Abstract
To clarify the relation between crowding dentition and masticatory function, arch length discrepancy (ALD), t he numbero f interocclusalc ontacts (ICP), and the EMG from four masticatorym uscles were recorded successively in each subject at different Hellman's dental age from II C to NA. The subjects were divided into four groups concerning their dentition at IVA: 1) normal males,2) crowding males,3) normal females and 4) crowding females. The results obtained were: a) At II C, ALD for crowding males and females was not different from each normal group; b) At II C, there was no significant difference between ICP for crowding males and normal males, and for crowding females and normal females, similarly. c) The frequency of free mastication in burst activity at II C and III A for crowding females was significantly larger than that for normal females, and the duration at II C for crowding females was significantly larger than that for normal females, while the difference decreased with increasing age to stage NA. Since functional differences in the EMG were observed at II C without obvious morphological differences, arch length discrepancy may be produced not only by acquired factors after II C, but also by functional factors before II C. Therefore, analysis of EMG recordings in detail at the deciduous stage may help predict a future occurrence of crowding dentition.
