Analysis Of Different Jaw Movements In Patients With Chewing-side Preference By FMRI

A highly precise nervous control system regulates and coordinates the activities of the entire masticatory system. At the same time, mastication has great effects on brain function as well as general health. Although it has been widely carried out on the research of central regulation mechanism on mastication in the world, however, the underlying mechanism hasn't been demonstrated completely. Functional magnetic resonance imaging (fMRI), as an advanced non-invasive neuroimaging technique, has made rapid progress in this field these years. The emerging of fMRI allows investigators to assess functional-anatomical concordances bilaterally and three-dimensionally. A chewing-side preference(CSP) is a preference for one side of the dentition during chewing. It sometimes results from other diseases of stomatognathic system. And long-term CSP may have great effects on the teeth, the peridontal membrane, the masticatory muscle and the temporomandibular joint. But its etiopathogenesis is not clear now. So it is important to explore central regulation mechanism of patients with CSP. The aim of the present study is to observe the effects of mastication of different pattern on brain function in patients with CSP by fMRI.This study consists of the following three parts:Part 1. Analysis of brain activity during clenching in patients with CSP by fMRI.Objective: To observe brain activity during clenching task in patients with CSP and to explore the effects of CSP on brain cotical response during clenching task. Methods: Three groups of right-handed subjects were studied, one group was nine patients with left CSP, one group was nine patients with right CSP, and another group was ten volunteers with healthy full and vital dentition. The subjects of the three groups performed the maximum voluntary clenching in intercuspal position, and block designed BOLD functional MRI scan covering the whole brain was carried out. The fMRI data were analyzed by SPM2 software with statistic t-test to generate the activation map. Results: In this study, two subjects in each test group were excluded because of excessive head motion andmachine trouble. Seven out of nine patients were available. 1.Group map analysis: During the clenching task, the primary motor cortex(Ml)N sensory cortex > insulan lentiform nucleus of basal ganglia > prefrontal cortex ^ parietal cortex and temporal cortex were all activated in the subjects of three groups. And there were some differences as follows: (1) The right Ml was activated in patients with left CSP. And the left Ml was activated in patients with right CSP. Moreover, the signal intensity of Ml in the patients was less than the healthy volunteers. (2) Supplementary motor area (SMA) was activated in patients with left CSP. But there was no activation in the SMA of the healthy volunteers and patients with right CSP. (3) Among three groups, the inferior frontal gyrus and inferior parietal lobule were most significantly activated in patients with right CSP. 2. Individual-based analysis: There was activation in the parahippocampal gyrus in four among seven patiens with left CSP. But there was no activation in the parahippocampal gyrus among the healthy voluntreers and patients with right CSP. Conclusions: l.CSP may change the central regulation mechanism of clenching task to some extent. 2. There may be some relationship between contralateral hemispheric dominance and chewing-side preference in Ml responsible for clenching task. 3. SMA may play an important role in regulating clenching task of patients with left CSP. 4.The prefrontal cortex and parietal cortex play a crucial role in regulating clenching task, especially in patients with right CSP. 5.The parahippocampal gyrus was activated in patients with left CSP, which may be related to the biting force increases.Part 2. Analysis of brain activity during bilateral chewing in patients with CSP by fMRI.Objective: To observe brain activity during bilateral chewing in patients with CSP and to explore the effects of CSP on brain cotical response during bilateral chewing. Try to find the pathogenesis of CSP from central regulation mechanism. Methods: Three groups of right-handed subjects were studied, one group was nine patients with left CSP, and one group was nine patients with right CSP, and another group was ten volunteers with healthy full and vital dentition. The subjects of the three groups performed the task of bilateral chewing, and block designed BOLD functional MRI scan covering the whole brain was carried out.The fMRI data were analyzed by SPM2 software with statistic t-test to generate the activation map. Results: In this study, two subjects in each test group were excluded because of excessive head motion and machine trouble. Seven out of nine patients were available. Group map analysis: 1. During the bilateral chewing, the activated pixels were in the unilateral or bilateral precentral gyrus > inferior frontal gyrus> parietal cortexN insulaN cingulate gyrus> thalamus> cerebellum and lentiform nucleus of basal ganglia. 2. The signal intensity of left Ml was significantly greater than right Ml in patients with right CSP. And only the signal intensity of left Ml was increased in patients with left CSP. Moreover, the value of cluster didn't satisfy the parameter requirement. But the signal intensity of right Ml was greater than left Ml of healthy volunteers. 3. Except for the usual chewing-related cortical activation, bilateral substantia nigra of midbrain was activated in patients with left CSP. And the BOLD signal in the right side was much greater. 4. The activation of the right inferior parietal lobule in patients with right CSP and the right inferior frontal gyrus in patients with left CSP was much greater than the activation of Ml. But the BOLD signal of Ml in the healthy volunteers increased significantly. Conclusions: l.CSP may change the central regulation mechanism of bilateral chewing to some extent. 2. There may be some relationship between contralateral hemispheric dominance and chewing-side preference in Ml responsible for bilateral chewing in patients with right CSP. 3.Compared with the right Ml, the left Ml plays an important role in regulating bilateral chewing of patients with left CSP. There's no obvious hemispheric dominance of Ml. Moreover, the substantia nigra of midbrain is activated. Whether this regulation mechanism is associated with the pathogenesis of CSP should be investigated further. 4.The right inferior parietal lobule in patients with right CSP and the right inferior frontal gyrus in patients with left CSP may play more important role than Ml in regulating bilateral chewing. The result of this study further confirmed that the prefrontal cotex and parietal cortex might play an important role in human chewing.Part 3. Analysis of brain activity during unilateral chewing in patients with right CSP by fMRI.Objective: To observe brain activity during unilateral chewing in patients with right CSP and to explore the character of regulation mechanism of brain coticalresponse on unilateral chewing in patients with right CSP. Methods: Two groups of right-handed subjects were studied, one group was nine patients with right CSP, the other was ten volunteers with healthy full and vital dentition. The subjects of the two groups performed the task of unilateral chewing, and block designed BOLD functional MRI scan covering the whole brain was carried out. The fMRI data were analyzed by SPM2 software with statistic t-test to generate the activation map. Results: In this study, four subjects were excluded because of excessive head motion and machine trouble. Five out of nine patients were available. The individual-based analysis showed as follows: l.BOLD signal increased in the unilateral or bilateral precentral gyrus> postcentral gyrus. supplementary motor area > premotor area> prefrontal cortex, temporal cortex -. insula, cerebellum % cingulate gyrus and occipital cortex during unilateral chewing. 2.The cortical activated regions were significantly wider during right chewing than left chewing in patients with right CSP. But there appeared to be no significant differences between right chewing and left chewing in the healthy volunteers. 3. The signal intensity of right Ml was significantly greater than left Ml of the four patients among five during left or right chewing. However, in the healthy volunteers, the cortical activation of left Ml was much greater during left chewing. And there was no significant tendency of the activation of Ml during right chewing. Conclusions: 1.Right CSP may change the central regulation mechanism of unilateral chewing to some degree. 2.The cortical activated regions were significantly more comprehensive during right chewing than left chewing in patients with right CSP. Patients with long-term CSP couldn't properly chew with the contralateral teeth, which might have effects on the cerebral blood flow. cerebral developments recognition, memory, and so on. 3.There may be some relationship between ipsilateral hemispheric dominance to the CSP and Ml responsible for regulating unilateral chewing in patients with right CSP. It seems that the regulation mechanism of Ml on different jaw movements isn't completely identical. However, the sample of our experiment is limited, we need further investigation to confirm it.