Bolton ratios in a sample of black South Africans

One of the many factors inherent in a good occlusion is the balanced proportionality in the sizes of the upper and lower teeth. Disproportion in the size of individual teeth may result in a malocclusion related to this discrepancy. It is therefore important in diagnosis and treatment planning to determine the amount and location of any tooth-size discrepancies that may exist. Bolton in 1958 developed two equations to calculate the mesio-distal crown size ratios between permanent maxillary and mandibular teeth. Bolton's anterior and overall ratios were 77.2% (SD +/- 1.65) and 91.3% (SD +/- 1.91) respectively. These ratios were used to identify areas of space deficiency or excess in the maxillary and mandibular arches. Individual teeth may differ in size in relation to gender and population groups; Blacks, for example, having generally larger teeth than Caucasians. The purpose of this study was to obtain measurements from a sample of Black South Africans and to compare the ratios derived from these when using the method described by Bolton, with those measurements that were obtained in Bolton's study of 55 Caucasian subjects having ideal occlusion. One hundred study models with excellent occlusion, were selected from the archives of patient records of the Department of Orthodontics, Medunsa Oral Health Centre, University of Limpopo. An equal number of males and females were selected. The anterior and overall tooth-width ratios were calculated from the data of this sample. The ratios obtained for the male and female groups did not differ significantly, although the teeth of males were significantly larger than those of the females. The anterior ratio was found to be 77.26% (SD +/- 2.65), equivalent to Bolton's anterior ratio of 77.2% (SD +/- 1.65), whereas the overall ratio was 92.31% (SD +/- 2), significantly larger than Bolton's overall ratio of 91.3% (SD +/- 1.91). The results indicate that the anterior ratio may be particularly useful when assessing and planning aesthetic alignment of the anterior segment. The overall ratio may be considered less clinically significant and its use in orthodontic treatment planning may require further investigation using the peer assessment rating.