Infraocclusion of primary molars: an epidemiologic and familial study

Abstract The prevalence of infraocclusion of primary molars was studied in 1059 Swedish children aged 3–12 years with an even distribution between the age groups. No extractions were performed due to infraocclusion. 94 children (8.9%) showed infraocclusion of primary molars Infraocclusion was found from 3 years of age. The prevalence varied between age groups, with a maximum of 14.3% in 8-and 9-year-old children and a minimum of 1.9% in 12-year-old children 49 children had a single tooth in infraocclusion. The primary mandibular molars were affected more than 10 times as often as the maxillary. The prevalence of infraocclusion of primary mandibular first molars rose to a maximum at 8 years. The prevalence of infraocclusion of the primary mandibular second molar showed a similar patten but with a 1–2-year delay, up to a maximum in 9-year-old children. After this age the mandibular second molar was the tooth most commonly found in infraocclusion. In a study of 138 3–12-year-old siblings of 109 children with infraocclusion the prevalence of infraocclusion was found to be 18.1 %. When compared with the frequency in the total material (8.9%), the difference proved to be significant, supporting the hypothesis that there is a familial tendency in infraocclusion of primary molars. The mode of inheritance is discussed and it is concluded that the most likely explanation is that the condition is inherited on a multifactorial basis.