Mandibular first molar root canal retreatment with the presence of a missed middle mesial root canal: a report of two cases

Aim: The purpose of the present case report is to document the root canal retreatment of two mandibular first molars with a previously unnoticed MMC. Summary: Mandibular molars may present a third root canal in the mesial root, defined as middle mesial root canal. This challenging anatomical variation should not be disregarded by the clinicians in order to minimize the possibility of an endodontic failure. This paper reports two cases of non-surgical endodontic retreatment of the mandibular first molar in which this complexity of the root canal system was missed in the first treatment, which may help to explain the treatment failure resulting in a periapical diagnosis of asymptomatic and symptomatic apical periodontitis in the first and second case, respectively. Key learning points: The use of magnification, with the dental operating microscope, and of ultrasonic tips was of the utmost importance in locating this additional root canal orifice. Both cases were able to achieve a successful outcome only after a correct chemical-mechanical disinfection and three-dimensional obturation of all identifiable anatomy.