Primary retention of first permanent mandibular molars in 29 subjects.

This study consisted of two parts: the first part describes the aetiology behind primary retention of first permanent mandibular molars by comparing the affected molar region with the contralateral region, and the second the follow-up of the retained molars. The material comprised dental pantomograms from 29 patients (17 males and 12 females; aged 6 years 2 months to 12 years 5 months) which were sent by Danish public dental clinics to the Department of Orthodontics at Copenhagen Dental School for treatment guidance (Part 1). Questionnaires were later sent to the dentists for follow-up information regarding the affected teeth (Part 2). Part 1-aetiological evaluation: From each radiograph, the number and location of the molars, maturity of individual molars, and deviations from normal morphology were recorded. The findings showed that, in an affected region, disruption of normal dental development and eruption had occurred, causing a delay in dental maturity as well as arrested eruption of the first molar. Part 2-follow-up of eruption: Completed questionnaires and radiographs were returned for 25 subjects. In 10, eruption had occurred, six after surgical removal of mucosa covering the retained first molar. In eight patients the molar had been removed while in seven the observation time from first diagnosis was too short to evaluate eruption. The results indicate that retained first permanent mandibular molars have the ability to erupt and suggest that a unilaterally retained first permanent mandibular molar may represent a temporary delay in eruption rather than permanent failure.