Bolton's ratio variations in Angle's Class I, Class II and Class III malocclusions: An observational study.

Background: The aim of this study was to compare Bolton's Overall and Anterior ratio in different types of malocclusions.

Material and methods: 105 study cast were taken from the patients undergoing orthodontic treatment and they were divided into three classes based on molar relation, i.e. Angle's Class I (n = 35), Angle's Class II (n = 35) and Angle's Class III (n = 35) according to the Angle's classification of malocclusion. The mesio-distal widths of all maxillary and mandibular teeth from right first molar to left first molar were measured with a digital calliper. The findings were then used to calculate the anterior and total Bolton's ratios. Statistical analysis was done using ANOVA and Tukey's test.

Results: The mean total ratio for the whole sample was 91.4±3.33, which is very close to Bolton's proposed ideal ratio. The anterior ratio for the whole sample was found to be 77.4±9.02, which is also similar Bolton's proposed ideal ratio. In Class I patients, the mean total ratio calculated was 91.2 ± 2.69, that is close to Bolton's proposed ideal ration and the mean anterior ratio calculated was 79.2±3.78, which is greater than Bolton's proposed ratio that signify increased mesio-distal width in mandibular anterior segment. The total mean ratio calculated for Class II was 91.1 ± 3.44) and for Class III patients was 92±3.77. The anterior mean ratio for class III patients was 78.6±5.24 and for Class II patients was 76.8± 5.28 which indicates higher anterior ration for class III patients and lower anterior ratio for class II patients compared to Bolton's ideal ratio that signifies mandibular anterior tooth material excess in Class III patients and maxillary anterior tooth material excess in class II cases.

Conclusions: In this study population there was increased mesio-distal width in mandibular anterior segment in patients with Class I and Class III malocclusion. Also, there is maxillary anterior tooth material excess in Class II patients. Key words:Angle's classification, Anterior ratio , Bolton's Ratio , Inter-arch relationship, Overall ratio.