{'fraction_non_alphanumeric': 0.03231531464911632, 'fraction_numerical': 0.020335724321526288, 'mean_word_length': 4.85708098744045, 'pattern_counts': {'":': 0, '<': 4, '<?xml version=': 0, '>': 2, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 3, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
EVALUATION OF CHANGES IN NASOPALATINE CANAL MORPHOLOGY ACCORDING TO DENTITION STATUS BY COMPUTED TOMOGRAPHY

Objective: The nasopalatine canal (NPC) is one of the important anatomic structures in anterior maxilla. The aim of this study was to evaluate the changes in NPC morphology according to dentition status in the maxillary anterior region by computed tomography (CT). Methods: Computed tomography images of 100 patients were screened retrospectively. Images were divided into two groups by dental status: an edentulous group (EG) of 50 patients who have edentulous premaxilla and a control group (CG) of 50 patients who have all incisor teeth in the premaxillary region. After recording the age, sex, and dentition status of the patients, the NPC diameter, NPC length, incisive foramen (IF) diameter, and angle between the NPC and palatine bone were measured in sagittal sections, and the number of NPCs was determined in axial sections. Results: There was no significant difference between NPC angle and dentition status ( p =0.151). The NPC diameter was significantly higher in the EG ( p =0.002), as was the IF diameter ( p =0.041). In addition, NPC length was significantly higher in the CG ( p <0.001). A statistically significant and negative correlation was found between age and NPC length ( p <0.001), and a positive correlation was found between age and NPC diameter ( p =0.004). In addition, no statistically significant difference was found between sex and other parameters ( p >0.05). Conclusion: The NPC length and diameter vary according to the age and dentition status of the patient. Changes in this anatomic structure should be evaluated pre-operatively in elderly patients by three-dimensional radiographic evaluation.


Introduction
The nasopalatine canal (NPC) is the anatomical structure located in the premaxilla region that connects the hard palate to the nasal floor. The NPC opens to the oral cavity with called incisive foramen which is behind the maxillary central teeth. 1 Considering the presence of neurovascular structures within the NPC, for surgical procedures, dental implant surgery, or anesthesia, evaluation of morphology and size before surgery is crucial to prevent possible complications. Contact of dental implants with neural structures may affect the implant osseointegration or may cause neural dysfunction. 2,3 In addition, difficulties related to NPC anatomy while performing local anesthesia in the maxillary anterior region have been reported in the literature. 4 The importance of preoperative evaluation of the NPC region has increased, with the increasing rehabilitation of toothless maxilla through dental implants. In the literature, there is a correlation between the loss of maxillary incisors and changes in NPC morphology. 5 Bone atrophy that develops after tooth loss may affect the surrounding structures, and the NPC may enlarge and the neurovascular structures within it may become close to the alveolar crest. 4 The NPC was evaluated by micro-computed tomography 6 or magnetic resonance imaging 7 , but to prevent perforation of the base of the nose and to prevent damage to neurovascular structures in the NPC, the use of computed tomography (CT) before surgical operations has been recommended in the literature. 8 It is stated that CT is preferred because it can transfer information in three dimensions, and distortions and superpositions are less common than in conventional radiography. 8,9 Although there are articles in the literature using cone-beam CT for NPC morphology 10,11 , and cone beam CT has a relatively lower radiation dose comparing with medical CT, CT images were preferred in this study because the contrast resolution of CT was higher than that of cone-beam CT. 12 Anatomical variations in the NPC; the form, length, location, and incisive foramen (IF) diameter; the number of openings in the nasal fossa; and other morphological changes have been evaluated in the literature. 11,13 However, there are few articles evaluating the relationship between dentition and NPC morphology in the literature. 4 Therefore, the aim of this study was to evaluate the changes in NPC morphology according to dentition status in the maxillary anterior region by CT. The null hypothesis stated that there were no differences between NPC morphology and dentition status.

Methods
The Local Ethics Committee of Hatay Mustafa Kemal University (Decision no: 20, Date: 31/10/2019) approved this retrospective study, and the study protocol was conducted following the principles of the Declaration of Helsinki. In this study, CT images of patients who applied to the Department of Dentomaxillofacial Radiology of our faculty for various reasons, such as temporomandibular joint disorders, maxillary sinus pathology, etc., between 2017-2019 were investigated. Poor quality images or artificial problems related to CT, patients who had undergone any operation or trauma to the maxillary anterior region, patients with any pathology affecting the maxilla anterior region, and patients with cleft palate in this region were excluded from the study. In total, 100 CT images taken with a 64-row MDCT scanner (Toshiba Aquilion, Toshiba Medical Systems, Otawara, Japan) in accordance with the standard maxillofacial radiography format for each patient were analyzed retrospectively. Computed tomography images were divided into two groups by dental status: an EG of 50 patients (21 females, 29 males) who have edentulous premaxilla and a CG of 50 patients (23 females, 27 males) who have all incisor teeth in the premaxillary region. After recording the age, sex, and dentition status of the patients, based on the study of Bahsi et al. 14 , the NPC diameter, NPC length, IF diameter, and angle between the NPC and palatine bone were measured in sagittal sections (Figure 1), and the number of NPCs was determined in axial sections ( Figure 2). All measurements were performed using Image J (1.4 v, National Institutes of Health, Bethesda, MD). Image evaluation and measurements were performed by two dentomaxillofacial radiologists, one with six years and one with five years of clinical experience, and calibrated for reference point selection. To assess inter-observer compliance, 20% of all measurements were repeated after two weeks.

Statistical analysis
Statistical analyses were evaluated using the SPSS 21.0 software (SPSS Inc., Chicago, IL, USA). The conformity of the parameters to a normal distribution was performed using the Kolmogorov-Smirnov test. Comparisons were made with the Student's t-test for normal distribution variables and the Mann-Whitney U test for non-normally distributed variables. The relationship between variables was analyzed by correlation analysis. P values <0.05 were considered to indicate statistical significance. Intraclass correlations (ICC) were calculated for inter-observer compliance.

Results
The inter-observer ICC value was 0.891 (95% CI: 0.743-0.942). The mean age in the EG and CG were 67±10.54 years (range 32-84 years) and 38±15.66 years (range 16-67 years), respectively. There was no significant difference between angle of NPC and two dentition status (p=0.151). The NPC diameter was significantly higher in the EG (2.19 mm) than the CG (1.62 mm) (p=0.002), and the IF diameter was significantly higher in the EG (2.69 mm) than the CG (2.31 mm) (p=0.041). The distribution of EG and CG according to angle of NPC, NPC diameter, and IF diameter is shown in Table 1. In the CG, one NPC was found in 41 CTs (82%), two NPCs were noted in six cases (12%), and three NPCs were noted in another three cases (17%). In the EG, one NPC was found in 35 CTs (70%), two in 10 CTs (20%), and three in five CTs (10%). There was no statistically significant difference in the number of NPCs between the groups. The NPC length was significantly longer in the CG (11.04 mm) than the EG (8.02 mm) (p=0.0001). A comparison between two dentition status and NPC length is shown in Table 2. There was a statistically significant and negative correlation between age and NPC length (p<0.001). On the other hand, there was a statistically significant and positive correlation between age and NPC diameter (p=0.004). It was found that NPC length decreased with increasing age, whereas NPC diameter increased. There was no statistically significant correlation between angle of NPC (p=0.966), IF diameter (p=0.068), and NPC number (p=0.882) and age. In addition, no statistically significant difference was found between sex and other parameters (p>0.05). A comparison between the other parameters and sex is shown in Table 3.

Discussion
The NPC is an anatomic landmark located at the palatine of the central maxillary incisors, connecting the nasal cavity to the palate and containing the NP (incisive) nerve, the terminal branch of the NP artery and fibrous connective tissue, fat and small salivary glands. 15,16 In the literature, it was stated that implant placement in this region is not possible in 4% of cases due to NPC size. 5 In such cases, techniques recommending implantation of the maxillary anterior by adjusting the bone graft to fit the foramen when retracting the soft tissue content have been proposed in the literature. 2 Another issue is, atrophic edentulous anterior maxilla rehabilitation using dental implant surgery, which becomes difficult as a result of shortening of NPC length after anterior region tooth extraction. 17 Liang et al. 18 in their study evaluated the anatomic variability and characteristics of the NPC using an anatomical, histological, and CT scan, and they stated that one NPC was detected in 53 cases (44%), two in 47 cases (39%), and three or four in 20 cases (17%). As another result, they reported that the mean NPC diameter was 3.5 mm and 3.6 mm, and the mean NPC length was 10.6 mm and 9.2 mm, respectively, in the dentate and edentulous groups. According to these findings, they identified a significant difference between age and NPC diameter but no significant difference between the NPC diameter and dentition. In addition, they found that the NPC was significantly longer in the dentate group and that males have significantly longer and wider canals. In present study, although there was no significant difference between genders in terms of NPC length, numerical results close to those of Liang et al. were obtained. 18 Bahsi et al. 14 reported a negative correlation between age and NPC angle. They thought that the angle of NPC decreased due to resorption of the palate as age progresses and a statistically significant difference was found between IF diameter and sex. Contrary to Bahsi et al. 14 , no significant difference was found between age and gender in terms of angle of NPC and IF diameter in our study. Mardinger et al. 4 stated that the diameter of the NPC widened with age, which could be confirmed in the present study. They reported that this was similar to hyperpneumatizing the maxillary sinus after tooth extraction in the maxillary posterior. They stated that the enlargements were mainly due to bone loss after tooth extraction. In another study, 10 examined the NPC morphometric and volumetric measurement in anterior edentulous and anterior dentate in cone beam CT images. They found that there was no relationship between two dentition status and NPC volume. Similar to present study, they stated that the NPC length decreased by bone resorption. The IF diameter is thought to be less than 6 mm in general, and it is accepted that it may be pathologic if it exceeds 10 mm. 19,20 In present study, the mean IF diameter was 2.5 mm (range 0.43-5.61 mm). Particular attention should be paid to the IF diameter during surgical procedures and implant operations in the maxilla anterior region. In current study, it was observed that the NPC angle did not differ with dentition status, but the NPC and IF diameters increased with tooth loss in the maxillary anterior region. The length of the NPC was shortened due to age and tooth loss in the maxillary anterior region. It was thought that there was a correlation between these parameters because of more frequent tooth loss in older patients. It was seen that gender did not affect NPC length, angle of NPC, NPC and IF diameters, NPC number. As a limitation of this study, it can be extended to reach morphological data in the population and to investigate average data in the general population by increasing the sample size. In addition, measurements of each IF diameter in patients with more than one IF can be included in the study. Another limitation is the selection of the same reference points in the measurements made by different observers. In order to solve this problem, both observers were calibrated for reference points before the study and measurements were repeated to test the reliability of the measurements. Also, in the measurements performed on standard maxillofacial radiographs taken from the same technique from each patient, measurements were made on the same screen and the same software to ensure standardization. In conclusion, especially in older patients, changes in NPC length and NPC diameter may occur with increasing tooth loss in the maxillary anterior region. These changes can be easily observed on three-dimensional radiographs. Therefore, it is recommended to evaluate the length and diameter of the NP canal, which changes with age, in threedimensional before surgical interventions such as dental implant, cyst operation etc. in the maxillary anterior region.