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Castable glass ceramic crowns and their reaction to endodontic therapy
Castable glass ceramic crowns and their reaction to endodontic therapy Bernard D. Cohen, DDS,“ and James A. Wallace, DDS, AIDS, MSD, MS,b Cleveland, Ohio SCHOOL OF DENTISTRY,
CASE WESTERN
RESERVE UNIVERSITY
The purpose of this investigation was to determine how castable glass (Dicer) crowns would react to both cold testing and endodontic access intervention. Full crown preparations were made on six extracted maxillary teeth. The teeth were then forwarded to Dentsply International. York, Pa. Six castable glass crowns were fabricated to fit these teeth and returned to us. Subsequently the teeth were dried and the crowns were cemented. Scanning electron micrographs of the cemented crowns were made, and endodontic access openings were drilled. The teeth were also cold tested with standard methods. The teeth were then again subjected to scanning electron microscopy to determine any changes the crowns might have undergone. One crown cracked around the gingival collar as scanning electron microscopy was performed. The other crowns did not exhibit any problems such as cracking or crazing from either the access openings or the cold testing.
(ORALSURCORALMEDORALP~~~0~1991;72:108-10)
E
nsuring that the crown doesnot fracture is always a concern for the practitioner while making access openings for endodontic therapy.’ This was never a problem with gold occlusal or lingual surfaces, but with the advent of porcelain fused to metal and the all-porcelain crown the incidence of shattering became a factor. Dicer crowns are composedof castable glass ceramic, which is then treated in a high-heat (1100” F) ceramics furnace to make the material more durable by altering the crystalline structure.* Subsequently, surface colorants are added and the final product is glazed in a regular porcelain-firing oven. This study concerned the effects of endodontic accessopenings through the occlusal surfaces of posterior teeth and the lingual surfaces of anterior teeth as well as the effects of cold testing. These tests are often done to obtain diagnostic data before possible endodontic intervention. MATERIAL
AND METHODS
Six extracted teeth, including maxillary anteriors, premolars, and molars, were selected.The teeth were aFormerly, Director, Fixed Prosthodontics, and Assistant Professor, Department of Restorative Dentistry; now Assistant Professor, Department of Adult Restorative Dentistry, College of Dentistry, University of Nebraska Medical Center, Lincoln. bDirector, Graduate Endodontics Program, and Assistant Professor, Department of Endodontics. 7/15/28825 108
Fig.
1. Upper
Dicer cuspidcrown. (SEM.)
stored in normal saline solution. Crown preparations were made according to manufacturer’s suggestions in the amounts of reduction: 2 mm on the occlusal surfaces and 1.5 mm on the buccal or facial, lingual, and interproximal surfaces. Full-shoulder preparations were made with rounded corners.’ The prepared teeth were then immersed again in normal saline solution and shipped to Dentsply International, York, Pa., for the manufacturing of Dicer crowns in their laboratories. After crowns were fabricated, the teeth were returned in the saline solution and the crowns in a
Glass ceramic crowns 109
Volume72 Number I
Fig.
Fig.
2. Upper Dicer premolar crown. (SEM.)
Fig. 4. Upper Dicer cuspid crown with endodontic access opening. (SEM.)
3. Upper Dicer molar crown. @EM.)
Fig. 5. Upper Dicer premolar crown with endodontic accessopening. (SEM.)
separate container. All the teeth were then dried with
air blasts, and the crowns were permanently cemented. Three crowns were sealed with zinc phosphate (Flecks) cement (Mizzy, Inc., Cherry Hill, N.J.) and three with polycarboxylate cement (Ceramco Inc., Burlington, N.J.). The six sampleswere sent to the scanning electron microscopy (SEM) laboratory for examination and photography. Figs. 1 to 3 illustrate the surface appearance on SEM. After this step, accessopenings were drilled through the crowns into the pulp chambers with diamond points (Robot Points Nos. 0875 and 0876; Shofu Dental Corp., Menlo Park, Calif.) under heavy water and air spray. The teeth were then returned to the laboratory for SEM. Cold tests were then performed on the buccal and labial surfaces with the use of established endodontic principles utilizing (Frigi-Dent (Ellman International Mfg. Inc., Hewlett, N.Y.) at a temperature of -10” C.
RESULTS
While a tooth was being placed into the microscope, a fracture around the gingival collar was noticed. This crown was not photographed becauseit also came off the tooth. The entire occlusal surface, including the accessopening, was intact. The other five crowns were completely intact and were studied under the scanning electron microscope. The access openings appeared as shown in Figs. 4 and 5. Some chipping was seenaround the openings, but no cracks or craze lines were evident. The molar crown that cracked circularly around the gingival collar was cemented with zinc phosphate cement, but both cements otherwise behaved the sameduring the accessdrilling. The cold tests had no apparent effect on the Dicer surfaces; however, all three crowns cemented with zinc phosphate lost their retention, two of them after the cold tests were run. The three crowns cemented with poly-
I IO
Cohen and Wallace
ORAL SURC ORAL MED ORAL PATHOL
July 1991
carboxylate cement stayed intact throughout the entire study. DISCUSSION
All three crowns cemented with zinc phosphate cement lost their retention to the teeth during this study and one of those cracked around the gingival collar. The others stayed intact. Zinc phosphate cement is merely a luting agent, whereas polycarboxylate cement is to a degree a bonding agent to dentin4 Sutherland et a1.5cemented the crowns with temporary cement so that they could be retrieved and inspected. These investigators also observed some breakage and did many more samples.In addition, the crowns exhibited cracks and craze lines, although the use of carbide burs was another variable. Newer methods of cementation employing silane coupling agents and composite cements would possibly stabilize the crowns to the dentin and increase resistance to the trauma we artificially imposed.
crowns to the die.6 When these crowns are luted with zinc phosphate cements, there can be a chattering effect, loosening the cement and contributing to cracking of the glass ceramic. New methods of permanent cementation with silane coupling agents and composite cements to bond Dicer to dentin may help to overcome some of this weakness. Therefore much more research needs to be done to determine whether bonding to dentin will help. REFERENCES
1. McLean JW. Dental ceramics. Chicago: Quintessence, 1983. 2. Grossman D. Cast glass ceramics. Dent Clin North Am 1985; 291125-39. 3. Adair P, Grossman D. The castable ceramic crown. Int J Periodontol Rest Dent 1984;2:33-5. 4. Shillinburg HT. Sumiya H, Whitsett LD. Fundamentals of fixed prosthodontics. Chicago: 1978;271-87. 5. Sutherland JK, Teplitsky PE, Moulding MB. J Prosthet Dent 1989;2:146-9. 6. Dickinson AJ, Moore BK, Harris RK, Dykema RW. A comparative study of the strength of aluminous porcelain and allceramic crowns. J Prosthet Dent 1989:3:297-304.
CONCLUSIONS
Dicer glass ceramic crowns are subject to some breakage during endodontic therapy. The crowns may break, but not necessarily where the accessopenings are made. Dicer is variable in adaptation of the
Reprint requests:
Bernard D:Cohen, DDS Department of Adult Restorative Dentistry 40th and Holdrege Lincoln. NE 68583-0740
CASE WESTERN
RESERVE UNIVERSITY
The purpose of this investigation was to determine how castable glass (Dicer) crowns would react to both cold testing and endodontic access intervention. Full crown preparations were made on six extracted maxillary teeth. The teeth were then forwarded to Dentsply International. York, Pa. Six castable glass crowns were fabricated to fit these teeth and returned to us. Subsequently the teeth were dried and the crowns were cemented. Scanning electron micrographs of the cemented crowns were made, and endodontic access openings were drilled. The teeth were also cold tested with standard methods. The teeth were then again subjected to scanning electron microscopy to determine any changes the crowns might have undergone. One crown cracked around the gingival collar as scanning electron microscopy was performed. The other crowns did not exhibit any problems such as cracking or crazing from either the access openings or the cold testing.
(ORALSURCORALMEDORALP~~~0~1991;72:108-10)
E
nsuring that the crown doesnot fracture is always a concern for the practitioner while making access openings for endodontic therapy.’ This was never a problem with gold occlusal or lingual surfaces, but with the advent of porcelain fused to metal and the all-porcelain crown the incidence of shattering became a factor. Dicer crowns are composedof castable glass ceramic, which is then treated in a high-heat (1100” F) ceramics furnace to make the material more durable by altering the crystalline structure.* Subsequently, surface colorants are added and the final product is glazed in a regular porcelain-firing oven. This study concerned the effects of endodontic accessopenings through the occlusal surfaces of posterior teeth and the lingual surfaces of anterior teeth as well as the effects of cold testing. These tests are often done to obtain diagnostic data before possible endodontic intervention. MATERIAL
AND METHODS
Six extracted teeth, including maxillary anteriors, premolars, and molars, were selected.The teeth were aFormerly, Director, Fixed Prosthodontics, and Assistant Professor, Department of Restorative Dentistry; now Assistant Professor, Department of Adult Restorative Dentistry, College of Dentistry, University of Nebraska Medical Center, Lincoln. bDirector, Graduate Endodontics Program, and Assistant Professor, Department of Endodontics. 7/15/28825 108
Fig.
1. Upper
Dicer cuspidcrown. (SEM.)
stored in normal saline solution. Crown preparations were made according to manufacturer’s suggestions in the amounts of reduction: 2 mm on the occlusal surfaces and 1.5 mm on the buccal or facial, lingual, and interproximal surfaces. Full-shoulder preparations were made with rounded corners.’ The prepared teeth were then immersed again in normal saline solution and shipped to Dentsply International, York, Pa., for the manufacturing of Dicer crowns in their laboratories. After crowns were fabricated, the teeth were returned in the saline solution and the crowns in a
Glass ceramic crowns 109
Volume72 Number I
Fig.
Fig.
2. Upper Dicer premolar crown. (SEM.)
Fig. 4. Upper Dicer cuspid crown with endodontic access opening. (SEM.)
3. Upper Dicer molar crown. @EM.)
Fig. 5. Upper Dicer premolar crown with endodontic accessopening. (SEM.)
separate container. All the teeth were then dried with
air blasts, and the crowns were permanently cemented. Three crowns were sealed with zinc phosphate (Flecks) cement (Mizzy, Inc., Cherry Hill, N.J.) and three with polycarboxylate cement (Ceramco Inc., Burlington, N.J.). The six sampleswere sent to the scanning electron microscopy (SEM) laboratory for examination and photography. Figs. 1 to 3 illustrate the surface appearance on SEM. After this step, accessopenings were drilled through the crowns into the pulp chambers with diamond points (Robot Points Nos. 0875 and 0876; Shofu Dental Corp., Menlo Park, Calif.) under heavy water and air spray. The teeth were then returned to the laboratory for SEM. Cold tests were then performed on the buccal and labial surfaces with the use of established endodontic principles utilizing (Frigi-Dent (Ellman International Mfg. Inc., Hewlett, N.Y.) at a temperature of -10” C.
RESULTS
While a tooth was being placed into the microscope, a fracture around the gingival collar was noticed. This crown was not photographed becauseit also came off the tooth. The entire occlusal surface, including the accessopening, was intact. The other five crowns were completely intact and were studied under the scanning electron microscope. The access openings appeared as shown in Figs. 4 and 5. Some chipping was seenaround the openings, but no cracks or craze lines were evident. The molar crown that cracked circularly around the gingival collar was cemented with zinc phosphate cement, but both cements otherwise behaved the sameduring the accessdrilling. The cold tests had no apparent effect on the Dicer surfaces; however, all three crowns cemented with zinc phosphate lost their retention, two of them after the cold tests were run. The three crowns cemented with poly-
I IO
Cohen and Wallace
ORAL SURC ORAL MED ORAL PATHOL
July 1991
carboxylate cement stayed intact throughout the entire study. DISCUSSION
All three crowns cemented with zinc phosphate cement lost their retention to the teeth during this study and one of those cracked around the gingival collar. The others stayed intact. Zinc phosphate cement is merely a luting agent, whereas polycarboxylate cement is to a degree a bonding agent to dentin4 Sutherland et a1.5cemented the crowns with temporary cement so that they could be retrieved and inspected. These investigators also observed some breakage and did many more samples.In addition, the crowns exhibited cracks and craze lines, although the use of carbide burs was another variable. Newer methods of cementation employing silane coupling agents and composite cements would possibly stabilize the crowns to the dentin and increase resistance to the trauma we artificially imposed.
crowns to the die.6 When these crowns are luted with zinc phosphate cements, there can be a chattering effect, loosening the cement and contributing to cracking of the glass ceramic. New methods of permanent cementation with silane coupling agents and composite cements to bond Dicer to dentin may help to overcome some of this weakness. Therefore much more research needs to be done to determine whether bonding to dentin will help. REFERENCES
1. McLean JW. Dental ceramics. Chicago: Quintessence, 1983. 2. Grossman D. Cast glass ceramics. Dent Clin North Am 1985; 291125-39. 3. Adair P, Grossman D. The castable ceramic crown. Int J Periodontol Rest Dent 1984;2:33-5. 4. Shillinburg HT. Sumiya H, Whitsett LD. Fundamentals of fixed prosthodontics. Chicago: 1978;271-87. 5. Sutherland JK, Teplitsky PE, Moulding MB. J Prosthet Dent 1989;2:146-9. 6. Dickinson AJ, Moore BK, Harris RK, Dykema RW. A comparative study of the strength of aluminous porcelain and allceramic crowns. J Prosthet Dent 1989:3:297-304.
CONCLUSIONS
Dicer glass ceramic crowns are subject to some breakage during endodontic therapy. The crowns may break, but not necessarily where the accessopenings are made. Dicer is variable in adaptation of the
Reprint requests:
Bernard D:Cohen, DDS Department of Adult Restorative Dentistry 40th and Holdrege Lincoln. NE 68583-0740