Designing maxillofacial prosthesis for bone reconstruction: an overview

A cranio-maxillofacial region contains several bones and serves to protect and support the area, from the brain to the masticatory system. In this paper the clinical and research aspects of craniomaxillofacial biomaterials have been highlighted to serve as a guide into the wide world of their reconstructions. After a quick look into the anatomy, the review focuses on the causes of large bone defects in this region, and how they influence the designing process of the implant. Since it is a large area to unfold, only the maxillary, the mandible and the temporomandibular joints are highlighted. Understanding the biomechanics of mandible and temporomandibular joints is quite important, as it strongly influences the choice of the biomaterial. Thus, the latest techniques implemented to understand the biomechanics of the mandible are also highlighted. Via the finite element analysis, a simulation can help to identify the forces and the movements of the mandible and to predict the possible outcome of the implantation influencing the choice of the biomaterial.

Modified transpalatal arch to correct sagging of palatal cusp of maxillary 2nd molar

“Sagging” of the palatal cusp of upper second molars is a common finding observed during orthodontic treatment which may develop heavy balancing side contacts, which have been found to be detrimental to harmonious function of the masticatory system. Various modifications of transpalatal arch (TPA) are advocated to correct crossbite, but most of them will utilize an additional step of soldering a wire attachment to TPA. In this clinical pearl, the TPA was fabricated using a single wire component, eliminating an additional step of soldering.

Detailed three-dimensional orthodontic tooth repositioning to improve restorative outcome:

ABSTRACT The case describes the interdisciplinary treatment of a 23-year-old woman with a Class III malocclusion, missing an upper right lateral incisor, abrasion of the maxillary incisal edges, anterior gingival margin discrepancies, and gingival recession. Initially, the patient was treated with fixed appliances combined with orthognathic surgery. The extraction of the upper left lateral incisor and bilateral canine substitution plan was chosen. At the end of the surgical and orthodontic treatment, the restorative treatment with six veneers was accomplished to improve smile esthetics. Despite the missing lateral incisors, the patient showed a natural, good-looking final result. A symmetric incisal plane was established, a functional occlusion with average vertical and horizontal overlap was set, and the bone scallop and consequently the gingival margins were leveled. The interdisciplinary approach hid all of the initial esthetic defects of the case. The result highlights how to obtain a remarkable improvement of the smile outcome with a well-functioning masticatory system.

Sandwich Integration Technique for the Pressure Sensor Detection of Occlusal Force In Vitro

Bite force measurement is an important parameter when checking the function and integrity of the masticatory system, whereas it is currently very difficult to measure bite force during functional movement. Hence, the purpose of this study is to explore the potential technique and device for the measurement and intervention of the continuous bite forces on functional and dynamic occlusal condition. A portable biosensor by sandwich technique was designed, and the validity, reliability, and sensitivity were determined by mechanical pressure loading tests; meanwhile, the pressure signal is acquired by, and transmitted to, voltage changes by the electrical measurements of the sensors. The result is that, when the mechanical stress detection device is thicker than 3.5 mm, it shows relatively ideal mechanical properties; however, when the thickness is less than 3.0 mm, there is a risk of cracking. Mechanical stress changing and voltage variation had a regularity and positive relationship in this study. The mechanical stress-measuring device made by medical and industrial cross has a good application prospect for the measurement of bite force during function.

A dental revolution: The association between occlusion and chewing behaviour

Dentistry is confronted with the functional and aesthetic consequences that result from an increased prevalence of misaligned and discrepant dental occlusal relations in modern industrialised societies. Previous studies have indicated that a reduction in jaw size in response to softer and more heavily processed foods during and following the Industrial Revolution (1,700 CE to present) was an important factor in increased levels of poor dental occlusion. The functional demands placed on the masticatory system play a crucial role in jaw ontogenetic development; however, the way in which chewing behaviours changed in response to the consumption of softer foods during this period remains poorly understood. Here we show that eating more heavily processed food has radically transformed occlusal power stroke kinematics. Results of virtual 3D analysis of the dental macrowear patterns of molars in 104 individuals dating to the Industrial Revolution (1,700–1,900 CE), and 130 of their medieval and early post-medieval antecedents (1,100–1,700 CE) revealed changes in masticatory behaviour that occurred during the early stages of the transition towards eating more heavily processed foods. The industrial-era groups examined chewed with a reduced transverse component of jaw movement. These results show a diminished sequence of occlusal contacts indicating that a dental revolution has taken place in modern times, involving a dramatic shift in the way in which teeth occlude and wear during mastication. Molar macrowear suggests a close connection between progressive changes in chewing since the industrialization of food production and an increase in the prevalence of poor dental occlusion in modern societies.

Restoration of the anterior guide with the fixed prosthesis

The anterior guide is a functional entity, which is part of the set of guidance provided by the dento-dental joints to the mandibular kinematics, essential for the establishment of harmonious occlusal relations. The anterior guide is a key to understanding and reconstructing the occlusion, playing both a role of protecting the posterior teeth and guiding the functional movements of the mandible. Currently, it also represents an “exteroceptive feeler” creating a cone of access to the occlusion in intercuspation. The restoration of functional and protective anterior guidance is therefore essential for the balance of the masticatory system. This rehabilitation can only be achieved by examining and accurately diagnosing the occlusion relationships maintained by the anterior teeth, associated with a reasoned therapeutic approach validated by a test phase. After a brief description of the anterior function and its role, this article aims to detail, through a clinical case, the procedure to follow for the restoration of a functional anterior guide.

Determination of Reference Values of the Masseter Muscle Stiffness in Healthy Adults Using Shear Wave Elastography

Shear wave elastography (SWE) is an objective and reliable method for the assessment of muscles and internal organs. Every organ exhibits its own stiffness characteristics and hence requires individual reference values. We aimed to determine the reference values of stiffness of the masseter muscle in healthy adult individuals using SWE. We analyzed the data of 140 participants (74 men, 66 women) with a median age of 50 years. The overall mean elasticity was 10.67 ± 1.77 kPa. The average values were lower by 2.25 kPa (9.15%) in women compared to men (9.48 ± 1.47 kPa vs. 11.73 ± 1.27 kPa; p < 0.0001). The values of stiffness increased with age, with a correlation coefficient of about 0.35 and a p < 0.0001. Age was a significant influencing factor of masseter muscle stiffness. The left and right masseters had similar stiffness. We conclude that stiffness values are significantly lower in women than in men with a difference of 9%. Age significantly influences the stiffness of masseter muscle, and the values of stiffness increase significantly with age, particularly in men. However, further studies are required to determine the precise ranges of stiffness accounting for age and sex in healthy subjects and people with disorders and conditions of the masticatory system.

A Redundantly Actuated Chewing Robot Based on Human Musculoskeletal Biomechanics: Differential Kinematics, Stiffness Analysis, Driving Force Optimization and Experiment

Human masticatory system exhibits optimal stiffness, energy efficiency and chewing forces needed for the food breakdown due to its unique musculoskeletal actuation redundancy. We have proposed a 6PUS-2HKP (6 prismatic-universal-spherical chains, 2 higher kinematic pairs) redundantly actuated parallel robot (RAPR) based on its musculoskeletal biomechanics. This paper studies the stiffness and optimization of driving force of the bio-inspired redundantly actuated chewing robot. To understand the effect of the point-contact HKP acting on the RAPR performance, the stiffness of the RAPR is estimated based on the derived dimensionally homogeneous Jacobian matrix. In analyzing the influence of the HKP on robot dynamics, the driving forces of six prismatic joints are optimized by adopting the pseudo-inverse optimization method. Numerical results show that the 6PUS-2HKP RAPR has better stiffness performance and more homogenous driving power than its non-redundant 6-PUS counterpart, verifying the benefits that the point-contact HKP brings to the RAPR. Experiments are carried out to measure the temporomandibular joint (TMJ) force and the occlusal force that the robot can generate. The relationship between these two forces in a typical chewing movement is studied. The simulation and experimental results reveal that the existence of TMJs in human masticatory system can provide more homogenous and more efficient chewing force transmission.

A transitional fossil mite (Astigmata: Levantoglyphidae fam. n.) from the early Cretaceous suggests gradual evolution of phoresy-related metamorphosis

Metamorphosis is a key innovation allowing the same species to inhabit different environments and accomplish different functions, leading to evolutionary success in many animal groups. Astigmata is a megadiverse lineage of mites that expanded into a great number of habitats via associations with invertebrate and vertebrate hosts (human associates include stored food mites, house dust mites, and scabies). The evolutionary success of Astigmata is linked to phoresy-related metamorphosis, namely the origin of the heteromorphic deutonymph, which is highly specialized for phoresy (dispersal on hosts). The origin of this instar is enigmatic since it is morphologically divergent and no intermediate forms are known. Here we describe the heteromorphic deutonymph of Levantoglyphus sidorchukae n. gen. and sp. (Levantoglyphidae fam. n.) from early Cretaceous amber of Lebanon (129 Ma), which displays a transitional morphology. It is similar to extant phoretic deutonymphs in its modifications for phoresy but has the masticatory system and other parts of the gnathosoma well-developed. These aspects point to a gradual evolution of the astigmatid heteromorphic morphology and metamorphosis. The presence of well-developed presumably host-seeking sensory elements on the gnathosoma suggests that the deutonymph was not feeding either during phoretic or pre- or postphoretic periods.