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CAM technology
Fabrication of an all-ceramic abutment crown under an existing removable partial denture using CAD/CAM technology Baldwin W. Marchack, DDS,a Linda B. Chen, DDS,b Christopher B. Marchack, DDS,c and Yukiko Futatsuki, CDTd University of Southern California School of Dentistry, Los Angeles, Calif Fabricating a crown beneath an existing removable partial denture is technique sensitive, difficult, and time consuming. A procedure is described using CAD/CAM technology to fabricate an all-ceramic crown under an existing removable partial denture that is simple, esthetic, and convenient for the patient and the clinician.(J Prosthet Dent 2007;98:478-482) The fabrication of a crown to restore an abutment for an existing removable partial denture (RPD) is a complicated procedure. The literature is replete with various direct and indirect techniques attempting to simplify the process. Direct techniques involve fabrication of an acrylic resin pattern intraorally,1,2 while indirect techniques involve a transfer impression of the framework and preparation.3,4 The latter procedure requires that the patient surrender the removable partial denture for the laboratory process. Other variations and combinations of indirect and direct procedures have also been described.3,5-14 Limitations are encountered with both direct and indirect techniques in the attempt to replicate ideal contours, rest seats, guiding planes, and undercuts of the abutment crown.15 The purpose of this article is to describe an alternative direct technique to produce a restoration with improved adaptation to the existing framework compared to a conventional metal ceramic restoration, using a CAD/CAM system (Procera; Nobel Biocare, Yorba Linda, Calif ).16 This technique uses a
computer-assisted design/computerassisted manufacturing (CAD/CAM) system to produce an all-ceramic crown. The crown consists of a zirconium-oxide coping combined with the appropriate veneering porcelain.
TECHNIQUE 1. Evaluate the existing RPD and the abutment tooth to ensure that both are functional and have a good prognosis. 2. Prepare the abutment tooth for the all-ceramic crown with a deep
chamfer or rounded shoulder, rounded line angles, and adequate reduction (Fig. 1). 3. Reseat the RPD framework intraorally to ensure adequate clearance for the crown and stability of the framework (Figs. 2 and 3). 4. Make an elastomeric definitive impression of the preparation and entire arch with polyether (Impregum; 3M ESPE, St. Paul, Minn). 5. With the framework in place, add a bis-GMA composite resin provisional restoration material (Protemp; 3M ESPE) to the abutment tooth
1 Occlusal view of prepared abutment for existing RPD.
Adjunct Clinical Professor, University of Southern California School of Dentistry. Clinical Assistant Professor, University of Southern California School of Dentistry. c Associate Professor, University of Southern California School of Dentistry. d Laboratory Technician, Pasadena, Calif. a
b
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2 RPD framework evaluated intraorally to ensure adequate reduction for all-ceramic restoration, occlusal view.
3 RPD framework evaluated intraorally to ensure adequate reduction for all-ceramic restoration, buccal view.
4 Bis-GMA restorative material placed under framework to fabricate composite resin coping on abutment.
5 Rest seat, guiding plane, and retentive undercut captured in composite resin coping.
underneath the framework. As the restorative material is added, ensure that the retentive area, guiding plane, and rest seat are registered in the coping. Wipe any excess material from the outer surface of the RPD framework before it polymerizes (Figs. 4 and 5). 6. Remove the composite resin pattern from the tooth preparation and removable partial denture. Trim the excess composite resin material and ensure that the rest seat, retentive area, and guiding plane are registered. Set aside the composite resin coping for the following laboratory procedures. 7. Fabricate the provisional restoration with the matrix of the unprepared tooth. 8. Lute the provisional restoration to the prepared tooth and return the RPD to the patient.
Marchack et al
9. In the laboratory, fabricate the working cast and trim the abutment die. 10. Using a digital scanner (Procera Forte; Nobel Biocare), scan the die first without the composite resin pattern to produce the digitized die (Fig. 6). 11. Cut back the composite resin coping in the areas where the veneering porcelain is desired, leaving the rest seat, guiding plane, and retentive undercut intact, similar to the cutback procedure for a metal ceramic crown (Fig. 7). 12. Place the composite resin coping on the die to ensure proper seating. 13. Reduce the margins of the composite resin pattern by 1-2 mm and recreate them in wax (Sculpturing wax, grey; YETI Dentalprodukte
GmbH, Engen, Germany). 14. Complete a second scan for a dual-scan procedure with the pattern secured to the die (Figs. 8 through 10). 15. Merge the computer data with information for the die and the crown coping and transmit it to the milling facility (Procera Production; Nobel Biocare) to manufacture the zirconium-oxide coping (Fig. 11). 16. Evaluate the coping intraorally to verify fit of the occlusal rest, distal guiding plane, proper contact of the buccal clasp, and sufficient occlusal clearance for the veneering porcelain (Figs. 12 through 14). 17. Apply veneering porcelain (Nobel Rondo; Nobel Biocare) to the coping in the cut-back areas (Figs. 15 and 16). 18. Evaluate the definitive restora-
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6 Image of digitized die after being scanned.
8 Image of digitized coping after being scanned by CAD/CAM system, highlighting buccal undercut.
10 Image of digitized coping after being scanned by CAD/CAM system, highlighting the distal guiding plane.
The Journal of Prosthetic Dentistry
7 Cut back prepared in composite resin coping to create adequate space for veneering porcelain. Notice that retentive undercut, guiding plane, and rest seat are untouched.
9 Image of digitized coping after being scanned by CAD/CAM system, highlighting mesial occlusal rest.
11 Completed zirconium-oxide coping.
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12 Coping evaluated on abutment tooth. RPD is evaluated to verify fit, occlusal view.
13 Coping evaluated on abutment tooth. RPD is evaluated to verify fit, buccal view.
14 Demonstration of adequate clearance for veneering porcelain on occlusal surface.
15 Occlusal view of crown with veneering porcelain applied.
16 Buccal view of crown with veneering porcelain applied.
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17 Framework with definitive restoration, buccal view. tion intraorally to verify the occlusal contacts, marginal adaptation, and fit to the RPD framework (Figs. 17 and 18). 19. Lute the all-ceramic crown using a conventional cement (Panavia F2.0; Kuraray America Inc, New York, NY).
DISCUSSION The application of CAD/CAM technology to fabricate a complete coverage crown beneath an existing removable partial denture is described. The advantages of this procedure include ease in replicating guiding planes, rest seats, and retentive undercuts with accuracy. The procedure allows the patient to keep the existing removable partial denture and is, therefore, more convenient for the patient as well as the clinician. The accuracy of the scanning technique allows for precise replication of the coping without the need to polish the porcelain surface, therefore reducing the possibility of overpolishing the coping as compared to metal copings. One potential limitation of the technique is the unknown wear caused by the removable partial denture metal framework where it contacts the ceramic coping. Another disadvantage is the contrast in color of the zirconium-oxide coping in comparison to
18 Framework with definitive restoration, occlusal view.
the veneering porcelain color. A third disadvantage could be an error in the fabrication of the composite resin coping, such as improper placement of the coping, resulting in poor fit of the removable partial denture.
SUMMARY The fabrication of an abutment crown using CAD/CAM technology enables the clinician to precisely replicate the contours of the existing abutment tooth, ensuring excellent adaptation to the existing removable partial denture framework, with minimal adjustment. Using this technique, the retentive areas, guiding planes, and rest seats are precisely reproduced in zirconium oxide.
REFERENCES 1. Hansen CA, Russell MM. Making a crown to fit accurately under an existing removable partial denture clasp assembly. J Prosthet Dent 1994:71;2:206-8. 2. Macpherson JR, Evans DB. Fabricating crowns to fit existing removable partial dentures: an illustration of two techniques. J Prosthodont 1993:2:199-205. 3. Jackson AD, Butler CJ. Fabrication of a new crown and provisional to an existing removable partial denture. J Prosthodont 1995:4:3:200-4. 4. Elledge DA, Schorr BL. A provisional and new crown to fit into a clasp of an existing removable partial denture. J Prosthet Dent 1990:63:541-4. 5. Gavelis JR. Fabricating crowns to fit claspbearing abutment teeth. J Prosthet Dent 1981:46:673-5.
6. Tran CD, Sherraden DR, Curtis TA. A review of techniques of crown fabrication for existing removable partial dentures. J Prosthet Dent 1986:55:671-3. 7. Lubovich RP, Peterson T. The fabrication of a ceramic-metal crown to fit an existing removable partial denture clasp. J Prosthet Dent 1977:37:610-4. 8. Hill GM. Construction of a crown to fit a removable partial denture clasp. J Prosthet Dent 1977:38:226-8. 9. Helvey GA. Retrofitting crowns to an existing removable partial denture clasp: a simple technique. J Prosthet Dent 2002:87:399-402. 10.Goldberg AT, Jones RD. Constructing cast crowns to fit existing removable partial denture clasps. J Prosthet Dent 1976:36:382-6. 11.Sigaroudi K. Restoring abutment teeth with cast restorations to fit existing removable partial dentures. J Prosthet Dent 1985:53:628-31. 12.Burns DR, Unger JW. The construction of crowns for removable partial denture abutment teeth. Quintessence Int 1994:25:4715. 13.Diaz-Arnold AM, Langenwalter EM, Hatch LK. Cast restorations made to existing removable partial dentures. J Prosthet Dent 1989:61:414-7. 14.Silberman DM. An indirect procedure for making a crown under an existing partial denture. J Prosthet Dent 1993:69;6:631-3. 15.Warnick ME. Cast crown restoration of a badly involved abutment to fit an existing removable partial denture. Dent Clin North Am 1970:14;3:631-44. 16.Kancyper S, Sierraalta M, Razzoog ME. All-ceramic surveyed crowns for removable partial denture abutments. J Prosthet Dent 2000:84:400-2. Corresponding author: Dr Baldwin Marchack 301 South Fair Oaks Ave, # 408 Pasadena, CA 91105 Fax: 626-793-8777 E-mail: [email protected] Copyright © 2007 by the Editorial Council for The Journal of Prosthetic Dentistry.
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computer-assisted design/computerassisted manufacturing (CAD/CAM) system to produce an all-ceramic crown. The crown consists of a zirconium-oxide coping combined with the appropriate veneering porcelain.
TECHNIQUE 1. Evaluate the existing RPD and the abutment tooth to ensure that both are functional and have a good prognosis. 2. Prepare the abutment tooth for the all-ceramic crown with a deep
chamfer or rounded shoulder, rounded line angles, and adequate reduction (Fig. 1). 3. Reseat the RPD framework intraorally to ensure adequate clearance for the crown and stability of the framework (Figs. 2 and 3). 4. Make an elastomeric definitive impression of the preparation and entire arch with polyether (Impregum; 3M ESPE, St. Paul, Minn). 5. With the framework in place, add a bis-GMA composite resin provisional restoration material (Protemp; 3M ESPE) to the abutment tooth
1 Occlusal view of prepared abutment for existing RPD.
Adjunct Clinical Professor, University of Southern California School of Dentistry. Clinical Assistant Professor, University of Southern California School of Dentistry. c Associate Professor, University of Southern California School of Dentistry. d Laboratory Technician, Pasadena, Calif. a
b
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2 RPD framework evaluated intraorally to ensure adequate reduction for all-ceramic restoration, occlusal view.
3 RPD framework evaluated intraorally to ensure adequate reduction for all-ceramic restoration, buccal view.
4 Bis-GMA restorative material placed under framework to fabricate composite resin coping on abutment.
5 Rest seat, guiding plane, and retentive undercut captured in composite resin coping.
underneath the framework. As the restorative material is added, ensure that the retentive area, guiding plane, and rest seat are registered in the coping. Wipe any excess material from the outer surface of the RPD framework before it polymerizes (Figs. 4 and 5). 6. Remove the composite resin pattern from the tooth preparation and removable partial denture. Trim the excess composite resin material and ensure that the rest seat, retentive area, and guiding plane are registered. Set aside the composite resin coping for the following laboratory procedures. 7. Fabricate the provisional restoration with the matrix of the unprepared tooth. 8. Lute the provisional restoration to the prepared tooth and return the RPD to the patient.
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9. In the laboratory, fabricate the working cast and trim the abutment die. 10. Using a digital scanner (Procera Forte; Nobel Biocare), scan the die first without the composite resin pattern to produce the digitized die (Fig. 6). 11. Cut back the composite resin coping in the areas where the veneering porcelain is desired, leaving the rest seat, guiding plane, and retentive undercut intact, similar to the cutback procedure for a metal ceramic crown (Fig. 7). 12. Place the composite resin coping on the die to ensure proper seating. 13. Reduce the margins of the composite resin pattern by 1-2 mm and recreate them in wax (Sculpturing wax, grey; YETI Dentalprodukte
GmbH, Engen, Germany). 14. Complete a second scan for a dual-scan procedure with the pattern secured to the die (Figs. 8 through 10). 15. Merge the computer data with information for the die and the crown coping and transmit it to the milling facility (Procera Production; Nobel Biocare) to manufacture the zirconium-oxide coping (Fig. 11). 16. Evaluate the coping intraorally to verify fit of the occlusal rest, distal guiding plane, proper contact of the buccal clasp, and sufficient occlusal clearance for the veneering porcelain (Figs. 12 through 14). 17. Apply veneering porcelain (Nobel Rondo; Nobel Biocare) to the coping in the cut-back areas (Figs. 15 and 16). 18. Evaluate the definitive restora-
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6 Image of digitized die after being scanned.
8 Image of digitized coping after being scanned by CAD/CAM system, highlighting buccal undercut.
10 Image of digitized coping after being scanned by CAD/CAM system, highlighting the distal guiding plane.
The Journal of Prosthetic Dentistry
7 Cut back prepared in composite resin coping to create adequate space for veneering porcelain. Notice that retentive undercut, guiding plane, and rest seat are untouched.
9 Image of digitized coping after being scanned by CAD/CAM system, highlighting mesial occlusal rest.
11 Completed zirconium-oxide coping.
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12 Coping evaluated on abutment tooth. RPD is evaluated to verify fit, occlusal view.
13 Coping evaluated on abutment tooth. RPD is evaluated to verify fit, buccal view.
14 Demonstration of adequate clearance for veneering porcelain on occlusal surface.
15 Occlusal view of crown with veneering porcelain applied.
16 Buccal view of crown with veneering porcelain applied.
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17 Framework with definitive restoration, buccal view. tion intraorally to verify the occlusal contacts, marginal adaptation, and fit to the RPD framework (Figs. 17 and 18). 19. Lute the all-ceramic crown using a conventional cement (Panavia F2.0; Kuraray America Inc, New York, NY).
DISCUSSION The application of CAD/CAM technology to fabricate a complete coverage crown beneath an existing removable partial denture is described. The advantages of this procedure include ease in replicating guiding planes, rest seats, and retentive undercuts with accuracy. The procedure allows the patient to keep the existing removable partial denture and is, therefore, more convenient for the patient as well as the clinician. The accuracy of the scanning technique allows for precise replication of the coping without the need to polish the porcelain surface, therefore reducing the possibility of overpolishing the coping as compared to metal copings. One potential limitation of the technique is the unknown wear caused by the removable partial denture metal framework where it contacts the ceramic coping. Another disadvantage is the contrast in color of the zirconium-oxide coping in comparison to
18 Framework with definitive restoration, occlusal view.
the veneering porcelain color. A third disadvantage could be an error in the fabrication of the composite resin coping, such as improper placement of the coping, resulting in poor fit of the removable partial denture.
SUMMARY The fabrication of an abutment crown using CAD/CAM technology enables the clinician to precisely replicate the contours of the existing abutment tooth, ensuring excellent adaptation to the existing removable partial denture framework, with minimal adjustment. Using this technique, the retentive areas, guiding planes, and rest seats are precisely reproduced in zirconium oxide.
REFERENCES 1. Hansen CA, Russell MM. Making a crown to fit accurately under an existing removable partial denture clasp assembly. J Prosthet Dent 1994:71;2:206-8. 2. Macpherson JR, Evans DB. Fabricating crowns to fit existing removable partial dentures: an illustration of two techniques. J Prosthodont 1993:2:199-205. 3. Jackson AD, Butler CJ. Fabrication of a new crown and provisional to an existing removable partial denture. J Prosthodont 1995:4:3:200-4. 4. Elledge DA, Schorr BL. A provisional and new crown to fit into a clasp of an existing removable partial denture. J Prosthet Dent 1990:63:541-4. 5. Gavelis JR. Fabricating crowns to fit claspbearing abutment teeth. J Prosthet Dent 1981:46:673-5.
6. Tran CD, Sherraden DR, Curtis TA. A review of techniques of crown fabrication for existing removable partial dentures. J Prosthet Dent 1986:55:671-3. 7. Lubovich RP, Peterson T. The fabrication of a ceramic-metal crown to fit an existing removable partial denture clasp. J Prosthet Dent 1977:37:610-4. 8. Hill GM. Construction of a crown to fit a removable partial denture clasp. J Prosthet Dent 1977:38:226-8. 9. Helvey GA. Retrofitting crowns to an existing removable partial denture clasp: a simple technique. J Prosthet Dent 2002:87:399-402. 10.Goldberg AT, Jones RD. Constructing cast crowns to fit existing removable partial denture clasps. J Prosthet Dent 1976:36:382-6. 11.Sigaroudi K. Restoring abutment teeth with cast restorations to fit existing removable partial dentures. J Prosthet Dent 1985:53:628-31. 12.Burns DR, Unger JW. The construction of crowns for removable partial denture abutment teeth. Quintessence Int 1994:25:4715. 13.Diaz-Arnold AM, Langenwalter EM, Hatch LK. Cast restorations made to existing removable partial dentures. J Prosthet Dent 1989:61:414-7. 14.Silberman DM. An indirect procedure for making a crown under an existing partial denture. J Prosthet Dent 1993:69;6:631-3. 15.Warnick ME. Cast crown restoration of a badly involved abutment to fit an existing removable partial denture. Dent Clin North Am 1970:14;3:631-44. 16.Kancyper S, Sierraalta M, Razzoog ME. All-ceramic surveyed crowns for removable partial denture abutments. J Prosthet Dent 2000:84:400-2. Corresponding author: Dr Baldwin Marchack 301 South Fair Oaks Ave, # 408 Pasadena, CA 91105 Fax: 626-793-8777 E-mail: [email protected] Copyright © 2007 by the Editorial Council for The Journal of Prosthetic Dentistry.
The Journal of Prosthetic Dentistry
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