Development of a synthetic bolus using silicone elastomer for the study of masticatory efficiency.

STATEMENT OF PROBLEM: Masticatory efficiency has been proposed as an outcome measure for prosthetic rehabilitation. However, no standardized method is available for this type of assessment. PURPOSE: This study developed a normalized synthetic test food with reproducible physical and rheologic properties. MATERIAL AND METHODS: Two silicone putties of different hardness were studied. The texture of each putty varied by the addition of silicone oil. Rheologic characteristics of 7 samples were compared with the same properties of 5 natural food substances. RESULTS: Seven varieties of synthetic bolus were produced, each of which were of a different hardness, modulus of elasticity, and tensile strength. The natural food substances demonstrated great rheologic variability. The synthetic bolus samples exhibited a texture profile approaching that of natural foods. The principal difference between the 2 groups tested was that of the homogeneity of the silicone samples. CONCLUSION: None of the samples reproduced all the rheologic properties of the natural food substances; however, the results showed that their characteristics were sufficiently similar for the silicone samples to be suggested as a reproducible alternative for the testing of masticatory efficiency.

[Removable prosthesis: masticatory efficiency]. / Prothese adjointe: efficacite masticatoire.

The late consultation in odontology often leads to tooth extraction. This negligence, in a long term, will cause complete toothlessness. This state of invalidity will be compensated by prosthesis. The removable prosthesis is often indicated because of the cost price. It is the result of a successful therapeutics, only if it fits aesthetically and functionally, within a chewing efficiency. In a first part, we will define masticatory efficiency, as different from masticatory capacity and capability. Then, in a second part, through some experimentation, we will show how fundamental research can guide the practitioner in his prosthetics choices and assessments.

Phosphoinositides in giant barnacle muscle fibers: a quantitative analysis at rest and following electrical stimulation.

Quantitative data are presented on the composition of the major phospholipids in isolated giant barnacle muscle fibers. It is shown, using internal perfusion techniques, that the high specific activity of labeling of polyphosphoinositides in vivo is attained by the activities of specific kinases. Electrical stimulation causes a reduction in the specific activity of labeling of PtdInsP2. This phospholipid, which is the immediate precursor for the release of InsP3, is found at a significant concentration (40 nmol/g wet weight) in single barnacle muscle fibers, sufficient to support a role as precursors of second messengers. The rapid catabolization of PtdInsP2 in the absence of external Ca2+ suggests that E-C coupling in barnacle muscle may be associated with a voltage-dependent, Ca(2+)-independent, activation of the breakdown of polyphosphoinositides.

Supraeruption of the unopposed maxillary first molar.

Supraeruption of the maxillary first molar in the absence of the mandibular first molar was observed in subjects with both normal and pathologic periodontics. Both the migration of the gingival margin and the increase in the crown height were evaluated in terms of the length of time the antagonist tooth had been missing. Values obtained were compared with those of a reference group with complete normal dentitions. The results show that in the first years following the loss of the opposing tooth, supraeruption is mainly due to growth of the periodontium. Later or in the case of periodontal pathosis, tooth movement beyond the occlusal plane is due principally to active eruption.

Imaging of calcium transients in skeletal muscle fibers.

Epifluorescence images of Ca2+ transients elicited by electrical stimulation of single skeletal muscle fibers were studied with fast imaging techniques that take advantage of the large fluorescence signals emitted at relatively long wavelengths by the dyes fluo-3 and rhod-2 in response to binding of Ca2+ ions, and of the suitable features of a commercially available CCD video camera. The localized release of Ca2+ in response to microinjection of InsP3 was also monitored to demonstrate the adequate space and time resolutions of the imaging system. The time resolution of the imager system, although limited to the standard video frequency response, still proved to be adequate to investigate the fast Ca2+ release process in skeletal muscle fibers at low temperatures.

[Measurement of supra-eruption of the human first upper molar in the absence of an opposing tooth]. / Mesure de l'egression de la premiere molaire superieure humaine en l'absence de dent antagoniste.

The situation and configuration of the occlusal plane can be modified by the process of supra-eruption, which can be split up into: active eruption (the tooth leaves its socket) and periodontal growth. In order to dissociate and better by understand them, supra eruption of the first upper molar was observed in the absence of the first lower molar. Three groups of subjects were selected, the first group, our reference group (n = 50), consisted of subjects with complete healthy dental arches for which we could determine the extent of the gingival margin and the crown height. The second group of subjects (n = 50) differed from the former by the presence of a supra-erupted first upper molar. This allowed us to evaluate the migration of the gingival margin and the crown height increase in terms of the length of time the antagonist tooth was missing. The analysis of these 2 values shows that in the early years after the tooth loss, supra-eruption is due mainly to periodontal growth. It is only later that tooth movement beyond the occlusal plane is due principally to active eruption. The third group was made up of subjects showing pathological conditions of the periodontium. We observed an apical migration of the gingival margin and in increase in crown height, resulting from a periodontal regression (passive eruption) and a rapid active eruption.

Tetrodotoxin-sensitive sodium channels in a continuously cultured cell line derived from the adult rat cerebellum.

A method to establish continuously cultured cell lines from adult cerebellar cortex is reported. Clones (prepared by this procedure) were isolated from cerebellar established cultures at the 25th passage and after 15 months in vitro. One clone (UCHCC1) was maintained in culture and studied while the others were frozen. The cerebellar cell line UCHCC1 retained a neuronal-like morphology; the addition of dimethylsulfoxide (DMSO) to the culture medium elicited a reproducible morphological 'differentiation' event, characterized mainly by process extension. In 'differentiated' cells, veratridine significantly increased the uptake of 22Na. Such enhanced uptake was blocked by tetrodotoxin (TTX) with a half-maximal inhibitory concentration of 0.9 nM. Binding of an [3H]ethylenediamine derivative of TTX ([3H]en-TTX) to the microsomal fraction prepared from same DMSO-treated cells, showed a single class of receptors with a maximal binding (Bmax) of 173 fmol/mg protein and a Kd of 1.1 nM. Thyroid UCHT1 cells and 'undifferentiated' (cultured without DMSO) cerebellar cells, did not show significant effects of veratridine on 22Na-uptake, or [3H]en-TTX binding. The 'differentiated' nerve-like properties, induced by appropriate environmental manipulation, demonstrate the usefulness of cerebellar UCHCC1 cells as a model system for the developing central neuron. On the other hand, the novel transforming procedure opens new possibilities for obtaining permanent cell lines from other regions of the adult CNS.