The important objectives of orthodontic treatment are to achieve excellent occlusion with Class I molar and canine relationship, normal overbite and overjet. Interarch tooth width proportion is an important factor in achieving these objectives. Tooth size is actually the “seventh key” to normal occlusion.1 Bolton’s analysis is widely used to assess tooth size discrepancy that helps in achieving excellent finish at the end of the treatment.
Tooth size discrepancy may vary in different population and ethnic groups. Gender differences have also been observed. Although there are various studies on Bolton’s analysis in different population and ethnic groups, few studies have reported tooth size discrepancies in Indian population. There is no published study on Bolton’s ratios in a South Indian population. Hence the aim of the study will be to assess the Bolton’s tooth size discrepancy in a sample of south Indian population.
6.2 Review of Literature:
Bolton2, 3 (1958, 1962) studied the maxillary and mandibular tooth size proportions on 55 patients with excellent occlusion. The casts were selected from a large number of excellent occlusions, most of which were treated orthodontically(non-extraction). The sample consisted of 44 orthodontically treated and 11 untreated subjects. The maximum mesiodistal widths of all teeth except second and third molars were measured on each cast. He established ideal ratios of anterior and overall maxillary and mandibular tooth size. The anterior and overall ratios were calculated by using the formulae. The mean value of anterior ratio was 77.2 ±0.22. The mean value of overall ratio was 91.3 ±0.26.
Prasad KK and Valiathan A4 (1994)compared norms for Indian and Chinese using Bolton’s index. Fifty cases each of normal Angle’s Class I occlusion were selected and measurements were carried out on casts. The overall ratio for Indian sample was 93.46 and for Chinese sample it was 90.84. No significant difference was apparent in the two groups.
Smith SS, Buschang PH, Watanabe E5 (2000) studied interarch tooth size relationships of three populations - whites, blacks or Hispanics. They collected pre-orthodontic casts of 180 patients and digitized forty-eight mesiodistal contact points on each model. They observed that the segments of males were significantly larger than females; the overall and posterior ratios were also significantly larger in males than in females.
posterior ratios were also significantly larger in males than in females. They concluded that interarch tooth size relationships are population and gender specific. Bolton ratios apply to white females only; the ratios should not be indiscriminately applied to white males, blacks or Hispanics.
They concluded that interarch tooth size relationships are population and gender specific. Bolton ratios apply to white females only; the ratios should not be indiscriminately applied to white males, blacks or Hispanics.
Bernabe E, Major PW and Flores-Mir C6 (2004) studied tooth-width ratio discrepancies in a sample of Peruvian adolescents. Two hundred children were selected and their casts were measured with a sliding caliper and a vernier scale. No significant differences were found in anterior and total tooth size sums according to sex. Then combined male and female anterior and total ratio was calculated. There were clinically significant tooth size discrepancies in almost one third of the sample.
Al-Tamimi T and Hashim HA7 (2005) studied tooth-size ratios in a Saudi sample with Class I normal occlusion. And compared tooth-size ratios between the present study and Bolton's study and between genders. Dental casts and cephalometric radiographs of 65 subjects (37 males and 28 females) were used in this study. The age range was 18 to 25 years. They found that there were no statistically significant differences between the mean values of the anterior ratio and the overall ratio of the present study and the mean values reported by Bolton and also between genders. Further, the results revealed a low correlation between the anterior ratio and the interincisal angle.
Paredes V, Gandia JL and Cibrian R8 (2006) did a study on Bolton ratio on Spanish population. They used a digital method and measured the casts to the nearest 0.05 mm. The sample consisted of 100 pairs of dental casts of Spanish subjects. They found out that twenty-one percent of the subjects had a significant anterior discrepancy and five percent had a total discrepancy. Differences between Spanish values and Bolton’s were significant.
Wedrychowska-Szulc B, Janiszewska-Olszowska J and Stepien P9 (2010) compared overall and anterior Bolton ratios in different malocclusion groups with Bolton’s standards. The material comprised of 600 pre-treatment study casts. Statistically significant differences were found for the mean overall ratio when compared with the original Bolton norm for the whole study group, as well as for patients with Class I and III malocclusions when the mean anterior ratio was compared with the original Bolton norm. Significant differences were observed in all groups of malocclusions for both genders. Discrepancies exceeding 2 SD were found in 31.2% of the studied population for the anterior ratio when compared with Bolton’s norm. The highest mean values for anterior ratio were in males with Class I (79.1) and Class III (80.1) malocclusions.
Dhar HCS, Bora M 10 (2010) studied the applicability of the Bolton’s tooth size ratio to Assamese population. Seventy Assamese subjects, having normal occlusion were selected. No statistically significant differences were found among males and females for the anterior and overall ratios. The anterior ratio was significantly higher from Bolton’s standard while the overall ratio was not. The anterior ratio showed a statistically significant difference and was lower than the ratio found in the Han Chinese and Blacks. The anterior ratio also showed a discrepancy from Bolton’s standard > 2SD in 27.14% of samples. The overall ratio showed a deviation>2SD in only 7.14% of the samples from Bolton’s standard which indicates that the majority of the samples are within 2 SD of Bolton’s mean overall ratio.
6.3 Aims and Objectives of the study: The aim of the study is to assess the Bolton’s tooth size discrepancies in a sample of South Indian population.
Objectives of the study :
To determine the Bolton’s anterior and overall ratios
To compare the ratios to Bolton’s norms
To determine gender differences
To test if any correlation exists between anterior and overall ratios
Method The sample will include both untreated and orthodontically treated dentitions (non-extraction). Informed consent will be taken from the untreated subjects to participate in the study. A total of fifty good quality study casts will be collected. Maximum mesio-distal widths of all teeth excluding second and third molar will be measured with a digital caliper to an accuracy of 0.01 mm. Anterior and Overall ratio for each cast will be calculated by Bolton’s formulae.
Sum mandibular 6 teeth
___________________ × 100 = Anterior ratio
Sum maxillary 6 teeth
Sum mandibular 12 teeth
_______________________ × 100 = Overall ratio
Sum maxillary 12 teeth
Only five pairs of casts will be measured per day to prevent the visual fatigue.
In order to determine method error, the study models of ten randomly selected individuals will be measured again two weeks later by the same examiner. The method error will be analysed by using Dalhberg’s formula.
The mean, standard deviation, co-efficient of variation for anterior and overall ratios will be calculated.
Student’s t-test will be used to compare the anterior and overall ratio in males and females. Pearson’s correlation test will be used to determine the correlation between anterior and overall ratio.