SEM and EPMA Study of a 20-year-old Glass Ionomer to Dentin Interface

Objectives:This project was designed as in depth study of a clinical interface between a glass ionomer cement and dentine. Methods: A total of 55 class V glass ionomer (Fuji II, G.C.Corp.,Japan) restorations were placed in 1980. Subsequently, one was extracted due to periodontal reasons in 2000. This restoration has performed well for 20 years. The extracted tooth was fixed, then subjected to light microscopy, cryo-stage SEM and conventional SEM. The interface was chemically analysed using EMPA to trace the ionic exchange between the glass ionomer and sourrounding dentine. Results: The cryo-stage SEM revealed an intact and tight interface between glass ionomer and dentine after 20 years in situ. There is evidence to suggest that remnants of the odontoblasts can be found immediately below the interface. The conventional SEM confirmed that the interface resisted excessive dehydration and the failure observed was cohesive within the glass ionomer. Finally, EMPA analysis revealed the migration of fluoride from the glass ionomer into sound dentine, up to a depth of 450 microns. Conclusions: The longevity of this restoration can be attributed to the excellent adhesion between glass ionomer and dentine. The migration of fluoride into the sound dentine may have a two fold effect: firstly it may contribute to the adhesion and secondly it may increase the resistance of the underlying dentine against further acid challenges.