Around 60,000 years ago in Siberia, a Neanderthal opened their mouth so that a rotten tooth could be drilled — and the case is the oldest evidence of an intentional dental treatment to date, a new study finds. A lower molar tooth belonging to a Neanderthal adult was originally unearthed in 2016 , but it was not clear what had caused the deep hole in its surface. Now, experimental evidence indicates the hole was made with a small stone drill used to clean out bits of severely rotten tooth tissue, according to a study published Wednesday (May 13) in the journal PLOS One . This intricate procedure shows Neanderthals — our closest human relatives who lived from around 400,000 to 40,000 years ago — had the brains to recognize this painful tooth cavity could be treated and possessed the fine motor skills to successfully execute the procedure.…