[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).

Cytotoxicity of orthodontic bands, brackets and archwires in vitro.

OBJECTIVES: In orthodontic therapy, different materials are used and subjected to a damp oral environment, which can modify their properties. In order to evaluate the biocompatibility of metallic and non-metallic orthodontic appliances their in vitro cytotoxicity has been measured. METHODS: Twenty-eight new and nine clinically used materials, including brackets, molar bands and archwires were used. The metallic materials were made of stainless steel, gold-plated steel, pure titanium, nickel-titanium, titanium-molybdenum and silver-based soldering alloy. The non-metallic materials were in polycarbonates and ceramics. After a release period of the material in the culture medium (0.1 mg/ml) for 3 and 14 days, the viability of fibroblasts L929 cultivated with this medium was compared to negative control with MTT assay. RESULTS: The results showed the non-cytotoxicity of the materials. The metallic and non-metallic materials were similar in terms of cytotoxicity. The cytotoxicity of clinically used samples was equivalent to that of the same non-used samples, except a cytotoxic sample, at 14 days, corresponding to a soldered and clinically used molar band. The 3 day results were different from the 14 day results in six cases out of 37. SIGNIFICANCE: In spite of the presence of one cytotoxic sample, the orthodontic materials can be considered as non cytotoxic. However, the practitioner should pay attention to the composition and the polish of soldering silver-based alloys containing copper and zinc in order to limit cytotoxic ion release. The cytotoxicity of the used sample related to ion release might be related to some clinical sub-acute effects related with orthodontic materials, thus a long term release period may be suitable to evaluate in vitro the sub-acute clinical effects of alloys.

[Schuchardt's procedure and surgery of open bite]. / Intervention de Schuchardt et chirurgie des béances.

Posterolateral segmentary maxillary impaction osteotomy has a role to play in the treatment of gaps between the upper and lower jaws. It has several advantages, especially an uncomplicated postoperative period and the single-maxillary contention it provides. The indication must be established after an articulator assessment in order to take into account the mandibular protrusion caused by autorotation and to prevent a sagittal shift. Associated marginal glossectomy will frequently be required. Similarly, in case of vertical excess, genioplasty for vertical reduction will improve the facial balance. This technique may also be proposed as "pre-prosthetic surgery" in cases of egression in the premolar and molar areas, for which it has shown excellent results.

[Do magnetic forces potentiate the histophysiology of orthodontic movement?]. / Les forces magnétiques potentialisent-elles l'histophysiologie du déplacement orthodontique?

A comparative clinical research has been made to prove if magnet forces can be superior to mechanical forces for tooth movement. Six dogs went through a distalazing movement of their lower premolars on one side with a magnet system and on the other side with a mechanical system producing similar forces. A histological analysis of the moved premolars has showed a more important rate of osteoclasts and a reduction of the hyalinisation area with the magnet system.

[Impact of early extraction of the 1st molars on vertical dimension]. / Incidence des extractions précoces des premières molaires sur la dimension verticale.

Early extractions of first permanent molars, done on twenty cases without any orthodontic treatment, have not shown, following the Student's analysis, any statistical difference relative to a pilot group as far as the angles. SN- ANS- PNS, SN-OP, SN-GoGn, FMA, Y-axis are concerned. On the other hand, it has been revealed a closure of the angle ANS- Xi- MP associated with an opening of the mandibular arch.