Armelle Manière-Ezvan

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 Youngs 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.

Therapeutic decisions in the presence of decayed permanent first molars in young subjects: A descriptive inquiry

UNLABELLED The aim of this exhaustive descriptive epidemiological study was to determine the clinical approach to be adopted by practitioners specializing exclusively in pediatric odontology and by orthodontists when confronted with decayed molars in children and adolescents. MATERIAL AND METHOD A questionnaire was sent out to all corresponding practitioners (n=2076). Six questions related to treatment decisions taken when faced with decayed permanent first molars (unfavorable short or middle-term prognosis) in patients needing, or not, orthodontic care. The Chi(2) test was used to compare responses. RESULTS Thirty-eight per cent of pedodontists (n=38) and 12.5% (n=246) of orthodontists answered the questionnaire. Faced with a permanent first molar with an unfavorable middle-term prognosis, 75.7% needed criteria to help them reach their treatment decision. In decreasing order of importance, these criteria were: presence of the third molar, patient motivation, inter-arch relationship, patients oral hygiene, facial type, anterior jaw-teeth discrepancy and the number of molars to be extracted. Faced with a permanent first molar requiring extraction and when orthodontic treatment was not required, 31.7% of practitioners decided to close the maxillary space immediately as opposed to 13.4% who closed the space at the mandible. In the presence of a single decayed first molar, 68.7% of practitioners did not extract the antagonist or contralateral first molars. CONCLUSION These treatment decisions were not always unanimous and call for a combined approach between dental surgeon and orthodontist.

Focus on the occlusal failure

The success is evidenced by the longevity of aesthetic and functional therapeutic result. The occlusal «postorthodontic» failure could result in dental instability, functional discomfort, dental or musculo-articular complaint. Analysis of the occlusion research potential occlusal pathogenic dysfunction listed in stabilizing (shimming), centering and guiding anomalies. The large capacity of tolerance of the masticatory system makes it difficult to define the border between physiology and pathology but it is necessary to have benchmarks that can be summarized as follows: - shimming: occlusal contact of mesio-lingual cusp of the first maxillary molars (in Class I, II or III) and occlusal contacts between the canines antagonists; - centering: no transversal deflected occlusion between maximal Intercuspation (ICP) and occlusion in Centric Relation (RCP); - guiding: absence of posterior interference, absence of anterior interference (locking).

Model to assess duration of distraction compared with degree of incisal crowding in symphyseal distraction osteogenesis

Our aim was to evaluate symphyseal distraction in relation to duration of expansion, and to propose an optimised procedure. Eighteen patients (mean (SD) age 19 (7) years) with transverse mandibular deficiency were treated by symphyseal distraction osteogenesis. The mean (SD) anterior dental crowding measured was 6.8 (4.2) mm. We retrospectively compared the width of expansion between the canines (ICE) and expansion between the first molars (IFME) after symphyseal distraction according to the distraction time. The median (range) duration of expansion was 13.6 (7-21) days. The median (range) ICE distraction width was 5.5 (3.4-8) mm and IFME width 3.3 (1-7.9) mm (p<0.001). There was a significant correlation between expansion width and distraction time (p<0.001). The transverse anterior and posterior expansion widths differed significantly until 14 days after expansion. The expansion ratio (ICE:IFME) decreased as expansion time increased. The results suggest that the duration of activated expansion can be predicted from the degree of incisal crowding using the formula: distraction time (days)=0.84+3.4×[IC (mm)]-0.2×[IC (mm)](2).