akage of cast gold crowns L. Tjan, DrDent, DDS,a James R. Dunn, Ben E. Grant, DMDC Loma Linda University, School of Dentistry, Loma Linda, Calif.
DDS,”
Wed
with
a
and
The microleakage of cast gold complete crowns cemented with Panavia EX cement was evaluated and compared with those luted with a standard zinc phosphate cement. The effect of water immersion of specimens for 30 and 90 days was also investigated. The finding of this study indicated that crowns cemented with Panavia EX cement exhibited substantially less marginal leakage than those cemented with zinc phosphate cement. No significant difference in marginal leakage was observed between 30-day and go-day water immersion of crowns cemented with Panavia EX cement. (J PROSTHET DENT 1992;67:11-5.)
ecause cast restorations cannot be made without leaving a marginal gap, luting cements still play a pivotal role in sealing the margins as a prevention against marginal
leakage. Unfortunately, most of the dental cements available cannot guarantee continual impermeability.1,2 Moreover, because of their relatively high solubility in oral fluids, a gap thus created at the restoration margin may become a protective repository for microorganisms that release toxic products. These toxins may eventually cause gingival inflammation, secondary caries, and/or inflammatory pulpal lesions.3-7 Resin-based cement is generally a low-viscosity, chemically cured composite resin, and is one of the newer classes
aProfessor and Direct.or of Biomaterials Research, Department of Restorative Dentistry, bAssociate Professor, Department of Restorative Dentistry, “Professor, Department of Restorative Dentistry. 10/l/29659
Fig. 2. Loading device used to provide S-kg static load during cementation.
Fig. 2. Custom-made teeth. TNE
JOURNAL
paralleling
OF PROSTI3ETXC
device used to prepare
DENTISTRY
Fig. 3. Diagram roleakage.
of criteria
for scoring values of mic-
11
TJAN,
DUNN,
AND
GRANT
Fig. 4. Micrographs of sectioned crown margins at x30 magnification. A, No microleakage of crown cemented with Panavia EX cement after 30-day water immersion. B, Despite significant cement margin, no microleakage of crown cemented with Panavia EX cement was observed after go-day water immersion. C, and D, Severe microleakage in crowns luted with zinc phosphate cement.
of 11 uting cements available commercially. Information conelerning clinical performance is still scarce. However, in vitrc ) studies reported severe marginal leakage of cast crov5ms luted with resin cement.4 g Further, Staninec et aLlo found that resin cement produced a substantially 12
greater cement film thickness compared with zinc: phosphate cement and concluded that its use for cemelntation of precision castings was inadvisable. Other shortcl omings of resin cements include short working time, irrita .tion to dental pulp, and difficulty in removing the cured excess
JANUARY
1992
VOLUME
67
NUMBER
1
MARGlNAL
Tablie
LEAKAGE
OF CAST
GOLD
CROWNS
I. Microleakage raw scores, median, and range
SpeCiXIHXl No.
Flecks
(30 d)
Panavia
(30 d)
T-C
M-C
T-C
M-C
i 2 3 4 5 6 7 8 9 10 Median
2.5 0 2 1.75 1 1.5 0 1.5 1 3.5 1.5
Range
3.5
Panavia T-C
(90 d) M-C
0 0 0 0.5 1 1 0 0 0.5 0
0 0 0 0.5 0.75 0.25 0.5 0 0 0.25
0 0 0 0 0 0 0 0 0 0
0 0 0 0.25 0 0 0 0 0.25 0.25
0 0 0 0 0 0 0 0 0 0
0.25 1.0
0.5 0.75
0.0 0.0
0.0 0.25
0.0 0.0
cement.3l 11,l2 Apparently, these inadequacies have discouraged the use of resin luting agents for cementation of precision restorations. A recently introduced adhesive resin cement, Panavia EX (Kuraray Co. Ltd., Osaka, Japan), is claimed to adhere chemically, as well as mechanically, to tooth substances, dental alloys, and porcelain. It is a quartz-filled BIS-GMA composite resin that has a low film thickness and low solubility in oral fluids, and it differs from conventional resin cements in that a phosphate ester is added to the monomer.13The addition of this phosphate monomer (MlOP or lo-methacryloyloxydecyl dihydrogen phosphate) contributes to its chemical adhesion to tooth structures and dental alloys, besides establishing the micromechanical bond. Another clinically important benefit inherent in the new adhesive resin cement is its anaerobic characteristic, because polymerization is retarded by oxygen in the air.13 This anaerobic property keeps the excess cement at the restorative margin uncured for a longer period of time, thereby facilitating its removal. This study evaluated the sealing ability of a new resin cement (Panavia EX) used in the cementation of cast-gold complete crown restorations, as compared with those cemented with a standard zinc phosphate cement.
Thirty freshly extracted human molar teeth of comparable crown length and size were selected. Each tooth was mounted with the long axes vertically positioned on phenolic rings with autopolymerizing methyl methacrylate resin (Orthocryl, Stratford-Cooksen, Newnan, Ga.). The teeth had been kept in water since extraction. The coronal portion of each tooth was prepared for a complete crown with nearly parallel walls and a chamfer finish line by use of a medium round-ended/tapered diamond bur (No. 767.9, ESPE-Premier, Norristown, Pa.) at high speed, cooled with an air and water spray. A custom-made paralleling device aided in attaining a con-
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Table
11. Summary of Kruskal-Wallis
one-way ANOVA
Significance
Interface
N
X2
T-C M-C
30 30
10.5596
0.0051
s
3.0968
0.2126
NS
Table
III.
Summary of Mann-Whitney
Interface
Groups compared
Grp I-Grp 2 Grp 1-Grp 3 Grp 2-Grp 3
T-C
tests u
17.0 12.0 33.0
Wailed
P
0.0062 0.0057 0.2299
sistent taper for each crown preparation (Fig. 1). Copper band impressions were then made of the tooth-preparations with an addition silicone (Express, 3M Dental Products, St. Paul, Minn.) and dies made from type IV stone (DieKeen, Columbus/Miles Dental Products, South Bend, Ind.), with a powder/water ratio of 50 gm/Y2 cc. Casting
the crowns
The dies were coated with four layers of die relief spacer (Tru-Fit Die Relief, George Taub Products, Jersey City, N.J.); patterns with flat occlusal surfaces were made with type I blue-inlay wax (Hard, Kerr/Sybron Mfg. Co., Emerville, Calif.). The patterns were sprued, invested in a gypsum-bonded investment (Cristobalite, Whip Mix Corp., Louisville, KY.), and cast in type III gold alloy (Harmony Line, Hard, Williams Dental Co. Inc., Buffalo, N.Y.) by using a standard lost-wax technique. Afterward, the castings were cleaned in pickling solution (Jel Pat, J. F. Jelenko, New Rochelle, N. Y.). Any nodules at the inner surface of the castings that interfered with complete seating were removed with a slow-speed bur. Finally, the inner surfaces of all castings were microblasted with 50 Frn alumina powder (Williams Gold Refining Co. Inc.) for 15 seconds and ultrasonically cleaned in deionized water for 10 minutes. The 30 specimens were randomly divided into three groups of 10 each, as follows: Group 1. Castings luted with zinc phosphate cement and stored for 30 days in water at 37’ C before thermocycling served as the control. Group 2. Castings were luted with an adhesive resin cement (Panavia EX) and stored for 30 days in water at 37O C before thermocycling. Group 3. Castings were luted with an adhesive resin cement (Panavia EX) as in group 2, but stored for 90 days in water at 37’ C!before thermocycling. Cementation
of crowns
Before cementation, the tooth-preparations were lightly pumiced and thoroughly cleaned with water, then dried with filtered compressed air. Type I zinc phosphate cement 13
TJAN,
(Flecks cement, powder batch No. D26070588, liquid No. H73110486, Mizzy, Inc., Clifton Forge, Va.) was mixed according to the manufacturer’s specification with a powder/ liquid ratio of 0.8 gm/0.3 cc and was used to cement the crowns in the control group (group 1). Standardization of successive mixes was accomplished by proportioning the cement powder on a precision scale and the liquid with a 1 cc graduated syringe. Two coats of copal varnish (Copalite, Cooley and Cooley, Ltd., Houston, Tex.) were applied to the tooth preparations of the control group before cementation. Groups 2 and 3 were cemented with an adhesive resin luting agent (Panavia EX, Batch No. 641310) mixed and applied according to manufacturer’s instructions. Each casting was then filled with sufficient cement to evenly cover the inner surface, seated on the tooth with digital pressure, and sustained under 5 kg static load for 10 minutes with a loading device as shown in Fig. 2. The room temperature during cementation was 22’ rt lo C, and relative humidity was 50 % + 5 % . After cementation the specimens were demounted from the phenolic rings and stored in water for the specified time intervals mentioned. The root apices were sealed by a cavity prepared with a No. 33 inverted cone to a depth of approximately 2 mm and filled with amalgam (Dispersalloy, regular set, Batch No. 75847, Johnson & Johnson Dental Care Co., New Brunswick, N.J.). The root surfaces were sealed with two coats of clear nail polish. The specimens were then subjected to 300 temperature cycles between 5O C and 55’ C with a l-minute dwell time in water baths containing 0.5% aqueous solution of basic fuchsin dye. The specimens were rinsed after thermocycling, and the root surfaces were lightly pumiced to remove any superficial dye, then embedded individually in phenolic rings with epoxy resin (Buehler Ltd., Lake Bluff, Ill.). Each tooth was further sectioned longitudinally through the center of the restoration, faciolingually and mesiodistally, with an lsomet low-speed diamond saw (Buehler Ltd.). The extent of dye penetration at the facial, lingual, mesial, and distal margins was assessedalong both tooth-cement (T-C) and metal-cement (M-C) interfaces with a microscope at xl00 magnification (Toolmakers, Mitutoyo, Tokyo, Japan), and scored ordinally according to the following scale (Fig. 3): O-No microleakage I-Microleakage to one third of axial wall 2-Microleakage to two thirds of axial wall 3-Microleakage along full length of axial wall 4-Microleakage over occlusal surface The marginal microleakage for each crown at each interface was the average of the scores of dye penetration recorded from the facial, lingual, mesial, and distal margins. The data for each interface (T-C or M-C) were separately
14
analyzed with a Kruskal-Wallis ance. A Mann-Whitney U-test among the groups. A statistical software package (SPSS/PC+,
DUNN,
AND
GRANT
one-way analysis of variwas used for comparison analysis was done with a SPSS, Inc., Chicago, Ill.).
RESULTS Marginal microleakage scores, median, and range of the three test groups are presented in Table I. Analysis of the data for T-C and M-C interfaces indicated a statistically significant difference at p < 0.01 and p < 0.05, respectively (Table II). The Mann-Whitney test indicated that crowns cemented with Panavia EX produced significantly less microleakage at both T-C and M-C interfaces as compared with those luted with zinc phosphate cement (Table III). No difference was found in the extent of dye penetration of crowns cemented with Panavia EX between immersion in water for 30 and for 90 days. Fig. 4 presents the photomicrographs of some representative specimens, showing the dye penetration at the margins. DISCUSSION Although tinplating is advocated to promote a chemical bond of Panavia EX resin cement to gold restoration,13 the findings of this study seemed to suggest that microblasting the cast gold crowns with 50 pm alumina powder only is adequate to prevent microleakage at the M-C interface. Perhaps this finding would be beneficial and even desirable to dentists, because tinplating unit is not readily available in most dental laboratories or dental offices. Microleakage was only observed at the T-C interfaces when crowns were cemented with Panavia EX. Phosphate-bonding to hydroxyapatite calcium in phosphorus-based dentin adhesives tends to degrade hydrolytically after prolonged immersion or thermal cycling in water.14 Diaz-Arnold et al.lj reported that Panavia EX exhibits a significant decrease in bond strength when subjected to longer storage time in water. In contrast, this study revealed no significant difference in marginal leakage between 30-day and go-day storage in water at 37’ C in addition to thermal cycling. Because hydrolytic stability of adhesive bonds is of primary concern in the clinical use of luting agents, further study is recommended to determine whether a storage time longer than 90 days could adversely affect the degree of microleakage. SUMMARY
AND
CONCLUSIONS
This study evaluated and compared the marginal leakage of cast gold complete crowns cemented with Panavia EX cement with those cemented with a standard zinc phosphate cement. The effect of storage time in water was also studied. The results were as follows. 1. Crowns cemented with Panavia EX cement exhibited substantially less marginal leakage than those cemented with zinc phosphate cement. 2. No significant difference in microleakage was ob-
JANUARY
1992
VOLUME
67
NUMBER
P
MARGINAL
LEAKAGE
OF GAST GOLD CROWNS
served between 30-day and go-day water immersion of crowns cemented with Panavia EX cement. 3. No dye penetration was observed at the microblasted M-6 interfaces of crowns cemented with Panavia EX cement. We thank J. Morita cement, and Williams
U.S.A., Inc. for supplying the Panavia EX Dental Gold for providing the gold alloy.
REFERENCES 1. Tjan AHL, Miller GD, Whang SB, Sarkissian R. The effect of thermal stress on the marginal seal of cast gold full crowns. J Am Dent Assoc 1979;100:48-51. 2. Tjan AHL, Peach KD, VanDenbergh SL, Zbaraschuk ER. Microleakage of crowns cemented with glass ionomer: effects of preparation finish and conditioning with polyacrylic acid. 3 PROSTHETDENT (in press). 3. Phillips RW. Skinner’s science of dental materials. 8th ed. Philadelphia: WI3 Saunders Co, 1982;23-5, 58-7, 478. 4. Da&i SF, Stigers RW. Reduction of pulpal inflammation and thermal sensitivity in amalgam-restored teeth treated with copal varnish. J Am Dent Assoc 196’7;74:1281-5. 5. Br$nnstriim M, Nyborg H. Cavity treatment with a microbicidal fluoride solution: growth of bacteria and effect on the pulp. J PROSTHET DENT 1973;30:303-10. 6. Bergenholtz G, Cox CF, Loeske WJ, Syed SA. Bacterial leakage around dental restorations: its effect on the dental pulp. J Oral Pathol 1982; 11:439-50.
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
7. Br&nstr& M. Communication between the oral cavity and the dental pulp associated with restorative treatment. Oper Dent 1984;9:5768. 8. Tjan AHL, Chiu J. Microleakage of core materials for complete cast goid crowns. J PROSTHETDENT 1989;61-659-64. 9. Leinfelder KF, Lemons JE. Clinical restorative materials and techniques. 1st ed. Philadelphia: Lea & Febiger, 1988;109. 10. Stanicec M, Giles WS, Saiku JM, Hattori M. Caries penetration and cement thickness of three luting agents. Int J Prosthodont 1988;1:25963. 11. Council on dental materials and devices. American Dental Association. Polymers used in dentistry. II. Resins containing BISGMA: coating and cementing uses. 3 Am Dent Assoc 1975;90:841. 12. Craig RG. Restorative dental materials. 7th ed. St Louis: CV Mosby Co., 1985;188-91. 13. Wada T. Development of a new adhesive material and its properties. In: Gettlemen L, Vryhoef MMA, Uchiyama Y, eds. Proceedings of the international symposium on adhesive prosthodontics. Nymegen, The Netherlands: Eurosound Drukkery BV, 1986;9-19. 14. Eliades CC, Vougiouklakis. 31P-NMR study of P-based dental adhesives and electron probe microanalysis of simulated interfaces with dentin. Dent Mater 1989;5:101-8. 15. Diaz-Arnold AM, Williams VD, Aquiline SA. Tensile strengths of three Iuting agents for adhesion fixed partial dentures. Int J Prosthodont 1989;2:115-22.
Reprintrequeststo: DR. ANTHONYH. L. TJAN SCHOOL OF DENTISTRY LOMA LINDA UNIVERSITY LOMA LINDA, CA 92350
DDS,”
Wed
with
a
and
The microleakage of cast gold complete crowns cemented with Panavia EX cement was evaluated and compared with those luted with a standard zinc phosphate cement. The effect of water immersion of specimens for 30 and 90 days was also investigated. The finding of this study indicated that crowns cemented with Panavia EX cement exhibited substantially less marginal leakage than those cemented with zinc phosphate cement. No significant difference in marginal leakage was observed between 30-day and go-day water immersion of crowns cemented with Panavia EX cement. (J PROSTHET DENT 1992;67:11-5.)
ecause cast restorations cannot be made without leaving a marginal gap, luting cements still play a pivotal role in sealing the margins as a prevention against marginal
leakage. Unfortunately, most of the dental cements available cannot guarantee continual impermeability.1,2 Moreover, because of their relatively high solubility in oral fluids, a gap thus created at the restoration margin may become a protective repository for microorganisms that release toxic products. These toxins may eventually cause gingival inflammation, secondary caries, and/or inflammatory pulpal lesions.3-7 Resin-based cement is generally a low-viscosity, chemically cured composite resin, and is one of the newer classes
aProfessor and Direct.or of Biomaterials Research, Department of Restorative Dentistry, bAssociate Professor, Department of Restorative Dentistry, “Professor, Department of Restorative Dentistry. 10/l/29659
Fig. 2. Loading device used to provide S-kg static load during cementation.
Fig. 2. Custom-made teeth. TNE
JOURNAL
paralleling
OF PROSTI3ETXC
device used to prepare
DENTISTRY
Fig. 3. Diagram roleakage.
of criteria
for scoring values of mic-
11
TJAN,
DUNN,
AND
GRANT
Fig. 4. Micrographs of sectioned crown margins at x30 magnification. A, No microleakage of crown cemented with Panavia EX cement after 30-day water immersion. B, Despite significant cement margin, no microleakage of crown cemented with Panavia EX cement was observed after go-day water immersion. C, and D, Severe microleakage in crowns luted with zinc phosphate cement.
of 11 uting cements available commercially. Information conelerning clinical performance is still scarce. However, in vitrc ) studies reported severe marginal leakage of cast crov5ms luted with resin cement.4 g Further, Staninec et aLlo found that resin cement produced a substantially 12
greater cement film thickness compared with zinc: phosphate cement and concluded that its use for cemelntation of precision castings was inadvisable. Other shortcl omings of resin cements include short working time, irrita .tion to dental pulp, and difficulty in removing the cured excess
JANUARY
1992
VOLUME
67
NUMBER
1
MARGlNAL
Tablie
LEAKAGE
OF CAST
GOLD
CROWNS
I. Microleakage raw scores, median, and range
SpeCiXIHXl No.
Flecks
(30 d)
Panavia
(30 d)
T-C
M-C
T-C
M-C
i 2 3 4 5 6 7 8 9 10 Median
2.5 0 2 1.75 1 1.5 0 1.5 1 3.5 1.5
Range
3.5
Panavia T-C
(90 d) M-C
0 0 0 0.5 1 1 0 0 0.5 0
0 0 0 0.5 0.75 0.25 0.5 0 0 0.25
0 0 0 0 0 0 0 0 0 0
0 0 0 0.25 0 0 0 0 0.25 0.25
0 0 0 0 0 0 0 0 0 0
0.25 1.0
0.5 0.75
0.0 0.0
0.0 0.25
0.0 0.0
cement.3l 11,l2 Apparently, these inadequacies have discouraged the use of resin luting agents for cementation of precision restorations. A recently introduced adhesive resin cement, Panavia EX (Kuraray Co. Ltd., Osaka, Japan), is claimed to adhere chemically, as well as mechanically, to tooth substances, dental alloys, and porcelain. It is a quartz-filled BIS-GMA composite resin that has a low film thickness and low solubility in oral fluids, and it differs from conventional resin cements in that a phosphate ester is added to the monomer.13The addition of this phosphate monomer (MlOP or lo-methacryloyloxydecyl dihydrogen phosphate) contributes to its chemical adhesion to tooth structures and dental alloys, besides establishing the micromechanical bond. Another clinically important benefit inherent in the new adhesive resin cement is its anaerobic characteristic, because polymerization is retarded by oxygen in the air.13 This anaerobic property keeps the excess cement at the restorative margin uncured for a longer period of time, thereby facilitating its removal. This study evaluated the sealing ability of a new resin cement (Panavia EX) used in the cementation of cast-gold complete crown restorations, as compared with those cemented with a standard zinc phosphate cement.
Thirty freshly extracted human molar teeth of comparable crown length and size were selected. Each tooth was mounted with the long axes vertically positioned on phenolic rings with autopolymerizing methyl methacrylate resin (Orthocryl, Stratford-Cooksen, Newnan, Ga.). The teeth had been kept in water since extraction. The coronal portion of each tooth was prepared for a complete crown with nearly parallel walls and a chamfer finish line by use of a medium round-ended/tapered diamond bur (No. 767.9, ESPE-Premier, Norristown, Pa.) at high speed, cooled with an air and water spray. A custom-made paralleling device aided in attaining a con-
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
Table
11. Summary of Kruskal-Wallis
one-way ANOVA
Significance
Interface
N
X2
T-C M-C
30 30
10.5596
0.0051
s
3.0968
0.2126
NS
Table
III.
Summary of Mann-Whitney
Interface
Groups compared
Grp I-Grp 2 Grp 1-Grp 3 Grp 2-Grp 3
T-C
tests u
17.0 12.0 33.0
Wailed
P
0.0062 0.0057 0.2299
sistent taper for each crown preparation (Fig. 1). Copper band impressions were then made of the tooth-preparations with an addition silicone (Express, 3M Dental Products, St. Paul, Minn.) and dies made from type IV stone (DieKeen, Columbus/Miles Dental Products, South Bend, Ind.), with a powder/water ratio of 50 gm/Y2 cc. Casting
the crowns
The dies were coated with four layers of die relief spacer (Tru-Fit Die Relief, George Taub Products, Jersey City, N.J.); patterns with flat occlusal surfaces were made with type I blue-inlay wax (Hard, Kerr/Sybron Mfg. Co., Emerville, Calif.). The patterns were sprued, invested in a gypsum-bonded investment (Cristobalite, Whip Mix Corp., Louisville, KY.), and cast in type III gold alloy (Harmony Line, Hard, Williams Dental Co. Inc., Buffalo, N.Y.) by using a standard lost-wax technique. Afterward, the castings were cleaned in pickling solution (Jel Pat, J. F. Jelenko, New Rochelle, N. Y.). Any nodules at the inner surface of the castings that interfered with complete seating were removed with a slow-speed bur. Finally, the inner surfaces of all castings were microblasted with 50 Frn alumina powder (Williams Gold Refining Co. Inc.) for 15 seconds and ultrasonically cleaned in deionized water for 10 minutes. The 30 specimens were randomly divided into three groups of 10 each, as follows: Group 1. Castings luted with zinc phosphate cement and stored for 30 days in water at 37’ C before thermocycling served as the control. Group 2. Castings were luted with an adhesive resin cement (Panavia EX) and stored for 30 days in water at 37O C before thermocycling. Group 3. Castings were luted with an adhesive resin cement (Panavia EX) as in group 2, but stored for 90 days in water at 37’ C!before thermocycling. Cementation
of crowns
Before cementation, the tooth-preparations were lightly pumiced and thoroughly cleaned with water, then dried with filtered compressed air. Type I zinc phosphate cement 13
TJAN,
(Flecks cement, powder batch No. D26070588, liquid No. H73110486, Mizzy, Inc., Clifton Forge, Va.) was mixed according to the manufacturer’s specification with a powder/ liquid ratio of 0.8 gm/0.3 cc and was used to cement the crowns in the control group (group 1). Standardization of successive mixes was accomplished by proportioning the cement powder on a precision scale and the liquid with a 1 cc graduated syringe. Two coats of copal varnish (Copalite, Cooley and Cooley, Ltd., Houston, Tex.) were applied to the tooth preparations of the control group before cementation. Groups 2 and 3 were cemented with an adhesive resin luting agent (Panavia EX, Batch No. 641310) mixed and applied according to manufacturer’s instructions. Each casting was then filled with sufficient cement to evenly cover the inner surface, seated on the tooth with digital pressure, and sustained under 5 kg static load for 10 minutes with a loading device as shown in Fig. 2. The room temperature during cementation was 22’ rt lo C, and relative humidity was 50 % + 5 % . After cementation the specimens were demounted from the phenolic rings and stored in water for the specified time intervals mentioned. The root apices were sealed by a cavity prepared with a No. 33 inverted cone to a depth of approximately 2 mm and filled with amalgam (Dispersalloy, regular set, Batch No. 75847, Johnson & Johnson Dental Care Co., New Brunswick, N.J.). The root surfaces were sealed with two coats of clear nail polish. The specimens were then subjected to 300 temperature cycles between 5O C and 55’ C with a l-minute dwell time in water baths containing 0.5% aqueous solution of basic fuchsin dye. The specimens were rinsed after thermocycling, and the root surfaces were lightly pumiced to remove any superficial dye, then embedded individually in phenolic rings with epoxy resin (Buehler Ltd., Lake Bluff, Ill.). Each tooth was further sectioned longitudinally through the center of the restoration, faciolingually and mesiodistally, with an lsomet low-speed diamond saw (Buehler Ltd.). The extent of dye penetration at the facial, lingual, mesial, and distal margins was assessedalong both tooth-cement (T-C) and metal-cement (M-C) interfaces with a microscope at xl00 magnification (Toolmakers, Mitutoyo, Tokyo, Japan), and scored ordinally according to the following scale (Fig. 3): O-No microleakage I-Microleakage to one third of axial wall 2-Microleakage to two thirds of axial wall 3-Microleakage along full length of axial wall 4-Microleakage over occlusal surface The marginal microleakage for each crown at each interface was the average of the scores of dye penetration recorded from the facial, lingual, mesial, and distal margins. The data for each interface (T-C or M-C) were separately
14
analyzed with a Kruskal-Wallis ance. A Mann-Whitney U-test among the groups. A statistical software package (SPSS/PC+,
DUNN,
AND
GRANT
one-way analysis of variwas used for comparison analysis was done with a SPSS, Inc., Chicago, Ill.).
RESULTS Marginal microleakage scores, median, and range of the three test groups are presented in Table I. Analysis of the data for T-C and M-C interfaces indicated a statistically significant difference at p < 0.01 and p < 0.05, respectively (Table II). The Mann-Whitney test indicated that crowns cemented with Panavia EX produced significantly less microleakage at both T-C and M-C interfaces as compared with those luted with zinc phosphate cement (Table III). No difference was found in the extent of dye penetration of crowns cemented with Panavia EX between immersion in water for 30 and for 90 days. Fig. 4 presents the photomicrographs of some representative specimens, showing the dye penetration at the margins. DISCUSSION Although tinplating is advocated to promote a chemical bond of Panavia EX resin cement to gold restoration,13 the findings of this study seemed to suggest that microblasting the cast gold crowns with 50 pm alumina powder only is adequate to prevent microleakage at the M-C interface. Perhaps this finding would be beneficial and even desirable to dentists, because tinplating unit is not readily available in most dental laboratories or dental offices. Microleakage was only observed at the T-C interfaces when crowns were cemented with Panavia EX. Phosphate-bonding to hydroxyapatite calcium in phosphorus-based dentin adhesives tends to degrade hydrolytically after prolonged immersion or thermal cycling in water.14 Diaz-Arnold et al.lj reported that Panavia EX exhibits a significant decrease in bond strength when subjected to longer storage time in water. In contrast, this study revealed no significant difference in marginal leakage between 30-day and go-day storage in water at 37’ C in addition to thermal cycling. Because hydrolytic stability of adhesive bonds is of primary concern in the clinical use of luting agents, further study is recommended to determine whether a storage time longer than 90 days could adversely affect the degree of microleakage. SUMMARY
AND
CONCLUSIONS
This study evaluated and compared the marginal leakage of cast gold complete crowns cemented with Panavia EX cement with those cemented with a standard zinc phosphate cement. The effect of storage time in water was also studied. The results were as follows. 1. Crowns cemented with Panavia EX cement exhibited substantially less marginal leakage than those cemented with zinc phosphate cement. 2. No significant difference in microleakage was ob-
JANUARY
1992
VOLUME
67
NUMBER
P
MARGINAL
LEAKAGE
OF GAST GOLD CROWNS
served between 30-day and go-day water immersion of crowns cemented with Panavia EX cement. 3. No dye penetration was observed at the microblasted M-6 interfaces of crowns cemented with Panavia EX cement. We thank J. Morita cement, and Williams
U.S.A., Inc. for supplying the Panavia EX Dental Gold for providing the gold alloy.
REFERENCES 1. Tjan AHL, Miller GD, Whang SB, Sarkissian R. The effect of thermal stress on the marginal seal of cast gold full crowns. J Am Dent Assoc 1979;100:48-51. 2. Tjan AHL, Peach KD, VanDenbergh SL, Zbaraschuk ER. Microleakage of crowns cemented with glass ionomer: effects of preparation finish and conditioning with polyacrylic acid. 3 PROSTHETDENT (in press). 3. Phillips RW. Skinner’s science of dental materials. 8th ed. Philadelphia: WI3 Saunders Co, 1982;23-5, 58-7, 478. 4. Da&i SF, Stigers RW. Reduction of pulpal inflammation and thermal sensitivity in amalgam-restored teeth treated with copal varnish. J Am Dent Assoc 196’7;74:1281-5. 5. Br$nnstriim M, Nyborg H. Cavity treatment with a microbicidal fluoride solution: growth of bacteria and effect on the pulp. J PROSTHET DENT 1973;30:303-10. 6. Bergenholtz G, Cox CF, Loeske WJ, Syed SA. Bacterial leakage around dental restorations: its effect on the dental pulp. J Oral Pathol 1982; 11:439-50.
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
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