Extended Abstract

Introduction
The infraorbital canal (IOC) is located in the floor of the orbit and terminates at the infraorbital foramen, which is situated below the infraorbital rim. The posterior part of the IOC is the infraorbital groove, which originates from the infraorbital fissure. The infraorbital nerve (ION) is the terminal and largest branch of the maxillary nerve. When the maxillary nerve enters the orbit through the maxillary fissure, it is referred to as the ION. In the floor of the orbit, the ION passes through the groove and IOC, and then descends from the superior wall of the maxillary sinus to the face through the infraorbital foramen (IOF). The ION innervates the upper cheek skin, mucous of the maxillary sinus, incisors, canines, and premolars of the maxilla, sometimes the mesiobuccal root of the first molar, and the adjacent gingiva, skin, and conjunctiva of the lower eyelid, a portion of the nose, and the skin and mucous of the upper lip. The ION block technique is used in regional anesthesia for oral and maxillofacial surgery, as well as in nasal surgery for both intraoperative and postoperative anesthesia. Additionally, the protrusion of the IOC into the maxillary sinus roof is considered a significant risk in fractures and various surgical procedures. Age and race can influence the morphometric measurements and position of the canal. Facial bones exhibit rapid growth from 3 to 4 years of age, and orbital maturation is complete by 16 years of age. Therefore, the mean distance from the IOF to the infraorbital rim remains constant after 20 years of age. There may also be a correlation between the types of canals and the anatomical variations around them (Haller’s cell, pneumatization of the concha, and thickening of the maxillary sinus mucosa). In maxillary sinus endoscopy, the probability of damaging the IOC is increased when the nerve is attached to the sinus roof by a septum. Cone beam computed tomography (CBCT) is an accepted method for radiographic evaluation of the paranasal sinuses and related structures, such as the IOC and IOF due to its low radiation dose, high bone resolution, and easy image processing. This study aimed to evaluate the position and dimensions of the IOC based on CBCT.
Methods
This descriptive-analytical study was conducted on CBCT images of 250 individuals (105 males and 145 females) with a mean age of 36.14±17.7 years who referred to a specialized oral and maxillofacial radiology clinic.
Subjects were categorized into four age groups, including 30 years or younger, 31-40 years, 41-50 years, and 51 years and older.
CBCT images were acquired using a Giano device (Newtom, Verona, Italy) with number needed to treat (NNT) software, at a slice thickness of 0.5 mm and an interval of 1 mm. The various pathways of the IOC from the sinus roof were classified into three types on parasagittal and coronal cross-sectional images: The IOC completely located within the maxillary sinus roof (type 1), located below the maxillary sinus roof (type 2), and suspended from the maxillary sinus roof within the septum or lamella of the infraorbital ethmoid cell (type 3).
The angle between the IOC and the infraorbital groove with the maxillary sinus roof, and the angle between the IOC and the infraorbital groove in sagittal section images were evaluated. The lengths of the IOC and the infraorbital groove in sagittal section images were assessed using Przygocka et al.’s method
To obtain the IOC reproducible position, images were aligned with specific landmarks (septum and nasal floor). The sagittal plane was adjusted so that the whole IOC was visible. The distance of the IOC from various anatomical points was measured. The distance from the canal to the midpoint of the root of the canine in all types of canals was measured in the coronal plane as follows: A vertical line was drawn from the apex to the crown of the canine tooth. Then, in the axial plane, the distance of this line to the center of the IOC was measured. The maximum vertical distance from the most distal part of the canal to the infraorbital rim was measured in the parasagittal section.
Results
In comparing the different types of IOC, Type 1 was found in 96 cases (38.4%) on the left side and 101 cases (40.4%) on the right side; Type 2 was found in 134 cases (53.6%) on the left side and 131 cases (52.4%) on the right side; and Type 3 was found in 20 cases (8%) on the left side and 18 cases (7.2%) on the right side. The distance from the IOC to the midpoint of the canine root was greater in males on both the right (P<0.056) and left (P<0.014) sides compared to females.
It was found that the length of the IOC and the angle between the canal and the infraorbital groove on the left side had a statistically significant correlation with the age groups. This correlation was significant between the age group less than 30 years (P<0.035) and 31-40 years (P<0.040), and with increasing age, the angle between the canal and the infraorbital groove, as well as the length of the canal, decreased.
When comparing the relationship between the position and types of the canal on the left and right sides, a statistically significant difference was found between the distance from the IOC to the infraorbital rim and the length of the IOC among the three types of canals (P<0.01). Comparisons between Type 1 and Type 2 canals, and between Type 2 and Type 3 canals, showed that the distance from the canal to the midpoint of the infraorbital rim and the length of the canal increased. No statistically significant correlation was found between the types of canals and gender.
Conclusion
Based on the results of this study, Type 2 (53%) was found to be the most frequent pathway of the IOC from the sinus roof, while Type 3 (7.6%) was the least frequent. Recognizing the morphology and types of IOC that can protrude from the sinus roof allows surgeons to have a clear and accurate understanding of the anatomy of this region and reduce the risks stemming from the damage to this nerve during facial surgeries.
Since the human skull and jaw vary based on different facial features, gender, genetic diversity, ethnicity, and geographic conditions, research has shown that these factors can affect the dimensions of the foramen and IOC. As a result, the position of the canal and foramen can vary in different races.
Ethical Statement
This study was approved by the Research Ethics Committees of Babol University of Medical Sciences (IR.MUBABOL.REC.1400.215).
Funding
This study has been extracted from a doctoral dissertation by Ms. Atena Sadat Jamali, a doctoral candidate in the field of Dentistry at the Faculty of Dentistry, Babol University of Medical Sciences.
Conflicts of Interest
No conflict of interest.

Key message: Type 2 was found to be the most common pathway of the IOC from the sinus roof. Although Type 3 was less prevalent, its high-risk nature necessitates surgeons to have a thorough understanding of the morphology and anatomical position of the IOC during surgeries in the sinus and orbital regions to minimize potential complications.