Objective: The aim was to study the in vitro hardening of dentin adjacent to two glass ionomers (GI) of different glass composition and to relate it to compositional changes at the respective dentin interfaces.

Methods: The materials studied were: (1) GC Fuji IX and (2) 3M ESPE Ketac Molar. The former contained a Sr-glass and the latter a Ca-glass. Cavities, 4 mm deep and 3 mm diameter, prepared in caries-free extracted human molars (n=5 for each material) were filled with the two GIs. All filled teeth were stored in a phosphate buffer saline solution (pH = 7.2) at 37^oC. After 5 months, all teeth were sectioned and the sectioned surfaces polished. For each tooth, hardness (Vickers) was measured at dentinal areas within 0.5 mm of the restoration interface. Ten measurements were carried out for each tooth. SEM and EDXA of polished cross-sections were conducted to obtain information on the microstructure and composition of respective interfaces and bulk dentin 2 mm away from the interface.

Results: Dentin hardness adjacent to Fuji IX was approximately 25% higher (significant at p < 0.01) than that exhibited by Ketac Molar at its dentinal interface. SEM examination revealed dentin bonding with both materials. X-ray analysis indicated that dentin adjacent to Fuji IX was enriched with Sr but the Ca-content of dentin adjacent to Ketac Molar was not much different from that of the bulk dentin.

Conclusions: This study suggests that the degree of hardening adjacent to glass ionomers is dependent upon their composition. The greater hardening effect of Fuji IX is attributed to the release of Sr from its component glass, its diffusion through the interface, and subsequent remineralization of dentin.

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