Middle mesial canal of a mandibular first molar--a case report

The mandibular first molar usually has only two mesial canals, a mesiolingual and a mesiobuccal. Cases of a third canal described as the middle mesial canal has been reported and is found to be uncommon. In this case report, three canals in the mesial root of a mandibular first molar were located, prepared and filled. The third canal presented as a fin when during instrumentation the instrument could pass freely between the mesiolingual canal and the middle mesial canal.