Six-Year Changes in Position and Periodontal Status of Retained Third Molars in Young Adults

Abstract

This study was designed to assess the changes over time in third molar position and periodontal status in asymptomatic subjects who had at least one third molar below the occlusal plane at enrollment, and retained all third molars from baseline to follow-up. Healthy subjects with four asymptomatic third molars and adjacent second molars were enrolled in an IRB-approved longitudinal trial. Inclusion criteria for these analyses dictated that patients have at least one third molar below the occlusal plane at enrollment and have a follow-up of at least 4 years from enrollment. At enrollment and longest follow-up full mouth periodontal probing, at six sites per tooth, including third molars was conducted. Third molars were initially categorized as “probed” or “not probed.” The periodontal status of the third molar region was defined as the periodontal probing depth (PD) for 6 sites around the third molars and the 2 sites on the distal of the second molars. A PD >4mm in the third molar region was considered indicative of periodontal pathology. Panoramic radiographs were taken at baseline and follow-up to assess the degree of eruption in relation to the occlusal plane, and angulation in relation to the long axis of the adjacent second molar. Descriptive statistics were employed for these analyses. Data were analyzed from 72 subjects with a total of 288 third molars. Fifty-seven percent were male; 81% were Caucasian. The median age at enrollment was 22.7 years (IQ 19.0-29.5y). Median follow-up was 6.0 years (IQ 5.0-7.0y). At baseline, 84% (241/288) of third molars were below the occlusal plane. At longest follow up, 27% (66/241) of these teeth erupted to the occlusal plane. At baseline, 80% (194/241) of unerupted third molars were not probed. At longest follow up, 34% (66/194) of these unerupted third molars were probed. If third molars could not be probed at follow up, 56% (72/128) of second molars had a PD >4mm. If third molars erupted during the course of the study, 70% (46/66) had a PD >4mm in the third molar region. Of all erupted third molars at follow up, 68% (77/113) had at least one PD >4mm in the third molar region. The angulation of third molars was variable during the course of the study. Fifty-seven percent (138/241) of third molars that were unerupted at baseline changed angulation; 25% (60/241) of these teeth changed angulation and erupted to the occlusal plane. Forty-five percent (78/175) of third molars that remained unerupted at follow up had changed angulation during the course of the study. Unerupted third molars change position over time and may become exposed to the oral cavity. This can lead to colonization by pathogens in an oral biofilm causing chronic inflammation with periodontal pathology. Therefore, unerupted third molars should be monitored as long as the teeth are retained.