| Objective: The aim of the study is to screen patients with unilateral mastication throughoral epidemiological survey and compare with the group with bilateral chewing.Theincidence of unilateral chewing has been analyzed; The another purpose is to comparethe mandibular movement trajectory and surface electromyography (sEMG) in thegroup of unilateral chewing with the group with bilateral chewing and to analyzemandibular movement characteristics in unilateral mastication group. It may provide thefoundation for further study of control mechanisms underlying unilateral chewing andthe experimental basis or appropriate theoretical basis to diagnose and prevent andcorrect the habit of unilateral chewing at the early stage finally.Methods:1) Epidemiological survey:263undergraduate students(127males and136females, age19.64±1.17years) who majored in Stomatology School in WannanMedical College were cluster sampled and evaluated by mens of clinical examinationand their oral health survey. The detection rate of the people with unilateral chewing.2)Screening and grouping the cases, detecting the surface electromyography and thetrajectory of mandibular incisor point simultaneously:30subjects(15males,15females)were checked out by random selection from the cases with unilateral chewing as thecase group, while screening30patients(15males and15females) by random selectionfrom the subjects with bilateral chewing as the case group. The sEMG of massetermuscle and anterovent of digastric muscle were separately recorded and the trajectoryof mandibular incisor point were recorded simultaneously in the group of bilateralchewing and the group of unilateral chewing in the mandibular postural position(MPP),maximum opening and closing movement and chewing.The results were used for statistical analysis.Results:1) There were89people (44males,45females, age19.53±1.13years)presenting the habit of unilateral chewing from a population of263subjects surveyed,The prevalence of unilatral mastication was33.84%; The incidence of unilatralmastication between males and females had no significance.2) There was no statisticaldifference in asymmetry index of masseter muscles and asymmetry index of anteroventof digastric muscle masseter during MPP, maximum opening and closing movement andchewing between the males and the females among bilateral chewing subjects. Therewas significantly statistical difference in asymmetry index of masseter muscles duringchewing between the males and the females among unilateral chewing group(P<0.01).There was no statistical difference in average electrical peak during MPP, maximumopening and closing movement and chewing between the males and the females inbilateral chewing subjects. There was significantly statistical difference in averageelectrical peak of LDA during maximum opening and closing movement between themales and the females among unilateral chewing group(P<0.01).3) asymmetry index ofmasseter muscles during MPP, maximum opening and closing movement and chewingin unilateral chewing group were higher than those in bilateral chewing group(P<0.05).AsDA during MPP and chewing in unilateral chewing group were higher than those inbilateral chewing group(P<0.05). Average electrical peak of LDA and RDA atmaximum opening and closing movement and chewing in unilateral chewing groupwere lower than those in bilateral chewing group(P<0.05). Average electrical peak ofLMM during chewing in unilateral chewing group were lower than those in bilateralchewing group (P<0.05).4) The jaw tangent point trajectory during opening movementand during closing movement was separate in unilateral chewing group. There werestatistically significant at the opening type or opening time between bilateral chewinggroup and unilateral chewing group(P <0.05); The shape of the mandibular incisorpoint trajectories is not smooth and uneven distributed at chewing in unilateral chewing group. There were statistically significant of opening time during chewing betweenbilateral chewing group and unilateral chewing group(P <0.05); Morphologicalcharacteristics of the mandibular incisor point trajectories from the maximum openingto intercuspal position were statistically significant in unilateral chewing group(P<0.05)compared with the bilateral chewing group.5) The trajectory parameters of mandibularincisor point during MPP, maximum opening and closing movement and chewing wereno statistical difference between the males and the females among bilateral chewingsubjects. There was significantly statistical difference in displacement of lateral duringmaximum opening and closing movement between the males and the females amongunilateral chewing group(P<0.05).6) The vertical displacement and the sagittaldisplacement during maximum opening and closing movement in unilateral chewinggroup were significantly lower than bilateral chewing group(P<0.01); The displacementof the left side during chewing movement in unilateral chewing group was lower thanbilateral chewing group(P <0.05); The displacement of anterior and posterior duringchewing movement in unilateral chewing group was higher than bilateral chewinggroup(P<0.05).7) In bilateral chewing group group: There was significant positivecorrelation between the average peak potential of MM and maximum closing velocity,or vertical displacement during chewing movement. In unilateral chewing group: Therewas significant positive correlation between the average peak potential of LDA andmaximum silent speed, or anterior and posterior displacement during MPP. There wassignificant positive correlation between the average peak potential of MM anddisplacement on the right side during maximum opening and closing movement. Therewas significant positive correlation between the average peak potential of LMM andmaximum closing velocity, vertical displacement, or lateral displacement, or sagittaldisplacement at chewing movement.Conclusions:1) The prevalence of unilatral mastication is33.84%; The incidence ofunilatral mastication between males and females has no significance.2) During MPP, maximum opening and closing movement and chewing, the bilateral symmetry ofmasseter muscles in unilateral chewing people is higher than bilateral chewing group;during MPP, maximum opening and closing movement and chewing, the bilateralsymmetry of anterovent of digastric muscle in unilateral chewing people is higher thanbilateral chewing subjects.3) Average electrical peak of LMM, LDA and RDA inunilateral chewing group decreased.4) Trajectory shape disordered relativly, the trackof open and close focus on one side, opening time shortened and67%individualspresented concave closing path in the vicinity of the intercuspal position duringchewing movement in unilateral chewing group. Jaw tracking deflects to working sideand isolated when opening and closing for50%individuals, Opening degree decreasedduring chewing movement in unilateral chewing group compared with bilateral chewinggroup.5) There is positive correlation between the average peak potential of MM anddisplacement on the right side during maximum opening and closing movement,between the average peak potential of LMM and vertical displacement, or lateraldisplacement,or sagittal displacement at chewing movement. It shows that unilateralchewing leads to changes in muscle performance, and result in trajectory anomalies atthe same time. |
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