Abstract:
One of the most important things in Orthodontic diagnosis is the relationships between teeth and jaws size. The teeth will align well with effective occlusal relation according to not only the size and shape of the jaws or teeth but also the relation between teeth size and jaw size. Because of lacking of Thais Standard, today orthodontic diagnosis for Thai patients are forced to utilize the Caucasians, that is terrible. The objective of this study was to search for the relation of size between upper and lower arches, ratio of the sum of upper incisors to lower incisors and the equation that could predict the arch width and arch height from sum of incisors. A Sample whose age ranging from 9-16 years, was composed children, 160 males and 160 females. For the reason that Bangkok Metropolitan is the center of Thai people from all districts. Samples were selected from many populations in Bangkok such as school children, patients in Government hospitals and private dental clinics. The criteria was set to select the child that has not loss as any teeth from first molar of one side to first molar on the other side, well aligned teeth, normal teeth form and shape and Angles Class I occlusion. Selected sample had their jaws recorded by irreversible hydrocolloid impression material and casts were measured. Manipulations of the raw data are Two Way ANOVA, Pearson Product-Moment of Correlation, Simple Regression. The results reveal the difference of arch width between two sexes. Mean of male arch width slightly larger than that of female. Upper and lower arch width are highly correlated, correlation coefficients were 0.9749 in the anterior and 0.9324 in the posterior, and those values are statistically significant at .01 level. The ratio of the sum of upper incisors to lower incisors is 1.3959. The prediction of arch width and arch height equation are in the form (Y ) ̂= a+bX. Further study should be done on the different types of arches and longitudinal study of annually growth of the jaws more over. The problem in this study was to select the samples that meet the requirement.