[TMJ and orthodontics, "past, present and future"]. / ATM et orthodontie, « passé, présent et futur ¼.

In the past, the ATM was mainly associated with the growth of the mandibular condyle. Many studies (on rats) showed the role of condylar cartilage in the growth response following stimulation by orthopedic appliances. From where, Class II dysmorphosis "orthopedic" treatments to grow the mandible; but this concept is discussed in the literature in the absence of fully conclusive results and especially since the contribution of orthognathic surgery. Currently, the operating concept is the mechanical stimulation and therefore the function will shape the ATM during growth and that, from an early age. Prevention of dysmorphoses must go through behavioral counseling to be adopted by parents from the birth of their child: to stimulate mandibular propulsion breastfeeding, then by a hard diet inducing an alternating unilateral chewing. Ignorance of the specificity of temporomandibular dysfunction (TMD) notably among teenagers has, in the past, left a doubt about the positive or negative role that could have orthodontic treatment on the TMJ. Currently, the best knowledge of TMJ and TMD provides a better therapeutic conduct: behavioral counseling especially for the girl hyperdivergente with small condyles, control of the condylar position, occlusal adjustments at the end of orthodontic treatment. The future of TMJ in relation with orthodontics is based on prevention, screening and deepening of our knowledge. The orthodontist will thus not make a treatment in patients at risk or will identify it and finish the treatment perfectly.

Transversal craniofacial growth evaluated on children dry skulls using V2 and V 3 canal openings as references.

PURPOSE: The aim of this study was to investigate the transversal relationships between two cephalometric landmarks and lines on the face using ovale, rotundum, greater palatine and infra-orbital foramina as references. METHOD: Thirty-four children dry skulls, 19 males and 15 females aged 0-6 years, were examined by computed tomography scanning by using constructed tomographic axial and frontal planes. The cephalometric transversal dimensions of the face skull were measured between the right and left landmarks from the orbital lateral wall and from the zygomatic arch. The cephalometric transversal dimensions of the base skull were measured between the right and left ovale, rotundum, greater palatine and infra-orbital foramina. RESULTS: Statistical analysis using partial correlations, regardless of the age, showed strong relationships (p < 0.05) among transversal measurements with nerve canal openings and transversal distances of skull face. CONCLUSION: We showed that the cranial base transversal growth was very strongly related to facial transversal growth from the postnatal period up to 6 years of age.

Comparison of stress distribution in the temporomandibular joint during jaw closing before and after symphyseal distraction: a finite element study.

The aim of this study was to predict stress modification in the temporomandibular joint (TMJ) after symphyseal distraction (SD). The study was performed using three-dimensional finite element analysis using a complete mastication model. Geometric data were obtained from MRI and CT scans of a healthy male patient and each component was meshed as various regions. The distraction was performed with a 10mm expansion after simulation of a surgical vertical osteotomy line on the model in the mandibular midline region. The geometry and mesh of the bone callus were constructed. The bone callus was modelled as a strengthened region characterized by a Young's modulus corresponding to consolidated bone to predict the long-term biomechanical effect of SD. Boundary conditions for jaw closing simulations were represented by different jaw muscle load directions. The von Mises stress distributions in both joint discs and condyles during closing conditions were analysed and compared before and after SD. Stress distribution was similar in discs and on condylar surfaces in the pre- and post-distraction models. The outcomes of this study suggest that anatomical changes in TMJ structures should not predispose to long-term tissue fatigue and demonstrate the absence of clinical permanent TMJ symptoms after SD.

[Histological analysis of dental follicles after unerupted mandibular third molar extraction]. / Analyse histologique des follicules dentaires après germectomies des troisièmes molaires mandibulaires.

INTRODUCTION: The extraction of third mandibular tooth germ (M3) is often prophylactic to avoid orthodontic treatment relapse and to prevent infectious or tumoral diseases developing from the dental sac. The purpose of this study was to screen for early histopathological modification of dental follicles (inflammatory, infiltration, or epithelial metaplasia) after extraction of third mandibular tooth germ (M3) on asymptomatic patients. The secondary objective was to study the proliferative activity of the epithelium by dosing the anti Ki-67 antibody. PATIENTS AND METHOD: Twenty dental follicles extracted from 12 boys and eight girls between 14 and 18 years of age were examined under phototonic microscopy. The proliferative activity of the epithelium was assessed by immuno-histochemistry. RESULTS: Three dental follicles presented with focal epidermoid metaplasia of the epithelium, without odontogenic tumoral proliferation. In all other cases, the cylindrical epithelial cell structure was normal. A mild chronic inflammatory infiltrate was present in 30% of the cases. Immuno-histochemical analysis revealed labeling of very rare epithelial lining cells, slightly more in cases presenting with metaplasia. DISCUSSION: The prevalence of early morphological changes of dental sac is low. This histo-morphological study does not support the systematic extraction of asymptomatic mandibular tooth germs (M3).

[Pathogenic occlusion and functional occlusion: definition of completion]. / Occlusion pathogène et occlusion fonctionnelle: définitions des finitions.

The masticatory system is widely adaptable and tolerant especially in young people ; this characteristic can be helpful but it can also incur risks because there are limits to everything. Guided solely by the insubstantial support provided by data derived from evidence-based medicine, a researcher would have to be both excessively clever and unusually cunning to define the borderline between physiological and pathological occlusion. Accordingly, the optimization of masticatory function through the intermediary of efficient occlusal interaction of upper and lower teeth remains a fundamental common sense objective of all dental treatment. This common sense is based on the fundamental principles of simplicity and of ergonomy that govern all biological "mechanisms ". By respecting the principles of "centering, stabilization, and guidance", dentists will adhere to a simple but precise manual for preserving or creating, if need be, the good occlusal relationships that encourage unfettered mandibular movement (fitting) and symmetrical global functioning (centring), and absence of interference (guiding).

[Hyperactivity of the muscles of the lip and chin and indications for surgery to reduce it]. / Dysfonctionnement des muscles labio-mentonniers et indications de la chirurgie d'affaiblissement.

Hyperactivity of the muscles controlling the lower lip and chin (muscles of the chin, buccinator, orbicularis, etc.) can be demonstrated at different levels of the muscular complex and may act as an elastic force against the mandibular alveolar process. Dysfunction in this region may lead to reduction of the alveolar bone quantity, reducing the tooth-bone equilibrium. If this balance is disturbed, periodontal lesions, a lower incisal crowding and a retrognathic mandibular process may result. Surgery to correct overactivity of the chin muscles is described here step by step. Resection of the muscles may be undertaken on a greater or lesser scale and striation of the muscle may also allow reduction of muscular strength. Reducing the muscular activity creates a better environment for the development of the mandible and its alveolar process. Depending on the clinical situation, these techniques can be associated with genioplasty, bone graft and/or mandibular orthognathic surgery.

[Proposal for a classification of Class II Division 1: contribution of Delaire's analysis]. / Proposition d'une classification des classes II division 1: contribution de l'analyse de Delaire.

Class II division 1 dental malocclusions are present in various forms depending on the site, direction and degree of discrepancy between the arches. The ability to recognize the origin of the malocclusion is essential to decide how, and when it is necessary to treat. In this study, the Delaire's analysis was performed for 111 individuals with a Class II division I malocclusion; a classification of these cases is proposed, according to the presence or the absence of a skeletal discrepancy. In 87% of the cases, a Class II division 1 dental malocclusion was associated with a Class II skeletal discrepancy (50% maxillary prognathism, 23.5% normal maxillary relationship and 13.5% maxillary retrognathism). The lines of the cranial base, the shape and size of the mandible varied considerably. In only 6% of cases, the dental malocclusion was associated with a skeletal Class I relationship, and in 7% of cases with a Class III relationship: it was often related to retruded mandibular teeth. It was shown that Class II division 1 dental malocclusions may result from differing causes: therefore, the identification of their etiology seems essential to provide the best possible treatment, at the right period in time.

Cinematic study of temporomandibular joint motion using ultra-fast magnetic resonance imaging.

Magnetic Resonance Images (MRI) of the temporomandibular joint (TMJ) are usually performed to study the opening/closing movements of the mandible and have up to now been pseudodynamic step-by-step images simulating condylar motion by post-processing reconstruction. The aim of this study was: 1. to optimize a TMJ cine-imaging method to give a better clinical result than the step-by-step methods; 2. to develop an ultra-fast MRI Gradient Echo (GE) sequence for this purpose; and 3. to analyze condylar movements in the sagittal, coronal and para-axial planes during border mandibular displacements and chewing. Both TM joints were studied in six asymptomatic volunteers. The method involved a compromise between in-plane resolution, slice thickness, signal-to-noise ratio and time resolution. Routine clinical use was found to be a GE pulse sequence providing three images per second with an isometric voxel resolution of approximately two millimeters in ridge. This did not allow visualization of the disk. Using this sequence enabled real and simultaneous condylar displacement observation in the three planes of space and therefore contributed to a better functional diagnosis of pathologic TMJ motions.

Ultrasonic assessment of the anatomy and function of the tongue.

The tongue is a complex muscular structure. Apart from its intrinsic strength, it has a major influence on the adjacent bony structures. Real time ultrasound appears to be the method of choice for assessing the topographic and functional anatomy. The examination was performed using an Acuson 128 scanner, with a 5 MHz probe, either a sector scanner (sagittal plane) or linear array probe (coronal plane). The scans were performed using the sub-hyoid approach, between the rami of the mandible. The images were stored on U-matic videotape. Thirty adult patients were included in the study population. The scan protocol consisted of an examination of the tongue at rest, a scan of the swallowing mechanism with and without a liquid bolus and a study of the posterior lingual positions (which show some anatomical variation). The intrinsic muscles of the tongue and the floor of the mouth could be identified on the "at rest" images. The lingual mass is the most important parameter and is opposed against the palate in order to propel a bolus during the swallowing mechanism. The mobility, shape and supporting structures of the tongue are variable depending on the nature of the bolus, the patient and the two imaging planes. Ultrasound is a simple and non-invasive method for the examination of the buccal cavity. The function of the posterior portion of the tongue must be taken into consideration prior to any treatment concerning the oral cavity.