Providing an environment for reparative dentine induction in amputated rat molar pulp by high molecular-weight hyaluronic acid

To study provision of this environment, wound healing was examined by light and electron microscopy following pulp amputation and direct capping with hyaluronic acid. Molar pulps of female Sprague-Dawley rats were mechanically exposed and directly capped; the cavities were then restored with glass-ionomer cement. As an experimental control, Calvital (a commercial preparation of calcium hydroxide paste) was used as the direct pulp-capping agent in other rats, and its effect on pulp healing was compared with that of hyaluronic acid. In hyaluronic acid-treated pulps, at 2 days after amputation, wound surfaces were covered with blood and fibrin clots and inflammatory cells such as neutrophils and macrophages. At I week, differentiation of fibroblastic and odontoblast-like cells was observed beneath the wound layer: and odontoblast-like cells produced globular calcified nodules along the existing dentine walls. At 2 weeks, a layer of reparative dentine had been formed by odontoblast-like cells over the dentine walls. Between 30 and 60 days, the formation of reparative dentine had extended throughout the pulp chamber. The healing observed after direct capping with hyaluronic acid was, except for the formation of dentine bridges, similar to that seen after Calvital capping. These results suggest that high molecular-weight hyaluronic acid can provide an environment suitable for reparative dentine formation through mesenchymal cell differentiation during healing of the amputated dental pulp.