Morphological Variations of the Nasopalatine Canal in the North Cyprus Population: A Cone Beam Computed Tomography Study

Introduction

The anterior maxillary region frequently necessitates surgical interventions within dentistry and oral-maxillofacial surgery. These procedures include various actions like placing implants, periodontal surgery, removing cysts from the nasopalatine canal (NPC), surgically facilitating rapid palatal expansion, orthognathic surgery, and extracting impacted or supernumerary teeth [1]. Clinically, significant resorption often occurs in the buccal part of the premaxilla, adjacent to the nasopalatine canal. This resorption makes it challenging to optimally place dental implants and can lead to esthetic and functional issues. Hence, a thorough understanding of the anatomical characteristics of this area is essential to prevent complications [2].

The nasopalatine canal is a maxilla anterior pathway connecting the hard palate to the nasal floor. Towards the oral cavity, it emerges behind the maxillary central incisors as a single opening known as the incisive foramen (IF), while within the nasal cavity, the opening typically appears as 2 small openings called the Stenson foramen. The NPC serves as a passage for the nasopalatine nerve and the sphenopalatine artery, traveling to the palatal region’s anterior part [3]. Anatomy textbooks commonly describe the canal as being positioned centrally, behind the central incisor teeth. When the palatine processes of the maxillae are joined, a funnel-like aperture, known as the incisive foramen, becomes evident in the midline, behind the central incisor teeth. Within this aperture, the openings of 2 lateral canals, known as incisive canals, are typically observable, ending at the level of the nasal floor in the Stenson’s foramina. These canals serve as passages for the nasopalatine nerve and the concluding branch of the nasopalatine artery [4,5].

Understanding the structure of the nasopalatine canal is important when performing oral surgery on the maxilla. It’s especially crucial in addressing conditions like nasopalatine canal cyst or other palatal issues that may need surgical treatment [4]. Esthetics are also an important issue for patients. Dental implantation has emerged as a new treatment modality for edentulous patients, allowing them to substitute missing teeth and restore functional and esthetic demands. While dental implants have become the primary choice in treatment plans, they are still associated with complications related to their placement [6].

Therefore, neglecting the anatomy in this area can result in nerve damage and hinder successful integration of dental implants into the bone [7]. Several approaches have been offered in published works to address these problems, including enucleation, implanting directly into the canal, guided bone regeneration (GBR), and placement of a bone graft [8]. Therefore, understanding the specific features, morphology, and dimensions of the NPC, which are critical anatomical elements in this area, is crucial [9].

Conventional X-ray methods might not adequately show these anatomical variations. Lately, cone-beam computed tomography (CBCT) in radiology studies has enabled thorough three-dimensional assessments of anatomical structures like the NPC, revealing detailed configurations [2]. Dentomaxillofacial researchers have widely embraced CBCT as a crucial imaging method due to its reduced radiation exposure and cost-effectiveness, in contrast to traditional computed tomography (CT) [10]. Also, there are no apparent differences between linear measurements with CBCT and direct measurements of maxillofacial structures [11].

Previous studies [8,12–14] reported that the shape and dimensions of the NPC and thickness of anterior maxillary bone can vary based on sex, age, and ethnicity. Therefore, this study aimed to evaluate the morphological characteristics of the anterior maxillary nasopalatine canal and width of the buccal bone using cone-beam computed tomography (CBCT) in 150 adults in Northern Cyprus.

Material and Methods

ETHICS APPROVAL AND SAMPLE SELECTION:

The research received approval from the Committee on Research and Ethics (100/050/REK.01), conforming to the 1964 Helsinki Declaration, its later revisions, or comparable ethical standards, as well as the institutional and/or national research committee’s ethical standards, for all procedures carried out in studies involving human participants. Informed consent was obtained from all individual participants included in the study.

A total of 150 CBCT scans were randomly selected and analyzed retrospectively, obtained from the archives of the private dental imaging center in Nicosia. CBCT images were performed from December 2020 to October 2023 for treatment planning in various oral surgical procedures. CBCTs were obtained previously for various purposes such as implant surgeries, orthodontics, or impacted teeth evaluation.

We included patients aged 18 years or older, having both maxillary central and lateral maxillary incisors, who agreed to use of their clinical information for scientific purposes. Exclusion criteria were impacted teeth in the area, presence of a radiolucent or radiopaque lesion, bone grafts, root fragments present, dental implants in the premaxilla, other metal restoration in the area of the premaxilla, nasopalatine canal cyst, and orthodontic treatment. The mean age of 150 participants was 45.8 years for the 62 male patients and 44.3 years for the 88 female patients.

CBCT IMAGE ACQUISITION:

These scans were conducted utilizing CBCT radiographs obtained by using a Newtom GO 3D/2D (Quantitative Radiology s.r.l., Verona, Italy). Scanning parameters were 90 kvP, 24 s, 4 mA, voxel size 0.3 mm, and field of view 10×10 cm.

MORPHOMETRIC PARAMETERS:

Based on the criteria reported earlier [1–14], each patient’s nasopalatine canal morphology was evaluated based on whether it had a cylindrical, funnel, hourglass, or banana-shaped in sagittal view (Figure 1). Additionally, by using the sagittal view, the horizontal dimension of the premaxilla region was assessed at specified levels using a sagittal cross-sectional CBCT image and measured in millimeters [15,16] (Figure 2).

A level: Distance between the cortical layer of the incisive foramen and the facial surface of the buccal bone layer.

B level: Distance between the cortical layer of the nasopalatine canal to the facial surface of the buccal bone plate measured along a horizontal line starting from the palatal edge of the incisive foramen.

C level: Distance between the cortical layer located at the middle point along the length of the nasopalatine canal to the facial surface of the buccal bone plate.

D level: Distance between the buccal border of the nasal foramen and the cortical layer.

For each distinct sagittal shape of the nasopalatine canal; the anteroposterior diameter(AP) of the nasal foramen, canal length, anteroposterior diameter (AP) of the incisive foramen, and mediolateral diameter (ML) of incisive foramen parameters were evaluated and recorded in millimeters (Figure 2).

STATISTICAL ANALYSIS:

Data analysis was performed using SPSS 24. Kolmogorov-Smirnov testing for each of the nasopalatine canal diameters showed that the data met the normality assumption, since the skewness and kurtosis values remained within the range of ±1.5. One-way ANOVA was used to compare the groups according to canal diameter, while LSD (least significant difference) analysis, which is a post hoc 2-way comparison test, was used due to the homogeneity of variance and the number of different samples in each group. The same analysis method was used for the horizontal dimension of the anterior maxilla. Visualization of the ANOVA results was done using Excel. In addition, Pearson correlation was used to determine the relationships between diameters and vertical sections, while the t test was used for comparisons between males and females. Cross-table analysis and chi-square results were used to compare the canal type and direction-course distributions in terms of sex. Since there are 4 different canal shapes, comparisons were made with one-way ANOVA to compare the nasopalatine canal diameters (in mm) according to the nasopalatine canal shape. The Leneve test and ANOVA showed variance homogeneity was achieved, but since the groups were not equal according to the canal shape, pairwise comparisons were made between the groups through the post hoc comparison test using the LSD test.

Results

EVALUATION OF THE MORPHOMETRIC PARAMETERS OF NPC:

The mean values of the AP-ML diameters of the incisor foramen, AP diameter of the nasal foramen, and NPC canal length are 4.83, 3.19, 3.62, and 12.49, respectively. When the mean values of horizontal dimensions of the anterior maxilla are analyzed, the average of level A was 7.19, level B was 7.10, level C was 7.45, and level D was 9.19 mm (Table 1).

DISTRUBITION OF THE NPC SHAPE:

According to the NPC shapes, 84 (54%) had a cylinder-shaped canal, 31 (20.6%) had an hourglass-shaped canal, 28 (18.6%) had a funnel-shaped canal, and 6 patients (4%) had a banana-shaped canal.

COMPARISON OF NASOPALATINE CANAL DIAMETERS AND THE NPC SHAPE:

Figure 2 illustrates the comparison of nasopalatine canal diameters (in mm) according to the nasopalatine canal shape. When the anteroposterior diameter of incisive foramen value was compared according to nasopalatine canal shape types, a significant difference was observed according to one-way ANOVA results, and the anteroposterior diameter of the incisive foramen in the banana-shaped canal was significantly smaller than funnel shape and hourglass shape (P<0.05). Similarly, the diameter of the cylindrical shape was significantly smaller than the hourglass-shaped and funnel-shaped canals (P<0.05). However, there was no significant difference between banana-shaped and cylinder-shaped canals (P>0.05) (Figure 3).

Also, when mediolateral diameter incisive foramen values were compared by ANOVA according to nasopalatine canal shapes, the funnel-shaped canal measurements were significantly largerer than the banana-shaped and cylinder-shaped canals (P<0.05). There was no significant difference between the hourglass-shaped canals and other canal types (P>0.05).

Additionally, the anteroposterior diameter nasal foramen values were compared according to the nasopalatine canal shape, showing that the hourglass shape had significantly higher values than all other shapes (P<0.05) and cylinder-shaped was significantly higher than funnel-shaped (P<0.05). There was no significant difference between the banana, cylinder, and funnel shapes (P>0.05). However, there was no significant difference in nasopalatine canal length measurement in terms of nasopalatine canal shapes (P>0.05).

RELATIONSHIP BETWEEN NPC DIAMETERS AND ANTERIOR MAXILLA DIMENSIONS:

Table 2 illustrates the relationship between the diameter of different parts of the nasopalatine canal and anterior maxilla dimensions, demonstrating a significant negative relationship between AP diameter of the incisive foramen and levels A and B (P<0.05). However, no significant relationship was found between the AP diameter of the incisive foramen and levels C and D (P>0.05). In terms of the ML diameter of the incisive foramen, there was a significant negative relationship between the ML diameter of the incisive foramen and levels A, level B, and C (P<0.05). However, there was no significant relationship for level D (P>0.05). There was no significant relationship between the AP diameter of the nasal foramen and levels A, B, C, and D (P>0.05). A similar finding was observed for canal length and no correlation was observed between levels A, B, C, and D (P>0.05).

EVALUATION OF THE HORIZONTAL DIMENSION OF THE ANTERIOR MAXILLA AND THE NPC SHAPE:

Figure 4 shows the comparison of the horizontal dimension of the anterior maxilla at different levels and the nasopalatine canal shape. When the types of nasopalatine canals were compared according to the A level of the horizontal dimension of the anterior maxilla, there was no significant difference between the banana shape and cylinder shape (P>0.05), but the diameter of the A level of the cylindrer- and banana-shaped canals was significantly larger than for hourglass- and funnel-shaped canals (P<0.05).

At level B, only the cylinder-shaped canal had a significantly larger diameter than the funnel shape (P<0.05). At level C, there was no significant difference among the diameters of canal shapes (P>0.05). At level D, the hourglass shape had a significantly smaller diameter than the cylinder and funnel shapes (P<0.05).

EVALUATION OF THE NPC DIAMETERS AND HORIZONTAL DIMENSIONS OF THE ANTERIOR MAXILLA ACCORDING TO SEX:

Nasopalatine canal diameters and horizontal dimensions of the anterior maxilla at different levels were compared according to sex. There was no significant difference between male and female patients in AP diameter of incisive, foramen, ML diameter of incisive foramen, and AP diameter of nasal foramen measurements (P>0.05). However, the nasopalatine canal length of males was significantly longer than in females (P<0.05). Horizontal dimensions of males were significantly greater at levels A and level B (P<0.05), but C and D levels were not significantly different by sex (P>0.05) (Table 3).

EVALUATION OF NPC SHAPE AND SEX:

The distribution of nasopalatine canal shapes was evaluated according to sex – 4.8% of men and 3.4% of women had banana-shaped canals, 14.5% of men and 25.3% of women had hourglass-shaped canals, 64.5% of men and 50.6% of women had cylinder-shaped canals, and 16.10% of men and 20.7% of women had funnel-shaped canals – but the differences between males and females were not significant (P>0.05) (Table 3).

DIRECTION-COURSE DISTRIBUTIONS OF THE NPC:

Regarding the sagittal direction or path of the nasopalatine canal, the most common type was slanted-straight (67.60%), followed by vertical-straight (19.6%), vertical-curvet (6.80%) and slanted-curved (6.10%)

Direction-course distributions also did not show a significant difference according to sex, with 25.8% of men and 15.10% of women having a vertical-straight direction, 9.7% of men and 4.7% of women having a vertical-curved direction, 61.3% of men and 72.1% of women having a slanted-straight direction, and 3.2% of men and 8.1% of women having a slanted-curved direction-course (P>0.05).

These findings show that sex is not significantly associated with nasopalatine canal shape and direction-course distribution (Table 4).

Discussion

We examined morphological characteristics of the nasopalatine canal across various CBCT scans and how these morphometric properties affect measurements of buccal bone structure in the anterior maxilla. The cylindrical shape was the most common form of nasopalatine canal, observed in 84 patients (54%). The anteroposterior diameter of the incisive foramen in the banana-shaped canal was significantly smaller than the funnel-shaped and hourglass-shaped canals (P<0.05). Similarly, the diameter of cylinder-shaped canals was significantly smaller than the hourglass- and funnel-shaped canals (P<0.05). Funnel-shaped canals had significantly wider ML diameters of the incisive foramen than banana- and cylinder- shaped canals. In terms of the anteroposterior diameter nasal foramen values and canal shape relationship, it was found that the hourglass shape was significantly higher than all other shapes (P<0.05), and cylinder-shaped canals had significantly higher values than funnel-shaped canals (P<0.05). There was a significant negative relationship between the AP diameter of the incisive foramen and levels A and B (P<0.05). In terms of the ML diameter of the incisive foramen, there was a significant negative relationship between the ML diameter of the incisive foramen and levels A, B, and C (P<0.05). The diameter of the A level of the cylinder- and banana-shaped canals was significantly wider than for the hourglass- and funnel-shaped canals (P<0.05). Only the cylindrical shape at level B had a significantly wider diameter than the funnel shape (P<0.05). At level D, the hourglass shape showed a significantly smaller diameter than cylindrical and funnel shapes (P<0.05). The nasopalatine canal length of males was significantly longer than in females (P<0.05). According to the horizontal dimension levels, values of males were significantly higher at levels A and B (P<0.05).

Understanding the morphology of the nasopalatine canal is essential in clinical practice. Diverse anatomical variations in structures can impact implant positioning. Implant surgery commonly faces complications like sensory problems and bleeding. Harm to the neurovascular bundles can significantly affect patients, leading to sensory disruptions or pain. Furthermore, the integration of implants with these bundles can cause unsuccessful osseointegration. Injuries to these important vessels can cause severe bleeding. Excessive bleeding during surgeries in the premaxilla region without a clear cause and ambiguous pain linked to placing implants in the same area have been reported. Accurately locating the nasopalatine canal is very important for procedures like administering local anesthesia and various surgeries in the premaxilla region. The closeness of the NPC to the roots of maxillary anterior teeth guides how an implant should be placed. Implants in the premaxilla region are often difficult because of the distance and shape of the NPC. Therefore, various features of the NPC, like shape, size, curve, and direction, are important to consider when planning surgeries in the premaxilla. Various methods have been used to evaluate the NPC’s position. However, conventional radiography is limited by its two-dimensional perspective [2,17–19].

Three-dimensional imaging can be conducted using spiral or multiplanar CT scans, but these approaches are less favored due to their high radiation exposure and cost. CBCT is regarded as the ideal imaging method for dentomaxillofacial diagnosis, primarily because it is more affordable and involves lower radiation exposure. Applying 3D imaging techniques through pre-surgical planning can prevent complications [4,18].

The investigation of the nasopalatine canal has been assessed by many researchers with different methods and populations using CBCT [1–4,19]. In this research, we assessed the NPC using CBCT data in the North Cyprus population. The morphology of the nasopalatine canal shows considerable variability, with distinct variations observed among different populations. Different classifications of morphology and shape of the nasopalatine canal have been used in past studies.

In 2014, Etoz et al [9] categorized the shape of the NPC into 6 groups: tree branch, cylinder, banana, funnel, cone, and hourglass. Güncü et al [20] and Mardinegar et al [21] used a four-category classification (hourglass, funnel, banana, and cylinder). Safi et al [21] classified the shapes into 4 groups but they used cylinder funnel, hourglass, and spindle shapes as classifications. Similar to Güncü et al [20] and Mardinegar et al [15], our classification also divided the NPC into 4 distinct groups based on specific shape differences: cylinder, funnel, hourglass, and banana.

According to the distribution of this classification, cylindrical shape has been reported as the most common shape by some previous studies [3,13,22,23], while banana-shaped canals have been reported as the least common type [9,24]. The second most common canal shape was reported as an hourglass shape canal [7,25]. Funnel-shaped canals are reported by some authors as the second least common canal [24,25]. These results resemble those of the present study; the most common nasopalatine canal shape was cylindrical, followed by hourglass, funnel, and banana shapes. On the other hand, Milanovic et al [17] reported that the shapes most commonly observed for the NPC were funnel and cylindrical, followed by hourglass and banana. Conversely, Etoz et al [9] and Sekerci et al [27] foundd that the most frequent shape of the NPC was hourglass. Gil-Marqueset al [1] indicated that the banana-shaped NPC was dominant. These differences could be the result of racial disparities, age differences, sex differences, and the methods used for assessment.

The common incisive foramen diameter was under 6 mm. If it exceeds 10 mm, it is crucial to consider the possibility of an underlying pathological issue such as cysts or tumors [13,17].

According to our results, the average AP diameter of the incisive foramen and nasal foramen was 4.83±1.42 and 3.62±1.76, respectively. These results are similar to those of previous studies [23,26] using multi-detector row computed tomography, showing moderately larger diameters for A-P diameters of the incisive and nasal foramen (6.31 mm and 3.29 mm, respectively). In terms of the ML diameter of the incisive foramen, we found an average of 3.62±1.76 mm. Milanovic et al [17], Salemi et al [27], and Friedrich et al [28] found results similar to ours. Mraiwa et al [5] found an average buccopalatal width of 7.6 mm, with a range of 2.9 mm to 13.6 mm.

We found that the average nasopalatine canal length was 12.49±3.39 mm. This outcome is closer to the findings of others [12,22,28]. However, in our study, the length of the NPC did not match the findings of Soumya et al [12], who reported an average value of 18.63 mm. This difference might be due to differences in population demographics.

Milanovic et al [17] found that in people with the banana-shaped canals the ML diameter of the incisive foramen was significantly wider than for cylinder-shaped canals. However, we found that the ML diameter of the incisive foramen at the funnel-shaped canal type was significantly wider than for banana and cylindrical types. Furthermore, Milanovic et al indicated that cylinder-shaped canals tended to have smaller AP diameters in the incisive foramen compared to the funnel-shaped canal. However, the AP diameter of the nasal foramen in the cylindrical shape was notably wider, consistent with our findings. We also found that the anteroposterior diameter of the incisive foramen at the cylindrical shape was significantly smaller than for hourglass and funnel shapes. In terms of AP diameter of the nasal foramen in the cylinder shape, our results were different, showing that the anteroposterior diameter of the nasal foramen with the hourglass shape was significantly wider than for all other shapes. However, Jain et al [23] assessed the effect of the sagittal shape of the nasopalatine canal dimensions and did not find any significant difference between measurements, unlike our results.

Sufficient width of the alveolar ridge is an initial important factor for successful placement of dental implants, considering the differences between implant diameter and the horizontal dimension of the ridge [17,29]. Some research has assessed buccal bone width at 3 different horizontal levels [1,22], but our study conducted a morphometric examination of the alveolar ridge across 4 specific levels, similar to the approach described by Salemi et al [27], aiming to encompass a broader spectrum of morphometric characteristics that can have greater practical relevance in clinical applications. Similar to Güncü et al [20], Panjnoush et al [22], and Milanovic et al [17], we found the greatest measurement for the buccal alveolar ridge was 9.19 mm at the apical section of the canal, which was the D level, while the smallest was 7.10 mm at the level of the palatal border of incisive foramen, which was at the B level. Panjnoush et al [22] evaluated measurements of bone width across 3 distinct levels and Milanovic et al [17] calculated the morphometric assessment of the alveolar ridge at 4 specific levels, resembling our study.

We assessed the relationship between the diameter of different parts of the nasopalatine canal and the dimensions of the anterior maxilla, similar to Milanovic et al [17], and we found a significant negative relationship between the AP diameter of the incisive foramen and levels A and B (P<0.05). Also, a significant negative relationship was detected between the ML diameter of the incisive foramen and levels A, B, and C (P<0.05). Milanovic et al [17] found a significant relationship between the AP diameter of the incisive foramen and levels A, B, and C, but we have only found a significant relationship at levels A and B.

Milanovic et al [17] stated that the AP diameter coincided with decreased horizontal bone dimensions in the premaxilla at levels A, B, and C for canals shaped like bananas or funnels. According to our results, the banana-shaped canal type caused an increase at the levels of A, B, and C but for the funnel shape there was a decrease in diameter at levels A and B. However, they found that an hourglass-shaped NPC was only linked to reduced bone thickness at level C. We found that less bone thickness in the hourglass-shaped canal only in level D. On the contrary, they reported that in cylindrical NPC types, a larger nasal foramen was associated with a notable decrease in horizontal bone dimension at level D. In our study, a larger nasal foramen was seen in an hourglass-shaped canal. This difference might be due to differences in population demographics.

Furthermore, the nasopalatine canal length of males was significantly longer than in females (P<0.05). According to the horizontal dimension levels, the measurement values of male patients were significantly higher both at level A and level B (P<0.05). Like our results, some previous studies found a significant relationship between nasopalatine canal morphology and sex [21,23]. On the other hand, some previous studies did not find any significant relationship between nasopalatine canal morphology and sex [3,12]. Regarding the direction-course of the nasopalatine canal, the most commonly observed type was the slanted-straight, making up 67.6% of cases, which is similar to the results of Gil-Marques et al [1], Thakur et al [13], and Fernández-Alonso et al [7]. On the contrary, Al-Amery et al [30] reported that the prevalent direction in their research was slanted-curved, while Song et al [31] found vertical-straight to be the most frequent direction.

The study is limited by its small sample size, and it did not investigate the influence of age on the nasopalatine canal and buccal bone width.

Conclusions

We found a correlation between NPC shapee and horizontal dimensions of the anterior maxilla’s anatomy. The measurements of NPC in a North Cyprus population slightly differed from the established standards found in the existing literature. Conducting more extensive studies with a larger number of CBCT images will offer additional insights.