The Effect Of Non-impacted Third Molars On The Condition Of Their Adjacent Teeth

Third molars, the last to erupt, the most frequent to be impacted, are also unfortunately the most frequent to be extracted in the dental arch[1]. The prevalence and pattern of impacted third molars can be very different among different races and regions in the world[2-4].It has always been controversial for the treatment of third molars[5, 6,]. The determination of the treatment plan of third molars needs to consider the different circumstances of each patient and the socioeconomic performance. Many studies have shown that, impacted third molars may be related with many diseases, such as periodontitis, dental caries, periodontal disease, root resorption, and cyst or tumor[7-11]. If a third molar is diseased or affects the health of the adjacent teeth, it is recommended to be removed. However, there hasn’t enough evidences to support the preventive extraction of asymptomatic third molars so far[12, 13].With the growth of the age, impacted third molars were removed gradually, and the proportion of non-impacted third molars is relatively higher[7, 14]. At the same time, more and more third molars have diseases, and the risk to extract the third molar increased gradually. This caused difficulties of clinical treatment of this kind of third molars. However, the research about the effect of the non-impacted third molar to the adjacent teeth is few[7, 15]. The effect of the non-impacted third molar on the health of the adjacent teeth haven’t clear yet[7]. So, it is difficult to make a proper treatment plan for the non-impacted third molar. To solve this problem, we designed this study. Objective:To investigate the prevalence of non-impacted third molars and the influence of them on the condition of adjacent second molars.Methods: 1 A cross-sectional study of the prevalence of non-impacted third molars.This cross-sectional study was performed in patients who were referred to the School of Stomatology between August 2015 and October 2015 and obtained an orthopantomogram. Patient’s age and gender and other epidemiological data were obtained from their cases. Prevalence of non-impacted third molars was obtained from orthopantomograms. The level of impaction and angulation of impacted teeth were also discussed by Pell and Gregory classification and Winter’s classification, respectively.2 A retrospective study of the effect of non-impacted third molars on the conditions of adjacent second molars.The records of 2395 patients were examined continued with study one. New inclusion and exclusion criteria were used for enrollment. Distal caries, external root resorption and alveolar resorption of second molars were examined through orthopantomograms. The odds rations(OR) of pathologies of second molars were valued with the third molars were non-impacted and impacted, respectively.3 A retrospective study of the effect of non-impacted third molars on the periodontal status of adjacent teeth.This retrospective study was performed in patients who were referred to the Department of Periodontology from Sep. 2014 to Jun. 2015. Subjects over 18 years old with at least 1 intact molar area and third molar in this quadrant being absent or non-impacted were enrolled in this study. Second molars were compared for periodontal pathology based on the presence or absence of a visible non-impacted third molar in the same quadrant. Periodontal measures included Gingival index(GI), plaque index(PLI), probing pocket depth(PPD), clinical attachment level(CAL), gingival recession and bleeding on probing(BOP) on 6 sites on third molars and adjacent second molars. Logistic regression was conducted in quadrant. The main independent variable was presence or absence of third molars assessed visually.4. Statistical analysis:All patients were examined using a standard chart established for teaching purposes, including the eruption status of third molars, the presence of caries, and periodontal disease of adjacent second molars. Data collected were entered into a spreadsheet(Excel 2007; Microsoft, US) and analyzed by SPSS(18.0, Chicago, US). Collected data were subjected to different types of statistical analyses such as X2 test, t-test and logistic regression models.Results:Among the 2395 patients evaluated, 1958 patients(37.2±17.0 yr.) were included, with 774 males and 1184 females. 45.1% of the included patients had at least one non-impacted third molar and 44.1% of the all the examined third molars were non-impacted. Besides, we also found that 54.3% of the patients had at least one impacted third molar. The most prevalent type of impaction angulation and level was mesioangular(37.3%) and level C(47.1%), respectively.6695 second molars from 1958(37.2±17.0 yr.) patients were examined for the prevalence of caries, external root resorption and alveolar resorption. With the non-impacted third molar adjacent, the prevalence of caries, external root resorption and alveolar resorption was 10.0%, 0.8% and 40.4%, respectively. Non-impacted third molars didn’t increase the risk of having caries or external root resorption of adjacent second molars. A non-impacted third molar was associated with 1.77 times the odds of the alveolar resorption of adjacent teeth(P<0.001).In the cross-sectional study, 135 subjects(43.7% male, 40.6±11.5 years) were enrolled in this study; 105 subjects had at least one quadrant with 3 intact molars and the third molar is non-impacted(Subjects A). Other 30 subjects had at least one quadrant with first and second molars while without third molar(Subjects B). There was no significant difference between Subjects A and B in demographic characteristics. Clinical parameters including GI, PLI, PPD, CAL, BOP and PPD5+(at least one site with PPD ? 5 mm) were significant higher in Subjects A when compared with those parameters in Subjects B.Conclusions:There was a high prevalence of non-impacted third molars in the study population. Both the retained impacted and non-impacted third molars can significantly increase the risk of illness of adjacent second molars. The presence of a non-impacted third molar has a negative effect on the periodontal condition of the adjacent second molar.