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.

References:

1. Mardini S, Gohel A. Exploring the Mandibular Canal in 3 Dimensions.
An Overview of Frequently Encountered Variations in Canal Anatomy. AADMRT Newsletter, Fall 2008.

2. Jacobs R, Mraiwa N, vanSteenberghe D, Gijbels F, Quirynen M. Appearance, location, course, and morphology of the mandibular incisive canal: an assessment on spiral CT scan. Dentomaxillofacial Radiology 31:322-327, 2002.

3. Langlais RP, Broadus R, Glass B. Bifid mandibular canals in panoramic radiographs. Journal of the American Dental Association 110:923-926, 1985.

4. ] Sanchis JM, Penarrocha M, Soler F. Bifid mandibular canal. J. Oral Maxillofac. Surg. 61: 422–424, 2003.

5. Rouas P, Nancy J, Bar D. Identification of double mandibular canals: literature review and three case reports with CT scans and cone beam CT. Dentomaxillofacial Radiology 36:34-38, 2007

6. Naitoh M, Hiraiwa Y, Aimiya H, Gotoh M, Ariji Y, Izumi M, Kurita K, Ariji E.
Bifid Mandibular Canal in Japanese. Clinical Science and Techniques Implant Dentistry. 16:24-32, 2007.

7. Claeys V, Wackens G. Bifid mandibular canal: literature review and case report. Dentomaxillofacial Radiology 34, 55-58, 2005.

8. Auluck A, Ahsan A, Pai KM, Shetty C. Anatomical variations in developing mandibular nerve canal: a report of three cases. Neuroanatomy; 4: 28–30, 2005.

9. Dario LJ. Implant placement above a bifurcated mandibular canal: A case report. Implant Dent 11: 258-261, 2002.

10. Auluck A, Ahsan A, Pai KM, Mupparapu M. Multiple mandibular nerve canals: Radiographic observations and clinical relevance. Report of 6 cases. Quintessence International. 38:781-787, 2007.

11. Winter AA. Bleeding from a Nutrient Canal: A Case Report. NY State Dent J 46:646, 1980.

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.

References

1.Valiathan A, Dhar S, Verma N: 3D CT imaging in Orthodontics: adding a new dimension to diagnosis and treatment planning. Trends Biomater. Artif. Organs 21:116-120, 2008

2.Winter AA, Yousefzadeh K, Pollack AS, Stein MI, Murphy FJ, Angelopoulos C. Dental Radiological Lab Usage and Findings: Part I Demographics (accepted for publication in JICAD 2009

3.Schick S, Zauza K, Watzek G. Lingual Vascular Canals of the Mandible: Evaluation with Dental CT. Radiology 220:186-189, 2001

4.Niamtu, J. Near-fatal airway obstruction after routine implant placement. Clinical notes. O Med, P Path, O Rad & End 92(6)597-600, 2001

5.Isaacson, T. Sublingual hematoma formation during immediate placement of mandibular endosseous implants. JADA 135:168-172, 2004.

6.Goldstein B. Acute dissecting hematoma: a complication of oral and maxillofacial surgery. J Oral Surg 39(1):40–3, 1981

7.Mordenfield A, Andersson L, Bergstrom B. Hemorrhage in the floor of mouth during implant placement in the edentulous mandible: a case report. Int J Oral Maxillofac Implants 12:558–61, 1997

8.ten Bruggenkate CM, Krekeler G, Kraaijenhagen HA, Foitzik C, Oosterbeek HS. Hemorrhage of the floor of the mouth resulting from lingual perforation during implant placement: a clinical report. Int J Oral Maxillofac Implants 8:329–34, 1993

9.Mason ME, Triplett RG, Alfonso WF. Life-threatening hemorrhage from placement of a dental implant. J Oral Maxillofac Surg 48: 201–4. 1990

10. Givol N, Chaushu G, Halamish-Shani T, Taicher S. Emergency tracheostomy following life-threatening hemorrhage in the floor of the mouth during immediate implant placement in the mandibular canine region. J Periodontol 71:1893–5, 2000

11.Burke R, Masch G. Lingual artery hemorrhage. Oral Surg Oral Med Oral Pathol 62:258–61, 1986

12.Krenkel C, Holzner K. Lingual bone perforation as causal factor in a threatening hemorrhage of the mouth floor due to a single tooth implant in the canine region. Quintessence 37:1003–8, 1986?

13.Laboda G. Life-threatening hemorrhage after placement of an endosseous implant: report of case. JADA 121:599–600, 1990?

14. Darriba MA, Mendonca-Caridad JJ. Profuse bleeding and life-threatening airway obstruction after placement of mandibular dental implants. J Oral Maxillofac Surg 55:1328–30, 1997

15. Panula K, Oikarinen K. Severe hemorrhage after implant surgery (letter). Oral Surg Oral Med Oral Pathol Oral Radiol 87(1):2, 1999

16. Mardinger O, Manor Y, Mijiritsky E, Hirshberg A. Lingual perimandibular vessels associated with life-threatening bleeding: an anatomic study. Int J Oral Maxillofac Implants. 22(1):127-31, 2007

17. Kattan B, Snyder H. Lingual artery hematoma resulting in upper airway obstruction. J Emerg Med 9:421-424, 1991

Dental 3D Cone Beam CT Imaging: Part I Demographics

Dental 3D cone beam CT imaging has replaced traditional medical CT scans that first became commonplace after endosseous dental implants were first introduced by Dr. Per-Ingver Brånemark (1) in the early 1980s. With the advent of the DentaScan software, dentists viewed CT images in multiple planes: coronal (known as panoramic), axial, and sagittal (known as cross-sectional or transaxial) for better and safer implant placement. Applications for CT scans extended from implantology to other oral and maxillofacial uses (2-9). Until recently, CT scanners were situated in medical radiological offices where dentists referred their patient for 3D studies for implant treatment planning. With the introduction of cone beam volumetric tomographic (CBVT) scanners in April, 2001, a new era of dental radiology was launched (10).

These 3D cone beam dental (CBVT) scanners, approved by the FDA as dental devices and often referred to as “dental CT scanners,” offered improved diagnostic tools over existing medical CT scanners due to their low-dose radiation requirements and more accurate, diagnostic images for implant placement, removal of impacted wisdom teeth, and more. Dental radiological labs first gained recognition (1972) in California when oral and maxillofacial radiological technicians were permitted to own and operate X-rays centers. Upon their introduction, these radiological labs embraced cone beam scanners (NewTom 9000).

The first change to a 3D dental scanner was introduced by Imaging Sciences International - the i-CAT™ - in March, 2004. This dental CT cone beam scanner had a smaller footprint and was designed for dental offices. Rather than lie on a gurney, patients would sit in a chair while the scan was taken. This version of the CBVT scanner enabled busy dental practitioners to buy 3D CT scanners. In addition to using it for their own patients, dentists often solicited colleagues in their community to their send patients for dental 3D CT images. In effect, they created de facto radiological practices. And still others, both dentists and/or entrepreneurs, created freestanding radiological labs for the express purpose of taking and processing 3D CT images for other dentists.

To date, data concerning the type of patient referred to a dental cone beam radiological center and the reason for the prescribed 3D CT scan has been anecdotal. While it is assumed that the main reason most dental patients are referred for CT scans is for pre-surgical dental implant analyses, no article has studied the demographics of this relatively new phenomenon: the dental cone beam 3D CT radiological lab.

The purpose of this study was to determine how and for what reason dentists currently utilize a 3D cone beam CT imaging center. In addition to the types of patients and the reasons they were referred for CT scans, the following were recorded from each study when appropriate: the incidence and location of the lingual artery inserting into the mandible, measurements and observations about the extension of the inferior alveolar canal anterior to the mental foramen, the incidence and location of bifid canals, the incidence of sinus pathology, and the identification of incidental findings other than the reason for the CT referral including impacted teeth, periapical radiolucencies, pathologies, retained roots, etc. All of these anatomical structures impact on the success, failure, and risk of dental implants, removal of impacted third molars, and other dental surgical procedures.

Part I of this study consists of data of patients referred to a dental radiological lab for 3D CT scans including age, gender, purpose of the CT study, which arch was requested, if a radiographic guide was used, and in which format the study was requested to be processed.

Methods and Materials

Data from five hundred (500) consecutive patients sent to i-dontics center from 9 centers located in 3 states were evaluated. Scans were taken on either a cone beam 3D i-CAT (8 centers) CT scanners or on a NewTom 3G (Manhattan) 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. The following parameters were recorded for each patient: age, gender, reason for the scan (i.e. dental implants), dental arch studied, the format for the delivery of the data, and whether or not a radiographic guide was used.

Results

One Hundred and ten (110) dentists referred 500 patients for 3D cone beam CT studies. Two hundred and twenty-eight (228) or 44.4 % of all patients referred for were male; two hundred and seventy-two (272) or 55.6% of the patients were females (Figure 1).


Figure 1. Gender of patients.


Patient ages ranged from 15 – 102 years (Figure 2). The mean age was 56.7 years.


Figure 2. Number of patients in each age category.

Reasons for CT scans. The predominant reason for referral for dental CT cone beam scan was for pre-surgical analysis for dental implants. Four hundred and fifty-one patients (451) were referred for dental 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.

Each 3D CT study was categorized either as a mandibular scan or a maxillary scan, or both, regardless of the reason for the dental CT 3D scan (implants, impactions, endodontic problems, or pathology). In the single instance of a TMJ study, the patient also had an edentulous mandibular site evaluated for an implant, so this patient was counted as a mandibular study (Figure 4).


Figure 4. CT scans for the maxilla = 40.8%; CT scans for the mandible = 43.4%; CT scans for both arches = 15.8%.


Delivery format. CT dental cone beam studies were requested in a variety of formats: via Internet; transparencies; CD; Prints. In 12 instances, studies were requested in multiple formats by students in the implant program at New York University College of Dentistry. Consequently, 512 different formats were requested for the studies: transparencies = 42; glossy prints = 55; CDs = 239; and 176 via the Internet (Figure 5).


Figure 5. Formats for CT scans were received in four ways: Film, Prints, Internet, and CD.

Software. Four hundred and four (404) requests were made for specific 3D CT dental treatment planning software. The requests were as follows: SimPlant™ = 273; DICOM = 114; i-CAT/i-Vision = 14; NobelGuide = 3. All DICOM cases, except for the 3 requested for NobelGuide, were imported into VIP software by Implant Logic Systems. When no request was made for a specific software format, then prints or film were printed in SimPlant™ format, but these numbers are not counted as specific software requests. The total number of requests + prints + film exceeds 500 patients since some doctors requested studies in multiple formats (Figure 6).


Figure 6. CT studies for the most common 3D third party software requested was SimPlant™, followed closely by DICOM used specifically for VIP software by Implant Logic Systems.

Over the years, SimPlant has issued many different versions of its 3D dental implant software. As a SimPlant™ Master Site, it was noted that dentists did not install each new version as they were released. Most of this study was compiled just before version 11 was released. As a result, of the 273 studies in SimPlant™, the following versions were requested: version 8 = 19; version 9 = 130; version 10 = 105; version 11 = 12; SimPlant viewer = 7 (Figure 7).


Figure 7. Demonstrates the proportion of the different versions of SimPlant™ requested.

Radiographic Guides. One hundred and eight patients (108) had radiographic guides fabricated by their dentists that were inserted during the CT scan. These guides helped pinpoint” more accurate dental implant placement, while reducing surgical risks. Of these, 3 were for NobelGuides. Patients presenting with guides = 21.6%.

DISCUSSION

Sir Godfrey Newbold Hounsfield conceived of creating a radiological (CT) machine to create cross-sectional views in 1967. In 1972, Hounsfield introduced the first Computed Tomographic scanner; CT reconstruction software dedicated to dental diagnostics has been available since the 1980s. This software, known as the DentaScan, enabled multi-planar views of the CT data into axial or occlusal, panoramic-like or coronal, and sagittal or cross-sectional images of either arch (2-4), which aided dental surgeons in implant placement.

The next milestone for dentists in 3D CT imaging was the introduction of the NewTom 9000 cone beam volumetric scanner by QR Verona in the late 1990s (10). This scanner received FDA approval in the United States in April, 2001. Unlike a medical scanner, the NewTom 9000 was designed specifically to image the maxillofacial region. The patient exposure effective dose is 50 μSv which is significantly less than a high-resolution medical CT scan and similar to that of a dental periapical full-mouth series.13,14 Since then, there has been a proliferation of manufacturers (the most notable was Imaging Sciences Inc., Hatfield, PA) introducing similar 3D cone beam CBVT scanners to the marketplace that took the scan with the patient sitting in a chair rather than lying on a gurney. In time, a host of 3D software vendors (Materialise, Glen Burnie, MD) entered the marketplace that enabled DICOM files created by these scanners to be imported into their respective software. Software frequently used for dental implants include NobelGuide™ by NobelBiocare, VIP™ by Implant Logic Systems, SimPlant™ by Materialise, and In Vivo™ by Anatomage. In orthodontics, Dolphin Imaging™ by Dolphin, SureCef™ etc. are also available.

As with other clinical innovations, common usage lags behind its introduction to the profession. This is true of dental implants, where market penetration is estimated to be in the range of 4-8%. Likewise, the utilization of diagnostic 3D imaging lags behind the long-time accepted use of 2D imaging of dental periapical and panoramic films, in spite of the fact that these images can be distorted (11). As such, the increased utilization of 3D diagnostic imaging is arguably becoming the standard of care when it comes to pre-surgical analyses of complex dental implant treatment plans (12).


In the present study 500 consecutive patients, referred by 110 different dentists, were evaluated as to their age, gender, and reason for being referred to a dental 3D imaging center that utilizes a CBVT (cone beam) scanner. Forty-four (44%) percent of the patients referred were male; 56% were female. Patients ranged from 15-102 years of age, with an average age of 56.7 years. Younger patients were most often referred for orthodontic reasons, to evaluate impacted teeth, or were post-orthodontic and were being evaluated for sites of congenitally missing teeth for implant placement, most often for missing maxillary lateral incisors.

The single reason for the vast majority of patients, 451 or 90.2% referred was for dental implants. Other reasons for CT scans included: evaluating impacted teeth (4%); pathology (2%); endodontics (1.4%); orthodontics (0.8%); TMJ disorder (0.2%) and 7 patients were referred for unknown reasons (1.4%).


Referrals for single arches – maxilla (40.8%) versus mandible (43.4%) - were similar, while 15.8% or 79 patients were referred for 3D CT cone beam scans of both arches.

There was diversity in how dentists wanted to receive the CT 3D dental studies. 512 different formats were requested: transparencies, glossy prints, studies on a CD or to receive the study via the Internet. Twelve dentists required multiple formats. The format dentists most preferred was CD (47%), followed by the Internet (34%). Glossy prints (11%) and 8 x 10 transparency format (8%) were the least requested. It should be noted that most of the Internet requests were for DICOM studies and were made by dentists using VIP™ software by Implant Logic Systems or SimPlant™ by Materialise. Those dentists, or a member of their staff, who were comfortable using the Internet had web access in their offices and took advantage of the speed, efficiency, and benefits of Internet transmission.


The most common third party 3D dental software used by dentists in this study was SimPlant™ (54.6%). One hundred and fourteen (114) DICOM images (22.8%) were requested, which were converted into VIP™ or NobelGuide™ software; 14 studies (2.8%) were requested for either i-CAT or i-Vision™ (by Imaging Sciences, Inc) and 3 studies (0.6%) required 2 scans for NobelGuide™ by NobelBiocare. The more common usage of SimPlant is not surprising since there are many SimPlant Master™ sites in the New York tri-state area and dentists have been accustomed to using this software for many years. The relatively high request for DICOM images was a function of geography due to the popularity of VIP software in the Brooklyn/Long Island area. While the different 3D dental software usage has been consistent in this study over a long period of time, regional trends may dictate which studies are requested from different CBVT radiological labs.

SimPlant™, long the established leader in 3D dental software, issues new versions of their treatment planning software frequently. Yet, the experience at this SimPlant Master Site indicates that dentists do not install the latest version when it is first received. While some dentists do install it immediately, many wait when they are comfortable with the present version they are using or, perhaps, they choose to wait to make certain “bugs” are not discovered by other users before they install it in their systems. Consequently, 19 studies were processed in version 8, while versions 9, 10, and the recently issue v. 11 were more commonly used. Since the data was collected, SimPlant™ version 12.0 has been issued.


The most unexpected finding of this study was that 108 or 21.6% of all patients referred for 3D CT scans came with radiological guides to be worn during the scan. These guides used gutta-percha, barium sulfate, or medical ball bearings as markers to be seen on the CT scans to help guide the dentist in interpreting where dental implants should be inserted. There was no attempt to determine how many surgical guides were created from the data in this study.

The results of this study demonstrate that while dentists use 3D cone beam imaging predominantly for dental implants, patients are referred to help diagnose and treat other dental entities. Future articles compiled from this data will report on the incidence and location of the lingual artery inserting into the mandible, measurements and observations about the extension of the inferior alveolar canal anterior to the mental foramen, the incidence of bifid canals, the incidence of sinus pathology, and the identification of incidental findings other than the reason for the CT referral including impacted teeth, periapical radiolucencies, pathologies, retained roots, and more.


Conclusion

A study of 500 patients referred to i-dontics dental radiological centers for 3D cone beam (CBVT) studies indicated the majority of patients were referred for pre-surgical analyses for dental implant insertion. Other reasons include impacted teeth, orthodontic problems, and a variety of oral and dental pathologies, recalcitrant endodontic lesions, and TMJ disorders. A significant number of patients (21.6%) presented with and wore radiological guides during the CT scan.

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

References

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2) Schwarz MS, Rothman SLG, Rhodes ML et al: Computed tomography: Part I. Preoperative assessment of the mandible for endosseous implant surgery. Int J Oral Maxillofac Implants 3: 137-141, 1987.

3) Schwarz MS, Rothman SLG, Rhodes ML et al: Computed tomography: Part II. Preoperative assessment of the maxilla for endosseous implant surgery. Int J Oral Maxillofac Implants 3: 143-148, 1987.


4) Casselman JW, Deryckere F, Robert Y et al: Denta Scan: program of x-ray computed tomographic reconstruction used for the anatomical evaluation of the mandible and maxilla in preoperative assessment of dental implants. Ann Radiol 33: 408-417, 1990.

5) King JM, Caldarelli DD, Petasnick JP: DentaScan: a new diagnostic method for evaluating mandibular and maxillary pathology. Laryngoscope 102: 379-387, 1992.

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7) Calgaro A, Bison L, Bellis GB, Pozzi Mucelli R: Dentascan computed tomography of the mandibular incisive canal. Its radiologic anatomy and the therapeutic implications. Radiol Med 98: 337-341, 1999.

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9) Abrahams JJ: Dental implants and multiplanar imaging of the jaw. In: Som PM, Curtin HD (eds). Head and neck imaging, 3rd ed, p 350-374. Mosby, St. Louis, 1996.

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Periodontist NYC - Second opinion for your dental health: is it time?

Few dental patients ever request a second opinion about their oral/dental health from another dentist when they seemingly have no dental emergencies or are unaware of any existing dental problems. But how do they know that their dental care is what it should be? Gum disease is chronic and silent. It creeps up on us without any advanced warning. And while our fillings may look good, do they fit properly?

Here are some guidelines for evaluating your present dentist and your dental care:

1. Are medical histories are updated?

2. Are cancer/cavity (caries or dental decay) checks are performed?

3. Are digital x-rays are used (less radiation than traditional film)?

4. Are bite wing X-rays taken for dental decay are taken periodically/is a lead apron used when X-rays taken/are full mouth sets of X-rays taken every few years?

5. Does your dentist/hygienist perform a periodontal exam with a millimeter probe to measure "pockets" on a routine basis?

6. Are oral hygiene techniques are reviewed and modified as needed/diet and nutrition discussed as they apply to caries and oral health?

7. If you have periodontal pockets and bleeding, are you told this is okay? Not to worry?

8. Do you know about the systemic links between gum disease and cardiovascular, stroke, pulmonary, etc.?

9. Are disposable products apparent in the treatment room? Are they used frequently?

10. Are OSHA protocols followed such as covering all surfaces with disposable plastic products?

11. Do you have frequent emergencies and have restorations that need replacing “too” often?

12. Are you emergency visits accommodated in a timely way?

13. Does the staff function smoothly with the doctor? Themselves?

14. Are treatment options always presented when dental care is required; are procedures explained and are you asked to give informed consent (this can take different forms)?

15. Does your family dentist utilize dental specialists for advanced problems?

16. Does the office looks clean and orderly?

17. Are new technologies introduced to the office as they are proven beneficial? Examples: implants, bleaching teeth.

18. 3D CT imaging for most dental implant cases

When to question your dentist:

1. When they don't follow most of the above guidelines.

2. When fillings continuously break.

3. When crowns continuously fall out.

4. When a patient goes to the dentist on a regular basis and is told one day (out of the blue) that their periodontal disease is advanced, surgery is needed, and teeth many need to be removed after never having been made aware of a problem beforehand. Periodontal disease takes years to form; it does not occur overnight.

5. When gums bleed all the time and patient is told that this is "normal".

6. When a patient is told that it's normal to "lose" teeth.

7. When treatment options are not discussed.

8. When a family does not use specialist for advanced problems.

9. When a patient experiences frequent emergencies without resolution or suitable consultations.

10. When dental implants are not discussed as an option to replace a missing tooth or an existing bridge that has to be remade.

11. When a dentist is unaware or does not use 3D CT technology for dental implant insertion