Association Between Over-erupted Third Molar And TMD

Objective To study the association between occlusal contacts from over-erupted third Molar and TMD.Methods 45 patients with TMD were selected as experimental group(15 cases(group A)with unilateral mandibular third molar over-eruption,15 cases(group B)with unilateral maxillary third molar over-eruption,15 cases(group C)with unilateral mandibular and the contralateral maxillary third molar over-eruption),and 15 cases with normal occlusion as control group.Data of occlusal contacts were recorded with T-ScanⅢ during the intercuspal position,protrusive movement and lateral movement.Craniomandibular index(CMI),visual analogue scale(VAS)and mandibular motor function before and after the extraction of over-erupted third molar(s)were evaluated.Results In each experimental group,the movement of center of force(MCOF)increased,and the closure time(CT)、lateral disclosure time(LDT)and protrusive disclosure time(PDT)were longer than those in the control group(P<0.05).MCOF、CT、LDT、PDT after the extraction of over-erupted teeth decreased compared with that before extraction(P<0.05),but larger than that of control group(P<0.05).The asymmetry index of contact in each experimental group increased during both intercuspal position and protrusive movement(P<0.05),and decreased after the extraction(P<0.05).The incidence of premature contact、protrusive interference and lateral interference in each experimental group were significantly higher than those in normal control group(P<0.05),and there was no significant difference in the incidence of premature contact and lateral interference between experimental group and control group after extraction(P<0.05).The CMI and VAS of TMD patients decreased significantly 1 month after the third molar(s)extraction(P<0.01).The maximum vertical opening(MVO),protrusive and lateral movement distance increased,and the differences were statistically significant.Conclusion ⑴Bilateral occlusal symmetry,balance and stability are poor in patients with third molar(s)over-eruption.⑵The occlusal interference caused by the hyper-erupted third molar(s)is closely related to the clinical symptoms of TMD.Removing the over-erupted third molar(s)can better improve the opening type and vertical opening of the patients with TMD,and relieve the joint noise and pain to a certain extent.