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Parry Romberg syndrome is a rare disorder described as facial asymmetry. It is of unknown aetiology, but trophic malfunction of the sympathetic system has been proposed as a cause. The syndrome results in specific soft tissue, skeletal, dental and skin changes in the affected side of the face, with or without neurological signs and symptoms.The case we present here is a 23 year old female with Parry Romberg syndrome. Clinically she has left sided facial atrophy affecting both the soft tissue and the bone structure. The patient received pharmacological and surgical treatments to slow the progression and correct the contour of her face. She complained lately from autophony, which is the unusual loud hearing of a person's own voice and own breathing. A diagnostic nasoendoscopy showed atrophied nasal mucosa and Eustachian tube dysfunction which has never been described before to be secondary to parry Romberg syndrome.

A bone plate is required to restore the load-bearing capacity of the mandible following a segmental resection. A good understanding of the underlying principles is crucial for developing a reliable reconstruction. A finite element analysis (FEA) technique has been developed to study the biomechanics of the clinical scenarios managed after surgical resection of a tumour or severe trauma to assist in choosing the optimal hardware elements. A computer aided design (CAD) model of an edentulous human mandible was created. Then 4 common segmental defects were simulated. A single reconstruction plate was designed to span the defects. The hardware variations studied were: monocortical or bicortical screw fixation and non-locking or locking plate design. A standardized load was applied to mimic the human bite. The von Mises stress and strain, spatial changes at the screw-bone interfaces were analysed. In general, the locking plate and monocortical screw fixation systems were most effective. Non-locking plating systems produced larger screw "pull-out" displacements, especially at the hemimandible (up to 5% strain). Three screws on either side of the defect were adequate for all scenarios except extensive unilateral defects when additional screws and an increased screw diameter are recommended. The simplification of screw geometry may underestimate stress levels and factors such as poor adaptation of the plate or reduced bone quality are likely to be indications for bicortical locking screw fixation. The current model provides a good basis for understanding the complex biomechanics and developing future refinements in plate or scaffold design.

Objective This study aimed to explore whether cone beam computed tomography (CBCT) and multislice computed tomography (MSCT) can be used to quantify tissue density and to determine if the Hounsfield unit scale is applicable. Study Design A clinical MSCT scanner and effective energy adjusted photon beam attenuation references were used to compare the gray scale of CBCT images of the mandible region. A phantom was scanned using axial cadaver slices and 4 different homogeneous reference objects. The consistency of the references' gray values and 12 linear profile lines from both scanner data sets were compared. Results The gray values of the 2 scans showed strong correlation with quantified position-dependent differences as an outcome of the validation process. Conclusions The introduced internal, in-scan validation is able to estimate and has a potential to compensate for the differences between MSCT and CBCT protocols. This validation serves as a guide in situations where the users can expect deviations.

a b s t r a c t Introduction: The strengthening effect of prophylactic internal fixation (PIF) with a bone plate at the radial osteocutaneous flap donor site has previously been demonstrated using the sheep tibia model of the human radius. This study investigated whether a finite element (FE) model could accurately represent this biomechanical model and whether stress or strain based failure criteria are most appropriate. Methods: An FE model of an osteotomised sheep tibia bone was strengthened using 4 types of plates with unilocking or bicortical screw fixation. Torsion and 4-point bending simulations were performed. The maximum von Mises stresses and strain failure criteria were studied. Results: The strengthening effects when applying stress failure criteria (factor 1.76-4.57 bending and 1.33-1.80 torsion) were comparable to the sheep biomechanical model (factor 1.73-2.43 bending and 1.54-2.63 torsion). The strongest construct was the straight 3.5 mm stainless steel unilocking plate. Applying strain criteria the strongest construct was the straight 3.5 mm stainless DCP plate with bicortical screw fixation. Conclusions: The FE model was validated by comparison with the sheep tibia model. The complex biome- chanics at the bone-screw interface require further investigation. This FE modelling technique may be applied to a model of the human radius and other sites.

Objective This study analyzed detailed models of human mandibles at 3 different stages of life with simulation of supra normal chewing forces at static conditions. Methods and materials Finite element analysis (FEA) was used to generate models from cone-beam computerized tomograms (CBCT) of 3 patients aged 12, 20, and 67 years, using numerically calculated material parameters. Estimated chewing forces were then applied to the simulations. Results The results reflect higher elasticity in younger models in all regions of the mandible. The experimental models show that physiologic load stress and strain distributional changes of the mandible vary according to age. Conclusion The CBCT-based model generation used in this study provided high-quality model definition of the 3 individual patients of different ages. FEA has great potential to predict bone responses to paradigms of mechanical activity. Future applications of FEA will include surgical planning, surgical hardware testing, and the design of scaffolds and tissue-engineered constructs.

The number of patients diagnosed with cancer is reaching a scarily high number worldwide. This is no different in the area of mandible cancer. Unfortunately Hungary is quite high up in the ladder. The registered known number of patients with mandible cancer and the associated number of death occurrences are also showing signifi cant data in the country. However it is easy to diagnose, alcohol consumption and smoking or just bad oral hygiene really pushes the statistics. Inside the oral cavity, in case of mandible cancer and late diagnosis the only viable solution is the bone resection. To determine the extent of the cancer and to carefully plan the surgery procedure or in case of models which were created for biomechanical examinations, the medical science more and more often uses the image based processes and tools. Next to the realistically built models a more punctual mechanical parameter simulation becomes possible. It is highly important that the necessary information is extracted from the patients with the least stress. With the shortest time and smallest radiation the image must be made in a way that the scan can be well evaluated and it is usable. Within the current examination in the medical fi eld of imaging methods a gold standard MSCT and a specifi cally in the head-neck region used CBCT methods will be compared specifi cally from biomechanical modelling point of view. During the comparison the gray value was examined by the use of a cadaver head. The results show that the gray values provided by CBCT differs slightly from the MSCT values that is considered as reference. The more extent absolute error occurs with less frequency. Based on these facts the CBCT can be used for the density based material comparison for biomechanical models with less radiation dose. DOI: 10.17489/biohun/2014/2/04

Objective With a double exposure overlapping cone beam computed tomography (CBCT) scan technique, using CBCT acquisition radiation dose, the objective was to obtain apparent density similar to that of multidetector computed tomography (MDCT). Study Design Factory quality-assurance phantom and water phantom were used for the evaluation of apparent density fidelity of iCAT scans in different modes. Each scan's apparent density was analyzed for identical regions using ImageJ, version 1.42q. Results The iCAT Classic extended height acquisition with 4-cm central overlap and reconstruction of 2 groups of 300 projections per rotation for the water and quality-assurance CBCT phantoms resulted in improved apparent density fidelity. This apparent density accuracy was superior to that of iCAT scan at high resolution (600 projections during 1 rotation). Conclusions Using double exposure overlapping CBCT scans allows the analysis quality to be comparable with that of MDCT.

Osteotomy cuts are typically made using a saw, and the meeting point acts as a focus for the concentration of stress and failure. We have studied the impact of different designs of osteotomy cut. Cadaver sheep tibias were scanned by computed tomography (CT) and transformed into a computer-aided design (CAD) model. A standard marginal resection defect was created and then modified, and a finite element analysis made. The relative stress concentrations at the intersection of osteotomy cuts were recorded using principal stresses S1, S3, and von Mises stress, von Mises under both 4-point bending and torsion testing. The osteotomy designs studied were: right-angled and bevelled osteotomy end cuts, overcutting, and a stop drill hole. Peak stress values for 4-point bending and torsion were 24-30% greater at the right-angled osteotomy than the bevelled end cut. Overcutting dramatically increased peak stress values caused by bending and torsion by 48% and 71%, respectively. Substantially lower concentrations of stress were noted with a stop hole using both a 90° (bending 38% and torsion 56%), and a tangential (bending 58% and torsion 60%) cut. A bevelled osteotomy has substantially lower concentrations of stress than a right-angled osteotomy. It is important to avoid creating an overcut as this causes an appreciable increase in the concentration of stress, while a stop drill hole substantially reduces the stress. The creation of a stop hole and the use of judicious bevelling techniques are modifications in the design of an osteotomy that are readily applicable to surgical practice.

Introduction This article reports experience relating to the measurement of orbital volume by means of cone beam computed tomography (CBCT) and Cranioviewer program software in patients who have undergone enucleation and orbital implantation. Patients and Methods CBCT scans were made in 30 cases, 10 of which were later excluded because of various technical problems. The study group therefore consisted of 20 patients (8 men and 12 women). The longest follow-up time was 7 years, and the shortest was 1 year. In all 20 cases, the orbital volume was measured with Cranioviewer orbital program software. Slices were made in the ventrodorsal direction at 4.8 mm intervals in the frontal plane, in both bony orbits (both that containing the orbital implant and the healthy one). Similar measurements were made in 20 patients with various dental problems. CBCT scans were recorded for the facial region of the skull, containing the orbital region. The Cranioviewer program can colour the area of the slices red, and it automatically measures the area in mm. Results In 5 of the 20 cases, the first 4 or all 5 slices revealed that the volume of the operated orbit was significantly smaller than that of the healthy orbit, in 12 cases only from 1 to 3 of the slices indicated such a significant difference, and in 3 cases no differences were observed between the orbits. In the control group of patients with various dental problems, there was no significant difference between the two healthy orbits. The accuracy of the volume measurements was assessed statistically by means of the paired samples t-test. Summary To date, no appropriate method is avaliable for exact measurement of the bony orbital volume, which would be of particular importance in orbital injury reconstruction. However, the use of CBCT scans and Cranioviewer orbital program software appears to offer a reliable method for the measurement of changes in orbital volume.

Substantial volume defects of the head and neck oftenrequire customized solutions to improve quality of life likefree flap transfers.Titanium and its alloys are versatile materialsproviding the feature of osteointegration. The conditionswhich facilitate the deposition of lamellar bone are underextensive research. Our project aimed to determine whethertitanium can function as a scaffold - unlike simple plates - toenhance bone regeneration for load bearing structures. Thereaction of stem cells to scaffolds with varying stiffness willbe presented.Additive manufacturing were used to produce a variety ofscaffolds to optimize titanium structures. Electric beam melting(EBM) manufacturing allowed us to optimize the elasticmodulus (Young) of the titanium to match with cadaveric bone from a previous project. Multidirectional mechanicaltests were performed on the various designs of titanium cellstructures (n=80). The predictability and quality of manufacturingwas assessed statistically and also with scanningelectron microscope (SEM).The results demonstrated structures matching the mechanicalproperties of bone and even anisotropy as our resultssuggest 3GPa elasticity. This allows the possibility to buildregenerating bone with predictable properties. In addition,predictable patterning - unlike etching and sandblasting - ofmicroscopic (nano) features found to be significant and nonhomogenous simple repetitive patterns provide better cellularresponse.The benefit that tissue engineering techniques offer isdecreased morbidity, relative independence from donor site,with a highly specific and customized shape. Titanium basedreconstruction constructs seems to offer an alternative futurefor bony reconstruction.

r e j s o d d s v i a i he cuts that are required to create a step osteotomy of the andible or a section defect are primarily in a linear plane. he point at which 2 cuts meet is a focus for the concenration of stress and the area is prone to failure. The “stop rill hole method” has been used to block the propagation f existing crack lines during aircraft maintenance1 and in ider mechanical engineering practice, but has not been ommonly applied to avoid iatrogenic fractures in surgical ractice. A stop-hole of sufficient diameter will prolong the ime to fatigue failure under cyclical loading.2 We have developed a finite element analysis technique to imulate stress levels within bone. We tested the mandible nder normal biting forces,3 long bones with plate fixation,4 nd differing designs of osteotomy end cuts5 for bending nd torsional loading. When compared with a baseline rightngled osteotomy (maximum stress level 100%), the peak tress concentration at a bevelled osteotomy was substanially lower (70–81%). It was further reduced when the orner of a right-angled osteotomy was rounded out with stop-hole, which could be entered tangentially (40–47%) Fig. 1) or at 90◦ (44–69%) (Fig. 2). In contrast, an overut oblique osteotomy (104–158%) substantially increased he stress concentration and implied a weakening effect.5 A top-hole at the corner of an osteotomy will therefore have a

Introduction – aims A reconstruction plate is conventionally used for internal fixation and load bearing across a segmental defect often created following a resection for malignancy. The aim of this study was to evaluate whether a uniform plate design is suitable for managing the more common types of segmental defects. This study may also promote a better understanding of the critical sites of a reconstructive structure and the ideal plate characteristics required to support bone regeneration whilst decreasing the likelihood of fixation failure. Materials – methods A detailed patient based edentulous mandible model was developed from CBCT/DVT scanning using standard reverse engineering techniques. A uniform reconstruction plate was modeled and utilized. The finite element analysis was used to compare the commonly used combinations of screw fixations (non-locking or locking and bicortical or monocortical). The most common symmetrical and asymmetrical segmental mandibular resections were analysed. The stress values within the plate, screws and implant/bone interface were recorded. Results The common practice of inserting a minimum of 3 screws either side of the resection was effective. In general the screws closest to the resection showed significantly higher stress levels (60–320 MPa). The inter-segmental movements with different plate strengths were studied as this can influence the potential for bone regeneration. The unilateral defect reconstruction allowed the smallest deformation while the symphyseal bone support was the highest quality. Conclusions This study has identified the most effective position, number and type of screw anchorage points for a uniform plate reinforcement of the common segmental defects. Future works will focus on the overall load bearing capacity and movements of differing types of reconstruction plate and screws to optimize and redistribute the remaining effective strength of the plate to facilitate the design of novel bone regenerative scaffolds.

The development of three-dimensional computer-aided surgical workfl ow has simplifi ed the planning of complex reconstruction cases. It can also be helpful in planning distraction osteogenesis cases. This article examines the evolving role of three-dimensional computer-aided surgical workfl ow in maxillofacial surgery.

Introduction – aims The section defect created in a bone using a saw is primarily in a linear plane. The meeting point of two cuts is a focus for stress concentration and under loading this area is prone to cracks and failure, especially if overcut. This is important for a marginal resection in a load bearing bone such as the mandible. The impact of different design factors were investigated with the aim of developing a simple surgical technique which could be combined with Prophylactic Internal Fixation (PIF) if required. Materials – methods Cadaver sheep tibia samples were scanned and transformed into high definition computer models. Standardized marginal resections evaluated the effect of right angled and sloped osteotomy cuts, different types of overcuts, and two novel design cuts to reduce the likelihood of crack formation and material failure. Four different PIF systems were tested. Numeric simulation using the Finite Element Method was applied to predict failure based on mechanical stress values. This aimed to reproduce our previous laboratory biomechanical bench testing of the sheep tibia model and validate the FEM model. Results – statistics The stress levels in the standard right angled and sloped resections were used as baselines. The overcuts substantially increased stress concentration (up to 196%). Both novel techniques (to be described) significantly reduced stress concentrations (down to 40%). The impact of different designs of PIF was also shown to offer a statistically significant improvement in strength (gained up to 2.6× in bench test and 3.71× in simulation). Conclusions – clinical relevance Avoiding an overcut has an obvious strengthening benefit. Both novel osteotomy techniques improve the stability of the osteotomised bone and are more precisely controlled than a conventional osteotomy technique. We will also illustrate this in clinical scenario.