measurement of paint-on die spacers used for

FIXED PROSTHODONTICS l OPERATIVE DENTISTRY SECTION EDITORS

GORDON J. CHRISTENSEN H. WILLIAM GILMORE SAMUEL E. GUYER WILLIAM LEFKOWITZ WILLIAM F. I’. MALONE

Measurement of paint-on die spacers used for casting relief

W. V. Campagni, D.M.D.,* J. D. Preston, D.D.S.,** and M. H. Reisbick, D.M.D., M.S.*** University of Southern California, School of Dentistry, Los Angeles, Calif.

I t has long been recognized that cast restorations, particularly complete veneer crowns, do not seat com- pletely when cemented. Film thicknesses of as little as 3 p for zinc phosphate cement have been found under certain laboratory conditions.’ But the results of most investigators have exceeded the maximum thickness of 25 p allowed in American Dental Association specifi- cation No. 8 for type I cements.

Fusayama et a1.2 reported more than 90 p thickness of cement on the occlusal floors of full crowns unless some special means were used to relieve the heavy resistance of the cementing substance. Grieve3 found that the film thickness under full crowns made by an indirect technique was 84 to 87 g after cementation with zinc phosphate cement. Eames et a1.4 found an average of 143 p (lo-degree taper preparations) and 112 ,u (20-degree taper preparations) of elevation of crowns made using similar techniques.

TECHNIQUES TO IMPROVE SEATING OF CASTINGS

The techniques to improve the seating of castings by relief of the hydrodynamics of cementation can be listed under two basic categories. These are (1) venting and (2) internal relief.

Venting

The use of a planned occlusal perforation for the venting of cement has been shown by numerous authors to reduce the cement film thickness under castings. Jorgensen,’ Cooper et a1.,6 Kaufman et al., Bassett,* and others have indicated that venting is a superior way to accomplish more complete seating of

*Assistant Professor and Chairman, Department of Advanced Pros- thodontics.

**Professor and Chairman, Department of Fixed Prosthodontics. ***Professor and Chairman, Department of Dental Materials.

606 JUNE 1982 VOLUME 47 NUMBER 6

crowns during cementation. The impracticality of repairing the perforation has prevented its being wide- ly accepted.

Internal relief

The methods for achieving internal relief can be listed as follows: (1) mechanical grinding, (2) carving of the wax pattern, (3) etching with aqua regia, (4) electrochemical milling, and (5) die spacing.

The first two methods are crude, inconsistent, and incapable of achieving a uniform space for cement.

Aqua regia etching, advocated by Hollenback9 in the 192Os, is considered effective but has never been measured to determine uniformity of relief in veneer crowns. This technique cannot be used with ceramo- metal crowns, is time-consuming, and requires a highly corrosive product.

Electrochemical milling (stripping) has been popu- lar with some clinicians, but the milling agent (potas- sium cyanide) is somewhat hazardous. This process is also impractical for relief of porcelain-fused-to-metal restorations.”

DIE SPACING

Paint applied to the surfaces of dies to achieve relief of castings has been advocated.4,“-‘3 The material is usually painted on the die in multiple coats to within 0.5 to 1 mm of the margins (Fig. 1). By varying the number of coats, different amounts of relief can be produced on the internal portions of wax patterns and, subsequently, on the resultant castings.

Fusayama et al.” showed that coating dies with manicure liquid (nail polish) or a 40 ~1 thickness layer of tin foil reduced cement thickness beneath cemented crowns to 34 to 44 CL. The results obtained were superior to those achieved with an occlusal perforation technique.

Eames et a1.4 showed that castings made from relieved dies decreased the film thickness to 45 p

002%3913/82/060606+06$00.60/0@1982 The C. V. Mosby Co.

MEASURING PAINT-ON DIE SPACERS

Fig. 1. Die is painted to within 0.5 to 1 mm of margins.

Fig. 4. A and B, Dies were embedded and sectioned

Fig. 2. Tooth preparations made on a standard dentoform.

Fig. 3. Dies were separated, trimmed, and marked.

(IO-degree taper preparations) and 33 p (20-degree taper preparations) and that this method was also superior to the results obtained with venting (64 and 63 p respectively). Eames used four coats of commercial products, which he said achieved 25 CL of relief.

Fig. 5. Polished embedded section.

PURPOSE

Evidence has not been published to show the actual thickness of the spacing materials. In addition, data have not been published to substantiate the number of coats needed to produce the thicknesses claimed by

THE JOURNAL OF PROSTHETIC DENTISTRY 607

CAMPAGNI, PRESTON, AND REISBICK

CUSPID

t

lst PREMOLAR (MAX.) 2nd PREMOLAR (MAX.)

/ t

2 MEASUREMENTS (thickest and thinnest areas)

Fig. 6. Sections were photographed at above locales and measured in thirds.

Table I. Means, standard deviations, and coefficients of variance for die spacer P (Pactra) (in microns)

Surfaces

No. of coats Axial Midocclusal Cusp tip All surfaces

X = 10.92 X - 8.26

2 + (3.78) k(3.73) cv = 34.6% CV = 45.2%

X = 20.54

4 k(4.89) CV = 23.8%

X = 16.35

k(7.83) cv = 47.9%

X = 33.92

6 + (7.9) CV = 23.3%

X = 25.4

+ (9.42) cv = 37.1%

X = IO.69

k(4.66) CV = 43.6%

X = 18.94 * (7.31)

CV = 38.6%

X = 27.98

k(8.09) CV = 28.9%

x = 10.14

k(3.91) CV = 38.6%

X = 18.96

+ (6.68) CV = 35.2%

X = 29.98 k(9.14)

cv = 30.5%

Legend: X = mean, + ( ) = standard deviation or SD, and CV = coeffkient of variation = SD/mean (figured to nearest 0.1%).

authors and manufacturers. This study was designed to determine the thickness of three paint-on die spacers. Two paints were specifically marketed as die spacers, and the third was a hobby shop item sold as model airplane paint.

MATERIAL AND METHODS

Three tooth preparations were made ‘on a standard dentoform (Columbia Dentoform Corp., ‘New York,

N.Y.): (1) porcelain-fused-to-metal maxillary left cuspid, (2) porcelain-fused-to-metal maxillary first premolar, and (3) three-quarter crown preparation on the second premolar (Fig. 2).

Impressions were made using thiokol rubber (Per- malastic, Kerr Mfg. Co., Romulus, Mich.) in a custom acrylic resin tray, silicone rubber in a custom silicone putty tray (Xantopren-Optosil, Unitek Corp., Mon- rovia, Calif.), and reversible hydrocolloid (Heavy-Body

608 JUNE 19.92 VOLUME 47 NUMBER 6


Fig. 7. Photographs were measured using photo- graph of micrometer scale made at same magnification.

Hydrocolloid, Van R Dental Products, Inc., Los Angeles, Calif.). Each series of three impressions was poured using a die stone (Vel-Mix, Kerr Mfg. Co.) with a water-powder ratio of 0:22.

Three die sets were poured for each impression material. The casts were removed from the impressions within 1 hour, and the dies were separated, trimmed, and marked according to set and impression material (Fig. 3). The dies were allowed to dry at least 48 hours before application of the die spacers.

Each set of dies was given either two, four, or six coats of the same die spacing material. The materials were designated P (Aerogloss, Silvaire-Aluminum, Hot Fuel Proof Dope, Pactra Industries, Upland, Calif.), B (Belle de St. Claire Cement Spacer, Technical Dental Products, Encino, Calif.), and T (Tru-fit Die Relief and Visual Aid Kit, George Taub Products and Fusion Co., Jersey City, N.J.). Products P and B were painted and allowed to dry before each additional coat was applied. Product T came in silver and gold, and the coats were alternated according to the manufacturer’s instructions. A sable brush (No. 1) was used to apply all three materials. The bottles were kept closed between applications, and the brush was cleaned frequently with thinner.

The dies were embedded with epoxy resin (Epoxide Resin, Buehler Ltd., Evanston, Ill.) poured in Bakelite rings (Buehler Ltd.) (Fig. 4, A). Each ring contained a set of the three different preparations. After setting, the rings were sectioned buccolingually in the long axis of the dies using a diamond saw (thin sectioning machine, Hamco Machines, Inc., Bronwill Scientific, Rochester, N.Y.) under constant water spray (Fig. 4, B). The sections were polished with 150 to 600 grit silicon carbide paper (Automet Paper Discs, Buehler

NUMBER OF COATS

Fig. 8. Mean thicknesses of all surfaces of three die spacers.

Ltd.) and water. Final polish was achieved with 1 cc aluminum oxide particles (Alumina Abrasive, Union Carbide Corp., New York, N.Y.) on a cloth polishing wheel (Fig. 5).

Each die was photographed at ~200 magnification using a Unitron microscope (Max Erb Inst. Co., Burbank, Calif.) and Polaroid film type j5/posiitve- negative (Polaroid Corp., Cambridge, Mass.). Four surfaces of the die were photographed: (1) midlingual, (2) midlabial, (3) occlusal-lingual cusp tip, and (4) midocclusal (Fig. 6). Measurements of the photographs were made using a micrometer scale reproduced photographically at the same magnification (Fig. 7). The thickest and thinnest widths in each third of the surface were recorded. This procedure generated six measurements for each of the four surfaces on each die except the three-quarter crown, on which three surfaces were measured (Fig. 6, inset).

RESULTS

The results of the measurements are shown in Tables I, II, and III. The spacer designated P had the smallest film thickness for two, four, and six coats; the values for the means of all the surfaces in microns were 10.14 -t (3.91), 18.96 2 (6.68) and 29.98 + (9.14). Considering the standard deviation, the values obtained


CAMPACNI, PRESTON, AND REISBICK

Table II. Means, standard deviations, and coefficients of variance for die spacer B (Belle de St. Claire) (in microns)

Surfaces


x = 22.86 x = 19.11 X = 26.83 X = 22.92

2 + (8.75) k(8.37) k(9.16) ~(9.18)

CV = 38.3% cv = 43.8% cv = 34.1% cv = 40.1%

x = 43.73 x = 37.13 X = 44.61 X = 42.17

4 k(11.02) k(14.43) k(12.35) + (12.72)

CV = 25.2% CV = 38.9% CV = 27.7% CV = 30.2%

X = 65.27 X = 54.2 X = 63.43 X = 61.75

6 k (14.52) k(15.53) f (26.33) k(19.2)

CV = 22.3% CV = 28.7% cv = 41.5% cv = 31.09%

Legend; X = mean, + ( ) = standard deviation or SD, and CV = coeffkient of variation = SD/mean (figured to nearest 0.1%).

Table III. Means, standard deviations, and coefficients of variance for die spacer T (Tru-fit) (in microns)

-

Surfaces


X = 22.67 X = 25.63 x = 33.93 X = 26.55

2 k (9.87) k (13.27) k(17.84) k(14.11)

cv = 43.5% CV = 51.8% CV = 52.5% CV = 53.2%

X = 61.17 X = 51.56 X = 61.94 X = 58.76

4 k(15.01) + (21.06) k(15.12) * (17.38)

CV = 24.5% cv = 40.9% CV = 24.4% CV = 29.6%

x = 80.59 X = 69.19 x = 81.39 x = 77.7

6 k(14.46) + (20.56) %(24.46) k(19.91)

cv = 17.9% CV = 29.7% cv = 30.1% CV = 25.6%

Legend: X = mean, k( ) = standard deviation or SD, and CV = coefficient of variation = SD/mean (figured to nearest 0.1%).

for six coats of this material would give a range of 20.84 to 39.12 CL, which would be within the suggested range of 20 to 40 ~1 indicated in the literature. The Pactra paint used for this study was a Silvaire- Aluminum paint. Preliminary studies done with these paints showed that two of the metallic paints had smaller film thicknesses than several of the other common hues. The difference may be due to the different type of pigment used in the acrylic resin paint.

77.7 ? (19.91), respectively. The gold paint was more dificult to handle than the silver paint in the pair. It tended to harden in the mouth of the bottle and clump on application to the die.

Regardless of the spacer used, it was observed that each multiple of two coats approximately doubled the thickness (Fig. 8).

The spacer B had slightly more than double the values found for spacer P. Values of 22.92 f (9.18), 42.17 -+ (12.72), and 61.75 + (19.2) p were found for two, four, and six coats. This spacer is strikingly similar in character and appearance to the Pactra product of the same color.

Because the amount of relief space suggested falls in a broad range of 20 to 40 p, differences between surfaces on individual dies were not considered clinically significant. Therefore, all surfaces were combined to compute the mean values. It was noted that midocclusal measurements tended to be less than axial measurements. The values for the cusp tips were the least consistent, probably representing an overlap of strokes when painting the dies.

Values for spacer T were slightly higher, yielding Statistical analyses to determine differences between means of 26.55 -t (14.11), 58.76 f (17.38), and, materials were not undertaken due to the wide variance

610 JUNE 1982 VOLUME 47 NUMBER 6


in hand painting technique. It is not possible to control painting to variations of less than 5 CL; therefore, clinical significance is reported.

Based on a range of 20 to 40 p space, the data are extrapolated to indicate that five to six coats of spacer P and two to three coats of spacer B and T would achieve the desired thickness.

There were no spacing thickness differences due to the type of impression material used. All die surfaces were equally receptive to the paint-on materials.

DISCUSSION

The ideal amount of casting relief to achieve maximum retention is not known. Eames et a1.4 and Eliasson and Lund” have suggested 25 CL. Fusayama et al.” implied that less than 30 p was undesirable; he used 40 p. Further, Fusayama and Iwamoto’4 found that the thickness of zinc-phosphate cement for optimum shear strength was 31 to 38 CL.

An added benefit of more complete seating has been an increase in retention of from 19% to 32%.’

The only other evidence on the acceptable range of spacing is that published by Jorgensen and Esbensen.15 They concluded that variations of from 20 to 140 p had only a moderate influence on retention. More research is necessary to determine the optimum space.

SUMMARY

Three paints used for die spacing were measured for film thickness. Two of the materials are marketed as die spacers, and the third is sold as a model airplane paint. The materials were applied to stone dies in multiple coats. They were embedded in resin, sectioned, and measured photographically through a microscope.

The three die spacing materials were capable of achieving clinically acceptable relief in the range of 20 to 40 1 by using a variable number of coats.

Different paints produced different thicknesses. The two paints sold specifically for die spacing gave 11 to 13 g per coat. The hobby shop paint had the smallest film thickness per coat, yielding approximately 5 b per layer. It also had the smallest standard deviation. This control plus the relative low cost and availability make it attractive for this purpose.

CONCLUSIONS

1. The measurements of the thickness of commercial die spacers were not consistent with those reported by manufacturers and authors.

2. A hobby shop paint used as a spacer had the smallest film thickness and the smallest standard deviation.

3. All materials had a consistent arithmetic progres- sion when multiple coats were applied, four coats being double and six coats triple the value of two coats.

4. Clinically significant differences were not found between surfaces or preparations.

5. Differences related to the surfaces produced by different impression materials were not found.

I.

2.

3.

4.

5.

6.

7.

8.

9.

IO.

11.

12.

1.3.

14.

IS.

Norman. R. D.. Sw~rtz, Xl. J., and Phillip\, R W.: studies on Iilm thickness. solubility, and marginal Ic:+k,tgc elf drntal cements. J Dent Res 42:950, 1963.

I~usa~ama. ‘I‘., lde, K.. Kurosa. A., and IIosad,~, H.: Cement thickness between cast restorations cind prcp,rration walls.

J PROSTHET DENT 13:354, 1963.

Grieve, .\. R.: A Ttudy of dental cements. 13r i)rnt J 127:403,

I’)00 Eames, W. B., O‘Neal. S. J., Montiero. J, hliller, Cl., Roan,

J. I).. and Cohen, K. S.: Technique\ to imIwow seating of castings. J ,\m Dent Assoc 96:432, 1978

Jorgensen. K. I).: Fatwrs aliecting the l~lm hicknrss of zinc phosphate cements. Acta Odontol Stand 18:4”9, 1960.

Cooper. T. M., Christensen, G. J, Lasweli, ti. R., and Baxter, R.: Ellwt of venting on cast-gold f’uli cm~~:~ J PROSTI-WI

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Kaufman, E. Cr., Win. L., Srhlagel, E.. and (:oelho. 11 Ii: Factors mtluencing the retention of cemrnted gold tastings:

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Hollenback. G. hi.. A practical contrihuuon ti, the standardiza-

twn oi casting technique. J Am Dent Assoc X0:5. 1928.

Baabetr, R. W., and Stauts, B. hl: E~aluai~,t~ of rlectrwhemi- cal milling (stripping) versus etching with aqua w$a. .J S Calif

Dent ASOC 34~478, 1066. k’usa)ama. T.. Idr, K., and Hosada. II.. KeLirt of resistance of cemrnt of full ~‘ast crowns. J PROSTINT I)E~‘I 14:95, 1964.

Lawson. P E.: Evaluation, Diagnosis arid Treatment of Occlusal Problems. ed 1. St. I.ouis. 1974, ?‘tw (! \’ \losby

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through finishing procedures. J Indiaw St,tte Dent Assoc 53:13, 197-l.

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between the film thickness of Lint phosphate cement and the retention clt sneer crowns. -2cra Od~mtrrl Stand 26~160, 1968.


measurement of paint-on die spacers used for

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