9 - The Main Occluding Area between opposing teeth during chewing: a comparison between Australians and Japanese

Summary

ABSTRACT

The Main Occluding Area (MOcA) defined by Kato (1996) has been found to almost always be located between the upper and lower first molars in Japanese. However, there have not been any reports of this feature in other human populations. In this study, the location of the MOcA was assessed in a sample of 80 Australian dental students as part of an exercise relating to dental occlusion. A piece of stopping material was used to locate the MOcA and to determine the preferred chewing side. There was no significant difference between published findings for Japanese and those for Australians in relation to the location of the MOcA, nor were there any significant differences between the ethnicities represented within the Australian sample. However, there was a difference between ethnicities within the Australian sample in the preferred chewing side, with Asians displaying a preference for the left side. We propose that the location of the MOcA is relatively stable across human populations, having been derived from the tribosphenic biting system of the earliest mammals. The difference observed in preferred chewing side between Europeans and Asians may relate to differences in the use of food utensils between these groups.

INTRODUCTION

During human chewing behaviour, only limited contact occurs between opposing surfaces of the dental crowns. Kato et al. (1996) examined the nature of this contact in Japanese and defined the region where maximum contact occurred as the Main Occluding Area (MOcA). He found that the MOcA was usually located between the functional cusps, ie supporting cusps, of the upper and lower first molars. The importance of this feature when chewing food, is that one tends to clench and begin to chew on the MOcA. An understanding of the position of the MOcA is important for dental treatment and also for placing the pattern of modern human masticatory activity into a broader evolutionary perspective.