Effects of cement, cement space, marginal design, materials, and seating force on crown cementation Chu-Jung Wang, Dan Nathanson,
DMD, DMD,
MSD,a MSDc
Philip
L. Millstein,
DMD,
MS,b
seating
aid
and
Boston University, Henry M. Goldman School of Graduate Dentistry, Boston, Mass. An evaluation of the effects of a die spacer, the seating force, the marginal design, seating aid materials, and the cement type during cementation was conducted. Two stainless steel dies were used: one with a 1 mm shoulder and the other with a shoulder and a 65degree bevel. Ten stone dies were produced from each metal die and half were painted with four layers of die spacer. The crowns were waxed on the dies and cast in a nonprecious alloy, and the seating of crowns was measured with a micrometer before and after cementation. Comparisons were made between zinc phosphate and glass ionomer cements under two seating forces of 5 and 30 lb using an orangewood stick or E-Z-bite seating aid. ANOVA and the Newman-Keuls test revealed that the use of a die spacer, a heavier force of 30 lb, and glass ionomer cement significantly improved crown seating. The beveled preparation led to superior crown seating when the heavier force or glass ionomer cement was used. The orangewood stick and bite device had a similar effect on crown seating. (J PROSTHET
DENT
1992;67:786-90.)
T
he incomplete seating of a crown during cementation may result in the failure of an otherwise adequate cast restoration. The marginal adaptation of a cast crown is clearly crucial for the success of a cast restorati0n.l However, there is no correlation between the precementation marginal fit and postcementation marginal seal because of the cement. The more accurately the casting fits the prepared tooth, the more difficult it is for cement to escape from the inner surface of the crown and the surface of the prepared tooth. 2,3 According to Hollenback,4 a minimum of 25 pm relief on the axial walls of a casting is necessary or the cast crown may fail to seat by approximately 100 pm. The adverse effects of viscous luting cements, variations in marginal designs, magnitudes of seating force, cements and different seating aid materials may complicate crown seating during cementation. This study evaluated the effects of cements, cement space, seating forces, marginal designs, and seating aids, including the interactions between these fa.ctors during cementation. MATERIALS
AND
METHODS
Two stainless steel dies, 6 mm high, were designed to simulate complete crown preparations, with lo-degree tapers and 1 mm wide shoulders. One die was further prepared with the shoulder margin at a 65-degree bevel Presented in part at the International Associationof Dental Researchmeeting, Cincinnati, Ohio, 1990. Submitted in partial fulfillment of the requirements of the Master of Sciencedegree in Prosthodontics. aFormer Graduate Student in Prosthodontics. bAssociateClinical Professor,Department of Biomaterials. cProfesaorand Chairman, Department of Biomaterials. 10/l/35959
786
(Fig. -1). A V-shaped notch was prepared on the occlusal surface of each die and a small dimple was carved on one side of the “V” for orientation. Ten impressions were made from each metal die with polyether impression material (Impregum-F, Premier, Norristown, Pa.). The impressions were poured with Super-Die die stone (Whip Mix Corp., Louisville, Ky.) using the manufacturer’s recommended powder/liquid ratio. Four coats of die spacer (Tru-Fit, George Taub Products and Fusion Co., Jersey City, N.J.) were painted on five dies of each type. New die spacer kits were used for every five stone dies and the kits were discarded after the first 30 minutes to maintain constant thickness of die spacer. Die spacer was applied alternately in coats of silver and gold for a total of four coats. Rieger et a1.5believed that this method would ensure 24 pm of thickness. After applying a thin layer of die lubricant (Die-Lube, Ney, Bloomfield, Conn.), the stone dies were submerged in melted wax (Inlay casting wax, hard, Type I, Class III, Kerr Co., Romulus, Mich.), and were then transferred to silicone molds for the final crown contour. The wax pattern was designed with an elevated flat ridge on the top and a hole through the ridge to facilitate the removal of the crown after cementation. A vertical line was scribed on the wax pattern to match the vertical line on the cervical root surface of the die. Marks and numbers were imprinted on the patterns for identification. The wax patterns were invested in phosphate-bound investment (Hi-Temp, Whip Mix Corp.). To compensate for the shrinkage of the nonprecious metal (Rexillium-III, Rx Jeneric Gold Co., Wallingford, Conn.), the percentage of the “special” liquid was increased to 80 % of the investment mix. The wax patterns were vaporized at 900’ F for half an
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1992
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6
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CROWN
CEMENTATION
Table I. The effects of die spacer, cement, and seating force on crown seating
Cement
Die spacer No die spacer No die spacer No die spacer No die spacer
ZPC
spacer spacer spacer Die spacer
ZPC ZPC
Die
Die Die
ZPC GIC GIC
GIC GIC
Zinc phosphate cement (Ketac-Cem, Premier).
ZPC,
(Flecks,
Force (lb) 5 30
5 30 5 30 5 30 Mizzy);
seating discrepancies (rm) 116 73 43 18
k r + t
14 16 15 8
12 f 8 2*5 4+3 -5 f 5 GIG, glass ionomer
cement
hour, and the investment was heat soaked at 1560’ F for 1 hour before casting. The temperature was carefully elevated 12” F/min, and an electronic induction casting machine (Autocast Digital Induction Casting Unit, Unitek/ 3M, Monrovia, Calif.) was selected for casting. Afterward, the castings were cleansed by sandblasting and the internal aspects (intaglio) of each casting were inspected. Stencil correction fluid was used to identify small nodules that were removed by a No. l/2 round bur from the internal surfaces of the castings until the castings appeared to fit their respective dies passively but were not easily dislodged. The castings were then cleaned with acetone followed by water in an ultrasonic machine. The occlusal loading table of each casting was made parallel to the base of the die and was polished. The crowns were loaded with 5 or 30 lb of force for 3 minutes, and precementation measurements were determined with a 25 mm digital linear micrometer (Starrett Co., Athol, Mass.) to the nearest 0.001 mm. The precementation loadings and measurements for the crown-die assembly were repeated until two consecutive measurements were identical. Zinc phosphate cement (Flecks, Mizzy Inc., Cherry Hill, N.J.) was incorporated incrementally over a large surface of a glass slab for 90 seconds with the powder/liquid ratio of 1 gm/0.56 ml at room temperature (25’ C). A small amount of cement was painted on the margin and axial walls of the inner surfaces of each crown.6 The casting was subjected to 5 lb of force from the Instron testing machine (Instron, Model 4202, Instron Corp., Canton, Mass.), using an orangewood stick (Aidaco, Interstate Dental Co., Freeport, N.Y.) within 2 minutes and 30 seconds from the initiation of the cement mix. The castings and metal dies were removed from the Instron machine after the cement had set, and postcementation measurements were recorded. The differences between postcementation and precementation measurements were designated as seating discrepancies. The same procedures were repeated for castings at
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JOURNAL
OF PROSTHETIC
DENTISTRY
Fig.
1. Metal test dies. A, Shoulder-bevel; B, shoulder.
A.
B.
Fig.
2. E-Z bite material. A, Lateral view; B, occlusal view.
30 lb loads with an orangewood stick, and at 5 lb and 30 lb loads with E-Z bite (Gingipak Co. Inc., Camerillo, Calif.), a three-layered seating aid material of varying consistency (Fig. 2). The same cementation procedures and measurements were repeated using glass ionomer cement (Ketac-Cem, Premier, Norristown, Pa.), with a powder/liquid ratio of 3.4 gm/l.O ml. The powder was added to the liquid in small, equal increments on a cold, dry glass slab, and the mixing was accomplished in 1 minute. The designated seating force was applied fully within 2 minutes from the start of mixing, and the cement set after 7 minutes. RESULTS Five factors were involved in the cementation of metal cast crowns: (1) die spacer (with or without); (2) marginal design (shoulder versus shoulder bevel); (3) cement (zinc phosphate versus glass ionomer cement); (4) seating force (5 versus 30 lb); and (5) seating aids (orangewood stick versus E-Z bite device). A five-factor analysis of variance (ANOVA) was used to determine the interactions that had significant effects on the seating discrepancy of crown ce-
787
WANG,
5 (Ibs. )
MILLSTEIN,
AND
NATHANSON
30 ( Ibs. )
Seating force 3. Effects of cement and seating force on the seating of artificial metal crowns without die spacer. ZPC, Zinc phosphate cement; GIG, glass ionomer cement.
Fig.
II. The interaction of cement and seating force on crown seating without die spacer
Table
ZPC 5 lb 30 lb Abbreviations
116 73 as in Table
GIC
pm pm
pm 18 pm
43
% Difference 170 305
I.
mentation. The statistical analysis disclosed no significant five-factor or four-factor interactions. However, significant three-factor interactions involving the combinations of die spacer, marginal design, seating force, and cement type were: (1) die spacer :X cement X seating force; (2) die spacer x marginal des,ign x seating force; and (3) die spacer X marginal design X cement. The seating aid materials did not appear to influence the interactions, and the overall comparison of orangewood stick versus E-Z bite revealed no appreciable difference in crown seating. However, the die spacer was a factor in all three significant interactions. The subgroup means in Table I revealed that the seating discrepancies in groups without the die spacer were greater than those in groups with die spacer. The data were separated into two subsets, namely no die spacer and die spacer, and a four-factor ANOVA was computed for each set. The cement by force interaction without die spacer was significant (p = 0.002, four-factor ANOVA). The NewmanKeuls test confirmed that the seating discrepancy was significantly greater with zinc phosphate cement than with glass ionomer cement (p < 0.01, Newman-Keuls). The crown seating was significantly improved as seating force was elevated from 5 to 30 lb with each cement (p < 0.01, Newman-Keuls) (Fig. 3). The difference in seating discrepancies between zinc phosphate cement and glass ionomer cement was 170% at the 5 lb seating force, while it was 788
305 % at the 30 lb seating force. This disparity in percentage indicated a strong interaction between cement type and seating force (Table II). The marginal design by seating force interaction using a die spacer was significant (p = 0.001, four-factor ANOVA). On a die-spaced shoulder-bevel preparation, crown seating upon cementation was significantly improved by an elevated seating force (p < 0.01, Newman-Keuls) (Fig. 4). Nevertheless, crown seating during cementation on a diespaced shoulder preparation was not significantly improved by raising the seating force (Fig. 4). The die-spaced shoulder-bevel preparation was also significantly superior to the die-spaced straight shoulder preparation with respect to crown seating using 30 lb of seating force (p < 0.05, Newman-Keuls). However, the die-spaced shoulder-bevel preparation was not superior to the die-spaced straight shoulder preparation with 5 lb of force. The marginal design with the die spacer by cement interaction was significant (p = 0.004, four-factor ANOVA). Crown seating upon cementation with a die-spaced shoulder-bevel preparation was significantly improved using a glass ionomer cement compared with a zinc phosphate cement (p < 0.01, Newman-Keuls) (Fig. 5). However, there was no significant difference with respect to crown seating upon cementation on a die-spaced shoulder preparation with different cements. The die-spaced shoulder-bevel preparation was substantially superior to the die-spaced straight shoulder preparation in crown seating using glass ionomer cement (p < 0.05, Newman-Keuls) (Fig. 5). The difference between the gingival finish line preparations was not significant using zinc phosphate cement. DISCUSSION The acquisition of cement space by applying a die spacer has been advocated by several investigators7-g to enhance the complete seating of crowns during cememation. The
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1992
VOLUME
67
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6
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, CROWN
CEMENTATION
Shoulder-bevel Shoulder
I
5 ( Ibs. ) 30 (Ibs. ) Seating force Fig. 4. Effects of marginal design and seating force on the seating of artificial metal crowns with die spacer.
Shoulder-bevel c> Shoulder
GIC
ZPC Cement
Fig. 5. Effects of marginal design and cement on the seating of artificial metal crowns with die spacer. Abbreviations as in Fig. 3. seating discrepancy during crown cementation decreased dramatically using a die spacer during the fabrication of cast crowns (Table I). Die spacer creates space for the cement film on the occlusal and axial surfaces of a prepared tooth, relieves the hydraulic pressure during the initial stage of cementation, and facilitates distribution of cement with minimal friction resistance or filtration along the axial walls. When internal relief is not provided, the cement film between the casting and the prepared tooth hinders seating of cast crowns. When die spacer was not applied, the increase of seating force from 5 to 30 lb resulted in a significant improvement in metal crown seating upon cementation (Fig. 3). According to JorgensenlO an increase in seating force significantly reduced cement film thickness until 12 lb of force had been reached. Apparently, 5 lb of force is an inordinately light force and less than ideal for clinically seating an artificial crown.
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JOURNAL
OF PROSTHETIC
DENTISTRY
It has been reported that Ketac-Cem glass ionomer cement possessed a lower cement film thickness’l and resulted in a smaller seating discrepancy compared with zinc phosphate cement. i2 The seating discrepancy on the cementation of artificial crowns without die spacer was significantly smaller with glass ionomer cement than with zinc phosphate cement (Fig. 3). This observation was attributed to the difference in the flow of each cement; namely, the viscosity of zinc phosphate cement increased with time13 while that of glass ionomer cement remained constant before setting.l* The difference in seating discrepancy between zinc phosphate and glass ionomer cements at different forces suggested that glass ionomer cement was more responsive to an elevated seating force than zinc phosphate cement (Table II). The designs for the marginal finish lines became a factor in crown seating upon cementation when the die-spaced cast crowns were cemented. The average seating discrep789
WANG,
ancy for a die-spaced shoulder-bevel preparation with 5 lb of seating force was 11 pm. This was not significantly larger than the discrepancy of a die-spaced straight shoulder preparation, which was 6 pm. However, when the seating force was elevated to 30 lb, the discrepancy for a die-spaced shoulder-bevel preparation became -4.3 pm, and this was significantly less than the discrepancy of a die-spaced straight shoulder preparation of 1.2 pm (Fig. 4). The negative values of crown seating upon cementation are attributed to the bevel configuration of a shoulder-bevel crown that directs the crown to its most cervical position. The beveled surface also functions as a machined guide plane that magnifies the seating force15 and burnishes the shoulder and beveled surfaces of the crown to produce the observed negative values. l6 The combination of heavy cementation force and the lubricating effects of the freeflowing cement improved the seating of crowns. According to Gavelis et a1.,17a shoulder-bevel margin closes the marginal gap more rapidly than a straight shoulder margin, thereby hindering the escape of cement during cementation. However, the increase of seating force from 5 to 30 lb on a die-spaced shoulder-bevel preparation compensated for this obstacle and improved the seating of crowns. The straight shloulder finish line acted as a vertical stop so that crown seating with this preparation design was not facilitated by increasing the seating force. When zinc phosphate cement was used for cementation, the mean seating discrepancy for a die-spaced shoulderbevel preparation appeared slightly greater than that of a die-spaced straight shoulder preparation (9.2 pm versus 5.2 pm). When glass ionomer cement was used, the mean seating discrepancy for a die-spaced shoulder-bevel preparation was significantly lessthan that of a die-spaced straight shoulder preparation (-2.8 pm versus 2.1 pm) (Fig. 5). According to Gavelis et al., I7 if shoulder-bevel margins encourage early closure of marginal gaps during cementation, a greater seating discrepancy should be expected with a bevelled shoulder configuration. However, the reverse was observed with glass ionomer cement (Ketac-Cem); that is, the seating discrepancy after crown cementation of a die-spaced shoulder-bevel preparation was significantly less than that of a die-spaced straight shoulder preparation. There are two plausible factors contributing to this phenomenon. First, the cement film thickness of the glass ionomer cement was less than the allotted cement space. Second, the bevel may magnify the seating force and act as a guide plane directing the crown to its most cervical position while the straight shoulder finish line preparation restricts the advancement of the crown. The comparison between an orangewood stick and an E-Z bite revealed no significant difference in cementation. The resistance of crown cementation to seating force is extremely complicated, 130 the particular influence of these seating aid materials warrants further investigation.
790
MILLSTEIN,
AND
NATAANSON
CONCLUSIONS 1. The application of a die spacer significantly improved crown seating during cementation. 2. An elevation in seating force from 5 to 30 lb significantly improved crown seating. 3. Crown seating during cementation was substantially improved using a glass ionomer cement compared with a zinc phosphate cement. 4. The die-spaced shoulder-bevel preparation resulted in significantly superior crown seating upon cementation with the use of heavy force or a glass ionomer cement, compared with the die-spaced straight shoulder preparaA:-LIOII. 5. An orangewood stick and an E-Z bite seating aid were equally effective during crown cementation. REFERENCES 1. Schwartz IS. A review of methods and techniques to improve the fit of cast restoration. J PROSTHET DENT 1986;56:279-83. 2. Pilo R, Cardash HS, Baharav H, Helft M. Incomplete seating of cemented crowns: a literature review. J PROSTHET DENT 1988,59:429-33. 3. Moore JA, Barghi N, Brukl CE, Kaiser DA. Marginal distortion of cast restorationsinduced by cementation. J PROSTHET DENT 1985;54:336-40. 4. Hollenback GM. Precision gold inlays made by a simple technic. J Am Dent Assoc 1943;30:99-109. 5. Rieger MR, Tanquist RA, Brose MO, Ali M. Measuring the thickness of paint-on die spacer. J PROSTHET DENT 1987;58:305-8. 6. Bolouri A, Marker VA, Sarampote RV. Technique-related variation of cement film thickness under full crown. Gen Dent 1987;35:26-8. 7. Fusayama T, Ide K, Hosoda H. Relief of resistance of cement of full cast crowns. J PROSTHET DENT 1964;14:95-106. 8. Eames WB, O’Neal SJ, Monteiro J, Miller C, Roan JD Jr, Cohen KS. Techniques to improve seating of castings. J Am Dent Assoc 1978; 96~432.7.
9. Campagni WV, Wright W, Martinoff seating of complete cast gold crowns
JT. Effect of die-spacer on the with grooves. J PROSTHET DENT
1986;55:324-8. 10. Jorgensen KD.
Factors affecting the film thickness of zinc phosphate cements. Acta Odontol Stand 1963;21:479-501. 11. McLean JW, Wilson AD, Prosser HJ. Development and use of waterhardening glass ionomer luting cements. J PROSTHET DENT 1984; 52:175-81. 12. Tjan AHL,
Sarkissian R. Effect of preparation finish on retention and fit of complete crowns. J PROSTHET DENT 1986;56:283-8. 13. Kay GW, Jablonski DA, Dogon IL. Factors affecting the seating and fit of complete crowns: a computer simulation study. J PROSTHET DENT 1986;55:13-8. 14. Hill RG, Wilson
AD. A rheological study of the role of additives on the setting of glass ionomer cements. J Dent Res 1988;67:1446-50. 15. Windeler AS. Powder enrichment effects on film thickness of zinc phosphate cement. J PROSTHET DENT 1979;42:299-303. 16. Rosenstiel SF, Gegauff AG. Improving the cementation of complete cast crowns: a comparison of static and dynamic seating methods. J Am Dent Assoc 1988;117:843-8. 17. Gavelis JR, Morency JD, Riley ED, Sosio RB. The effect of various finish line preparations on the marginal seal and occlusal seat of full crown preparations. J PROSTHET DENT 1981;45:138-45. Reprirat requests to: DR. PHILIP L. MILLSTEIN BOSTGN UNIVERSITY SCHOOL OF GRADUATE DENTISTRY DEPARTMENT OF BIOMATERIALS 100 EAST NEWTON ST. BOSTGN, MA 02118
JUNE
1992
VOLUME
67
NUMBER
6
DMD, DMD,
MSD,a MSDc
Philip
L. Millstein,
DMD,
MS,b
seating
aid
and
Boston University, Henry M. Goldman School of Graduate Dentistry, Boston, Mass. An evaluation of the effects of a die spacer, the seating force, the marginal design, seating aid materials, and the cement type during cementation was conducted. Two stainless steel dies were used: one with a 1 mm shoulder and the other with a shoulder and a 65degree bevel. Ten stone dies were produced from each metal die and half were painted with four layers of die spacer. The crowns were waxed on the dies and cast in a nonprecious alloy, and the seating of crowns was measured with a micrometer before and after cementation. Comparisons were made between zinc phosphate and glass ionomer cements under two seating forces of 5 and 30 lb using an orangewood stick or E-Z-bite seating aid. ANOVA and the Newman-Keuls test revealed that the use of a die spacer, a heavier force of 30 lb, and glass ionomer cement significantly improved crown seating. The beveled preparation led to superior crown seating when the heavier force or glass ionomer cement was used. The orangewood stick and bite device had a similar effect on crown seating. (J PROSTHET
DENT
1992;67:786-90.)
T
he incomplete seating of a crown during cementation may result in the failure of an otherwise adequate cast restoration. The marginal adaptation of a cast crown is clearly crucial for the success of a cast restorati0n.l However, there is no correlation between the precementation marginal fit and postcementation marginal seal because of the cement. The more accurately the casting fits the prepared tooth, the more difficult it is for cement to escape from the inner surface of the crown and the surface of the prepared tooth. 2,3 According to Hollenback,4 a minimum of 25 pm relief on the axial walls of a casting is necessary or the cast crown may fail to seat by approximately 100 pm. The adverse effects of viscous luting cements, variations in marginal designs, magnitudes of seating force, cements and different seating aid materials may complicate crown seating during cementation. This study evaluated the effects of cements, cement space, seating forces, marginal designs, and seating aids, including the interactions between these fa.ctors during cementation. MATERIALS
AND
METHODS
Two stainless steel dies, 6 mm high, were designed to simulate complete crown preparations, with lo-degree tapers and 1 mm wide shoulders. One die was further prepared with the shoulder margin at a 65-degree bevel Presented in part at the International Associationof Dental Researchmeeting, Cincinnati, Ohio, 1990. Submitted in partial fulfillment of the requirements of the Master of Sciencedegree in Prosthodontics. aFormer Graduate Student in Prosthodontics. bAssociateClinical Professor,Department of Biomaterials. cProfesaorand Chairman, Department of Biomaterials. 10/l/35959
786
(Fig. -1). A V-shaped notch was prepared on the occlusal surface of each die and a small dimple was carved on one side of the “V” for orientation. Ten impressions were made from each metal die with polyether impression material (Impregum-F, Premier, Norristown, Pa.). The impressions were poured with Super-Die die stone (Whip Mix Corp., Louisville, Ky.) using the manufacturer’s recommended powder/liquid ratio. Four coats of die spacer (Tru-Fit, George Taub Products and Fusion Co., Jersey City, N.J.) were painted on five dies of each type. New die spacer kits were used for every five stone dies and the kits were discarded after the first 30 minutes to maintain constant thickness of die spacer. Die spacer was applied alternately in coats of silver and gold for a total of four coats. Rieger et a1.5believed that this method would ensure 24 pm of thickness. After applying a thin layer of die lubricant (Die-Lube, Ney, Bloomfield, Conn.), the stone dies were submerged in melted wax (Inlay casting wax, hard, Type I, Class III, Kerr Co., Romulus, Mich.), and were then transferred to silicone molds for the final crown contour. The wax pattern was designed with an elevated flat ridge on the top and a hole through the ridge to facilitate the removal of the crown after cementation. A vertical line was scribed on the wax pattern to match the vertical line on the cervical root surface of the die. Marks and numbers were imprinted on the patterns for identification. The wax patterns were invested in phosphate-bound investment (Hi-Temp, Whip Mix Corp.). To compensate for the shrinkage of the nonprecious metal (Rexillium-III, Rx Jeneric Gold Co., Wallingford, Conn.), the percentage of the “special” liquid was increased to 80 % of the investment mix. The wax patterns were vaporized at 900’ F for half an
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1992
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6
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CROWN
CEMENTATION
Table I. The effects of die spacer, cement, and seating force on crown seating
Cement
Die spacer No die spacer No die spacer No die spacer No die spacer
ZPC
spacer spacer spacer Die spacer
ZPC ZPC
Die
Die Die
ZPC GIC GIC
GIC GIC
Zinc phosphate cement (Ketac-Cem, Premier).
ZPC,
(Flecks,
Force (lb) 5 30
5 30 5 30 5 30 Mizzy);
seating discrepancies (rm) 116 73 43 18
k r + t
14 16 15 8
12 f 8 2*5 4+3 -5 f 5 GIG, glass ionomer
cement
hour, and the investment was heat soaked at 1560’ F for 1 hour before casting. The temperature was carefully elevated 12” F/min, and an electronic induction casting machine (Autocast Digital Induction Casting Unit, Unitek/ 3M, Monrovia, Calif.) was selected for casting. Afterward, the castings were cleansed by sandblasting and the internal aspects (intaglio) of each casting were inspected. Stencil correction fluid was used to identify small nodules that were removed by a No. l/2 round bur from the internal surfaces of the castings until the castings appeared to fit their respective dies passively but were not easily dislodged. The castings were then cleaned with acetone followed by water in an ultrasonic machine. The occlusal loading table of each casting was made parallel to the base of the die and was polished. The crowns were loaded with 5 or 30 lb of force for 3 minutes, and precementation measurements were determined with a 25 mm digital linear micrometer (Starrett Co., Athol, Mass.) to the nearest 0.001 mm. The precementation loadings and measurements for the crown-die assembly were repeated until two consecutive measurements were identical. Zinc phosphate cement (Flecks, Mizzy Inc., Cherry Hill, N.J.) was incorporated incrementally over a large surface of a glass slab for 90 seconds with the powder/liquid ratio of 1 gm/0.56 ml at room temperature (25’ C). A small amount of cement was painted on the margin and axial walls of the inner surfaces of each crown.6 The casting was subjected to 5 lb of force from the Instron testing machine (Instron, Model 4202, Instron Corp., Canton, Mass.), using an orangewood stick (Aidaco, Interstate Dental Co., Freeport, N.Y.) within 2 minutes and 30 seconds from the initiation of the cement mix. The castings and metal dies were removed from the Instron machine after the cement had set, and postcementation measurements were recorded. The differences between postcementation and precementation measurements were designated as seating discrepancies. The same procedures were repeated for castings at
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JOURNAL
OF PROSTHETIC
DENTISTRY
Fig.
1. Metal test dies. A, Shoulder-bevel; B, shoulder.
A.
B.
Fig.
2. E-Z bite material. A, Lateral view; B, occlusal view.
30 lb loads with an orangewood stick, and at 5 lb and 30 lb loads with E-Z bite (Gingipak Co. Inc., Camerillo, Calif.), a three-layered seating aid material of varying consistency (Fig. 2). The same cementation procedures and measurements were repeated using glass ionomer cement (Ketac-Cem, Premier, Norristown, Pa.), with a powder/liquid ratio of 3.4 gm/l.O ml. The powder was added to the liquid in small, equal increments on a cold, dry glass slab, and the mixing was accomplished in 1 minute. The designated seating force was applied fully within 2 minutes from the start of mixing, and the cement set after 7 minutes. RESULTS Five factors were involved in the cementation of metal cast crowns: (1) die spacer (with or without); (2) marginal design (shoulder versus shoulder bevel); (3) cement (zinc phosphate versus glass ionomer cement); (4) seating force (5 versus 30 lb); and (5) seating aids (orangewood stick versus E-Z bite device). A five-factor analysis of variance (ANOVA) was used to determine the interactions that had significant effects on the seating discrepancy of crown ce-
787
WANG,
5 (Ibs. )
MILLSTEIN,
AND
NATHANSON
30 ( Ibs. )
Seating force 3. Effects of cement and seating force on the seating of artificial metal crowns without die spacer. ZPC, Zinc phosphate cement; GIG, glass ionomer cement.
Fig.
II. The interaction of cement and seating force on crown seating without die spacer
Table
ZPC 5 lb 30 lb Abbreviations
116 73 as in Table
GIC
pm pm
pm 18 pm
43
% Difference 170 305
I.
mentation. The statistical analysis disclosed no significant five-factor or four-factor interactions. However, significant three-factor interactions involving the combinations of die spacer, marginal design, seating force, and cement type were: (1) die spacer :X cement X seating force; (2) die spacer x marginal des,ign x seating force; and (3) die spacer X marginal design X cement. The seating aid materials did not appear to influence the interactions, and the overall comparison of orangewood stick versus E-Z bite revealed no appreciable difference in crown seating. However, the die spacer was a factor in all three significant interactions. The subgroup means in Table I revealed that the seating discrepancies in groups without the die spacer were greater than those in groups with die spacer. The data were separated into two subsets, namely no die spacer and die spacer, and a four-factor ANOVA was computed for each set. The cement by force interaction without die spacer was significant (p = 0.002, four-factor ANOVA). The NewmanKeuls test confirmed that the seating discrepancy was significantly greater with zinc phosphate cement than with glass ionomer cement (p < 0.01, Newman-Keuls). The crown seating was significantly improved as seating force was elevated from 5 to 30 lb with each cement (p < 0.01, Newman-Keuls) (Fig. 3). The difference in seating discrepancies between zinc phosphate cement and glass ionomer cement was 170% at the 5 lb seating force, while it was 788
305 % at the 30 lb seating force. This disparity in percentage indicated a strong interaction between cement type and seating force (Table II). The marginal design by seating force interaction using a die spacer was significant (p = 0.001, four-factor ANOVA). On a die-spaced shoulder-bevel preparation, crown seating upon cementation was significantly improved by an elevated seating force (p < 0.01, Newman-Keuls) (Fig. 4). Nevertheless, crown seating during cementation on a diespaced shoulder preparation was not significantly improved by raising the seating force (Fig. 4). The die-spaced shoulder-bevel preparation was also significantly superior to the die-spaced straight shoulder preparation with respect to crown seating using 30 lb of seating force (p < 0.05, Newman-Keuls). However, the die-spaced shoulder-bevel preparation was not superior to the die-spaced straight shoulder preparation with 5 lb of force. The marginal design with the die spacer by cement interaction was significant (p = 0.004, four-factor ANOVA). Crown seating upon cementation with a die-spaced shoulder-bevel preparation was significantly improved using a glass ionomer cement compared with a zinc phosphate cement (p < 0.01, Newman-Keuls) (Fig. 5). However, there was no significant difference with respect to crown seating upon cementation on a die-spaced shoulder preparation with different cements. The die-spaced shoulder-bevel preparation was substantially superior to the die-spaced straight shoulder preparation in crown seating using glass ionomer cement (p < 0.05, Newman-Keuls) (Fig. 5). The difference between the gingival finish line preparations was not significant using zinc phosphate cement. DISCUSSION The acquisition of cement space by applying a die spacer has been advocated by several investigators7-g to enhance the complete seating of crowns during cememation. The
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1992
VOLUME
67
NUMBER
6
SUCCESSFUL
, CROWN
CEMENTATION
Shoulder-bevel Shoulder
I
5 ( Ibs. ) 30 (Ibs. ) Seating force Fig. 4. Effects of marginal design and seating force on the seating of artificial metal crowns with die spacer.
Shoulder-bevel c> Shoulder
GIC
ZPC Cement
Fig. 5. Effects of marginal design and cement on the seating of artificial metal crowns with die spacer. Abbreviations as in Fig. 3. seating discrepancy during crown cementation decreased dramatically using a die spacer during the fabrication of cast crowns (Table I). Die spacer creates space for the cement film on the occlusal and axial surfaces of a prepared tooth, relieves the hydraulic pressure during the initial stage of cementation, and facilitates distribution of cement with minimal friction resistance or filtration along the axial walls. When internal relief is not provided, the cement film between the casting and the prepared tooth hinders seating of cast crowns. When die spacer was not applied, the increase of seating force from 5 to 30 lb resulted in a significant improvement in metal crown seating upon cementation (Fig. 3). According to JorgensenlO an increase in seating force significantly reduced cement film thickness until 12 lb of force had been reached. Apparently, 5 lb of force is an inordinately light force and less than ideal for clinically seating an artificial crown.
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
It has been reported that Ketac-Cem glass ionomer cement possessed a lower cement film thickness’l and resulted in a smaller seating discrepancy compared with zinc phosphate cement. i2 The seating discrepancy on the cementation of artificial crowns without die spacer was significantly smaller with glass ionomer cement than with zinc phosphate cement (Fig. 3). This observation was attributed to the difference in the flow of each cement; namely, the viscosity of zinc phosphate cement increased with time13 while that of glass ionomer cement remained constant before setting.l* The difference in seating discrepancy between zinc phosphate and glass ionomer cements at different forces suggested that glass ionomer cement was more responsive to an elevated seating force than zinc phosphate cement (Table II). The designs for the marginal finish lines became a factor in crown seating upon cementation when the die-spaced cast crowns were cemented. The average seating discrep789
WANG,
ancy for a die-spaced shoulder-bevel preparation with 5 lb of seating force was 11 pm. This was not significantly larger than the discrepancy of a die-spaced straight shoulder preparation, which was 6 pm. However, when the seating force was elevated to 30 lb, the discrepancy for a die-spaced shoulder-bevel preparation became -4.3 pm, and this was significantly less than the discrepancy of a die-spaced straight shoulder preparation of 1.2 pm (Fig. 4). The negative values of crown seating upon cementation are attributed to the bevel configuration of a shoulder-bevel crown that directs the crown to its most cervical position. The beveled surface also functions as a machined guide plane that magnifies the seating force15 and burnishes the shoulder and beveled surfaces of the crown to produce the observed negative values. l6 The combination of heavy cementation force and the lubricating effects of the freeflowing cement improved the seating of crowns. According to Gavelis et a1.,17a shoulder-bevel margin closes the marginal gap more rapidly than a straight shoulder margin, thereby hindering the escape of cement during cementation. However, the increase of seating force from 5 to 30 lb on a die-spaced shoulder-bevel preparation compensated for this obstacle and improved the seating of crowns. The straight shloulder finish line acted as a vertical stop so that crown seating with this preparation design was not facilitated by increasing the seating force. When zinc phosphate cement was used for cementation, the mean seating discrepancy for a die-spaced shoulderbevel preparation appeared slightly greater than that of a die-spaced straight shoulder preparation (9.2 pm versus 5.2 pm). When glass ionomer cement was used, the mean seating discrepancy for a die-spaced shoulder-bevel preparation was significantly lessthan that of a die-spaced straight shoulder preparation (-2.8 pm versus 2.1 pm) (Fig. 5). According to Gavelis et al., I7 if shoulder-bevel margins encourage early closure of marginal gaps during cementation, a greater seating discrepancy should be expected with a bevelled shoulder configuration. However, the reverse was observed with glass ionomer cement (Ketac-Cem); that is, the seating discrepancy after crown cementation of a die-spaced shoulder-bevel preparation was significantly less than that of a die-spaced straight shoulder preparation. There are two plausible factors contributing to this phenomenon. First, the cement film thickness of the glass ionomer cement was less than the allotted cement space. Second, the bevel may magnify the seating force and act as a guide plane directing the crown to its most cervical position while the straight shoulder finish line preparation restricts the advancement of the crown. The comparison between an orangewood stick and an E-Z bite revealed no significant difference in cementation. The resistance of crown cementation to seating force is extremely complicated, 130 the particular influence of these seating aid materials warrants further investigation.
790
MILLSTEIN,
AND
NATAANSON
CONCLUSIONS 1. The application of a die spacer significantly improved crown seating during cementation. 2. An elevation in seating force from 5 to 30 lb significantly improved crown seating. 3. Crown seating during cementation was substantially improved using a glass ionomer cement compared with a zinc phosphate cement. 4. The die-spaced shoulder-bevel preparation resulted in significantly superior crown seating upon cementation with the use of heavy force or a glass ionomer cement, compared with the die-spaced straight shoulder preparaA:-LIOII. 5. An orangewood stick and an E-Z bite seating aid were equally effective during crown cementation. REFERENCES 1. Schwartz IS. A review of methods and techniques to improve the fit of cast restoration. J PROSTHET DENT 1986;56:279-83. 2. Pilo R, Cardash HS, Baharav H, Helft M. Incomplete seating of cemented crowns: a literature review. J PROSTHET DENT 1988,59:429-33. 3. Moore JA, Barghi N, Brukl CE, Kaiser DA. Marginal distortion of cast restorationsinduced by cementation. J PROSTHET DENT 1985;54:336-40. 4. Hollenback GM. Precision gold inlays made by a simple technic. J Am Dent Assoc 1943;30:99-109. 5. Rieger MR, Tanquist RA, Brose MO, Ali M. Measuring the thickness of paint-on die spacer. J PROSTHET DENT 1987;58:305-8. 6. Bolouri A, Marker VA, Sarampote RV. Technique-related variation of cement film thickness under full crown. Gen Dent 1987;35:26-8. 7. Fusayama T, Ide K, Hosoda H. Relief of resistance of cement of full cast crowns. J PROSTHET DENT 1964;14:95-106. 8. Eames WB, O’Neal SJ, Monteiro J, Miller C, Roan JD Jr, Cohen KS. Techniques to improve seating of castings. J Am Dent Assoc 1978; 96~432.7.
9. Campagni WV, Wright W, Martinoff seating of complete cast gold crowns
JT. Effect of die-spacer on the with grooves. J PROSTHET DENT
1986;55:324-8. 10. Jorgensen KD.
Factors affecting the film thickness of zinc phosphate cements. Acta Odontol Stand 1963;21:479-501. 11. McLean JW, Wilson AD, Prosser HJ. Development and use of waterhardening glass ionomer luting cements. J PROSTHET DENT 1984; 52:175-81. 12. Tjan AHL,
Sarkissian R. Effect of preparation finish on retention and fit of complete crowns. J PROSTHET DENT 1986;56:283-8. 13. Kay GW, Jablonski DA, Dogon IL. Factors affecting the seating and fit of complete crowns: a computer simulation study. J PROSTHET DENT 1986;55:13-8. 14. Hill RG, Wilson
AD. A rheological study of the role of additives on the setting of glass ionomer cements. J Dent Res 1988;67:1446-50. 15. Windeler AS. Powder enrichment effects on film thickness of zinc phosphate cement. J PROSTHET DENT 1979;42:299-303. 16. Rosenstiel SF, Gegauff AG. Improving the cementation of complete cast crowns: a comparison of static and dynamic seating methods. J Am Dent Assoc 1988;117:843-8. 17. Gavelis JR, Morency JD, Riley ED, Sosio RB. The effect of various finish line preparations on the marginal seal and occlusal seat of full crown preparations. J PROSTHET DENT 1981;45:138-45. Reprirat requests to: DR. PHILIP L. MILLSTEIN BOSTGN UNIVERSITY SCHOOL OF GRADUATE DENTISTRY DEPARTMENT OF BIOMATERIALS 100 EAST NEWTON ST. BOSTGN, MA 02118
JUNE
1992
VOLUME
67
NUMBER
6
