A systematic review and meta-analysis on Bolton’s ratios: Normal occlusion and malocclusion

Abstract

Introduction: The purpose of this study was to seek and summarise the Bolton overall index (OI) and anterior index (AI) regarding normal occlusion and Angle’s malocclusion according to gender, and to assess if these indices support Bolton’s standards as general references. Methods: PubMed, LILACS, Embase, CENTRAL and Google Scholar databases were searched up to June 2019 (CRD42018088438). Non-randomised clinical studies, published in English and assessing Bolton’s OI and/or AI in normal occlusion and Angle’s malocclusion groups, were included. OI and AI means, sample size and SDs were collected. The National Heart, Lung, and Blood Institute’s Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies was used to assess the risk of bias. Pairwise random-effects and multilevel Bayesian network meta-analyses were used to synthesise available data. Results: Fifty-three observational studies were included (11,411 participants; 3746 men, 4430 women; 15 studies lacked gender information). For normal occlusion, pooled estimates for OI and AI means were 91.78% (95% confidence interval [CI] = 91.42–92.14; I2 = 92.87%) and 78.25% (95% CI = 77.87–78.62; I2 = 90.67%), respectively. We could identify in Angle’s Class III patients meaningful OI and AI mean deviations from normal occlusion (0.76, 95% credible interval [CrI] = 0.55–0.98 and 0.61, 95% CrI = 0.35–0.87, respectively), while in Class II patients we found a meaningful mean deviation from normal occlusion only for OI (−0.28, 95% CrI = −0.52–−0.05). Concerning gender impact, male patients presented higher OI (0.30, 95% CI = 0.00–0.59) and AI (0.41, 95% CI = 0.00–0.83) mean values than female patients in Class I. Conclusion: Normal occlusion OI and AI mean values differ from Bolton’s original values. Class II division 2, for OI mean values, and Class III, for both OI and AI, are proportionally larger than normal occlusion patients. Gender had almost no impact on teeth mesiodistal proportion.

Buccolingual and Mesiodistal Dimensions of the Permanent Teeth, Their Diagnostic Value for Sex Identification, and Bolton Indices

“…The Bolton ratios found in this study were within the range reported earlier [ 6 , 7 , 11 , 33 , 34 ]. In comparison to the original Bolton ratios, our sample's anterior Bolton ratio was larger.…”

“…In comparison to the original Bolton ratios, our sample's anterior Bolton ratio was larger. This should be considered when practicing on Iranian patients; still, it should be noted that such results are not definitive, and sometimes, even studies conducted within the same ethnicity and country yield different results [ 6 , 11 ]. The Angle classes were not associated with the anterior and posterior Bolton ratios in this sample.…”

“…Therefore, the buccolingual dimensions of the teeth are related to the correct arrangement of the posterior teeth [ 5 ]. The mesiodistal dimension of the teeth has crucial orthodontic implications: to obtain an optimal occlusion, the mesiodistal measurements of the mandibular and maxillary teeth should relate to each other [ 6 , 7 ]. Considerable intermaxillary mesiodistal size discrepancies—which are not uncommon—disallow aligning the teeth into an optimal occlusion [ 7 – 9 ].…”

“…To account for such intermaxillary relationships, Bolton [ 10 ] devised the concept of anterior and overall intermaxillary mesiodistal tooth size ratios (Bolton indices). Later, it was shown that Bolton ratios might be ethnic-specific and therefore should be assessed in different populations [ 6 , 7 , 11 ].…”

New Approach to Dental Morphometric Research Based on 3D Imaging Techniques

“…They are still a conventional part of anthropological research, even though they are more suited for general assessments rather than more or less detailed descriptions of dental morphology. As an example of practical application of odontometry, we can mention measurements conducted on teeth and dental arches as diagnostics in orthodontic treatment planning and post-treatment assessment of the results [6]. Thus, we can see that measurements are widely used for studies in dental research as a method of obtaining objective data for immediate assessments or further calculations.…”