined with widening of the paranasal, upper lip and nostrils. Minor changes were noticed at the tip of the nose and oral commissures. The main soft tissue changes associated with mandibular advancement surgery were advancement and downward displacement of the chin and lower lip regions, limited widening of the lower lip and slight reversion of the lower lip vermilion combined with minimal backward displacement of the upper lip were recorded. Minimal changes were observed on the oral commissures. The main soft tissue changes associated with bimaxillary advancement surgery were generalized advancement of the middle and lower thirds of the face combined with widening of the paranasal, upper lip and nostrils regions. In Le Fort I cases, the correlation between the changes of the facial soft tissue and the skeletal surgical movements was assessed using PCA. A statistical method known as ’Leave one out cross validation’ was applied on the 30 cases which had Le Fort I osteotomy surgical procedure to effectively utilize the data for the prediction algorithm. The prediction accuracy of soft tissue changes showed a mean error ranging between (0.0006mm±0.582) at the nose region to (-0.0316mm±2.1996) at the various facial regions

Spatially-dense 3D facial asymmetry assessment in both typical and disordered growth

Mild facial asymmetries are common in typical growth patterns. Therefore, detection of disordered facial growth patterns in individuals characterized by asymmetries is preferably accomplished by reference to the typical variation found in the general population rather than to some ideal of perfect symmetry, which rarely exists. This presents a challenge in developing an asymmetry assessment tool that is applicable, without modification, to detect both mild and severe facial asymmetries. In this paper we use concepts from geometric morphometrics to obtain robust and spatially-dense asymmetry assessments using a superimposition protocol for comparison of a face with its mirror image. Spatially-dense localization of asymmetries was achieved using an anthropometric mask consisting of uniformly sampled quasi-landmarks that were automatically indicated on 3D facial images. Robustness, in the sense of an unbiased analysis under increasing asymmetry, was ensured by an adaptive, robust, least-squares superimposition. The degree of overall asymmetry in an individual was scored using a root-mean-squared-error, and the proportion was scored using a novel relative significant asymmetry percentage. This protocol was applied to a database of 3D facial images from 359 young healthy individuals and three individuals with disordered facial growth. Typical asymmetry statistics were derived and were mainly located on, but not limited to, the lower two-thirds of the face in males and females. The asymmetry in males was more extensive and of a greater magnitude than in females. This protocol and proposed scoring of asymmetry with accompanying reference statistics will be useful for the detection and quantification of facial asymmetry in future studies

The 3D maxillary orientation device (3DMOD) - a novel device for measuring post-surgical three-dimensional maxillary changes

Objectives: To assess the validity and reproducibility of the 3D Maxillary Orientation Device to assess the simulated post-surgical 3D changes of the maxilla using an in vivo model. Methodology: A 3D maxillary orientation device (3DMOD) was developed based on a modified Fox’s occlusal plane guide. Equidistant points were marked on the extra-oral arms of the 3DMOD creating nine landmarks for data analysis. Reproducibility of 3DMOD insertion and removal was assessed by placing the 3DMOD onto the maxillary dentition of five volunteers and taking extra-oral facial 3D stereophotogrammetry images (Di4D SNAP system) at one-week intervals (T1 and T2). To measure the post-surgical changes of the maxilla, the 3DMOD was secured to the maxillary dentition of an in vivo skull model. The position of the 3DMOD changed a known amount using modified Lego® blocks attached to the 3DMOD, to simulate various maxillary movements. Baseline images of the 3DMOD were taken with 0mm displacement and again with the 3DMOD advanced and vertically impacted by 3mm, 6mm and 9mm. Additionally a left and right cant and 3mm advancement with posterior differential impaction were simulated. Images were re-taken one-week later (T1 and T2). Following baseline and simulated maxillary movement, the changes of the landmarks in the x, y and z direction were determined using Di3D viewing software for data analysis. Results: For 3DMOD insertion on replacement the mean differences in the x, y and z direction were all significantly less than 0.5mm. The difference between the simulated maxillary movements (advancement and impaction) and the 3DMOD derived measurements were all statistically significantly 0.5mm or less. The device was reproducible, none of the mean differences between T1 and T2 were significantly greater than 0.5mm (95% CI range 0.0mm and 1.1mm). Conclusion: The 3DMOD, coupled with stereophotogrammetry, is an acceptable method to measure 3D simulated maxillary movements. Further studies are needed to assess the validity and reproducibly of using the 3DMOD in patients undergoing maxillary osteotomies

Determining normal and abnormal lip shapes during movement for use as a surgical outcome measure

Craniofacial assessment for diagnosis, treatment planning and outcome has traditionally relied on imaging techniques that provide a static image of the facial structure. Objective measures of facial movement are however becoming increasingly important for clinical interventions where surgical repositioning of facial structures can influence soft tissue mobility. These applications include the management of patients with cleft lip, facial nerve palsy and orthognathic surgery. Although technological advances in medical imaging have now enabled three-dimensional (3D) motion scanners to become commercially available their clinical application to date has been limited. Therefore, the aim of this study is to determine normal and abnormal lip shapes during movement for use as a clinical outcome measure using such a scanner. Lip movements were captured from an average population using a 3D motion scanner. Consideration was given to the type of facial movement captured (i.e. verbal or non-verbal) and also the method of feature extraction (i.e. manual or semi-automatic landmarking). Statistical models of appearance (Active Shape Models) were used to convert the video motion sequences into linear data and identify reproducible facial movements via pattern recognition. Average templates of lip movement were created based on the most reproducible lip movements using Geometric Morphometrics (GMM) incorporating Generalised Procrustes Analysis (GPA) and Principal Component Analysis (PCA). Finally lip movement data from a patient group undergoing orthognathic surgery was incorporated into the model and Discriminant Analysis (DA) employed in an attempt to statistically distinguish abnormal lip movement. The results showed that manual landmarking was the preferred method of feature extraction. Verbal facial gestures (i.e. words) were significantly more reproducible/repeatable over time when compared to non-verbal gestures (i.e. facial expressions). It was possible to create average templates of lip movement from the control group, which acted as an outcome measure, and from which abnormalities in movement could be discriminated pre-surgery. These abnormalities were found to normalise post-surgery. The concepts of this study form the basis of analysing facial movement in the clinical context. The methods are transferrable to other patient groups. Specifically, patients undergoing orthognathic surgery have differences in lip shape/movement when compared to an average population. Correcting the position of the basal bones in this group of patients appears to normalise lip mobility