Evaluation Of The Effection Of Mandibular Third Molars On Pathological Changes Of Mandibular Second Molars

Objective: Study the impacts on mandibular second molar(MSM) periodontal-endodontic pathological changes including distal alveolar bone resorption(DBR) and distal proximal caries(DPC)with different eruption status of mandibular third molar(MTM).To provide experimental data for the clinical judgment of MTM’s threaten to adjacent teeth. Methods: The samples which were retrospectively analyzed were collected from 500 patients’ CBCT databases of Stomatological Hospital of Chongqing Medical University Oct.2013 to Oct.2015. The five groups were as follows: 25 to 34 years old,35 to 44 years old,45 to 54 years old,55 to 64 years old,after 65 tyears old,each group of 100 cases. Using software built in CBCT-imaging systems to measure the distance between enametocemental junction of the left MSM to the bottom of the bony defect beiside root(CEJ-BD), root length of the left MSM,the distance between MTM mesial cementoenamel junction and MSM distal cementoenamel junction(TMCEJ-DCEJ), the angle of occlusal plane of MSM and MTM(AOP). Simultaneously we recorded the impacted type of MTM,the situation of MSMDPC,caries in MTM and the patients’ age.Using SPSS19.0 statistical software for statistical analysis: To comparative analysis the extent of mesial and distal alveolar bone resorption, the impaction on the extent of MSMDBR and the situation of MSMDPC with different AOP, TMCEJ-DCEJ, impacted types of MTM, patients’ age.To analyze the situation of caries of MTM with aging. Results First, comparison of the extent of mesial and distal alveolar bone resorption: It can be considered the degree of DBR was significantly greater than the extent of mesial alveolar bone resorption before 65 years old(P<0.05) and the gap got smaller and with increasing age. The difference was not statistically significant after 65~years old(P>0.05). Second,Comparison of the degree of mesial and distal alveolar bone resorption in different ages: It was statistically significant in the extent of mesial and distal alveolar bone resorption(P<0.05). But the change modes of the mesial and distal alveolar bone resorption were different:mesial’s increased by degrees but distal’s increased the interval.Third, The correlation between the degree of DBR and eruption status of MTM or patients’ age: 1) Nonparametric Kruskal Wallis test analysis showed the influence on the degree of DBR with different AOP, TMCEJ-DCEJ, impacted types of MTM and patients’ age was statistically significantly different(P<0.05).2) Single factor ordinal logistic regression analysis was used to show the dgree of MSMDBR had relativity with different AOP, TMCEJ-DCEJ, impacted type of MTM, patients’ age. Multivariate ordinal logistic regression analysis was used,results showed AOP and patients’ age were independent influencing factors of the dgree of MSMDBR. It may be judged that the greater degree of DBR in elder, but after 55 years old there was not different in the extent of absorption. The extent of DBRwas the most serious when AOP was in the range of 11o~79o. Risk factors for MSM were smaller when MTM in lower impaction than higher impaction. It was not determined that TMCEJ-DCEJ was independent factors. Fourth, the correlation between MSMDPC and eruption status of MTMS or patients’ age:1) Chi-square test analysis showed the impaction on the situation of MSMDPC with different AOP, impacted types of MTM, patients’ age was statistically significantly different(P<0.05).But there was not significantly different with different TMCEJ-DCEJ(P>0.05).2)Using single factor ordinal logistic regression analysis, the older the incidence rate of DPC was greater. The incidence rate of DPC was greater when AOP was in the range of-10o~ 10oand 11o~79othan the other range’s.It can be judged that the incidence rate of was greater when AOP in the range of 11o~79othan in the range of-10o~ 10o. No difference in the effects of TMCEJ-DCEJ and impacted type of MTM on MSMDPC. 3)Applying multivariate ordinal logistic regression analysis, AOP and patients’ age were independent influencing factors for MSMDPC, Fifth, there was statistically significant difference in caries of MTM with different age groups(P<0.05), it can be considered that the older the incidence was greater.Pairwise comparison showed that after 55 years old the change was not significantly notable.Conclusion First,When the AOP is in the range of 11o ~ 79o MTM is most serious risk factor for distal periodontal-endodontic of MSM. Second, patient’s age is independent factor for distal periodontal-endodontic of MSM,the more serious lesions with aging.But after 65 years old MSMDBR and caries of MTM do not change significantly, so it’s not supported that removing MTM unessentially when the patient is older than 65 years old.Third, TMCEJ-DCEJ is not independent influencing factors for distal periodontal-endodontic of MSM,that is we can’t judge distal periodontal-endodontic of MSM according to TMCEJ-DCEJ. Fourth, it was suggested that CBCT can accuratly evaluate the effection of eruption status of MTM on distal periodontal-endodontic of MSM,this method is worth popularizing in clinical.