Dental 3D Cone Beam CT Imaging: Part II Insertion of Lingual Artery

With the proliferation of more 3D dental cone beam CT scanners, more and more patients arebeing prescribed to have dental CT scans taken for a variety of reasons. At the present time, many scans are taken within the treating dentist’s office where the clinician owns his/her own3Dscanner. However, most dentists do not own their own cone beam 3D CT scanner. In instanceswhen 3D images are needed, patients may be referred to a dental radiological lab that isspecifically designed as a freestanding office that performs CT scanning for the dental community. While a majority of dental patients currently referred for CT scans are for pre-surgical dental implant analyses to avoid injuring the mandibular nerve or violating the maxillary sinuses, other common reasons for 3D imaging include identifying the precise location of impacted teeth, studies for an assortment of pathologies, views of the condyles, and for orthodontic analyses (1).

Part I of this dental cone beam CT study analyzed the demographics of 500 consecutive patients referred to i-dontics, llc radilogical labs (2). This article, Part II, consists of observations regarding the frequency, width, and location of the insertion of the lingual artery into the mandible on 296 out of 500 consecutive patients referred to a dental radiological lab for 3D CT scans. This study identified the radiographic presence or absence of the lingual artery, where it inserted into the mandible, how many branches of the lingual artery were present and what was the diameter of the most superior branch of the lingual artery. A discussion of the clinical ramifications of identifying the width and location of the insertion of the lingual artery as they relate to dental implant insertion follows.

Methods and Materials

Dental 3D CT scans of the dental arches from five hundred (500) consecutive patients taken in nine (9) centers located in three (3) states were uploaded to the main processing center of a single dental radiological practice (i-dontics, llc., New York, N.Y. USA) which is limited to taking and processing 3D CT images for the dental community. Dental scans were taken on either i-CAT scanners (8 centers) or on a (1) NewTom 3G scanner. All studies were converted to SimPlant™ (Materialise, Glen Burnie, MD, USA). When not specified, the data was converted to SimPlant™ version 10. The following parameters were recorded for each patient: age, gender, reason for the dental 3D CT scan, which dental arch was to be studied, the format for the delivery of the data, and whether or not a radiographic guide was used. These results were published in Part I of the study.

In this study, mandibles were evaluated for the following: the radiographic presence or absence of the lingual artery, where it inserted into the mandible, how many branches of the lingual artery were present and what was the diameter of the most superior branch of the lingual artery. These anatomic structures are vital to recognize in order to reduce risk and optimize dental implant placement.

Results

3D cone beam dental CT scans from 500 consecutive patients requiring were included in this study. Of them, 296 cases were of the mandible. The following observations were noted:

# of lingual arteries:

1. 290 or 98% had observable insertions of the lingual artery into the mandible.

2. 119 or 40.2% had one lingual artery

3. 139 or 47% had 2 lingual arteries

4. 31 or 10.7% had 3 lingual arteries.

5. 1 or 0.34% had four lingual arteries

Figure 1. 40.2% had one lingual artery; 47% had 2 branches; 10.7% had 3 branches and there was 1 patient with 4 branches of the lingual artery.

Location of insertion of lingual artery relative to mandibular height:

A. Average length of lingual artery inserted into the alveolar bone = 9.6mm

B. 10 cases inserted in the crestal 1/3 = 3.44%

C. 262 cases inserted in middle 1/3 = 88.5%

D. 176 cases inserted in apical 1/3 = 59.45%

Location of insertion of lingual artery relative to the genial tubercle:

a. 271 cases of lingual artery inserted above tubercle = 91.55%

b. 170 cases of lingual artery inserted below tubercle = 57.43%

c. 37 cases of lingual artery inserted on tubercle = 12.76%

Diameter of lingual artery measured by “rule” calibrated in software:

i. 233 lingual arteries less than 1mm diameter = 80.3%

ii. 57 lingual arteries greater than 1mm in diameter = 19.7%

Examples

Increasingly dental 3D cone beam CT imaging is being utilized for dental implant placement, yet many clinicians continue to rely on 2D dental X-rays including periapical films and panoramic images. Patients may be referred for a dental CT scan when there is limited bone available above the inferior alveolar canal or for atrophic bone under the maxillary sinuses. Oftentimes, there is a sense of security when dental implants are being placed anterior to the mental foramina, especially when two or more implants are utilized to help stabilize a mandibular denture or fixed prosthesis. While the risks remain limited, a review of the literature minimally suggests that the location and diameter of the insertion of the lingual artery into the mandible is as important as knowing the width and density of the available bone. The following examples demonstrate the value of 3D imaging in preparation for placement of anterior mandibular dental endosseous implants.

Figure 2 is a panoramic view of an edentulous site in the mandibular anterior where dental implants were to be considered for insertion. In this image, there is no way to determine the width of the available bone or where the lingual artery inserts into the mandible without the benefit of 3D cone scan CT imaging.

Figure 2. Panoramic view does not reveal the width of the bone or the location of the insertion of the lingual artery into the mandible.

Figure 3 is a transaxial view through the #25 site. It reveals a narrow, spinous crest of bone that contains very little cancellous bone which is too narrow – at that point - to insert a dental implant. Midway down the lingual plate, the lingual artery can be observed inserting into the mandible. This artery is not very wide but may be of concern should a dental implant be inserted through it, piercing the lingual plate of bone. This information was not clinically evident on conventional 2D X-ray imaging.

Figure 3. Transaxial (cross-sectional) view demonstrates the value of 3D imaging by exposing the narrow width of the crestal bone and the location of where the lingual artery inserts into the mandible.

Figure 4 is an example (no implant is planned in this case) of a wide-diameter lingual artery that puts the patient in jeopardy should this artery be severed during implant surgery. This is an example of a critical anatomic structure that cannot be observed through conventional 2D X-ray imaging (dental periapical films or panoramic images) but is readily apparent in transaxial (cross-sectional) views from dental CT cone beam scanners.

Figure 4. An example of a wide lingual artery viewed in cross-section than cannot be seen in 2D images.

While atrophy compromises any edentulous area adjacent or proximal to key anatomic structures for dental implant placement, the mandibular anterior region is vulnerable to potential risk relative to the width and insertion of the lingual artery. Seemingly harmless perforations can lead to large hematomas or an arterial bleed that could discharge a considerable amount of blood into the lingual soft tissues. Sometimes, a delayed sublingual hematoma forms as the result of reflex or it my rebound by dilating after the effect of vasoconstrictors wears off from the local anesthetic. Oftentimes, the adjacent soft tissues exert enough pressure to tamponade itself to avert a bleeding crisis (5). If this does not happen, the surgeon needs an action plan to control sublingual hemorrhaging or dire consequences may result from continued bleeding. Employing the benefits of 3D dental cone beam scanners mitigates these risks to the patient.

Discussion

In this study, the presence, location, length and diameter of the insertion of the lingual artery into the mandible in 296 mandibles were evaluated by 3D cone beam CT dental scanners. Two hundred and ninety (290) or 98% of the patients had identifiable lingual arteries with the remainder having vessels inserting in the premolar areas. Eighty-seven percent (87.2%) had either one or two lingual arteries with the superior most vessel inserting through the middle of the lingual plate in 88.5% of the patients. Over 91% (91.55%) of the vessels inserted above the genial tubercle and 80.3% of the vessels were less than 1mm in diameter.

Schick et al (3) scanned 32 patients scheduled for mandibular dental implants to determine if CT scans could depict the presence, diameter, position, direction and frequency of vessels. In their study, lingual vascular canals were demonstrated in all patients. Most lingual canals were located in the midline and the mean diameter of the lingual canals was 0.7mm. Similar studies in 3 cadavers confirmed these findings, concluding that the occurrence, position and size of the lingual vessels could be depicted on CT scans.

As more patients seek dental implant placement in order to avoid or stabilize mandibular dentures, it is important for dentists to understand the limitations of 2D X-rays imaging especially when it comes to identifying the presence, location, and diameter of the lingual artery and its insertion into the mandible. Niamtu described a case of a near-fatal airway obstruction that resulted from sublingual bleeding following dental implant placement (4).

Isaacson (5) described the incidence and possible causes for a sublingual hematoma including dental implant insertion in the mandible likely caused by bleeding from perforation of the lingual cortex and violation of one of the branches of the sublingual or facial arteries. A review of the literature revealed that these occurrences could be life-threatening and that clinicians need to be prepared for the management of an acute airway obstruction that could result in intubation or tracheotomy (6-17)

Conclusion

Part II of this study evaluated parameters involving the lingual artery on dental 3D CT cone beam studies in 296 patients. Observations included the radiographic presence or absence of the lingual artery, where it inserted into the mandible, how many branches of the lingual artery were present and what was the diameter of the most superior branch of the lingual artery.

Dental implant placement in the mandibular anterior region is most often a benign procedure. However, dentists should bear in mind the potential risk of severing the lingual artery and piercing the lingual plate. The limitations of 2D X-rays compared to value of 3D cone beam CT images were discussed, including limiting risk and enhancing the clinical outcome for dental implant placement and subsequent restorations.

Acknowledgements: Support for this study was generously given by Nobel Biocare AB Gothenberg, Sweden (Grant 2006-492) and Imaging Sciences Inc., Hatfield, PA.

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