Relationship Between Body Mass Index and Dental Age in 8-15- Year-Old Orthodontic Patients

Objective: To investigate the relationship between Body Mass Index (BMI) and dental age in 8-15-yearold orthodontic patients. Material and Methods: Forty-eight children (25 males, 23 females) aged 8-15 years requiring orthodontic treatment participated in this retrospective study. The dental development ages were determined using the Demirjian method and panoramic radiographs. Afterwards, chronological age, height, and weight were recorded. Using the standard equation developed by the Center for Disease Control and Prevention, BMI value was calculated and grouped according to BMI percentile classification according to age and gender. Data were analyzed using the Pearson correlation test. The level of significance was set at p<0.05. Results: Dental age was significantly accelerated in subjects with increased BMI percentile after adjusting for age and gender (p<0.05). The mean dental age among all subjects was 10.58 ± 2.40. The correlation coefficient (r) showed a strong correlation with a positive direction, which means that the dental age also accelerated by 44.6% in the subjects with increased BMI. Conclusion: There was a linear correlation between increased BMI with accelerated dental age. BMI value and dental age can be considered in determining orthodontic treatment time.


Introduction
The growth and development stages of patients during mixed dentition is crucial to understand by orthodontist. Data regarding active facial growth (growth spurt) may assist the orthodontist in determining a treatment plan particularly appropriate initial time of orthodontic treatment. The entry time of the growth spurt period can be determined by predicting maturation stages accurately and appropriately [1].
Generally, the parameter used in determining maturation stage is chronological age, which is assessed according to date, month and year of birth [2]. However, a chronological age provided less precise information about human growth making it less effective to be used as a maturation assessment parameter. Therefore, a more proper maturation assessment through other parameters such as biological age has been recommended [3,4].
Dental age as one of biological age indicator has been of particular interest to orthodontists since it is still the most effective and accurate indices in assessing craniofacial development stages [5]. Dental maturity determined based on the tooth calcification stages has been proposed as a more reliable criterion rather than tooth eruption stages because it exhibits less variability and is less affected by environmental factors. Previous authors formulated the method of dental age assessment by reference to the radiological appearances of the seven teeth on the left side of the mandible [6]. However, dental maturity indicator is multifactorial. Recent studies suggest that Body Mass Index (BMI) is one of the significant factors suspected to affect the occurrence of dental age variations [7].
Several studies have validated that obese adolescents tend to experience early craniofacial growth and development than their normal BMI peers. These findings indicated that nutrition status may correlate to dental maturation [8,9]. In other studies, no correlation was found between the two variables [10,11].
Recently, the rates of malnutrition in the Indonesian population have been increasing among both children and adults. In 2013 the percentage of obesity and underweight people in 21 provinces was still above the national standard average (5.4%). The incidence of undernutrition is increasing every year by 18.4% while for obesity by 16%. The dramatic and widespread increase in the prevalence of malnutrition in Indonesia could have an impact on the demographics of the average orthodontic practice [12].
No previous study has evaluated the effect of BMI on dental age, especially in Indonesia. Therefore, the purpose of this study was to investigate the relationship between BMI and dental age in 8-15-year-old orthodontic patients.

Study Design
This research was designed as a cross-sectional descriptive study and was conducted between May-

Data Collection
The measured variables comprised of dental age and Body Mass Index percentile. The pretreatment panoramic radiographs were assessed on the box tracing by a single investigator independently from their BMI data. Dental calcification stages, dental maturity score, and corresponding dental age were determined according to the method described by Demirjian (Table 1). Using this protocol, seven mandibular teeth (left central incisor to left second molar) were scored based on eight stages of dental calcification [6]. Scoring was based on the criterion from crown calcification, root development, and apex characteristics. After that, the scores were added together to give a dental maturity reading and then converted to a dental age using a gender-specific table. The Body Mass Index was calculated by dividing weight (kg) by height squared (m 2 ) and then BMI percentiles were assessed using specific BMI percentile charts for age and gender produced by the Center of Disease Control and Prevention (CDC). A child with a BMI percentile <5th is considered underweight, 5th-85th percentile is normal weight, 85th-95th is overweight, and 95th or greater is obese.

Data Analysis
All data were statistically analyzed and organized by using SPSS 18.0 software. Normality distribution of samples was analyzed using Shapiro-Wilk test. Pearson correlation test was performed to determine the relationship between variables (dental age and Body Mass Index), the direction and magnitude of the relationship between the two variables. The level of significance was set at p<0.05.

Results
Forty-eight children consisting of 25 males (52.1%) and 23 women (47.9%) met all inclusion criteria and were included in the study (  Subjects included in the 7-9 years of dental age group have an average BMI value of 14.7, while in the 13-15 years of dental age group, the average BMI value was 21.58. The obese group had an average dental age up to 12 years, while the underweight group was only nine years. Pearson correlation test showed significant values (p<0.05) in all age groups, indicating that there was a significant correlation between Body Mass Index with dental age for 8-10, 10-12 and 12-15 years old ( Table   4). The correlation coefficient (r) value showed a significantly strong correlation with a positive direction. This was described further in the coefficient of determination value (r2). When evaluating for statistical significance, as BMI increased, dental age was more advanced, 53.8% in 8-10 age group, 84.6% in 10-12 age group, and 36.3% in 12-15 age group. Overall, statistical tests results also showed a significant correlation between BMI values with dental age in which the dental age was more advanced, 44.6% as the BMI increased (p<0.001).

Discussion
In this study, dental age was measured using the Demirjian method. This method is conducted by observing root and crown development stages of the seven left mandibular permanent teeth through panoramic radiographs [6]. In contrast to Star methods, which require CBCT radiographs and Kohler method, which requires the presence of third molars, the Demirjian method is more preferred because the criteria of each stage is clearly described, which is based on the shape and proportion of root length. Besides, this method is quite simple since it only requires reviewing panoramic appearances [13,14].
Body Mass Index (BMI) was selected as the method to measure body status because this method is not only simple but also non-invasive and less expensive. In contrast to other methods such as Rohrer index, BMI only rely on the information of height and weight data that can be obtained with simple equipment with accurate results [15].
Based on gender, the mean BMI in females reached 17.77, followed by 10.60 years in dental age, whereas in males, the mean BMI was only 17.02, followed by 10.57 years in dental age. This result showed that females were more advanced in dental age and had greater BMI than males. Dental age differences between males and females, where accelerated dental development in males ranged from 0.09-2.83 years, while females ranged from 0.72-3.33. Females are more likely to enter a growth spurt period earlier than males (females: 10 years old, males: 12 years old). The growth spurt is a period when the growth occurs more rapidly and the tooth undergoes movement more actively [9,16].
Based on chronological age, as BMI increased, dental age was more advanced, 53.8% in the 8-10 age group, 84.6% in the 10-12 age group, and 36.3% in the 12-15 age group. Overall, statistical tests results also showed a significant correlation between BMI values with dental age in which the dental age was more advanced, 44.6% as BMI increased (p<0.05). The obese group had an average dental age up to 12 years old, while the underweight group was only nine years old. Advanced dental age accompanied by increased BMI indicating dental age acceleration. This finding supports the evidence that overweight and obese children experience accelerated dental development compared to their normal and underweight peers. Dental age was more advanced as BMI increased. Conversely, as BMI decrease, the dental age becomes delayed. Delayed deciduous and permanent tooth emergence in children with under-nutrition and, subsequently, low body mass [7,17].
Previous studies have been conducted to validate the effect of BMI on dental development. Correlation between childhood obesity and dental maturation reported an accelerated dental maturation occurred in overweight and obese children. Teenagers and pre-teens body size have a significant impact on the dental growth and development wherein overweight and obese children were more advanced in dental development compared to their normal and underweight peers. Malnourished children are slightly experiencing a delayed eruption of deciduous and permanent teeth compared to normal-weight children [9,18,19].
The main cause of the dental age acceleration in children with a high BMI value has not been thoroughly and scientifically known yet. Accelerated dental maturation allegedly associated with increased levels of free IGF-1 (Insulin-Like Growth Factor-1), IGF-Binding protein-1 and GH-Binding protein (a main circulating growth factor). Obese children have been shown to have decreased levels of growth hormone resulting in increased secretion of free IGF-1, which plays an essential role in accelerating the growth process.
It is assumed that free IGF-1 will indirectly affect craniofacial growth and development, including dentalrelated growth [8,20].
The present study proved the relationship existed between Body Mass Index and dental age.
Accelerated dental maturation indicating the peak height velocity and pubertal growth spurt occurs earlier.
The appropriate time for initiating orthodontic treatment is when a person has entered a growth spurt period where the tooth movement is more active. Overweight and obese patients may require earlier treatment due to dental maturation occurs more quickly; otherwise, treatment for underweight patients may be delayed due to dental maturation occurs slowly. Seeing the relationship between Body Mass Index and dental age could affect orthodontic treatment, BMI data is important to consider before determining orthodontic treatment time [1].

Conclusion
There was a linear correlation between increased BMI with accelerated dental age in orthodontic patients aged 8-15 years. Advanced dental age accompanied by increased BMI indicating dental age acceleration. Conversely, decreased BMI indicating delayed in dental age. BMI value and dental age can be considered in determining orthodontic treatment time.

Financial Support
None.

Conflict of Interest
The authors declare no conflicts of interest.