FIXED PROSTHODONTICS SECTION
. OPERATIVE
DENTISTRY
EDITORS
DAVID E. BEAUDREALJ 1-I. WILLIAM GILMORE SAMUEL E. GUYER HAROLD F. KLEIN WILLIAM
LEFKOWITZ
Aluminous porcelain and its role in fixed prosthodontics Milton H. Brown, D.D.S.,* and Soren E. Sorensen, D. D. S., M. S. ** State University of New York, School of Dentistry, Buffalo, N. Y.
F
ixed prosthodontics would be greatly advanced if high-strength aluminous porcelain were perfected to the point that it would replace the widely used porcelain-fused-to-metal restoration eliminating the need for making a metal substructure and improving esthetics. Investigation into increasing the strength of dental porcelain has continued but has not been successful probably due to the static fatigue of the quartz-reinforced feldspathic porcelain in the presence of moisture.‘. ’ LITERATURE
SURVEY
In 1965 McLean3 presented a procedure for reinforcing ceramic restorations with ceramic oxides. A year later he reported the development of a ceramic oxide-reinforced dental porcelain with increased strength.* In 1974 Southanj described raising the strength of dental porcelain by immersing samples in molten potassium nitrate at 600” C for 4% hours. Using a process of ion exchange, Dunn6 was able to increase the strength of ceramco body porcelain approximately twofold. Recently, McLean and Seed’ reported increasing the resistance to fracture by bonding aluminous porcelain to platinum foil having a tin-oxide coating. According to Eichner and Gewehr,* the strength of aluminous profiles is sufficiently high for use in posterior fixed partial dentures. METHODS AND MATERIALS Diametral samples Commercially available porcelain? was mixed to a creamy consistency and condensed with a mechan-
Read before the Academy of Dentutx Prosthetics, San Antonio, Texas. *Professor and Chairman, Department of Fixed Prosthodontics. **Professor and Chairman, Department of Dental Materials. ?Vitadur, Unitck Corp., Monrovia, Calif.
0022-3913/79/l
10507 + 08$00.80/00
1979 The C. V. Mosby Co.
ical vibrator into stainless steel molds (8 mm in diameter by 4 mm deep). After drying slowly in front of the muffle for 5 minutes, the specimens were placed on the firing tray of the porcelain oven for an additional 5 minutes. All samples were dried in this manner and fired under vacuum, After cooling in open air, the samples were abraded with No. 240 silicon carbide paper and measured for utiformity in thickness and diameter. One group was glazed at 940” C for 3 minutes, and other groups were prepared for chemical strengthening by immersing for 4% hours at 550”, 600”, and 650” C in molten potassium nitrare.j The samples were tested on the Instron universal tester* under moist conditions with a c sl”cxf of 0.5 mm/minute and the strengths recorded. The values were calculated by applying the tensile strength (diametral) formula. Crowns Because Vitadur core material shows greater resistance to cracking, it was decided to test the strength of crowns and fixed partial restorations made of this material under the following conditions: (1) standard procedure, platinum foil removed; (2) platinum foil left in specimen; (3) platinum foil, tin oxide coated; (4) heat hardened; and (5) chemically strengthened. A die was machined from stainless steel having slightly larger dimensions than the maxillary canine preparation (Fig. 1). Platinum foil 0.001 inch thick was adapted to the steel die using the tinner’s joint and then swaged. The matrix was annealed at 2,050” F, and Vitadur core material was condensed to the shoulder of the matrix, dried, and fired, Upon cooling, a three-thickness cylinder of scotch tape 14 mm long was placed over the shoulder with the ‘Inswon
Corp., Canton, Mass.
THE JOURNAL
OF PROSTHETIC
DENTISTRY
aSO7
BROWN AND SORENSEN
Fig. 1. Stainless steel die for making crown specimens.
Fig. 2. The crown is held in the jig at an angle of 70 degrees to the applied force. matrix on the die. Wet-core porcelain was condensed into the cylinder by vibrating, tamping, and drying. The tape was burned off in an oven at 800” F for 30 minutes. The dry porcelain cylinders were introduced into the porcelain oven and matured at 2,050” F. Vitadur body porcelain was condensed over the core and the excess trimmed to approximately 1 mm thickness at the shoulder. A trimming jig with a micrometer attached was used to approximate the thickness of body material on all samples. Twenty-five specimens were prepared in this manner and tested under each of the previously stated conditions. The foil was removed from one group and left in another group. The third group was prepared according to the newly developed McLean-Seed’ tinplating process. * The platinum matrix was covered with a layer of tin oxide 0.2 to 2 *Appreciation is extended to the Unitek Corp. for the loan of the tinplating equipment and supplying the Vita N porcelains used in this project.
508
p thick which serves as the bonding surface for the porcelain. After tin plating, the matrix was placed in the oven at 800” C and the temperature elevated to 1,000” C under vacuum. The vacuum was then released and the temperature maintained for 2 minutes. Under vacuum, the 1,000’ C temperature fused the tin to the platinum, and the 2 minutes maintained in air oxidized the metal and provided a bonding surface. Vita PT* core and N* body porcelains were then applied and fired to the plated matrix of these samples in the conventional manner. According to the manufacturer, these newly developed aluminous powders have better optical properties for covering the tinplated surface. The next group was prepared for heat hardening by removing the platinum matrix, heating in an oven to 600” C for 1 minute, and immediately subjecting the samples to a cold stream of compressed air. This is the same recommended procedure as that required by state law for heathardened eyeglass lenses. The platinum matrix was removed from the last group and placed in molten potassium nitrate at 600” C for 4% hours to allow chemical strengthening. In this heat-hardening process, the smaller sodium ion in the porcelain is driven off and replaced by the larger potassium ion. This leaves the ceramic surface under slight compression, thereby increasing the resistance to fracture. The crowns were made 14 mm long, placing the center of applied force outside the supporting surface of the die to reproduce the frequently seen ellipticalshaped fracture of porcelain jacket crowns. The insides of the crowns were sandblasted. The crowns were then cemented to the steel die. The cement was weighed (1.2 gm of power to 0.5 ml liquid) and mixed in a humidity-controlled room. The cemented crowns were then placed in an oven at 37” C and allowed to set for 1 hour. After setting, the crowns were placed in a special jig which held them at an angle of 70 degrees to the applied force (Fig. 2). The point of the applied force was located at 13 mm from the shoulder on each crown. The jig was placed in the Instron testing machine. Force was applied, and the moment of rupture was recorded at the first drop of the needle of the chart recorder. Fixed partial dentures Since very little is known about the strength of porcelain fixed partial dentures, it was decided to *Manufactured Calif.
by Vita, distributed
NOVEMBER 1979
by Unitek Corp., Monrovia,
VOLUME 42
NUMBER 5
ALUMINOUS PORCELAIN IN FIXED PROSTHODONTICS
1400
1200
1
1
600
400
200
0 Vitadur
s
N
Aluminous
Trubyte
Steele's
PT
Core Porcelains
Fig. 3. Bars indicate the tensile strength of aluminous core porcelains tested. evaluate the strength of a three-unit restoration. Eighteen restorations were made with Vitadur aluminous porcelain which had been reinforced with oval-shaped, extruded aluminous rods 2Y7 X 3 mm in size. For comparison, three porcelain-fused-tometal restorations were included in this study. The following conditions were evaluated: (1) standard procedure, platinum foil removed; (2) platinum foil, tin oxide coated; (3) heat hardened; (4) chemically strengthened; and (5) porcelain fused to metal. The usual porcelain crown preparation was made on a Viade No. 3103* dentoform. This preparation was made with 5 degree taper and a 1 mm rightangle shoulder. The surfaces were smooth and rounded and had a 2 mm reduction occlusally/ incisally. The impression of the prepared teeth was made with Kerr Citricon? impression material in a custom tray. Duralayt resin was poured into the impression, and the pattern was cast in Vital1ium.t An impression of this cast was made in Kerr’s Permlastict impression material and then silver-
*Viade Products Inc., Camariflo, Calif. tKerr Mfg. Co., Romulus, Mich. THE JoURNAL OF PROSTHETIC DENTISTRY
plated. Platinum matrices were adapted to the silverplated dies. Vitadur core material was condensed to the matrix in a thin layer. The porcelain on the shoulder was removed, and the core was fired. After cooling, the cores were returned to the dies, the foil was rebumished, and the cracks and shoulders were filled. Upon completion fusualky after three firings) the cores were transferred to the Vitallium cast and connected with an aluminous rod. The rod was attached to the coping with sticky wax, and the entire assembly was then removed and invested in Neo-Brillat inlay investment.* Investing the cores in this manner preserves the relationship. Another aluminous rod of the same size was used at the base as a firing support. The investment was allowed to set for 30 minutes. The invested support stand was dried at 2,050” F, and the cores connected by firing core material in the joints. All cracks were filled, and the pontic was built up with core porcelain. Body porcelains were added to the reinforced copings, and the teeth were modeled approximately 10% oversize to compensate for shrinkage.
*Vita, distributed
by Unitek Corp., Monrovia,
Calif. 509
BROWN AND SORENSEN
1400
1200
600
400
200
0 S
Vitadur N
Aluminoru
Trubyte
Steele's
PT
Body Porcelains
Fig. 4. Bars indicate the tensile strength of the aluminous body porcelains tested.
After the individual teeth were separated to prevent distortion, they were fired. Embrasures were filled and refired. The samples were then smoothed with a minimum of grinding and glazed at 940’ C for 3 minutes. All the fixed partial denture specimens for heat hardening and chemical strengthening were prepared as described for the crown specimens. The porcelain-fused-to-metal fixed partial dentures were made on the same metal cast using William’s Y ceramic metal* and Vita VMKT porcelain. They were designed with all-porcelain occlusal surfaces and had approximately the same dimensions as the all-porcelain fixed partial dentures. All restorations were cemented to the vitallium cast (using the same method described for the crowns) and were tested under moist conditions. The jig used for testing the crowns (Fig. 2) was again used, but the direction of force was located in the center of the pontic, providing a vertical force. *Williams Gold Refining Co., Inc. TVita, distributed by Unitek Corp.
510
RESULTS Diametral samples Core material. Fig. 3 shows the tensile strength (diametral) of aluminous core porcelains of three manufacturers: Vitadur, Trubyte, and Steele’s. The core material had an average strength of 800 kg/cm2. There was no significant difference in the strength of the three materials tested at the 0.05 significance level. Body porcelains. Fig. 4 shows the tensile strength (diametral) of aluminous body porcelains as approximately 400 kg/cm*. Trubyte material showed the lowest value of approximately 300 kg/cm*. VitadurPt was the strongest with a strength value of 500 kg/cm*. The body porcelains exhibited about 50% lower strength than the core materials (Fig. 3). Incisal porcelains. Fig. 5 shows that the incisal porcelains also had an average strength of 400 kg/cm* with the exception of Trubyte, which showed a strength of 300 kg/cm2. Core porcelain, various conditions. Fig. 6 shows the tensile strengths (diametral) of Vitadur-S core porcelains tested under various conditions. The
NOVEMBER 1979
VOLUME 42
NUMBER 5
ALUMINOUS
PORCELAIN
IN FJXED PROSTHODONTICS
1200,
N
1000
5 \ 2
200
0 s
Vitadur N Aluminous
Trubyte
SXele's
PT Incisal
Porcelains
Fig. 5. Bars indicate the tensile strength of the aluminous incisal
listed specimens were abraded, annealed, glazed, and chemically strengthened at 500” C, 600” C, and 650’ C. Glazing increased the strength of the specimen. This may have been due to sealing the microflaws in the surface. Chemical strengthening at 600” C for 4% hours increased the strength approximately 30%. There was no significant statistical difference between the strength values at varying temperatures of chemical strengthening. Body porcelains, chemical strengthening. Fig. 7 shows tensile strengths (diametral) of Vitadur-S body porcelains. Samples that had been annealed, glazed, and chemically strengthened at 550” C, 600” C and 650” C were compared. Again, at the listed temperatures, chemical strengthening tended to yield 30% higher strength values than in the glazed condition. There was no difference in the three conditions of chemical strengthening (Fig. 7). Crowns Fig. 8 shows the strength values of the crowns. The standard, (foil-removed) procedure and the heathardened specimens gave the lowest values. The highest values were obtained using the platinum
THE JOURNAL
OF PROSTHETIC
DENTISTRY
porcelains
tested.
foil-tin-coated (McLean-Seed) technique and chemical strengthening and by leaving the platinum foil in the crown. The increase in strength, as compared to the standard procedure, was approximately 28%. Fixed partial dentures Fig. 9 shows the strength values of fixed partial dentures. The porcelain-fused-to-metal specimens showed a higher value than heat-hardened and tinplated specimens. It is interesting to note that the all-porcelain fixed partial dentures resisted a load of approximately 105 kg exerted on the pontic, whereas the porcelain-fused-to-metal fixed partial denture was approximately 25% stronger (Fig. 9). DISCUSSION When tested, several of the crowns became unseated from the die and had to be recemented, demonstrating clearly that the crown must be properly supported by the preparation. The procedure for joining the aluminous rods to the core thimbles needs improvement. Only three of the substructures for the fixed partial dentures could
511
BROWN
Abrade
Anneal
Gla.32
Porcelain
512
SORENSEN
Chem. Strygthening$t 650 c 550°c 600 C
Treatment
Fig. 6. Bars indicate the tensile strength of Vitadur-S conditions.
be seated accurately on the Vitallium cast. Placing the glazed restoration in the salt bath for chemical strengthening removes the glaze. Thus the finished restoration has to be polished, because reglazing or heating above 650” C will drive off the ion exchange strengthening effect. The tin-plated and foil-left-in samples had similar strength values, possibly because of the better fit on the die (rather than the tin oxide coating). Although the all-porcelain restoration eliminates the need for a metal substructure, it can be questioned whether there is a savings in cost as compared to the porcelain-fused-to-metal restoration. The number of firings necessary to fabricate the aluminous rod substructures may require as much effort as making the casting. However, the cost of the metal is eliminated, and the esthetic value is improved. These tests were carried out using a rigid cast to support the cemented restoration when force was applied. The results might have been different if the testing had been done using a slightly movable support similar to the periodontal membrane.
AND
core porcelains
under various test
CONCLUSIONS Tylman9 states, “It is the exception rather than the rule for a patient to bite regularly on any one tooth in excess of 100 pounds or 45 kg.” Therefore, the fixed partial denture would be subjected to approximately 26.5 kg.s Test restorations consistently fractured above this figure, at approximately 100 kg. With the limited number of samples in this study, and without extensive clinical evaluation, concrete conclusions cannot be drawn. However, there is sufficient evidence to support the belief that crowns and short-span fixed partial dentures made of aluminous rods and aluminous porcelain have adequate strength to withstand the forces of occlusion. The weakest parts of the all-porcelain restoration are the body and incisal portion, because they contain less aluminous material. The restorations should be made using the maximum amount of core material that is consistent with esthetics. We gratefully acknowledge the laboratory assistance of Dr. Chin Choung and Mr. Robert Johnson in preparing and testing the specimens.
NOVEMBER
1979
VOLUME
42
NUMBER
5
ALUMINOUS
PORCELAIN
IN FIXED PROSTHODONTICS
Anneal
Glaze
~pm. 550
Porcelain
Strepheningdt 600
c
C
650
c
nm3tment
Fig. 7. Bars indicate the tensile strength of Vitadur-5 conditions.
body porcelains under various test
‘r 240.
zoo. 2 $ 2
160.
40,
FOIL REMOVED
FOIL LEFT IN
FOIL TIN COATED
Specimen
HEAT NARO.
CHEH. STREW.
Treatment
Fig. 8. Bars indicate the strength value of crowns under various test conditions.
THE JOURNAL
OF PROSTHETIC
DENTISTRY
1
0 FOIL REMOVE0
FOIL TIN COATED Specimen
HEAT HARO.
CHEN. STREN
PORCL. FU?.EWfETAL
Treatwent
Fig. 9. Bars indicate the strength value of fixed partial dentures under various test conditions.
513
BROWN AND SORENSEN
REFERENCES
7.
1. Southan, D. E., and Jorgensen, K. D.: Faulty porcelain in Jacket crowns. Aust Dent J 17:436, 1972. 2. Southan, D. E.: The endurance limit of dental porcelain. Aust Dent J 19~7, 1974. 3. McLean, J. W., and Hughes, T. H.: The reinforcement of dental porcelain with ceramic oxides. Br Dent J 119:251, 1965. 4. McLean, J. W.: The Development of Ceramic Oxide Reinforced Dental Porcelains with an Appraisal of their Physical and Clinical Properties, Thesis, University of London, 1966. 5. Southan, D. E.: Strengthening modern dental porcelain by ion exchange. Aust Dent J 15:507, 1970. 6. Dunn, B., and Reisbick, M. H.: Strengthening of dental ceramics by ion exchange. IADR Abstr No. 503, 1976.
Journal
adopts new policy
McLean, J. W., and Seed, I. R.: The bonded alumina crown I: The bonding of platinum to aluminous dental porcelain using tin oxide coatings. Aust Dent J 21:119, 1976. 8. Eichner, K., and Gewehr, L.: Investigations of dental porcelain reinforced with high alumina for bridgeworks. IADR Abstr No. 497, 1976. 9. Tylman, S. G.: Theory and Practice of Crown and Bridge Prosthodontics, ed 5. St. Louis, 1965, The C. V. Mosby Co., p 166. Reprint requeststo: DR. MILTON H. BROWN STATE UNIVERSITY OF NEW YORK SCHOOL OF DENTISTRY BUFFALO, N. Y. 14214
for illustrations
in color
The Editorial Council and publisher of THE JOURNAL OF PROSTHETIC DENTISTRY have agreed to publish articles that contain color illustrations at a reduced cost to authors. Authors will pay only $225 per color page, or part thereof, and can present from one to eight illustrations on each page. Two high-quality 35 mm color transparencies (an original and duplicate) must be submitted for each illustration, and manuscript length cannot exceed 10 to 12 double-spaced typewritten pages. The Editor and his reviewers have final authority to determine if color illustrations afford the most effective presentation. Articles containing color will appear in selected issues beginning in 1980. Authors are requested to include a statement when they submit their manuscript agreeing to pay $225 for each page of color. Billing will come from the publisher after the author has approved color proofs and the article is scheduled for publication. Manuscripts for evaluation. and illustrations will be accepted immediately
514
NOVEMBER
1979
VOLUME
42
NUMBER
5
. OPERATIVE
DENTISTRY
EDITORS
DAVID E. BEAUDREALJ 1-I. WILLIAM GILMORE SAMUEL E. GUYER HAROLD F. KLEIN WILLIAM
LEFKOWITZ
Aluminous porcelain and its role in fixed prosthodontics Milton H. Brown, D.D.S.,* and Soren E. Sorensen, D. D. S., M. S. ** State University of New York, School of Dentistry, Buffalo, N. Y.
F
ixed prosthodontics would be greatly advanced if high-strength aluminous porcelain were perfected to the point that it would replace the widely used porcelain-fused-to-metal restoration eliminating the need for making a metal substructure and improving esthetics. Investigation into increasing the strength of dental porcelain has continued but has not been successful probably due to the static fatigue of the quartz-reinforced feldspathic porcelain in the presence of moisture.‘. ’ LITERATURE
SURVEY
In 1965 McLean3 presented a procedure for reinforcing ceramic restorations with ceramic oxides. A year later he reported the development of a ceramic oxide-reinforced dental porcelain with increased strength.* In 1974 Southanj described raising the strength of dental porcelain by immersing samples in molten potassium nitrate at 600” C for 4% hours. Using a process of ion exchange, Dunn6 was able to increase the strength of ceramco body porcelain approximately twofold. Recently, McLean and Seed’ reported increasing the resistance to fracture by bonding aluminous porcelain to platinum foil having a tin-oxide coating. According to Eichner and Gewehr,* the strength of aluminous profiles is sufficiently high for use in posterior fixed partial dentures. METHODS AND MATERIALS Diametral samples Commercially available porcelain? was mixed to a creamy consistency and condensed with a mechan-
Read before the Academy of Dentutx Prosthetics, San Antonio, Texas. *Professor and Chairman, Department of Fixed Prosthodontics. **Professor and Chairman, Department of Dental Materials. ?Vitadur, Unitck Corp., Monrovia, Calif.
0022-3913/79/l
10507 + 08$00.80/00
1979 The C. V. Mosby Co.
ical vibrator into stainless steel molds (8 mm in diameter by 4 mm deep). After drying slowly in front of the muffle for 5 minutes, the specimens were placed on the firing tray of the porcelain oven for an additional 5 minutes. All samples were dried in this manner and fired under vacuum, After cooling in open air, the samples were abraded with No. 240 silicon carbide paper and measured for utiformity in thickness and diameter. One group was glazed at 940” C for 3 minutes, and other groups were prepared for chemical strengthening by immersing for 4% hours at 550”, 600”, and 650” C in molten potassium nitrare.j The samples were tested on the Instron universal tester* under moist conditions with a c sl”cxf of 0.5 mm/minute and the strengths recorded. The values were calculated by applying the tensile strength (diametral) formula. Crowns Because Vitadur core material shows greater resistance to cracking, it was decided to test the strength of crowns and fixed partial restorations made of this material under the following conditions: (1) standard procedure, platinum foil removed; (2) platinum foil left in specimen; (3) platinum foil, tin oxide coated; (4) heat hardened; and (5) chemically strengthened. A die was machined from stainless steel having slightly larger dimensions than the maxillary canine preparation (Fig. 1). Platinum foil 0.001 inch thick was adapted to the steel die using the tinner’s joint and then swaged. The matrix was annealed at 2,050” F, and Vitadur core material was condensed to the shoulder of the matrix, dried, and fired, Upon cooling, a three-thickness cylinder of scotch tape 14 mm long was placed over the shoulder with the ‘Inswon
Corp., Canton, Mass.
THE JOURNAL
OF PROSTHETIC
DENTISTRY
aSO7
BROWN AND SORENSEN
Fig. 1. Stainless steel die for making crown specimens.
Fig. 2. The crown is held in the jig at an angle of 70 degrees to the applied force. matrix on the die. Wet-core porcelain was condensed into the cylinder by vibrating, tamping, and drying. The tape was burned off in an oven at 800” F for 30 minutes. The dry porcelain cylinders were introduced into the porcelain oven and matured at 2,050” F. Vitadur body porcelain was condensed over the core and the excess trimmed to approximately 1 mm thickness at the shoulder. A trimming jig with a micrometer attached was used to approximate the thickness of body material on all samples. Twenty-five specimens were prepared in this manner and tested under each of the previously stated conditions. The foil was removed from one group and left in another group. The third group was prepared according to the newly developed McLean-Seed’ tinplating process. * The platinum matrix was covered with a layer of tin oxide 0.2 to 2 *Appreciation is extended to the Unitek Corp. for the loan of the tinplating equipment and supplying the Vita N porcelains used in this project.
508
p thick which serves as the bonding surface for the porcelain. After tin plating, the matrix was placed in the oven at 800” C and the temperature elevated to 1,000” C under vacuum. The vacuum was then released and the temperature maintained for 2 minutes. Under vacuum, the 1,000’ C temperature fused the tin to the platinum, and the 2 minutes maintained in air oxidized the metal and provided a bonding surface. Vita PT* core and N* body porcelains were then applied and fired to the plated matrix of these samples in the conventional manner. According to the manufacturer, these newly developed aluminous powders have better optical properties for covering the tinplated surface. The next group was prepared for heat hardening by removing the platinum matrix, heating in an oven to 600” C for 1 minute, and immediately subjecting the samples to a cold stream of compressed air. This is the same recommended procedure as that required by state law for heathardened eyeglass lenses. The platinum matrix was removed from the last group and placed in molten potassium nitrate at 600” C for 4% hours to allow chemical strengthening. In this heat-hardening process, the smaller sodium ion in the porcelain is driven off and replaced by the larger potassium ion. This leaves the ceramic surface under slight compression, thereby increasing the resistance to fracture. The crowns were made 14 mm long, placing the center of applied force outside the supporting surface of the die to reproduce the frequently seen ellipticalshaped fracture of porcelain jacket crowns. The insides of the crowns were sandblasted. The crowns were then cemented to the steel die. The cement was weighed (1.2 gm of power to 0.5 ml liquid) and mixed in a humidity-controlled room. The cemented crowns were then placed in an oven at 37” C and allowed to set for 1 hour. After setting, the crowns were placed in a special jig which held them at an angle of 70 degrees to the applied force (Fig. 2). The point of the applied force was located at 13 mm from the shoulder on each crown. The jig was placed in the Instron testing machine. Force was applied, and the moment of rupture was recorded at the first drop of the needle of the chart recorder. Fixed partial dentures Since very little is known about the strength of porcelain fixed partial dentures, it was decided to *Manufactured Calif.
by Vita, distributed
NOVEMBER 1979
by Unitek Corp., Monrovia,
VOLUME 42
NUMBER 5
ALUMINOUS PORCELAIN IN FIXED PROSTHODONTICS
1400
1200
1
1
600
400
200
0 Vitadur
s
N
Aluminous
Trubyte
Steele's
PT
Core Porcelains
Fig. 3. Bars indicate the tensile strength of aluminous core porcelains tested. evaluate the strength of a three-unit restoration. Eighteen restorations were made with Vitadur aluminous porcelain which had been reinforced with oval-shaped, extruded aluminous rods 2Y7 X 3 mm in size. For comparison, three porcelain-fused-tometal restorations were included in this study. The following conditions were evaluated: (1) standard procedure, platinum foil removed; (2) platinum foil, tin oxide coated; (3) heat hardened; (4) chemically strengthened; and (5) porcelain fused to metal. The usual porcelain crown preparation was made on a Viade No. 3103* dentoform. This preparation was made with 5 degree taper and a 1 mm rightangle shoulder. The surfaces were smooth and rounded and had a 2 mm reduction occlusally/ incisally. The impression of the prepared teeth was made with Kerr Citricon? impression material in a custom tray. Duralayt resin was poured into the impression, and the pattern was cast in Vital1ium.t An impression of this cast was made in Kerr’s Permlastict impression material and then silver-
*Viade Products Inc., Camariflo, Calif. tKerr Mfg. Co., Romulus, Mich. THE JoURNAL OF PROSTHETIC DENTISTRY
plated. Platinum matrices were adapted to the silverplated dies. Vitadur core material was condensed to the matrix in a thin layer. The porcelain on the shoulder was removed, and the core was fired. After cooling, the cores were returned to the dies, the foil was rebumished, and the cracks and shoulders were filled. Upon completion fusualky after three firings) the cores were transferred to the Vitallium cast and connected with an aluminous rod. The rod was attached to the coping with sticky wax, and the entire assembly was then removed and invested in Neo-Brillat inlay investment.* Investing the cores in this manner preserves the relationship. Another aluminous rod of the same size was used at the base as a firing support. The investment was allowed to set for 30 minutes. The invested support stand was dried at 2,050” F, and the cores connected by firing core material in the joints. All cracks were filled, and the pontic was built up with core porcelain. Body porcelains were added to the reinforced copings, and the teeth were modeled approximately 10% oversize to compensate for shrinkage.
*Vita, distributed
by Unitek Corp., Monrovia,
Calif. 509
BROWN AND SORENSEN
1400
1200
600
400
200
0 S
Vitadur N
Aluminoru
Trubyte
Steele's
PT
Body Porcelains
Fig. 4. Bars indicate the tensile strength of the aluminous body porcelains tested.
After the individual teeth were separated to prevent distortion, they were fired. Embrasures were filled and refired. The samples were then smoothed with a minimum of grinding and glazed at 940’ C for 3 minutes. All the fixed partial denture specimens for heat hardening and chemical strengthening were prepared as described for the crown specimens. The porcelain-fused-to-metal fixed partial dentures were made on the same metal cast using William’s Y ceramic metal* and Vita VMKT porcelain. They were designed with all-porcelain occlusal surfaces and had approximately the same dimensions as the all-porcelain fixed partial dentures. All restorations were cemented to the vitallium cast (using the same method described for the crowns) and were tested under moist conditions. The jig used for testing the crowns (Fig. 2) was again used, but the direction of force was located in the center of the pontic, providing a vertical force. *Williams Gold Refining Co., Inc. TVita, distributed by Unitek Corp.
510
RESULTS Diametral samples Core material. Fig. 3 shows the tensile strength (diametral) of aluminous core porcelains of three manufacturers: Vitadur, Trubyte, and Steele’s. The core material had an average strength of 800 kg/cm2. There was no significant difference in the strength of the three materials tested at the 0.05 significance level. Body porcelains. Fig. 4 shows the tensile strength (diametral) of aluminous body porcelains as approximately 400 kg/cm*. Trubyte material showed the lowest value of approximately 300 kg/cm*. VitadurPt was the strongest with a strength value of 500 kg/cm*. The body porcelains exhibited about 50% lower strength than the core materials (Fig. 3). Incisal porcelains. Fig. 5 shows that the incisal porcelains also had an average strength of 400 kg/cm* with the exception of Trubyte, which showed a strength of 300 kg/cm2. Core porcelain, various conditions. Fig. 6 shows the tensile strengths (diametral) of Vitadur-S core porcelains tested under various conditions. The
NOVEMBER 1979
VOLUME 42
NUMBER 5
ALUMINOUS
PORCELAIN
IN FJXED PROSTHODONTICS
1200,
N
1000
5 \ 2
200
0 s
Vitadur N Aluminous
Trubyte
SXele's
PT Incisal
Porcelains
Fig. 5. Bars indicate the tensile strength of the aluminous incisal
listed specimens were abraded, annealed, glazed, and chemically strengthened at 500” C, 600” C, and 650’ C. Glazing increased the strength of the specimen. This may have been due to sealing the microflaws in the surface. Chemical strengthening at 600” C for 4% hours increased the strength approximately 30%. There was no significant statistical difference between the strength values at varying temperatures of chemical strengthening. Body porcelains, chemical strengthening. Fig. 7 shows tensile strengths (diametral) of Vitadur-S body porcelains. Samples that had been annealed, glazed, and chemically strengthened at 550” C, 600” C and 650” C were compared. Again, at the listed temperatures, chemical strengthening tended to yield 30% higher strength values than in the glazed condition. There was no difference in the three conditions of chemical strengthening (Fig. 7). Crowns Fig. 8 shows the strength values of the crowns. The standard, (foil-removed) procedure and the heathardened specimens gave the lowest values. The highest values were obtained using the platinum
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porcelains
tested.
foil-tin-coated (McLean-Seed) technique and chemical strengthening and by leaving the platinum foil in the crown. The increase in strength, as compared to the standard procedure, was approximately 28%. Fixed partial dentures Fig. 9 shows the strength values of fixed partial dentures. The porcelain-fused-to-metal specimens showed a higher value than heat-hardened and tinplated specimens. It is interesting to note that the all-porcelain fixed partial dentures resisted a load of approximately 105 kg exerted on the pontic, whereas the porcelain-fused-to-metal fixed partial denture was approximately 25% stronger (Fig. 9). DISCUSSION When tested, several of the crowns became unseated from the die and had to be recemented, demonstrating clearly that the crown must be properly supported by the preparation. The procedure for joining the aluminous rods to the core thimbles needs improvement. Only three of the substructures for the fixed partial dentures could
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Abrade
Anneal
Gla.32
Porcelain
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SORENSEN
Chem. Strygthening$t 650 c 550°c 600 C
Treatment
Fig. 6. Bars indicate the tensile strength of Vitadur-S conditions.
be seated accurately on the Vitallium cast. Placing the glazed restoration in the salt bath for chemical strengthening removes the glaze. Thus the finished restoration has to be polished, because reglazing or heating above 650” C will drive off the ion exchange strengthening effect. The tin-plated and foil-left-in samples had similar strength values, possibly because of the better fit on the die (rather than the tin oxide coating). Although the all-porcelain restoration eliminates the need for a metal substructure, it can be questioned whether there is a savings in cost as compared to the porcelain-fused-to-metal restoration. The number of firings necessary to fabricate the aluminous rod substructures may require as much effort as making the casting. However, the cost of the metal is eliminated, and the esthetic value is improved. These tests were carried out using a rigid cast to support the cemented restoration when force was applied. The results might have been different if the testing had been done using a slightly movable support similar to the periodontal membrane.
AND
core porcelains
under various test
CONCLUSIONS Tylman9 states, “It is the exception rather than the rule for a patient to bite regularly on any one tooth in excess of 100 pounds or 45 kg.” Therefore, the fixed partial denture would be subjected to approximately 26.5 kg.s Test restorations consistently fractured above this figure, at approximately 100 kg. With the limited number of samples in this study, and without extensive clinical evaluation, concrete conclusions cannot be drawn. However, there is sufficient evidence to support the belief that crowns and short-span fixed partial dentures made of aluminous rods and aluminous porcelain have adequate strength to withstand the forces of occlusion. The weakest parts of the all-porcelain restoration are the body and incisal portion, because they contain less aluminous material. The restorations should be made using the maximum amount of core material that is consistent with esthetics. We gratefully acknowledge the laboratory assistance of Dr. Chin Choung and Mr. Robert Johnson in preparing and testing the specimens.
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1979
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ALUMINOUS
PORCELAIN
IN FIXED PROSTHODONTICS
Anneal
Glaze
~pm. 550
Porcelain
Strepheningdt 600
c
C
650
c
nm3tment
Fig. 7. Bars indicate the tensile strength of Vitadur-5 conditions.
body porcelains under various test
‘r 240.
zoo. 2 $ 2
160.
40,
FOIL REMOVED
FOIL LEFT IN
FOIL TIN COATED
Specimen
HEAT NARO.
CHEH. STREW.
Treatment
Fig. 8. Bars indicate the strength value of crowns under various test conditions.
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DENTISTRY
1
0 FOIL REMOVE0
FOIL TIN COATED Specimen
HEAT HARO.
CHEN. STREN
PORCL. FU?.EWfETAL
Treatwent
Fig. 9. Bars indicate the strength value of fixed partial dentures under various test conditions.
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REFERENCES
7.
1. Southan, D. E., and Jorgensen, K. D.: Faulty porcelain in Jacket crowns. Aust Dent J 17:436, 1972. 2. Southan, D. E.: The endurance limit of dental porcelain. Aust Dent J 19~7, 1974. 3. McLean, J. W., and Hughes, T. H.: The reinforcement of dental porcelain with ceramic oxides. Br Dent J 119:251, 1965. 4. McLean, J. W.: The Development of Ceramic Oxide Reinforced Dental Porcelains with an Appraisal of their Physical and Clinical Properties, Thesis, University of London, 1966. 5. Southan, D. E.: Strengthening modern dental porcelain by ion exchange. Aust Dent J 15:507, 1970. 6. Dunn, B., and Reisbick, M. H.: Strengthening of dental ceramics by ion exchange. IADR Abstr No. 503, 1976.
Journal
adopts new policy
McLean, J. W., and Seed, I. R.: The bonded alumina crown I: The bonding of platinum to aluminous dental porcelain using tin oxide coatings. Aust Dent J 21:119, 1976. 8. Eichner, K., and Gewehr, L.: Investigations of dental porcelain reinforced with high alumina for bridgeworks. IADR Abstr No. 497, 1976. 9. Tylman, S. G.: Theory and Practice of Crown and Bridge Prosthodontics, ed 5. St. Louis, 1965, The C. V. Mosby Co., p 166. Reprint requeststo: DR. MILTON H. BROWN STATE UNIVERSITY OF NEW YORK SCHOOL OF DENTISTRY BUFFALO, N. Y. 14214
for illustrations
in color
The Editorial Council and publisher of THE JOURNAL OF PROSTHETIC DENTISTRY have agreed to publish articles that contain color illustrations at a reduced cost to authors. Authors will pay only $225 per color page, or part thereof, and can present from one to eight illustrations on each page. Two high-quality 35 mm color transparencies (an original and duplicate) must be submitted for each illustration, and manuscript length cannot exceed 10 to 12 double-spaced typewritten pages. The Editor and his reviewers have final authority to determine if color illustrations afford the most effective presentation. Articles containing color will appear in selected issues beginning in 1980. Authors are requested to include a statement when they submit their manuscript agreeing to pay $225 for each page of color. Billing will come from the publisher after the author has approved color proofs and the article is scheduled for publication. Manuscripts for evaluation. and illustrations will be accepted immediately
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