Long-term follow-up of delayed development of maxillary right second premolar with inversely positioned corresponding primary molar

Impaction is defined as a condition in which a tooth fails to erupt within a normal range of functional position. The condition is generally found in permanent teeth, while impaction of primary teeth is considered to be uncommon. We previously presented a rare case of delayed development of a maxillary right second premolar with an inversely positioned corresponding primary molar identified in a girl aged 10 years and 4 months. In the present report of the same patient, we show transitional changes in location and developmental stage of the affected permanent tooth and impacted primary tooth noted during periodical examinations over a 5.5 year period. At 13 years and 2 months, the root of the permanent tooth began to develop, after which the root extended to half of the entire length at 15 years and 3 months. At the most recent examination conducted at 15 years and 9 months, the permanent successor had emerged into the oral cavity and the impacted primary molar maintained a similar position close to the inferior wall of the maxillary sinus without any symptoms. Throughout the observation period, the dental age of the maxillary right second premolar was calculated to be approximately 3 to 4 years behind those of the other second premolars. Our findings in the present case led us to consider that careful observation of the developmental stage of an unerupted permanent tooth is important, while no intervention is required before confirming tooth development as the patient grows, even if the dental age of the corresponding tooth is much later than the ages of other teeth.