Bolton ratios on a sample of South African blacks

Abstract

Good occlusion requires that teeth be proportional in size. If large upper teeth occlude with small lower teeth, it would be almost impossible to achieve ideal occlusion. The concept of ideal intercuspation assumes a strict relationship between tooth size and the size of maxillary and mandibular arches. Specific dimensional relationships must exist between the maxillary and mandibular teeth to ensure proper interdigitation, overbite, and overjet. It is important to determine the amount and location of tooth size discrepancies that may exist as a part of treatment planning. The relationship between maxillary and mandibular tooth sizes were established by Wayne A. Bolton in 1958 on a Caucasian sample. Bolton’s anterior ratio was 77.2% (SD 1.65) and the Bolton overall ratio was 91.3% (SD 1.91) (Bolton, 1958). Previous studies have shown that populations differ with respect to inter-arch tooth size relationships, and Blacks have larger teeth than Caucasians (Schirmer and Wiltshire, 1997; Khan, Seedat, and Hlongwa, 2007). A ratio that has been formulated on a Caucasian sample will over calculate or over predict tooth size discrepancies when used on a Black sample (Richardson and Malhotra, 1975; Smith, Buschang and Watanabe, 2000). The purpose of this study was to establish mesio-distal tooth width ratios for a select sample of South African Blacks. One hundred study models of untreated cases with excellent occlusion were obtained from the Department of Orthodontics archive records at the Medunsa Oral Health Centre, University of Limpopo. This sample were of South African Blacks (50 males and 50 females) selected according to a set criteria. The mesio-distal widths of permanent teeth up to and including the xvii first permanent molar in each arch were measured using a digital vernier caliper. The anterior and overall tooth width ratios were calculated on this sample. The mean, range and standard deviation were calculated for the size of the teeth, and a co-efficient of variation was obtained for the tooth size ratio. The results indicated that the male and female groups did not differ significantly and were therefore combined into one group. A 2-sample t-test was used to test for the statistical difference between means. The tooth size ratios obtained were compared to the Bolton’s ratios. Ninety five percent confidence intervals were calculated for the anterior and overall tooth width ratios for the select sample of South African Blacks. The anterior ratio was found to be 77.26% (SD 2.65), equivalent to Bolton’s anterior ratio 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). These results indicated that an overall tooth size ratio of this select sample differed from that of Bolton’s overall ratio and therefore, Bolton’s overall ratio may not be fully applicable to this select sample. KEY WORDS: Tooth size, tooth size discrepancy, Bolton’s ratios, South African Blacks.