FREQUENCY,CLASSIFICATION AND PATHOLOGY OF THE THIRD MOLARS IN TROMS COUNTY,NORTHERN-NORWAY

Abstract

Aim: To investigate the prevalence and condition of third molars associated with the adjacent structures in adults, aged 20 to 35 years, living in Troms County, Northern Norway Methods: This study was a part of a cross-sectional, population-based s tudy Tromstannen ( TOHNN).

Methods: A random sample of 700 20-35 year-olds living in Troms County were invited to participate and orthopantomograms (OPGs) were taken for 505 of them during October 2013-November 2014. Out of 505, 254 OPGs were excluded due to; i) poor quality, ii) none of the third molars presented, iii) incomplete dentition, iv) retainer presence or obvious orthodontic treatment. The remaining 251 OPGs (130 of females and 121 of males with total 763 third molars) were assessed in this study. Calibration of the two assessors was performed by evaluation of ten OPGs (40 third molars) with a maxillofacial radiologist on a calibrated monitor for radiographic purposes under the optimal dim light in a darkroom. Differences were discussed and agreed upon. After two weeks, the OPGs were re-assessed and the inter- and intra-observer reliability were calculated. The position of third molars was assessed according Winter`s, Pell and Gregory`s and Archer`s classifications. The study was approved by the regional ethical committee in Northern Norway (2013/348/REK Nord).

Results: The average number of third molars was 2.5 per person (females 2.35, males 2.67). Vertical angulation was the most common position (325 molars (42,6%)) and 269 molars (35.3%) had disto-angular impaction. The most common impaction in the maxilla was disto- angular (205, 52.4%) and vertical in the mandible (189, 50.1%). There were significantly more molars impacted in mandible (272, 73.5%) compared to maxilla (167, 42.7%) (p<0.0001). Females had a significantly higher number of impacted third molars (242, 63%) than males (198, 52%) ( p=0.002). Sinus approximation to the roots was found in 216 (55.2%) of maxillary third molars. In the mandible 148 (39.8%) of third molars showed at least one radiological sign of a close relation to the mandibular canal. An enlarged follicle was seen in 28 molars (3.7%) of third molars with a significantly higher number in the mandible (p<0.0001). Root resorption of second molar due to the third molar was seen in seven molars (0.9%) all in males.

Conclusions: In the population examined, nearly 60% had at least one impacted third molar and there was a higher percentage in women. In general, it was unlikely to find an enlarged follicle. Root resorption of a second molar due to a third molar was found only in men.