Research On The Effect Of Different Dentist Operation Postures To The Self-comfort And The Emg Of Neck And Shoulder Muscles

The backbone of the newborn is made up of the meta-prominence of Brustwirbel and Resurrection bone, both of which contain the viscera of pectoral cavity and pelvic cavity. Three months after birth, babies begin raise their heads, and form the permanent lordotic neck flexure to keep balance of their head. Eighteen months after birth, when the children learn to walk, the permanent lordotic lumbar flexure will form to make the body straight above the sacrum. In this way, four flexures of the back bone which are unique for human beings are formed. The back bone coordinates with the surrounding muscle tissue, functioning normally under healthy conditions. Because of the heavy pressure from working, less exercise and holding the same posture for a long time, the over pressure on neck and over load of neck muscles leads to the structural distortions of cervical flexion, oppression of cervical nerve and vertebral artery, inducing the symptoms of neck pain, headache, dizziness, tinnitus, insomnia, cranial nerve weakness, and neurasthenia. For instance, dentists and computer operators, who keep a posture such as bowing or slanting head for a long time, will induce shoulders and neck muscle ache and dysfunction. The scientific study showed that, the main reason of neck and shoulder muscle ache was the long-time posture and unhealthy postures.This research got the quantified data through analysis on the self-comfort index and the muscle function of neck and shoulder of dentists with different postures in different period of time to objectively analyze the influence on shoulder and neck muscles with different postures, and provide a research and theory foundation for the standardization of dentists postures.The first research was the effect on self-comfort index and the EMG of neck and shoulder between dentist and non-dentist with three different postures.20 dentists with 10 years working experience were selected as experimental group, and 20 non-dentists were selected as control group.(non-computer operators).The VAS method was applied to evaluate the self-comfort index of dentists with different postures which are Proprioceptive Derivation station(P1),lower head with 45 degrees position(P2) and lower plus right inline head with 45 degree position (P3), within different periods of time(15s, 30s, 60s). Besides, the electromuograph (EMG) area and the symetric index of the Stermocleidomastoideus (SCMM) and trapezius in three postures were recorded.Comparing the self-comfort index inside the dentist group with three different postures within 15 seconds and 30 seconds and that of the non-dentist group, the P1 posture index was lower than that of P2 posture and that of P3 posture. Within 60 seconds, the self-comfort index consequence of the two groups with three postures was P1<P2<P3. That is to say, the self-comfort index of P1 posture was minimum and P1 was the most comfortable posture. The self-comfort index of P3 was maximum and P3 was the most uncomfortable. Along with the changing of the three postures and the prolonging of the lasting time, the self-comfort index was increasing. It showed that the unhealthy posture was the major cause induced shoulders and neck muscle ache. Through the comparative study of the dentist group and the non-dentist group in P2 posture and P3 posture, the self-comfort index of dentist group was higher than non-dentist group within 30 seconds and 60 seconds. The dentists were more sensitive than non-dentists on three operating postures, and the adaptive index of the P2 posture and the P3 posture was much lower.The measurements of the EMG area of neck and shoulder muscles in the dentist group and the non-dentist group with three postures within 60 seconds showed that EMG area of SCMM and trapezius in the dentist group was significantly larger than that of the non-density group, no matter in the left side or the right side. That is to say, the tension of neck and shoulder muscle of density group was larger than the non-density group, regardless of the postures. Comparing the value of EMG area inside the dentist group in three postures within 60 seconds and that of the non-dentist group, when the value of SCMM area P1 posture was lower than that of P3 posture of the dentist group, long-time keeping head on the right side made the right ECMM contract and be in tension. Within the dentist group, there was no significant difference of the value of the trapezius area in three postures and the value of left SCMM in the three postures. Within the non-dentist group, there was no significant difference between the value of the EMG area in three postures and the value of trapezius area in three postures. From the comparative results of symmetric index of the EMG area of the three postures in P3 posture within 60 seconds, the asymmetry index of SCMM of dentist group was significantly higher than that of the non-density group. The dentist group was closer to 1, the bilateral SCMM of the dentists showed more asymmetry. However, there was no significant difference of the symmetry of EMG in the three postures within 60 second within the dentist group and within the non-dentist group. This experiment confirmed that, the most comfortable posture in the dentist group was the Pd position, the least comfortable posture was 45 degree position, the much higher muscle tension, the more asymmetry of SCMM.The second part was the research on the effect on self-comfort index and the electromuograph (EMG) of neck and shoulder between dentists with 10 years working experience and dentists with 5 years working experience with three different postures. Measuring the EMG and symmetric index of the EMG, self-comfort index was same as the first part.In the second part, 20 dentists with 10 years working experience were selected as group 1 (G₁), and 20 dentists with 5 years working experience were selected as group 2 (G₂).Comparing the self-comfort index inside these two groups with three postures within 60 seconds, the P1 postures index was significantly lower than that of P3 posture, that is to say, the most comfortable posture was P1 posture, and the most uncomfortable posture was P3 posture. However, there was no significant difference of self-comfort index between G₁ and G₂ in the same posture within the same time.Through the comparative study of the three postures within 60 second in two groups, which was based on the EMG area of neck and shoulder muscles, P1 posture index was lower than that of P3 posture, and there was no significant difference in muscle tension of neck and shoulder between densities who with 5 years and 10 years working experiences. The research compared the value of the EMG area respectively inside the G₁ group and the G₂ group in three postures within 60 seconds. The value of the right of SCMM in the P1 posture was lower of that of the P3 posture, and the comparing result of the value of the right trapezius was the same in the G₁ group. The two comparison result was the same in G2 group. It indicated that within the G1 and G2 group, the right of SCMM and the right trapezius was in tension in P3 posture and the muscle function was greatly changed. However, there was no significant difference in the left of SCMM with three postures.For the comparative study of the symmetry of EMG area of the three postures within 60 second between these two groups show that for the symmetry of the left and right side of the trapezius muscle in the P3 postures, the groups of the dentists who had 10 years working experience was significantly higher than that of the 5 years group. The symmetric index was closer to 1 and more asymmetrical in the group of the dentists who had 10 years working experience. and there was no significant difference of the symmetry of EMG of the three postures within the G1 group and G2 group.The second experimental result showed that, the P1 posture was the most comfortable posture, no matter the years of being a dentist. It also showed that the muscle tension could be affected by postures, for example, the muscle tension in P1 posture was lower, and the muscle of neck and shoulder was much more symmetrical in 5-year working experience dentist group than the 10 years'.Experimental results:1. The Pd postures should be encouraged, for its high degree of self-comfort, low muscle tone, functional coordination of the bilateral muscle, and smaller effect of neck and shoulder muscles. 2. The self-comfort of the clinical dentists could be affected by unhealthy postures, and on the muscle tension of the neck and shoulder of the dentists.