Abstract
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. 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. 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. 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.
Highlights
The purposes of this study were to seek for overall ratio (OR) and anterior ratio (AR) patients data in normal occlusion and Angle’s malocclusion studies, and to assess if such results support Bolton’s standards as general references
The African continent is portrayed only by Libya, Egypt, Morocco and Sudan, the European continent is represented mainly by Turkey and Ireland investigations, the Asia continent is mostly represented by studies from India, and the American continent only had two study from North America and the remaining studies are from Brazil
The results indicate that the discrepancy of intermaxillary tooth size may be one of the important factors in the cause of malocclusions, especially in Angle’s Class III
Summary
The purposes of this study were to seek for overall ratio (OR) and anterior ratio (AR) patients data in normal occlusion and Angle’s malocclusion studies, and to assess if such results support Bolton’s standards as general references. An appropriate balance of mesiodistal tooth widths between maxillary and mandibular arches allows for a proper interdigitation, overbite, and overjet in a normal occlusion, with the best possible esthetic and function [1]. The concept of a proportional balance between the mesiodistal sums of maxillary and mandibular teeth may have had its origins in the geometric theories of dental articulation previously proposed. The proportions of upper teeth to the lower teeth are as exact as any”. This nature theory was pervasive in early orthodontics and was seen in the strict non-extraction period started by Edward Angle. To account and aware this proportion, several methods have been proposed to assess interarch tooth size relationship [1,8,9,10,11], but Bolton’s ratios have become widely applied in orthodontics’ research
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