Comparison of mandibular bone density and morphology in patients with Angle Class I, II, and III malocclusion using panoramic radiography: a cross-sectional study

Abstract

Background

Variations in sagittal jaw relationships may be accompanied by adaptive changes in mandibular cortical thickness and contour, potentially affecting bone quality and the biomechanical response to orthodontic forces. In this context, the present cross-sectional study aimed to investigate the relationship between different sagittal malocclusion types and mandibular bone morphology through comparison of radiomorphometric parameters obtained from panoramic radiographs.

Methods

A total of 150 female patients were included and equally divided into three groups according to their Angle malocclusion classification: Class I, Class II, and Class III. Measurements of mental index (MI), panoramic mandibular index (PMI), gonial index (GI), antegonial index (AI), antegonial notch depth (AND), mandibular cortical index (MCI), and grayscale value (GS) were performed using ImageJ software. Intergroup comparisons were analyzed by Kruskal-Wallis tests followed by Bonferroni-corrected pairwise comparisons.

Results

Significant differences were identified among groups in MI, PMI, and AND measurements. Specifically, Angle Class III subjects exhibited significantly lower MI and PMI values than Angle Class I and II groups (p < 0.001), indicating thinner mandibular cortical bone. AND was shallower in Angle Class III individuals compared to Class I (p = 0.005) and Class II (p = 0.049), indicating a less pronounced antegonial concavity along the mandibular lower border. No statistically significant differences were observed among the groups in GI, AI, or GS measurements (p > 0.05). Mandibular cortical index (MCI) categorical distributions also showed no significant intergroup differences.

Conclusions

These findings demonstrate that mandibular cortical bone thickness and antegonial notch morphology vary with sagittal malocclusion, with Class III malocclusion associated with thinner cortical bone and altered mandibular contours. These morphological differences highlight the importance of considering bone quality and morphology during orthodontic diagnosis and treatment planning, since they may influence treatment biomechanics and long-term stability.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-026-07719-7.

Background

Panoramic radiography is a two-dimensional radiological technique that enables visualization of the entire maxillofacial region in a single image and has become a routine record in dentistry due to its diagnostic and treatment-planning value. Its main advantages include rapid imaging time, low cost, ease of patient positioning, and a relatively low radiation dose [1]. Additionally, panoramic radiographs allow for early detection of jawbone pathologies, dental anomalies, impacted teeth, jaw fractures, and bone changes related to systemic diseases [2, 3]. Due to all these features and its ease of archiving, it is also frequently preferred as a diagnostic tool in the field of orthodontics.

The use of panoramic radiographs in orthodontics provides information that guides tooth movements, such as tooth alignment, missing teeth, and root morphology. Moreover, it offers the opportunity to evaluate temporomandibular joint morphology and bone quality prior to treatment. Fractal analysis applied to panoramic radiographs has revealed significant alterations in mandibular bone structure in patients with bruxism [4, 5], temporomandibular joint disorders [6], different malocclusion patterns during growth [7], and after functional appliance therapy, particularly in the condylar and corpus regions [8]. Therefore, it can be stated that panoramic radiographs are not only effective for evaluating dental structures but also serve as a valuable tool for the qualitative and quantitative analysis of alveolar and cortical bone structures, providing important information regarding the orthodontic treatment process.

Mandibular bone density is an important parameter for both orthodontics and other fields of dentistry when planning procedures related to the bone. In addition to various radiomorphometric measurements, categorical classifications can also be used to assess bone density. Klemetti et al. [9] developed methods for determining the risk of osteoporosis through panoramic radiographs by evaluating changes in the mandibular cortical bone. Furthermore, parameters such as the gonial index, antegonial index, mental index, and mandibular cortical width have been investigated to identify morphological changes in the mandible in cases of edentulism [10, 11]. In individuals with bruxism, additional parameters such as antegonial notch depth, panoramic mandibular index, and grayscale values have been assessed, and these measurements have been shown to reflect statistically significant changes in mandibular bone morphology in the presence of bruxism [5, 12, 13].

In orthodontic treatment planning, an accurate evaluation of mandibular bone density and morphology can have a direct impact on treatment duration, post-treatment stability, and complication management, as well as on anchorage strategies such as orthodontic mini-screw stability. Therefore, the aim of this study was to compare mandibular radiomorphometric measurements obtained from panoramic radiographs in individuals with Angle Class I, II, and III malocclusions. By analyzing the obtained data, it was intended to reveal the effects of different malocclusion types on mandibular bone morphology and to develop more predictable approaches regarding bone quality in orthodontic treatment planning.

Methods

Study design and reporting

This retrospective cross-sectional study was conducted in the Department of Orthodontics, Hacettepe University, Ankara, Türkiye, and included pretreatment panoramic radiographs of patients who applied for orthodontic treatment between 2022 and 2025.

Ethical approval

Ethical approval for the study was granted by the Health Sciences Research Ethics Committee of Hacettepe University (Approval No: SBA 25/471).

Participants

Using G*Power software (version 3.1.9.7; Heinrich-Heine University, Düsseldorf, Germany), it was determined that a total of 144 participants would be required, with 48 individuals in each group, to achieve an effect size of f = 0.26, a significance level of 5%, and a power of 80% [13]. Considering possible data losses, it was decided to include panoramic radiographs of 150 patients, with 50 individuals in each group. Sagittal skeletal classification was based on ANB angles, which were measured on lateral cephalometric radiographs available for all participants. Individuals were categorized into groups based on their type of sagittal malocclusion: if the ANB angle was between 0 and 4 degrees, they were classified as having Angle Class I malocclusion; if greater than 4 degrees, Angle Class II malocclusion; and if less than 0 degrees, Angle Class III malocclusion.

Participants were selected from pretreatment orthodontic records according to predefined eligibility criteria. The inclusion criteria were: (1) having passed the pubertal growth spurt, (2) being female, (3) having a pre-treatment panoramic radiograph obtained using the Planmeca Promax 2D device (Planmeca, Helsinki, Finland), and (4) not exhibiting vertical facial growth beyond normal limits. Vertical facial pattern was assessed using the SGo/NMe ratio, and only normodivergent individuals were included in the study. The exclusion criteria were: (1) presence of any bone metabolism disorder, (2) presence of any craniofacial anomaly such as cleft lip or palate, (3) congenital tooth agenesis, (4) presence of artefacts and/or poor image quality on the panoramic radiograph, and (5) severe asymmetry (greater than 4 degrees) that could affect mandibular morphology.

Procedure

To minimize potential measurement and technical bias, all panoramic radiographs were taken by the same operator using the same panoramic imaging device (Planmeca ProMax 2D, Planmeca OY, Helsinki, Finland) under identical exposure and acquisition parameters (66.0 kV, 8.0 mA, 15.8 s). All images were coded to ensure confidentiality of personal data and then classified according to their respective groups.

Radiomorphometric measurements

Radiomorphometric measurements were performed using ImageJ software (NIH, Bethesda, MD, USA). For grayscale value analysis, a standardized rectangular region of interest (ROI) was placed on the mandibular trabecular bone, and the mean grayscale value within the ROI, expressed on a scale from 0 to 255 without unit, was recorded for each radiograph. The use of the same device and identical imaging parameters was intended to minimize technical variability in grayscale measurements. All measurements taken on the panoramic radiographs are described in Table 1 and illustrated in Fig. 1.

Table 1.

Definitions of panoramic radiomorphometric indices used to evaluate mandibular bone density and morphology

Measurement	Definition
Mental index [14]	The vertical thickness of the inferior mandibular cortex measured at the level of the mental foramen.
Panoramic mandibular index [14]	The ratio of the mandibular cortical thickness at the mental foramen level to the distance from the inferior border of the mandible to the inferior margin of the mental foramen.
Gonial index [15]	The cortical thickness measured at the point where a tangent line drawn along the posterior border of the ramus intersects with a tangent line along the inferior border of the mandible.
Antegonial index [16]	The cortical thickness measured along the line drawn from the anterior border of the ramus to the inferior border of the mandible.
Antegonial notch depth [11]	The vertical distance measured between the deepest point of the antegonial concavity observed on the inferior border of the mandible and the tangent line drawn along the inferior border.
Grayscale value [12]	The density value determined on the trabecular bone located 3 mm apical to the apex of the mandibular first premolar.
Mandibular cortical index [9]	A classification of the inferior mandibular cortex: C1 indicates a clear and even endosteal margin of the mandibular cortex bilaterally. C2 indicates the presence of semilunar defects on the endosteal margin. C3 indicates the presence of severe endosteal cortical defects and porosity [see Additional file 1].

Fig. 1.

Presentation of mandibular radiomorphometric measurements on a panoramic radiograph. (1) Mental index, (2) measurement for panoramic mandibular index (PMI), (3) gonial index, (4) antegonial index, (5) antegonial notch depth, and (6) area used for grayscale value analysis. All white lines represent tangents used for the mandibular posterior and inferior borders. The green line indicates the anterior border of the ramus. The black circular marker denotes the mental foramen. The figure is provided for illustrative purposes; all measurements were performed digitally using ImageJ software

Statistical analysis

The data obtained in this study were analyzed using IBM SPSS Statistics (version 23.0; IBM Corp., Armonk, NY, USA). There were no missing data for the analyzed variables. The Shapiro–Wilk test was applied to assess the normality of distribution of measurements between groups. The Kruskal–Wallis test for independent samples was used to assess differences in age, vertical facial pattern, radiomorphometric index measurements, and gray values among the groups. For variables that showed significance in the Kruskal–Wallis test, pairwise comparisons with Bonferroni correction were conducted to identify between which groups the differences existed. The chi-square test was employed to analyze the differences in the distribution of categorical variables (mandibular cortical index scores) between groups. Intraobserver reliability was assessed by repeating radiomorphometric measurements on a randomly selected 25% subset of the radiographs, and agreement was evaluated using the intraclass correlation coefficient (ICC). A significance level of p < 0.05 was considered for tests. Descriptive statistics were presented as mean ± standard deviation.

Results

Intraobserver reliability analysis demonstrated good to excellent agreement, with ICC values ranging from 0.800 to 0.927 across all radiomorphometric measurements. The mean ages of the groups were determined as 17.35 ± 3.47 years for Angle Class I, 17.10 ± 2.67 years for Angle Class II, and 16.70 ± 3.29 years for Angle Class III (p = 0.738). No significant difference was found in the age distribution among the groups (Table 2). The vertical facial pattern, assessed using the SGo/NMe ratio, did not differ significantly among the Angle Class I, Class II, and Class III groups (p = 0.067), indicating comparable vertical skeletal characteristics across the study groups (Table 2). A statistically significant difference was observed in the mental index values among the groups (p < 0.001). Pairwise comparisons revealed that Angle Class III group had significantly lower mental index values than both Angle Class I (p < 0.001) and Class II (p = 0.001). A significant difference was also found in the panoramic mandibular index measurements between the groups (p < 0.001), with Angle Class III showing significantly lower values than both Angle Class I (p = 0.014) and Class II (p < 0.001).

Table 2.

Comparison of age, vertical pattern and panoramic radiographic indices among malocclusion groups

Parameter	Class I (mean ± SD) (n = 50)	Class II (mean ± SD) (n = 50)	Class III (mean ± SD) (n = 50)	p	Pairwise comparison
Age (years)	17.35 ± 3.47	17.10 ± 2.67	16.70 ± 3.29	0.738
Vertical pattern (ratio)	66.1 ± 1.16	64.54 ± 2.02	63.88 ± 2.04	0.067
Mental index (mm)	31.41 ± 13.91	30.82 ± 8.74	18.38 ± 8.10	< 0.001***	I-III p < 0.001***, II-III p = 0.001**
Panoramic mandibular index (ratio)	0.29 ± 0.08	0.32 ± 0.07	0.25 ± 0.07	< 0.001***	I-III p = 0.014*, II-III p < 0.001***
Gonial index (mm)	16.31 ± 10.32	12.30 ± 5.20	14.43 ± 9.96	0.183
Antegonial index (mm)	29.06 ± 13.42	28.24 ± 12.02	24.62 ± 12.55	0.088
Antegonial notch depth (mm)	16.03 ± 9.36	13.59 ± 7.70	10.65 ± 5.80	0.005**	I-III p = 0.005*, II-III p = 0.049*
Grayscale value (0-255)	90.09 ± 32.86	87.46 ± 23.70	97.49 ± 30.00	0.198

SD, standard deviation. The Kruskal–Wallis test was applied. *p < 0.05, **p < 0.01, ***p < 0.001

For antegonial notch depth, a significant difference was detected among the groups (p = 0.005). Pairwise analyses indicated that Angle Class III had significantly lower antegonial notch depth values than both Angle Class I (p = 0.005) and Class II (p = 0.049), corresponding to a shallower and less pronounced antegonial concavity along the mandibular lower border.

In contrast, no statistically significant differences were found among the groups in gonial index (p = 0.183), antegonial index (p = 0.088), or grayscale value (p = 0.198) measurements (Table 2). Additionally, no significant differences were identified in the distribution of mandibular cortical index categories according to malocclusion groups (Pearson chi-square test, p = 0.431), with the distributions of C1, C2, and C3 categories being similar across the three groups (Table 3).

Table 3.

Results of the distribution of mandibular cortical index categories according to malocclusion groups

Mandibular cortical index category	Class I (n = 50)	Class II (n = 50)	Class III (n = 50)	Total (n = 150)	p
C1	27 (%28.7)	35 (%37.2)	32 (%34.0)	94 (%62.7)	0.431
C2	22 (%40.7)	14 (%25.9)	18 (%33.3)	54 (%36.0)
C3	1 (%50.0)	1 (%50.0)	0 (%0.0)	2 (%1.3)

Data are presented as frequency (percentage). Distributions between groups were evaluated using the Pearson chi-square test

Discussion

This study aimed to compare mandibular radiomorphometric measurements obtained from panoramic radiographs in individuals with Angle Class I, II, and III malocclusions. The limited number of studies comprehensively evaluating the impact of malocclusion type on mandibular bone morphology and density highlights the need for such an investigation. In the present study, significant intergroup differences were observed, particularly in mental index, panoramic mandibular index, and antegonial notch depth, suggesting that different malocclusion types may be associated with distinct patterns of mandibular bone morphology. These findings contribute to the current understanding of bone structure assessment in orthodontic treatment planning and may support more informed decisions when tailoring treatment strategies according to malocclusion type.

In this study, only female individuals were included. Previous research has demonstrated statistically significant differences in bone density and cortical thickness between males and females [17, 18]. Although some studies have reported no significant sex-related differences in panoramic mandibular index values [19], other radiomorphometric parameters such as gonial index, mental index, antegonial notch depth, and antegonial index have been shown to differ between sexes [5, 13, 20]. Therefore, restricting the sample to female participants eliminated sex as a potential confounding factor. Moreover, given the dynamic changes in bone structure and morphology during growth and development, including only individuals who had completed their growth spurt helped to minimize age-related variability in the measurements. In addition, the inclusion of only normodivergent individuals minimized the potential confounding effect of vertical skeletal pattern on mandibular bone density and morphological assessments.

The fact that all panoramic radiographs were obtained using the same device is important for methodological consistency and measurement repeatability. Variability in technical parameters such as focal distance, magnification factor, and distortion ratio between devices can lead to differences in radiomorphometric measurements. Particularly in sensitive measurements such as mandibular cortical thickness, studies have reported reduced measurement consistency when images are acquired from different devices, which can negatively affect data reliability [11]. Therefore, the use of a single device in the present study minimized magnification- and distortion-related variability and allowed all measurements to be performed under standardized imaging conditions.

Although not all radiomorphometric measurements reached statistical significance, Angle Class I malocclusion showed higher mean values for all variables except grayscale value. Statistically significant differences were observed in mental index, panoramic mandibular index, and antegonial notch depth, and these differences were consistently found between individuals with Angle Class III malocclusion and those with Angle Class I and II malocclusions, while no significant difference was observed between Angle Class I and Class II malocclusions. Furthermore, no statistically significant intergroup differences were detected for the remaining parameters. In the present study, the parameters found to be significant were particularly related to the cortical region along the lower border of the mandible. Collectively, these results suggest that Angle Class III malocclusion is associated with marked alterations in the quality and morphology of the mandibular cortical bone, especially along the inferior cortical border.

The mental index reflects the mandibular cortical bone thickness at the level of the mental foramen and has been reported to decrease significantly with age, as well as to be potentially associated with bone mineral density [16]. Similarly, Sghaireen et al. [20] reported that the mental index value decreases with advancing age and that this reduction could be an early indicator of osteoporotic changes. On the other hand, in a study by Eninanç et al. [5], it was demonstrated that individuals with bruxism had significantly higher mental index values compared to the control group, suggesting that bruxism may have an effect on mandibular cortical thickness. Furthermore, previous studies have shown that sagittal malocclusion is associated with mandibular and maxillary basal widths [21] and mandibular symphysis morphology [22]. In a study comparing the bone morphology of individuals with high-angle Angle Class II and Class III malocclusions, it was found that the anterior alveolar bone area of the mandible, close to the mental region, and the vertical bone level were thinner in Angle Class III malocclusion [23]. In our study, the significantly lower mental index values found in individuals with Angle Class III malocclusion suggest that mandibular cortical thickness may vary depending on the type of malocclusion and that there may be a tendency for cortical bone thinning in Angle Class III individuals. This finding is consistent with the study by Tayebi et al. [24], which included growing individuals and found the highest mental index in Angle Class I malocclusion and the lowest in Angle Class III malocclusion.

Another parameter found to be significantly lower in individuals with Angle Class III malocclusion compared to the other malocclusion groups was the panoramic mandibular index. This finding parallels the markedly lower mental index values also measured in the same anatomical region, supporting the notion that the mandibular cortex may be thinner in individuals with this malocclusion type. Previous studies have reported that the panoramic mandibular index decreases significantly with age [16, 20] and emphasized its potential association with systemic conditions such as osteoporosis and low bone mineral density [9]. However, no statistically significant difference has been observed between bruxism and non-bruxism patients. This study supports that the panoramic mandibular index value may reflect structural differences in mandibular morphology depending on the type of skeletal malocclusion.

Among the parameters evaluated concerning the posterior lower border of the mandible, only antegonial notch depth showed a statistically significant difference. The antegonial notch represents the depth of the notch located along the inferior border of the mandible, and this measurement can be considered an indicator of morphological changes in the mandibular contour in Angle Class III malocclusion. In a study by Kolodziej et al. [25], antegonial notch depth was reported to be a statistically significant predictor of growth patterns. This study noted a negative correlation between antegonial notch depth and horizontal growth pattern, suggesting that individuals with a horizontal growth tendency have a notch reduced in depth. Interestingly, antegonial notch depth has been found to be significantly deeper in patients with bruxism, indicating that the mandibular angle region may be influenced not only by muscle patterns and vertical growth pattern but also by sagittal malocclusion [13]. In a study evaluating antegonial notch depth according to malocclusions using lateral cephalometric radiographs, the deepest measurements were observed in Angle Class I malocclusion, consistent with our findings; however, statistical significance was reported only between Angle Class I and Class II malocclusions when comparing malocclusion groups [26].

This study provided a comparative evaluation of mandibular bone density- and morphology-related parameters on panoramic radiographs in individuals with different Angle malocclusion types, suggesting that malocclusion may influence bone structure not only dental level but also at the skeletal level. However, several limitations should be acknowledged. As the study included only female individuals who had completed their growth, the external validity of the findings is limited. Accordingly, the results can be primarily generalized to adult female orthodontic patients with similar skeletal characteristics and should be interpreted with caution when extrapolating to male patients or younger, growing individuals. Future studies including both sexes and a broader age range are warranted to enhance generalizability. In addition, although all panoramic radiographs were obtained by the same operator with the same device under standardized acquisition parameters, the inherent limitations of two-dimensional panoramic imaging—such as magnification, distortion, and anatomical superimposition—may have introduced measurement deviations. Furthermore, grayscale value assessments are known to be sensitive to technical and imaging-related factors and may exhibit variability despite efforts to minimize such effects through standardized imaging conditions.

From a clinical perspective, the thinner mandibular cortical bone observed in Angle Class III individuals may have practical implications for orthodontic treatment planning. Reduced cortical thickness has been associated with altered biomechanical responses to orthodontic forces and may influence anchorage strategies, particularly in cases requiring skeletal anchorage. In such patients, careful consideration of force magnitude and direction may be necessary to minimize undesirable side effects. Moreover, thinner cortical bone in the posterior mandibular region may be relevant when planning orthodontic mini-implant placement, as cortical bone quality is a key determinant of primary stability. Therefore, the radiomorphometric differences identified in this study may assist clinicians in anticipating biomechanical challenges and optimizing individualized treatment approaches in Class III malocclusion cases.

Differences in mandibular morphology and bone density are likely influenced by variations in mandibular growth patterns, functional loading, muscle forces, and growth balance associated with malocclusion. With advances in imaging technology, future studies should include larger and more heterogeneous populations, preferably adopting prospective and multicenter designs with standardized imaging protocols. The application of three-dimensional morphometric methods, together with assessments of muscle characteristics and, where feasible, clinical or biochemical markers of bone metabolism, may provide more comprehensive insights into the underlying mechanisms. Furthermore, longitudinal evaluation of mandibular morphology before and after orthodontic or orthognathic treatment could help clarify dynamic changes in bone structure and may contribute to the identification of patient-specific risk factors and the development of more predictable and individualized treatment protocols in orthodontic planning.

Conclusions

In this study, mandibular radiomorphometric measurements obtained from panoramic radiographs of individuals with different Angle malocclusion types were compared. It was determined that individuals with Angle Class III malocclusion had significantly lower mental index, panoramic mandibular index, and antegonial notch depth values. It should be considered during orthodontic treatment planning and application that mandibular cortical bone thickness and morphology may vary depending on the type of malocclusion, with a tendency towards cortical thinning in Angle Class III individuals.

Abbreviations

MI

Mental index

PMI

Panoramic mandibular index

GI

Gonial index

AI

Antegonial index

AND

Antegonial notch depth

MCI

Mandibular cortical index

GS

Grayscale value

ROI

Region of interest

kV

kilovolts

mA

milliamperes

s

seconds

mm

milimeters

Author contributions

IO: Conceptualization, methodology, supervision, manuscript writing. BK: Data collection, radiographic measurements, statistical analysis, manuscript drafting. GAO: Literature review, data interpretation, critical revision of the manuscript. All authors have read and approved the published version of the manuscript.

Funding information

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This study was performed in line with the principles of the Declaration of Helsinki. Ethical approval was obtained from the Health Sciences Research Ethics Committee of Hacettepe University (Approval number: SBA 25/471). There was no need for individual consent, and the need for informed consent was waived by the Health Sciences Research Ethics Committee of Hacettepe University for this retrospective study because the data and patient details were anonymized.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.