Clinical Study Of Mandibular Movement Pre And Post RPD Treatment Among Subjects With Dentition Defects Of Kennedy â…  Or â…¡

Objective To investigate the differential and regularity of mandibular motion track,the electoromyography masticatory muscles and masticatory efficiency pre and post RPD treatment among 8 subjects with dentition defects of Kennedy Ⅰ or Ⅱ.Providing an objective reference and basis to evaluate the efficacy of the RPD restoration.Methods We selected two groups of distal extention edentulous subjects with and without restorative history, each group of 4 cases.Using the SAM axioquick recorder to record the incisal track and rang pre and post RPD treatment in different mandibular movement, including masticatory movement, notch movement and border movement. Evaluating the track features of the condylar kinematic center in the frontal, sagittal and horizontal planes, measuring the protrusive condylar path inclination, detecting the lateral condylar path inclination of non-working side in the sagittal and horizontal planes. Simultaneously, recording the surficial myoelectricity of bilateral masseter and temporalis. At last, measuring one minute masticatory efficiency of each subject by light absorption method. The data was analyzed with SPSS 17.0 software package for paired t test and two independent sample t test.Results 1.The range of chewing movement increased after RPD restored 6 months, the incisal path showed a good regularity and repeatability in the frontal plane.The width of chewing ring increased significantly from 0.73±0.34mm to 2.58±1.01mm(P<0.05) in group Ⅰ2.The incisal border movement showed a better smoothness, repetitiveness, symmetry and anastomosis than previous.3.The range of incisal border movement were increased after a new RPD restored. Range of opening and protrusion increased significantly(P<0.05) among the subjects with restorative history, opening range increased from 31.51±6.37mm to 61.95±12.42mm while protrusion increasing from 4.22±2.85mm to 8.38±1.13mm. However, range of right laterotrusion was less than restored before in group Ⅰ who had never restored, no significant differences were observed(P>0.05).4.The track of condylar center improved obviously in group Ⅰ.The maximum opening curve zigzag and separation were reduced in the frontal and sagittal plane.The symmetry, anatomosis improved significantly in protrusion and laterotrusion. In group Ⅱ, the track of maximum opening and protrusion were more smooth but the rang in three dimensions were decreased than previous. Laterotrusion track was similar to the old denture.5.1n group Ⅰ, the protrusive condylar path inclination,the Fisher Angle and Bennett Angle were increased after RPD restored. The lateral condylar path inclination of non-working side increased obviously from 22.56±44.65° to 55.82±42.26° in the sagittal plane(P<0.05). Bennett Angle increased significantly from 10.26±9.07° to 24.97±0.62°(P<0.05) in group Ⅱ, the rest results were reduced after a new RPD restored, no significant differences were observed(P>0.05). Comparing the change of pre and post new RPD wearing in lateral condylar path inclination of non-working side, there was a significant difference between the two groups(P<0.05).6.New RPD restored later, all cases’ abnormal EMG activity were relieved. The muscle coordination between masseter and temporalis were improved. The cyclicity, regularity, symmetry and masseter biting amplitude increased significantly.7.Wearing new RPD, two groups’ chewing efficiency were improved obviously(P<0.05), changes in group Ⅰ increased from 0.96±0.39 to 1.36±0.20 were more significant.Conclusion 1.Prosthetic treatment later, edge motion trajectory of incisor and condylar center were more smooth and regular than restorde before. Range of motion and movement Angle were close to the normal. Indicating that RPD promoted the mandibular physiological motor function.2.Incisal chewing ring and EMG activity coordination were superior to restored before. New RPD played a role of relieving the masticatory muscles and joint activities in the stomatognathic system.3.Chewing efficiency was improved significantly while denture restoring. Posterior teeth played a major role in chewing function, which losing may reduce patients’ chewing ability, thereby affecting the digestive function. Early restoration should be promoted for the patients who suffered from dentition defects of Kennedy I or II.4.Clinical application of mandibular trajectory and EMG of masticatory muscle can provide an objective reference and basis to evaluate the efficacy of the RPD restoration.