By Joanna Lyford, Senior medwireNews Reporter
Delayed root development of the mandibular third molar (M3 inf) at age 15 years predicts subsequent impaction, according to a prospective observational study.
The researchers surmise that radiographic assessment of teenage patients could help dentists and orthodontists with treatment planning.
The etiology of M3 inf impaction is complex and no accurate prediction method has yet been developed. In this study, Søren Lauesen (University of Copenhagen, Denmark) and team monitored a cohort of 132 young patients to identify risk factors for impaction.
The participants, 71 of whom were male, underwent standardized intraoral radiographs of the M3 inf region annually between the ages of 15 and 20 years. By the end of this period, 155 (59%) of the M3 inf had erupted and 109 (41%) were impacted.
In 44 (33%) patients both M3 inf were impacted, in 21 (16%) patients one tooth was erupted and the contralateral tooth impacted, and in 67 (51%) patients both M3 inf were erupted.
Based on examination of radiographs at age 15, Lauesen and team categorized root development stage for right and left M3 inf for each participant. They used a quantitative method that describes eight discrete stages, from stage 5 (crown three-quarters completed) to stage 12 (apex closed).
At age 15, median root development of M3 inf was at stage 8, indicating the transition from initial root formation to one-quarter root length.
However, median root development at age 15 was lower, at stage 7, among participants whose M3 inf subsequently impacted. This difference was apparent in both male and female patients, note the authors.
Indeed, in logistic regression analysis, the stage of root development at age 15 was a significant independent predictor for the probability of eruption at age 20, with an odds ratio of 3.89 per 1-stage increment.
The growth rate of the root development stage was also significantly associated with the probability of eruption, with an odds ratio of 10.50.
Writing in The Angle Orthodontist, the researchers say that their finding could aid decision-making by dentists, orthodontists, and oral and maxillofacial surgeons. It could also be useful in the field of forensic science to help determine biologic age post-mortem.
They conclude: "Radiographs taken at age 15 may predict the risk of impaction… The association between delayed root development and impaction needs further investigation to determine its relative importance in the multifactorial etiology of third mandibular molar impaction."
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