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FP5

MATRIX Report Summary

Project ID: QLK3-CT-2001-00090
Funded under: FP5-LIFE QUALITY
Country: Sweden

Data on regeneration of dental pulp tissue

Enamel matrix proteins have a capacity to induce rapid pulpal wound healing in pulpotomized teeth.

Enamel matrix proteins seems to induce dentin formation by turning on developmental processes in resting or immature pulpal cells in contrast to the widely used calcium hydroxide, which probably activates a purely reparative pathway in the mature pulp tissue.

Pulpotomy was performed in lower incisor teeth of adult miniature swine. The exposed pulp tissue was treated with EMD or covered with a calcium hydroxide paste (positive control). Following observation periods from 4 days to 12 weeks the experimental teeth were extracted and examined by light microscopy and immunohistochemistry with antibodies against collagen type I, DSP (dentin sialoprotein), sheathlin, and EMD.

In EMD treated teeth, a substantial amount of new dentin formation was observed at the application site, completely bridging the pulpal wound. Dentin formation was also observed in calcium hydroxide-treated teeth, however the amount of new dentine was significantly lesser than in EMD treated teeth (p<0.005). Moreover, in control teeth the new hard tissue did not bridge the pulpal wound, but formed at the expense of pulp chamber width, causing narrowing of the root canal. Immunohistochemical analysis also demonstrated an earlier onset of expression of dentin related proteins in the wounded pulp treated with EMD as compared to control treatment.

The mechanism(s) underlying induction of dentin formation by EMD is not known in detail. Immunogenically intact, and thus presumably active, EMD remains at the application site for more than three weeks after application, as demonstrated with immunohistochemistry. During the three weeks proteins closely associated with dentinogenesis were sequentially expressed by cells situated in regions with dentin formation. Notably, expression of sheathlin was detected in pulpal cells already four days after EMD application, as compared to after 2-3 weeks after application of calcium hydroxide. The expression of the rat homologue for sheathlin, amelin, has previously been observed in severely traumatized embryonic pulp tissue directly prior to the differentiation of a new odontoblast cell layer and subsequent onset of reparative dentin formation, suggesting that this protein is part of a signal pathway for induction of new dentin formation. Moreover, using in situ hybridisation assays and immunohistochemistry, expression of the amelin mRNA and the corresponding protein has been demonstrated in pulpal mesenchymal cells as well as in the preodontoblasts and in young odontoblasts at the early stages of dentinogenesis prior to onset of mantle dentin mineralisation. The precise functions of sheathlin remain largely unknown, but the abundant expression and wide distribution of sheathlin in mineralizing dentin and enamel ECM suggests possible roles in cell matrix interactions and biomineralisation.

The new hard tissue formed following EMD application stained positive for collagen I and DSP, using immunohistochemistry with specific antibodies. Collagen I and especially DSP are regarded dentin specific proteins, confirming that the biochemical composition as well as the morphology of the newly formed hard tissue resembles true dentin. This is also the case for the calcium hydroxide induced hard tissue, albeit the onset of the expression of these molecules here are delayed with about two weeks compared to the EMD treated teeth.

Following the positive findings in the animal model, a clinical experimental study in nine pairs of contralateral premolars scheduled for extraction was performed by the industrial partner. Postoperative symptoms were less frequent in the EMD-treated teeth, but the hard tissue barrier formed was not as good as expected. It was concluded that either the operative procedure and/or the formulation of EMD would need improvement for the clinical situation.

Contact

Christian JOHANSSON, (SITE MANAGER)
Tel.: +46-40-321349
Fax: +46-40-321335
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