Implant site assessment using panoramic cross-sectional tomographic imaging

Implant site assessment using panoramic cross-sectional tomographic imaging Brad J. Potter, DDS, MS, a Michael K. Shrout, DMD, a Carl M. Russell, DMD, PhD, b Mohamed Sharawy, BDS, PhD, c Augusta, Georgia MEDICAL COLLEGE OF GEORGIA

Objectives. The purpose of this study was to evaluate the ability of two different panoramic imaging systems to produce crosssectional images with accurate vertical dimensions of the posterior mandible. Study design. Three partially edentulous human cadaver mandibles were used for this study. On each mandible, three potential implant sites were arbitrarily identified in an area between the mental foramen and the ascending ramus. Each site was imaged using two different panoramic machines. Using each image, the mandible's outline, cortical thickness, and position of the mandibular canal were traced on clear acetate film. The mandibles were then sectioned at each site to serve as a gold standard. The cadaver sections and tracings (corrected for magnification) were measured, recording the overall mandibular height, distance from the crest of the ridge to the superior aspect of the mandibular canal, and the thickness of the cortical bone at the most inferior aspect of the mandible. Results. There were no significant differences between either of the system's image measures and the gold standard when considering the distance between the crest and the mandibular canal. Differences were noted between the systems measures and the gold standard in the assessment of the cortical bone thickness and the overall mandibular height. Conclusions. Both imaging systems can be useful for vertical measurements of a potential implant site in the posterior mandible. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1997;84:436-42)

Patient care in implant dentistry requires many specialized skills of the practitioner. These not only include knowledge and expertise in anatomy, dental materials science, surgery, and specialized restorative techniques, but also demand an emphasis on diagnosis and treatment planning. The diagnosis should integrate information obtained from a thorough clinical examination with the information gained from a properly conducted radiographic examination. Although this is essential for the proper care of a patient, it gains more significance in light of today's litigious society. Pollack 1 suggested that the use of dental implants in dental practice places the practitioner at a higher risk of malpractice litigation. Incomplete or outdated radiographic studies that adversely affec t the patient's care may be grounds for malpractice. 2 In addition, the insurance industry is recommending that practitioners investigate newer techniques for implant imaging, suggesting that standard radiographs may be insufficient in the diagnostic process) This issue gains considerable

aAssociate Professor, Department of Oral Diagnosis and Patient Services, School of Dentistry, Department of Oral Biology, School of Graduate Studies. bAssociate Professor. CProfessor, Department of Oral Biology, Section of Anatomy, Department of Oral and Maxillofacial Surgery, School of Dentistry, School of Graduate Studies. Received for publication Jan. 13, 1997; returned for revision Mar. 27, 1997; accepted for publication April 15, 1997. Copyright © 1997 by Mosby-Year Book, Inc. 1079-2104/97/55.00 + 0 7/16/82745

436

credence in light of reports of serious complications during implant surgery. 4,5 To properly diagnose a patient and treatment plan a case for implant dentistry, a variety of advanced imaging modalities have been recommended for the presurgical assessment of potential dental implant sites. These include plain film tomography as well as computed tomography (CT). 6-t5 Regardless of which imaging modality is chosen, certain basic goals of implant imaging should be adhered to. The technique should be able to assess normal anatomic structures from all perspectives, evaluate proposed sites for pathoses, indicate possible surgical paths of insertion, aid in postoperative evaluations, and provide diagnostic and treatment documentation. Plain film tomography is one of the imaging modalities that will allow a practitioner to meet these goals. The utility of plain film cross-sectional tomography is well established in the literature. Petrikowski et al. 16 used hypocycloidal t0mography to show vertical height and horizontal width errors of less than 1 m m when compared to direct measurements made of anatomic specimens. This small amount of error was recorded when the specimen height ranged from 16.36 to 21.36 m m and the width ranged from 7.2 to 12.47 mm. Lindh and Petersson 17 found that tomography produced a more diagnostic image of the mandibular canal in the region of the mental foramen as compared to panoramic radiography. They concluded that this is of particular importance in patients who have had considerable alveolar ridge resorption. Gher and Richardson 18 compared

ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY

Potter et al.

437

Volume 84, Number 4

Fig. 1. Preimaging cadaver mandible specimen showing the arbitrarily selected implant sites. Three orthodontic arch-stop tubing sections are embedded in wax at the crest of the alveolar ridge, one over each proposed site. The imaging lines are drawn perpendicular to the crest of the ridge.

several different imaging modalities and noted that linear tomograms were comparatively as accurate as computed tomography. Tomography has likewise been shown to provide accurate images of the maxilla in implant dentistry. 19-21 In considering cross-sectional imaging using panoramic machines, Chen and Hollender22 evaluated the frequency domain of cross-sectional images produced by one panoramic unit. They concluded that the images lacked diagnostic usefulness because of the narrow tomographic angle used by the machine's software program. Cross-sectional imaging performance evaluations are not yet available for other panoramic units, even though they are rapidly coming into use. The purpose of this study was to evaluate the ability of two different panoramic imaging systems to produce crosssectional images with accurate vertical dimensions of the posterior mandible. MATERIAL AND METHODS Three partially edentulous degloved human cadaver mandibles were used in this study. Approval for acquisition and use of the human specimens was obtained before the commencement of this study from the Human Assurance Committee of the Medical College of Georgia. On each mandible, three potential implant sites were arbitrarily identified in an area between the mental foramen and the ascending ramus. Each site was marked by placing an orthodontic arch-stop tubing (American Orthodontics, Sheboygan, Wisc.) in wax at

the crest of the alveolar ridge. This radiopaque marker would serve later as verification that the appropriate site was in the image layer of each of the cross-sectional images produced. A line was then drawn from the archstop tubing to the inferior border of the mandible, perpendicular to the crest of the ridge (Fig. 1). Following the imaging equipment manufacturer's protocol, each mandible was positioned in the panoramic unit using bite forks supplied by the manufacturers and a heavy bodied putty impression material (Extrude Putty, Kerr, Romulus, Mich.). It should be noted that during clinical use, it is recommended that a bite registration material be used instead of an impression material. However, positioning and suspension of the mandibles in this study was more accurately accomplished using the impression material. Each site was subsequently imaged along the identified lines using the Orthopantomograph OP100 equipped with the Ortho Trans hardware and software package (Instrumentarium Imaging Inc, Tuusula, Finland) and the Planmeca 2002CC equipped with the Transversal Slicing hardware and software package (Planmeca Oy, Helsinki, Finland). The OP100's Ortho Trans system is programmable to obtain both cross-sectional and sagittal images of a proposed site. Image layer thickness ranging between 2 and 8 mm (in 1 mm increments) can be selected with a variety of display options on a single piece of panoramic film. The images produced by the OP100 have 40% magnification (Fig. 2). Positioning of the image layer is

438

Potter et aL

ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY October 1997

Fig. 2. A cross-sectional image of one of the experimental implant sites acquired using the Ortho Trans Program of the Orthopantomograph OP 100. The image of the orthodontic arch-stop tubing section is seen superior to the alveolar crest.

accomplished on the OP 100 by the use of a set of laser lights that project at right angles (a "cross-hair" appearance) over the proposed site. The PM 2002CC's Transversal Slicing system has the ability to produce cross-sectional images with either an image layer thickness of 4 or 8 ram. These images have 45% magnification (Fig. 3). Positioning of the image layer for this equipment is accomplished manually by sighting through a clear acrylic plate. To standardize for comparison of images, only cross-sectional images were acquired at each site with a selected 4 mm thick image layer. A combination aluminum-acrylic beam filter (10 m m thickness of each material) was fashioned on site and secured on the tubehead to simulate soft tissue scatter and allow for clinically acceptable film density and contrast. The range of exposure values used was between 66 kVp and 4 mA to 72 kVp and 5 mA. All images were acquired with Kodak Lanex Regular screens and T-Mat G film (Eastman Kodak, Rochester, N.Y.), using a grid cassette (6:1 ratio, parallel focus, 57 lines/cm).

Fig. 3. A cross-sectional image acquired using the Transversal Slicing Program of the Planmeca 2002CC panoramic machine. The image of the orthodontic arch-stop tubing section is seen superior and slightly medial to the alveolar crest.

Following image acquisition, the images were randomly mixed between sites and imaging equipment used, and arbitrarily marked, later to be cross-referenced to a particular cadaver site. One of the mandible's sites was excluded from the study because of a technical error. The mandible's outline, cortical thickness, and position of the mandibular canal were then traced on a clear acetate film by an oral and maxillofacial radiologist for each of the remaining 16 images. Each tracing was then measured with vernier calipers, specifically recording the overall mandibular height, distance from the crest of the alveolar ridge to the most superior aspect of the mandibular canal, and the thickness of the cortical bone at the most inferior aspect of the mandible (Fig. 4). The cadaver mandibles were then sectioned at each of the proposed sites, and the identical measurements were made, thereby serving as a gold standard (Fig. 5). Finally, the tracing measurements and cadaver measurements were cross-referenced according to the imaging equipment used, and each image measure was appropriately corrected for magnification. Measurements obtained from the PM 2002CC's images were divided by a factor of 1.45, and those obtained from the OP 100's images were divided by a factor of 1.40.

ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY

Potter et al. 439

Volume 84, Number 4

bit

Fig. 4. Schematic showing the three measurements taken from each cross-sectional image. CAN, the distance from the crest of the alveolar ridge to the most superior aspect of the mandibular canal; OH, the distance from the crest of the alveolar ridge to the most inferior aspect of the mandible; CORT, the thickness of the cortical bone at the most inferior aspect of the mandible.

Differences from the gold standard for each of the panoramic imaging systems were analyzed using the paired t test. Differences from the gold standard were also expressed as a percentage of the gold standard. All testing was done with a two-tailed alternative hypothesis and considered significant if p _<0.05.

Fig. 5. One of the partially edentulous human cadaver mandibles sectioned at a proposed implant site. Measurements acquired directly from these anatomic sections served as the gold standard. Note the centrally located inferior alveolar neurovascular bundle.

Cortical thickness Significant differences (p < 0.05) existed between both imaging system's cortical bone thickness measurements and the gold standard measurements. The OP100 underestimated the thickness by 24.99%, whereas the PM 2002CC underestimated the thickness by 17.32% (Table III).

DISCUSSION RESULTS Crest-to-canal measures Comparison of the mean differences showed that there were no statistically significant differences (p > 0.05) between either of the imaging system's image measurements and the gold standard when considering the distance between the crest of the alveolar ridge and the superior aspect of the mandibular canal (Table I).

Overall height measures There were no statistically significant differences (p > 0.05) between the OP100 image measurements and the gold standard for the overall height of the mandible at the proposed sites. However, significant differences (p < 0.05) were present between the PM 2002CC image measurements and the cadaver measurements. When expressed as a percentage of the gold standard, the PM 2002CC overestimated the overall height by 6.05% (Table lI).

Most of the major manufacturers of panoramic imaging systems are now marketing some type of cross-sectional capabilities for their particular unit. This may be of considerable interest to practitioners who are actively involved in implant dentistry. Whether the involvement is in the actual surgical placement, the diagnosis and treatment planning phase, or the restorative phase, dentists are likely to be interested in multitask radiography equipment. Although new imaging systems are thoroughly tested by their respective manufacturer, it is essential that all of these systems be evaluated independently for their ability to provide accurate and useful images. Both of the panoramic machines used in this experiment were able to produce images that were accurate in assessing the distance from the crest of the alveolar ridge to the mandibular canal. This study was limited to the evaluation of the posterior mandible, which is of critical concern in implant dentistry. The position and

440

ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY

Potter et aL

October 1997

Table I. Alveolar crest to mandibular canal distance.

Gold standard OP 100 PM 2002CC

Mean (mm) *

S.D.

Mean difference (mm) from gold s t a n d a r d

14.77 15.03 15.21

1.95 1.98 2.39

0.26 0.44

S.D. of differences 0.92 1.45

% difference from gold standard

S.D. of % difference

1.96 3.06

6.15 10.17

% difference from gold standard

S.D. of % difference

1.56 6.05 t

3.34 6.74

% difference from gold standard

S.D. of % difference

-24.99~ -17.32 t

6.40 7.15

*n=8. tp < 0.05.

Table II. Overall height of the mandible.

Gold standard OP 100 PM 2002CC

Mean (mm)*

S.D.

Mean difference (ram) from gold standard

26.16 26.52 27.68

2.03 1.52 1.92

0.36 1.52~

S.D. of differences 0.84 1.70

*n=8. ~p < 0.05.

Table III. Cortical thickness at the inferior border of the mandible.

Gold standard OP 100 PM 2002CC

Mean (mm) *

S.D.

Mean difference (ram) from gold standard

3.76 2.82 3.11

0.19 0.24 0.26

~).94 t -0.65 t

S.D. of differences 0.27 0.29

*n=8. tp < 0.05.

course of the inferior alveolar nerve and vessels are highly variable and somewhat unpredictable. 23-25 Therefore accurate images are essential when implants are proposed for the posterior mandible. Overextension of an implant into the canal carries considerable risk of prolonged or permanent injury. The OP100 was superior to the PM 2002CC in depicting the overall height of the mandible at the proposed sites. The PM 2002CC overestimated the available height by a mean of almost 2 mm. Certainly, some level of concern is justified when a diagnostic system indicates to the practitioner that more space is available than is actually present. If these findings are ultimately found to apply to the maxilla and the anterior mandible, however, slight overextensions are often more easily tolerated in these locations. The thickness of the cortical bone at the inferior aspect of the mandible was assessed as an indication of accuracy over small distances. Both systems produced images of the thickness that were significantly different from the gold standard. In both cases, the mean measures were underestimates of the amount of cortex that was available. Although the percentage difference from

the gold standard mean was high (17.32% for the PM 2002CC and 24.99% for the OP 100), the actual mean values were less than 1 ram. This is likely to be of little significance in a clinical setting. One possible explanation for this finding is that the inferior border of the mandible is not often parallel to the crest of the alveolar ridge. The alignment of the specimens (and patients in a clinical setting) is best if the alveolar ridge is perpendicular to the x-ray beam. When there is lack of this ideal perpendicular alignment, the inferior cortex will be imaged at a slightly oblique angle, and therefore the anatomic details may not be as clearly resolved in the resulting images. Before the use of these systems at this institution, many of the implant cases depended on either routine panoramic radiographs or CT reformatted images for radiographic evaluation. Although there are indications for both of these imaging modalities in implant dentistry, the availability of plain film panoramic crosssectional imaging has been a welcomed addition. Both the Planmeca and Orthopantomograph cross-sectional imaging programs have been used for a variety of implant cases. Image acquisition is considerably differ-

ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY

Potter et al.

441

Volume 84, Number 4

ent for both of these machines. The Planmeca 2002CC, with the Transversal Slicing Program, essentially positions the patient such that a panoramic-like image layer is obtained of the region of interest. The film cassette translates as it does in traditional panoramic radiography, and therefore the center of rotation is located at a distance from the actual i m a g e layer position, Generally, positioning of the patient is straightforward except in the anterior region. In these situations, the patient is turned to the side almost 90 degrees, so larger patients are often cramped between the head positioner and the tubehead. The program is limited to axially corrected cross-sectional images of either 4 or 8 m m thickness, but it can be p r o g r a m m e d to acquire three sequential images of a region, the patient being moved 4 m m posteriorly between each image. This can be a useful tool, but angular changes (relative to the sagittal plane) within the patient's anatomy often prevents the acquisition of a total of three useful images. The Ortho Trans Program o f the OP 100 will acquire both axially corrected cross-sectional and sagittal images. The sagittal image is useful for correlation with the respective cross-sectional view, as well as providing insight into potential surgical paths of implant insertion. 26 Flexibility in image layer thickness is very good, ranging between 2 and 8 m m for both cross-sectional, as well as sagittal images. Patient positioning is very straightforward for the OP 100. Once the bite registration is made, including any imaging stent, the bite fork is attached to the machine. The laser lights are aligned on the identified site, thus allowing for precise image layer positioning. The patient is then guided to the machine, and he or she rearticulates into the bite registration. This ease and precision of patient positioning has been useful in those cases where slight angular adjustments are required to obtain optimal images. The design of the OP 100 permits the location of the center of rotation to coincide with the actual site, and therefore the film cassette does not need to translate during image acquisition. The i m a g e layer is thus produced at the center of rotation. The OP 100 can be programmed to display a variety of images on film, ranging from one to six images. The cross-sectional i m a g e selection can include zero, one, or three (one at site, one posterior, and one anterior to the site) images. The sagittal image selection can include zero, one, or three (one at site, one facial, and one lingual to the site) images. The results of this study indicate that both of these imaging systems can be useful for vertical measurements of posterior mandible implant sites. Although this initial study limited itself to vertical measurements, additional research is certainly indicated. This is especially true in regard to panoramic cross-sectional imaging's ability to reproduce anatomic morphology, pro-

vide horizontal measurement accuracy, and image other anatomic locations. These new p a n o r a m i c imaging technologies should also be compared directly to other, more sophisticated, plain film tomographic units. REFERENCES 1. Pollack BR. Legal risks associated with implant dentistry. In'. Hardin JF, editor. Clark's clinical dentistry. Vol 5. Philadelphia: JB Lippincott; 1992. p. 1. 2. Bundy AL. Radiology and the law. Rockville: Aspen Publishers; 1988. p. 95-107. 3. SAFECO Insurance Company. Implants: growing concern. Dental Claims and Insurance Newsletter. Vol 8. Seattle: SAFECO Insurance Company; 1994. 4. Mason ME, Triplett RG, Alfonso WF. Life-threatening hemorrhage from placement of a dental implant. J Oral Maxillofac Surg 1990;48:201-4. 5. Laboda G. Life-threatening hemorrhage after placement of an endosseous implant: report of a case. J Am Dent Assoc 1990; 121:599-600. 6. Kassebaum DK, Nummikoski PV, Triplett RG, Langlais RR Cross-sectional radiography for implant site assessment. Oral Surg Oral Med Oral Pathol 1990;70:674-8. 7. Miles DA, Van Dis ML. Implant radiology. Dent Clin North Am 1993;37:645-68. 8. Frederiksen NL. Diagnostic imaging in dental implantology. Oral Surg Oral Med Oral Pathol 1995;80:540-54. 9. Pharoah MJ. Imaging techniques and their clinical significance. Int J Prosthodont 1993;6:176-9. 10. Abrahams JJ. The role of diagnostic imaging in dental implantology. Radiol Clin North Am 1993;31:163-80. 11. Ismall YH, Azarbal M, Kapa SF. Conventional linear tomography: protocol for assessing endosseous implant sites. J Prosthet Dent 1995;73:153-7. 12. Schwartz M, Rothman S, Rhodes M, Chafetz N. Computed tomography. Part I. Preoperative assessment of the mandible for endosseous implant surgery. Int J Oral Maxillofac Implants 1987;2:137-41. 13. James RA, Lozada JL, Tmitt HR Computer tomography (CT) applications in implant dentistry. J Prosthet Dent 1991;17:10-5. 14. Smith JR Borrow JW. Reformatted CT imaging for implant planning. Oral Maxillofac Surg Clin North Am 1991;3:805-25. 15. Lam EW, Ruprecht A, Yang J. Comparison of two-dimensional orthoradially reformatted computed tomography and panoramic radiography for dental implant treatment planning. J Prosthet Dent 1995;74:42-6. 16. Petrikowski CG, Pharoah MJ, Schmitt A. Presurgical radiographic assessment for implants. J Prosthet Dent 1989;61:5964. 17. 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 1989;4:249-53. 18. Gher ME, Richardson AC. The accuracy of dental radio~aphic techniques used for evaluation of implant fixture placement. Int J Periodont Rest Dent 1995;l 5:268-83. 19. Fredholm U, Bolin A, Andersson L. Preimplant radiographic assessment of available maxillary bone support: comparison of tomographic and panoramic technique. Swed Dent J 1993;17:103-9. 20. Petersson A, Lindh C, Carlsson L. Estimation of the possibility to treat the edentulous maxilla with osseointegrated implants. Swed Dent J 1992;16:1-6. 21. Bolin A, Eliasson S. Panoramic and tomographic dimensional determinations for maxillary osseointegrated implants. Swed Dent J 1995;19:65-71. 22. Chen S, Hollender L. Frequency domain analysis of cross-sectional images of the posterior mandible. Oral Surg Oral Med Oral Pathol 1994;77:290-5.

442 Potter et al.

ORAL SURGERY ORAL MEDICINE ORAL P A T H O L O G Y October 1997

23. Carter RB, Keen EN. The intramandibular course of the inferior alveolar nerve. J Anat 1971 ;108:433-40. 24. O'Dell NL. Selected anatomic correlations in implant dentistry. In: Hardin JF, editor. Clark's clinical dentistry. Vol 5. Philadelphia: JB Lippincott; 1993. p. 3. 25. Nortje CJ, Farman AG, Grotepass FW. Variations in the normal anatomy of the inferior dental (mandibular) canal: a retrospective study of panoramic radiographs from 3612 routine dental patients. Br J Oral Surg 1977-78;15:55-63. 26. Monahan R, Furkart AJ. Technical note: sagittal tomography as

O

an adjunct to cross-sectional evaluation of selected implant sites. Dentomaxillofac Radiol 1996;25:298-301.

Reprint requests: Brad J. Potter, DDS, MS Department of Oral Diagnosis and Patient Services Medical College of Georgia School of Dentistry Augusta, GA 30912-1241

N THE MOVE? ~end u s y o u r n e w a d d r e s s at l e a s t s i x w e e k s a h e a c

Don't miss a single issue of the journal! To ensure prompt service when you change your address, please photocopy and complete the form below. Please send your change of address notification at least six weeks before your move to ensure continued service. We regret we cannot guarantee replacement of issues missed due to late notification.

JOURNAL TITLE: Fill in the title of the journal here.

OLD ADDRESS:

NEW ADDRESS:

Affix the address label from a recent issue of the journal here.

Clearly print your n e w address here. Name Address City/State/ZIP

COPY A N D MAIL THIS FORM TO: Journal Subscription Services Mosby-Year Book, Inc. 11830 Westline Industrial Dr. St. Louis, MO 63146-3318

OR FAX TO:

OR PHONE:

314-432-1158

1-800-453-4351 Outside theU.S.,call 314-453-4351

Mosby