Dental 3D Cone Beam CT Imaging: Part V Dental Incidentalomas (Pre-surgical analysis for the insertion of dental implants)

Using 3D CT imaging for diagnostic purposes in medicine has uncovered incidental tumors that had no clinical symptoms in various tissues when there was no previous suspicion that they were present. These incidental tumors have been dubbed “incidentalomas,” and been discovered in adrenal glands, kidneys, pituitary glands, thyroid glands, liver, lungs, and the parathyroid glands (1-18). It has been estimated that approximately 7% of all patients over 60 may harbor a benign growth (often of the adrenal gland) and with the increase of “whole-body CT scanning” as part of health screening programs, the chance of finding incidentalomas is expected to increase to 37% (19). These chance findings will, in many cases, require further investigation.

A search of the dental literature did not reveal any studies that dealt with incidental findings on 3D CT studies taken on cone beam scanners. Nor has the term “incidentaloma” been applied to dentistry.

In this 3D CT cone beam study, 500 consecutive patients sent to one of nine i-dontics, llc radiologic labs were analyzed for a variety of normal and abnormal findings. Part I studied why patients were referred for CT studies including their age, gender, and format of the requested study. Part II studied the lingual artery and its insertion into the mandible. Part III studied the frequency and location of bifid canals. Part IV studied the length and location of the anterior canal extending anterior to the mental foramen. And in this study, Part V, the frequency and type of incidental findings on patients ostensibly sent to a dental CT radiological lab for 3D scans for dental implants were analyzed.

Methods and Materials

Data from five hundred (500) consecutive patients sent for 3D CT cone beam studies to one of 9 centers located in 3 states were evaluated. Scans were taken on either i-CAT (8 centers) or on a NewTom 3G scanner, and uploaded to a central data center. All studies were converted to SimPlant™ (Materialise, Glen Burnie, MD.). When not specified, the data was converted to SimPlant™ version 10.

In this part of the 3D study, the following parameters were recorded for each patient: if the maxillary sinuses were free of pathology or to what extent pathology was present. In addition, the following were noted: the presence of radiolucencies at the apices of teeth; were the teeth noted with radiolucencies vital or non-vital; impacted teeth and supernumeraries, retained roots, cysts, the presence of dental implants, and the radiopaque presence of bone graft material. Other incidental findings noted on the 3D Ct images included the notation of severe periodontal bone loss, fourth molars, condensing osteitis, surgical tacks, etc.
Results

Five hundred (500) patients were included in this study. Of the five hundred, two hundred and four (204) were referred exclusively for maxillary studies and an additional seventy-nine (79) (refer to Part I of this study), were referred for both maxillary and mandibular studies. A total of two hundred and eighty-three maxillas studied (Figure 1) for observations about the maxillary sinus. The CT scans for all 500 patients were analyzed for incidental findings.

Figure 1. Of the 500 patients in this study, 279 had maxillary scans evaluated.

Ninety-one (91) patients had both maxillary sinuses free of pathology while ninety (90) patients had pathology in both sinuses at the same time, as noted on the CT images. Pathology was defined as less than 1mm of a mucosal thickening measured at any part of the sinus visible in the CT scan. When pathology was present (1mm or greater of mucosal thickening), one maxillary sinus remained clear or free of pathology in 78 patients: 41 in the right and 37 in the left.

When present, the amount of mucosal thickening was measured in each sinus. The mucosal thickening in the right sinus averaged 5.3mm and it measured 5.6mm in the left sinus.

In addition, 26 patients had polyps in the right maxillary sinus and 22 patients had polyps in the left maxillary sinus. Six maxillary sinuses were totally blocked both right and left (Figure 2). Polyps were observed in some patients with mucous thickenings, so that the total number of observations is greater than the 283 maxillary sinuses studied.

Figure 2. 91 of the 283 maxillary scans had no pathology in both the right and left maxillary sinuses. 90 patients had pathology noted in both maxillary sinuses and 78 patients had pathology in only one of the maxillary sinuses. 48 patients had a polyp noted in either the right or left maxillary sinus, or both.

Reasons for dental 3D CT scans. The predominant reason for referral for dental CT scans was for pre-surgical analysis for the insertion of dental implants. Four hundred and fifty-one patients (451) were referred for implants; 20 for impacted teeth; 10 for pathology; 7 for endodontics; 4 for orthodontics; 1 for TMJ disorder; 7 unknown (Figure 3).

Figure 3. A = 451 Patients referred for CTs for implants; B = 20 patients for impacted teeth; C = 10 patients for pathology; D = 7 patients for endodontics; E = 4 patients for orthodontics; F = 1patient for TMJ; G = 7 patients unknown reason for referral for CT.

Incidental findings. While 451 patients (out of 500) were referred for a 3D dental CT scan for the express purpose of pre-surgical planning for implant insertion, many incidental findings were noted. The most common incidental findings (Figure 4) were periapical radiolucencies (229), socket preservation bone grafts (46), impacted teeth (27), retained root tips (24), sinus grafts (12), cysts (8), and supernumerary teeth (2). In addition, 70 dental implants were previously inserted in these patients. Other observations (142) included cementomas, surgical screws and tacks, assorted opacities within the body of either arch, 4th molars, blunted apices (due to orthodontics), blocked ethmoid sinus, condensing osteitis, and advanced periodontal disease nearly to the apices of many teeth.

Figure 4 The most common incidental findings were: 229 periapical radiolucencies; 46 socket preservation bone grafts; 27 impacted teeth; 24 retained root tips; 12 sinus grafts; 8 cysts; 2 supernumerary teeth.

Discussion

In the medical literature, the term “incidentaloma” refers to the discovery of a previously unsuspected tumor when taking a CT scan for another purpose. This term has not entered the dental literature. It is suggested that a dental “incidentaloma” be defined as the discovery of any unsuspected pathology, anomaly, dental structure (such as a retained root tip, impacted tooth, or supernumerary), or deviation from normal anatomy on a CT scan. The implications of these findings challenge the dentist and dental surgeon to be familiar with both normal and abnormal structures as they present on 3D cone scan imaging, which can appear different and unfamiliar compared to traditional 2D X-ray images such as periapical dental films or panoramic X-rays. Furthermore, it is incumbent for the dentist to interpret the entire field of view of each CT scan, and not just the area of concern, such as a dental implant site or a recalcitrant endodontic lesion or where the IAN is relative to an impacted third molar.

The most frequent incidental finding in this study was periapical radiolucencies. Many authors have acknowledged that 3D cone beam CT scans are extremely accurate and can be relied on for making a diagnosis of periapical pathology (20-23). For purposes of this study, periapical pathology was defined as a lesion expanding larger than 1mm from the apex. This was chosen to remove doubt that a pseudoperiapical lesion was not a thickened PDL due to trauma from occlusion. There was no attempt to obtain the previous history of teeth with root canal therapy to compare the size of the present lesion with past X-rays. No determination was made if a periapical lesion noted in this study was old, non-expanding, or a healing granuloma.

This 3D CT study noted trends in therapy. For instance, 46 extraction sockets were treated with graft material and the dental surgeon was interested in a 3D analysis of the healing lesion. Likewise, patients who had previously had maxillary sinus grafts (12) received 3D CT scans to determine the success of these surgeries.

Twenty-seven (27) teeth other than the ones patients who were originally referred for CT scans, were impacted, and two supernumeraries were noted. These “incidental” findings were sent in a report to each dentist for their review, final approval, and action when they deemed it necessary.

It is apparent that with the advent of dental cone beam scanners, more dentists will take advantage of 3D technology for better surgical planning, improved diagnostic preparation for orthodontic patients, all of which contribute to lower risk and more successful outcomes for the patients. While dentists embrace 3D technology, they need to become familiar with normal and abnormal landmarks. In addition, they need to be prepared to identify incidental findings and inform their patients as to the existence of these findings and their clinical relevance.

Conclusion

This study noted many incidental findings on 3D dental CT scans and suggests that these findings be described as “incidentalomas.” These unexpected findings include sinus pathology, cysts, impacted teeth, supernumeraries, periapical radiolucencies, and more. It is suggested that dentists become more familiar with normal and abnormal landmarks in the increased field of view of CT studies, especially when these 3D images are taking in preparation for dental implant treatment planning.
Acknowledgements: Support for this study was generously given by Nobel Biocare AB Gothenberg, Sweden (Grant 2006-492) and Imaging Sciences Inc., Hatfield, PA.

References

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11. Gould MK, Fletcher J, Iannettoni MD, et al. Evaluation of Patients With Pulmonary Nodules: When Is It Lung Cancer?: ACCP Evidence-Based Clinical Practice Guidelines (2nd Edition). Chest 132 (3_suppl): 108S–130S, 2007

12. Mirilas P, Skandalakis JE. Benign anatomical mistakes: incidentaloma. The American surgeon 68 (11): 1026–8, 2002

13. Yanagi Y, Asaumi J, Maki Y, Murakami J, Hisatomi M, Matsuzaki H, Konouchi H, Honda Y, Kishi K. Incidentally found and unexpected tumors discovered by MRI examination for temporomandibular joint arthrosis. European Journal of Radiology, Volume 47, Number 1, July 2003 , pp. 6-9(4)

14. Inagaki K, Otsuka F, Miyoshi T, Watanabe N, Suzuki J, Ogura T, Makino H. Reversible pituitary dysfunction in a patient with Cushing’s syndrome discovered as adrenal incidentaloma. Endocr J. 51(2):201-6., 2004.

15. Moretti, A, Bernini G, Argenio G, Salvetti A. Primary hyperaldosteronism in normokaliemic patients with adrenal incidentalomas. Am J Hypertens 14, 254A–254A: 672: 2001

16. Miyoshi T, Otsuka F, Suzuki J, Inagaki K, Kano Y, Ogura T, Kiura K, Saika T, Makino H. Abrupt enlargement of adrenal incidentaloma: a case of isolated adrenal metastasis. Endocr J. 54 (5):829, 2007

17. El Fakih RO, Encel ML, Kumar, NG Lung Incidentaloma November 1, 2008 Consultant. Vol. 48 No.

18. Howlett DC, Speirs A. The Thyroid Incidentaloma—Ignore or Investigate? J Ultrasound Med 26:1367-1371, 2007

19. Furtado CD, Aguirre DA, Sirlin CB, et al. Whole-body CT screening: spectrum of findings and recommendations in 1192 patients. Radiology 237 (2): 385–94, 2005

20. Simon , R . Enciso , J . Malfaz , R . Roges , M . Bailey-Perry , A . Patel. Differential Diagnosis of Large Periapical Lesions Using Cone-Beam Computed Tomography Measurements and Biopsy . ?Journal of Endodontics, 32:833 – 837, 2006

21. Nakata K, Naitoh M, Izumi M, Inamoto K , Ariji E , Nakamura H. Effectiveness of Dental Computed Tomography in Diagnostic Imaging of Periradicular Lesion of Each Root of a Multirooted Tooth: A Case Report . ?Journal of Endodontics, 32:583 – 587,? 2006

22. Lofthag-Hansen , S . Huumonen , K . Gröndahl , H . Gröndahl. Limited cone-beam CT and intraoral radiography for the diagnosis of periapical pathology . ?Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontology , 103:14 -119?, 2005

23. Cotton , T . Geisler , D . Holden , S . Schwartz , W . Schindler. Endodontic Applications of Cone-Beam Volumetric Tomography . ?Journal of Endodontics, 3:1121-1132, 2007

Dental 3D Cone Beam CT Imaging: Part IV Anterior Extension of IAN from Mental Foramen (Pre-surgical analysis for the insertion of dental implants)

Dental 3D CT cone beam imaging has many purposes including accurate dental implant placement and the identification of key anatomic structures. While there is an extensive literature analyzing the many aspects of the anterior loop extending from the mental foramen which compare the frequency and accuracy of this landmark from radiographs, cadaver dissection, and CT imaging (1-5), no study has measured the anterior extension of the inferior alveolar nerve (IAN) relative to distance from the edentulous crest, apices of teeth, and more. In Greenstein and Tarnow’s exhaustive literature review of the anatomy and clinical ramifications of the mental foramen, they conclude that since there is little correlation between viewing the anterior loop on radiographic and its actual clinical location, they recommend “leaving a 2mm zone of safety between an implant and the coronal aspect of the nerve” (6). In their literature review, it is suggested to use CT scans to help identify the anterior loop. They recommend that particular attention to variations in the anatomy in the area of the mental foramen be considered in addition to both functional and esthetic demands in order to avoid complications to the neurovasculature.

This study, using dental cone beam 3D CT scanners, evaluated various normal and abnormal landmarks noted in 500 consecutive patients referred to dental CT radiological labs for a variety of reasons, but most of which were for the insertion of dental implants. Part I of this study analyzed the demographics and reasons for the patients being referred for CT scans; Part II studied anatomic considerations of the insertion of the lingual artery into the mandible; Part III analyzed the frequency and location of bifid canals. In this study, Part IV, the anterior extension of the inferior alveolar nerve is studied on 3D CT images, and its clinical ramifications are discussed.

Methods

Data from five hundred (500) consecutive patients sent to i-dontics center from 9 centers located in 3 states for 3D dental CT studies, were evaluated. Scans were taken on either i-CAT (8 centers) or NewTom 3G scanners and uploaded to a central data center. All studies were converted to SimPlant™ (Materialise, Glen Burnie, MD). When not specified, the data was converted to SimPlant™ version 10.

Two hundred and Ninety-six (296) mandibles were studied on 3D CT studies using the measuring tool on the SimPlant Master™ Program. The following were measured: the length of the anterior extension of the IAN from the most mesial aspect of the mental foramen as identified in a 1mm slice; the distance of the anterior extension from the edentulous alveolar crest; the distance of the anterior extension from the apices of teeth; how many anterior extensions of the IAN were connected from right to left at the midline; and how many mental foramina were located on the alveolar crest.

Results

Almost 97% of the 296 mandibles analyzed in this study had at least one measurable extension of the IAN anterior to the most mesial aspect of the mental foramen (Figure 1), as noted on cone beam dental CT studies.


Figure 1. Nearly 97% of all mandibles had an anterior extension; nine patients did not have a measureable anterior extension of the IAN as seen on a 3D cone beam study.

Fourteen patients (4.73%) did not have an extension on the right side; eleven patients (3.72%) did not have an extension on the left side.

The average length of the anterior extension extending from the mesial rim of the mental foramen is 12.0 mm on the right and 11.8 mm on the left (Figure 2).


Figure 2. The average length of the anterior extension from the mental foramen bilaterally is nearly 12.0 mm.

The distance from the superior most portion of the anterior extension of the IAN to the edentulous crest was measured on images from a 3D dental cone beam scanner. In most instances, the bone loss was level and the radiographic extension was parallel to the crest enabling a single measurement either on the right or left side, or both. The average depth of the extension under an edentulous right crest was 10.5mm and 11.0mm under the left side (Figure 3-3A).


Figure 3. Average measurement to edentulous alveolar crest was 10.5mm on right anterior mandible. (Stereolithographic model courtesy of BioMedical Modeling, Boston, MA).


Figure 3A. Average measurement to edentulous alveolar crest was 11.0mm on left anterior mandible. (Stereolithographic model courtesy of BioMedical Modeling, Boston, MA).

The distance from the anterior extension of the canal to the apex of a tooth measured from 3D CT images when the dentition was present was measured from the most anterior extent of the canal vertically to the apex of the adjacent tooth. The preponderance of teeth measured in this situation were situated under the apices of the lateral incisors. In all instances, the measurement was vertical from the tooth apex to the top of the extended canal. Both right and left measurements, seen on 3D CT images, were identical: 17.0mm from the anterior extent of the canal to the nearest root apex.

A continuous loop, defined as an extension of the canal that emanates from both the right and left mental foramina and is seen to connect in the midline was viewed on 77 patients (26.01%). In Figure 4, the anterior extensions of the canal can be seen in different coronal (panoramic) slices of the same individual.


Figure 4. Coronal slices in the same patient demonstrate examples of a continuous canal as observed and noted in this study.

Figures 5 and 5A demonstrate a continuous anterior extension that joins in the midline. Various branches emanate from the canal displaying that may be viewed in CT cone beam images but not 2D dental X-rays.


Figure 5. Example of a continuous anterior extension of the canal with multiple branches extending from the main trunk.


Figure 5A. Some of the many branches extending from the main canal and the anterior extension are highlighted.

Eight (8) edentulous patients (2.70%) had the mental foramina exit on top of the alveolar crest.

Discussion

The anterior loop of the mental nerve is commonly described as that part of the neurovascular bundle that transverses anterior and inferior to the mental foramen only to loop back to exit the mental foramen (8-11). While it is often difficult to follow its extend on 2D dental X-rays, it is easier to view these anterior loops on 3D CT images.

When mandibles were dissected, the anterior loop was detected in 60% of 37 cadaver mandibles (12). The length of the loop in this 3D CT study (12) ranged from 0.5 to 5mm. In another study, Neiva et al (13) probed the anterior loop in 22 cadavers, noting that it was present in 88% of the patients and that its mean length was 4.13mm ranging from 1.0 – 11.0mm.

Studies have found CT scans more accurate than traditional 2D dental imaging (14-18) and they should be considered for locating inferior alveolar canals or mental foramina not easily viewed on traditional 2D dental images (periapical films or panoramic images) when considering implant placement, removal of impacted teeth, or treating pathologic lesions.

This 3D Ct cone beam study confirmed, along with other studies, that the alveolar ridge resorbs approximately 6.0-6.5mm when teeth are extracted, which is the average distance noted between the ridge to the anterior extension when compared to root apices to the anterior extension of the canal (1-2).

Using CT scans, Rothman found that the length of the anterior loop could be as long as 10.0mm (19) compared to this study, where it was found the average length for the anterior continuation of the nerve 11.8mm on the left side and 12.0 mm on the right. What is apparent in this study is that the average length of the anterior extension of the canal is greater than in other reported studies. It is unclear if this finding is a function of interpretation or is a result of the accuracy of dental cone beam scanners. What is clear is that these radiographic canals exist, but their clinical importance is a matter of speculation and requires further investigation.

For example, are these radiographic canals filled with nerve and vascular tissues or are they empty? Do they innervate gingival tissues? The answers to these questions are clinically relevant for a host of reasons. When these anterior extensions of the canal are identified on 3D CT images, should they be avoided during dental implant placement? Should increased bleeding be anticipated? Should the patient be informed that there is a chance there will be an altered sensation to the gingiva and adjacent tissues if these canals are penetrated during dental implant surgery? Further investigation will help determine the answers to these questions.

Conclusions

In this 3D dental cone beam CT study, 296 mandibles were studied on dental cone beam scanners. The anterior extension of the IAN was measured relative to length and distance from edentulous ridges or apices of teeth. The clinical ramifications of this anatomic entity were discussed, including the value of 3D imaging when inserting dental implants.

Acknowledgements

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


References

1. Gershenson A, Nathan H, Luchansky E. Mental foramen and mental nerve: changes with age. Acta Anat (Basel) 126:21-28, 1986.

2. Ulm CW, Solar P, Biahout R, Marejka M, Watzek G, Gruber H. Location of the mandibular canal within the atrophic mandible. Br J Oral Maxillofac Surg 31:370-375, 1993.

3. Dharmar S. Locating the mandibular canal in panoramic radiographs. Int J Oral Maxillofac Implants 12:113-117, 1997.

4. Kieser J, Kuzmanovic D, Payne A, Dennison J, Herbison P. Patterns of emergence of the human mental nerve. Arch Oral Biol 47:743=747, 2002.

5. Oguz O, Bozkir MG. Evaluation of location of mandibular and mental foramina in dry, young, adult human male, dentulous mandibles. West Indian Med J 1:14-16, 2002.

6. Greenstein G, Tarnow D. The Mental Foramen and Nerve: Clinical and Anatomical Factors Related to Dental Implant Placement: A Literature Review. J

7. Mraiwa N, Jacobs R, van Steenberghe D, Quirynen M. Clinical Assessment and Surgical Implications of Anatomic Challenges in the Anterior Mandible Clinical Implant Dentistry and Related Research 5:219-225, 2006

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10. Bavitz JB, Harn SD, Hansen CA, Lang M. An anatomical study of mental neurovascular bundle-implant relationships. In J Oral Maxillofac Implants 8:563-567, 1993.

11. Jalbout Z, Tabourian G. Glossary of Implant Dentistry. Upper Montclair, NJ International Congress of Oral Implantologists 16, 2004

12. Solar P, Ulm C, Frey G, Matejka M. A classification of the intraosseous paths of the mental nerve. Int J Oral Maxillofac Implants. 9:339-344, 1994.

13. Neiva RF, Gapski R. Wang HL. Morphometric analysis of implant-related anatomy in Caucasian skulls. J Periodontol 75:1061-1067, 2004.

14. Polland KE, Munro S, Reford G, et al. The mandibular canal of the edentulous jaw. Clin Anat. 14:445-452, 2001.

15. Sonick M, Abrahams J, Faiella RA. A comparison of the accuracy of periapical panoramic, and computerized tomographic radiographs in locating the mandibular canal. Int J Oral Maxillofac Implants 9:455-460, 1994.

16. Lindh C, Petersson A. Radiologic examination for location of the mandibular canal: A comparison between panoramic radiography and conventional tomography. Int J Oral maxillofac Implants 4:249-253 1989.

17. Bou Serhal C, Jacobs R, Flygare L, Quirynen M, van Steenberghe D. Perioperative validation of localization of the mental foramen Dentomaxillofac radiol 31:39-43, 2002.

18. Klinge B, Petersson A, Maly P. Location of the mandibular canal: Comparison of macroscopic findings, conventional radiography, and computed tomography. In J Oral Maxillofac Implants 4:327-332, 1989.

19. Rothman SLG. Dental Applications of Computerized Tomography. Chicago: Quintessence 42-24, 1998.

Dental 3D Cone Beam CT Imaging: Part III

Dental cone beam 3D CT scans enable dentists to view anatomic structures not easily seen on 2D dental x-rays, including bifid mandibular canals, which is a common variation of the mandibular canal. The mandibular canal may split along different positions of the mandibular nerve; one branch may be smaller than the other (1-2). Langlais et al reported a 0.95% prevalence of bifid mandibular canals (3) while Sanchis (4) reported an incidence of bifid nerves as 0.4%, finding 7 out of 2012 mandibles that were studied. Many authors have investigated the incidence of bifid canals using panoramic or CT 3D images or both, and have concluded that while uncommon, they need to be identified when surgical procedures, such as removal of impacted third molars, insertion of dental implants in NYC, and osteotomies, are to be performed (5 - 9).

Once multiple (bifid) canals are identified, the local anesthetic injection technique, prosthetic design, and surgical procedures can need to be modified to prevent pain and discomfort during treatment procedures (10) in order to insure better outcomes.

The purpose of this study was to identify the incidence of bifid and/or multiple branches emanating from the inferior alveolar canal in 500 consecutive patients needing dental implants in NYC using cone beam 3D CT imaging .

Methods and Materials

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.), which is limited to taking and processing 3D CT images for the dental community. Scans were taken on either i-CAT scanners (8 centers) or on a (1) NewTom 3G scanner. All studies pertaining to gum disease in New York City were converted to SimPlant™ (Materialise, Glen Burnie, MD). When not specified, the data was converted to SimPlant™ version 10.

In Part I of the cone beam 3D CT study, the following parameters were recorded for each patient: age, gender, reason for the 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. Parameters relative to the prevalence, location, and diameter of the lingual artery were measured and reported in Part II. The value and relevance of 3D imaging was also discussed in this paper.

In this study, Part III, the incidence of bifid nerves of the inferior alveolar canal were recorded by viewing images from a 3D dental cone beam CT scan. The position of the second canal was noted and listed as posterior to the teeth, within the body of the mandible but posterior to the mental foramen, coincident with the mental foramen, or anterior to the mental foramen. Multiple branches (more than two) were identified and recorded.

All CT studies were made into 1.0 mm slides and viewed both in the coronal and transaxial planes. To be counted as a bifid canal, each offshoot had to be continuous with the main inferior alveolar canal in each slice. For consistency, all CT studies were examined for bifid or multiple branches that were offshoots of the inferior alveolar canal by one examiner. A proper CT investigation is essential for perfect diagnosis of gum disease in NYC.

Results

Two hundred and ninety-six (296) mandibles were included in this 3D CT dental cone beam study. Of these, 186 patients or nearly sixty-three percent (62.84%) did not demonstrate evidence of a bifid canal. In contrast, 110 patients or more than thirty-seven percent (37.16%) had one or more bifid canals.


Figure 1. Nearly 63% of the mandibles studied did not have evidence of a bifid canal. However, 37,16% of the patients had one or more bifid canals.

Of the 110 patients demonstrating bifid canals, 56 or 50.9% had one bifid canal. Two bifid canals, as noted on CT scans, were demonstrated in 37 or 33.6% of the mandibles and 17 or 15.45% had three or more canals.


Figure 2. Of the mandibles demonstrating a bifid canal, more than half (50.9%) had one canal, while 33.6% had two canals and 15.45% had three or more canals.

Fifty-five (55.45%) of bifid canals were unilateral. Two thirds (67%) of the unilateral bifid canals were on the right side of the mandible; one third (33%) of the unilateral bifid canals were on the left side of the mandible. Nearly 46% (45.55) of the bifid canals were bilateral. These findings determined by viewing 3D CT images.


Figure 3. Fifty-five percent of the bifid canals were unilateral while nearly 46% were identified bilaterally.

In addition to identifying if a bifid canal was present, if it was in only the right or left side of the mandible or if they were bilateral, the location of each bifid canal was noted in the following manner: did it end at the mental foramen, posterior to mental foramen, or continue anterior to the mental foramen. Nine (9) bifid canals (8.18%) ended at the mental foramen, 94 or 85.45% ended posterior to the mental foramen and 7 or 6.36% continued anterior to the mental foramen.


Figure 4. The majority of the bifid canals (85%) ended posterior to the mental foramen, with 8 percent ending at the mental foramen and 6% extending beyond (anterior) the mental foramen.

Discussion

The relative incidence of bifid canals has been reported as less than 1% (3,4) of all gum disease in NYC, while it has been shown that the split of the mandibular nerve may be of unequal sizes (1,2). Regardless of the frequency of identifying bifid canals, various authors have identified the surgical risks and complications that may be experienced when they are encountered, including an inability to obtain profound anesthesia using a local anesthetic (5-9), injury from NYC dental implants, removing impacted wisdom eeth, and more.

In order to achieve standardization and consistency, the authors agreed as to what constitutes a bifid canal as identified on the 3D image: any branch that appeared as a continuous radiolucent canal extending from the inferior alveolar nerve. All 3D CT slices were 1mm in thickness and all bifid canals were viewed and appeared to emanate from the IAN in three planes: axial, coronal, and sagittal. Once the parameters were defined, one researcher examined and identified all of the bifid canals noted in this study, which were then verified by a second author.

Based on these parameters, the incidence of identifying bifid canals in this study was greater than in previously reported studies: 37%. The concept of bi- means “two,” and bifid means forked or cleft. While the purpose of this CT cone beam study in NYC gum disease was to identify the incidence of bifid canals, more than two canals of the IAN were identified in 17 patients or 15.45% of the cases. In most instances, 3 branches were identified; in one case, 8 branches were identified.

A relative few bifid canals ended at the mental foramen or extended anterior to it: 16 patients in total, or 14.54%. More than 85% of the bifid nerves identified in this study, as determined by 3D CT cone beam images, ended posterior to the mental foramen.

The significance of the findings in this study matters relative to the size and location of the bifid canals, and what clinical procedure is anticipated being performed. When it comes to operative dentistry, it has been postulated that bifid nerves may explain why anesthesia is not as profound as it should be when employing a local anesthetic. When encountered, infiltration of the local anesthetic to anesthetize these extra branches of the IAN may help achieve greater local anesthesia.

When planning New York City dental implants surgery, it is helpful to identify if bifid canals exist in the surgical site. Encountering these extra canals may not only contribute to unwanted local paresthesias of the gingival that these aberrant nerve branches may serve, but may explain unusual bleeding that emanates from the alveolar bone (10-11) during periodontal osseous or dental implant surgeries.

Figures 5 and 6 illustrate an example of multiple canals as they were identified in this study of gum disease in New York. While the widest branch, which is anterior to tooth #18, is evident on the panoramic slice, smaller canals are highlighted in Figure 6. Note the arrow in Figure 5 that highlights another bifid canal. Careful inspection will note additional canals emanating from the right IAN.


Figure 5. Arrow indicates a small bifid canal that starts and ends distal to tooth #31. A larger canal can be seen anterior to tooth #18.


Figure 6. The canal is highlighted in red, illustrating 3 bifid canals.

Mention must be made of the value of 3D images identifying normal and abnormal structures when compared to 2D images. Figure 7 is a panoramic image (formatted in a 15 mm trough) taken on a patient that was referred to the CT lab after an implant was inserted that resulted in paresthesia in the patient.


Figure 7. Patient presented after an implanted was inserted in the #30 site resulting in paresthesia.

Figure 8 highlights a bifid branch of the IAN that was traumatized by the implant. This aberrant branch was not evident in the panoramic view due to the dense cortical bone. Traditional 2D imaging - both panoramic or periapical film – is limited in revealing key anatomic structures that are obscured by thick buccal and/or lingual bone. In this example, using 3D imaging prior to implant insertion would have identified the bifid (aberrant) branch and altered the surgical site.


Figure 8. A bifid nerve rises from the IAN and was traumatized by the implant insertion.
It is suggested that more studies be undertaken to identify bifid canals and their clinical significance.

Conclusion

Utilizing 3D cone beam CT scanning images, this study identified bifid canals in 110 out of 296 patients. The incidence (37%) was greater than reported in other studies. The clinical implications of bifid canals were discussed, as well as an appreciation for the value of utilizing 3D CT cone beam scanners when possibly considering dental implants in New York City.

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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