Estimation of the Predictive Effect of Body Mass Index-Percentile on Skeletal Maturation in a Nigerian Population.

Aim: To determine the predicting effect of BMI-index percentile on the skeletal maturation of Nigerian children. Materials and Methods: A cross-sectional descriptive study. This study was conducted in a tertiary health care facility in North-Central Nigeria. Participants were children between the ages of 5-17 years consisting of 44 males and 30 females who presented in the child dental clinic over a period of eight months were recruited for the study. Skeletal maturation was assessed using the middle phalanx of the third finger (MP3), while the standard WHO growth chart specific for age (2-20 years) and sex was used for grading BMI-percentile. The unpaired t-test was used to compare mean chronological age of the various stages of MP3 according to sex. Multinomial logistic regression was used to determine the predictive effect of age, sex, and BMI percentile on pubertal growth spurt. Results : The BMI-percentile did not show a significant correlation with the pubertal growth spurt (r=0.089, p=0.448). Sex (p=0.004) and chronological age had significant (p<0.001) predictive effect on the skeletal maturation, unlike the BMI-percentile. A one-percentile increase in the BMI-percentile decreases the likelihood of healthy children to be in the peak-pubertal by 1.504 when compared to obese children (p=0.305). Conclusion : This study showed that BMI-percentile is a weak predictor of skeletal maturation. However, obese children had a tendency towards advanced skeletal maturation than healthy participants. It is therefore suggested that orthodontists should consider early implementation of jaw modification treatments among obese children


Introduction
The periods of childhood and adolescence are important periods where critical decisions concerning orthodontic treatment modalities are taken, especially with improvement of dental and facial aesthetics. 1 The diagnosis and commencement of orthodontic treatment should therefore be based on individualized assessment of the maturation status of the patient. 2 Maturation status of an individual can be evaluated using body height, skeletal maturation, dental calcification, dental emergence, and chronological age. [3][4][5][6] Generally, skeletal maturation is closely related to the growth of the craniofacial growth, and is largely affected by nutrition, genetic make-up, and hormonal variation. 7,8 The body mass index (BMI) was first described by Keys and his colleagues to be used among adults to classify the level of adiposity. 9 It has since become a popular screening tool among children and adolescents to determine those who are underweight, healthy, overweight, and obese. 10 The prevalence of body mass discrepancy especially with overweight and obesity is on the increase and appears to be more common among children attending private school. 11,12 Since BMI-for-age is used to grade body size (underweight, healthy, overweight, obesity), determination of its effect on skeletal maturation among the age-seeking orthodontic patients (childhood and adolescents) has received the attention of some researchers. [13][14][15] Evaluation of skeletal maturation is particularly important to the orthodontist when there is consideration for growth modification, when using functional and orthopaedic appliances.
Therefore, factors like BMI-percentile that could affect it should be duly considered during orthodontic treatment planning. 16 The effect of BMI-percentile on skeletal maturity has been researched by several authors among different population using different methods for the evaluation of skeletal maturation. 13 anomaly, and those who refused consent and assent were excluded from the study.

Sample size calculation
The prevalence (p) of obese (≥95th percentile) in North Central Nigeria has been reported to be 3.1%. 12 Therefore, a minimum sample size of 44 was arrived at using the above formulae.
Participants were thereafter recruited using convenience sampling method. Our study sample consisted of 74 participants comprising 44 males (mean age of 10.75 ± 2.73 years) and 30 females (10.00 ± 3.01 years).

Variables measured
The development stages of the middle phalanx of the third finger were used to evaluate the skeletal maturation status of the study participants. Also, the body mass index was calculated from the height (m) and weight (kg) measured using a stadiometer. BMI percentile for each participant was obtained using the growth charts specific for age and sex according to the standard WHO growth chart specific for age (2-20 years) and sex.

Data collection
A digital peri-apical x-ray sensor was used to

Description of equipment and machines
The Carestream peri-apical x-ray machine model CS2100 with a standard wall-mounted unit was used for this study. It has an exposure dose of 60KV-7mA at a distance of 20cm from the x ray tube focal spot to the skin. Carestream digital sensor, RVG 142 size 1 (24mm x 40mm), was used to obtain the radiographs of the study participants. The exposure time was 0.016 seconds and the dose emitted was 0.10mGy. The optimal dose deliver to patients was 1.21mGy.cm 2 , as the exposure surface of the size 1 sensor is 12.1cm.

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BMI also plotted against sex, as shown in table 3. It was observed that females had lesser mean BMI at the pre-peak and at the peak of pubertal growth spurt, with no statistical, significant difference. The mean BMI at the post-peak pubertal stage for females was significantly higher (p=0.046) than males.      BMI-percentile is now a screening tool for categorising children and adolescents as either underweight, healthy, overweight, or obese. 10,29 It is important to note that the prevalence of obesity is gradually on the increase globally. 12,30 Children and adolescents are the major age groups who seek orthodontic care for the purpose of improving their aesthetics and better oral functions. Since findings from our present study reveal that an increase in BMI-percentile has a tendency towards accelerated skeletal maturation, orthodontists should make it a routine practice to determine the BMI-percentile of their patients. Advanced skeletal maturation among those who are obese means that the implementation of growth modification treatment should be done earlier than healthy group individuals. 31 This is important so that the active period of growth needed for skeletal modification will not be missed.

Conclusion
The following conclusions were arrived at from our study: 1. BMI-Percentile did not show a statistically significant correlation with skeletal maturation.
2. Age and sex were significant predictive factors of skeletal maturation.

Individuals with higher BMI-Percentile
have a tendency towards advanced skeletal maturation but it was not statistically significant.