[Can bite force be predicted from the shape of the face?]. / La force d'occlusion peut-elle prédire la forme de la face?

The relationships between maximum bite force (MBF) and facial architecture have been tested in a sample of 118 dental students. The strongest correlations were seen with the variables representative of posterior face height and facial divergence. No correlation could be seen between MBF and incisor's position. MBF allowed only partial discrimination of the individuals in different subgroups constituted by cluster analysis. MBF is to consider as a representation of the individual aptitude to develop more or less powerful forces. It summarises only part of the functional information influencing facial form.

The cranial base in subjects with dental and skeletal Class II.

The aim of this study was to test to what extent the cranial base variations may be involved in Class II facial organization. Using Bonferonni probabilities, cranial base size and shape, and facial divergence were compared in two groups: an experimental group of 45 subjects with dental and skeletal Class II and an homologous control group of 41 subjects with a natural Class I ideal occlusion. In all individuals of the experimental group the Class II molar relationship was at least equal to the width of one premolar and the ANB angle was greater than the value of the mean +2 standard deviations of the ANB in the control group. Spacing and crowding was less than 2 mm at each arch in both groups; all subjects were between 10 and 12 years old. The anterior part of the cranial base (SN length and SNBa angle) was identical in the two groups, but in Class II, cranial base flexure (BaSN angle) was more obtuse (P less than 0.05) and posterior cranial base angle (SBaN) was more acute (P less than 0.01). These variations co-existed in the same group with a more retruded position of the condylar neck in the face (P less than 0.01) favouring per se a post-normal relationship of the mandible to the maxilla. The increased extension of the saddle angle in Class II could not be considered here as related to an hyperdivergent facial pattern since facial divergence was unchanged in Class II. Saddle angle and divergence correlated in Class I (r = 0.40; P less than 0.01), but not in Class II.(ABSTRACT TRUNCATED AT 250 WORDS)

[Pharyngeal obstruction and the functional adaptation of the natural posture of the head and the hyoid bone in sleep apnea syndrome]. / Obstruction pharyngienne et adaptation fonctionnelle de la posture naturelle de la tête et de l'os hyoïde dans le syndrome d'apnées du sommeil.

Variations in natural head posture (NHP) and hyoid bone (HB) positioning impart changes in the size and shape of the pharyngeal airways. In SAS, which was shown to be correlated with detrimental craniofacial anatomical conditions, control of pharyngeal permeability is lost during sleep. The aim of this study was determine if functional adaptation of NHP and HB position to these detrimental conditions could be observed, using Bonferonni probabilities, in a cephalometric comparison of 38 SAS adults in the wakeful state and a control group of 38 healthy adults. Since HB relationships with craniofacial anatomical structures vary with the positioning of the head, the cephalograms were taken according to the preliminarily tested NHP, thus making the method reproducible. In SAS craniovertical angulation was unchanged, but the head was maintained in a forward position (increased cervico-vertical angulation, P < 0.001). Maintenance of an acceptable pharyngeal permeability was associated with a more distant positioning of HB from the cervical column (P < 0.01) and from craniofacial references (P < 0.001). In spite of these facts lower pharynx opening was still reduced (P < 0.05). Soft palate and facial divergence were expectedly increased in the apneic group. All the individuals but one control could be correctly reclassified with the help of soft palate length, facial divergence, and two HB related variables. Prevention of pharyngeal collapsibility in SAS seems to be commonly associated with functional adaptation of NHP and HP position. The precise control mechanisms of this adaptation remains to be elucidated. Skeletal predispositions to SAS do probably develop already during infancy.

[Vertical typology and natural posture of the head]. / Typologie verticale et posture naturelle de la tête.

The relationship between head posture and vertical typology were evaluated in a sample of 98 young adults. Sub groups of opposite typology were also compared. A strong correlation existed between head posture and facial divergence when evaluated with the variable SN/PM and face post./face ant. Head posture is in extension when facial divergence is important. No correlation existed between posture and % face inf. Face post./face ant. was the best variable in evaluating the relationship between vertical typology and head posture.

[Bone resorption in orthodontic tooth movement: an attempted schematization]. / La résorption osseuse dans les déplacements dentaires orthodontiques: essai de schématisation.

The osteoclast is the major cellular agent of bone resorption. Hormonal stimulation of bone resorption is indirect and depends on the osteoblastic function. Protease production is the final common pathway through which osteoblastic cells initiate osteoclastic resorption. Exposition of the mineralised matrix and contact with the osteoclasts always comes before resorption, regardless of the stimulating agent involved in the resorption process. In orthodontic conditions, production and activation of osteoclasts may be attained through different ways. Inflammation subsequent to tissue damage and bioelectric perturbations associated to alveolar bending can be considered as two major events which may lead to increase bone resorption and orthodontic tooth displacement. The precise transduction mechanism of an orthodontic force into cellular resorbing activity is still obscure.