Reparative dentin formation after pulp capping with a curable Hydrogel compared with a calcium hydroxide liner, Dycal®

Objectives: The formation of reparative and reactionary dentin was compared after pulp capping either with Hydrogel or a calcium hydroxide liner, Dycal^®, for 1 to 4 weeks.
Methods: Occlusal cavities were drilled in the 1^st maxillary molar of rats and pulp exposures done in the deepest part of the dentin cavity. Direct capping was carried out with a two-component self-cured gel (Hydrogel) composed of Bovine Serum Albumin and glutaraldehyde (group 1: G1), compared with a self-cured Dycal (group 2: G2). G1 were the right molars of twenty 6 week-old rats, whereas G2 involved left molar of the same animals. After 1, 2, 3, and 4 weeks, the rats were anaesthetized intraperitoneally, intracardially perfused with buffered 4% paraformaldehyde fixative. Molar’s blocks were demineralized with a 4.13% EDTA solution under microwave, dehydrated and paraffin embedded. Rehydrated sections were stained with Masson trichrome or immunostained.
Results: One week in G2, inflammatory cells formed aggregates, with mild pulpal necrosis. At 2-3 weeks, a dentinal bridge started to be formed at the junction between the necrotic and vital tissue. At 4 weeks, reactionary dentin was formed at the periphery of the pulp chamber, beneath a calcio-traumatic line. In G1, 1 week after Hydrogel capping, the inflammatory process was less visible, and apparently solved afterwards. Reactionary dentin displayed an increased thickness compared with G2, with a thick layer of osteodentin-like tissue. Hydrogel also contributed to the massive formation of a reparative dentinal bridge, with tunnels disturbances. Immunostaining for type 1 collagen, dentin matrix protein-1, bone sialoprotein and dentin sialoprotein was systematically weaker after Hydrogel implantation compared to Dycal.
Conclusions: Dycal appeared to involve an initial inflammatory process, whereas the Hydrogel pathway was controlled primarily by non-inflammatory events. Unpredictably, a reverse relationship was detected by immunostaining between extracellular matrix molecules and pulp reparative mineralization.