Phosphoric acid (P.A.; 37%) can induce necrosis on the oral mucosa and cause the ulceration of periodontal tissue. However, most studies reported are clinical case studies, with few basic science studies on oral epithelial cells. Our study aimed to investigate the effects of dental acid etchants on oral epithelial cells. After treatment with dental acid etchants for the indicated periods (0 second, 10 seconds, 30 seconds, 1 minute, and 5 minutes), cell damage, including vacuoles, pyknosis, and karyolysis, was observed by hematoxylin-eosin staining. The percentage of cell damage significantly increased after 10 seconds of etchant application. Furthermore, as the etchantapplied time increased from 10 seconds, 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay results showed that cell viability was significantly reduced. Dental acid etchants were diluted with distilled water at ratios of 1:2 (18.5% P.A.) to 1:10 (3.7% P.A.). After the application of 1:5 (7.4% P.A.) diluted etchants, cells were enlarged, with some cells showing nuclear injury, including pyknosis. When treated with 1:2 (18.5% P.A.) diluted etchants, karyorrhexis and vacuoles were observed. The percentage of damaged cells significantly increased after the application of 1:2 (18.5% P.A.) diluted etchants. Moreover, cell viability significantly decreased in cells treated with 1:5 (7.4% P.A.) and 1:2 (18.5% P.A.) diluted etchants. This study examined the effects of dental acid etchants on oral epithelial cells as a basic experimental study in vitro and demonstrated the risks of dental acid etchants. Therefore, dentists and dental hygienists should pay strict attention to the handling of acid etchants during restoration and orthodontic treatments.

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