The Difference Of Occlusal And Maxillofacial Characteristics In RP-ICP In Malocclusion Patients With TMD

The etiological mechanism of temporomandibular disorders(TMD)is complex among which the relationship between occlusion and TMD is controversial.Some scholars believe that occlusion or centric occlusion(CO)-centric relation(CR)discrepancy is a potential factor causing TMD,that is,discrepancy of CO-CR will lead to occlusal instability,which may lead to temporomandibular joint dysfunction and develop into TMD.Roth put forward the orthodontic concept of "functional occlusion".In addition to the stability of static occlusion,we should also pay more attention to the coordination of CO-CR,so as to ensure the long-term stability of orthodontic results.Therefore,in the pre-orthodontic clinical examination,doctors pay more attention to the status of temporomandibular joint,occlusal and jaw position.So what are the differences of occlusal and maxillofacial characteristics in malocclusion patients with TMD in different jaw positions,and is there any correlation between discrepancy of jaw position and the occurrence of TMD? The purpose of this study is to study the changes of occlusion and maxillofacial characteristics of malocclusion patients with TMD in intercuspal position(ICP)and reference position(RP),including the difference of mandibular position,condylar position and occlusal relationship,so as to help orthodontists introduce jaw position factors in the design of orthodontic plan,obtain stable orthodontic effect,and provide reference for the diagnosis and treatment of TMD.Objective:By analyzing the changes of condylar position,mandibular position and occlusal relationship in different mandibular positions of RP-ICP,the differences of occlusal and maxillofacial characteristics of RP-ICP in malocclusion patients with TMD were discussedMethods:Patients and volunteers recruited from the Department of Orthodontics of Tianjin Stomatological Hospital between 2017 and 2019 were divided into four groups:normal occlusion subjects without TMD(group A),normal occlusion subjects with TMD(group B),malocclusion subjects without TMD(group C)and malocclusion subjects with TMD(group D)according to the diagnostic criteria for the most temporomandibular disorders(DC/TMD)and the diagnostic criteria of individual normal occlusion.Condylar position measurement(CPM)was used to locate the position of condyle in RP and ICP,and the displacement and direction of condyle in three-dimensional direction from RP to ICP were measured by vernier caliper.Lateral cephalograms were taken at RP and ICP,cephalometric measurements were made with GAMMA Document Browser and the difference of measurement was calculated.The sagittal displacement of molars,the change of overjet and overbite and the midline displacement were measured from RP to ICP.All the data are averaged three times and analyzed by SPSS20.0 statistical software.Results:1.In anterior-posterior direction,there were significant differences in condylar displacement between group A and group B,group C and group D,group A and group D(P <0.01),group D was larger than group A than group C.Vertically,the displacement of the right condyle in group D was larger than that in group A,and the difference was statistically significant(P<0.05).There was no significant difference among the other groups.The difference of transversal displacement of condyle among the four groups was not statistically significant.When the mandiblular position from RP to ICP,there are eight different directions of condylar deviation in the sagittal plane: anterior-superior,anterior-inferior,posterior-superior,posterior-inferior,forward,backward,upward,and unchanged.The largest proportion of condylar displacement was anterior in group A and group D,accounting for 35% in group A and 42.5% in group D,while more condylar displacement was found in group B and group C,accounting for 50% and 33.33%,severally.Among the four groups,the condyle without deviation was the most in group A.2.There were significant differences in SNa Pog between group A and group B,group C and group D,group A and group D(P<0.05),the difference between group A and group D was more significant.There were significant differences in Facial Depth and LFH between group C and group D,group A and group D(P<0.05),group D was higher than group A and group C.3.Under the two different jaw positions of ICP and RP,the change of molar relationship in group B was larger than that in group A,and the difference was statistically significant(P<0.05).There were significant differences in overbite,overbite and molar relationship between group A and group D,group C and group D(P<0.05).The changes of overbite,overbite,molar relationship and midline displacements in group C were larger than those in group A,but the difference was not statistically significant.There was no statistical difference in midline displacement among the four groups.Conclusion:1.In normal occlusion subjects with TMD,sagittal condylar displacement of RP-ICP,changes of mandibular position and the molar relationship were often observed.2.In malocclusion patients without TMD,the changes of condyle displacement,mandible position and occlusal relationship in different jaw position were not significantly different from normal occlusion subjects without TMD.3.Malocclusion patients with TMD had larger RP-ICP discrepancy than those normal occlusion subjects without TMD,specifically manifested in vertical and sagittal condylar displacement,mandibular position and occlusal relationship changes.4.The condylar displacement,change of mandibular position and occlusal relationship in RP-ICP are interrelated and influence each other.