Seating and retention of complete adhesive resin cement

crowns

with

a new

Anthony

L-I. L. Tjan, DrDent, DDS,* and Tao Li, BDSb Loma Linda University, School of Dentistry, Loma Linda, Calif. The retentive property of cast gold complete crowns cemented with an adhesive resin cement (Panavia Ex) was compared with retention of crowns cemented with zinc phosphate cement (Flecks) and the conventional resin cement (Comspan). The effect of these agents on seating of crowns also was evaluated. Panavia cement exhibited the highest retentive strength, with values almost twice those obtained with zinc phosphate cement. However, the diiTerence in mean retention values of crowns cemented with Comspan cement or with zinc phosphate cement was not statistically significant. Both resin cements used in this study provided better seating of crowns than did zinc phosphate cement. (J PROSTHET DENT 1992;67:47884.)

T

he use of conventional resin-based cements for cementation of crowns and traditional fixed partial dentures experienced limited acceptance because of inherent problems such as high film thickness, short working time, irritation to dental pulp, and difficulty in cleaning the excess cured cement from the margins.lm6 An adhesive resin cement (Panavia, Kuraray Co., Ltd., Osaka, Japan) then became commercially available. Panavia is a filled BIS-GMA composite resin differing from conventional resin cements in that a phosphate ester is added to the monomer.7 The addition of this phosphate monomer contributes to a specific or chemical adhesion to tooth substances and dental alloys as well as the micromechanical bond. Claims include a low film thickness (19 pm), a compressive strength almost twice that of zinc phosphate cement,7 and virtual insolubility in oral fluids. Because polymerization of Panavia cement is strongly retarded by oxygen in the air, it is called an anaerobic cement.7 This anaerobic property keeps the excess cement at the restorative margin uncured for a longer time, thus it can be more easily removed. This study evaluated and compared the retention and seating of cast gold crowns cemented with Panavia Ex cement, conventional resin cement (Comspan), and zinc phosphate cement (Flecks).

MATERIAL

AND METHODS

Thirty freshly extracted human maxillary premolar teeth of comparable crown length and size were selected.

aProfessor and Director of Biomaterials Research, Department of Restorative Dentistry. bVisiting Research Fellow, Department of Restorative Dentistry; Norman Bethune Medical Science University, People’s Republic of China. 10/l/33691

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Five teeth were mounted in a row on a stone block to allow making impressions of multiple crown preparations. The teeth were prepared to receive complete cast gold crowns with a medium round-ended tapered diamond bur (No.767.9,Espe-Premier, Norristown, Pa.) at high speed, cooled with an air/water spray. The occlusogingival length of the preparation was approximately 5 mm, with a 6-degree convergence angle and a chamfer finishing line. All margins were placed above the cementoenamel junction. A custom-made paralleling device was used to prepare the axial walls of these teeth to ensure a consistent degree of taper (Fig. 1). Putty-wash impressions of the finished preparations were made with a polyvinyl siloxane material (Express, 3M Dental Products, St. Paul, Minn.) in custom trays made from autopolymerizing acrylic resin (CutterTray, Cutter Dental, Berkeley, Calif.). The impressions were then poured in high-strength stone (DieKeen, Columbus Dental, St. Louis, MO.) to construct the dies. Wax patterns with flat occlusal surfaces were made on the dies with a type I blue inlay wax (Hard, Kerr Mfg. Co., Emerville, Calif.) after the dies were coated with four layers of die spacer (Tru-Fit Die Relief, George Taub Products, Jersey City, N.J.) to approximately 1 mm from the finish line, as suggested by the manufacturer to attain 25 pm thickness. A ringlike attachment (loop) with a small platform (loading table) was added to the occlusal portion of the pattern as described by Tjan and Sarkissian8 (Fig. 2). The ring was used for tensile testing with an Instron universal testing machine (Model No. 1125, Instron Corp., Canton, Mass.) after cementation and the table was used to apply the seating pressure during cementation. Casting the crowna. The patterns were sprued, invested with a gypsum-bonded investment material (Cristobalite, Whip Mix Corp., Louisville, KY.) and cast in type III gold alloy (Harmony Line, hard, Williams Dental Co., Inc., Buffalo, N.Y.). The castings were recovered and

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Fig. 1. Mounted teeth are placed under custom-made paralleling device. Handpiece is fixed to movable arm, which allows preparation of teeth with consistent degree of taper. Fig. 2. Cast gold crown with ringlike attachment and loading table seated on mounted tooth preparation. Fig. 3. Specimen placed under facing drill. Upper surface of loading table is made parallel with base by grinding with Carborundum disk.

cleaned in pickling solution (Jel Pat, J. F. Jelenko Co., New Rochelle, N.Y.) and fitted on their respective prepared teeth. Internal nodules that prevented complete seating were removed with a No. 3 round bur in a slow-speed handpiece under stereomicroscope (American Optical Co., Buffalo, N.Y.) at ~5 magnification. The root portion of each tooth was lightly notched with a diamond bur, and the teeth were individually mounted in phenolic rings (Buehler Ltd., Evanston, Ill.) with epoxy resin (Buehler Ltd.) extending approximately 2 mm below the cementoenamel junction, with the path of placement positioned vertically. The resin bases of the mounted teeth were smoothed and wet-polished by use of a Handimet grinder (Buehler Ltd.) with progressively finer silicon carbide (Sic) abrasive papers from 280- to 600~grit size. The loading tables of the casting were made parallel with the resin bases by placing the mounted tooth and casting on the porcelain facing drill (Micra Drill, Model 164D-7, Cameron Precision Engineering Co., Sonora, Calif.). The upper surface of the loading

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table was then trued and smoothed with a disklike stone (Fig. 3). An indexing indentation was milled into the center of the loading table with a No. 6 bur with the same facing drill (Fig. 2). The indentation was used as a reference index for determining the height discrepancy of the specimen before and after cementation, using a Digimatic indicator with a resolution of 1 pm (Mitutoyo, Tokyo, Japan). The mounted teeth with their respective castings were randomly assigned to the following three groups of 10 specimens each: Group 1. Castings luted with zinc-phosphate cement, as controls GFOUP 2. Castings luted with a conventional resin cement (Cornspan) GFOUP 3. Castings luted with an adhesive resin cement (Panavia Ex)

All castings were air abraded with 50 pm alumina powder for 15 seconds and ultrasonically cleaned in deionized water for 10 minutes. In addition, castings luted with Panavia Ex resin were tin plated using dental electrodepo-

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4. Vertical height of specimen is measured with Digimatic Indicator instrument. 5. Specimen is placed under loading apparatus and torqued with stick to simulate clinical technique of cementation. Fig. 6. Specimen is placed in aluminum receptacle attached to self-aligning assembly, which is connected to load cell of Instron tester. Fig.

Fig.

Table I. Retention values, means, and standard deviations (in kgf) Group

x

SD

1

2

3

42 67.5 36 42 53 41 51 58 34.5 55 48.0 10.60

47 60.5 53 58 48 57 50 66 50 41 53.0 7.37

70.5 75 70 102 76 99 78 96 83 88 83.7 11.87

Group 1, cemented with Flecks cement; group 2, cemented with Comspan cement; group 3, cemented with Panavia Ex cement.

sition apparatus (Kura Ace mini, Kuraray Co. Ltd.), as recommended by Wada, to promote adhesion to noble alloy. Provisionale restoration. The tooth preparations were stored in water at 37O C prior to provisional restoration. The preparations were dried with filtered compressed air before the aluminum provisional crowns were cemented with noneugenol temporary cement (G-C Freegenol, G-C Dental Industr. Corp., Scottsdale, Ariz.), simulating clinical conditions. The teeth were again stored in an incubator in water at 37OC. After 7 days’ storage, the provisional res480

torations were removed, and the prepared surfaces were cleaned with a slurry of pumice in a prophylaxis cup, washed with a water spray, and dried with filtered compressed air. Meawring seating of castings before cementation. Completely seated, uncemented castings were held on the tooth preparation under a 5 kg static load for 10 minutes, then transferred to a Digimatic Indicator instrument (Mitutoyo) to measure the vertical height of the casting-tooth assembly before cementation (Fig. 4). The measurement was repeated three times and the values were averaged. The indentation on the loading table served as the reference point. A mechanism was provided for checking the possible unseating of a crown, caused by rebound after releasing the load, by tacking sticky wax at the facial and lingual margin as described.g Cementation of castings. Type I zinc phosphate cement (Flecks powder batch No. D26-070588, liquid batch No. H73-110486; Mizzy, Inc., Clifton Force, Va.) was mixed according to the manufacturer’s instructions. A ratio of 0.8 gm powder to 0.3 ml liquid was used to cement the crowns in group 1. Standardization of successive mixes was accomplished by proportioning the cement powder on a precision scale and dispensing the liquid with a graduated 1 cc syringe. Two coats of copal varnish (Copalite, Cooley and Cooley, Ltd., Houston, Tex.) were applied to the preparation before cementation. Group 2 crowns were cemented with a conventional resin luting agent (Comspan, L.D. Caulk, Milford, Del.; base batch No. 030789; catalyst No. 0307891), and group 3 crowns were cemented with an adhesive resin luting agent (Panavia Ex, Kuraray Co. Ltd., APRIL

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Fig. 7. Bar graph presents means and significance levels of retentive values of crowns cemented with three luting agents.

Table II.

Summary of ANOVA for retention value Sum of Source

DF

Between groups

2 21 29

Within groups Total

7486.8500 2768.3500 10255.2000

Table III. Relative frequency distribution location (interface) Interface Cement

Flecks

Comspan Panavia Ex

T-C

M-C

100 100

0 0

90

0

Mean squares

squares

of failure

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.OOOO

Table IV. Vertical discrepancy, mean, and standard deviation (in pm)

(%)

Group

Combination

0 0 10

Osaka, Japan, Batch No. 64131), each mixed and used according to manufacturer’s specifications. The cement was applied evenly over the inner surface of the casting with a brush, and the casting was seated by hand. The assembly was transferred immediately to a loading apparatus where a 5 kg load was applied. The clinical cementation technique was simulated by rocking a loaded orange wood stick several times, as recommended by Rosenstiel and Gegauff.‘O A static load of 5 kg was then applied for 10 minutes (Fig. 5). The room temperature during cementation was 22O + lo C and relative humidity was 50% -t 5%. JOURNAL

P

36.51

3743.4250 102.5315

T-C, Tooth-cement interface; M-C, metal-cement interface; combination, failure occurs at both T-C and M-C interface, approximately half of the cement remains on the tooth and another half on the crown.

THE

F value

x SD

1

2

3

20 17 4 7 5 6 9 5 11 17 10.1 5.63

-34 -36 -22 -4 -26 -23 -26 -20 -14 -21 -22.6 9.20

-13 -18 -4 -21 -34 -4 -32 -18 -10 -12 -16.6 10.32

Group 1, cemented with Flecks cement; group 2, cemented with Comspan cement; group 3, cemented with Panavia Ex cement.

Measuring seating of castings after cementation. After cementation, three additional readings were made and averaged. The height discrepancy of the specimen before and after cementation indicated the vertical dis481

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8. Bar graph depicts means and significance levels of vertical discrepancy values of crowns cemented with three luting agents.

Fig.

Table V. Summary of ANOVA for vertical discrepancy Source

DF

Sum of squares

Mean squares

F value

P

Between groups Within groups Total

2 27 29

6060.6000 2031.7000 8092.3000

3030.3000 75.2481

40.2708

o.oooo

crepancy or the amount of elevation caused by the cement. Measuring crown retention. The cemented specimens were stored in water at 37” C for 21 days before testing. The tensile load required to dislodge the crowns was determined with an Instron universal testing machine (Instron Corp.) with a crosshead speed of 0.1 cm/min (Fig. 6). The data were analyzed with a one-way analysis of variance (ANOVA). Duncan’s multiple range test was used to compare the group means. A statistical software package (SSPWPC, Inc., Chicago, Ill.) was used for the analyses. Table I presents the raw retention values, means, and standard deviations of the three test groups. Analysis of the data using one-way ANOVA revealed highly significant differences between groups atp < 0.0001 (Table II). Crowns cemented with Panavia Ex cement exhibited significantly the highest retention value with failures occurring primarily at tooth-cement interfaces (Fig. 7 and Table III). No significant difference was found between the values for group 1 (cemented with Flecks cement) and group 2 (cemented with Comspan cement).

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Both resin cements tested enhanced the seating of crowns as indicated by negative values (Table IV). In contrast, zinc phosphate cement produced an increase of vertical height compared with the precementation height (average elevation of 10 pm). No statistically significant difference was found between the vertical discrepancy values obtained in groups 2 and 3, but their differences with group 1 were highly significant at p < 0.01 (Table V and Fig. 8)

DISCUSSION Although clinically a casting must be well fitted before cementation, it is the fit achieved after cementation that is more relevant to long-term performance of the restoration. Therefore, it was considered important that this study also measure the marginal discrepancy of the crown after cementation. Incomplete seating of complete cast crowns is a multifaceted problem, and the various factors include preparation design, cementation technique, viscosity of cement mix, and type of cement used.ll* l2 One study reported sig-

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The retentive property of crowns cemented with Panavia EX resin was almost twice the average value obtained with zinc phosphate cement. Thus the results of this study indicated that, because of its high retentive strength, Panavia resin may provide the solution for the cementation of an overtapered or short preparation. SUMMARY

Fig. 9. Fracture of root resulting from retention testing of molar crown cemented with Panavia cement.

nificantly improved crown-seating when a dynamic technique was compared with the static loading procedure commonly used for in vitro studies of cementation.‘O Conventional resin cement provides excellent initial retention that decreases over time because of fluid penetration into the interface between the resin cement and tooth structure,5 possibly softening the resin. The use of conventional composite resin cements results in incompletely seated castings, and resin cement has been reported to produce the greatest vertical discrepancy.3*516 The use of varnish has been shown to improve the seating of complete cast crowns, but it decreasesthe retentive property.i2 It was postulated that cavity varnish may promote the flow of the cement. Contrary to general belief, the two resin cements tested improved the seating of crowns, compared with zinc phosphate cement. The reason for the seating improvement using these resin cements is not fully understood. However, since all groups were subjected to identical cementing procedures, it can be assumed that the seating differences were related to the luting agent. Possible cement properties explaining this phenomenon are the thixotropic property and/or good flow of the cement or that the cement may have a lubricating effect, thereby eliminating or reducing the coefficient of friction between the casting and the prepared tooth. Premolars with long roots were used in this study because a preliminary study resulted in root fractures when molars were used (Fig. 9). In this study, the cemented specimens were stored for only 21 days before testing. Diaz-Arnold et a1.13reported a significant decrease in bond strength with Panavia resin subjected to a Ionger storage time.

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CONCLUSIONS

The retentive property of cast-gold complete crowns cemented with an adhesive resin cement (Panavia EX) was compared with that of crowns cemented with zinc phosphate cement (Flecks) and with the conventional resin cement (Comspan). The effect of these agents on seating was also evaluated. Findings indicated the following: 1. Panavia EX cement yielded the highest retentive strength, with values almost twice those obtained with zinc phosphate cement. 2. The difference in the mean retentive values of crowns cemented with Comspan and with zinc phosphate cement was not statistically significant. 3. In contrast to zinc phosphate cement, which prevents the complete seating of crowns, both resin cements used in this study improved the seating of crowns. REFERENCES 1. Council on Dental Materials and Devices. Polymers used in dentistry. II. Resins containing BISGMA: coating and cementing uses. J Am Dent Assoc 1975;90841. 2. Eames WB, G’NeaI SF, Mont&o J, Miller C, Roan RD, Cohen KS. Techniques to improve the seating of castings. J Am Dent Assoc 1978;96:432-7. Phillips RW. Skinner’s science of dental materials. 8th ed. Philadelphia: WB Saunders, 1982;478. Craig RG. Restorative dental materials. 7th ed. St Louis: CV Mosby, 1985;188-99. Leinfelder KF, Lemons JE. Clinical restorative materials and techniques. 1st ed. Philadelphia: Lea and Febiger, 1988,109. Staninec M, Giles WS, Sarku JM, Hattori M. Caries penetration and cement thickness of three iuting agents. Int J Prosthodont 1988,1:25& 63. 7. Wada T. Development of a new adhesive material and its properties. In: Gettleman L, Vryhoef MMA, Uchiyama Y, eds. Proceedings of the International Symposium on Adhesive Prosthodontics. Nymegen, The Netherlands: Eurosound Drukkery BV, 1986;9-19. 8. Tjan AHL, Sarkissian R. Comparison of internal escape channels with die spacing and occlusaI venting. J PROSTHET DENT 1985;53:613-7. 9. Rosenstiel SF, Gegauff AG. Miming variables of zinc phosphate cement and their influence on the seating and retention of complete crowns. Int J Prosthodont 1989;2:138-42. 10. Tjan AHL, Sarkissian R. EXect of preparation finish on retention and fit of complete crowns. J PROSTHET DENT 1966;56:263-8. 11. Jorgensen KD. Factors affecting the film thickness of zinc phosphate cements. Acta Odontol Stand 1960;18:479-90. 12. Kaufman EG, C&ho DH, Cohn L. Factors influencing the retention of cemented gold castings. J PROSTHETDENT 1961;11:487-502. 13. Dias-Arnold AM, Williams VD, Aquihno SA. Tensile strengths of three luting agents for adhesion fixed partial dentures. Int J Prosthodont 1989;2:115-22. Reprint requests to: DR. ANTHONY H. L. TJAN SCHOOL OF DENTISTRY LOMA LINDA UNIVERSITY LOMA LINDA, CA 92350

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Seating and retention of complete crowns with a new adhesive resin cement.

The retentive property of cast gold complete crowns cemented with an adhesive resin cement (Panavia Ex) was compared with retention of crowns cemented...
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