Impacted lower third molars and periodontal health. An epidemiological, methodological, retrospective and prospective clinical, study.

The main objective of this series of investigations was to study periodontal health of the adjacent second molars (M2) in cases of impacted lower third molars (M3) and after impacted lower third molar surgery. An epidemiological study, comprising 693 dentate individuals, was undertaken in order to obtain the prevalence, impaction and positional relationship of third molars in a normal Swedish population. The prevalence of all third molars in individuals aged 20 years was 77.0%. One in four of the vertically positioned third molars, three in four of the mesioangular, nine in ten of the distoangular and all those horizontally placed were impacted to some extent. 68.5% of the impacted third molars were in close proximity to the root of the adjacent second molars. In order to evaluate the precision and accuracy of the radiographic assessment of intrabony defects (IBD), i.e. the distance between the cemento-enamel junction and the bottom of the pocket to firm osseous contact, on the distal surface of M2, a methodological study was performed on 25 subjects. Using conventional free hand technique, intraoral radiographs were taken in the deepest part of IBD with and without a probe as indicator. Comparing the two sets of radiographs, the deviation was 1 mm or less in 87.9% of the cases. The radiopaque marker enhanced the accuracy of assessment of IBD to 96.7%. The effects of impacted lower third molar surgery on periodontal tissues of the M2 area were investigated in a retrospective clinical study comprising 215 subjects. The results two years postoperatively showed a higher prevalence of plaque, gingivitis and periodontal pockets on the distal surface of M2 than on other surfaces of the two molars adjacent to the extraction site. IBD greater than or equal to 4 mm were registered in 32.1% of the cases. The long term effects on periodontal tissues after impacted lower third molar surgery was investigated in a comparative retrospective study, two and four years postoperatively, comprising 51 cases. The improvement concerning postoperative IBD, between the two examinations, was mainly seen in individuals less than or equal to 25 years of age. No case in this age group increased in depth, while 29.6% of postoperative IBD deteriorated in individuals greater than or equal to 26 years. A multiple regression analysis was used to identify some predictors of postoperative IBD, and the material consisted of the 215 cases from the retrospective study.(ABSTRACT TRUNCATED AT 400 WORDS)