Acid challenge exacerbates activation of matrix metalloproteinases in permanent teeth undergoing radiotherapy.

The aim of this study was to investigate the effect of acid challenge on the activation of matrix metalloproteinases (MMPs) in the Dentinoenamel junction of primary and permanent teeth submitted to radiotherapy. For this purpose, a total of 178 dental fragments obtained from molars were used, and randomly divided into 2 groups (primary and permanent teeth) / 4 experimental subgroups (irradiated and non-irradiated, demineralized and non-demineralized). The fragments were exposed to radiation, with a dose fraction of 2 Gy, for 5 consecutive days, until a total dose of 60 Gy was reached, with a total of 30 cycles, for 6 weeks. To determine the activity of MMPs on the dentinoenamel junction (DEJ), in situ zymography assays on 0.6mm dental fragments were performed. To assess whether MMP activity would be impacted by an acidic environment, the fragments were placed in a demineralizing solution (pH of 4.8). The finding was that irradiation activated MMPs in DEJ and these effects were more evident in permanent when compared with primary teeth. When the effect of an acid challenge on MMPs activity was investigated, demineralization was observed not to increase MMPs activity in non-irradiated teeth, but it did increase MMPs activity in irradiated teeth. In conclusion, an acid challenge was found to exacerbate activation of MMPs in DEJ of permanent teeth submitted to irradiation, but not in primary teeth.

Radiotherapy Activates and Protease Inhibitors Inactivate Matrix Metalloproteinases in the Dentinoenamel Junction of Permanent Teeth.

The objectives of this study were to investigate changes in the activity and expression of matrix metalloproteinase (MMP)-2 and MMP-9 in permanent teeth with or without exposure to radiotherapy, and the role of proteinase inhibitors in their inactivation. In situ zymography and immunofluorescence assays were performed to evaluate the activity and expression of two key gelatinases (MMP-2 and MMP-9) in sections of permanent molars, assigned to irradiated and nonirradiated subgroups. Dental fragments were exposed to radiation at a dose of 2 Gy fractions for 5 consecutive days until a cumulative dose of 60 Gy was reached. To evaluate the effect of protease inhibitors on MMPs, teeth were immersed in 0.5 mL of 0.12% chlorhexidine digluconate (CHX), 0.05% sodium fluoride (NaF), 400 µM polyphenol epigallocatechin-3-gallate (EGCG), or distilled water (control) for 1 h. Fluorescence in the dentinoenamel junction (DEJ) was evaluated in 3 areas of the tooth: cervical, cuspal, and pit. These regions were photographed using a fluorescence microscope at 1.25× and 5× magnifications. Results were analyzed using the D'Agostino-Person normality test, and the Kruskal-Wallis, Dunn, and Wilcoxon tests for intergroup and paired comparisons (α = 0.05). The fluorescence intensity/mm2 in the DEJ at the three regions studied was higher in the irradiated teeth (p < 0.05) than in the nonirradiated teeth, revealing regions of expression of MMP-2 and MMP-9 by immunofluorescence. Postradiotherapy treatment with different solutions (CHX, NaF, and EGCG) led to lower fluorescence intensity/mm2 in irradiated teeth than in the control group (distilled water; p < 0.05), as a result of MMP inactivation. In conclusion, irradiation increased gelatinase activity in all regions of the DEJ. Treatment with 0.12% CHX, 0.05% NaF, and 400 µM polyphenol EGCG postradiotherapy inactivated enzyme activity.