INTRODUCTION

Cephalometric radiographs are used in orthodontics to evaluate the development, growth, and morphometric relationships of craniofacial and dental structures, but they also include other diagnostic information about the skull, face, and upper cervical spine. Various occult pathologies and rare normal variants involving the head or spine have been reported thanks to this information.1–8

On the other hand, most of these pathologic conditions, developmental abnormalities, or normal variants are associated with a significant problem in other systems.4910 Interestingly, some of these findings are detectable very early in life11 and often precede other signs or symptoms in syndromes. Therefore, in some cases, they could potentially be valuable for an early diagnosis.

Recently a higher incidence of interclinoid ligament (ICL) or sella turcica bridge calcification has been associated with palatally displaced canines (PDC).5 Thus the occurrence of a new sign in craniofacial skeletal anomalies, concomitant with PDC, has been established. This relationship may be based on the involvement of neural crest cells (NCCs) and/or homeobox or hox genes during the development stage.12 It appears that tooth formation and eruption and sella turcica bridge calcification, as well as neck and shoulder skeletal development, are influenced by NCCs.13

The aims of this study were: (1) to describe the skeletal anomalies and normal variants of the cervical column (partial cleft of the posterior portion of the arch of atlas and ponticulus posticus) in patients with PDC, (2) to evaluate the presence of “sella turcica bridge” in patients with PDC, and (3) to compare the findings of the PDC group with those found in subjects with normal craniofacial morphology and no obvious dental anomalies. The null hypothesis that there is no increased prevalence of skeletal anomalies and/or normal variants seen in cephalometric radiographs of patients with PDC was tested.

MATERIALS AND METHODS

The treatment records of 38 white subjects (16 male and 22 female subjects, ages 14 to 20 years; mean age 16.3 years) with PDC were collected retrospectively from a large number of patients seen over a 24-month period in the Department of Orthodontics, University of Catania, Italy, and the Department of Orthodontics, University of Roma “La Sapienza,” Italy. The diagnosis was made on the basis of clinical examinations and standardized radiographs and confirmed visually during surgery according to established standardized techniques.14

To be included in the study, the case records needed to include good-quality dental panoramic and lateral cephalometric radiographs with at least the first four cervical vertebrae visible. The exclusion criteria were the presence of a cleft lip and palate or other dental or craniofacial anomaly or syndromes, trauma, and multi-reagent chemotherapy.

A power analysis suggested that a control sample size of 70 patients was sufficient to evaluate significant differences in the skeletal anomalies between subjects with PDC and a control group. Thus the control group consisted of 70 subjects (41 female and 29 male subjects ages 15 to 19 years; mean age 15.5 years) who had no other dental anomalies and whose maxillary canines had erupted normally. This group represented randomly selected white subjects treated at the orthodontic clinics of both universities during the previous 24 months. The exclusion criteria were the same as those for the study group. The study was approved by the ethical committees of the relevant institutions.

Visual assessment of skeletal anomalies and normal variants of the cervical column on lateral profile radiographs and measurements to evaluate a “sella turcica bridge” was performed by two of the authors. The tracings were made on ultrathin 0.003-inch transparent acetate sheets using a Pentel 0.5-mm lead pencil.

The cephalometric radiographs were evaluated on a masked, illuminated viewbox in a room with reduced lighting and were measured manually. Before starting the study, the authors calibrated themselves by scoring the first 30 radiographs together to establish agreement. Radiographs were interpreted and scored independently.

RESULTS

Data regarding the age and gender distribution for the study sample are reported in Table 1. The prevalence of incomplete and complete (sella bridge) ICL calcification (Figure 1) in the subjects with PDC was higher than that in the control group. In fact, 34.2% of patients with PDC versus 25.7% of control patients showed an ICL that was more than half calcified. Complete calcification of the ICL (sella turcica bridge) was observed in 18.4% of subjects with PDC and only 5.7% of the control subjects. These differences were statistically significant according to Pearson's chi-square test (P < .042) and Fisher's exact test (P < .042) (Table 2).

Table 1.  Age and Gender Distribution of Patient Sample

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Table 2.  Interclinoid Ligament Calcification Among Patients and Control Subjects

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More PDC subjects (18.4%) showed complete calcification of the atlanto-occipital ligament (ponticulus posticus), as opposed to the control group (4.3%) (Figure 2). Incomplete calcification of the atlanto-occipital ligament was observed in 15.8% of patients with PDC and 15.7% of the control subjects. These were statistically significantly different according to Pearson's chi-square test (P < .050) and Fisher's exact test (P < .052) (Table 3).

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Table 3.  Atlanto-occipital Ligament Calcification among Patients and Control Subjects

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The prevalence of partial cleft in the posterior portion of the neural arch of the atlas was also increased in patients with PDC (15.8%). This difference was statistically significant according to Pearson's chi-square test (P < .047) and Fisher's exact test (P < .039) (Table 4).

Table 4.  Posterior Arch Deficiency among Patients and Control Subjects

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However, no statistically significant associations were observed between bridged sella and ponticulus posticus (chi-square = 2.736, P = .615); bridged sella and partial cleft of the atlas (chi-square = 3.484, P = .179); and ponticulus posticus and partial cleft of atlas (chi-square = 1.181, P = .736); although these characteristics were observed in some patients (Figure 3).

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DISCUSSION

Anomalies of the cervical vertebrae have been described in several syndromes,9 and associations between cervical vertebrae and maxillary malformations152122 and condyle and vertical craniofacial morphology (deep bite)6723 have been reported more recently.

On the other hand, a greater frequency of sella turcica bridge has been described in patients with severe craniofacial deviations4 and tooth anomalies5 and has also been noted in some patients with other disorders and syndromes.1024–26 The results of the present study demonstrate an increased prevalence of posterior arch deficiency, ponticulus posticus, and sella turcica bridge in patients with PDC.

With regard to ponticulus posterior or arcuate foramina, we observed an increased prevalence (34.2%) of complete and incomplete arcuate foramina in subjects with PDC, in contrast to the prevalence (15.8%) observed in the control group. This finding is consistent with the literature.111718 An increased prevalence of complete and partial ICL calcification was also detected in patients with PDC compared to the control sample. These results are consistent with the reported radiographic data of sella turcica bridge in patients with dental anomalies.5

Posterior arch deficiency of the atlas occurred more frequently in individuals with PDC (15.8%) compared to the control sample (4.3%). In fact, no anomaly was detected in our sample of orthodontic patients without PDC. In this study, we deliberately did not evaluate cervical vertebrae fusion, as this is best determined with the use of flexion and extension radiographs, which can demonstrate a change in the distance between vertebrae if they are not fused.16 Thus, to avoid false-positive or false-negative results, these data were recorded but were not evaluated from a statistical point of view.

Overall, these findings indicate that some skeletal anomalies and normal variants seen in cephalometric radiographs are associated not only with malformations of the jaw, craniofacial morphology, and occlusion152125 but also with tooth anomalies such as PDC.

This relationship seems to be based on the involvement of NCCs and/or homeobox or hox genes during the developmental stages1227 and formation of teeth and sella turcica. Therefore, neck and shoulder skeletal development27 is influenced in the same way; in fact, homeobox gene mutation may be responsible for congenital cervical spine anomalies. Because the teeth, the head, and the cervical spine are influenced in their development by NCCs, it is conceivable to assume that any disturbance of NCCs might interfere with the development of one or more systems that are under their influence.

The etiology of PDCs has been debated for a long time. Data from multiple sources support a genetic etiology.2829 Tests of genetic influence have focused on bilateral PDC, sex and population differences in the incidence of PDC, familial occurrence of PDC, and the occurrence of other dental anomalies concomitant with PDC.28 Bearing this in mind, our findings broaden the concept somewhat that PDC is seen only in conjunction with other dental anomalies29 or skeletal anomalies and normal variants of skull and cervical vertebrae in patients with PDC. In fact, PDC is associated with other clinically recognizable features that often occur together and could be considered part of a “syndrome.”

We believe that future research into the molecular basis of dentofacial abnormalities could benefit from the reporting of new clinical interrelationships such as those presented here. Our findings are consistent with the hypothesis that a common pathogenesis probably relates to a simultaneous embryogenesis of some skull structures. Moreover, from a clinical point of view, these skeletal anomalies and/or normal variants may be considered risk factors that could enable the clinician to make an early diagnosis and thus treat the eruption disturbance at an early stage.

CONCLUSIONS

• The null hypothesis was rejected. There was a statistically significant increase in the prevalence of skeletal anomalies and/or normal variants in patients with PDC versus the control group.

• Because many of these skeletal anomalies and normal variants are present early in life, their early detection can be used to forecast the presence of PDC later in life, enabling the clinician to adopt preventive measures.