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Purpose The aim of this investigation was to generate a statistical shape model (SSM) of the midface and evaluate symmetry, gender aspects, and bone thickness. Methods About 102 computed tomography scans were analyzed to create the SSM. This included segmentation, landmark attribution, and Procrustes and principal component analysis. Afterward, symmetry and gender differences were visualized by registration and color coding. Bone thickness was calculated by measuring the distance between outer and inner surfaces. Results Symmetry was high in all models. The male model showed a more prominent forehead, nasal bones, and larger bizygomatic width. Bone thickness resembled the concept of vertical and horizontal maxillary pillars and buttresses. Conclusions SSM can be used to analyze midface morphology and help in virtual surgery planning. Calculation of bone thickness could also be a useful tool in surgical planning and biomechanics.

Background Clinical studies report on vision impairment after blunt frontal head trauma. A possible cause is damage to the optic nerve bundle within the optic canal due to microfractures of the anterior skull base leading to indirect traumatic optic neuropathy. Methods A finite element study simulating impact forces on the paramedian forehead in different grades was initiated. The set-up consisted of a high-resolution skull model with about 740 000 elements, a blunt impactor and was solved in a transient time-dependent simulation. Individual bone material parameters were calculated for each volume element to increase realism. Results Results showed stress propagation from the frontal impact towards the optic foramen and the chiasm even at low-force fist-like impacts. Higher impacts produced stress patterns corresponding to typical fracture patterns of the anterior skull base including the optic canal. Transient simulation discerned two stress peaks equalling oscillation. Conclusions It can be concluded that even comparatively low stresses and oscillation in the optic foramen may cause micro damage undiscerned by CT or MRI explaining consecutive vision loss. Higher impacts lead to typical comminuted fractures, which may affect the integrity of the optic canal. Finite element simulation can be effectively used in studying head trauma and its clinical consequences.

Introduction Polydioxanone (PDS) sheets are commonly used in the treatment of orbital wall fractures. A potential drawback of PDS is that it may be difficult to adapt to the anatomy of the orbital walls. Therefore a study was conceived to test the feasibility of preforming PDS sheets. Material and methods PDS sheet material was water-heated and preformed using a template based on a statistical anatomical model. Then the deformed sheet was cooled, stored and compared to the original model to investigate post-deformation changes. Results PDS sheet material could easily be deformed using a mould. No significant post-cooling shape changes were noticed. Conclusions PDS sheet material can be preformed into complex geometric shapes. This could be a benefit in the treatment of orbital wall fractures.

Naso-orbitoethmoid fractures account for 5% of all facial fractures. We used data derived from a white 34-year-old man to make a transient dynamic finite element model, which consisted of about 740 000 elements, to simulate fist-like impacts to this anatomically complex area. Finite element analysis showed a pattern of von Mises stresses beyond the yield criterion of bone that corresponded with fractures commonly seen clinically. Finite element models can be used to simulate injuries to the human skull, and provide information about the pathogenesis of different types of fracture.

As the biomechanical mechanisms of orbital wall fractures are still under research, three different fracture mechanisms were tested in a finite element based investigation. In contrast to earlier studies, a finer skeletal model and a transient dynamic simulation were used to test pure hydraulic, pure buckling and a mixed force transmission. Results showed that each set-up led to different orbital fracture patterns, which correlate well with clinical findings. Therefore the conclusion is that different mechanisms may act together explaining the variety of clinical fracture situations. Biomechanical testing has proven to be appropriate in answering questions regarding fracture mechanisms.

Purpose Aim of this study was to investigate whether a mold generated from a statistical shape model of the orbit could be generated to provide a cost-efficient means for the treatment of orbital fractures. Materials and Methods A statistical shape model was created from 131 computed tomographic (CT) scans of unaffected adult middle European human orbits. To generate the model, CT scans were segmented in Brainlab software, preregistered using anatomic landmarks, trimmed to an identical size, and definitely registered. Then, the model was created using the global master algorithm. Based on this model, a mold consisting of a male part and a female part was constructed and printed using a rapid prototyping technique. Results A statistical shape model of the human orbit was generated from 125 CT scans. Six scans (4.5%) presented major anatomic deviations and were discarded. A solid mold based on this model was printed. Using this mold, flat titanium mesh could be successfully deformed to serve as an orbital implant. Conclusion A mold based on the statistical orbital shape could serve as a cost-effective means for the treatment of orbital fractures. It allows the anatomic preformation of titanium or resorbable implant material for orbital reconstruction. Because these materials could be cut from larger sheets, the use of a mold would be a cost-effective treatment alternative.

Tracheostomy is a common procedure in head and neck surgery and emergency medicine to secure a patent airway. Surgeons should always be aware of anatomical variants of the branches of the aortic arch, which could lead to life-threatening complications. Open tracheostomy is the safest emergency procedure.

Distraction osteogenesis is an established procedure to cope with marked skeletal retrusion or deficiency. A principal theoretical problem with this method is the given length of the distractor unit. Regarding mandibular distraction, some devices allow reactivation of the distractor. For maxillary and midfacial distraction osteogenesis, to date, no report on how to achieve this has been found, creating the rationale for this technical note. Midfacial and maxillary distraction osteogenesis is an accepted therapy for maxillary retrusion and hypoplasia. External, halo-borne devices have been used for more than 15 years as a technical means for that purpose. Under most conditions, a distractor spindle length of over 3 cm will be sufficient for maxillary protraction. Under certain circumstances, however, this length will not be sufficient. A possible reason is subtotal osteotomy, which necessitates higher forces. Therefore forward bending of the extraoral connection rods instead of pure protraction will result, consuming spindle unit length. A further possible reason necessitating resetting is sutural distraction. Within sutural distraction, no osteotomies are perormed and miniplate-based anchoring devices are fixed o the maxilla and inferior zygoma. Because high forces re needed initially, which again lead to an initial bendng of the extraoral rods, the spindle unit length may e exhausted before the desired outcome has been eached.

Background Severe facial trauma is often associated with intracerebral injuries. So it seemed to be of interest to study stress propagation from face to neurocranium after a fistlike impact on the facial skull in a finite element analysis. Methods A finite element model of the human skull without mandible consisting of nearly 740,000 tetrahedrons was built. Fistlike impacts on the infraorbital rim, the nasoorbitoethmoid region, and the supraorbital arch were simulated and stress propagations were depicted in a time-dependent display. Results Finite element simulation revealed von Mises stresses beyond the yield criterion of facial bone at the site of impacts and propagation of stresses in considerable amount towards skull base in the scenario of the fistlike impact on the infraorbital rim and on the nasoorbitoethmoid region. When impact was given on the supraorbital arch stresses seemed to be absorbed. Conclusions As patients presenting with facial fractures have a risk for craniocerebral injuries attention should be paid to this and the indication for a CT-scan should be put widely. Efforts have to be made to generate more precise finite element models for a better comprehension of craniofacial and brain injury. Electronic supplementary material The online version of this article (doi:10.1186/s13049-015-0117-z) contains supplementary material, which is available to authorized users.

Purpose Preformed orbital titanium meshes have been introduced to improve outcomes in the treatment of orbital wall fractures. This study evaluated the geometry of different commercially available orbital meshes and compared them with an average human orbit. Materials and Methods Seven commercially available preformed orbital meshes were scanned using an optical scanner. For comparison, an average orbit was generated from 113 computed tomographic scans of unaffected orbits. Meshes and the average orbit were compared by registration and the calculation of congruence. Results All meshes showed a high similarity within a ±1.5-mm deviation corridor. Major differences were seen in the slope between the orbital floor and the medial wall and in the upturning toward the lateral orbital rim. Conclusion Preformed orbital meshes conform highly to an average orbit, but differ in size and geometry. Using special software, the best fitting mesh could be chosen preoperatively to improve surgical outcome if its geometry were published.

Introduction As fractures of the supraorbital region are far less common than midfacial or orbital fractures, a study was initiated to investigate whether fist blows could lead to fractures similar to those often seen in the midface. Methods A detailed skull model and an impactor resembling a fist were created and a fist blow to the supraorbital region was simulated. A transient finite element analysis was carried out to calculate von Mises stresses, peak force, and impact time. Results Within the contact zone of skull and impactor critical stress values could be seen which lay at the lower yield border for potential fractures. A second much lower stress zone was depicted in the anterior-medial orbital roof. Conclusions In this simulation a fist punch, which could generate distinct fractures in the midface and naso-ethmoid-orbital region, would only reach the limits of a small fracture in the supraorbital region. The reason is seen in the strong bony architecture. Much higher forces are needed to create severe trauma in the upper face which is supported by clinical findings. Finite element analysis is the method of choice to investigate the impact of trauma on the human skeleton.

Midfacial fractures rank first concerning maxillofacial traumatology. Collisions of two heads or head to object are the main causes for these fractures. An investigation based on a transient simulation using the finite element method was performed. A biomechanical head model was created and tested. A transient collision of two heads was simulated. The results were compared to a typical real patient case. This comparison revealed an identical fracture pattern, which can be interpreted as a clinical match of the simulation. The results of this study show the validity of biomechanical investigations, which may serve as a method to better understand maxillofacial fracture patterns. These results will be used for the optimization of fracture therapy or trauma prevention in the future.

This chapter discusses the requirements of an image analysis tool designed for dentistry and oral and maxillofacial surgery focussing on 3D-image data. As software for the analysis of all the different types of medical 3D-data is not available, a model software based on VTK (visualization toolkit) is presented. VTK is a free modular software which can be tailored to individual demands. First, the most important types of image data are shown, then the operations needed to handle the data sets. Metric analysis is covered in-depth as it forms the basis of orthodontic and surgery planning. Finally typical examples of different fields of dentistry are given.