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A positioning device for computed tomography: A clinical report
A positioning device for computed tomography: A clinical report Giuseppe Varvara, DDS,a Paola Esposito, DDS,b Federico Franchini, DDS,c Giuseppe Perinetti, DDS,d and Sergio Caputi, MD, DDSe Dental School, University of Chieti, Chieti, Italy This clinical report describes a device (Centrascan) used to assist in the correct alignment of the patient’s head during computed tomography (CT) assessment of a proposed implant site. To obtain the desired anatomic detail, CT requires precise alignment of the axial images at right angles to the long axis of the proposed implant. This clinical report compared the anatomic morphology of a projected implant site derived from axial images provided by DentaScan software analysis of the CT scan acquisition. Images from a conventional scan, with the patient’s head aligned along the frontal plane (perpendicular to the Frankfort plane) and along the sagittal plane (coinciding with either the cortical bone of the hard palate or the inferior border of the mandible), were compared with images acquired by use of the Centrascan device. The two scans differed substantially. In particular, the cross-sectional images obtained by the conventional procedure showed a distorted anatomy; conversely, the images obtained by the Centrascan procedure showed a better reproduction of the examined area. The Centrascan device seemed to help the radiologist achieve a more correct alignment of the patient’s head during CT scan acquisition. Further studies are necessary to fully explore the relative technical merits of the Centrascan device. (J Prosthet Dent 2003;89:123-6.)
A
ccomplishing predictable reconstruction and esthetics for single- or multiple-tooth dental implants is challenging. The long-term success of osseointegrated dental implants is influenced by several factors, including the length and alignment of the implant, as well as the bone anatomy of the implant site.1 Dental implant treatment often requires a combination of several radiologic techniques to correctly evaluate the anatomic morphology, including the bone width, the presence and amount of cortical bone on the ridge crest, and the degree of mineralization of the trabecular bone.2 The preferred position and orientation of each implant, its optimal length and diameter, and its position or relationship to the vital structures at the proposed implant sites are also determined by radiologic evaluation.3 Several imaging modalities have been used in implant imaging, such as periapical, panoramic, occlusal, cephalometric, and tomographic radiography; computed tomography (CT); and magnetic resonance imaging.4 In implant dentistry, the CT technique has been reported to be superior to other radiographic techniques.3,5 CT allows the evaluation of proposed implant sites and provides diagnostic information that other techniques or combinations of techniques cannot.4 In preoperative implant imaging, the CT scan should provide all necessary surgical and prosthetic orientation information, including the quantity and quality of bone, the desired angulation of the implant(s), and the relaa
Professor, Department of Odontostomatology Sciences. Professor, Department of Odontostomatology Sciences. c Professor, Department of Odontostomatology Sciences. d Research Fellow, Department of Odontostomatology Sciences. e Professor and Chairman, Department of Odontostomatology Sciences.
tionship of vital structures to the prospective implant in its terminal position.2 To obtain reliable information from the CT scan, all distortion factors must be avoided. To accomplish the desired outcome, correct alignment of the patient’s head with the x-ray source is essential.4,6,7 However, the reformatted axial images may lead to dimensional errors due to inclination of the scanning plane.8,9 In the conventional procedure, along the frontal plane, the radiologist refers to the sagittal axis of the face through the perpendicular to the Frankfort plane.10,11 The axes of the teeth coincide with the sagittal axis of the face only at the central incisors, whereas the other teeth are placed along the curve of Wilson.12 Along the sagittal plane, the radiologist refers to the cortical bone of the hard palate for the maxillary arch and the lower mandibular line for the mandibular arch.10,13 However, in this plane the long axes of the teeth are placed along the curve of Spee.12 The scanning plane should be perpendicular to the long axis of the implant position in both the frontal and sagittal planes. To obtain this positioning, the patient’s head should be aligned at right angles to the long axis of the proposed implant position, following the curves of Wilson and Spee (as compensating curve) of the teeth that are being replaced.12 This clinical report describes the Centrascan (Anthos, Imola, Italy), a device that serves to help the radiologist obtain the desired alignment of the patient’s head to the long axis of the proposed implant during the scanning procedure.
b
FEBRUARY 2003
CLINICAL REPORT A patient was examined to assess suitability for the placement of 2 implants to replace the first and second THE JOURNAL OF PROSTHETIC DENTISTRY 123
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VARVARA ET AL
Fig. 1. Guide with holes filled with gutta-percha radiopaque material (arrows), connected to intraoral fork (IOF).
Fig. 3A. Transfer of the long axis of teeth to be replaced was achieved by tipping extraoral arch (EOA) along axis of teeth to be replaced until parallelometer (P) angle coincided with vertical reference of Centrascan fork (arrow).
Fig. 2. Centrascan device demonstrating intraoral fork (IOF) with support surface that connects it to extraoral arch (EOA), which includes extremities to orientate it in space, and adjustable joint (J) to allow necessary orientation of extraoral arch to fork.
Fig. 3B. Lateral extremity present on extraoral arch (arrow).
right mandibular premolars. The patient was free from signs or symptoms of stomatognathic system dysfunction and other general illnesses that would preclude implant placement.14 Stone casts obtained from irreversible hydrocolloid impressions were appropriately mounted in an articulator. A diagnostic wax-up was made to visualize the anatomic and prosthetic outcomes. A combination surgical and radiographic guide was fabricated from a cast of the diagnostic wax-up. The cast with the guide was mounted on the base of a parallelometer (Artiglio Mickey 90; Base REP, Milan, Italy). The parallelometer was used to identify the projected long axis of the teeth to be replaced by the implants. Two 4-mm holes, one for each of the teeth to be replaced, were drilled into the guide following their projected long axis. The holes were filled with a gutta-percha radiopaque material (Inline; BM Dentale, Torino, Italy). The guide was 124
Fig. 4. Centrascan guide during CT scan.
mounted on the intraoral fork of the Centrascan (Figs. 1 and 2). The angle of the long axis of the teeth to be replaced was then transferred to the extraoral arch (Fig. 3). The system was locked in this set position by applying autopolymerizing resin into the fork/arch joint. The patient was then sent to the radiology laboratory, where VOLUME 89 NUMBER 2
VARVARA ET AL
THE JOURNAL OF PROSTHETIC DENTISTRY
Fig. 5. Details of CT panoramic images obtained by aligning patient’s head. A, Conventional procedure, in which scanning plane coincided with inferior mandibular border. B, Centrascan parameters, in which scanning plane was perpendicular to axis of teeth to be replaced. Gutta-percha radiopaque material references are indicated (arrows).
Fig. 6. Details of CT cross-sectional images obtained by aligning patient’s head. A, Conventional procedure, in which scanning plane coincided with inferior mandibular border. B, Centrascan parameters, in which scanning plane was perpendicular to axis of teeth to be replaced. Gutta-percha radiopaque material references are indicated (arrows).
the radiologist obtained 2 CT scans of the area of interest: one by the conventional procedure10,11,13 and the other by use of the Centrascan guide (Fig. 4). These scans were both processed by means of DentaScan software (General Electric, Milwaukee, Wis.). FEBRUARY 2003
The CT images obtained from the 2 different scans are shown in Figure 5 and 6. These images show differences according to the scanning plane used by the radiologist. The bone dimensions and the distance of anatomic structures from the alveolar ridge are visually 125
THE JOURNAL OF PROSTHETIC DENTISTRY
different between the 2 scans, demonstrating that the direction of the scanning plane affected the resulting images. In the cross-sectional images obtained by the standard imaging protocol (Fig. 6, A), an altered morphology of the teeth and the gutta-percha radiopaque material references (arrows) included in the scanned areas can be seen. This is probably a result of the inappropriate direction of the scan, which appears to have also caused a distortion in the image. Conversely, the same images obtained by the Centrascan procedure (Figs. 5, B, and 6, B) show more detailed morphology of both the examined area and gutta-percha radiopaque material references (arrows), as the scans were performed following the long axis of the teeth to be replaced.
SUMMARY To derive accurate information from CT scans, all potential distortion factors must be avoided and correct alignment of the patient’s head with the x-ray source is essential. This clinical report describes the Centrascan device, which allows the generation of more precise CT scans through the adjustment of the axial images at right angles to the long axis of the proposed implant position. We wish to thank Dr Christopher P. Berrie for his excellent critical appraisal of the text.
REFERENCES 1. Weinberg LA. CT scan as a radiologic data base for optimum implant orientation. J Prosthet Dent 1993;69:381-5. 2. Lindh C, Petersson A, Klinge B. Visualisation of the mandibular canal by different radiographic techniques. Clin Oral Implants Res 1992;3:90-7. 3. Ekestubbe A, Grondahl K, Grondahl HG. The use of tomography for dental implant planning. Dentomaxillofac Radiol 1997;26:206-13.
VARVARA ET AL
4. Kircos LT, Misch CE. Diagnostic imaging and techniques. In: Misch CA, editor. Contemporary implant dentistry. 2nd ed. St. Louis: Mosby; 1999. p. 73-87. 5. Tyndall AA, Brooks SL. Selection criteria for dental implant site imaging: a position paper of the American Academy of Oral and Maxillofacial radiology. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89: 630-7. 6. Frederiksen NL. Diagnostic imaging in dental implantology. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1995;80:540-54. 7. Schwarz MS, Rothman SL, Rhodes ML, Chafetz N. Computed tomography. Part I. Preoperative assessment of the mandible for endosseous implant surgery. Int J Oral Maxillofac Implants 1987;2:137-41. 8. Verstreken K, Van Cleynenbreugel J, Marchal G, Naert I, Suetens P, van Steenberghe D. Computer-assisted planning of oral implant surgery: a three-dimensional approach. Int J Oral Maxillofacial Implants 1996;11: 806-10. 9. Kohavi D, Bar-Ziv J, Marmary Y. Effect of axial plane deviation on crosssectional height in reformatted computed tomography of the mandible. Dentomaxillofac Radiol 1997;26:189-91. 10. Abrahams JJ. The role of diagnostic imaging in dental implantology. Radiol Clin North Am 1993;31:163-80. 11. Smith JP, Borrow JW. Reformatted CT images for implant planning. Oral Maxillofac Surg Clin North Am 1991;3:805-25. 12. Ferrario VF, Sforza C, Poggio CE, Serrao G, Colombo A. Three-dimensional dental arch curvature in human adolescents and adults. Am J Orthod Dentofacial Orthop 1999;115:401-5. 13. Schwarz MS, Rothman SL, Chafetz N, Rhodes M. Computed tomography in dental implantation surgery. Dent Clin North Am 1989;33:555-97. 14. Misch CE. Medical evaluation of the implant patient. In: Misch CA, editor. Contemporary implant dentistry. 2nd ed. St. Louis: Mosby; 1999. p. 33-72. Reprint requests to: DR GIUSEPPE VARVARA DIPARTIMENTO DI SCIENZE ODONTOSTOMATOLOGICHE UNIVERSITA DI CHIETI, VIA DEI VESTINI 31 66100 CHIETI ITALY FAX: 0039-0871-3554072 E-MAIL: [email protected] Copyright © 2003 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2003/$30.00 ⫹ 0 doi:10.1067/mpr.2002.83
Availability of JOURNAL Back Issues As a service to our subscribers, copies of back issues of The Journal of Prosthetic Dentistry for the preceding 5 years are maintained and are available for purchase from the publisher, Mosby, until inventory is depleted. Please write to Mosby, Subscription Customer Service, 6277 Sea Harbor Dr, Orlando, FL 32887, or call 800-654-2452 or 407-345-4000 for information on availability of particular issues and prices.
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A
ccomplishing predictable reconstruction and esthetics for single- or multiple-tooth dental implants is challenging. The long-term success of osseointegrated dental implants is influenced by several factors, including the length and alignment of the implant, as well as the bone anatomy of the implant site.1 Dental implant treatment often requires a combination of several radiologic techniques to correctly evaluate the anatomic morphology, including the bone width, the presence and amount of cortical bone on the ridge crest, and the degree of mineralization of the trabecular bone.2 The preferred position and orientation of each implant, its optimal length and diameter, and its position or relationship to the vital structures at the proposed implant sites are also determined by radiologic evaluation.3 Several imaging modalities have been used in implant imaging, such as periapical, panoramic, occlusal, cephalometric, and tomographic radiography; computed tomography (CT); and magnetic resonance imaging.4 In implant dentistry, the CT technique has been reported to be superior to other radiographic techniques.3,5 CT allows the evaluation of proposed implant sites and provides diagnostic information that other techniques or combinations of techniques cannot.4 In preoperative implant imaging, the CT scan should provide all necessary surgical and prosthetic orientation information, including the quantity and quality of bone, the desired angulation of the implant(s), and the relaa
Professor, Department of Odontostomatology Sciences. Professor, Department of Odontostomatology Sciences. c Professor, Department of Odontostomatology Sciences. d Research Fellow, Department of Odontostomatology Sciences. e Professor and Chairman, Department of Odontostomatology Sciences.
tionship of vital structures to the prospective implant in its terminal position.2 To obtain reliable information from the CT scan, all distortion factors must be avoided. To accomplish the desired outcome, correct alignment of the patient’s head with the x-ray source is essential.4,6,7 However, the reformatted axial images may lead to dimensional errors due to inclination of the scanning plane.8,9 In the conventional procedure, along the frontal plane, the radiologist refers to the sagittal axis of the face through the perpendicular to the Frankfort plane.10,11 The axes of the teeth coincide with the sagittal axis of the face only at the central incisors, whereas the other teeth are placed along the curve of Wilson.12 Along the sagittal plane, the radiologist refers to the cortical bone of the hard palate for the maxillary arch and the lower mandibular line for the mandibular arch.10,13 However, in this plane the long axes of the teeth are placed along the curve of Spee.12 The scanning plane should be perpendicular to the long axis of the implant position in both the frontal and sagittal planes. To obtain this positioning, the patient’s head should be aligned at right angles to the long axis of the proposed implant position, following the curves of Wilson and Spee (as compensating curve) of the teeth that are being replaced.12 This clinical report describes the Centrascan (Anthos, Imola, Italy), a device that serves to help the radiologist obtain the desired alignment of the patient’s head to the long axis of the proposed implant during the scanning procedure.
b
FEBRUARY 2003
CLINICAL REPORT A patient was examined to assess suitability for the placement of 2 implants to replace the first and second THE JOURNAL OF PROSTHETIC DENTISTRY 123
THE JOURNAL OF PROSTHETIC DENTISTRY
VARVARA ET AL
Fig. 1. Guide with holes filled with gutta-percha radiopaque material (arrows), connected to intraoral fork (IOF).
Fig. 3A. Transfer of the long axis of teeth to be replaced was achieved by tipping extraoral arch (EOA) along axis of teeth to be replaced until parallelometer (P) angle coincided with vertical reference of Centrascan fork (arrow).
Fig. 2. Centrascan device demonstrating intraoral fork (IOF) with support surface that connects it to extraoral arch (EOA), which includes extremities to orientate it in space, and adjustable joint (J) to allow necessary orientation of extraoral arch to fork.
Fig. 3B. Lateral extremity present on extraoral arch (arrow).
right mandibular premolars. The patient was free from signs or symptoms of stomatognathic system dysfunction and other general illnesses that would preclude implant placement.14 Stone casts obtained from irreversible hydrocolloid impressions were appropriately mounted in an articulator. A diagnostic wax-up was made to visualize the anatomic and prosthetic outcomes. A combination surgical and radiographic guide was fabricated from a cast of the diagnostic wax-up. The cast with the guide was mounted on the base of a parallelometer (Artiglio Mickey 90; Base REP, Milan, Italy). The parallelometer was used to identify the projected long axis of the teeth to be replaced by the implants. Two 4-mm holes, one for each of the teeth to be replaced, were drilled into the guide following their projected long axis. The holes were filled with a gutta-percha radiopaque material (Inline; BM Dentale, Torino, Italy). The guide was 124
Fig. 4. Centrascan guide during CT scan.
mounted on the intraoral fork of the Centrascan (Figs. 1 and 2). The angle of the long axis of the teeth to be replaced was then transferred to the extraoral arch (Fig. 3). The system was locked in this set position by applying autopolymerizing resin into the fork/arch joint. The patient was then sent to the radiology laboratory, where VOLUME 89 NUMBER 2
VARVARA ET AL
THE JOURNAL OF PROSTHETIC DENTISTRY
Fig. 5. Details of CT panoramic images obtained by aligning patient’s head. A, Conventional procedure, in which scanning plane coincided with inferior mandibular border. B, Centrascan parameters, in which scanning plane was perpendicular to axis of teeth to be replaced. Gutta-percha radiopaque material references are indicated (arrows).
Fig. 6. Details of CT cross-sectional images obtained by aligning patient’s head. A, Conventional procedure, in which scanning plane coincided with inferior mandibular border. B, Centrascan parameters, in which scanning plane was perpendicular to axis of teeth to be replaced. Gutta-percha radiopaque material references are indicated (arrows).
the radiologist obtained 2 CT scans of the area of interest: one by the conventional procedure10,11,13 and the other by use of the Centrascan guide (Fig. 4). These scans were both processed by means of DentaScan software (General Electric, Milwaukee, Wis.). FEBRUARY 2003
The CT images obtained from the 2 different scans are shown in Figure 5 and 6. These images show differences according to the scanning plane used by the radiologist. The bone dimensions and the distance of anatomic structures from the alveolar ridge are visually 125
THE JOURNAL OF PROSTHETIC DENTISTRY
different between the 2 scans, demonstrating that the direction of the scanning plane affected the resulting images. In the cross-sectional images obtained by the standard imaging protocol (Fig. 6, A), an altered morphology of the teeth and the gutta-percha radiopaque material references (arrows) included in the scanned areas can be seen. This is probably a result of the inappropriate direction of the scan, which appears to have also caused a distortion in the image. Conversely, the same images obtained by the Centrascan procedure (Figs. 5, B, and 6, B) show more detailed morphology of both the examined area and gutta-percha radiopaque material references (arrows), as the scans were performed following the long axis of the teeth to be replaced.
SUMMARY To derive accurate information from CT scans, all potential distortion factors must be avoided and correct alignment of the patient’s head with the x-ray source is essential. This clinical report describes the Centrascan device, which allows the generation of more precise CT scans through the adjustment of the axial images at right angles to the long axis of the proposed implant position. We wish to thank Dr Christopher P. Berrie for his excellent critical appraisal of the text.
REFERENCES 1. Weinberg LA. CT scan as a radiologic data base for optimum implant orientation. J Prosthet Dent 1993;69:381-5. 2. Lindh C, Petersson A, Klinge B. Visualisation of the mandibular canal by different radiographic techniques. Clin Oral Implants Res 1992;3:90-7. 3. Ekestubbe A, Grondahl K, Grondahl HG. The use of tomography for dental implant planning. Dentomaxillofac Radiol 1997;26:206-13.
VARVARA ET AL
4. Kircos LT, Misch CE. Diagnostic imaging and techniques. In: Misch CA, editor. Contemporary implant dentistry. 2nd ed. St. Louis: Mosby; 1999. p. 73-87. 5. Tyndall AA, Brooks SL. Selection criteria for dental implant site imaging: a position paper of the American Academy of Oral and Maxillofacial radiology. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89: 630-7. 6. Frederiksen NL. Diagnostic imaging in dental implantology. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1995;80:540-54. 7. Schwarz MS, Rothman SL, Rhodes ML, Chafetz N. Computed tomography. Part I. Preoperative assessment of the mandible for endosseous implant surgery. Int J Oral Maxillofac Implants 1987;2:137-41. 8. Verstreken K, Van Cleynenbreugel J, Marchal G, Naert I, Suetens P, van Steenberghe D. Computer-assisted planning of oral implant surgery: a three-dimensional approach. Int J Oral Maxillofacial Implants 1996;11: 806-10. 9. Kohavi D, Bar-Ziv J, Marmary Y. Effect of axial plane deviation on crosssectional height in reformatted computed tomography of the mandible. Dentomaxillofac Radiol 1997;26:189-91. 10. Abrahams JJ. The role of diagnostic imaging in dental implantology. Radiol Clin North Am 1993;31:163-80. 11. Smith JP, Borrow JW. Reformatted CT images for implant planning. Oral Maxillofac Surg Clin North Am 1991;3:805-25. 12. Ferrario VF, Sforza C, Poggio CE, Serrao G, Colombo A. Three-dimensional dental arch curvature in human adolescents and adults. Am J Orthod Dentofacial Orthop 1999;115:401-5. 13. Schwarz MS, Rothman SL, Chafetz N, Rhodes M. Computed tomography in dental implantation surgery. Dent Clin North Am 1989;33:555-97. 14. Misch CE. Medical evaluation of the implant patient. In: Misch CA, editor. Contemporary implant dentistry. 2nd ed. St. Louis: Mosby; 1999. p. 33-72. Reprint requests to: DR GIUSEPPE VARVARA DIPARTIMENTO DI SCIENZE ODONTOSTOMATOLOGICHE UNIVERSITA DI CHIETI, VIA DEI VESTINI 31 66100 CHIETI ITALY FAX: 0039-0871-3554072 E-MAIL: [email protected] Copyright © 2003 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2003/$30.00 ⫹ 0 doi:10.1067/mpr.2002.83
Availability of JOURNAL Back Issues As a service to our subscribers, copies of back issues of The Journal of Prosthetic Dentistry for the preceding 5 years are maintained and are available for purchase from the publisher, Mosby, until inventory is depleted. Please write to Mosby, Subscription Customer Service, 6277 Sea Harbor Dr, Orlando, FL 32887, or call 800-654-2452 or 407-345-4000 for information on availability of particular issues and prices.
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