The aim of this study was to verify the presence, spatial location, and calibre of the accessory canals (AC) of the canalis sinuosus by cone beam computed tomography, and their relationship to the anterior maxilla. This retrospective analysis included the scans of 1000 subjects. Parameters registered were sex, age, number of AC, presence or absence of AC with a diameter <1.0 mm, AC diameter (only for AC with a diameter >1.0 mm), and AC location in relation to the adjacent teeth. Males showed a statistically higher frequency of AC than females. The difference in age distribution was not statistically significant. Twenty percent of all AC presented a diameter of a least 1.0 mm. The end of the AC trajectory was most frequently located palatal to the anterior maxillary teeth. All relationships analyzed here were very weak (age vs. number of AC, age vs. AC diameter, number of AC vs. sex). Overall, the results of this study showed that AC of the canalis sinuosus are a common anatomical structure in the anterior maxilla, regardless of age and sex.
Several surgical procedures are performed in the anterior maxilla, such as endodontic surgery, periodontal surgery, surgical removal of impacted or supernumerary teeth, the placement of dental implants, cyst therapy, and orthognathic surgery. The neurovascular supply to this region is provided mainly by the infraorbital nerve. The infraorbital nerve is a branch of the maxillary nerve, and it supplies the skin and midface mucosa. At the point where it emerges on the face via the infraorbital foramen, the infraorbital nerve divides into three alveolar proximal branches and four distal branches. Some publications have drawn attention to radiographically visible ramifications that may carry neurovascular structures to the anterior maxilla. For example, the infraorbital canal issues a small branch on its lateral face close to its midpoint to allow passage of the anterior superior alveolar nerve, which is called the canalis sinuosus. Fig. 1 shows examples of the canalis sinuosus leaving the bilateral infraorbital canals (canals with a larger diameter), with some accessory canals (AC) at the end of their trajectory: two AC ending in the region of the anterior maxillary teeth and two AC ending in the nasal cavity floor.
There are some issues associated with neurovascular bundles in the anterior maxilla. First, the lesion of such structures can cause sensory dysfunction and the risk of haemorrhage. Second, it is hypothesized that contact with a local neurovascular bundle can lead to non-integration of a dental implant. Third, such anatomical structures may also be interpreted as other anatomical structures or lesions, resulting in diagnostic confusion and possibly leading to a mistaken or unnecessary procedure. Therefore, the preoperative identification of the course of nerves and vessels through radiographic evaluation is essential for safe surgical procedures.
The presence of accessory foramina and canals is often neglected in clinical procedures. Precise knowledge of the location of reference points in the oral and maxillofacial area provides important data for local anaesthesia and maxillofacial operations. The most certain way to avoid damage to these structures is to know their location. The aim of the present study was to verify the presence, spatial location, and calibre of AC of the canalis sinuosus by cone beam computed tomography (CBCT), and their relationship to the anterior maxilla.
Materials and methods
The present retrospective analysis included the scans of a total of 1000 subjects selected randomly from 1181 out of 3298 cases that fulfilled the inclusion criteria. The database of Slice Diagnóstico Volumétrico por Imagem, in Belo Horizonte, Brazil, was used.
Inclusion and exclusion criteria
The following inclusion criteria were applied: (1) CBCT examinations from patients who allowed the use of their scans; (2) CBCT examinations of the maxilla. The following exclusion criteria were applied: (1) the presence of technical artefacts that would hinder the evaluation of the necessary structures; (2) images that had a missing tooth, an implant, or grafted alveolar ridge; (3) the presence of a supernumerary or retained tooth in the anterior maxilla; (4) the presence of a pathological lesion in the anterior maxilla; (5) patients who had previously undergone a surgical procedure in the maxilla (e.g. orthognathic surgery); (6) CBCT scans that did not show satisfactory quality of acquisition (minimum voxel size of 0.20 mm, in a 40-s examination).
Hardware and software
The CBCT scans were performed with an i-CAT CBCT system (Imaging Sciences International, Hatfield, PA, USA). The scans were acquired using the i-CAT 3D imaging system (i-CAT Vision Software; Imaging Sciences International) and included the entire maxilla. The following CBCT scan parameters were used for all patients: a tube voltage of 120 kV, 5–7 mA, field of view of 8 cm, emission of X-rays over an interval of 40 s, a 0.20-mm voxel size, and an effective dose of 136 μSV. Measurements were obtained with the use of computer software (OnDemand3D) version 220.127.116.1147 (Cybermed Inc., Tustin, CA, USA).
The canalis sinuosus were identified on the CBCT scans according to their anatomical description in the literature. Bony canals present in the anterior maxilla and with a clear upward direction towards the canalis sinuosus were identified. The following parameters were registered: sex, age, number of AC, presence or absence of AC with a diameter of <1.0 mm, diameter of the AC (only for those AC with a diameter of ≥1.0 mm), location of the AC in relation to the adjacent teeth, spatial location in the anterior maxilla (palatal, transversal, buccal), and status of the dentition in the anterior maxilla. The diameter of each canal was measured at the median distance of its total length (from the point of origin at the canalis sinuosus to the end of its trajectory). Axial, coronal, sagittal, panoramic, and cross-sectional reconstructions were analyzed in every case. Diameters were determined by measuring the palatine opening of the additional canal on both coronal and cross-sectional images. Assessment of the location of the AC was performed twice by the same observer with an interval of at least 2 months between evaluations.
A descriptive statistical analysis of the results is presented. The Student’s t -test or Mann–Whitney test (when indicated, depending on the normality of data) and the χ 2 test were used to assess the differences between males and females. Spearman’s correlation was performed to determine the relationship between the number of AC and sex. Pearson’s correlation and linear regression were performed to verify the relationship between age and two other factors: the diameter of the AC and the number of AC. Cohen’s kappa was used to assess intra-observer agreement for categorical data. Statistical significance was set at the level of P < 0.05. All data were analyzed using IBM SPSS Statistics version 20.0 software (IBM Corp., Armonk, NY, USA).
This study was approved by the local ethics committee. The patients were contacted by telephone call, and a signed informed consent form was obtained from each patient approving the use of their scans. The patients were not identifiable in any way, and a decoding list linking patient names and numbers was used and stored by the principal investigator, which was destroyed after completion of the study.