Comparative Evaluation Of Temporomandibular Joint Responses To Maxillary Protraction Treatment Outcomes Between The Early Permanent Dentition And The Late Mixed Dentiton Of Skeletal Class Ⅲ Malocclusions

Objective: In this study,the patients of the late mixed dentition and late permanent dentition were treated by maxillary protraction and temporomandibular joint reponses to maxillary protraction treatment were analyzed by X-ray to compare and analyze temporomandibular joint reponses in the two groups and to investigate the remodeling and characteristics of temporomandibular joint responses to maxillary protraction treatment of different types of malocclusion.This study was to provide the basis for the clinical treatment of skeletal class Ⅲ patients.Method: 58 patients were selected,among them,29 patients with late mixed dentition,with an average age of(9.7±1.16)years(16 males and 13females);29 patients with early permanent dentition,with an average age of(12.9±0.99)years(18 males and 11 females).All patients were treated with maxillary premature traction,the average treatment time of(13.45±1.28)months.All patients underwent X-ray cephalometric lateral radiographs(SOREDEX,CRANEX TOME CEPH)before and at the end of the treatment and established a coordinate system to analyze the remodeling of glenoid fossa,condyle and temporomandibular joint space.The study included 14 angle measurement items and 25 line distance measurement items.In this study,SPSS21.0 paired samples t-test was used to evaluate the remodeling of the temporomandibular joint with maxillary protraction in the early permanent dentition and late mixed dentition.The independent sample t-test was used to compare remodeling of the temporomandibular joint in different types occlusion.Result:1 Changes in temporomandibular joint of late mixed dentition:(1)changes in the gleniod fossa: in the sagittal direction,the whole glenoid fossa was posterior displacement,the difference was significant(P<0.01);while in the vertical direction,the location of the glenoid fossa did not change significantly(P>0.05);(2)changes in the condyle: in the sagittal direction,the whole condyle posteriorly displaced,the difference was significant(P<0.01);in the vertical direction,only the front of condyle was displaced downward(P<0.05);(3)changes in temporomandibular joint space: only posterior joint space was significantly reduced(P<0.05).There was no significant difference between the anterior joint space and the upper joint space(P>0.05).2 Changes in temporomandibular joint of early permanent dentition:(1)changes in glenoid fossa: the glenoid fossa had no significantly displacement occurred in the sagittal and vertical directions(P>0.05);(2)changes in condyle: there were no significant displacement of condyle in the sagittal direction(P>0.05).While only the anterior condyle has significantly posteriorly: the anteriojoint space,upper joint space and posterior joint space had no significant difference after maxillary protraction treatment(P>0.05);(3)changes in temporomandibular joint space: there was no significant difference in the anterior joint space,the upper joint space and the posterior joint space(P>0.05).3 Comparison in temporomandibular joint of late mixed dentition and early permanent dentition:(1)comparison of changes in glenoid fossa: in the sagittal direction,the upper glenoid fossa in the early mixed dentition had moved(1.18±1.45)mm,which was higher than the posterior displacement(0.19±1.55)mm of the upper glenoid fossa in the early permanent dentition(P<0.05);the difference of the posterior margin position between the two groups was also significant(P<0.01).The displacement of the posterior glenoid fossa was significantly larger than that in the early permanent displacement of posterior glenoid fossa in the early mixed dentition was(0.88±1.80)mm,while the displacement in the early permanent dentition was(-0.02±1.67)mm.There had no significant differences in the vertical direction between the late mixed dentition and the early permanent dentition(P>0.05);(2)comparison of changes in condyle: in the sagittal direction,displacements of the condyle in the late mixed dentition were significantly larger than which in the early permanent dentition(P<0.05),(0.84±1.69)mm in the late mixed dentition was higher than that in the early permanent dentition(0.01±1.58)mm.(1.03±1.47)mm in the late mixed dentition was higher than that in the early permanent dentition(0.18±1.49)mm.The direction of displacement of the condylar process in the late mixed dentition was opposite to that in the early distension group.(0.88±1.80)mm in the late mixed dentiton,while the upper margin of the early dentition group’s displacement was(0.02±1.67)mm;both of the groups had no significant difference of the condyle’s displacement in the vertical direction(P>0.05);(3)comparison of changes in joint space: there was no significant difference in the anteroposterior space,the upper space and the posterior space of the late mixed dentition group and the early permanent dentition group.Conclusions:1 After maxillary protraction,the late mixed dentiton and early permanent dentition of skeletal class Ⅲ malocclusion patients’ temporomandibular joint position has changed,the changes of the late mixed dentiton are more obvious than these of the early permanend dentiton.2 After maxillary protraction,late mixed dentiton of class Ⅲmalocclusion’s temporomandibular joint fossa and condylar obvious posteriorly shift.3 After maxillary protraction,the posterior joint space of the late mixed dentiton class Ⅲ malocclusion obviously reduces.