- Email: [email protected]
Expediting the fabrication of a nickel-chromium casting
WOLFAARDT,
CLEATON-JONIS
AND
FA ITI
tions. It would also seem that previous attempts to relate void size to the mechanism of generation of porosity did not always provide a suitably precise and constant relationship. The results of this study showed that it is seldom possible to isolate a single causative factor responsible for the generation of porosity in poly (methyl methacrylate) on the basis of void shape, size, concentration, and position, as had been done so often in the literature reviewed. The generation of porosity in poly (methyl methacrylate) denture base resin is apparently a complex phenomenon with a multifactorial origin. REFERENCES I. 2. \. 3.
i
0
Donald R. Nelson, D.D.S.,* Martin C. Cornella, D.M.D.,** and Marcus N. Williams****
Ann Sue van Go&en, D.DS.,***
University of North Carolina, School of Dentistry, Chapel Hill, N.C., and U.S. Army Area Dental Laboratory, Fort Sam Houston, Tex
N
umerous clinical situations require a minimum turnaround time in the laboratory for fabrication of removable partial denture frameworks as well as vari-
ous types of surgical splints. The management of trauma and orthognathic surgery patients often necessitates the prompt fabrication of high quality prostheses and appliances invohing base metal fxsbgs. This article describes technique variatAs that significantly shorten by at least 50% the working time required to produce a high quality x$ckci-Mum (Ticonium 100, Timnium Co., CMF k&u&es, Albany, N.Y.) casting. B--w 1. Transfer the design to the master east. 2. Blockout and relieve the master cast.’ 3. Rehydrate the master cast prior to duplication with MARCH
1986
VOLUME
55
KUMBER
3
EXPEDITING
NICKEL-CHROME
CASTING
FABRICATION
Fig. 1. Desiccator approximately half full of water. Overfilling jar will result in water being drawn into vacuum source. Note: Top part of desiccator with glass spout is adjustable.
Fig. 3. Vacuum source connected to desiccator.
Fig. 2. Cast inverted in desiccator to preclude displacement of blockout and relief wax. Air vent and tubing connection (arrow) are aligned prior to engagement of the vacuum source. reversible hydrocolloid impression material. Rehydration is normally accomplished by placing the master cast in tepid slurry water for 20 to 30 minutes.1.2 The time required to rehydrate the master cast is reduced considerably with the use of a vacuum source (Vat-U-Vestor, Whip-Mix, Louisville, Ky.) and a 250 mm Pyrex desiccator (Corning Glass Works, Corning, N.Y.) (Fig. 1). 4. Place the cast base up in the desiccator (Fig. 2). Inverting the cast resists dislodgment of blockout and THE JOURNAL
OF PROSTHETIC
DENTISTRY
relief wax when the vacuum is engaged. Adjust the movable portion of the desiccator lid to ensure proper alignment of the air vent and tubing connection (Figs. 1 and 2). 5. Position the glass lid on the desiccator and attach the vacuum tubing. 6. Connect the desiccator to the vacuum source (Fig. 3). 7. Engage the vacuum (Fig. 4). Approximately 60 seconds are required to eliminate air and rehydrate the stone cast, which substantially reduces rehydration time. 8. Duplicate the rehydrated, blocked-out master cast with reversible hydrocolloid, and pour the refractory cast in Investic (Investic Investment, Ticonium Company, CMP Industries). 9. Recover the refractory cast from the reversible hydrocolloid and dry the surface with an air source. PREPARATION
OF REFRACTORY
CAST
Average drying time for a refractory cast is 1% hours in a 200” F oven.‘x4 Drying time can be decreased by using a microwave oven. Luebke and SchneideS compared the compressive strength of three gypsum products 401
NELSON
Fig. 4. Air being extracted
from stone cast to be replaced with slurry water.
Fig. 5. Cast placed on its heel in microwave
by using air, conventional oven, and microwave oven drying techniques. Investic had a similar compressive strength for the first 24 hours regardless of the drying technique used. Drying time of the refractory cast is reduced in the microwave oven as follows: 1. Place the refractory cast on its heel in a microwave oven and set the oven controls at normal heat for 1 minute (Fig. 5). 2. Remove the cast from the microwave oven, and hold it in a conventional drying oven (180 to 200” F) for 15 minutes.’ 3. Dip the cast in beeswax at 280” to 300” F.’ 4. Complete the framework wax-up.
402
ET AL
oven
INVESTING 1. Mix Investic according to the manufacturer’s recommendations.’ 2. Paint a uniform ‘%-inch thickness of Inwestic over the framework wax-up using a camel hair brush. 3. Invest the second half when the sheen is lost from the surface of the first investment layer. 4. Allow the investment to set approximately 1 hour prior to burning out. BURNOUT
AND
CASTING
Conventional burnout time is 2 to 3 hours from room temperature to 1350” F, plus a heat-so& period of 1 to 2 hours at 1350” F.’ The total burnout time can be as long
MARCH
1986
VOLUME
55
NUMBER
3
EXPEDITING
NICKEL-CHROME
CASTING
FABRICATION
as 5 hours. This can be substantially reduced by placing the invested waxed framework directly into an oven preheated to 1350“ F for 1 to 1% hours. Cast, finish, and polish the framework in the usual manner. REFERENCES
4.
Sowter B: Dental Laboratory Technology. Chapel Hill, NC, 1968, University of North Carolina, p 180. Terkla LG, Laney WR: Partial Dentures. ed 3. St. Louis, 1963, The CV Mosby Co, p 225. Luebke RJ, Schneider RL: Microwave drying of artilicial stone. J PROSTHET DENT 53:261, 1985.
Repmt rqur.rl\ lo.
1. Ticonium Technique Manual. Albany, NY, 1966, Ticonium Company, Division of CMP Industries, Inc., p 2. 2. Rudd KD, Morrow RM, Eissmann HF: Dental Laboratory Procedures. Vol III: Removable Partial Dentures. St. Louis, 198 1, The CV Moshy Co, p 203.
Light-activated overdentures
3.
DR. DONALD R. NELSON UNIVERSITV OF NORTH CAROLINA SCHOOL OF DENTISTRY CHAPEL HILL, NC 27514
composite-amalgam copings for
John Holt, D.M.D.,* Robert Todd, D.M.D.,** and Robert Quinn, D.M.D.*** Oregon Health Sciences University, School of Dentistry, Portland, Ore.
0
verdentures have become a standard mode of treatment for many dental patients, and many of these patients have progressed to this dental situation because of their high incidence of caries. The caries problem is not alleviated by the overdenture construction, and a continual recurrence of caries on the treated roots can be expected for many of these patients. Gold copings have been used extensively to reduce the incidence of.caries,’ however, they are relatively expensive and may not prevent caries at the margins. They also create a space problem in the esthetic placement of the denture teeth for some patients. Treatment of the exposed root portion of the retained teeth with fluoride and silver nitrate is effective in reducing caries incidence.2Recent improvements in the light-activated composites make this material a viable method of protecting exposed dentin. This article describes an alternate method of treatment that takes some of the beneficial features from both of these procedures.
TREATMENT PROCEDURES 1. Prepare the tooth by reducing the occlusal surface to the shape of a flattened dome extending to the crest of the gingival margin. *Professor, Department of Removable Prosthodontirs. **Assistant Professor, Department of Removable Prosthodontics. ***Associate Professor, Department of Operative Dentistry.
THE JOURNAL
OF PROSTHETIC
DENTISTRY
view, composite-amalgam overdenture tooth coping. A, Cementurn; B, composite; C, amalgam; D, retentive groove. Fig. 1. Top
2. Place a supplemental groove midway between the canal and the cementum margin (Fig. 1). An inverted cone bur (No. 33 or No. 35) of appropriate size is used for this purpose. The groove provides mechanical retention in addition to bonding of the composite to the dentin with a dentin bonding agent. 3. Treat the tooth with the bonding agent and restore it with a thin layer of light-activated composite (Scotch-
403
CLEATON-JONIS
AND
FA ITI
tions. It would also seem that previous attempts to relate void size to the mechanism of generation of porosity did not always provide a suitably precise and constant relationship. The results of this study showed that it is seldom possible to isolate a single causative factor responsible for the generation of porosity in poly (methyl methacrylate) on the basis of void shape, size, concentration, and position, as had been done so often in the literature reviewed. The generation of porosity in poly (methyl methacrylate) denture base resin is apparently a complex phenomenon with a multifactorial origin. REFERENCES I. 2. \. 3.
i
0
Donald R. Nelson, D.D.S.,* Martin C. Cornella, D.M.D.,** and Marcus N. Williams****
Ann Sue van Go&en, D.DS.,***
University of North Carolina, School of Dentistry, Chapel Hill, N.C., and U.S. Army Area Dental Laboratory, Fort Sam Houston, Tex
N
umerous clinical situations require a minimum turnaround time in the laboratory for fabrication of removable partial denture frameworks as well as vari-
ous types of surgical splints. The management of trauma and orthognathic surgery patients often necessitates the prompt fabrication of high quality prostheses and appliances invohing base metal fxsbgs. This article describes technique variatAs that significantly shorten by at least 50% the working time required to produce a high quality x$ckci-Mum (Ticonium 100, Timnium Co., CMF k&u&es, Albany, N.Y.) casting. B--w 1. Transfer the design to the master east. 2. Blockout and relieve the master cast.’ 3. Rehydrate the master cast prior to duplication with MARCH
1986
VOLUME
55
KUMBER
3
EXPEDITING
NICKEL-CHROME
CASTING
FABRICATION
Fig. 1. Desiccator approximately half full of water. Overfilling jar will result in water being drawn into vacuum source. Note: Top part of desiccator with glass spout is adjustable.
Fig. 3. Vacuum source connected to desiccator.
Fig. 2. Cast inverted in desiccator to preclude displacement of blockout and relief wax. Air vent and tubing connection (arrow) are aligned prior to engagement of the vacuum source. reversible hydrocolloid impression material. Rehydration is normally accomplished by placing the master cast in tepid slurry water for 20 to 30 minutes.1.2 The time required to rehydrate the master cast is reduced considerably with the use of a vacuum source (Vat-U-Vestor, Whip-Mix, Louisville, Ky.) and a 250 mm Pyrex desiccator (Corning Glass Works, Corning, N.Y.) (Fig. 1). 4. Place the cast base up in the desiccator (Fig. 2). Inverting the cast resists dislodgment of blockout and THE JOURNAL
OF PROSTHETIC
DENTISTRY
relief wax when the vacuum is engaged. Adjust the movable portion of the desiccator lid to ensure proper alignment of the air vent and tubing connection (Figs. 1 and 2). 5. Position the glass lid on the desiccator and attach the vacuum tubing. 6. Connect the desiccator to the vacuum source (Fig. 3). 7. Engage the vacuum (Fig. 4). Approximately 60 seconds are required to eliminate air and rehydrate the stone cast, which substantially reduces rehydration time. 8. Duplicate the rehydrated, blocked-out master cast with reversible hydrocolloid, and pour the refractory cast in Investic (Investic Investment, Ticonium Company, CMP Industries). 9. Recover the refractory cast from the reversible hydrocolloid and dry the surface with an air source. PREPARATION
OF REFRACTORY
CAST
Average drying time for a refractory cast is 1% hours in a 200” F oven.‘x4 Drying time can be decreased by using a microwave oven. Luebke and SchneideS compared the compressive strength of three gypsum products 401
NELSON
Fig. 4. Air being extracted
from stone cast to be replaced with slurry water.
Fig. 5. Cast placed on its heel in microwave
by using air, conventional oven, and microwave oven drying techniques. Investic had a similar compressive strength for the first 24 hours regardless of the drying technique used. Drying time of the refractory cast is reduced in the microwave oven as follows: 1. Place the refractory cast on its heel in a microwave oven and set the oven controls at normal heat for 1 minute (Fig. 5). 2. Remove the cast from the microwave oven, and hold it in a conventional drying oven (180 to 200” F) for 15 minutes.’ 3. Dip the cast in beeswax at 280” to 300” F.’ 4. Complete the framework wax-up.
402
ET AL
oven
INVESTING 1. Mix Investic according to the manufacturer’s recommendations.’ 2. Paint a uniform ‘%-inch thickness of Inwestic over the framework wax-up using a camel hair brush. 3. Invest the second half when the sheen is lost from the surface of the first investment layer. 4. Allow the investment to set approximately 1 hour prior to burning out. BURNOUT
AND
CASTING
Conventional burnout time is 2 to 3 hours from room temperature to 1350” F, plus a heat-so& period of 1 to 2 hours at 1350” F.’ The total burnout time can be as long
MARCH
1986
VOLUME
55
NUMBER
3
EXPEDITING
NICKEL-CHROME
CASTING
FABRICATION
as 5 hours. This can be substantially reduced by placing the invested waxed framework directly into an oven preheated to 1350“ F for 1 to 1% hours. Cast, finish, and polish the framework in the usual manner. REFERENCES
4.
Sowter B: Dental Laboratory Technology. Chapel Hill, NC, 1968, University of North Carolina, p 180. Terkla LG, Laney WR: Partial Dentures. ed 3. St. Louis, 1963, The CV Mosby Co, p 225. Luebke RJ, Schneider RL: Microwave drying of artilicial stone. J PROSTHET DENT 53:261, 1985.
Repmt rqur.rl\ lo.
1. Ticonium Technique Manual. Albany, NY, 1966, Ticonium Company, Division of CMP Industries, Inc., p 2. 2. Rudd KD, Morrow RM, Eissmann HF: Dental Laboratory Procedures. Vol III: Removable Partial Dentures. St. Louis, 198 1, The CV Moshy Co, p 203.
Light-activated overdentures
3.
DR. DONALD R. NELSON UNIVERSITV OF NORTH CAROLINA SCHOOL OF DENTISTRY CHAPEL HILL, NC 27514
composite-amalgam copings for
John Holt, D.M.D.,* Robert Todd, D.M.D.,** and Robert Quinn, D.M.D.*** Oregon Health Sciences University, School of Dentistry, Portland, Ore.
0
verdentures have become a standard mode of treatment for many dental patients, and many of these patients have progressed to this dental situation because of their high incidence of caries. The caries problem is not alleviated by the overdenture construction, and a continual recurrence of caries on the treated roots can be expected for many of these patients. Gold copings have been used extensively to reduce the incidence of.caries,’ however, they are relatively expensive and may not prevent caries at the margins. They also create a space problem in the esthetic placement of the denture teeth for some patients. Treatment of the exposed root portion of the retained teeth with fluoride and silver nitrate is effective in reducing caries incidence.2Recent improvements in the light-activated composites make this material a viable method of protecting exposed dentin. This article describes an alternate method of treatment that takes some of the beneficial features from both of these procedures.
TREATMENT PROCEDURES 1. Prepare the tooth by reducing the occlusal surface to the shape of a flattened dome extending to the crest of the gingival margin. *Professor, Department of Removable Prosthodontirs. **Assistant Professor, Department of Removable Prosthodontics. ***Associate Professor, Department of Operative Dentistry.
THE JOURNAL
OF PROSTHETIC
DENTISTRY
view, composite-amalgam overdenture tooth coping. A, Cementurn; B, composite; C, amalgam; D, retentive groove. Fig. 1. Top
2. Place a supplemental groove midway between the canal and the cementum margin (Fig. 1). An inverted cone bur (No. 33 or No. 35) of appropriate size is used for this purpose. The groove provides mechanical retention in addition to bonding of the composite to the dentin with a dentin bonding agent. 3. Treat the tooth with the bonding agent and restore it with a thin layer of light-activated composite (Scotch-
403