An Anatomical Study of Incisive Canal and its Foramen

Introduction: Anatomically, the incisive canals start on the nasal fossa oor, close to the septum, and open at the incisive foramen of the maxillary palatine process. The nasopalatine nerve passes through the incisive foramen as well as the septal artery and the sphenopalatine vein. Also, there may be accessory canals. Typically, the incisive foramen has two incisive canals. This work aimed to analyze the morphology and morphometry of the foramen and incisive canals in the macerated cephalic skeletons. Material and methods: For this purpose, we selected 150 samples of adult individuals, with no distinctions of sex and ethnicity. We analyzed the frequency of incisive canals in the foramen was analyzed as well the area, diameter, and communications of incisive canals with the fossa and nasal cavity. Results: The cephalic analysis results showed that most incisive foramina have at least two canals that communicate the nasal cavity with the oral cavity. The right-side canal had an average of 1.975mm² in area and 1.281mm in diameter. Also, the left-side canal had an average of 1.468mm² in area and 1.182mm in diameter. The average area and total diameter of the incisive foramen were 8.148mm² and 3.101mm, respectively. Conclusion: Hence, understanding anatomy and its variations is essential for clinical applications, as it may alter surgical technique and prognosis. Besides, it can be said all incisive canals have communication with the nasal cavity.


Introduction
The incisive canals have been described beginning on the nasal fossa oor, close to the nasal septum, and openin the incisive foramen of the maxillary palatine process 1,2 . Moreover, there are two incisive canals in the incisive foramen and, additional canals may exist 3 .
Furthermore, anatomical study of the foramen and incisive canals is critical in the dental practice, as the nasopalatine nerve, the septal artery, and the sphenopalatine vein pass through incisive canals 3, 4 are responsible for innervation, blood supply, and drainage of the soft tissue of the hard palate 5 .
The anterior maxilla is considered esthetic, phonetic, and functionally important 7 ; however, it is the most common region exposed to trauma and tooth loss 6 . Surgeries in this site have been regarded as safe, although iatrogenic injury has been increasingly reported due to the growing surgical interventions in this 8,9 . Besides, in a hospital environment is common to use the procedure The LeFort I, which is one of the most commonly used techniques to correct midface deformities. In this case, the most important anatomical structures in this region must be well-known in order to prevent complications during and after surgery 7, 8, 9 . For example, the knowledge of critical anatomical structures as the incisive canals and the incisive foramen is vital during dental implant procedures 10,11,12 . In this way, the comprehension of these structures' anatomy, morphology, and morphometry is crucial to perform surgical procedures without harming the patients 13,14 . For this reason, this study aimed to analyze the morphology and morphometry of the incisive foramen and the incisive canals in macerated cephalic skeletons.

Materials And Methods
The present study was carried out at the Department of Biological Science of the Bauru School of Dentistry -University of São Paulo, Brazil.

Ethical statements
This study was approved by the Institutional Ethics Committee of the São Paulo University (n°1.713.069) and this work has followed the set of ethical principles from the Declaration of Helsinki in all methods that have been done. The informed consent was obtained from all subjects and/or their legal guardian(s).
Design of study 150 macerated cephalic skeletons of adult individuals, which belong to the Anatomy discipline of Bauru School of Dentistry -University of São Paulo, were selected without identifying sex and ethnicity. The following procedures were performed: 1. The frequency of incisive canals presented in the incisive foramen. In all the samples, frequency, area, and the incisive foramen's total diameter were analyzed and also, the area and diameter of each incisive canal ( Figure 1).
In the incisive foramina analysis, we determined the number of canals presented at each incisive foramen, with a minimum numerical variation of one ( Figure 2) to a maximum of six incisive canals Additionally, to the number of canals, the canal's name was established according to its location, which can be: anterior, posterior, right lateral, left lateral, right medial, and left medial ( Figure 5).

Statistical methods
Both measurements were assessed using descriptive statistics, using absolute frequency (N), relative frequency (%), mean and standard deviation with a probability of 5 percent being regarded as signi cant.

Area and diameter of the incisive foramina
Regarding the average area and diameter of incisive foramina, it is possible to state that the average total area of 150 incisive foramina analyzed was equal to 8.148mm². The average of the entire diameter of the foramina was equal to 3.101mm (Table 1). Table 1 The description of the incisive foramina averages of the area and total diameter.

Parameters
Average Standart deviation The total area of the foramen 8,148 4,616 The total diameter of the foramen 3,101 0,884

Communication of the incisive canals with the fossa and nasal cavity
In brief, in all of the incisive analyzed canals, communication between the nasal cavity and the oral cavity has occurred.
Therefore, from the results obtained, it is possible to state that the most incisive foramina have at least two canals, which communicate the nasal fossa, being the right lateral canal with an average of 1.975mm² in area and 1.281mm in diameter. Also, in the left lateral canal, with an average of 1.468mm² in area and 1.182mm in diameter, the average area and total diameter of incisive foramina were 8.148mm² and 3.101mm, respectively.

Discussion
This study aimed to analyze the morphology and morphometry of incisive foramen also incisive canal in macerated cephalic skeletons. Our results showed that most incisive foramina have at least two canals, which communicate with the nasal cavity and the oral cavity .
Because of its location, the incisive foramen could target the installation of osseointegrated implants to compose a sound protein structure and protect through a balance between distribution and distance 10, 11, 12 . Thus, prior knowledge of its anatomy and physiology is critical since the proximity of the incisive foramen with the anterior central elements affects the ability to place immediate implants on the ideal position 11 . On the other hand, the patient's age also hinders the ability to place immediate implants since the typical clinical pro le of individuals seeking this type of treatment, in most cases, are over 60 years. In which it is demonstrated that the thickness of the anterior maxillary bone is affected by aging 11 .
In implantology, the necessity for implant installations over the incisive canals and their foramen is common. Thus, it is necessary to have anatomical expertise, in agreement with other authors, not to cause damage and harm to the patient. For example, the structures that pass through the incisive foramen, such as the sphenopalatine vein, are responsible for the hard palate's irrigation and drainage 1, 2, 11, 12 , 13 .
In the literature, other authors have described the importance of anatomical variations for corrective surgeries in the craniomaxillofacial region 10,11 . Some surgical techniques used in clinical practice, such as the Le Fort I, require anatomical knowledge of the incisive canal and its foramen 6 , 7 .
To date, there are some morphological and morphometric studies of the incisive canals with also their foramen; however, using diagnostic imaging 3, 10, 11 . Considering the scarcity of studies on incisive canals and their foramen, performed on macerated skulls, the data of this study were compared with those from research using diagnostic imaging methods 12 .
In our study, we checked the frequency of the incisive canals and measured each canal's diameter with the Dino Lite® microscope, and performed the analysis of the images captured using the software DinoCapture 2.0. To check the incisive canal communication with the nasal cavity, we used stainless steel orthodontic wires in the macerated skulls to obtain a privileged view. It showed that the most macerated cephalic skeletons had two incisive canals, the right-lateral canal, and the left-lateral canal.
Thus, some works have described the incisive canal as a duct of the oral cavity, which divides into two canaliculi, and ends at the nasal cavity oor next to the nasal septum 5 . Other authors have classi ed the incisive canal based on symmetry, the number of canaliculi, and shape 10,12,13 .
A study carried out by Mraiwa et al. (2004) using the 2D, and 3D images showed that at the level of the nasal oor, commonly two, sometimes three or four ori ces, referring to the incisive canals could be seen.
In contrast, in some particular individuals, the incisive canal emerged as a single-cylinder with only one nasal opening 16 . This result agrees with our work since we observed accessory canals during the analysis of the macerated skulls. However, the numbers obtained were higher, reaching up to six openings.
As a result, most adult individuals have two incisive canals with insigni cant length differences between them, varying only in diameter and width according to gender 10,12,13 . In our study, the canals' average area and diameter were 1.975mm² and 1.281mm for the right-lateral canal. Furthermore, for the left-lateral canal, the average area and diameter were 1.468mm² and 1.182mm. To date, no other study has individually evaluated the diameter of accessory canals.
As a result, our work shows that the average area and total diameter of the incisive foramina is 8.148mm² and 3.101mm, respectively, similar to others described by other authors 3,4,14 . However, recent research carried out by Reinhard et al. (2015) showed that the average diameter of incisive foramen varies according to its trajectory. Thus, at the oral cavity opening, the diameter was 4.49mm and 3.43mm at the nasal oor level.

Conclusion
In conclusion, our study shows that it is possible to a rm that the anatomy of the incisive canals and their foramen are variable. Therefore, the knowledge and analysis of these structures are crucial for surgical procedures in the maxilla's anterior region.  The presence of a single canal.