OBJECTIVE In the past decades, X-rays have been used widely for diagnosis in dentistry. However, it is well known that ionizing radiation causes damage (including single- and double-strand breaks) to deoxyribonucleic acid (DNA) and DNA-protein crosslinks, and induces cellular death. Therefore, outlining the cytogenetic effects induced by X-ray is necessary to identify the degree of cancer risk and minimize potential risks to patients and clinicians. To date, a variety of assays have been proposed in cytogenetic biomonitoring studies, including those that assess metaphase chromosomal aberrations and sister chromatid exchanges, and micronucleus and single-cell gel (comet) assay. METHODS Cytogenetic biomonitoring studies focusing on oral mucosa cells in individuals exposed to dental X-ray were reviewed. RESULTS Dental X-ray can induce DNA damage and cytotoxicity in oral mucosa cells. CONCLUSIONS These results will contribute to a better understanding of X-ray-induced effects upon the cellular system in individuals continually exposed to known genotoxic/cytotoxic agents.