Association between third mandibular molar impaction and degree of root development in adolescents.
OBJECTIVE
To compare the root development and the growth rate of the mandibular third molar (M3 inf) in individuals where the M3 inf erupted vs individuals exhibiting M3 inf impaction.


METHODS
Serial standardized intraoral radiographs (Eggen technique) were taken annually of the mandibular third molar region from 132 subjects (71 male and 61 female) from 15 to 20 years of age. Based on the films, 264 lower third molars were classified into an eruption and an impaction group. Root development was recorded according to a quantitative method described by Haavikko (1970), and the eruption status was analyzed using logistic regression.


RESULTS
In total, 155 (59%) of the M3 inf erupted, and 109 (41%) were impacted at age 20. 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. The more mature a tooth was at age 15, the higher was the probability of eruption (odds ratio: 3.89, P < .001). The growth rate of the root development stage was statistically significantly associated with the probability of eruption (odds ratio: 10.50, P  =  .041).


CONCLUSIONS
Delayed mandibular third molar root development is associated with impaction. Radiographs taken at age 15 may predict the risk of impaction and thereby guide decision making for the orthodontist or the oral and maxillofacial surgeon.
Department of Oral and Maxillofacial Surgery, Faculty of Health and Sciences, Institute of Odontology, University of Copenhagen, Denmark. sorenrodsgaard@gmail.com
Søren Rødsgaard
SR
Lauesen
Jens O
JO
Andreasen
Thomas Alexander
TA
Gerds
Søren Steno Ahrensburg
SS
Christensen
Mette
M
Borum
Søren
S
Hillerup
D000293:Adolescent; D000367:Age Factors; D005260:Female; D006801:Humans; D016018:Least-Squares Analysis; D016015:Logistic Models; D008137:Longitudinal Studies; D008297:Male; D008334:Mandible / Q000000981:diagnostic imaging; D008964:Molar, Third / Q000000981:diagnostic imaging / Q000254:growth & development* / Q000503:physiopathology; D009811:Odontometry; D011446:Prospective Studies; D011862:Radiography, Panoramic; D012737:Sex Factors; D014078:Tooth Eruption / Q000502:physiology*; D014092:Tooth Root / Q000000981:diagnostic imaging / Q000254:growth & development*; D014095:Tooth, Impacted / Q000000981:diagnostic imaging / Q000503:physiopathology*; D055815:Young Adult