3D Printed Surgical Simulation Models as educational tool by maxillofacial surgeons.

INTRODUCTION: The aim of this study was to evaluate whether inexpensive 3D models can be suitable to train surgical skills to dental students or oral and maxillofacial surgery residents. Furthermore, we wanted to know which of the most common filament materials, acrylonitrile butadiene styrene (ABS) or polylactic acid (PLA), can better simulate human bone according to surgeons' subjective perceptions. MATERIALS AND METHODS: Upper and lower jaw models were produced with common 3D desktop printers, ABS and PLA filament and silicon rubber for soft tissue simulation. Those models were given to 10 blinded, experienced maxillofacial surgeons to perform sinus lift and wisdom teeth extraction. Evaluation was made using a questionnaire. RESULTS: Because of slightly different density and filament prices, each silicon-covered model costs between 1.40-1.60 USD (ABS) and 1.80-2.00 USD (PLA) based on 2017 material costs. Ten experienced raters took part in the study. All raters deemed the models suitable for surgical education. No significant differences between ABS and PLA were found, with both having distinct advantages. CONCLUSION: The study demonstrated that 3D printing with inexpensive printing filaments is a promising method for training oral and maxillofacial surgery residents or dental students in selected surgical procedures. With a simple and cost-efficient manufacturing process, models of actual patient cases can be produced on a small scale, simulating many kinds of surgical procedures.

[Chronic myofacial pain. Reduced pain through psychoeducation and physiotherapy]. / Chronische Kiefer- und Gesichtsschmerzen. Verringerte Schmerzen durch Psychoedukation und Physiotherapie.

BACKGROUND: Psychological factors are associated with the emergence and persistence of pain perception. The aim of this pilot study was to assess the psychological factors relating to pain perception in patients with chronic myofacial pain and to investigate the influence of patient information, education and physiotherapy on pain perception and functional jaw opening examined over a 6-month period. PATIENTS AND METHODS: In accordance with the research diagnostic criteria for temporomandibular disorders (RDC/TMD), 40 patients (31 females and 9 males, mean age 38.6 years) with chronic myofacial pain were assessed at 3 time points: on admission (T1), after 3 months (T2) and 6 months (T3). The study included a structured interview and five psychological questionnaires. At all time points patients were informed about the development of pain and the relationship between chronification of pain and psychological risk factors. RESULTS: After 6 months significant improvements in jaw function and quality of life, as well as a decrease in psychological parameters, such as fear and depression were found. Improvement was related to the severity of pain chronification. CONCLUSION: The results show the necessity of early identification of patients with severe pain chronification and the need for psychological pain therapy.

Do we need real-time MRI for diagnosis of temporomandibular joint disorders?

INTRODUCTION: Magnetic resonance imaging (MRI) has been approved as an appropriate radiological modality for temporomandibular joint (TMJ) diagnosis, whereas the results of international multicenter studies impressively show the limitations of static three-dimensional MRI. The state of the art for dynamic imaging of the TMJ in real-time are TrueFISP sequences in one sagittal plane. In order to support the diagnostics, a computer-assisted visualization procedure has been developed by the authors for both the static and dynamic MRI. METHODS: A number of validated sequences are available for the static 3D-MRI within the clinical routine. For dynamic MRI in real-time, True-FISP sequences in one sagittal plane with a slice thickness of 5-10 mm and 1.3 mm x 1.3 mm spatial resolution were applied. Both the dynamic and static MRI datasets are animated and visualized using the computer-assisted procedure. RESULTS: The computer-assisted procedure reliably supported the clinical diagnosis, especially the visibility of the articular disc was enhanced. On the basis of the static MRI, a 60-year-old patient was diagnosed with anterior disc displacement without reduction. In contrast, by the dynamic MRI, it was recognized how the articular disc was firstly somehow stretched and flattened before the mandibular condyle again glided under the disc, thus resulting in an anterior disc displacement with reduction. CONCLUSION: These results endorse the relevance of real-time diagnosis for the TMJ. The computer-assisted visualization has been approved as a reliable help for clinical diagnosis.

[Rare complication after Le Fort I osteotomy]. / Eine seltene Komplikation nach Le-Fort-I-Osteotomie.

Malfunctions of the eustachian tube after Le Fort I osteotomies are rare. A 22-year-old woman was treated by Le Fort I osteotomy for maxillary retrognathism. Postoperatively she developed recurrent tubal malfunction and middle ear effusions on the left side, with no improvement after adenotomy, tonsillectomy, and grommet insertion. In consecutive computed tomography and magnetic resonance imaging scans, a forward dislocation of the left pterygoid hamulus was demonstrated. In addition, damage to the tensor veli palatini muscle was evident. Both postoperative sequelae appear to be responsible for the unilateral tubal dysfunction.

Finite element simulation of the human mandible: the role of (natural) teeth.

INTRODUCTION: Individual bone quality depends on genetic, biological, and mechanical influencing factors, where the latter is accessible via Finite Element Simulation. This work is part of an interdisciplinary research project with the purpose of stepwise refinement towards anatomical reality. This approach opened the door for many interrelated applications such as atrophy of the jaw bone, periodontology, implantology, or TMJ disorders. This lecture is dedicated to the influence of dental anatomy on mandibular biomechanics. MATERIALS AND METHODS: In general, biomechanical simulation requires reconstruction of the individual anatomy, implementation of the inhomogeneous and anisotropic material law of bone, and realization of the load case due to tooth, muscle and joint forces. The simulation chain ranges from image processing of CT data up to specifically adapted post-processing of the simulation results. In spite of ongoing research, there is still a fundamental difference of dental implants compared to natural teeth: the periodontal ligament (PDL) present at the interface between teeth and mandibular corpus. Due to its thickness of about 0.2 mm, the PDL was introduced to the simulation model by a special semiautomatic procedure. RESULTS: Simulations "with and without PDL" proved remarkable force absorption due to the PDL, as well as qualitative changes of the stress/strain profiles of the alveolar ridge. Concerning the simulation without PDL, the observed high compressive strains at the adjacent bone were in agreement with regions of frequent implant failure. CONCLUSION: The PDL is essential for the structural behavior of the human mandible. Based on the mechanical adaptation of bone, the comparison of the simulation with and without PDL provided special insight to the changes due to dental implants, in particular implant loss and bone resorption. Finally, the simulation will serve as a virtual platform for further evaluation (a) of implant design (b) of implant placement.

Mandibular finite element simulation as a tool for trauma surgery.

PURPOSE: Despite remarkable progress within the last decade, the treatment of mandibular fractures is still a highly discussed topic in oral and cranio-maxillofacial surgery. The possible traumatologic scenarios are characterized by high variability. A current project is focused on "resimulation" of traumatologic cases given by clinical radiographs by means of finite element method. METHODS: The applied finite element model of the mandible is very refined, providing detailed dental anatomy especially of the periodontal ligament. The mandible was modelled as inhomogeneous and anisotropic. The temporomandibular joints were realized as simplified joint capsules, wherein the mandibular condyles are freely mobile with certain limitations. The user has the choice of 5 regions on the mandibular surface where the virtual injury can be inflicted. Power and direction of the impact force vector can be set at will. The masticatoy system including the digastrics and the mylohyoid muscles can be activated. RESULTS: The situations given by radiographs could be "reproduced" by a simulation scenario characterized by high compressive strain at the location of fractures. If masticatory muscles were activated and teeth clenched, the stress/strain profiles were qualitatively changed. DISCUSSION: The approach may be of benefit for optimized behavior with regard to certain sports or vocations. For forensic analysis, the method will contribute by elimination of scenarios not matching the given fracture locations. Nevertheless, the immediate purpose of our approach is a better understanding of the injured organ's condition. Fractures of bone as an adaptive biological tissue differ fundamentally from mechanical failure in engineering. Many of our trauma simulations showed elevated stress/strain around the fracture, leading to the suggestion of weakened bone there. This finding was confirmed by surgical observation.

Central nervous malformations in presence of clefts reflect developmental interplay.

Children with cleft lip and/or cleft palate (CLP) often have additional congenital malformations. The reported incidences are variable and presumed underlying mechanisms are rarely discussed. In this study, 245 CLP patients of a geographically defined population were retrospectively reviewed for additional major malformations and minor anomalies. Malformation incidences in the CLP population were compared to those in a literature-based cohort from the general population. Of the CLP patients, 21% showed either major malformations or minor anomalies. In one-fifth of them a recognized syndrome was identified. Two thirds of the CLP patients with minor anomalies also had major malformations. Major malformations in non-syndromic CLP patients were found with decreasing frequency in the musculoskeletal (5.1%), central nervous (4.2%), urogenital (3.8%) and cardiovascular (3.4%) systems. Malformations in these organ systems and minor anomalies should be ruled out by a specialist. The rise in malformation incidence, when compared to the general population, was highest for organs of ectodermal and ecto-mesodermal origin: central nervous system (13 times), ocular (7 times) and craniofacial system (7 times). The result reflects the close interplay of craniofacial and brain development.

Accuracy and precision of the three-dimensional assessment of the facial surface using a 3-D laser scanner.

Three-dimensional (3-D) recording of the surface of the human body or anatomical areas has gained importance in many medical specialties. Thus, it is important to determine scanner precision and accuracy in defined medical applications and to establish standards for the recording procedure. Here we evaluated the precision and accuracy of 3-D assessment of the facial area with the Minolta Vivid 910 3D Laser Scanner. We also investigated the influence of factors related to the recording procedure and the processing of scanner data on final results. These factors include lighting, alignment of scanner and object, the examiner, and the software used to convert measurements into virtual images. To assess scanner accuracy, we compared scanner data to those obtained by manual measurements on a dummy. Less than 7% of all results with the scanner method were outside a range of error of 2 mm when compared to corresponding reference measurements. Accuracy, thus, proved to be good enough to satisfy requirements for numerous clinical applications. Moreover, the experiments completed with the dummy yielded valuable information for optimizing recording parameters for best results. Thus, under defined conditions, precision and accuracy of surface models of the human face recorded with the Minolta Vivid 910 3D Scanner presumably can also be enhanced. Future studies will involve verification of our findings using test persons. The current findings indicate that the Minolta Vivid 910 3D Scanner might be used with benefit in medicine when recording the 3-D surface structures of the face.

Consideration of anisotropic elasticity minimizes volumetric rather than shear deformation in human mandible.

This article is focused on the role of anisotropic elasticity in the simulation of the load distribution in a human mandible, due to a lateral bite on the leftmost premolar. Based on experimental evidence, orthotropy of the elastic properties of the bone tissue has been adopted. The trajectories of anisotropic elasticity are reconstructed from (i) the organ's geometry and (ii) from coherent structures which can be recognized from the spatial distribution of the grey values coming from computer tomography (CT). A sensitivity analysis comprising various three-dimensional (3D) finite element (FE) simulations reveals the relevance of elastic anisotropy for the load carrying behavior of a human mandible: comparison of the load distributions in isotropic and anisotropic simulations indicates that anisotropy seems to "spare" the mandible from loading. Moreover, a maximum degree of anisotropy leads to kind of load minimization of the mandible, expressed by a minimum of different norms of local volumetric strain, evaluated throughout the organ. The observed optimization with respect to volumetric rather than shear strain seems to confirm the frequently emphazised role of volumetric-strain-induced fluid flow for the stimulation of cellular activity.

Computer aided surgical reconstruction after complex facial burn injuries -- opportunities and limitations.

In severe facial burn injuries with extensive destruction of anatomical structures, cosmetic and functional outcome of treatment are frequently not satisfactory. Although operative therapy is being continuously refined, the variety and proximity of structures in the facial region is considered a major challenge in reconstructive surgery. We present the case of a 16-year-old patient with a severe facial burn injury. In planning the reconstructive procedures, we used a multimodal approach employing data from computerized tomography imaging, as well as from surface laser scanning, which provided three-dimensional visualization of facial soft tissues. Amount and pattern of structural loss could thus be determined more precisely and studied more vividly than by inspection of two-dimensional imaging alone. Anatomical features to be reconstructed could be projected onto the skin area of the prelaminated vertical rectus abdominis muscle (VRAM) flap that has been chosen to cover the defect. Prior to surgery, correction of the defects was simulated and the results of the virtual procedure superimposed on a three-dimensional head model of the patient. Tissue elasticity and thickness of the flap, however, could not be ascertained in advance, indicating the limitations of the method.

Clinical applicability of robot-guided contact-free laser osteotomy in cranio-maxillo-facial surgery: in-vitro simulation and in-vivo surgery in minipig mandibles.

Laser was being used in medicine soon after its invention. However, it has been possible to excise hard tissue with lasers only recently, and the Er:YAG laser is now established in the treatment of damaged teeth. Recently experimental studies have investigated its use in bone surgery, where its major advantages are freedom of cutting geometry and precision. However, these advantages become apparent only when the system is used with robotic guidance. The main challenge is ergonomic integration of the laser and the robot, otherwise the surgeon's space in the operating theatre is obstructed during the procedure. Here we present our first experiences with an integrated, miniaturised laser system guided by a surgical robot. An Er:YAG laser source and the corresponding optical system were integrated into a composite casing that was mounted on a surgical robotic arm. The robot-guided laser system was connected to a computer-assisted preoperative planning and intraoperative navigation system, and the laser osteotome was used in an operating theatre to create defects of different shapes in the mandibles of 6 minipigs. Similar defects were created on the opposite side with a piezoelectric (PZE) osteotome and a conventional drill guided by a surgeon. The performance was analysed from the points of view of the workflow, ergonomics, ease of use, and safety features. The integrated robot-guided laser osteotome can be ergonomically used in the operating theatre. The computer-assisted and robot-guided laser osteotome is likely to be suitable for clinical use for ostectomies that require considerable accuracy and individual shape.

Investigation on plasma immersion ion implantation treated medical implants.

In this work the biocompatibility of osteosynsthesis plates treated with plasma immersion ion implantation (PIII) was tested using a rat model. Small rods (Ø 0.9 mm, and length 10 mm) prepared from different materials-pure Ti, anodised Ti, and two NiTi alloys (SE 508, and SM 495)-were implanted with oxygen by PIII to form a rutile surface layer and subsequently inserted into rat femurs, together with a control group of untreated samples. The results of the biomechanical tests correlate with the histological results, and show that plasma immersion ion implantation leads to an increase of biocompatibility and osseointegration of titanium and NiTi, albeit no improvement of the (bad) biocompatibility of the anodised Ti. Despite the layer thickness of up to 0.5 microm a strong influence of the base material is still present.

Levatorplasty, a new technique to treat hypernasality: anatomical investigations and preliminary clinical results.

BACKGROUND: Velopharyngoplasty is the most commonly used operative technique for the treatment of velopharyngeal insufficiency. By attaching a posterior pharyngeal flap to the velum, a nonphysiological situation is created in the upper airway. PURPOSE: The aim of this investigation was to find a new surgical approach to physiological reconstruction of the velopharyngeal sphincter. MATERIAL: Anatomical investigations were performed in four cadavers. From this study a new surgical technique was developed and called 'levatorplasty': the musculus longus capitis was taken to create a new muscular loop leading to (a) an augmentation of the posterior wall, (b) a medial shift of the lateral pharyngeal wall; and (c) stretching of the velum posteriorly. Thus, the velopharyngeal space was reduced and a physiological closure of the nasal airway space could be obtained. STUDY DESIGN: The levatorplasty was employed in nine cleft palate patients with velopharyngeal insufficiency. Pre- and postoperatively the velopharyngeal closure was evaluated by phonetic and radiological examination. RESULTS: The operation was easily performed without major complications. A concentric constriction with decrease of the velopharyngeal space was achieved and a definitive decrease of nasalance and hypernasality resulted. CONCLUSION: Long-term follow-ups have to verify whether these results will be stable. They also have to be compared with functional improvements following velopharyngoplasty or pharyngoplasty. Of special interest will be evaluation of the altered mobility of the lateral pharyngeal walls.

Rapid protyping technology in medicine--basics and applications.

Using medical models built with Rapid Prototyping (RP) technologies represents a new approach for surgical planning and simulation. These techniques allow one to reproduce anatomical objects as 3D physical models, which give the surgeon a realistic impression of complex structures before a surgical intervention. The shift from the visual to the visual-tactile representation of anatomical objects introduces a new kind of interaction called 'touch to comprehend'. As can be seen, from the presented case studies of maxillo-cranio-facial surgery, the RP models are very well suited for use in the diagnosis and the precise preoperative simulation of skeleton modifying interventions.

[Fetal wound healing: current status and new perspectives]. / Fetale Wundheilung. Aktueller Stand und neue Perspektiven.

The characteristic of fetal wound healing is scarless wound repair in early gestation. During the last two decades, intensive research efforts have focused on unraveling the molecular regulations underlying the phenomenon of scarless wound healing. Better understanding of synthesis and degradation will enable us to develop important therapeutic options for the prevention and reduction of scarring. The aim of this article is to present an overview, discuss the most important research works of the last two decades on the field of fetal wound healing, and report current therapeutic developments for the modulation of adult wound repair. Recent experimental results using these new therapeutic approaches are very promising and present great possibilities and chances for future surgery.

Surgery planning tools for the osseous grafting treatment.

This paper presents a method for computer assisted selection of optimal donor sites for autologous grafts in the craniofacial surgery planning. The method consists of two stages. The non-automatic graft design step is followed by a fully automatic procedure to find the best harvesting site in the predefined donor region. The main idea of the proposed method is based on the registration paradigm. The optimal donor site is identified by performing an optimization of the surface based similarity measure between the donor region and the designed graft template. An efficient optimization method based on the Levenberg-Marquardt algorithm has been implemented. It enables, once the preprocessing step has been performed, selection of the optimal donor site in time less than one minute.

[Numerical simulation (FEM) of the human mandible: validation of the function of the masticatory muscles]. / Numerische Simulation (FEM) des menschlichen Unterkiefers: Validierung der Umsetzung der Kaumuskulatur.

The article describes part of a research project aiming to develop a new modular software tool for the individual dynamic numerical simulation of the human mandible using the finite element method (FEM). Its planned use in the clinical setting makes it very important to validate the results of the simulations. Here, the function of the masticatory muscles is to be tested. On the basis of biomechanical data from the literature, standard movements, such as closing the mouth, forward movement, lateral movement or backward movement, were dynamically simulated. Apart from muscle activity, the movements of the mandible are defined by the temporomandibular joint. At present, translating the condylar dynamics to the simulation still poses problems. For this reason, therefore, simulations of the two extreme cases "fixed" and "force-free" condyles are compared. While in the case of fixed condyles, some of the movements could be reproduced either not at all or only weakly, in the case of force-free condyles, all standard movements were reproduced qualitatively, albeit without the guiding effect of the joint capsule or the articular disc.

[A modular software concept for individual numerical simulation (FEM) of the human mandible]. / Ein modulares Software-Konzept für individuelle numerische Simulation (FEM) des menschlichen Unterkiefers.

A new modular software concept for individual numerical simulation of the human mandible using the finite element method (FEM) is presented. The main task is an individual analysis of regional stress and stress-compatibility on the basis of computed tomographic data in individual patients. Simulation should, however, also be possible in parallel with biomechanical experiments, or for further research projects. For this purpose, rapid and uncomplicated generation of the FEM model, easy modification of input data, and short computation times are required. Practical use in the clinical setting makes appreciable additional demands on the individual software components.

Traumatology of the facial skeleton in octogenarian patients: a retrospective analysis of 96 cases.

AIM: The aim of this retrospective study was to evaluate the frequency and distribution of maxillofacial trauma patients over 80 years, with regard to type and environment of accidents as well as treatment and complications. PATIENTS AND METHODS: Data for 94 patients (96 cases; aged 80-94 years) with maxillofacial fractures were retrospectively analysed. RESULTS: Data of 30 male and 64 female patients with an average age of 85 years were analysed. In 90% of the study population, the cause of fractures was a fall, followed by traffic accidents (9%) and assault (1%). Seventy-two patients had fractures of the midface, 10 had factures of the mandible, 9 had fractures of both the midface and mandible and 5 had fractures of the neurocranium and midface. Surgical intervention was required in 57% of the patients. Post-operative complications were: four cases of diplopia, two cases of infected plates, four cases of lower eyelid ectropion and in one case a retrobulbar haematoma. CONCLUSION: Facial trauma in the elderly can often be treated conservatively unless the patient complains of functional problems. Due to co-morbidities, special attention should be paid to hypertension, anticoagulant agents and the surgical approach.