In vitro effect of resin infiltrant on resistance of sound enamel surfaces in permanent teeth to demineralization

Abstract

Objective: To investigate the effect of resin infiltrant on resistance of sound permanent enamel surfaces to demineralization.

Method: Eighty healthy premolars were sectioned to obtain enamel blocks from the buccal surface. Specimens with baseline surface microhardness values of 320-370 were selected. The experimental group were treated with resin infiltrant, while the control group was not. Specimens from each group were artificially demineralized and the surface microhardness values were measured again. Confocal laser scanning microscopy was used to measure the depth of demineralization and detect the penetration ability of the resin infiltrant. The specimens were subjected to a simulated toothbrushing abrasion test. Scanning electron microscopy was used to observe changes in the surface morphology of specimens after each of these procedures.

Results: No significant differences between the experimental and control groups were observed in the baseline microhardness values or in the experimental group after resin infiltration compared with the baseline conditions. After artificial demineralization, the microhardness value in the control group was significantly lower than that in the experimental group (266.0 (±34.5) compared with 304.0 (±13.0), P = 0.017). Confocal laser scanning microscopy results showed that the demineralization depth in the control group was significantly deeper than that in the experimental group (97.9 (±22.8) µm vs. 50.4 (±14.3) µm, P < 0.001), and that resin infiltrant completely penetrated the acid-etched demineralized area of the tooth enamel with a mean penetration depth of 31.6 (±9.0) µm. Scanning electron microscopy showed that the surface morphology was more uniform and smoother after simulated toothbrushing. The enamel surface structure was more severely destroyed in the control group after artificial demineralization compared with that of the experimental group.

Conclusion: Resin infiltrant can completely penetrate an acid-etched demineralized enamel area and improve resistance of sound enamel surfaces to demineralization. Our findings provide an experimental basis for preventive application of resin infiltrant to sound enamel surfaces to protect tooth enamel against demineralization.

Keywords: Artificial demineralization; Fluorescence staining; Permanent tooth enamel; Resin infiltrant; Simulated toothbrushing.

Figure 1. Experimental flow chart related to the experimental procedures in this study.

Figure 2. Comparison of surface microhardness values of specimens between control and experimental groups at each time point (n = 10, mean ±  SD).

^∗P < 0.05, ^∗∗∗P < 0.001, ns = no significant difference.

Figure 3. Comparison of demineralization depth of specimens between control and experimental groups (n = 10, mean ±  SD).

^∗∗∗P < 0.001.

Figure 4. CLSM images of the specimens after rhodamine B staining, the width of the red area reflects the demineralization depth of enamel.

(A) Staining results of the experimental group specimens after artificial demineralization 96 h. (B) Staining results of the control group specimens after artificial demineralization 96 h. Scale bar represents 25 µm.

Figure 5. CLSM images of the specimens after double-fluorescence staining.

(A) Rhodamine B staining results of the specimens after etched with Icon-Etch; red area represents the depth of the acid etched demineralized enamel areas sealed by resin infiltrant. (B) Sodium fluorescein staining results of the specimens after treated with resin infiltrant, sectioned and bleached; green area represents the demineralized microporous areas that are not sealed by resin infiltrant. (C) Merge of (A) with (B); shows that resin infiltrant almost completely penetrated into the etched demineralized enamel areas. Scale bar represents 25 µm.

Figure 6. SEM resutls of surface morphology.

(A) Sound enamel blocks that did not treated with resin infiltrant. (B) Sound enamel blocks that were treated with resin infiltrant and not polished. (C) Sound enamel blocks treated with resin infiltrant following polishing. (D) Sound enamel blocks treated with resin infiltrant following 96 h of artificial demineralization. (E) Sound enamel blocks that were not treated with resin infiltrant following 96 h of artificial demineralization. (F) Sound enamel blocks treated with resin infiltrant following 6 months of simulated toothbrushing. (G) Sound enamel blocks that were not treated with resin infiltration following 6 months of simulated toothbrushing.