The rate of obesity in children and adolescents is a current public health concern. The aim of this study was to investigate the relationship between body mass index (BMI) percentile and skeletal and dental maturity in adolescent orthodontic patients.
Orthodontic patients between 8 and 17 years of age were assessed with a retrospective chart review. Skeletal maturation was assessed by using the cervical vertebral method, dental age with the Demirjian assessment method, and weight status with the BMI percentile. Linear regression and logistic regression models were used to assess the effect of the BMI percentile on dental age and cervical vertebral stage, respectively.
For this study, 540 subjects met the inclusion criteria; 27% of the boys and 32% of the girls were either overweight or obese. Cervical vertebral stage and dental age were more advanced in subjects with increased BMI percentiles. For dental age, the coefficient for the BMI percentile was 0.005 year per 1 unit of increase ( P <0.001), and the odds ratio for the effect of the BMI percentile on the cervical vertebral method was 1.02 ( P <0.001).
Orthodontists should consider weight status when evaluating growing children and adolescents because it can affect skeletal and dental development.
Recently, the rates of obesity in the United States have been increasing among both children and adults. Children are living more sedentary lifestyles and are less likely to participate in structured physical activities at school. People are also less likely to perceive themselves as overweight or obese, regardless of their actual weight status, thus reducing their motivation for increased physical activity.
Many methods for assessing weight status have been described, including waist circumference, skinfold thickness, biomass impedance, body mass index (BMI), and age- and weight-specific BMI percentiles. Raw BMI scores, calculated from height and weight measurements, are virtually meaningless in growing children because of age- and sex-related growth patterns. Age- and sex-specific BMI percentiles offer a quick, noninvasive, and readily accessible method to assess a child’s weight status. Children who are above the 95th percentile are described as obese, those from the 85th to the 95th percentile are overweight, those between the fifth and 85th percentiles are considered normal weight, and those below the fifth percentile are underweight.
Long-term sequelae of childhood obesity have been well documented in the medical literature. Elevated blood pressure, lipid levels, insulin levels, and growth hormone levels, decreased bone mass and testosterone levels, and psychological effects such as feelings of loneliness and low self-esteem have all been shown to be associated with childhood obesity. The suggested dental sequelae of obesity include a tendency for prognathic jaws and an increased dental caries rate.
In growing patients, dental development and skeletal maturation are widely used to determine the timing of orthodontic treatment and the selection of treatment modalities. No previous study has evaluated the relationship between BMI percentile and both dental age and skeletal maturation, and only 1 study has comprehensively evaluated the relationship between dental age and any measure of obesity.
The objective of this retrospective study was to assess the relationship between weight status by using BMI percentiles and skeletal and dental development in a large group of actively growing orthodontic patients.
Material and methods
The protocol for this retrospective research project was reviewed and approved by the Biomedical Institutional Review Board at the University of North Carolina, Chapel Hill.
Potential subjects consisted of consecutive patients who had initial pretreatment orthodontic records in the graduate orthodontic clinic at the University of North Carolina. Patient records were reviewed in reverse chronologic order starting from July 31, 2009, by using the following criteria.
The inclusion criteria were (1) pretreatment panoramic and lateral cephalometric radiographs of adequate diagnostic quality taken within 1 month of each other; (2) height and weight recorded within 1 month of the panoramic and lateral cephalometric radiographs; (3) age greater than or equal to 8 years but less than 17 years at the time of pretreatment records; and (4) a full complement of mandibular permanent teeth excluding the third molars.
The exclusion criteria were (1) second, third, and fourth cervical vertebrae not completely or clearly visible on the lateral cephalometric radiograph; (2) congenital anomalies of the second, third, and fourth cervical vertebrae; (3) any congenital tooth anomalies; and (4) any significant medical history that would affect physical development and growth.
The goal for the sample size was set at 500 subjects. This sample size was selected to ensure sufficient numbers of subjects in each cervical vertebral maturation stage and to provide a reasonable distribution across the BMI percentile range.
A computer search of the permanent patient database in the Department of Orthodontics identified all subjects seen for initial records between July 1, 2005, and July 31, 2009, along with their height, weight, date of birth, sex, and race. For analysis purposes, race was categorized as African American, Latino, white, or other.
At the initial records appointment, height and weight were assessed after removing any overgarments by using a wall-mounted stadiometer and a standard mechanical scale (Continental Scale Works, Chicago, Ill) and recorded in the subject’s treatment record by the treating resident. Digital panoramic and cephalometric radiographs were also obtained at the initial records appointment.
Digital radiographs were retrieved independently of the demographic data to eliminate as much as possible any examiner bias resulting from contemporaneous viewing of the demographic data. Panoramic and cephalometric radiographs were evaluated by using the inclusion and exclusion criteria. Subjects who met the radiographic criteria, in addition to other inclusion criteria, were included until a sample of 540 eligible subjects had been identified. These subjects had been seen between September 14, 2006, and July 20, 2009.
Panoramic radiographs for each subject were reviewed by 1 investigator (K.B.M.) to determine the dental maturity score and dental age using a protocol developed by Demirjian et al. In this protocol, a maturity score of 100 denotes complete tooth development. This protocol was modified slightly: in girls, a maturity score of 100 yields a dental age of 16 years; in boys, a maturity score of 98.4 yields a dental age of 16 years. Extrapolation of the original tables and graphs was necessary to assign dental ages to boys with a maturity score between 98.4 and 100.
The development of the second, third, and fourth cervical vertebrae in the lateral cephalometric radiograph for each subject was reviewed by the same investigator (K.B.M.) to determine the cervical vertebrae maturation stage according to a recent modification to the Lamparski method. Raw BMI scores were calculated by using height and weight data. The raw BMI score, age, and sex were used to obtain the BMI percentile value for each subject with age- and sex-specific growth charts from the Centers for Disease Control. By using established conventions, BMI percentile categories were designated as follows for descriptive purposes: less than the fifth BMI percentile, underweight; fifth to 85th percentile, normal weight; 85th to 95th percentile, overweight; and greater than the 95th percentile, obese. All data were recorded in 1 electronic spreadsheet.
Fifty subjects were randomly selected, and their dental maturity and skeletal maturity measures were repeated 2 weeks after the initial assessments. A weighted kappa score was used to assess examiner reliability. Weighted kappa values ranged from 0.66 for the first molar to 0.94 for the second premolar. All other weighted kappa values, including cervical vertebral maturation staging, were greater than 0.80 ( Table I ). The central and lateral incisors had 100% intraexaminer agreement among the 50 repeated measures and little variability throughout the entire sample because of the natural course of near-complete development of the mandibular incisors before age 8 years.
Bivariate analyses were performed with analysis of variance (ANOVA) (race vs BMI percentile and dental age), unpaired t tests (sex vs BMI and dental age), and chi-square tests (sex and race vs cervical vertebral maturation). Before the multivariate analysis, age was centered at the sample mean to aid in interpretation. Linear regression analysis was used to determine whether the demographic variables (age, sex, race) or the BMI percentile was associated with dental age. After we collapsed the cervical vertebral maturation stages 1 through 3 into “prespurt” and stages 4 through 6 into “postspurt,” we used logistic regression to examine the associations with cervical vertebral maturation. Lack-of-fit testing was used for the linear regression, and the Wald test was used for the logistic regression analysis. Sex and age, centered at the sample mean of 13.07 years, were forced in the models, and BMI percentile and race were assessed to determine whether inclusion would add significantly to the explanation of dental age or cervical vertebral maturation.
We reviewed 813 patient records to obtain 540 subjects who met all inclusion criteria. Of the 273 potential subjects who were excluded, 176 did not meet the age requirements, 52 had incomplete or nondiagnostic radiographs, 22 did not have all of their radiographs taken within the allotted time period, 20 had missing or supernumerary teeth, 1 had a cervical vertebrae anomaly, and 2 had recording errors or omissions in their charts.
Approximately 70% of the sample was white, 12% African American, 12% Latino, and 6% other. Slightly more than half of the sample was female (56.3%). Thirty percent of the sample was categorized as overweight or obese, and only 3.8% was underweight. All cervical vertebral maturation stages were represented, although most subjects were in stage 3, 4, or 5.
The mean chronologic age (13.07 ± 1.63 years) was statistically different from the mean dental age (14.24 ± 1.84 years) (paired t test, P <0.01). The difference between dental age and chronologic age was calculated as a proxy for the subject’s degree of dental advancement. The mean dental advancement overall was 1.17 ± 1.29 years. On average, boys were more dentally advanced than girls: 1.33 vs 1.05 years, respectively (unpaired t test, P = 0.01).
The bivariate relationships among measurements are provided in Table II . There were no statistically significant mean differences among the racial groups for chronologic age (ANOVA, P = 0.16), dental age ( P = 0.34), difference between chronologic and dental ages ( P = 0.48), or BMI percentiles ( P = 0.18). The distribution across the BMI percentile categories was also fairly even for race, except for a smaller percentage of the “other” group classified as obese ( Table III ).
|n||Chronologic age||Dental age||BMI percentile|
|Mean||SD||P value||Mean||SD||P value||Mean||SD||P value|
|Race||n||Underweight %||Normal weight %||Overweight %||Obese %|
Boys and girls were not statistically significantly different in chronologic age (unpaired t test, P = 0.19) but were significantly different, on average, with respect to dental age and BMI percentile (unpaired t test, P <0.01 and P <0.01, respectively). Boys were more advanced in dental age and had lower BMI percentiles than girls ( Table II ). In general, slightly more girls were overweight (4% greater) and obese (1% greater) compared with boys ( Fig 1 ).
Although there was no difference among the racial groups in age or BMI percentile, there was a statistically significant difference in the prevalence of prespurt (cervical vertebral maturation stages 1-3) vs postspurt (cervical vertebral maturation stages 4-6) stage among the racial groups (chi-square test, P <0.05) and between boys and girls (chi-square test, P <0.001) ( Table IV ).
|CVM stage (n)||CVM category (n) (%)||Significance|
|1||2||3||4||5||6||Prespurt (CVM stage 1-3)||Postspurt (CVM stage 4-6)|
|African American||6||7||12||19||11||8||25 (39.68%)||38 (60.32%)||P = 0.04|
|White||30||38||71||109||85||45||139 (36.77%)||239 (63.22%)|
|Latino||0||6||6||22||21||8||12 (19.05%)||51 (80.95%)|
|Other||3||4||6||9||8||5||13 (37.14%)||22 (62.86%)|
|Male||29||33||58||71||27||18||120 (50.84%)||116 (49.15%)||P <0.001|
|Female||10||22||37||89||98||48||69 (22.70%)||235 (77.30%)|
Both chronologic and dental ages increased incrementally with increases in cervical vertebral maturation stage ( Table V ). The difference between the mean dental and chronologic ages was similar across all cervical vertebral maturation stages.
|CVM stage||n||Mean chronologic age (y)||Mean dental age (y)|