Related Factors Of Distal Interproximal Caries In The Mandibular Second Molar Caused By The Compacted Mandibular Third Molar In Yanbian Area

Objective:To analyze the related factors of distal proximal caries of the mandibular second molar induced by impacted mandibular third molar(MTM),providing a reference for clinical preventive removal of high-risk MTM and caries prevention of adjacent second molars.Method:A total 500 panaromic radiography of MTM impacted patients who were treated in the Department of Stomatology of the Affiliated Hospital of Yan Bian University from October 2017 to October 2019 were selected.The clinical data(gender,ethnicity)of all patients were recorded,and it was categorized as aged 17-30 years old group and 31-63-year-old group.The effect of the posterior margin of the mandibular second molar on the impacted condition of the MTM were analyzed on all patients under panaromic radiography.Also,analysis of the correlation between impaction of the mandibular third molar and distal proximal caries of the mandibular second molar includes MTM impaction depth,impaction,direction,impaction angle,eruption status,the distance between the mesia cemento-enamel junction(CEJ)of MTM and the distal CEJ of mandibular second molar.Eventually,further analyze the influence of the impacted mandibular third molar on the severity of distal proximal caries of the mandibular second molar.Univariate analysis results were used for significant factors and logistic regression was used for multivariate analysis.Results:1.The gap between the posterior margin of the mandibular second molar in men(13.5mm)is larger than that in women(11.1mm;P<0.001);as the gap decreases,the impaction depth gradually increases(P<0.001);as the gap increases,the degree of eruption gradually increase(P<0.001);This gap has no statistical significance for different impacted directions of MTM.2.In 500 cases,the prevalence of the distal proximal caries of the mandibular second molar was 37.6%,which has no statistically differences from ethnicity and gender.While the age difference was statistically significant(P<0.001)that the prevalence of caries was 50.8%for those who aged over 30 years old.3.The influence of different types of impacted MTM on the incidence of distal proximal caries of the mandibular second molar was statistically significant(P<0.001),and it is highest when the impaction occurs mesially(49.0%)and distally(68.2%).4.The influence of different angles of impacted MTM on the incidence of distal proximal caries of the mandibular second molar was statistically significant(P<0.001),and it is highest when the impaction angle is between 40°-80°.5.The influence of eruption status of impacted MTM on the incidence of distal proximal caries of the mandibular second molar was statistically significant(P<0.001),and it is highest when the eruption is partial.6.The influence of the distance between the mesia cemento-enamel junction(CEJ)of MTM and the distal CEJ of mandibular second molar on the incidence of distal proximal caries of the mandibular second molar was statistically significant(P<0.001),and it is highest when the distance between them is 4-6mm.7.The results of Logistic multivariate analysis showed that distal proximal caries of the mandibular second molarhe is easily induced under the circumstances of impaction high site and impaction medium site,mesial impaction,impaction angle lower than 80° and entirely or partial erusion at the age of 31-63 years.However,CEJ distance is not an independent factor of caries.8.The influence of distal proximal caries of the mandibular second molar on the impaction depth and impaction angle was statistically significant(P<0.001);the severity of caries in the group aged 17-30 years old was less than that in the group aged 31-63 years old(P=0.001);there was no statistical difference in the median,low and high impaction depth,and the severity of caries in patients with an impaction angle of 40°-80° is greater than that with impaction angle<40°and impaction angle>80°(P<0.001).Conclusion:1.The posterior margin space of mandibular second molars has an influence on the impaction of MTM.2.There was no statistical significance on the incidence of distal proximal caries of mandibular second molar.3.The severity of distal proximal caries of the mandibular second molar increases when the MTM impact angle is between 0°-80°,especially when between 40°-80°.4.The patient’s age and impacted condition are of great significance to the impact of impacted MTM on the distal proximal cariesof the second molar.Therefore,it can be considered that a preventive removal should be done as early as possible of the fully and partially erupted MTM when the impaction angle is found to be less than 80°before the age of 30,especially at the high and median proximal position.