Evaluation and association of cervical vertebral morphology, inclination and cranial base angle among various sagittal skeletal malocclusion

INTRODUCTION

Cervical vertebrae have always played a vital role in cephalometric diagnosis and treatment planning in the field of orthodontics.^[1] The cervical vertebral column, as a reference structure, is taken to evaluate natural head position (NHP) in lateral cephalograms.^[2] It is important to determine whether variations in craniocervical morphology and craniomandibular systems can lead to changes in one another.^[3]

Various studies have been done to assess whether cervical vertebrae morphology is affected by age, posture of the head, and the skeletal growth pattern.^[4] Mandibular and maxillary prognathism can lead to a shift in the center of gravity of the head, causing compensatory activity of the neck and head muscles and alterations in the alignment of the cervical spine [Figures 1-5].^[5] Dimensions of cervical vertebrae are associated with head posture, angulation of cranial base, and mandibular shape and growth.^[6]

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Figure 1:

Landmarks used in the study. PNS: Posterior nasal spine, ANS: Anterior nasal spine, Cv2tg: Tangent point of odontoid process tangent (OPT) line on the odontoid process of the second cervical vertebra, Cv2ip: The most inferior posterior point on the corpus of the second cervical vertebra, Cv4ip: The most inferior posterior point on the corpus of the fourth cervical vertebra.

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Figure 2:

Planes used in the study. NSL (red line): Cranial base, OPT (blue line): Posterior tangent to the odontoid process through Cv2ip to cranial base, CVT (green line): Cervical vertebra tangent, Ver: True vertical line, Hor: True horizontal line, Mandibular plane (yellow line).

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Figure 3:

Linear parameters used in the study Cv1sl (red line), Cv2sl (green line), Cv3sl (yellow line), Cv4sl (blue line), Cv1bl (white line), Cv2bl (white line), Cv3bl (white line), Cv4bl (white line).

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Figure 4:

Linear parameters used in the study Cv1ht (red line), Cv2ht (blue line), Cv3ht (green line), Cv4ht (yellow line).

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Figure 5:

Angular parameters used in the study SN/OPT, SN/CVT, CVT/Hor, OPT/ Hor. SN: Sella-Nasion, OPT: Odontoid process tangent, CVT: Cervical vertebra tangent, SN: Sella-Nasion, Hor: Horizontal.

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The relationship between head posture and craniomandibular morphology has been stated by Schwartz, and many clinical studies were performed to evaluate it.^[7,8] Furthermore, several hypotheses have been proposed to describe the relationship between craniocervical posture and mandibular position.

This study draws a correlation between cervical vertebrae morphometry, inclination, and cranial base angle among adolescents of Solan district in Himachal Pradesh with various skeletal malocclusions.

MATERIAL AND METHODS

This retrospective study was carried out at the Department of Orthodontics and Dentofacial Orthopedics, Bhojia Dental College and Hospital, Baddi, Himachal Pradesh. 90 subjects were selected from the lateral cephalometric records of the patients who had undergone fixed mechanotherapy from the department. The pre-treatment cephalometric radiographs were divided into 3 groups on the basis of their ANB angle with 30 subjects in each group.

RESULTS

The descriptive statistics for all the parameters are depicted in Table 6. When the mean of the parameters were analyzed by comparing all the three groups using one-way Analysis of variance (ANOVA), it was seen that Cv1sl was found to be highly significant with the highest mean value for Class I followed by Class II and then Class III. Cv2sl length among all the groups was found to be significant, with the highest mean value for Class I, followed by Class II and Class III, respectively. Cv3sl were found to be significant, with the highest mean value for Class I, then Class II, followed by Class III. Cv4sl were also found to be greatly significant, with the highest mean value for Class I, followed by Class II and Class III, respectively. Cv1bl length was found to be significant, with the highest mean value for Class III, followed by Class II and then Class I. Cv2bl length was found to be significant, with the highest mean value for Class I, followed by Class III and then by Class II. Cv3bl was also found to be significant, with the highest mean value for Class I, followed by Class II and then by Class III. Cv4bl was found to be significant, with the highest mean value for Class I, followed by Class III and then by Class II.

Cv3ht was found to be significant, with the highest mean value for Class I, followed by Class II and then by Class III. Cv4ht was found to be significant, with the highest mean value for Class I, followed by Class II and then by Class III. OPT/Hor shows the highest mean values for Class III, followed by Class II and then Class I.

The correlation of Cv2sl, Cv3sl, and Cv3bl was found to be statistically significant with Sella-Nasion-A point angle (SNA) angle, respectively. The correlation of SN/OPT angle with Sella-Nasion, Sella-Nasion-B point angle (SNB) angle was found to be statistically significant. The correlation of Cv2bl with Lower Anterior Facial Height (LAFH) was found to be statistically significant.

The correlation of Cv1ht was found to be statistically significant with SNA angle. The correlation of Cv2ht and SN/ OPT angle was found to be statistically significant with SNA angle.

The correlation of Cv4bl was found to be statistically significant with incisor-mandibular plane angle (IMPA) angle. The correlation of Cv2bl was found to be statistically significant with LAFH.

DISCUSSION

Sagittal skeletal relations play an important role in the diagnosis and treatment planning of patients seeking orthodontic treatment. Using an adjunct parameter such as cervical vertebral morphology would enhance and favour the outcome of treatment for patients with sagittal skeletal discrepancies. The head and vertebral column function as a unified biomechanical system known as the craniocervicalmandibular system. This system consists of three primary components: The temporomandibular joint, the occipital-atlas-axis articulation, and the hyoid bone with its suspensory structures. These elements are interdependent and are connected to the rest of the body through muscles and ligaments. As a result, cervical posture is likely to influence craniofacial morphology.^[10] Several studies have explored the relationship between head posture and anteroposterior skeletal patterns.^[11,12] Notably, Marcotte found a significant correlation between head posture and discrepancies in the anteroposterior positioning of the upper and lower jaws.^[13]

The atlas represents the transition between the skull and the axial skeleton, and it is reported that both the facial skeleton and the cervical column are affected by the dimensions of this vertebra.^[14] Recent studies examining linear, volumetric, and geometric measurements within the craniofacial complex have highlighted a positive correlation between the dimensions of the atlas vertebra and the skeletal jaw bases.^[15,16]

In the present study, Cv1sl and Cv2sl were found to be increased in skeletal Class I patients, followed by Class II and Class III patients. This correlation is attributed to the deep attachments of the broad cervical spine ligaments– including the anterior and posterior longitudinal ligaments, ligamentum flavum, interspinous ligament, nuchal ligament, and the transverse ligament of the atlas–which extend from the foramen caecum to the successive vertebrae.^[16] Inferences seen in the study are in favor of the study conducted by Sharma et al.^[17] and our results are not in concordance with the study done by Maniyar et al. which showed the highest dimension in the Class II group, and is not in favour of the study.^[18] In cases of Class II and Class III, the soft-tissue stretching mechanism causes reduced height and altered inclination of the dens. Results found are concordant with the study by Sharma et al.^[17] A study by Nambiar and Mogra^[9] showed different inferences in comparison to the present study.

The highest mean value of SN/OPT was seen in skeletal Class I patients, suggestive of backward position of anterior cranial base is because foramen magnum is displaced backward and upward and the foramen angle increases, resulting in an upward tilt of the face, as similarly observed in the study by Bjork,^[19] Afrand et al.,^[20] and Rawat et al.^[21] The results are non-concordant with the study by Hedayati et al.,^[22] Arntsen and Sonnesen,^[23] Gonzalez and Manns^[24] and Festa et al.,^[10] where the upright posture of the head and spinal column was more evident in individuals with Class II malocclusion. Inter-group comparison of SN/OPT showed a non-significant value. SN/cervical vertebra tangent (CVT) values of Class III patients show the greatest mean value among all the groups because of the upward head movement in Class III patients. The results are not in favour of the study conducted by Hedayati et al.,^[22] where the average SN/CVT angle in skeletal Class I was higher than in individuals with skeletal Class III, which suggests that Class III individuals place their chin towards their chest more than participants with normal occlusion.^[19] OPT/Hor and CVT/Hor show the highest mean values for Class III, then Class II and Class I, due to forward positioning of the mandible, and demonstrate that the cervical spine is inclined more dorsally in skeletal Class III malocclusion. Results are consistent with studies by Peng et al.,^[25] Liu et al.,^[26] and Qadir and Mushtaq.^[27] Inter-group comparison among the parameters shows non-significant results. Higher angle in Class III patients represents the tendency of this group of patients to a more backward inclination of the cervical column, while Class II patients tend to have a more forward position of the column.^[28]

Pearson correlation among the study parameters showed good correlation of Cv1sl with SNA and LFAH in Class I patients and with SNB and IMPA in Class III patients, since the occipital extension of the atlas is accompanied by sliding of the maxilla, following which the mandible positions itself behind the maxilla. Cv2sl showed poor correlation with SNA angle (although significant) in Class I patients, but good correlation with IMPA in skeletal Class II patients. A strong correlation is also observed for Cv2sl with SNB. The mandible, being placed in close approximation to the axis, is responsible for the above correlations. In Class III patients, Cv1sl is correlated directly with SNB, IMPA, and gonial angle, and the same for Cv1bl with SNA. LAFH showed good correlation with Cv1bl in Class I as well as Class II patients. Cv1ht shows good correlation with SNA for Class III patients, but did not show the same for Class II patients (a significant result was obtained). This correlation is of the same nature as that in the study conducted by Nambiar and Mogra.^[9] Cv2ht, too, shows poor correlation with SNB angle but good correlation with SNA angle in skeletal Class II patients due to an anteriorly positioned maxilla. Cv2bl shows good correlation with LAFH in Class II individuals, whereas it shows poor correlation in Class III individuals. In Class II patients, CVT/Hor angle shows good correlation with SNB angle as well as gonial angle due to the reference planes connecting the condylion of the mandible, whereas poor correlation with SNA angle. For Class I patients, CVT/Hor shows good correlation with SNA angle and IMPA as well, due to the sliding of the maxilla. The study by Janson et al.^[29] is also concordant with our results in Class II subjects.

OPT/Hor angle shows a positive correlation with IMPA and gonial angle in Class III individuals and with SNB in Class I individuals. SN/CVT angle shows good correlation with LAFH and gonial angle in skeletal Class I patients and with SNA in skeletal Class III patients.

CONCLUSION

• Individuals with skeletal Class I malocclusion have a greater correlation in terms of cervical vertebral morphology and cranial base relationship among all the skeletal malocclusion groups in the study

• A good correlation was observed with atlas height and SNA in Class I patients, suggestive of a standard maxillomandibular skeletal relationship with respect to the morphology of cervical vertebrae

• Inter-group comparison showed statistically significant result in the study parameters Cv1sl, Cv2sl, Cv3sl, Cv4sl, Cv1bl, Cv2bl, Cv3bl, Cv4bl, Cv1ht, Cv3ht, and Cv4ht when compared using one-way ANOVA

• Difference in results in the study is pertaining to difference in the sample size among all related studies and difference in the geographical location.