[The coherence between 3 evaluation methods of biocompatibility]. / Etude de la coherence entre trois modes d'évaluation de la biocompatibilité.

Three successive series of tests (the primary including cytocompatibility tests and the secondary in vivo and usage tests) can be used to evaluate the biocompatibility of dental materials. The products are only submitted to secondary tests in case of satisfactory results obtained with primary tests. A coherence between the results of primary and secondary tests is necessary before performing in vivo tests. The aim of this paper is to study the coherence between two primary tests and a secondary test. The biocompatibility of Sealite and a pulp canal sealer was studied 4 and 12 weeks after mixing, according to two primary models (cell culture on agarose and a toxicity study of the extraction products) and a secondary model (intrabony implantation in the rabbit). The two primary tests gave different results for Sealite and the pulp canal sealer. Only the agarose cell culture and the intrabony implantation in the rabbit have given similar statistical results. The biological evaluation of biomaterials should begin with a study of the mechanism of action of the cytotoxic products using several in vitro tests. These latter are unable to predict the behaviour of a biomaterial in an in vivo test.

Scanning electron microscopy of the forming enamel of rat incisor: influence of fixative and treatments interacting with the organic matrix.

The forming enamel of rat incisor was either treated before fixation with one of these five treatments: ultrasonication, NaOCl, chloroform/methanol, NaOH or tween 20; or the incisors were first fixed and then submitted to one of these treatments. The structure of the forming enamel, compared with sections fixed with aldehyde and submitted to osmic maceration, depends on the way the samples were treated and on the fixative used. An amorphous material, removed by osmium tetroxide but not by aldehyde solution was seen to be located between fiber-like structures. In the region of inner enamel secretion the thickness of interrod septa was fairly constant, whereas in the region of outer enamel secretion, transverse septa of interrod enamel gradually became thinner and finally disappeared. The longitudinal septa did not display such changes. Longitudinal grooves and ridges were seen at the end of enamel completion. These longitudinal septa finally merged and formed a flat surface.

Ultrastructure of inter-odontoblastic fibres in the rat molar.

Radially directed inter-odontoblastic collagen fibres were observed in ultra-thin sections of the radicular pulp/predentine complex of rat molars. Bundles of fibres crossed the distal junctional complexes of the odontoblasts, went through the whole thickness of the predentine and were incorporated into the mineralized dentine. Scanning electron microscopy showed that bundles of radial fibres are not found between the coronal odontoblasts of the rat molar but only in the root. The radial fibres were inserted into the predentine along vertical long-axial crests. The intercrest interval was not tightly fixed and the pattern of fibre-bundle insertion did not show a regular periodicity.

A radioautographic comparison of in vivo 3H-proline and 3H-serine incorporation in the pulpal dentine of rat molars: variations according to the different zones.

3H proline and 3H serine were injected intraperitoneally to rats which were killed 4 and 24 hours later. The incorporation of the labelled precursors was studied in the odontoblasts, predentine and dentine of the first lower molars. After radioautography, statistically significant differences in grain density appeared between the furcation, occlusal and lateral areas of the pulp chamber. The incorporation of predentine components into dentine was faster in the lateral than in the occlusal area, the slowest being detected in the furcation area. These differences may be related to the distribution of occlusal forces in the rat molar.

[Osseous biocompatibility of Endomethasone(R)]. / Biocompatibilité osseuse de l'Endométhasone(R).

The root canal filling paste "Endométhasone" was tested, following the F.D.I. criterions by bone implants on rabbits. The tissue reaction after four weeks can be appreciated as moderate and as mild after twelve weeks. Taking in count the criterions selected and the experimental conditions of this study, the "Endométhasone" can be considered as a root canal cement with acceptable in vivo tolerance.

[Pulp-dentin reactions after CO2 laser treatment of the dentin]. / Réactions pulpo-dentinaires après traitement de la dentine au laser à CO2.

The use of a CO2 laser in the treatment of dentinal caries in vital teeth seemed to be an important therapeutical progress compared to traditional means of carious tissue removal with rotary mechanical instruments. Forty sound premolars from patients with a mean age of twelve years were prepared according to a standard method for biological controls and submitted to the action of a CO2 laser of 3 Watts, equipped with a convergent lens of a 38 mm focal distance. The pulpal reactions were observed on day 15, 30, 50 and 80. No clinical post-operative symptomatology was observed in all treated teeth. The pulpal reactions related to the thickness of residual dentine consisted in the presence of reversible inflammatory changes, in the absence of degenerative processes and in an important production of tertiary dentine. The structural modifications occurring on the dentinal walls in these experimental conditions seemed not to induce a barrier totally tight to bacterial penetration.