Glass-ionomer transforms into enamel-like substance

Preventive Dentistry Glass-ionomer transforms into enamel-like substance Background.—Inorganic glass-ionomer is appropriate for resin fissure sealing because of its ability to be applied under humid conditions and to bond directly to tooth enamel. Its bond strength is not as great as that of resinbased materials, but its adaptation is reportedly superior. Glass-ionomer has the drawback of low wear resistance, with its visual disappearance soon after placement, although its effect remains as long as 6 years. Recent scanning electron microscopy (SEM) has revealed that clinically imperceptible material is retained. Evaluation of this material has failed to elucidate why this retained material is more resistant to erosion, although theories have emerged. It has been hypothesized that glass-ionomer transforms into an enamel-like structure called pseudo enamel. Whether saliva serves as a reinforcing agent for restorative materials such as glass-ionomer required further investigation. Methods.—Between 1999 and 2001, 3179 fissures in 532 patients were sealed using the glass-ionomer materials Ketac Fil and Ketac Molar. The teeth were cleaned mechanically, then washed with polyacrylic acid 10%, rinsed with a water spray, and isolated using cotton rolls and vacuum suction. The restorative materials were inserted and varnished with Ketac Glaze, then the occlusion was checked. Clinical macro pictures and SEM images were obtained for replicas in 1 patient and 2 sectioned primary molars in 2 additional patients who had the restorations present for several years. Results.—Seventy percent retention was found for the glass-ionomer sealants. Twenty randomly selected replicas of sealed surfaces showed altered glass-ionomer at the border with the fissure. This material demonstrated an unexpected cutting resistance. In 1 patient for whom replicas were studied, all glass-ionomer sealants showed a changed surface structure, with the transformation more notable at the interface with the enamel walls and less so at the mid-

182 Dental Abstracts

dle of the fissure. Some glass filler particles were dissolved, but their imprints remained in the altered structure. SEM revealed a smooth surface structure comparable to natural enamel. Analysis of the sealant material found calcium and phosphate uptake and loss of silica and aluminum. In a second patient, 2 primary molars were analyzed directly. The results were similar to those of the first case. Cross-sections of deeper areas of the fissure showed no chemical components of the original glass-ionomer. In a third patient, analysis of the saliva-exposed side of a fragment of the material showed more calcium and phosphate uptake than was noted in deeper areas. Discussion.—When glass-ionomer is present for a longer period, it appears to gradually transform into a material with enamel-like properties as far as optical and mechanical aspects are concerned. Further evaluation of this material is warranted.

Clinical Significance.—Generally shunned as a sealant in favor of the seemingly more durable composite resins, an in vivo alteration of glass-ionomers is suggested, given sufficient dwell time under oral conditions, to a material more closely resembling enamel.

Van Duinen RNB, Davidson CL, de Gee AJ, et al: In situ transformation of glass-ionomer into an enamel-like material. Am J Dent 17:223-227, 2004 Reprints available from RNB Van Duinen, Academic Ctr for Dentistry Amsterdam (ACTA), Universiteit van Amsterdam and Vrije Universiteit, Dept of Dental Materials Science, Louwesweg 1, 1066 EA Amsterdam, The Netherlands; e-mail: [email protected]