Radiation from dental radiographs is quite minimal and very safe for healthy patients to be exposed to. This chart shows the amount of radiation a person receives from various activities.

Dental X-Ray Radiation Comparison Chart_Page_1

Sources
https://www.radiologyinfo.org/en/info.cfm?pg=safety-xray
https://www.epa.gov/radiation/radiation-sources-and-doses
https://www.epa.gov/radiation/calculate-your-radiation-dose
https://www.nrc.gov/about-nrc/radiation/health-effects/info.html#dose
http://www.ada.org/en/member-center/oral-health-topics/x-rays
https://www.ncbi.nlm.nih.gov/pubmed/15897284
https://www.ncbi.nlm.nih.gov/pubmed/18762634