ORIGINAL RESEARCH

https://doi.org/10.5005/jp-journals-10015-2234
World Journal of Dentistry
Volume 14 | Issue 5 | Year 2023

Variation in the Dimensions of the Atlas Vertebra among Patients with Class I, II, and III Skeletal Bases: A Cephalometric Study

Nikunj Maniyar¹ https://orcid.org/0000-0002-3801-7313, A T Prakash² https://orcid.org/0000-0001-5013-0370, HC Kiran Kumar³ https://orcid.org/0000-0003-2264-554X

^1-3Department of Orthodontics and Dentofacial Orthopedics, Bapuji Dental College & Hospital, Davangere, Karnataka, India

Corresponding Author: Nikunj Maniyar, Department of Orthodontics and Dentofacial Orthopedics, Bapuji Dental College & Hospital, Davangere, Karnataka, India, Phone: +91 9726992969, e-mail: maniar09@gmail.com

Received on: 04 April 2023; Accepted on: 05 May 2023; Published on: 02 August 2023

ABSTRACT

Aim: To quantify and compare the variation in the dimensions of the atlas vertebra among patients with classes I, II, and III skeletal bases on a lateral cephalogram.

Materials and methods: Lateral cephalograms of 75 patients aged 19–43 years were evaluated. Subjects were divided into three groups (25 each) based on their A point, nasion, B point (ANB) angle. Group I included class I subjects with ANB angle 0–4^°, group II included class II subjects with ANB angle >4^°, and group III included class III subjects with ANB of <0^°. Three linear measurements, that is, the anteroposterior dimension, height of the slimmest part of the posterior neural arch, and height of the dorsal arch were used to assess the dimensions of the atlas vertebra. The data were recorded, tabulated, and statistically analyzed.

Results: Mean difference in the anteroposterior dimension of the atlas vertebra was statistically significant with the highest dimension in the class II group followed by classes I and III (p < 0.001) whereas, the mean height of the dorsal arch was found to be the highest in the class III group followed by classes I and II (p < 0.000).

Conclusion: There are variations in the anteroposterior dimension and height of the dorsal arch of the atlas vertebra among patients with classes I, II, and III skeletal bases.

Clinical significance: Dimensional measurements of the atlas vertebra and its specific variations in patients with different skeletal base patterns performed on a lateral cephalogram itself give an endowment to study the morphology of the atlas vertebra in routine clinical status quo without the requisite of any added diagnostic investigations such as cone-beam computed tomography (CBCT). Understanding of such variances can be integrated during diagnosis and treatment planning to take suitable preventive and interceptive procedures in any developing patterns of malocclusion.

How to cite this article: Maniyar N, Prakash AT, Kiran Kumar HC. Variation in the Dimensions of the Atlas Vertebra among Patients with Class I, II, and III Skeletal Bases: A Cephalometric Study. World J Dent 2023;14(5):409–413.

Source of support: Nil

Conflict of interest: None

Patient consent statement: The author(s) have obtained written informed consent from the patient for publication of the case report details and related images.

Keywords: Atlas vertebra, Cervical vertebrae, Dorsal arch, Skeletal bases

INTRODUCTION

The establishment of cephalometric radiography in orthodontics made it possible to accurately evaluate the sagittal skeletal relationship of individuals with different types of malocclusion. This anteroposterior skeletal association between the apical bases of the maxilla and mandible is an imperative aspect appraised during the orthodontic diagnosis and treatment planning, aiding to set treatment goals and treatment mechanics. From an orthodontic slant, the facial profile of an individual is best defined by the corresponding sagittal jaw relationship with reference to the cranial anatomy.¹

The structure and growth of the cervical vertebrae have been an area of particular research intrigue since several authors have suggested some developmental associations concerning different anatomical variables of cervical vertebrae and dentofacial build.² Morphology of the first cervical vertebra, the atlas (C1), which sculpts the related component between the vertebral column proper and the head, expedites to be of specific interest to the orthodontist. It varies considerably from the other vertebrae in terms of both phylogeny and anatomy.³ The atlas vertebra dimensions have been presented to be allied with morphology and growth of the craniofacial structures, particularly of the mandible.⁴ Head and neck posture and dimensions of the C1 vertebra are well related to craniofacial morphology, including factors like the cranial base,² occlusions,⁵^,⁶ upper airway,⁷ and temporomandibular joint disorders.⁸ Association between dimensions of atlas vertebra and craniocervical posture has also been premeditated wherein cervical posture was found to be related to the length of the lower jaw, with cervical columns being more inclined to the true horizontal in individuals with the longer mandible.⁹

Furthermore, eccentricities in the morphology of the upper spine and reduced dimensions of the C1 vertebra have been linked with retrusion of jaws, an increased cranial base angle, and a greater jaw inclination.¹⁰ A possible explanation for this connotation between the cervical spine and the morphology of the craniofacial structures including the posterior cranial fossa could be established during early embryogenesis. The upper spine and the posterior cranial fossa are consequential derivatives of the same developmental notochord.¹¹ Since the notochord governs the development of the upper spine as well as that of the basilar part of the occipital bone, that is, the posterior part of the cranial base angle, the cranial base to which the jaws are attached could be the mounting link between the cervical vertebrae and the jaws.¹¹^,¹²

A lateral cephalogram is used customarily by orthodontists to analyze craniofacial structures for accurate diagnosis and treatment planning. Such cephalograms also depict the cervical vertebrae, including the morphology and size of the atlas vertebra. Since orthodontist accords with fluctuating growth and development of the structures in the craniofacial region and its modulations, there is a need for an improved understanding of the morphology and dimensions of the first cervical vertebra between diverse craniofacial skeleton patterns in the anteroposterior plane without any inquisitive effects of growth.¹³ Measuring the dimensions of the atlas vertebra and understanding its specific variations among patients with different anteroposterior skeletal patterning on a lateral cephalogram itself gives a provision to study the morphology of C1 in routine clinical situations without the need for any additional diagnostic investigations. Therefore, the aim of the current study was to quantify and compare the variation in the dimensions of the atlas vertebra in individuals with classes I, II, and III skeletal base patterns on a lateral cephalogram.

MATERIALS AND METHODS

The present retrospective study was based on pretreatment lateral cephalogram of patients with classes I, II, and III skeletal bases that were obtained from the file section of the Department of Orthodontics and Dentofacial Orthopedics at Bapuji Dental College & Hospital, Davangere, Karnataka, India, in the period from 2015 to 2021. The study was approved by the ethics committee and institutional review board (Ref. No. BDC/Exam/548/2021 - 2022). The sample size was calculated using the following formula¹⁴:

Where,

n is the calculated sample size.
μ is expected mean (μ_A = 8.5 and μ_B = 9.9).
σ is standard deviation = 2.6.
α is a type I error = 5%.
τ is the number of comparisons to be made = 3.
β is a type II error, meaning 1− β is power = 80%.

The calculated sample size was 72 and rounded up to 75. In each study group, a sample size of 25 was considered. Subjects who met the following criteria were included in the study—(1) age range between 19 and 43 years, (2) A point, nasion, B point (ANB) angle as assessed by Steiner’s analysis of 0–4^° for class I group, >4^° for class II group and <0^° for class III group, (3) no history of growth modulation or orthodontic treatment till growth cessation, (4) no any systemic joint or muscle pathology, and (5) retrospective lateral cephalometric radiographs in good condition. Subjects with the following conditions were excluded from the study—(1) patients with a history of craniofacial trauma/surgery and (2) patients with congenital anomalies or syndromes.

Method of Study

Cases with pretreatment lateral cephalogram selected for the study were ranged into three groups, that is, classes I, II, and III based on their ANB angle (Table 1). Dimensions of the atlas vertebra were measured (in mm) manually with the measurement ruler on the lateral cephalograms as per the parameters described by Oh et al.¹⁰ A total of three linear measurements were used to measure the atlas vertebral morphology of each individual included in the study—(1) anteroposterior dimension, (2) height of the slimmest part of the posterior neural arch, and (3) height of the dorsal arch (Table 2 and Fig. 1).²^,¹³

**Table 1:** ANB characteristics of groups I, II, and III
	N	Mean	Std. deviation	Std. error	Lower bound	Upper bound	Min	Max	F value	p–value of one–way ANOVA
Group I	25	2.56	1.044	0.209	2.13	2.99	1	4	183.495	0.000**
Group II	25	6.24	1.451	0.290	5.64	6.84	5	10
Group III	25	−2.80	2.291	0.458	−3.75	−1.85	−10	−1

Max, maximum; Min, minimum, Std., standard; **, statistically highly significant difference (p < 0.01)

**Table 2:** Linear measurements used to assess the cervical vertebra morphology
	Parameter	Measurement
A	Anteroposterior dimension	Distance between an extreme anterior point on the anterior tubercle and an extreme posterior point on the dorsal arch of the atlas
B	Height of the slimmest part of the posterior neural arch	Vertical height of the slimmest part of the posterior neural arch of the atlas
C	Height of the dorsal arch	Distance between the superior most point to the inferior most point on the posterior arch of the atlas

Fig. 1: Linear measurements to assess the dimensions of atlas vertebra on a lateral cephalogram: (A) Anterior-posterior dimension; (B) Height of the slimmest part of the posterior neural arch; (C) Height of the dorsal arch

Reliability and Measurement Error

Four lateral cephalograms from each group were randomly selected on two separate occasions to determine measurement error. A one-way analysis of variance (ANOVA) that was used to check the mean values of the three parameters indicated that this sampling was dependable. The mean scores of the three measurements did not differ significantly. Hence, the measurement error was deliberated to be insignificant.

Statistical Analysis

Data were entered into a computer by giving a coding system that was proofed for entry errors. Collected data was compiled on a Microsoft Office Excel Sheet (version 2019, Microsoft Redmond Campus, Redmond, Washington, United States). Statistical analysis was done using a statistical package for social sciences (SPSS version 26.0, IBM). Descriptive statistics like frequencies and percentage for categorical data, and mean and standard deviation for numerical data has been depicted. Intergroup comparison was done using one-way ANOVA followed by pairwise comparison of groups using post hoc Tukey honest significant difference test. For all the statistical tests, p-value of <0.05 was considered to be statistically significant, keeping α error at 5% and β error at 20%, thus giving power to the study as 80%.

RESULTS

The mean age of individuals included in the study was 21.12 years for group I, 21.44 years for group II, and 20.72 years for group III. There was a statistically highly significant difference seen for the values between the groups (p < 0.01) for ANB, with ANB of higher values in class II group as per magnitude (Table 1). Tables 3 to 5 detail the mean value of an anteroposterior dimension, height of the slimmest part of the posterior neural arch, and height of the dorsal arch of the atlas vertebra in classes I, II, and III groups. A statistically highly significant difference was seen for the values of anteroposterior dimension and height of the dorsal arch between the groups (p < 0.01), with higher values in the class II group and in the class III group, respectively (Tables 3 and 5). There was a statistically nonsignificant difference seen for the values between the groups (p > 0.05) for the height of the slimmest part of the posterior neural arch (Table 4).

**Table 3:** Anteroposterior dimension of the atlas vertebra
	N	Mean	Std. deviation	Std. error	Lower bound	Upper bound	Min	Max	F value	p–value of one–way ANOVA
Group I	25	45.60	3.884	0.777	44.00	47.20	38	54	7.644	0.001**
Group II	25	48.48	4.165	0.833	46.76	50.20	41	59
Group III	25	44.36	3.377	0.675	42.97	45.75	38	51

Max, maximum; Min, minimum, Std., standard; **, statistically highly significant difference (p < 0.01)

**Table 4:** Height of the slimmest part of the posterior neural arch of the atlas vertebra
	N	Mean	Std. deviation	Std. error	Lower bound	Upper bound	Min	Max	F value	p–value of one–way ANOVA
Group I	25	4.96	1.369	0.274	4.40	5.52	3	8	0.145	0.866#
Group II	25	4.92	1.412	0.282	4.34	5.50	2	8
Group III	25	5.12	1.394	0.279	4.54	5.70	3	8

Max, maximum; Min, minimum, Std., standard; #, nonsignificant difference (p > 0.05)

**Table 5:** Height of the dorsal arch of the atlas vertebra
	N	Mean	Std. deviation	Std. error	Lower bound	Upper bound	Min	Max	F value	p–value of one–way ANOVA
Group I	25	9.24	1.985	0.397	8.42	10.06	6	15	12.475	0.000**
Group II	25	8.36	1.114	0.223	7.90	8.82	6	10
Group III	25	10.80	2.000	0.400	9.97	11.63	8	15

Max, maximum; Min, minimum, Std., standard; **, statistically highly significant difference (p < 0.01)

A pairwise comparison of the mean values among the three groups is represented in Table 6. There was a statistically highly significant difference (p < 0.01) observed for the values between classes II and III groups for the anteroposterior dimension and between classes I and III groups and classes II and III groups for the height of the dorsal arch of the atlas vertebra. A statistically significant difference (p < 0.05) was noted for the anteroposterior dimension of the atlas vertebra between classes I and II groups. Overall, the results suggest that the anteroposterior dimension of the atlas vertebra is highest in class II subjects followed by class I, and the least in class III, whereas, the height of the dorsal arch is highest in class III group, followed by classes I and II.

**Table 6:** Pairwise comparison of groups for dimensions of the atlas vertebra
Dependent variable	(I) group	(J) group				95% confidence interval
Dependent variable	(I) group	(J) group	Mean difference (I–J)	Std. error	p–value	Lower bound	Upper bound
Anteroposterior dimension	1	2	−2.880^*	1.081	0.026*	−5.47	−0.29
	1	3	1.240	1.081	0.489#	−1.35	3.83
	2	3	4.120^*	1.081	0.001**	1.53	6.71
Height of slimmest part of dorsal arch	1	2	0.040	0.394	0.994#	−0.90	0.98
	1	3	−0.160	0.394	0.913#	−1.10	0.78
	2	3	−0.200	0.394	0.868#	−1.14	0.74
Height of the dorsal arch	1	2	0.880	0.495	0.184#	−0.30	2.06
	1	3	−1.560^*	0.495	0.007**	−2.74	−0.38
	2	3	−2.440^*	0.495	0.000**	−3.62	−1.26

*, statistically significant difference (p < 0.05); **, statistically highly significant difference (p < 0.01); #, nonsignificant difference (p > 0.05)

DISCUSSION

Skeletal jaw relationship and upper vertebral anatomy are both allied with craniofacial structure. Recent association studies for linear, volumetric, and geometric measurements within the craniofacial complex have emphasized a positive correlation between the dimensions of the atlas vertebra and the skeletal jaw bases.⁹ Few studies have been reported in the literature that analyzed the morphological variations of the atlas vertebra and its association with different skeletal malocclusions and growth patterns.¹^,²^,⁴^,⁹^,¹⁰ Moreover, Watanabe et al.⁹ conducted a three-dimensional cone-beam computed tomography (CBCT) evaluation to understand the variations in the measurements of the atlas vertebra in classes II and III malocclusions. However, the results from this study cannot be readily inferred to establish particular norms for different skeletal malocclusions and their differing atlas dimensions as CBCT is not a commonly advised diagnostic aid for day-to-day clinical practice. Since lateral cephalogram is one of the routinely advocated investigations for orthodontic diagnosis and treatment planning, measuring the dimensions of the atlas vertebra and understanding its specific variations among patients with different anteroposterior skeletal jaw relations on a lateral cephalogram itself without any additional investigating modalities stands more convenient and meaningful. Additionally, the present study takes into account patients with class I skeletal jaw bases which are considered to be the most prevailing type of malocclusion in the general population.¹⁵ This study demonstrates significant differences in the atlas vertebral dimensions in subjects with various sagittal jaw interrelations on lateral cephalograms.

The present study demonstrates a significant difference in anteroposterior dimension and height of the dorsal arch of the atlas vertebra among the classes I, II, and III groups. Considering the early growth completion of the central nervous system, specifically in the case of upper vertebrae it could be anticipated that the structure protecting and supporting the spinal cord would remain essentially unpretentious by environmental influences later in life.³ Ronaldo et al.,¹⁶ suggested a positive correlation between the length of the mandible and the anteroposterior dimension of the atlas vertebra that increased linearly in growing subjects. Moreover, morphological scrutiny of the dorsal arch of the atlas vertebra discovered a strong association with the mandibular growth pattern, whereby a lower atlas dorsal arch flagged reduced horizontal growth of the mandible. This can be attributed to the datum that subjects with a low dorsal arch had a comparatively elevated head position that altered the muscular activity of suprahyoid muscles, which would in turn perpetually alter the mandibular position.⁴ Hence, it was anticipated that understanding the form of the atlas vertebra and the orthodontic treatment would augment the treatment plan for subsequent growth.

The results of the present study support the fact that the anteroposterior dimension of the atlas vertebra is more in class II subjects when compared to classes I and III. This is in contrast to the results of the studies by Baydaş et al.¹ and Watanabe et al.⁹ who found no difference in the anteroposterior length of atlas vertebrae among Class II and Class III subjects. Variances in these associations might be ascribed to factors like racial difference, though the association between the morphology of the atlas vertebra and craniofacial structures varied with age and gender. On comparing the height of the dorsal arch of the atlas vertebra, a significant difference in the vertical height was observed in this study among all three groups, with the highest mean value found in class III subjects when compared to classes I and II. This is in agreement with the results by Watanabe et al.⁹ who found that class II subjects have considerably short atlas dorsal arch height. Moreover, no significant differences in height of the slimmest part of the posterior neural arch of the atlas vertebra are observed amongst the three groups in the present study.

Early versus late treatment has been a topic of great controversy in orthodontics. Clinicians find themselves in a dilemma as to when is the appropriate time to intervene for a patient presenting with classes II or III skeletal dysplasia with problems in the maxilla or mandible or a combination of both.¹⁷ Though it is widely accepted that some transitory disharmonies of the early mixed dentition are self-correcting or can be corrected by simple means if properly timed, it is essentially difficult to foresee the future growth potential of the maxilla and mandible.¹⁸ Results from the present study indicate that it may now be likely to not only establish the skeletal age of an individual by studying the cervical vertebrae on lateral cephalogram but also to predict the pattern of skeletal malocclusion that may occur. Once the cephalometric norms for the dimensions of atlas vertebrae are established for different skeletal jaw relationships in adults, this acquaintance can be integrated to take appropriate interceptive measures in any developing malocclusion in earlier age-groups.

We further recommend studies in this direction to identify various morphological differences in the atlas vertebra among patients with different jaw relationships and growth patterns. A similar study is commended with a larger sample size to be carried out in growing individuals presenting with different anteroposterior skeletal jaw relationships.

CONCLUSION

The anteroposterior dimension and height of the dorsal arch of the atlas vertebra are associated with the anteroposterior skeletal jaw relationships, with the highest anteroposterior dimension of C1 in subjects with skeletal class II malocclusion and increased height of the dorsal arch of C1 in subjects with skeletal class III malocclusion. Thus, there is variation in the dimension of atlas vertebra among patients with classes I, II, and III skeletal bases.

Previous Presentation

The study was selected as a “Best Paper per Session” during the 25th IOS National PG Student’s Convention held from 28^th April to 1^st May 2022 at Mangaluru, Karnataka, India.

ORCID

Nikunj Maniyar https://orcid.org/0000-0002-3801-7313

A T Prakash https://orcid.org/0000-0001-5013-0370

HC Kiran Kumar https://orcid.org/0000-0003-2264-554X

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