Three-Dimensional Evaluation of the Tongue Volume in Different Dentoskeletal Patterns - A Cone Beam Computed Tomographic Study.

AIM: The aim of this study is to evaluate tongue volume using cone-beam computed tomographic (CBCT) and its correlation to different growth patterns in patients.
MATERIALS AND METHODS: Sixty preorthodontic records of CBCT scans of subjects ranging from 14 to 25 age group from retrospective data of department were selected for the study. Patients were classified into three groups based on angle FMA; Group I (n = 20) with average growth pattern (FMA 22°-28°); Group II (n = 20) vertical growth pattern (FMA >28°); Group III (n = 25) horizontal growth pattern (FMA <20°). Tongue volume evaluation was done using Myrian® Software. Dentoskeletal features and parameters related to archform such as palatal vault depth, interpremolar, and intermolar distance were evaluated in all the subjects. ANOVA test was used for intergroup comparison of tongue volume and dentoskeletal parameters in all three groups. Correlation of the tongue volume to dentoskeletal parameters was done using Pearson's correlation test.
RESULTS: Mean tongue volume in Group I was 66.10 cm3, Group II, 66.04 cm3 and Group III was 66.72 cm3. There was a statistically significant correlation (P < 0.5) of tongue volume with palatal vault width, maxillary length, and mandibular interpremolar and intermolar distance among dentoskeletal parameters.
CONCLUSION: Tongue volume was found equal in all groups despite the variation in growth patterns. Skeletal differences leading to different growth patterns were found to be related to mandibular morphology. The results indicate the indirect role of the tongue in causing malocclusion in orthodontic patients. Copyright:

INTRODUCTION

The functionally stable position of teeth within the alveolar bone and hence, the arch form is determined by the interaction between the tongue and facial musculature. According to Scott “tongue form and archform are mutually dependent on one another.[1] Hence, tongue and the dental archform have cause- and effect relationship with each other.[23]

Tongue posture plays a major role in causing anterior open bite and a lower threshold is shown by genioglossus during opening of the jaw in these type of cases.[4] The interrelation of tongue form and its relation to the growth of dentoskeletal structures has been highly controversial and a debatable topic with great concern to orthodontists and oral physiologists.[56] According to Proffit et al., forces during the rest position of the tongue was more detrimental to the archform than the forces developed during swallowing or in function.[78]

Tongue volume is a critical factor in biomechanics, and it also has a direct influence on dental occlusion, growth and facial form.[9] Numerous studies attempted to correlate the tongue volume to multiple factors, including the position of the teeth, archform and size of the mandibular arch and posture.[101112] The role of the size of the tongue as an important causative factor of malocclusion was established in previous studies.[71314] According to Cheng et al. showed that arch length is related to the volume of the tongue.[15] Correlation between the tongue volume estimated by CT scan and airway estimation was done by Lowe et al. in a previous study.[16] The present study evaluated the tongue volume using CBCT and its correlation to different vertical skeletal growth patterns.

MATERIALS AND METHODS

This observational study was conducted at the Department of Orthodontics, Faculty of Dental Sciences, SGT University and the institutional regulatory body has given the ethical clearance for the study (SGTU/FDS/24/1465). Sample for this study was drawn from the retrospective data of cone-beam computed tomographic (CBCT) scans of sixty preorthodontic records of subjects scans that were performed from April 2013 to October 2017. Inclusion criteria included; age 14–25 years, complete superimposition of left and right lower borders of the mandible with special reference to the growth pattern of an individual, inclusion of posteroinferior borders of the tongue and visibility of both hyoid bone and nasion. The exclusion criterion was; any scan with missing teeth except third molars, orthognathic surgery, or with congenital deformity. All CBCT scans were taken with the use of i-CAT CBCT scanner (Next Generation-Imaging Sciences International, Hatfield, PA, USA). Results of power analysis indicated that to reach 80% power, 20 subjects per group were required to identify minimum size difference of 1 cm2 of tongue volume between any two subjects of different groups. Initially selected 68 patients based on the selection criteria were divided into three groups according to growth pattern based on Frankfurt mandibular plane angle; average (FMA 22°–28°), vertical (FMA >28°), and horizontal growth pattern (FMA <22°). To ensure equal distribution among three groups, balanced block randomization method was used (www.randomizer.org) with 20 samples in all three groups.

Evaluation of the tongue volume

The volume of the tongue was measured in rest position was done using Dicom (digital imaging and communication in medicine) images which were imported to the Myrian® software (Intersense Co In Myrian®); (Montpellier, France) it was possible to rotate the image in all the three dimensions to facilitate the segmentation of the tongue with each of the axial, sagittal, and coronal planes perpendicular to one another [Figure 1]. The region of interest was automatically reconstructed and volume calculations were done by Myrian® software. The method was slightly modified from the previous studies[1718] [Figures 2 and 3].

Figure 1

Cone-beam computed tomographic scan of data of subject showing (a) axial view, (b) sagittal, (c) coronal and (d) oblique view

Figure 2

Sagittal view of the tongue: Line differentiating genioglossus muscle from geniohyoid muscle

Figure 3

Axial view of the tongue: Inferior border of the tongue showing genioglossus muscle and associated structures

Manual sculpting of the tongue was done in axial section to calculate the volume of the tongue followed by projection of a three-dimensional image of the tongue with the help of the Myrian® software [Figure 4].

Figure 4

Three-dimensional reconstruction of the tongue by Myrian® software and volume calculation

CBCT generated lateral cephalograms were used to determine the dentoskeletal pattern by Nemoceph NX software (Visiodent, Saint-Denis, France). Interpremolar and intermolar distance were measured as the distance between permanent first premolars and molars, respectively, at palatal root cervical margin in the mandible for all subjects in the axial view of CBCT [Figure 5]. Palatal vault arch width, overjet, and overbite were also evaluated.

Figure 5

Mandibular intermolar and interpremolar width

Statistical analysis

SPSS software version (25.0; IBM Corp, Armonk, NY, USA) was used for all statistical analysis. Intergroup comparison of archform parameters and tongue volume was made using analysis of variance (ANOVA). Intragroup correlation of dentoskeletal parameters and tongue volume was done using Pearson's correlation test.

RESULTS

Descriptive details of characteristics and parameters measured in the study were given [Table 1]. Comparison of tongue volume in all three groups is shown in Table 2. Individual interpair comparison of tongue volume is shown in Table 3. ANOVA was used for intergroup comparison of dentoskeletal and archform parameters among three groups, as shown in Tables 1 and 4. Pearson's correlation test was used to evaluate correlation between tongue volume and dentoskeletal parameters [Table 4].

Table 1

Intergroup comparison of parameters under study – analysis of variance test

Characteristic/parameter	Groups, mean+SD			F	P
	Group I (average growth) (n=20)	Group II (vertical growth) (n=20)	Group III (horizontal growth) (n=20)
Age	20.5±7.6	19.2±6.9	18.9±9.3	0.20
Mean tongue volume (in cm3)	66.10±11.09	66.04±9.33	66.72±10.60	0.006	0.994
Dentoskeletal parameters
SNA (°)	84.50±3.23	85.48±4.16	84.80±4.31	1.912	0.157
SNB (°)	79.70±2.41	77.16±3.22	77.96±10.37	0.456	0.636
ANB (°)	4.80±0.92	6.40±1.63	4.72±2.41	5.425	0.007*
FMA (°)	24.80±0.92	32.26±2.93	19.04±2.65	165.827	0.0001*
Gonial angle (°)	118.10±4.22	125.76±6.62	112.44±5.44	2.658	0.038*
Palatal plane angle (°)	21.10±2.64	24.36±4.11	14.48±4.25	39.257	0.001*
ANS-PNS (mm)	56.90±3.18	57.40±3.79	59.84±4.08	0.175	0.840
Go-Gn (mm)	68.90±3.18	71.04±5.16	96.64±8.49	3.385	0.041*
U1-NA angle (°)	20.10±7.37	23.52±5.28	21.80±8.35	0.848	0.433
L1-NB angle (°)	34.20±5.39	31.44±8.37	29.24±8.81	0.921	0.404
U1 inclination (°)	105.20±8.14	108.52±5.88	106.20±8.28	1.383	0.259
IMPA (°)	106.30±5.81	97.52±7.82	105.60±8.63	1.312	0.277
Archform Characterstics
Palatal vault width (mm)	13.30±2.87	13.56±1.61	13.76±2.24	8.040	0.001*
Intermolar distance (mm)	33.80±2.04	33.36±2.55	33.36±2.22	0.148	0.863
Interpremolar distance (mm)	25.60±1.65	25.96±1.77	25.28±1.93	0.875	0.422
Overjet (mm)	3.90±1.20	3.68±1.25	4.32±2.72	0.651	0.525
Overbite (mm)	2.30±1.49	2.28±1.51	2.96±2.28	0.945	0.395

ANOVA test: *P<0.05 (significant), P>0.05 (not significant). ANOVA: Analysis of variance, SD: Standard deviation

Table 2

Intragroup and intergroup comparison of tongue volume (in cm3) - One-way analysis of variance test

	Sum of squares	Df	Mean square	F	P
Between groups	0.4	2	0.2	0.006	0.994
Within groups	1797.2	57	31.53
Total	1797.6	59

*P<0.05 (significant), P>0.05 (not significant). df: Degree of freedom

Table 3

Interpair comparison of tongue volume (in cm3) between different groups

Groups	t	P
Group 1 - Group 2	0.055	0.956
Group 2 - Group 3	0.129	0.898
Group 1 - Group 3	0.051	0.959

Independent sample t-Test: *P<0.05 (significant), P>0.05 (not significant)

Table 4

Correlation of tongue volume (in cm3) to dentoskeletal parameters and the Archform characteristics in the three different groups- Pearson’s Correlation test

Dentoskeletal parameters	Group I (average growth) (n=20)		Group II (vertical growth) (n=20)		Group III (Horizontal growth) (n=20)
	Pearson correlation	P	Pearson correlation	P	Pearson correlation	P
SNA (°)	0.077	0.832	0.199	0.127	0.167	0.424
SNB (°)	0.180	0.618	0.280	0.030*	0.338	0.098
ANB (°)	-0.059	0.872	-0.209	0.110	-0.322	0.117
FMA (°)	-0.140	0.701	-0.052	0.696	-0.154	0.463
Gonial angle (°)	0.568	0.086	0.227	0.081	-0.037	0.861
Palatal plane angle (°)	0.185	0.608	-0.152	0.247	-0.403	0.045*
ANS-PNS (mm)	0.215	0.550	0.344	0.007*	0.444	0.026*
Go-Gn (mm)	0.423	0.224	0.415	0.001*	0.477	0.016*
U1-NA angle (°)	0.218	0.545	-0.069	0.599	-0.134	0.524
L1-NB angle (°)	0.242	0.501	-0.031	0.790	-0.036	0.865
U1 inclination (°)	-0.088	0.810	-0.128	0.328	-0.179	0.393
IMPA (°)	0.271	0.449	0.034	0.799	-0.031	0.881
SNA (°)	-0.126	0.728	-0.132	0.316	-0.173	0.409
Palatal vault width (mm)	0.506	0.023*	0.488	0.029*	0.492	0.027*
Intermolar distance (mm)	0.647	0.043*	0.479	0.001*	0.502	0.001*
Interpremolar distance (mm)	-0.033	0.929	-0.127	0.334	-0.215	0.302
Overjet (mm)	-0.391	0.264	-0.017	0.900	-0.068	0.748

Pearson’s Correlation 0-0.25-weak, 0.25-0.75-moderate, 0.75-1.00 strong, +1 to-1 Perfect positive or negative correlation, *P<0.05 (significant), P>0.05 (not significant)

DISCUSSION

This study was taken up to assess the relationship between the volume of tongue and three different vertical patterns of skeletal growth. CBCT is advantageous due to the upright position of patient favoring tongue position, shorter exposure time, and lesser artifacts than magnetic resonance imaging (MRI).[1819] Tongue volume was measured in all subjects with the mandible in the resting position. Tongue volume was found to be equal in all three groups, in spite of different growth pattern [Table 2]. This may indicate the indirect role of tongue in causing malocclusion in orthodontic patients. Tongue volume obtained in the present study closely matches to that of previous studies done by conventional CT scans by Lowe et al[16] and Roehm[17] Tongue volume was also established by MRI in the previous studies[192021] Liégeois et al. found that correlations between tongue volume and body height, weight, and the body mass index were highly significant using MRI.[21]

Correlation of tongue volume the to maxillary length in this study was found to be statistically significant in Group II (vertical growth) (r = 0.415) and Group III (horizontal growth) (r = 0.477) which shows that tongue volume influences the maxillary length [Table 4]. These findings are in accordance with the study of Fields[22] and Xiao[23] suggesting that in vertical dysplasia has little effect on the sagittal development of the mandibular body.

Gonial angle, mandibular plane to palatal plane angle, palatal vault width, in horizontal growers showed statistically significant correlation with tongue volume in the present study. Whereas subjects with increased large gonial angle, large overjet, and vertical growth pattern are found to have tongue tip ahead of lower central incisors and above lower occlusal plane.[24] Maxillary length and Upper molar to palatal plane angle were found to be correlated with tongue volume in the current study in vertical growers [Table 4].

Correlation of tongue volume with interpremolar and intermolar distance in the mandibular arch was highly significant in our study [Table 4]. This is coincident with findings of Tamari et al.[12] where they interrelated tongue volume with dental arch sizes. It was observed that the tongue volume is significantly correlated with the with and the surface area of the dental arch width and was more prominent toward the molar area than the premolar regions of the dental arch [Table 4]. This indicates that interpremolar and intermolar width is one of the important morphologic factor in maintaining dental arch sizes. Uysal et al.[25] found a statistically significantly higher value of tongue volume in mild irregularity than severe irregularity group in the lower incisor region.[19] Proportionate relationship of tongue mass to the dimensions of the oral cavity is exceedingly difficult to measure. There are very few studies in literature correlating tongue volume to dentoskeletal malocclusion. Hence, further studies with a large sample are encouraged to compare and correlate tongue volume to oropharynx volume in normal growing subjects.

Clinical significance

Tongue volume was measured and found to be nonsignificant correlation with various growth patterns. The results indicate the indirect role of the tongue in causing malocclusion in orthodontic patients.

CONCLUSIONS

Mean tongue volume evaluation in average, vertical and horizontal growth pattern showed no significant difference. Maxillary length and palatal vault depth had a significant correlation to tongue volume in vertical and horizontal growth patterns

Interpremolar and intermolar width had a significant correlation with tongue volume in average growth pattern and highly significant correlation in vertical and horizontal growth patterns.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.