Ultrasonographic and cephalometric assessment of tongue thickness across angle’s classes of malocclusion in skeletal class I patients

Abstract

The aim of this study was to investigate the association between tongue thickness and dental malocclusions, to compare the diagnostic reliability of ultrasonography (USG) and lateral cephalometry in tongue assessment, and explore potential sex-related differences in tongue morphology. Ninety participants (54 females, 36 males; mean age: 16.01 ± 2.26 years) with a skeletal Class I relationship were included and divided into three groups according to Angle’s classification: Class I, Class II, and Class III. Tongue thickness measurements were obtained from lateral cephalometric radiographs as cephalometric tongue thickness (CTT) and from USG as ultrasonographic tongue thickness (UTT). Intraobserver reliability was evaluated using Dahlberg’s formula and Cronbach’s alpha. Statistical analyses included one-way ANOVA, independent-samples t-tests, the Wilcoxon signed-rank test, and Pearson correlation analysis. Statistical significance was set at p < 0.05. Tongue thickness differed significantly among dental malocclusion groups (Class III> Class I > Class II; p < 0.001). For UTT, mean ± SD values were 35.97 ± 2.6 mm for Class I, 35.18 ± 2.2 mm for Class II, and 40.81 ± 1.9 mm for Class III. For CTT, mean ± SD values were 34.97 ± 4.6 mm for Class I, 31.63 ± 3.1 mm for Class II, and 39.06 ± 3.4 mm for Class III. UTT showed higher precision and lower variability than CTT (mean absolute difference: 0.32 mm vs. 0.75 mm; p = 0.002). Males had significantly greater tongue thickness than females (p < 0.05). Correlations between CTT and UTT within malocclusion groups were positive but not significant. Tongue thickness is significantly associated with sagittal dental malocclusion. USG provides a reliable and reproducible method for tongue assessment, demonstrating superior precision compared with lateral cephalometry. Incorporating ultrasonographic evaluation of the tongue into orthodontic planning may facilitate individualized treatment strategies and improve the predictability of clinical outcomes.

Introduction

The tongue is a muscular organ surrounded by a specialized mucosal membrane that plays a vital role in several key functions, such as chewing, swallowing, speaking, and taste perception¹. It is also considered a crucial factor in the development of dentoalveolar structures. Studies have suggested that habitual tongue posture and muscle activity, particularly, in early ages, can influence the shaping of these structures and potentially contribute to malocclusions^2–4.

Malocclusions can be caused by deviations of teeth from their ideal positions in the jaws, developmental discrepancies between the jawbones, or imbalances in the forces exerted by soft tissues, such as the tongue, cheeks, and lips. Skeletal malocclusions are classified based on the ANB angle on lateral cephalometric radiographs: 0°–4° indicates Class I, greater than 4° indicates Class II, and less than 0° indicates Class III relationships^5–7. On the other hand, dental malocclusions are defined based on the occlusal relationships of the permanent first molars, as developed by Edward Angle’s classification⁸. In Class I, the mesiobuccal cusp of the maxillary first molar occludes with the buccal groove of the mandibular first molar, forming an anatomical cusp-groove relationship; in Class II, this relationship is positioned distally, whereas in Class III it is shifted mesially⁶.

Several studies have demonstrated that malocclusion is not solely determined by hard tissue factors, but that soft tissues also play a critical role in this process^2–4. A balance exists between the forces exerted by the tongue and those from the cheeks and lips, which significantly influences tooth position, arch form, and occlusion⁹. Among soft tissues, the tongue is the most influential, applying both passive and active forces on teeth and jaw structures^2,3. Increases in tongue size and muscle tone can alter pressure on dentoalveolar structures, leading to deviations in the direction of tooth movement^3,4. In pathological conditions, such as macroglossia, increased tongue pressure may contribute to anomalies including mandibular prognathism, anterior open bite, and an increased gonial angle^3,10. Abnormal tongue size, when combined with infantile swallowing or thumb sucking habits, can result in persistently anterior tongue posture, causing proclination and intrusion of anterior teeth and extrusion of molars^11,12. Furthermore, the tongue’s influence is not limited to the sagittal plane; it also affects the transverse dimension and may contribute to maxillary arch deficiencies¹³.

Tongue position, size, muscle activity, and function are considered critical factors for understanding the etiology of malocclusion, planning orthodontic treatment, and ensuring the stability of treatment outcomes^2–4. Numerous studies have investigated tongue dimensions and their relationship with malocclusions, employing a variety of measurement techniques, including lateral cephalometric radiography^4,14,15, computed tomography (CT)^16,17, magnetic resonance imaging (MRI)², cone-beam computed tomography (CBCT)¹⁸, and ultrasonography (USG)^9,19.

USG, as one of the most effective soft tissue imaging modalities, enables clear visualization of the tongue surface and differentiation between the tongue muscles and the floor of the mouth. Measurements obtained via USG can be standardized and potentially provide more accurate results; additionally, its lack of ionizing radiation, reliability in soft tissue assessment, and accessibility represent significant advantages^20,21. Although tongue dimensions can also be assessed using lateral cephalometric radiography, the two-dimensional nature of this method, its limited ability to delineate soft tissue boundaries, and the presence of superimposition effects have led to inconsistent results^9,21–25. The radiation exposure associated with CBCT^26,27and the high cost and susceptibility to motion artifacts in MRI²⁸further highlight USG as a safe and suitable alternative for evaluating tongue dimensions.

To the best of our knowledge, this study is the first to evaluate tongue thickness in patients with different sagittal dental malocclusion types (Angle Class I, II, and III) within the same skeletal class using both USG and lateral cephalometric radiography. The study seeks to elucidate variations in tongue dimensions across different malocclusion types more accurately and reliably, thereby providing valuable insights into the etiology of malocclusion. Additionally, by comparing the two measurement methods, the study seeks to determine which technique offers greater reliability for clinical and radiological assessment. This approach may enable more precise evaluation of tongue dimensions in orthodontic diagnosis and treatment planning, facilitate the development of individualized treatment strategies, and enhance the predictability of treatment outcomes.

The aim of this study was to investigate the association between tongue thickness, as measured using cephalometric and USG imaging methods, and sagittal dental malocclusions, as well as to compare the measurements obtained from both imaging modalities. Additionally, the study examined whether tongue thickness differs according to sex. The first null hypothesis posited that there would be no difference in tongue thickness measurements obtained via ultrasonography and lateral cephalometric imaging. The second null hypothesis stated that tongue thickness does not differ among individuals with dental Class I, Class II, and Class III malocclusions. The third null hypothesis proposed that tongue thickness does not vary according to sex.

Materials and methods

This study was designed as a prospective, single-center, cross-sectional study. Ethical approval for the study was obtained from the Non-Interventional Clinical Research Ethics Committee of Zonguldak Bülent Ecevit University (Decision No: 2023/23 − 5, dated November 29, 2023) prior to the commencement of the study. All procedures were conducted in accordance with the approved protocol and relevant ethical guidelines and regulations. All participants received both verbal and written information regarding the procedures, and informed consent forms were obtained prior to the measurements.

The sample size was calculated using G^*Power 3.1.9.7 software (Franz Faul, Kiel University, Kiel, Germany). An effect size of Cohen’s d = 1.167769 derived from a comparable previously published two-group study by Mehra et al.²⁹ was used as a reference and converted to Cohen’s f for a one-way ANOVA design (f ≈ d/2 ≈ 0.584). Because effect sizes reported in previous studies—particularly those based on simpler or lower-powered designs—are known to overestimate the true magnitude of effects, conservative assumptions are recommended when planning sample size to avoid overly optimistic power estimates³⁰. Therefore, to obtain a more realistic estimation for a three-group analysis and to account for increased within-group variability and potential heterogeneity, the effect size was deliberately reduced by 20% (f = 0.47). Using this adjusted effect size (α err prob = 0.05, power (1-β err prob) = 0.95, three groups with equal allocation), the required total sample size was calculated as 75 participants. To further enhance robustness and ensure adequate statistical power under stricter assumptions, an additional 20% increase was applied, resulting in a final sample size of 90 participants (30 per group).

The study included individuals between the ages of 14 and 20 years who had minimal crowding or diastema (< 3 mm), skeletal Class I malocclusion (ANB between 0 and 4 degrees), normal swallowing function, no transverse or vertical anomalies, and no missing permanent teeth except for third molars. Individuals with intellectual disability, significant compliance issues, a medical or surgical history of conditions affecting tongue size, previous orthodontic treatment, skeletal abnormalities, thumb-sucking habits, mouth breathing, abnormal swallowing function, or those in the primary dentition stage were excluded from the study.

From January 2022 to September 2023, a total of 90 participants (54 females and 36 males; mean age: 16.01 ± 2.26 years; range: 14–20 years) who met the inclusion criteria were enrolled in the study at the Department of Orthodontics. Skeletal relationships were assessed using cephalometric analysis, and dental malocclusions were determined through intraoral examination. All participants exhibited a skeletal Class I relationship based on the ANB angle. According to Angle’s classification, participants were divided into three equal groups based on dental malocclusion type: Class I (30 participants: 19 females, 11 males; mean age: 16.17 ± 2.48 years), Class II (30 participants: 24 females, 6 males; mean age: 15.50 ± 1.96 years), and Class III (30 participants: 11 females, 19 males; mean age: 16.37 ± 2.28 years).

Lateral cephalometric radiographs of patients referred from the Orthodontics Clinic to the Department of Oral and Maxillofacial Radiology were acquired using the Veraviewepocs 2D device (J. Morita Mfg. Corp., Kyoto, Japan). During imaging, patients were positioned in centric occlusion with relaxed lips and their heads maintained in a natural position to ensure standardization. Based on these radiographs, SNA, SNB, and ANB angles were measured to determine the sagittal positions of the maxilla and mandible relative to the cranial base and to each other. Cephalometric analyses were performed by the same orthodontist (OC) using the digital analysis software NemoCeph (Nemotec, 2006, Madrid, Spain). Tongue thickness measurements from the lateral cephalometric radiographs were subsequently carried out using the Mediadent V8 Dental Imaging Software (Corilus SA, Ghent, Belgium). The cephalometric reference points shown in Fig. 1 were used for the measurements.

Fig. 1.

Measurement of tongue thickness on a lateral cephalometric radiograph, v (red): Vallecula, the junction point between the tongue base and the epiglottis, t (red): The most anterior point of the tongue, x (black): Cephalometric tongue thickness, h (red): The most convex point on the dorsum of the tongue.

Cephalometric tongue thickness (CTT) was defined as the perpendicular distance from the most convex point of the tongue dorsum (h) to the line extending between the vallecula and the tongue tip (v–t)⁹. Ultrasonographic tongue thickness (UTT) was assessed using the MyLab™ Twice US device (Esaote SpA, Genoa, Italy) available at our clinic, employing an extraoral linear probe with a frequency range of 4–13.0 MHz. All measurements were calculated in millimeters (mm).

UTT measurements were performed using a conventional B-mode grayscale ultrasound imaging protocol. During imaging, patients sat in a position that formed a 30° angle between their back and the ground. To prevent air entrapment, a water-based gel was applied between the probe and the soft tissue. Before beginning the measurement, patients were asked to swallow several times to allow their tongues to reach their natural resting position. Once this position was visually confirmed, the measurement began. The linear probe was placed submentally (extraorally) and positioned perpendicular to the Frankfort horizontal plane^31,32.

Tongue thickness was determined by measuring the vertical distance between the mylohyoid muscle and the dorsum of the tongue (Fig. 2). The software integrated into the USG device was used to record vertical tongue thickness measurements. Each ultrasonographic measurement was performed twice during the assessment, and the mean of the two values was recorded. All CTT and UTT measurements were performed by the same researcher (R.Ç.).

Fig. 2.

Measurement of tongue thickness and identification of anatomical structures on a frontal section of the USG image. (1 – Red: Mylohyoid muscle, 2 – Gray: Anterior digastric muscle, 3 – Pink: Geniohyoid muscle, 4 – Orange: Sublingual gland, 5 – Green: Genioglossus muscle, 6 – Blue: Hyoglossus muscle, 7 – Brown: Superior longitudinal muscle, 8 – Navy Blue: Tongue dorsum, 9 – Purple: Submandibular gland, 10 – Yellow: Tongue thickness)

Method error

Intraobserver reliability was assessed using repeated measurements performed by the same researcher (R.Ç.) with a two-month interval. Measurement error was calculated using Dahlberg’s formula, where d represents the difference between the first and second measurements, and n denotes the number of subjects. The repeated linear measurements were reported to fall within the acceptable error limit of 1 mm^33,34.

Secondly, a reliability analysis was conducted to calculate Cronbach’s alpha in order to assess the internal consistency of the repeated measurements. The obtained Cronbach’s alpha value, along with its 95% confidence interval (lower and upper bounds), was used to quantitatively interpret the level of agreement between the measurements.

Statistical analysis

Data were analyzed using IBM SPSS Statistics 20.0 (Statistical Package for the Social Sciences, Chicago, IL, USA), and a p-value of < 0.05 was considered statistically significant. The normality of data distribution was assessed using the Shapiro–Wilk and Kolmogorov–Smirnov tests. Based on these assessments, the dataset was determined to be suitable for the use of parametric tests. One-way analysis of variance (ANOVA) was employed to compare tongue thickness measurements among the dental malocclusion groups. The homogeneity of variances across groups was confirmed using Levene’s test, allowing for post hoc pairwise comparisons to be performed with the Tukey HSD test.

Sex-related differences in tongue thickness were assessed within each malocclusion group using the independent-samples t-test. Furthermore, the mean absolute differences between repeated UTT and CTT measurements, which did not follow a normal distribution, were assessed using the Wilcoxon signed-rank test. The correlation between cephalometric and ultrasonographic measurements was assessed using the Pearson correlation test.

Results

The results presented in Table 1 demonstrate high intraobserver reliability in repeated measurements across all dental classes and measurement types. Cronbach’s alpha coefficients ranged from 0.940 to 0.989, indicating excellent internal consistency. Specifically, Class I showed alpha values of 0.986 for UTT and 0.958 for CTT; Class II exhibited values of 0.989 (UTT) and 0.974 (CTT); and Class III had alpha coefficients of 0.988 (UTT) and 0.940 (CTT). The 95% confidence intervals for these coefficients were narrow, further supporting the reliability of the measurements. Dahlberg error values ranged from 0.298 to 0.421 for UTT and from 0.703 to 1.248 for CTT, indicating that while both methods are reliable for repeated measurements, UTT showed lower measurement error compared with CTT.

Table 1.

Method errors in repeated measurements using cronbach’s alpha and dahlberg’s formula.

Groups	Imaging modalities	Cronbach’s apha	95% CI		Dahlberg error
			Lower bound	Upper bound
C I	UTT	0.986	0.971	0.993	0.421
	CTT	0.958	0.912	0.980	1.248
C II	UTT	0.989	0.978	0.995	0.324
	CTT	0.974	0.946	0.988	0.703
C III	UTT	0.988	0.974	0.994	0.298
	CTT	0.940	0.874	0.971	1.119

CI: Dental Class I malocclusion, CII: Dental Class II malocclusion, CIII: Dental Class III malocclusion, %:percentage, CI: Confidence Interval, CTT: Cephalometric tongue thickness, UTT: Ultrasonographic tongue thickness.

Furthermore, the mean absolute difference of all UTT measurements was 0.32 mm (SD = 0.38; median = 0.20 mm), while that of all CTT measurements was 0.75 mm (SD = 1.29; median = 0.40 mm). The variability among individuals was lower and the distribution more symmetrical for UTT measurements, whereas some CTT measurements showed considerably higher differences and a more variable distribution. According to the Wilcoxon test, UTT measurements showed significantly smaller and more consistent differences compared with CTT [Z = − 3.172, p = 0.002].

Among the 90 individuals included in the study, 54 were female and 36 were male, with a mean age of 16.01 ± 2.26 years. The descriptive statistics for SNA, SNB, and ANB measurements across the dental Class I, Class II, and Class III malocclusion groups are summarized in Table 2. All participants exhibited ANB values within the normal range, confirming a skeletal Class I relationship across the entire sample.

Table 2.

SNA, SNB, and ANB values of individuals according to malocclusion groups.

Groups	SNA		SNB		ANB
	Mean	S.D.	Mean	S.D.	Mean	S.D.
C I	81.23	4.22	79.30	4.32	2.13	1.48
C II	79.13	3.2	75.87	2.84	3.23	1.07
C III	81.67	4.06	79.93	3.73	1.70	1.29

CI: Dental Class I malocclusion, CII: Dental Class II malocclusion, CIII: Dental Class III malocclusion, S.D.: Standard Deviation.

Using descriptive statistical methods, tongue thickness measurements were evaluated across the dental malocclusion groups. Overall, both CTT and UTT values differed significantly among the malocclusion classes (p < 0.001), with the ranking observed as Class III > Class I > Class II, as shown in Table 3. Post-hoc comparisons revealed that mean CTT values were significantly different among all three groups (p < 0.05). For UTT, no significant difference was detected between Class I and Class II (p = 0.421); however, the comparisons between Class II–Class III and Class I–Class III demonstrated statistically significant differences (p < 0.05) (Fig. 3).

Table 3.

Comparison of CTT and UTT measurements across dental malocclusion groups.

Imaging Modalities	Groups	N	Mean (mm)	S.D.	F	p
CTT	C I	30	34.97	4.67	28.415	< 0.001
	C II	30	31.63	3.18
	C III	30	39.06	3.43
	Total	90	35.22	4.85
UTT	C I	30	35.93	2.61	53.643	< 0.001
	C II	30	35.18	2.25
	C III	30	40.81	1.94
	Total	90	37.31	3.37

CI: Dental Class I malocclusion, CII: Dental Class II malocclusion, CIII: Dental Class III malocclusion, N: Sample, S.D.: Standard Deviation, p: significance value, CTT: Cephalometric tongue thickness, UTT: Ultrasonographic tongue thickness.

Fig. 3.

Graph of CTT and UTT values according to dental malocclusion groups. CI: Dental Class I malocclusion, CII: Dental Class II malocclusion, CIII: Dental Class III malocclusion, CTT: Cephalometric tongue thickness, UTT: Ultrasonographic tongue thickness.

To evaluate potential sex-related differences in tongue size, intra-group comparisons were conducted between male and female participants (Table 4). Within the malocclusion subgroups, a statistically significant association was observed between CTT values and sex in individuals with Class I malocclusion, with males exhibiting significantly greater CTT values than females (p < 0.05). Furthermore, when data were analyzed irrespective of malocclusion type, both UTT and CTT values were found to be significantly higher in males compared with females (p < 0.05) (Table 5).

Table 4.

Sex-based comparison of CTT and UTT measurements across dental malocclusion groups.

Groups	Imaging modalities	Sex	N	Mean (mm)	S.D.	t	p
C I	UTT	Female	19	35.62	2.71	-0.850	0.403
		Male	11	36.46	2.44
	CTT	Female	19	33.25	0.38	-2.987	0.006
		Male	11	37.95	0.47
C II	UTT	Female	24	34.81	2.29	-1.923	0.65
		Male	6	36.7	1.35
	CTT	Female	24	31.77	0.33	0.467	0.644
		Male	6	31.08	0.28
C III	UTT	Female	11	40.36	1.57	-0.949	0.351
		Male	19	41.06	2.15
	CTT	Female	11	38.13	0.26	-1.126	0.270
		Male	19	39.6	0.38

CI: Dental Class I malocclusion, CII: Dental Class II malocclusion, CIII: Dental Class III malocclusion, N: Sample, S.D.: Standard Deviation, p: significance value, CTT: Cephalometric tongue thickness, UTT: Ultrasonographic tongue thickness.

Table 5.

Comparison of mean CTT and UTT measurements independent of malocclusion.

Imaging modalities	Dependent variable	N	Mean (mm)	p
CTT	Female	54	33.59	< 0.001
	Male	36	37.67
UTT	Female	54	36.23	< 0.001
	Male	36	38.93

N: Sample, p: significance value, CTT: Cephalometric tongue thickness, UTT: Ultrasonographic tongue thickness, p: significance value.

The relationship between UTT and CTT measurements was analyzed for each malocclusion group separately. A positive correlation was found between UTT and CTT measurements in the Class I and Class III malocclusion groups; however, this correlation was not statistically significant (p > 0.05). In the Class II group, the correlation was negative and also not statistically significant (p > 0.05) (Table 6) (Fig. 4).

Table 6.

Comparison of UTT and CTT values in class I, class II, and class III patients.

Groups	Imaging modalities	t	p
C I	UTT	0.085	0.654
	CTT
C II	UTT	0.095	0.619
	CTT
C III	UTT	0.330	0.075
	CTT

CI: Dental Class I malocclusion, CII: Dental Class II malocclusion, CIII: Dental Class III malocclusion, p: significance value, CTT: Cephalometric tongue thickness, UTT: Ultrasonographic tongue thickness, p: significance value.

Fig. 4.

Scatter plot of the correlation between UTT and CTT. CTT: Cephalometric tongue thickness, UTT: Ultrasonographic tongue thickness.

Discussion

The growth of the jaws is influenced by a variety of genetic and environmental factors. According to Moss’s functional matrix theory of growth, the development of the soft tissues surrounding the skeleton directly affects skeletal growth³⁵. In this context, the impact of the perioral muscles, particularly the tongue, which is considered one of the most important intraoral muscles, on craniofacial development has been investigated for many years. The literature extensively discusses the role of the tongue in positioning dentoalveolar structures, and reports that changes in tongue size, function, and position significantly affect these structures^35–37.

Studies indicate that an increase in soft tissue volume may trigger an osteogenic response in areas of bone growth³⁸. Brodie demonstrated that tongue size significantly influences the width and morphology of the dental arches³⁶, while Köle³⁹reported that an enlarged tongue may contribute to mandibular prognathism. These findings emphasize the importance of tongue size and position in dentofacial development and the etiology of malocclusions. In this context, precise measurement of tongue dimensions using appropriate radiological techniques is essential for accurately characterizing the anatomical features of the tongue. Such assessments provide a clearer understanding of the tongue’s role in the etiology of malocclusion, allowing it to be considered a more reliable parameter in the planning of individualized orthodontic treatment. In the present study, both lateral cephalometric radiography (selected for its accessibility and availability to all participants)^9,22–24and USG (a validated method for soft tissue imaging) were employed to measure tongue thickness^9,19. This study therefore aimed to investigate the relationship between tongue thickness, as assessed by cephalometric and ultrasonographic imaging, and sagittal dental malocclusions, while also comparing the results obtained from the two imaging modalities.

The present study demonstrated that CTT and UTT measurements varied across different malocclusion types (p < 0.05), although correlations between CTT and UTT within each group were not statistically significant (p > 0.05). The mean absolute difference for UTT measurements was 0.32 mm (SD = 0.38), whereas CTT measurements exhibited greater variability, with a mean difference of 0.75 mm (SD = 1.29). These results indicate that UTT measurements were characterized by lower inter-measurement variability and a more symmetrical distribution, while certain CTT measurements showed considerable dispersion and heterogeneity. UTT measurements were significantly more consistent than CTT measurements (p = 0.002), indicating that USG offers a more reliable and consistent method of assessing tongue thickness. Accordingly, both the first and second null hypotheses were rejected.

Various methods have been used in previous studies to evaluate tongue dimensions. Among the pioneering studies aimed at directly determining the dimensions of the tongue were Hopkin’s measurements on cadavers⁴⁰. However, due to the impracticality of applying these methods to living individuals, alternative techniques have been developed. Bandy and Hunter, for example, measured tongue volume using the water displacement method to evaluate its relationship with mandibular dentition⁴¹. Takada et al.⁴²used a custom-designed tray adapted to the size of the tongue to take alginate impressions and analyze its functional movements. However, the positions adopted by the tongue during these procedures prevented an accurate assessment of its normal posture and condition.

Subsequent studies have widely used lateral cephalometric radiographs to evaluate the resting position and size of the tongue due to their ease of access^14,15,43,44. With advancements in technology, CT scans were found to be more effective in assessing tongue dimensions and began to be used in studies¹⁶. However, due to the high radiation dose associated with CT scanning, MRI, which is a more effective method for soft tissue imaging, became the preferred modality in later research^2,45,46. CBCT has also been used to evaluate tongue size. Compared to conventional CT, CBCT offers lower radiation exposure, and compared to MRI, it is more accessible, which contributes to its popularity in such studies^18,27,47,48.

The limitations of conventional physical measurement methods and the inadequate visualisation of soft tissues with cephalometric radiographs, as well as the radiation exposure associated with CT and CBCT and the high cost of MRI, have led to USG being adopted as an alternative in several studies^{9,19–21,49–52}. Ultrasound imaging provides clear visualization of the tongue surface and allows differentiation between the tongue muscles and the floor-of-the-mouth muscles. As it is non-invasive, rapid, reliable, and repeatable, USG has become the preferred method for assessing tongue dimensions. In contrast, despite their widespread use, lateral cephalometric radiographs can be affected by factors such as calibration, magnification, and patient posture, which may compromise measurement standardization. These limitations are largely avoided with USG, where measurement error is generally lower^14,15,20,21.

In the present study, a statistically significant association was observed between mean UTT and CTT values and sex, independent of malocclusion type (p < 0.05), with males exhibiting higher measurements than females. These findings are supported by previous research; for instance, Dempsey et al.⁵³reported that males generally possess larger structural dimensions compared to females. Similarly, Tamari et al.⁵⁴and Mandich¹⁸found that males have greater tongue volumes than females. Conversely, the study by Uysal et al.²⁶reported no statistically significant relationship between sex and tongue dimensions (p > 0.05). This inconsistency suggests that the association between tongue size and sex may be influenced by both environmental and genetic factors. Furthermore, investigations into the relationship between tongue thickness and sex across different malocclusion types have produced mixed results, with some studies reporting significant associations¹⁹while others found no such relationship^9,27,55. Accordingly, the third null hypothesis—that tongue thickness does not vary according to sex—was rejected.

Notably, most previous studies of tongue dimensions have focused on individuals with skeletal malocclusions. In contrast, the present study was carried out on patients with dental malocclusions that were classified as skeletal Class I in the sagittal plane. This approach enables a more precise evaluation of the direct relationship between tongue thickness and dental malocclusion. Therefore, caution should be exercised when comparing our findings with those of studies that primarily address skeletal malocclusions. Numerous studies have examined the influence of tongue volume on skeletal malocclusions, suggesting that tongue size may vary according to malocclusion type^19,27,47,48. While these earlier studies concentrated on skeletal relationships, our research provides a distinct perspective by evaluating tongue thickness in the context of dental malocclusions within a consistent skeletal Class I framework.

In the literature, the only study investigating the association between tongue thickness and skeletal malocclusions was conducted by Amuk⁹. Both Amuk’s study and the present study demonstrated that CTT and UTT values varied across malocclusion types. Amuk reported the highest UTT and CTT values in individuals with skeletal Class III malocclusion, followed by those with Class I and Class II. A statistically significant difference in UTT values was observed among skeletal Class I, Class II, and Class III groups (p < 0.05). However, no significant differences in CTT values were found between Class I–Class II and Class I–Class III groups (p > 0.05), whereas a significant difference was detected between Class II and Class III groups (p < 0.05)⁹. The discrepancies between our findings and those of Amuk may be explained by differences in the study populations. While Amuk’s study was based on individuals with skeletal malocclusions⁹, our study focused on patients with dental malocclusions. In skeletal sagittal malocclusions, dimensional and volumetric discrepancies of the jaws—particularly in the sagittal plane—may accentuate variability in tongue thickness. In this context, our study elucidated the influence of tongue thickness on dentoalveolar sagittal relationships within a skeletally standardized Class I sample.

There is a paucity of research on the relationship between tongue dimensions and dental malocclusions, which motivated the present study. Our findings suggest that variations in both the maxillary and mandibular arches may influence tongue size. Previous studies have shown that individuals with skeletal Class III malocclusion typically exhibit larger mandibular arch volumes than those with skeletal Class II malocclusion⁴⁷. In skeletal Class I dental Class III malocclusions, the mandibular molars are positioned more mesially, and an anterior reverse overjet may occur⁶. In our sample, however, an ideal overjet and overbite were maintained, suggesting compensatory changes in arch perimeters. Such adaptations may contribute to an increase in tongue size to accommodate the expanded arch dimensions.

By contrast, in dental Class II malocclusions, the mandibular molars are positioned more distally than normal, typically resulting in an increased anterior overjet⁶. However, in our patient groups, ideal overjet and overbite relationships were preserved, which may suggest a narrowing of the mandibular arch perimeter. This constriction could necessitate a reduction in tongue size to adapt to the limited intraoral space. Previous studies support the idea that tongue size can affect dental arch dimensions^18,54,56. Moreover, the association between dental Class II and Class III malocclusions and tongue thickness, in the absence of vertical and transverse discrepancies, may involve different underlying mechanisms. Further research, including assessments of cheek and lip thickness alongside tongue measurements, is warranted to elucidate these relationships more comprehensively.

A major strength of the present study is its focus on dental malocclusions within a skeletally standardised Class I population. This allowed for a precise assessment of the direct relationship between tongue thickness and sagittal dentoalveolar characteristics, independent of skeletal variations. By employing both USG and lateral cephalometric radiography, the study compared measurement reliability across these two imaging modalities and highlighted the clinical utility of USG as a rapid, non-invasive and reproducible method for evaluating tongue dimensions. From a clinical perspective, an understanding of the variations in tongue thickness in relation to different types of dental malocclusion can inform the planning of orthodontic treatments on an individual basis, particularly with regard to decisions relating to arch expansion, space management and the prediction of functional adaptations. These insights provide an evidence-based framework for incorporating tongue morphology into diagnostic assessments and therapeutic strategies, ultimately supporting more precise, patient-specific orthodontic interventions.

On the other hand, this study has several limitations. The sample was restricted to individuals with a skeletal Class I relationship, excluding those with transverse or vertical skeletal anomalies, which limits the generalizability of the findings to other skeletal types. Tongue measurements were conducted only at rest, preventing the assessment of dynamic changes during functional activities such as speech or swallowing, as well as during treatment. Additionally, although the tongue is a three-dimensional structure, our analysis was limited to thickness, constraining volumetric assessments and the exploration of complex anatomical relationships. Each imaging modality also presents inherent limitations: lateral cephalometry is two-dimensional and subject to superimposition and positional distortion, while USG is operator-dependent and limited by penetration depth.

Conclusion

This study revealed the value of radiological assessment of tongue morphology in the context of dental malocclusions. USG demonstrated high measurement reliability, lower variability, and superior reproducibility compared with lateral cephalometric radiography, highlighting its strength as a non-invasive, radiation-free imaging modality for the quantitative evaluation of tongue thickness. These findings support the integration of ultrasonographic tongue assessment into dentomaxillofacial imaging workflows to enhance soft-tissue characterization and improve the precision of radiological diagnostics.

From an orthodontic perspective, the variations in tongue thickness observed across different dental malocclusion patterns indicate that tongue morphology constitutes a relevant anatomical factor within the dentoalveolar environment; therefore, it should be taken into consideration when planning interventions such as arch expansion or space management. Accordingly, ultrasonographic evaluation of the tongue in appropriately indicated patients may improve the accuracy of orthodontic diagnosis and treatment planning.

Author contributions

Conceptualization, R.Ç.A and G.G.; methodology, G.G, R.Ç.A. and O.C.; software, R.Ç.A and G.G.; validation, R.Ç.A., G.G. and O.C.; formal analysis, R.Ç.A., G.G. and O.C.; investigation, R.Ç.A. and G.G.; resources, R.Ç.A., G.G. and O.C.; data curation, R.Ç.A. and G.G.; writing—original draft preparation, R.Ç.A. and G.G.; writing—review and editing, R.Ç.A., G.G. and O.C.; visualization, G.G. and R.Ç.A; supervision, G.G. All authors read and approved the final manuscript.

Funding

The authors declare that no funds, grants or other support were received during the preparation of this manuscript.

Data availability

Most of the data generated or analyzed are included in the article. The remaining datasets used and/or analyzed during the current study are available from the corresponding author upon re-quest.

Declarations

Consent for publication

Patients signed informed consent forms regarding the publication of their data and photographs.

Informed consent

Informed consent was obtained from the legal guardians of all participants included in the study.

Competing interests

The authors declare no competing interests.