The Mmaticatory Muscles Activity Changes with Different Bite Height Activators During Dry and Night

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This study was conducted to investigate how the difference of the construction bite height of the activator would make effects on the masticatory muscles activity of functional mandibular protrusion patients during their treatment. They were treated by two different types of activators. One type of the activators employed high construction bite (HBA) which had about 10mm interincisal distance, such as Woodside type activator, and the other type employed low construction bite (LBA) which had about 2mm interincisal distance. The EMG records of the maximum clenching, the gum chewing and the tooth tapping movement were taken at the beginning of the treatment, one month after and five months after the correction of the anterior crossbite. As the results, after the crossbite correction, HBA cases took less time to achieve occlusal contacts in molar area and to stabilize the occlusion than LBA cases. During stabilizing phase, some unstable occlusions were temporarily observed at LBA cases. This finding was supported by the facts that the integrated EMG values of the masticatory muscles of HBA cases during the maximum clenching showed no reduction while some reductions were seen of LBA cases, and the duration of the silent period of the masticatory muscles EMG of HBA cases showed less prolonged tendency than of LBA cases. The masticatory muscles activity with an activator in place during night time sleep was also investigated. HBA like bite block and LBA like bite block were worn by the adults who had the individual normal occlusion during night time sleep and the EMG records of masticatory muscles were taken respectively. In the result of the analysis, no clear differences of the integrated EMG values with the amount of the bite height were observed.