[Effect of protection and remineralization of glass ionomer protective film and fluoride varnish on enamel: an in vitro study].

Purpose: To compare the remineralization and protection effect of glass ionomer protective film and fluoride varnish on enamel.

Methods: One hundred and twenty-two premolars were collected and made into enamel blocks, two enamel blocks were randomly selected for scanning electron microscope(SEM) observation, the others were used for two experiments. In enamel protection test (experimental A), 60 enamel blocks were divided into 3 groups (n=20) randomly and treated with glass ionomer protective film(A1) and fluoride varnish(A2), the control group(A3) was not treated. In remineralization test (experimental B), sixty enamel blocks were demineralized for 72 h, which were randomly divided into 3 groups(B1, B2 and B3)(n=20) , and the treatment method was the same as that of the enamel protection group. To simulate oral environment, in experiment A and B, six groups of samples were treated with pH cycling in demineralization liquid and artificial saliva alternately for 30 days. The surface morphology of enamel was observed under SEM, surface microhardness(SMH) changes of enamel was measured by microhardness tester, the calcium-phosphorus ratio of the enamel surface was analyzed by X-ray energy spectrum analyzer. The data was analyzed statistically by using SPSS 26.0 software package.

Results: In enamel protection test, the results of SEM observation showed that the untreated enamel surface was flat and even. After treatment with demineralization liquid, group A1 was basically intact. In group A2, a large number of flaky sediments were found on the enamel surface. Group A3 presented typical honeycomb structure caused by demineralization. Pairwise comparison of ΔSMH among the groups showed A1A2>A3(P<0.05). In remineralization test, the results of SEM observation showed that group B1 and B2 all had deposits adhered to the enamel surface. The surface of group B3 enamel was rough and uneven, and showed the shape of a honeycomb. Pairwise comparison of ΔSMH among the groups showed B1>B2>B3(P<0.05). The results of calcium-phosphorus ratio by X-ray energy spectrum analyzer was group B1>B2>B3(P<0.05).

Conclusions: Both glass ionomer protective film and fluoride varnish can prevent and cure enamel demineralization, while glass ionomer protective film is more effective in protection and remineralization because of its wear resistance and durability.