Pre-eruptive intracoronal lesion of a mandibular first molar.

A patient developed an acute apical abscess on a mandibular first molar with an intact occlusal sealant. Radiographs reveal no typical patterns of decay on occlusal or proximal surfaces. An unusual lesion within dentin and an apparent extension from it to the external tooth surface are visible on films at the time of onset of symptoms as well as prior to eruption. Possible explanations for the lesion and its progression are discussed.