A 4-year-old Japanese girl was referred to the Pedodontic Clinic of the Tohoku University Dental Hospital for treatment of a completely impacted second deciduous molar and gingival swelling at the site of the tooth.
Oral examination showed that all deciduous teeth except the lower left second deciduous molar had erupted, and all of them were carious. Examination of the lower left second deciduous molar by X-ray photographs revealed that the tooth was completely impacted and had a radiolucent caries-like lesion in the mesial half of the occlusal surface. It was also shown that the tooth germ of the lower left second premolar, which was a successor to the impacted tooth, was located between the impacted tooth and the first molar.
The impacted tooth was extracted, and was shown to have gross caries as indicated by the X-ray photographs. Due to the mesially inclined eruption of the lower left first molar, the space for the second premolar was lost. To regain the space, the first molar was moved to the distal by using a bilatelal splitbasetype space regainer.
The pathological factor(s) for the tooth impaction was not determined. Development of the caries of the impacted tooth may have been due to the bacterial invasion from the periodontal pocket. It is probable that the impacted tooth caused an abnormality in the location of the tooth germ of the second premolar.