Primary failure of eruption or severe infra-occlusion: a misdiagnosis?

The literature considers primary failure of eruption (PFE) and infra-occlusion as two separate clinical entities and there are no clearly identified signs and symptoms that aid to facilitate a definitive diagnosis between these two conditions. Therefore, it is the purpose of this report to illustrate a case to emphasise the potential for misdiagnosis when categorising these conditions as two separate clinical entities.

A 5-year-old Chinese boy was referred for the management of an unerupted primary mandibular left second molar tooth (75). Intra-oral examination revealed a primary dentition, with a PFE of tooth 75. He was scheduled for surgical removal of tooth 75 and placement of a space maintainer. Following improvements in the position of tooth 75 in the subsequent visits, the surgical option was disregarded and eventually tooth 75 erupted and exfoliated despite apparent mechanical obstructions.

During the 6-year follow-up period, tooth 75 moved mesially resorbing the distal root of tooth 74 which was later extracted to facilitate the eruption of tooth 75; which then underwent normal exfoliation.

While the present case could indicate the unpredictability of infra-occluded teeth, it is postulated that infra-occluded teeth erupt to the occlusal plane and then remain static due to mechanical obstructions, while the adjacent teeth accompany the growing alveolar bone. Conversely, teeth with PFE do not erupt and the mechanical obstructions are secondary factors. Therefore, the patient's age, at the time of diagnosis, may lead to the diagnosis of infra-occlusion; but it could have been PFE.