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KJO Korean Journal of Orthodontics

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Original Article

Korean J Orthod 2025; 55(1): 3-14   https://doi.org/10.4041/kjod24.001

First Published Date August 29, 2024, Publication Date January 25, 2025

Copyright © The Korean Association of Orthodontists.

Evaluation of the effects of obesity on orthodontic tooth movement

Mustafa Uzuna , Mine Geçgelen Cesura , Ömer Erdoğanb

aDepartment of Orthodontics, Aydın Adnan Menderes University, Aydın, Türkiye
bDepartment of Medical Biochemistry, Gaziantep İslam Bilim ve Teknoloji University, Gaziantep, Türkiye

Correspondence to:Mustafa Uzun.
Research Assistant, Department of Orthodontics, Aydın Adnan Menderes University, Hastane Street, No:1, Efeler, Aydın 9020, Türkiye.
Tel +90-533-833-19-27 e-mail mustafa.uzunn0@gmail.com

How to cite this article: Uzun M, Geçgelen Cesur M, Erdoğan Ö. Evaluation of the effects of obesity on orthodontic tooth movement. Korean J Orthod 2025;55(1):3-14. https://doi.org/10.4041/kjod24.001

Received: January 5, 2024; Revised: June 25, 2024; Accepted: August 28, 2024

Abstract

Objective: This study aimed to evaluate bone remodeling in gingival crevicular fluid (GCF) during canine distalization in obese individuals and compare it to that in normal-weight individuals. Additionally, the orthodontic tooth movement rates of obese individuals were measured and compared with those of normal-weight individuals. Methods: Thirty-six patients (18 obese and 18 normal-weight) aged 12–18 years who were candidates for maxillary first premolar extraction for Angle Class II malocclusion were included in the study. The two groups were formed according to World Health Organization guidelines. A normal-weight group (body mass index [BMI] 16–85%) and an obese group (BMI ≥ 95%). Gingival crevicular fluid samples were collected before, 24 hours after, and on the 7th, 14th, and 21st days after the application of the distalization force. Enzyme-linked immunosorbent assay was used to measure leptin, receptor activator of nuclear factor kappa-Β ligand (RANKL), osteoprotegerin (OPG) and interleukin-6 (IL-6) levels in GCF samples. In addition to the recorded GCF sampling times, the amount of canine tooth movement was calculated using digital models obtained on the 28th day and 3rd month. Results: Leptin, RANKL, OPG, and IL-6 levels were significantly higher in the obese group (P < 0.05). The digital model measurements displayed high rates of repeatability (ICC 0.990). The difference in the amount of tooth movement between groups was not statistically significant (P > 0.05). Conclusions: Although obese and normal-weight individuals showed different biomarker levels during tooth movement, there were no significant differences in the amount of movement.

Keywords: Leptin, Biomarker, Obesity, Orthodontic tooth movement

INTRODUCTION

Obesity is a serious health problem rapidly emerging worldwide.1 It is known that bone density increases in obese individuals, and that some hormones and cytokines that play a role in the development of obesity also affect bone metabolism. Between normal-weight and obese individuals, there are reported differences in the levels of leptin, receptor activator of nuclear factor kappa-Β ligand (RANKL), osteoprotegerin (OPG), and interleukin-6 (IL-6), which are thought to be responsible for bone remodeling and orthodontic tooth movement.2-4

The fact that leptin induces osteoblast differentiation and reduces adipocyte differentiation in humans explains the negative correlation between bone mineral density and the body fat ratio. Therefore, while leptin stimulates bone formation, it also inhibits bone resorption.5

RANKL induces osteoclast differentiation. IL-6 stimulates bone resorption by increasing RANKL expression. OPG produced by osteoblasts functions as an inhibitor of osteoclast function by competing with RANKL for the membrane receptor receptor activator of nuclear factor kappa-Β (RANK).6,7

Orthodontic force changes periodontal tissue vascularity, leading to the synthesis of various signaling molecules and metabolites. The released molecules generate cellular responses around the teeth, providing a favorable microbiological environment for tissue deposition or resorption.8 Biochemical markers released during inflammatory events can be detected in the gingival crevicular fluid (GCF).9

This prospective clinical study aimed to biochemically evaluate bone remodeling in the GCF during canine distalization in obese individuals and compare it with that in normal-weight individuals.

The null hypothesis of our study was as follows: There is no difference between obese and normal-weight individuals in terms of bone metabolism during orthodontic tooth movement.

MATERIALS AND METHODS

Participants

In this study, individuals who applied to the Aydın Adnan Menderes University Faculty of Dentistry, Department of Orthodontics for orthodontic treatment were included, according to the inclusion criteria. These individuals were obese and normal-weight patients with Angle Class II molar and canine dental relationship who were scheduled to be treated by extraction of the maxillary first premolar teeth.

Criteria for inclusion were determined as:

  • Absence of any systemic disease that will affect tooth movement other than obesity;

  • The patients would be in the permanent dentition period;

  • Patient ages would be between 12 to 18 years of age.

Criteria for exclusion were determined as:

  • Use of anti-inflammatory drugs within a month before the start of the study;

  • Poor periodontal health;

  • Smoking or alcohol habits.

Since there were no similar or pilot studies in the literature, when calculating the sample size, the required effect width was considered medium (f = 0.25). Accordingly, it was determined that at least 12 individuals per group would be sufficient if Type I error was taken as 0.05 and Type II as 0.20 to establish a difference between the groups in measurements made at five separate instances. To preserve the power of the study against possible data loss, such as dropping out of the study or follow-up, the dropout rate was set at 35%. In this case, it was found that at least 18 (12/0.65) participants were required per group and a total of 36 individuals were included in the study. Equal numbers of male and female individuals were included in the study to ensure homogeneity within and between the groups, as recommended in the literature.10-12

To separate participants into their respective groups, the classification of obesity in children was made as suggested by the World Health Organization, which identified body mass index (BMI) values as very underweight (< 5%), underweight (5–15%), normal (16–85%), overweight (86–95%) and obese (≥ 95%).13 All participants had their heights measured in meters, barefeet, and using a tape measure fixed to the wall. Their weights were measured in kilograms using a digital scale. Considering that all the participants lived in Turkey, their percentile values were calculated with reference to a study by Neyzi et al.14

Approval for the study was obtained from the Clinical Research Ethics Committee of Aydın Adnan Menderes University, Faculty of Dentistry (Document Date and Number: 22.04.2021-28009). Written informed consent was obtained from all participants and their families.

Treatment protocol

To standardize the orthodontic treatment, 0.022 × 0.028-inch slotted Roth metal brackets and tubes (Mini Master Series; American Orthodontics, Sheboygan, WI, USA) were used. Bracketing, leveling, and alignment protocols were applied to all patients. As a final measure before canine distalization, 0.019 × 0.025-inch stainless steel arch wires were applied to the bracket slots of the patients, after which a 2-month waiting period ensued until the wires became passive. To avoid loss of anchorage during canine distalization in the study, mini-screws 1.5 mm in diameter and 8 mm in length (The Aarhus System; Royal College, Aarhus, Denmark) were applied between the roots of the maxillary first molar and second premolar teeth. NiTi sealing springs were attached to the distal hook of the bracket on the teeth using a mini-screw anchor to apply 150 g of force for canine distalization mechanics (Figure 1).

Figure 1. Distalization mechanics with mini-screws.

Collection and storage of GCF samples

In our study, samples were collected from the distal gingival groove of the canines that were chosen for distalization. Gingival crevicular fluid samples were taken from the distal regions of the canine teeth using a periopaper (Gingival Fluid Collection Strips; Oraflow, Smithtown, NY, USA) before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), and 21st days (T4) of the application of the distalization force.15 Due to the diurnal rhythm of leptin, GCF samples were collected from all participants at the same time and before meals.5 Paper strips contaminated with blood, saliva, or plaque were excluded. After the paper strips were left in the gingival pocket for 1 minute, the volume of the liquid absorbed was measured using a pre-calibrated electronic device (Periotron 8010; Oraflow, Amityville, NY, USA). Each paper strip was placed in a different Eppendorf tube and stored at –80°C until analysis.

Digital model measurements

Since the distalization rates of canine teeth will be evaluated in obese and normal-weight individuals in the study, all patients were scanned intraorally before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), 21st (T4), 28th day (T5), and 3rd month (T6) of the application of the distalization force to the canine tooth. The OrthoAnalyzer program (3Shape A/S, Copenhagen, Denmark) was used to measure the amount of tooth movement in the models obtained digitally from the scans. Because the mini-screws may have been positioned differently between patients, they were projected onto the occlusal plane, and the distance from the canine tooth perpendicular to this point was measured (Figure 2). The differences between the distance measurements obtained (T0-T1, T1-T2, T3-T4, T4-T5, T5-T6) were calculated to determine how much the tooth moved in each measurement. In addition, the amount of tooth movement was calculated at the end of 21 days (T0-T4), 1 month (T0-T5) and 3 months (T0-T6).

Figure 2. Distance measurement through digital model.

To evaluate intraobserver agreement, it was calculated that to test the hypotheses H0: ρ = 0.70 and H1: ρ = 0.90 at a Type I error level of 0.05 and a Type II error level of 0.20, the amount of tooth movement should be measured again in at least 18.4 images.16 Digital models of 19 randomly selected patients were re-evaluated 1 month after the first evaluation.

Periodontal measurements

In this study, periodontal measurements were made during the time periods in which GCF was measured (T0, T1, T2, T3, and T4), and the periodontal health of the individuals was evaluated. The plaque index, gingival index, and bleeding on probing were examined as previously described.

Statistical analyses

The suitability to the normal distribution of numerical variables such as age, biochemical measurements, etc. included in the study was examined with the Shapiro–Wilk test. The intra-observer agreement level for distance measurements was determined using the intraclass correlation coefficient (ICC).

The ages of patients in the study and control groups were compared using an independent two-sample t test. Differences between groups in terms of changes in distance measurements over time were examined using two-way mixed analysis of variance (ANOVA). However, because the sphericity assumption was not met, the Greenhouse–Geisser correction was applied. Because the group and time interaction effect was not statistically significant, the difference between groups at each measurement time point was examined using an independent two-sample t test. The difference between time points in each group was examined using repeated-measures ANOVA, and the Greenhouse–Geisser correction was applied. Since it was determined that there were outliers with Mahalanobis distance in biochemical and periodontal measurements and these measurements did not meet at least one assumption, the difference in the change of measurements over time between groups was examined with a non-parametric Factorial 1-Longitudinal Data-Factorial 1 (F1-LD-F1) design. The ANOVA-type test statistic and P values obtained from the F1-LD-F1 design were provided for group and time interaction effects. The groups were compared using the Mann–Whitney U test for relevant measurements and the rate of tooth movement at each measurement time. The relationship between the change observed in leptin level and the rates of tooth movement in the first 21 days of the study was examined using Pearson correlation analysis.

The statistical significance level was accepted as P ≤ 0.05.

RESULTS

The demographic characteristics of the study and control groups are shown in Table 1. There was no significant difference in demographic characteristics between the two groups, except for BMI percentile (P < 0.001) (Table 1).

Table 1 . Demographic characteristics of the participants

DemographicOverallNormal-weightObeseP value
Patients361818
Female/Male18/189/99/9
Age (mean ± SD)15.34 ± 1.1315.18 ± 1.4215.32 ± 1.570.775
BMI percentile (mean ± SD)78.24 ± 23.9455.79 ± 15.9196.03 ± 0.76< 0.001***

SD, standard deviation; BMI, body mass index.

Independent t test.

Statistically significant, ***P < 0.001.



The GCF volume did not show a statistically significant difference over time between the study and control groups (P = 0.592 and P = 0.315, respectively) (Table 2).

Table 2 . Distribution of gingival crevicular fluid (GCF) volume by groups and time

GCF volume (µL)Study groupControl groupComparison result
Time of
measurement
Mean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
ZP value
T00.34 ± 0.190.36 ± 0.140.7280.467
0.32 (0.22–0.40)0.33 (0.26–0.42)
T10.38 ± 0.190.35 ± 0.160.3170.752
0.33 (0.24–0.44)0.33 (0.25–0.42)
T20.31 ± 0.130.29 ± 0.100.5070.612
0.29 (0.24–0.43)0.32 (0.19–0.37)
T30.40 ± 0.190.31 ± 0.141.5520.121
0.43 (0.26–0.51)0.30 (0.22–0.37)
T40.33 ± 0.140.38 ± 0.131.1080.268
0.29 (0.21–0.45)0.39 (0.30–0.48)
χ2, P value2.797, 0.5924.737, 0.315

ANOVA-type test statistic for Group × Time interaction effect = 1.362, P = 0.248.

Gingival crevicular fluid samples were taken from the distal regions of the canine teeth using a periopaper (Gingival Fluid Collection Strips; Oraflow, Smithtown, NY, USA) before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), and 21st days (T4) of the application of the distalization force.

SD, standard deviation; IQR, interquartile range.



The levels of leptin, RANKL, OPG, and IL-6 in the study and control groups did not show a significant change over time (P > 0.05); however, at each measurement time point, the levels of leptin, OPG, and IL-6 were significantly higher in the study group than in the control group (P < 0.05). RANKL levels did not show a significant difference between the groups at T0 (P = 0.121) (Tables 36).

Table 3 . Distribution of leptin levels according to groups and time

Leptin (ng/mL)Study groupControl groupComparison result
Time of
measurement
Mean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
ZP value
T02.90 ± 0.721.70 ± 0.474.272< 0.001***
2.82 (2.55–3.39)1.76 (1.41–1.85)
T12.88 ± 1.561.65 ± 0.392.7530.006**
2.91 (1.71–3.46)1.73 (1.35–1.97)
T22.74 ± 0.751.59 ± 0.563.829< 0.001***
2.87 (2.01–3.27)1.56 (1.30–1.84)
T32.62 ± 1.031.57 ± 0.313.577< 0.001***
2.51 (1.79–3.67)1.53 (1.38–1.73)
T42.54 ± 0.641.58 ± 0.364.303< 0.001***
2.38 (2.03–3.09)1.59 (1.35–1.87)
χ2, P value2.978, 0.5621.600, 0.809

ANOVA-type test statistic for Group × Time interaction effect = 0.207, P = 0.912.

Gingival crevicular fluid samples were taken from the distal regions of the canine teeth using a periopaper (Gingival Fluid Collection Strips; Oraflow, Smithtown, NY, USA) before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), and 21st days (T4) of the application of the distalization force.

SD, standard deviation; IQR, interquartile range.

Statistically significant, **P < 0.01, ***P < 0.001.



Table 4 . Distribution of RANKL level by groups and time

t-RANKL (pg/mL)Study groupControl groupComparison result
Time of
measurement
Mean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
ZP value
T0267.95 ± 138.74195.32 ± 80.141.5510.121
257.75 (152.06–330.21)172.17 (156.73–197.49)
T1278.98 ± 65.08208.54 ± 63.573.2780.001**
279.94 (205.02–349.21)188.53 (173.67–213.87)
T2292.28 ± 85.99219.27 ± 88.752.8480.004**
280.38 (215.94–340.02)176.69 (161.82–250.63)
T3284.22 ± 119.91211.93 ± 60.561.9780.048*
277.08 (191.16–349.86)190.27 (168.45–218.11)
T4263.09 ± 68.00196.26 ± 43.263.1660.002**
260.62 (215.94–307.01)180.28 (164.39–204.63)
χ2, P value3.042, 0.5512.212, 0.712

ANOVA-type test statistic for Group × Time interaction effect = 0.266, P = 0.872.

Gingival crevicular fluid samples were taken from the distal regions of the canine teeth using a periopaper (Gingival Fluid Collection Strips; Oraflow, Smithtown, NY, USA) before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), and 21st days (T4) of the application of the distalization force.

RANKL, receptor activator of nuclear factor kappa-Β ligand; SD, standard deviation; IQR, interquartile range.

Statistically significant, *P < 0.05, **P < 0.01.



Table 5 . Distribution of OPG level by groups and time

t-OPG (ng/mL)Study groupControl groupComparison result
Time of
measurement
Mean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
ZP value
T07.16 ± 2.914.31 ± 2.513.736< 0.001***
6.08 (5.00–8.45)3.81 (3.02–4.23)
T16.86 ± 3.684.18 ± 1.703.4500.001**
6.18 (4.50–7.24)3.72 (3.38–4.66)
T27.10 ± 1.874.08 ± 1.634.130< 0.001***
6.99 (5.51–8.39)4.03 (3.04–4.55)
T37.66 ± 3.094.43 ± 1.843.2280.001**
8.09 (6.05–9.22)3.92 (3.23–5.11)
T48.28 ± 5.554.24 ± 1.543.2770.001**
6.88 (5.10–9.35)4.03 (3.15–4.65)
χ2, P value4.533, 0.3391.867, 0.760

ANOVA-type test statistic for Group × Time interaction effect = 0.323, P = 0.811.

Gingival crevicular fluid samples were taken from the distal regions of the canine teeth using a periopaper (Gingival Fluid Collection Strips; Oraflow, Smithtown, NY, USA) before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), and 21st days (T4) of the application of the distalization force.

OPG, osteoprotegerin; SD, standard deviation; IQR, interquartile range.

Statistically significant, **P < 0.01, ***P < 0.001.



Table 6 . Distribution of IL-6 level by groups and time

t-IL-6 (ng/L)Study groupControl groupComparison result
Time of
measurement
Mean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
ZP value
T0222.50 ± 79.3072.93 ± 62.984.148< 0.001***
232.41 (191.66–257.32)58.84 (35.18–92.22)
T1258.28 ± 73.4094.84 ± 71.284.337< 0.001***
254.19 (223.17–307.31)72.59 (58.06–104.53)
T2280.61 ± 60.90100.24 ± 39.935.080< 0.001***
259.84 (235.13–329.09)92.56 (72.19–111.36)
T3234.38 ± 66.1985.06 ± 60.034.526< 0.001***
241.21 (190.29–260.47)67.12 (36.91–116.83)
T4225.10 ± 91.2476.24 ± 36.454.115< 0.001***
251.43 (168.44–297.57)65.22 (55.00–85.54)
χ2, P value2.800, 0.5925.538, 0.236

ANOVA-type test statistic for Group × Time interaction effect = 0.028, P = 0.997.

Gingival crevicular fluid samples were taken from the distal regions of the canine teeth using a periopaper (Gingival Fluid Collection Strips; Oraflow, Smithtown, NY, USA) before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), and 21st days (T4) of the application of the distalization force.

IL-6, interleukin-6; SD, standard deviation; IQR, interquartile range.

Statistically significant, ***P < 0.001.



The ICC was calculated as 0.990 (95% confidence interval: 0.975–0.996) for the distance measurements to determine the amount and rate of movement of the canine teeth (P < 0.001). Accordingly, the intra-observer agreement for these measurements was excellent.

When distance measurements in the study and control groups were considered, there was a statistically significant change in the distance between these points over time in both groups (P < 0.001 for both); however, the change was similar (P = 0.172). When the two groups were compared in terms of changes between consecutive time points, the decrease between T3 and T4 was significantly greater in the control group (P = 0.002), whereas all other changes were similar between the two groups (P > 0.05) (Table 7 and Figure 3).

Figure 3. Change of distance measurements in groups over time.
Before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), 21st (T4), 28th (T5) days and 3rd month (T6) of the application of the distalization force.
**P < 0.01.

Table 7 . The mean amount of tooth movement by groups and periods

Amount of movement (mm)Study groupControl groupComparison result
PeriodMean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
tP value
T0–T10.31 ± 0.150.24 ± 0.081.6780.103
0.28 (0.23–0.39)0.23 (0.18–0.30)
T1–T20.19 ± 0.130.17 ± 0.080.5290.601
0.13 (0.11–0.28)0.17 (0.11–0.21)
T2–T30.17 ± 0.120.21 ± 0.101.0370.307
0.13 (0.11–0.20)0.19 (0.14–0.25)
T3–T40.21 ± 0.110.35 ± 0.133.3950.002**
0.23 (0.13–0.28)0.38 (0.25–0.47)
T4–T50.19 ± 0.100.18 ± 0.100.3260.747
0.18 (0.11–0.30)0.16 (0.11–0.24)
T5–T62.36 ± 0.512.42 ± 0.400.4250.674
2.34 (1.94–2.85)2.45 (2.08–2.70)

F statistic = 0.992, Greenhouse–Geisser corrected P = 0.364.

The amount of tooth movement was calculated at the end of 21 days (T0–T4), 1 month (T0–T5) and 3 months (T0–T6).

SD, standard deviation; IQR, interquartile range.

Statistically significant, **P < 0.01.



The average amount of tooth movement in the T0-T4 period was 0.88 ± 0.21 mm in the study group and 0.97 ± 0.17 mm in the control group. Although the amount of tooth movement during this process was greater in the control group, the difference was not statistically significant (P = 0.167). The average amount of tooth movement was similar (P > 0.05) between the two groups during the T0-T5 and T0-T6 periods (Supplementary Table 1).

When the relationship between the change in leptin level (T4-T0) and tooth movement in the first 21 days of the study was examined, the correlation coefficient was calculated as r = –0.002 (P = 0.994) in the study group and r = –0.121 (P = 0.634) in the control group. There was no statistically significant linear relationship between changes in leptin levels and tooth movement (Figure 4).

Figure 4. Scatter plot of change in leptin level and tooth movement in the first 21 days.

Among the periodontal measurements, the plaque index, gingival index, and bleeding on probing values showed significant changes over time in both groups (P < 0.001), but the changes were similar (P > 0.05) (Supplementary Tables 2–4).

DISCUSSION

Studies have investigated the effects of obesity on oral and dental health, and orthodontic treatment procedures for obese individuals have often been a subject of discussion.17 Since orthodontic tooth movement depends on many factors, it is difficult to understand the effects of obesity on periodontal tissues.18 Considering the worldwide increase in obesity, our study aimed to evaluate the effect of obesity on the periodontal tissue during orthodontic movement.

Leptin is a signaling molecule with growth factor properties. It stimulates osteoblasts, inhibits osteoclast formation and activity and promotes osteogenesis. Leptin also plays a role in anti-osteogenic effects via its central effect on the hypothalamus.19 High concentrations of leptin protect bone.20 While some studies argue that the rate of tooth movement increases in individuals with increased serum leptin levels, others show a decrease in the rate of tooth movement.2,10-12,21-24

When studies on canine distalization with elastomeric chains and NiTi closed-coil springs were examined, leptin levels were found to be lower than the initial levels after applying a distalization force.10,12,25 In this study, similar to the literature, leptin levels started to decrease in both groups after the distalization force was applied and remained below the initial value at the end of 21 days; however, this change was not statistically significant. Considering that high concentrations of leptin help maintain bone levels, leptin levels may decrease during resorption.

Leptin, which is synthesized in adipocytes, is secreted mostly from white adipose tissue and, to a lesser extent, brown adipose tissue.26 For this reason, there is a consensus in the literature that the level of leptin parallels the increase in BMI and, therefore, the amount of fat in the body.27 Studies have suggested that during orthodontic treatment, leptin levels in individuals with an increased BMI are higher than those in normal-weight individuals.2,10,28 The results of all these studies are compatible with those of our study.

RANKL binds to its receptor, RANK, and stimulates cells. RANK by RANKL initiates intracellular signaling. This stimulation enables precursor osteoclasts to transform into mature osteoclasts and become active. RANKL and its receptor RANK are the main regulatory factors in bone formation and resorption.7,29

Several factors that induce RANKL synthesis in osteoblasts also regulate OPG expression. OPG binds to RANKL and prevents its binding to RANK. Thus, RANKL prevents bone resorption by preventing osteoclast differentiation and activation.30

If RANKL synthesis in the tissue increases compared with OPG production, the RANKL receptor binds to RANK, causing mature osteoclast formation and disrupting the balance in favor of bone resorption. If OPG production is higher than RANKL production, OPG binds to RANKL and osteoclast formation decreases because the RANK-RANKL connection is blocked.31

Few studies have compared obese and normal-weight individuals in terms of RANKL levels during orthodontic treatment. Saloom et al.2 reported that RANKL levels were higher in obese individuals. Another study found that obese mice have higher RANKL levels than normal-weight mice.32 RANKL levels were higher in the obese group when examined in postmenopausal women.33 The findings of these studies are similar to those of our study. Madak10 reported that RANKL levels are higher in normal-weight individuals.

According to our findings, the RANKL levels in the study and control groups increased in the first week after the distalization force was applied, then decreased, and approached a value close to the initial level on the 21st day. This change in RANKL expression is consistent with other studies.10,34 For example, Iwasaki et al.35 reported that cytokine levels may fluctuate over a 28-day cycle as long as orthodontic force is applied. This is in accordance with the literature showing that during the evaluation of tooth movement mechanisms and bone metabolism, RANKL levels increase in the initial phase of bone resorption and approach the initial levels when measured on the 21st day.

Studies examining OPG levels according to BMI have yielded different results.10,36,37 In our study, we found that OPG levels in obese individuals were significantly higher than those in normal-weight individuals.

Kanzaki et al.38 reported that the OPG remained balanced during orthodontic tooth movement. Kawasaki et al.34 found that the OPG level was significantly lower 24 hours after force application, but no statistically significant differences emerged at other time periods. Madak10 and Flórez-Moreno et al.39 stated that the OPG first decreased slightly and then increased slightly. In this study, we observed that changes in OPG levels were not statistically significant in either group.

An increase in the number of white adipose tissue cells is induced by hyperplasia and hypertrophy in obese patients. This situation causes metabolic disorder, adipocyte hypertrophy, and the secretion of tumor necrosis factor-α (TNF-α) and IL-6, which are pro-inflammatory cytokines.40,41 In our study, IL-6 levels in obese individuals were found to be statistically significantly higher than those in normal-weight individuals at each time point.

IL-6 has a significant effect on the bone formation-resorption balance. Disruption of this balance may lead to bone erosion and loss. It increases the accumulation of osteoclasts over IL-6 hematopoietic root cells, decreases the number of osteoblasts, accelerates bone resorption, and damages the ossification. In contrast, an increase in RANK Ligand expression and decrease in the expression of osteoprotegerin, a bone-protective peptide, result in increased osteoclastogenesis.42

When studies evaluating the relationship between orthodontic tooth movement and IL-6 levels were examined, Padisar et al.43 reported that although the IL-6 level was higher than the initial level 1 hour after the orthodontic force was applied, the cytokine level was similar to the initial level after 28 days. Acun Kaya et al.44 reported that the IL-6 level reached its maximum level 3 days after the application of force and started to decrease within a period of 1 week to 10 days. In this study, for both obese and normal-weight individuals, the IL-6 level initially increased after the distalization force was applied, reached the maximum level in the 1st week, and then tended to decrease and reached a value close to the initial level at the end of the 21st day, which was similar to the results from other studies.

von Bremen et al.45 reported in their study that overweight individuals showed less cooperation in orthodontic treatment, and accordingly, the duration of orthodontic treatment was longer than that in normal-weight individuals. In a similar study, von Bremen et al.46 reported that the treatment period for obese patients was longer than that for normal-weight individuals; however, the difference was not statistically significant. Saloom et al.2 stated that the leveling time in obese patients is faster than that in individuals of normal-weight, and the amount of tooth movement is greater at the beginning of treatment. In our study, there was no statistically significant difference between obese and normal-weight individuals regarding the effect of orthodontic treatment on tooth movement during canine distalization phase. However, there were differences in the cytokine levels, except for RANKL, between the two groups at the beginning of the study. The fact that differences in cytokine levels expected to occur after applying force also existed in the T0 phase was due to the effects of obesity on cytokine levels. This may explain why increases and decreases in cytokine levels did not cause a difference in the amount of tooth movement during the canine distalization phase between the groups.

Madak10 compared normal-weight and overweight individuals in terms of canine distalization. According to the results of this study, the time required to complete canine distalization was significantly longer in overweight individuals than in normal-weight individuals. When the common time intervals of both studies were compared according to the average orthodontic tooth movement at the end of the first and third months, more orthodontic tooth movement occurred in normal-weight individuals than in obese individuals.

Madak10 reported that there was a negative relationship between the change in leptin level at the end of one month and the amount of tooth movement in both groups. Jayachandran et al.24 reported that there was a positive correlation between leptin level and the amount of orthodontic tooth movement. Srinivasan et al.47 also reported that there was a positive correlation between the amount of tooth movement and leptin level. When considering the correlation between leptin level and the amount of tooth movement in our study, no linear relationship was found between the change in leptin level at 21-days and the amount of orthodontic tooth movement at 21-days in both groups.

Limitations of the study

The differences in the findings of our study may be attributed to the use of different obesity classification methods, differences in orthodontic treatment mechanics, or differences in demographic characteristics of the participants.

A limitation of this study is that it assumes that the miniscrew positions are fixed during distance measurements. Mini-screws can be displaced to a certain degree after an orthodontic force is applied.48

CONCLUSIONS

1. The investigated leptin, RANKL, OPG and IL-6 biomarker levels show statistically significant differences between obese and normal-weight individuals.

2. There was no statistically significant difference between the groups in terms of the rate of orthodontic tooth movement.

3. There was no correlation between the amount of orthodontic tooth movement and the leptin levels throughout the first 21 days.

4. Considering the results of our study, there is no harm in applying routine orthodontic treatment procedures in the orthodontic treatment of obese individuals.

AUTHOR CONTRIBUTIONS

Formal analysis: ÖE. Funding acquisition: MU, MGC. Investigation: MU. Methodology: MU, MGC. Project administration: MU, MGC. Supervision: MGC. Writing–original draft: MU. Writing–review & editing: MU.

CONFLICTS OF INTEREST

No potential conflict of interest relevant to this article was reported.

FUNDING

Supported by Aydın Adnan Menderes University Scientific Research Projects (Project No: DHF-21006).

SUPPLEMENTARY MATERIAL

Supplementary data is available at https://doi.org/10.4041/kjod24.001

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Article

Original Article

Korean J Orthod 2025; 55(1): 3-14   https://doi.org/10.4041/kjod24.001

First Published Date August 29, 2024, Publication Date January 25, 2025

Copyright © The Korean Association of Orthodontists.

Evaluation of the effects of obesity on orthodontic tooth movement

Mustafa Uzuna , Mine Geçgelen Cesura , Ömer Erdoğanb

aDepartment of Orthodontics, Aydın Adnan Menderes University, Aydın, Türkiye
bDepartment of Medical Biochemistry, Gaziantep İslam Bilim ve Teknoloji University, Gaziantep, Türkiye

Correspondence to:Mustafa Uzun.
Research Assistant, Department of Orthodontics, Aydın Adnan Menderes University, Hastane Street, No:1, Efeler, Aydın 9020, Türkiye.
Tel +90-533-833-19-27 e-mail mustafa.uzunn0@gmail.com

How to cite this article: Uzun M, Geçgelen Cesur M, Erdoğan Ö. Evaluation of the effects of obesity on orthodontic tooth movement. Korean J Orthod 2025;55(1):3-14. https://doi.org/10.4041/kjod24.001

Received: January 5, 2024; Revised: June 25, 2024; Accepted: August 28, 2024

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Objective: This study aimed to evaluate bone remodeling in gingival crevicular fluid (GCF) during canine distalization in obese individuals and compare it to that in normal-weight individuals. Additionally, the orthodontic tooth movement rates of obese individuals were measured and compared with those of normal-weight individuals. Methods: Thirty-six patients (18 obese and 18 normal-weight) aged 12–18 years who were candidates for maxillary first premolar extraction for Angle Class II malocclusion were included in the study. The two groups were formed according to World Health Organization guidelines. A normal-weight group (body mass index [BMI] 16–85%) and an obese group (BMI ≥ 95%). Gingival crevicular fluid samples were collected before, 24 hours after, and on the 7th, 14th, and 21st days after the application of the distalization force. Enzyme-linked immunosorbent assay was used to measure leptin, receptor activator of nuclear factor kappa-Β ligand (RANKL), osteoprotegerin (OPG) and interleukin-6 (IL-6) levels in GCF samples. In addition to the recorded GCF sampling times, the amount of canine tooth movement was calculated using digital models obtained on the 28th day and 3rd month. Results: Leptin, RANKL, OPG, and IL-6 levels were significantly higher in the obese group (P < 0.05). The digital model measurements displayed high rates of repeatability (ICC 0.990). The difference in the amount of tooth movement between groups was not statistically significant (P > 0.05). Conclusions: Although obese and normal-weight individuals showed different biomarker levels during tooth movement, there were no significant differences in the amount of movement.

Keywords: Leptin, Biomarker, Obesity, Orthodontic tooth movement

INTRODUCTION

Obesity is a serious health problem rapidly emerging worldwide.1 It is known that bone density increases in obese individuals, and that some hormones and cytokines that play a role in the development of obesity also affect bone metabolism. Between normal-weight and obese individuals, there are reported differences in the levels of leptin, receptor activator of nuclear factor kappa-Β ligand (RANKL), osteoprotegerin (OPG), and interleukin-6 (IL-6), which are thought to be responsible for bone remodeling and orthodontic tooth movement.2-4

The fact that leptin induces osteoblast differentiation and reduces adipocyte differentiation in humans explains the negative correlation between bone mineral density and the body fat ratio. Therefore, while leptin stimulates bone formation, it also inhibits bone resorption.5

RANKL induces osteoclast differentiation. IL-6 stimulates bone resorption by increasing RANKL expression. OPG produced by osteoblasts functions as an inhibitor of osteoclast function by competing with RANKL for the membrane receptor receptor activator of nuclear factor kappa-Β (RANK).6,7

Orthodontic force changes periodontal tissue vascularity, leading to the synthesis of various signaling molecules and metabolites. The released molecules generate cellular responses around the teeth, providing a favorable microbiological environment for tissue deposition or resorption.8 Biochemical markers released during inflammatory events can be detected in the gingival crevicular fluid (GCF).9

This prospective clinical study aimed to biochemically evaluate bone remodeling in the GCF during canine distalization in obese individuals and compare it with that in normal-weight individuals.

The null hypothesis of our study was as follows: There is no difference between obese and normal-weight individuals in terms of bone metabolism during orthodontic tooth movement.

MATERIALS AND METHODS

Participants

In this study, individuals who applied to the Aydın Adnan Menderes University Faculty of Dentistry, Department of Orthodontics for orthodontic treatment were included, according to the inclusion criteria. These individuals were obese and normal-weight patients with Angle Class II molar and canine dental relationship who were scheduled to be treated by extraction of the maxillary first premolar teeth.

Criteria for inclusion were determined as:

  • Absence of any systemic disease that will affect tooth movement other than obesity;

  • The patients would be in the permanent dentition period;

  • Patient ages would be between 12 to 18 years of age.

Criteria for exclusion were determined as:

  • Use of anti-inflammatory drugs within a month before the start of the study;

  • Poor periodontal health;

  • Smoking or alcohol habits.

Since there were no similar or pilot studies in the literature, when calculating the sample size, the required effect width was considered medium (f = 0.25). Accordingly, it was determined that at least 12 individuals per group would be sufficient if Type I error was taken as 0.05 and Type II as 0.20 to establish a difference between the groups in measurements made at five separate instances. To preserve the power of the study against possible data loss, such as dropping out of the study or follow-up, the dropout rate was set at 35%. In this case, it was found that at least 18 (12/0.65) participants were required per group and a total of 36 individuals were included in the study. Equal numbers of male and female individuals were included in the study to ensure homogeneity within and between the groups, as recommended in the literature.10-12

To separate participants into their respective groups, the classification of obesity in children was made as suggested by the World Health Organization, which identified body mass index (BMI) values as very underweight (< 5%), underweight (5–15%), normal (16–85%), overweight (86–95%) and obese (≥ 95%).13 All participants had their heights measured in meters, barefeet, and using a tape measure fixed to the wall. Their weights were measured in kilograms using a digital scale. Considering that all the participants lived in Turkey, their percentile values were calculated with reference to a study by Neyzi et al.14

Approval for the study was obtained from the Clinical Research Ethics Committee of Aydın Adnan Menderes University, Faculty of Dentistry (Document Date and Number: 22.04.2021-28009). Written informed consent was obtained from all participants and their families.

Treatment protocol

To standardize the orthodontic treatment, 0.022 × 0.028-inch slotted Roth metal brackets and tubes (Mini Master Series; American Orthodontics, Sheboygan, WI, USA) were used. Bracketing, leveling, and alignment protocols were applied to all patients. As a final measure before canine distalization, 0.019 × 0.025-inch stainless steel arch wires were applied to the bracket slots of the patients, after which a 2-month waiting period ensued until the wires became passive. To avoid loss of anchorage during canine distalization in the study, mini-screws 1.5 mm in diameter and 8 mm in length (The Aarhus System; Royal College, Aarhus, Denmark) were applied between the roots of the maxillary first molar and second premolar teeth. NiTi sealing springs were attached to the distal hook of the bracket on the teeth using a mini-screw anchor to apply 150 g of force for canine distalization mechanics (Figure 1).

Figure 1. Distalization mechanics with mini-screws.

Collection and storage of GCF samples

In our study, samples were collected from the distal gingival groove of the canines that were chosen for distalization. Gingival crevicular fluid samples were taken from the distal regions of the canine teeth using a periopaper (Gingival Fluid Collection Strips; Oraflow, Smithtown, NY, USA) before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), and 21st days (T4) of the application of the distalization force.15 Due to the diurnal rhythm of leptin, GCF samples were collected from all participants at the same time and before meals.5 Paper strips contaminated with blood, saliva, or plaque were excluded. After the paper strips were left in the gingival pocket for 1 minute, the volume of the liquid absorbed was measured using a pre-calibrated electronic device (Periotron 8010; Oraflow, Amityville, NY, USA). Each paper strip was placed in a different Eppendorf tube and stored at –80°C until analysis.

Digital model measurements

Since the distalization rates of canine teeth will be evaluated in obese and normal-weight individuals in the study, all patients were scanned intraorally before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), 21st (T4), 28th day (T5), and 3rd month (T6) of the application of the distalization force to the canine tooth. The OrthoAnalyzer program (3Shape A/S, Copenhagen, Denmark) was used to measure the amount of tooth movement in the models obtained digitally from the scans. Because the mini-screws may have been positioned differently between patients, they were projected onto the occlusal plane, and the distance from the canine tooth perpendicular to this point was measured (Figure 2). The differences between the distance measurements obtained (T0-T1, T1-T2, T3-T4, T4-T5, T5-T6) were calculated to determine how much the tooth moved in each measurement. In addition, the amount of tooth movement was calculated at the end of 21 days (T0-T4), 1 month (T0-T5) and 3 months (T0-T6).

Figure 2. Distance measurement through digital model.

To evaluate intraobserver agreement, it was calculated that to test the hypotheses H0: ρ = 0.70 and H1: ρ = 0.90 at a Type I error level of 0.05 and a Type II error level of 0.20, the amount of tooth movement should be measured again in at least 18.4 images.16 Digital models of 19 randomly selected patients were re-evaluated 1 month after the first evaluation.

Periodontal measurements

In this study, periodontal measurements were made during the time periods in which GCF was measured (T0, T1, T2, T3, and T4), and the periodontal health of the individuals was evaluated. The plaque index, gingival index, and bleeding on probing were examined as previously described.

Statistical analyses

The suitability to the normal distribution of numerical variables such as age, biochemical measurements, etc. included in the study was examined with the Shapiro–Wilk test. The intra-observer agreement level for distance measurements was determined using the intraclass correlation coefficient (ICC).

The ages of patients in the study and control groups were compared using an independent two-sample t test. Differences between groups in terms of changes in distance measurements over time were examined using two-way mixed analysis of variance (ANOVA). However, because the sphericity assumption was not met, the Greenhouse–Geisser correction was applied. Because the group and time interaction effect was not statistically significant, the difference between groups at each measurement time point was examined using an independent two-sample t test. The difference between time points in each group was examined using repeated-measures ANOVA, and the Greenhouse–Geisser correction was applied. Since it was determined that there were outliers with Mahalanobis distance in biochemical and periodontal measurements and these measurements did not meet at least one assumption, the difference in the change of measurements over time between groups was examined with a non-parametric Factorial 1-Longitudinal Data-Factorial 1 (F1-LD-F1) design. The ANOVA-type test statistic and P values obtained from the F1-LD-F1 design were provided for group and time interaction effects. The groups were compared using the Mann–Whitney U test for relevant measurements and the rate of tooth movement at each measurement time. The relationship between the change observed in leptin level and the rates of tooth movement in the first 21 days of the study was examined using Pearson correlation analysis.

The statistical significance level was accepted as P ≤ 0.05.

RESULTS

The demographic characteristics of the study and control groups are shown in Table 1. There was no significant difference in demographic characteristics between the two groups, except for BMI percentile (P < 0.001) (Table 1).

Table 1 . Demographic characteristics of the participants.

DemographicOverallNormal-weightObeseP value
Patients361818
Female/Male18/189/99/9
Age (mean ± SD)15.34 ± 1.1315.18 ± 1.4215.32 ± 1.570.775
BMI percentile (mean ± SD)78.24 ± 23.9455.79 ± 15.9196.03 ± 0.76< 0.001***

SD, standard deviation; BMI, body mass index..

Independent t test..

Statistically significant, ***P < 0.001..



The GCF volume did not show a statistically significant difference over time between the study and control groups (P = 0.592 and P = 0.315, respectively) (Table 2).

Table 2 . Distribution of gingival crevicular fluid (GCF) volume by groups and time.

GCF volume (µL)Study groupControl groupComparison result
Time of
measurement
Mean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
ZP value
T00.34 ± 0.190.36 ± 0.140.7280.467
0.32 (0.22–0.40)0.33 (0.26–0.42)
T10.38 ± 0.190.35 ± 0.160.3170.752
0.33 (0.24–0.44)0.33 (0.25–0.42)
T20.31 ± 0.130.29 ± 0.100.5070.612
0.29 (0.24–0.43)0.32 (0.19–0.37)
T30.40 ± 0.190.31 ± 0.141.5520.121
0.43 (0.26–0.51)0.30 (0.22–0.37)
T40.33 ± 0.140.38 ± 0.131.1080.268
0.29 (0.21–0.45)0.39 (0.30–0.48)
χ2, P value2.797, 0.5924.737, 0.315

ANOVA-type test statistic for Group × Time interaction effect = 1.362, P = 0.248..

Gingival crevicular fluid samples were taken from the distal regions of the canine teeth using a periopaper (Gingival Fluid Collection Strips; Oraflow, Smithtown, NY, USA) before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), and 21st days (T4) of the application of the distalization force..

SD, standard deviation; IQR, interquartile range..



The levels of leptin, RANKL, OPG, and IL-6 in the study and control groups did not show a significant change over time (P > 0.05); however, at each measurement time point, the levels of leptin, OPG, and IL-6 were significantly higher in the study group than in the control group (P < 0.05). RANKL levels did not show a significant difference between the groups at T0 (P = 0.121) (Tables 36).

Table 3 . Distribution of leptin levels according to groups and time.

Leptin (ng/mL)Study groupControl groupComparison result
Time of
measurement
Mean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
ZP value
T02.90 ± 0.721.70 ± 0.474.272< 0.001***
2.82 (2.55–3.39)1.76 (1.41–1.85)
T12.88 ± 1.561.65 ± 0.392.7530.006**
2.91 (1.71–3.46)1.73 (1.35–1.97)
T22.74 ± 0.751.59 ± 0.563.829< 0.001***
2.87 (2.01–3.27)1.56 (1.30–1.84)
T32.62 ± 1.031.57 ± 0.313.577< 0.001***
2.51 (1.79–3.67)1.53 (1.38–1.73)
T42.54 ± 0.641.58 ± 0.364.303< 0.001***
2.38 (2.03–3.09)1.59 (1.35–1.87)
χ2, P value2.978, 0.5621.600, 0.809

ANOVA-type test statistic for Group × Time interaction effect = 0.207, P = 0.912..

Gingival crevicular fluid samples were taken from the distal regions of the canine teeth using a periopaper (Gingival Fluid Collection Strips; Oraflow, Smithtown, NY, USA) before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), and 21st days (T4) of the application of the distalization force..

SD, standard deviation; IQR, interquartile range..

Statistically significant, **P < 0.01, ***P < 0.001..



Table 4 . Distribution of RANKL level by groups and time.

t-RANKL (pg/mL)Study groupControl groupComparison result
Time of
measurement
Mean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
ZP value
T0267.95 ± 138.74195.32 ± 80.141.5510.121
257.75 (152.06–330.21)172.17 (156.73–197.49)
T1278.98 ± 65.08208.54 ± 63.573.2780.001**
279.94 (205.02–349.21)188.53 (173.67–213.87)
T2292.28 ± 85.99219.27 ± 88.752.8480.004**
280.38 (215.94–340.02)176.69 (161.82–250.63)
T3284.22 ± 119.91211.93 ± 60.561.9780.048*
277.08 (191.16–349.86)190.27 (168.45–218.11)
T4263.09 ± 68.00196.26 ± 43.263.1660.002**
260.62 (215.94–307.01)180.28 (164.39–204.63)
χ2, P value3.042, 0.5512.212, 0.712

ANOVA-type test statistic for Group × Time interaction effect = 0.266, P = 0.872..

Gingival crevicular fluid samples were taken from the distal regions of the canine teeth using a periopaper (Gingival Fluid Collection Strips; Oraflow, Smithtown, NY, USA) before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), and 21st days (T4) of the application of the distalization force..

RANKL, receptor activator of nuclear factor kappa-Β ligand; SD, standard deviation; IQR, interquartile range..

Statistically significant, *P < 0.05, **P < 0.01..



Table 5 . Distribution of OPG level by groups and time.

t-OPG (ng/mL)Study groupControl groupComparison result
Time of
measurement
Mean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
ZP value
T07.16 ± 2.914.31 ± 2.513.736< 0.001***
6.08 (5.00–8.45)3.81 (3.02–4.23)
T16.86 ± 3.684.18 ± 1.703.4500.001**
6.18 (4.50–7.24)3.72 (3.38–4.66)
T27.10 ± 1.874.08 ± 1.634.130< 0.001***
6.99 (5.51–8.39)4.03 (3.04–4.55)
T37.66 ± 3.094.43 ± 1.843.2280.001**
8.09 (6.05–9.22)3.92 (3.23–5.11)
T48.28 ± 5.554.24 ± 1.543.2770.001**
6.88 (5.10–9.35)4.03 (3.15–4.65)
χ2, P value4.533, 0.3391.867, 0.760

ANOVA-type test statistic for Group × Time interaction effect = 0.323, P = 0.811..

Gingival crevicular fluid samples were taken from the distal regions of the canine teeth using a periopaper (Gingival Fluid Collection Strips; Oraflow, Smithtown, NY, USA) before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), and 21st days (T4) of the application of the distalization force..

OPG, osteoprotegerin; SD, standard deviation; IQR, interquartile range..

Statistically significant, **P < 0.01, ***P < 0.001..



Table 6 . Distribution of IL-6 level by groups and time.

t-IL-6 (ng/L)Study groupControl groupComparison result
Time of
measurement
Mean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
ZP value
T0222.50 ± 79.3072.93 ± 62.984.148< 0.001***
232.41 (191.66–257.32)58.84 (35.18–92.22)
T1258.28 ± 73.4094.84 ± 71.284.337< 0.001***
254.19 (223.17–307.31)72.59 (58.06–104.53)
T2280.61 ± 60.90100.24 ± 39.935.080< 0.001***
259.84 (235.13–329.09)92.56 (72.19–111.36)
T3234.38 ± 66.1985.06 ± 60.034.526< 0.001***
241.21 (190.29–260.47)67.12 (36.91–116.83)
T4225.10 ± 91.2476.24 ± 36.454.115< 0.001***
251.43 (168.44–297.57)65.22 (55.00–85.54)
χ2, P value2.800, 0.5925.538, 0.236

ANOVA-type test statistic for Group × Time interaction effect = 0.028, P = 0.997..

Gingival crevicular fluid samples were taken from the distal regions of the canine teeth using a periopaper (Gingival Fluid Collection Strips; Oraflow, Smithtown, NY, USA) before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), and 21st days (T4) of the application of the distalization force..

IL-6, interleukin-6; SD, standard deviation; IQR, interquartile range..

Statistically significant, ***P < 0.001..



The ICC was calculated as 0.990 (95% confidence interval: 0.975–0.996) for the distance measurements to determine the amount and rate of movement of the canine teeth (P < 0.001). Accordingly, the intra-observer agreement for these measurements was excellent.

When distance measurements in the study and control groups were considered, there was a statistically significant change in the distance between these points over time in both groups (P < 0.001 for both); however, the change was similar (P = 0.172). When the two groups were compared in terms of changes between consecutive time points, the decrease between T3 and T4 was significantly greater in the control group (P = 0.002), whereas all other changes were similar between the two groups (P > 0.05) (Table 7 and Figure 3).

Figure 3. Change of distance measurements in groups over time.
Before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), 21st (T4), 28th (T5) days and 3rd month (T6) of the application of the distalization force.
**P < 0.01.

Table 7 . The mean amount of tooth movement by groups and periods.

Amount of movement (mm)Study groupControl groupComparison result
PeriodMean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
tP value
T0–T10.31 ± 0.150.24 ± 0.081.6780.103
0.28 (0.23–0.39)0.23 (0.18–0.30)
T1–T20.19 ± 0.130.17 ± 0.080.5290.601
0.13 (0.11–0.28)0.17 (0.11–0.21)
T2–T30.17 ± 0.120.21 ± 0.101.0370.307
0.13 (0.11–0.20)0.19 (0.14–0.25)
T3–T40.21 ± 0.110.35 ± 0.133.3950.002**
0.23 (0.13–0.28)0.38 (0.25–0.47)
T4–T50.19 ± 0.100.18 ± 0.100.3260.747
0.18 (0.11–0.30)0.16 (0.11–0.24)
T5–T62.36 ± 0.512.42 ± 0.400.4250.674
2.34 (1.94–2.85)2.45 (2.08–2.70)

F statistic = 0.992, Greenhouse–Geisser corrected P = 0.364..

The amount of tooth movement was calculated at the end of 21 days (T0–T4), 1 month (T0–T5) and 3 months (T0–T6)..

SD, standard deviation; IQR, interquartile range..

Statistically significant, **P < 0.01..



The average amount of tooth movement in the T0-T4 period was 0.88 ± 0.21 mm in the study group and 0.97 ± 0.17 mm in the control group. Although the amount of tooth movement during this process was greater in the control group, the difference was not statistically significant (P = 0.167). The average amount of tooth movement was similar (P > 0.05) between the two groups during the T0-T5 and T0-T6 periods (Supplementary Table 1).

When the relationship between the change in leptin level (T4-T0) and tooth movement in the first 21 days of the study was examined, the correlation coefficient was calculated as r = –0.002 (P = 0.994) in the study group and r = –0.121 (P = 0.634) in the control group. There was no statistically significant linear relationship between changes in leptin levels and tooth movement (Figure 4).

Figure 4. Scatter plot of change in leptin level and tooth movement in the first 21 days.

Among the periodontal measurements, the plaque index, gingival index, and bleeding on probing values showed significant changes over time in both groups (P < 0.001), but the changes were similar (P > 0.05) (Supplementary Tables 2–4).

DISCUSSION

Studies have investigated the effects of obesity on oral and dental health, and orthodontic treatment procedures for obese individuals have often been a subject of discussion.17 Since orthodontic tooth movement depends on many factors, it is difficult to understand the effects of obesity on periodontal tissues.18 Considering the worldwide increase in obesity, our study aimed to evaluate the effect of obesity on the periodontal tissue during orthodontic movement.

Leptin is a signaling molecule with growth factor properties. It stimulates osteoblasts, inhibits osteoclast formation and activity and promotes osteogenesis. Leptin also plays a role in anti-osteogenic effects via its central effect on the hypothalamus.19 High concentrations of leptin protect bone.20 While some studies argue that the rate of tooth movement increases in individuals with increased serum leptin levels, others show a decrease in the rate of tooth movement.2,10-12,21-24

When studies on canine distalization with elastomeric chains and NiTi closed-coil springs were examined, leptin levels were found to be lower than the initial levels after applying a distalization force.10,12,25 In this study, similar to the literature, leptin levels started to decrease in both groups after the distalization force was applied and remained below the initial value at the end of 21 days; however, this change was not statistically significant. Considering that high concentrations of leptin help maintain bone levels, leptin levels may decrease during resorption.

Leptin, which is synthesized in adipocytes, is secreted mostly from white adipose tissue and, to a lesser extent, brown adipose tissue.26 For this reason, there is a consensus in the literature that the level of leptin parallels the increase in BMI and, therefore, the amount of fat in the body.27 Studies have suggested that during orthodontic treatment, leptin levels in individuals with an increased BMI are higher than those in normal-weight individuals.2,10,28 The results of all these studies are compatible with those of our study.

RANKL binds to its receptor, RANK, and stimulates cells. RANK by RANKL initiates intracellular signaling. This stimulation enables precursor osteoclasts to transform into mature osteoclasts and become active. RANKL and its receptor RANK are the main regulatory factors in bone formation and resorption.7,29

Several factors that induce RANKL synthesis in osteoblasts also regulate OPG expression. OPG binds to RANKL and prevents its binding to RANK. Thus, RANKL prevents bone resorption by preventing osteoclast differentiation and activation.30

If RANKL synthesis in the tissue increases compared with OPG production, the RANKL receptor binds to RANK, causing mature osteoclast formation and disrupting the balance in favor of bone resorption. If OPG production is higher than RANKL production, OPG binds to RANKL and osteoclast formation decreases because the RANK-RANKL connection is blocked.31

Few studies have compared obese and normal-weight individuals in terms of RANKL levels during orthodontic treatment. Saloom et al.2 reported that RANKL levels were higher in obese individuals. Another study found that obese mice have higher RANKL levels than normal-weight mice.32 RANKL levels were higher in the obese group when examined in postmenopausal women.33 The findings of these studies are similar to those of our study. Madak10 reported that RANKL levels are higher in normal-weight individuals.

According to our findings, the RANKL levels in the study and control groups increased in the first week after the distalization force was applied, then decreased, and approached a value close to the initial level on the 21st day. This change in RANKL expression is consistent with other studies.10,34 For example, Iwasaki et al.35 reported that cytokine levels may fluctuate over a 28-day cycle as long as orthodontic force is applied. This is in accordance with the literature showing that during the evaluation of tooth movement mechanisms and bone metabolism, RANKL levels increase in the initial phase of bone resorption and approach the initial levels when measured on the 21st day.

Studies examining OPG levels according to BMI have yielded different results.10,36,37 In our study, we found that OPG levels in obese individuals were significantly higher than those in normal-weight individuals.

Kanzaki et al.38 reported that the OPG remained balanced during orthodontic tooth movement. Kawasaki et al.34 found that the OPG level was significantly lower 24 hours after force application, but no statistically significant differences emerged at other time periods. Madak10 and Flórez-Moreno et al.39 stated that the OPG first decreased slightly and then increased slightly. In this study, we observed that changes in OPG levels were not statistically significant in either group.

An increase in the number of white adipose tissue cells is induced by hyperplasia and hypertrophy in obese patients. This situation causes metabolic disorder, adipocyte hypertrophy, and the secretion of tumor necrosis factor-α (TNF-α) and IL-6, which are pro-inflammatory cytokines.40,41 In our study, IL-6 levels in obese individuals were found to be statistically significantly higher than those in normal-weight individuals at each time point.

IL-6 has a significant effect on the bone formation-resorption balance. Disruption of this balance may lead to bone erosion and loss. It increases the accumulation of osteoclasts over IL-6 hematopoietic root cells, decreases the number of osteoblasts, accelerates bone resorption, and damages the ossification. In contrast, an increase in RANK Ligand expression and decrease in the expression of osteoprotegerin, a bone-protective peptide, result in increased osteoclastogenesis.42

When studies evaluating the relationship between orthodontic tooth movement and IL-6 levels were examined, Padisar et al.43 reported that although the IL-6 level was higher than the initial level 1 hour after the orthodontic force was applied, the cytokine level was similar to the initial level after 28 days. Acun Kaya et al.44 reported that the IL-6 level reached its maximum level 3 days after the application of force and started to decrease within a period of 1 week to 10 days. In this study, for both obese and normal-weight individuals, the IL-6 level initially increased after the distalization force was applied, reached the maximum level in the 1st week, and then tended to decrease and reached a value close to the initial level at the end of the 21st day, which was similar to the results from other studies.

von Bremen et al.45 reported in their study that overweight individuals showed less cooperation in orthodontic treatment, and accordingly, the duration of orthodontic treatment was longer than that in normal-weight individuals. In a similar study, von Bremen et al.46 reported that the treatment period for obese patients was longer than that for normal-weight individuals; however, the difference was not statistically significant. Saloom et al.2 stated that the leveling time in obese patients is faster than that in individuals of normal-weight, and the amount of tooth movement is greater at the beginning of treatment. In our study, there was no statistically significant difference between obese and normal-weight individuals regarding the effect of orthodontic treatment on tooth movement during canine distalization phase. However, there were differences in the cytokine levels, except for RANKL, between the two groups at the beginning of the study. The fact that differences in cytokine levels expected to occur after applying force also existed in the T0 phase was due to the effects of obesity on cytokine levels. This may explain why increases and decreases in cytokine levels did not cause a difference in the amount of tooth movement during the canine distalization phase between the groups.

Madak10 compared normal-weight and overweight individuals in terms of canine distalization. According to the results of this study, the time required to complete canine distalization was significantly longer in overweight individuals than in normal-weight individuals. When the common time intervals of both studies were compared according to the average orthodontic tooth movement at the end of the first and third months, more orthodontic tooth movement occurred in normal-weight individuals than in obese individuals.

Madak10 reported that there was a negative relationship between the change in leptin level at the end of one month and the amount of tooth movement in both groups. Jayachandran et al.24 reported that there was a positive correlation between leptin level and the amount of orthodontic tooth movement. Srinivasan et al.47 also reported that there was a positive correlation between the amount of tooth movement and leptin level. When considering the correlation between leptin level and the amount of tooth movement in our study, no linear relationship was found between the change in leptin level at 21-days and the amount of orthodontic tooth movement at 21-days in both groups.

Limitations of the study

The differences in the findings of our study may be attributed to the use of different obesity classification methods, differences in orthodontic treatment mechanics, or differences in demographic characteristics of the participants.

A limitation of this study is that it assumes that the miniscrew positions are fixed during distance measurements. Mini-screws can be displaced to a certain degree after an orthodontic force is applied.48

CONCLUSIONS

1. The investigated leptin, RANKL, OPG and IL-6 biomarker levels show statistically significant differences between obese and normal-weight individuals.

2. There was no statistically significant difference between the groups in terms of the rate of orthodontic tooth movement.

3. There was no correlation between the amount of orthodontic tooth movement and the leptin levels throughout the first 21 days.

4. Considering the results of our study, there is no harm in applying routine orthodontic treatment procedures in the orthodontic treatment of obese individuals.

AUTHOR CONTRIBUTIONS

Formal analysis: ÖE. Funding acquisition: MU, MGC. Investigation: MU. Methodology: MU, MGC. Project administration: MU, MGC. Supervision: MGC. Writing–original draft: MU. Writing–review & editing: MU.

CONFLICTS OF INTEREST

No potential conflict of interest relevant to this article was reported.

FUNDING

Supported by Aydın Adnan Menderes University Scientific Research Projects (Project No: DHF-21006).

SUPPLEMENTARY MATERIAL

Supplementary data is available at https://doi.org/10.4041/kjod24.001

Fig 1.

Figure 1.Distalization mechanics with mini-screws.
Korean Journal of Orthodontics 2025; 55: 3-14https://doi.org/10.4041/kjod24.001

Fig 2.

Figure 2.Distance measurement through digital model.
Korean Journal of Orthodontics 2025; 55: 3-14https://doi.org/10.4041/kjod24.001

Fig 3.

Figure 3.Change of distance measurements in groups over time.
Before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), 21st (T4), 28th (T5) days and 3rd month (T6) of the application of the distalization force.
**P < 0.01.
Korean Journal of Orthodontics 2025; 55: 3-14https://doi.org/10.4041/kjod24.001

Fig 4.

Figure 4.Scatter plot of change in leptin level and tooth movement in the first 21 days.
Korean Journal of Orthodontics 2025; 55: 3-14https://doi.org/10.4041/kjod24.001

Table 1 . Demographic characteristics of the participants.

DemographicOverallNormal-weightObeseP value
Patients361818
Female/Male18/189/99/9
Age (mean ± SD)15.34 ± 1.1315.18 ± 1.4215.32 ± 1.570.775
BMI percentile (mean ± SD)78.24 ± 23.9455.79 ± 15.9196.03 ± 0.76< 0.001***

SD, standard deviation; BMI, body mass index..

Independent t test..

Statistically significant, ***P < 0.001..


Table 2 . Distribution of gingival crevicular fluid (GCF) volume by groups and time.

GCF volume (µL)Study groupControl groupComparison result
Time of
measurement
Mean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
ZP value
T00.34 ± 0.190.36 ± 0.140.7280.467
0.32 (0.22–0.40)0.33 (0.26–0.42)
T10.38 ± 0.190.35 ± 0.160.3170.752
0.33 (0.24–0.44)0.33 (0.25–0.42)
T20.31 ± 0.130.29 ± 0.100.5070.612
0.29 (0.24–0.43)0.32 (0.19–0.37)
T30.40 ± 0.190.31 ± 0.141.5520.121
0.43 (0.26–0.51)0.30 (0.22–0.37)
T40.33 ± 0.140.38 ± 0.131.1080.268
0.29 (0.21–0.45)0.39 (0.30–0.48)
χ2, P value2.797, 0.5924.737, 0.315

ANOVA-type test statistic for Group × Time interaction effect = 1.362, P = 0.248..

Gingival crevicular fluid samples were taken from the distal regions of the canine teeth using a periopaper (Gingival Fluid Collection Strips; Oraflow, Smithtown, NY, USA) before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), and 21st days (T4) of the application of the distalization force..

SD, standard deviation; IQR, interquartile range..


Table 3 . Distribution of leptin levels according to groups and time.

Leptin (ng/mL)Study groupControl groupComparison result
Time of
measurement
Mean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
ZP value
T02.90 ± 0.721.70 ± 0.474.272< 0.001***
2.82 (2.55–3.39)1.76 (1.41–1.85)
T12.88 ± 1.561.65 ± 0.392.7530.006**
2.91 (1.71–3.46)1.73 (1.35–1.97)
T22.74 ± 0.751.59 ± 0.563.829< 0.001***
2.87 (2.01–3.27)1.56 (1.30–1.84)
T32.62 ± 1.031.57 ± 0.313.577< 0.001***
2.51 (1.79–3.67)1.53 (1.38–1.73)
T42.54 ± 0.641.58 ± 0.364.303< 0.001***
2.38 (2.03–3.09)1.59 (1.35–1.87)
χ2, P value2.978, 0.5621.600, 0.809

ANOVA-type test statistic for Group × Time interaction effect = 0.207, P = 0.912..

Gingival crevicular fluid samples were taken from the distal regions of the canine teeth using a periopaper (Gingival Fluid Collection Strips; Oraflow, Smithtown, NY, USA) before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), and 21st days (T4) of the application of the distalization force..

SD, standard deviation; IQR, interquartile range..

Statistically significant, **P < 0.01, ***P < 0.001..


Table 4 . Distribution of RANKL level by groups and time.

t-RANKL (pg/mL)Study groupControl groupComparison result
Time of
measurement
Mean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
ZP value
T0267.95 ± 138.74195.32 ± 80.141.5510.121
257.75 (152.06–330.21)172.17 (156.73–197.49)
T1278.98 ± 65.08208.54 ± 63.573.2780.001**
279.94 (205.02–349.21)188.53 (173.67–213.87)
T2292.28 ± 85.99219.27 ± 88.752.8480.004**
280.38 (215.94–340.02)176.69 (161.82–250.63)
T3284.22 ± 119.91211.93 ± 60.561.9780.048*
277.08 (191.16–349.86)190.27 (168.45–218.11)
T4263.09 ± 68.00196.26 ± 43.263.1660.002**
260.62 (215.94–307.01)180.28 (164.39–204.63)
χ2, P value3.042, 0.5512.212, 0.712

ANOVA-type test statistic for Group × Time interaction effect = 0.266, P = 0.872..

Gingival crevicular fluid samples were taken from the distal regions of the canine teeth using a periopaper (Gingival Fluid Collection Strips; Oraflow, Smithtown, NY, USA) before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), and 21st days (T4) of the application of the distalization force..

RANKL, receptor activator of nuclear factor kappa-Β ligand; SD, standard deviation; IQR, interquartile range..

Statistically significant, *P < 0.05, **P < 0.01..


Table 5 . Distribution of OPG level by groups and time.

t-OPG (ng/mL)Study groupControl groupComparison result
Time of
measurement
Mean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
ZP value
T07.16 ± 2.914.31 ± 2.513.736< 0.001***
6.08 (5.00–8.45)3.81 (3.02–4.23)
T16.86 ± 3.684.18 ± 1.703.4500.001**
6.18 (4.50–7.24)3.72 (3.38–4.66)
T27.10 ± 1.874.08 ± 1.634.130< 0.001***
6.99 (5.51–8.39)4.03 (3.04–4.55)
T37.66 ± 3.094.43 ± 1.843.2280.001**
8.09 (6.05–9.22)3.92 (3.23–5.11)
T48.28 ± 5.554.24 ± 1.543.2770.001**
6.88 (5.10–9.35)4.03 (3.15–4.65)
χ2, P value4.533, 0.3391.867, 0.760

ANOVA-type test statistic for Group × Time interaction effect = 0.323, P = 0.811..

Gingival crevicular fluid samples were taken from the distal regions of the canine teeth using a periopaper (Gingival Fluid Collection Strips; Oraflow, Smithtown, NY, USA) before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), and 21st days (T4) of the application of the distalization force..

OPG, osteoprotegerin; SD, standard deviation; IQR, interquartile range..

Statistically significant, **P < 0.01, ***P < 0.001..


Table 6 . Distribution of IL-6 level by groups and time.

t-IL-6 (ng/L)Study groupControl groupComparison result
Time of
measurement
Mean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
ZP value
T0222.50 ± 79.3072.93 ± 62.984.148< 0.001***
232.41 (191.66–257.32)58.84 (35.18–92.22)
T1258.28 ± 73.4094.84 ± 71.284.337< 0.001***
254.19 (223.17–307.31)72.59 (58.06–104.53)
T2280.61 ± 60.90100.24 ± 39.935.080< 0.001***
259.84 (235.13–329.09)92.56 (72.19–111.36)
T3234.38 ± 66.1985.06 ± 60.034.526< 0.001***
241.21 (190.29–260.47)67.12 (36.91–116.83)
T4225.10 ± 91.2476.24 ± 36.454.115< 0.001***
251.43 (168.44–297.57)65.22 (55.00–85.54)
χ2, P value2.800, 0.5925.538, 0.236

ANOVA-type test statistic for Group × Time interaction effect = 0.028, P = 0.997..

Gingival crevicular fluid samples were taken from the distal regions of the canine teeth using a periopaper (Gingival Fluid Collection Strips; Oraflow, Smithtown, NY, USA) before (T0), 24 hours after (T1), and on the 7th (T2), 14th (T3), and 21st days (T4) of the application of the distalization force..

IL-6, interleukin-6; SD, standard deviation; IQR, interquartile range..

Statistically significant, ***P < 0.001..


Table 7 . The mean amount of tooth movement by groups and periods.

Amount of movement (mm)Study groupControl groupComparison result
PeriodMean ± SD
Median (IQR)
Mean ± SD
Median (IQR)
tP value
T0–T10.31 ± 0.150.24 ± 0.081.6780.103
0.28 (0.23–0.39)0.23 (0.18–0.30)
T1–T20.19 ± 0.130.17 ± 0.080.5290.601
0.13 (0.11–0.28)0.17 (0.11–0.21)
T2–T30.17 ± 0.120.21 ± 0.101.0370.307
0.13 (0.11–0.20)0.19 (0.14–0.25)
T3–T40.21 ± 0.110.35 ± 0.133.3950.002**
0.23 (0.13–0.28)0.38 (0.25–0.47)
T4–T50.19 ± 0.100.18 ± 0.100.3260.747
0.18 (0.11–0.30)0.16 (0.11–0.24)
T5–T62.36 ± 0.512.42 ± 0.400.4250.674
2.34 (1.94–2.85)2.45 (2.08–2.70)

F statistic = 0.992, Greenhouse–Geisser corrected P = 0.364..

The amount of tooth movement was calculated at the end of 21 days (T0–T4), 1 month (T0–T5) and 3 months (T0–T6)..

SD, standard deviation; IQR, interquartile range..

Statistically significant, **P < 0.01..


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