An evaluation of five inlay investing techniques employed with different types of wax patterns

An evaluation of five inlay investing techniques employed with different types of wax patterns

An evaluation employed of five inlay with different investing types of wax techniques patterns Clive B. G. Jenkins, B.D.S., M.S.D.,* and Ralph...

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An evaluation employed

of five inlay





of wax

techniques patterns

Clive B. G. Jenkins, B.D.S., M.S.D.,* and Ralph W. Phillips, Indiana


School of Dentistry,


MS., D.Sc.



number of investigators1-13 have attempted to determine the accuracy of castings prepared with different investments for dies which were representative of various types of crown and cavity preparations. The results of these studies have been somewhat contradictory, For example, while variations as great as 1 per cent occurred in the size of individual castings produced from one standardized investing technique,z marginal discrepancies as low as 15 p have been reported for porcelain inlays.Q In a comprehensive evaluationI of 9 different investing techniques used in conjunction with three types of cavity designs, discrepancies in the fit of castings ranged from 0.04 to 1.6 mm. with various combinations of investments and cavity preparations. None of these studies have presented evaluated differences which might exist in the fit of castings in different areas of the preparation. It is apparent that further research is needed to characterize ( 1) the accuracy of castings possible with the currently available investments and (2) the range of cavity preparations encountered in a conventional dental practice. That was the purpose of this investigation. METHOD AND MATERIALS The investments included Kerr’s Cristobalite inlay investment,? Lustercast,t Beauty-Cast,$ HygrotrolJ and Ceramigo1d.S The patterns were prepared on 5 metal dies which represented a range of conventional-type crown and cavity preparations. They contained a long parallel-wall full crown for a molar, a short tapered-wall Portions of this article are taken from a thesis by the senior author in partial of the M.S.D.

degree, Indiana


This research was supported in part by United States Public Health 00433-15, from the National Institute of Dental Research, Bethesda, Md. *Now

at University


Mfg. Company,



of Bristol, Detroit,

Corp., Louisville,


1968. Grant

No. DE

England. Mich. Ky.



Jenkins and Phillips

J. Prosth. Dent. February, 1971

Fig. 1. Three views of the metal dies used. full crown for a molar, a three-quarter crown for a premolar, an MOD cavity for a premolar, and a small mesial-occlusal cavity for a premolar (Fig. 1). The three-quarter crown die, comparable to one used by Teteruck,” was prepared from a low-fusing chrome-cobalt alloy. The other preparations were made from brass rods using a lathe and drill press. A flat occlusal wall was produced on the MOD and MO dies in order to provide a right-angle cavosurface margin. This facilitated the measurement of the space between the casting and the die, yet it did not significantly alter the size or configuration of the pattern. For the same reason, shoulder preparations were used on the molar, premolar, and three-quarter crown preparations. The patterns were formed by dipping the warmed, lubricated die into molten wax. The patterns were trimmed to the margins with a warm knife and polished with silk. The full crown and MOD patterns were sprued in the center of the occlusal surface. The three-quarter crown was sprued similarly on the tip of the lingual cusp. The MO pattern, because of its small size, was sprued on the proximal surface with a 1.5 mm. orthodontic steel tubing. The burn-out schedules and casting procedures were carried out according to the manufacturers’ directions. The water/powder ratios for the various investments were selected on the basis of the manufacturers’ recommendations and on the basis of the optimal results attained in another study conducted in this laboratory.14 A water/power ratio of 19 ml./50 G m. was used with Kerr’s Cristobalite. Two liners




of inlay





[email protected]+p? t-q) I





Fig. 2. Points where marginal discrepancy was measured.

were used for the extracoronal castings, as recommended by the manufacturer for expansion, and one liner for intracoronal castings. For Lustercast Investment, the water/powder ratio was 15.5 ml./50 Gm. The ratio for the Beauty-Cast inlay investment was 15 ml./50 Gm., and hygroscopic expansion was obtained with a water bath at 100’ F. Ceramigold investment was used with a liquid/powder ratio of 11 ml. of special liquid to 60 Gm. of powder and with immersion in a 100° F. water bath. With Hygrotrol, a water/powder ratio of 16 ml./50 Gm. was employed with 0.6 ml. of added water and a 100’ F. water bath. Five castings were made for each die with each investment. Castings were seated under an applied load of 2.3 Kg. on a Gillmore needle apparatus. Measurements of the marginal discrepancies between the casting and the metal die were made to the nearest 10 ,u with a comparator microscope at predetermined points on the die. The full crown castings were meaured at one area on the cervical margin. The points of measurement for the other types of castings are demonstrated in Fig. 2. These points were arbitrarily selected as being representative of the various dimensions of the castings. Unfortunately, the permissible marginal discrepancy of a cemented gold restoration has not been established. If one accepts the finding of Jorgensen and Wakumoto I1 that a marginal discrepancy of 0.05 mm. is the maximum that can be classified is clinically acceptable, then at least that figure might be used as a starting point for evaluating the clinical acceptability of castings. Those which have marginal discrepancies above this figure could be considered unsatisfactory, However, that investigation was concerned with amalgam restorations, and its direct application to gold castings is based on the hypothesis that the clinical influence of marginal discrepancies in amalgam restorations would be comparable to that which would occur with a cemented gold restoration. There are, of course, valid reasons to question that hypothesis, but in the authors’ opinion, it is the best figure currently available. Furthermore, it approximates the 0.04 mm. measurement that Christensenl” found was the maximum occlusal discrepancy for gold inlays that could be classified as “acceptable” when 10 examining dentists used a mirror and explorer to detect marginal deficiencies. maximum


Jenkins and Phil&x

J. Prosth. Dent. February, 1971

Therefore, a value of 0.05 mm. was arbitrarily selected as the maximal discrepancy that could be tolerated in the clinical restoration, and the data were reviewed with that concept in mind. RESULTS The tables show the mean marginal discrepancies. In the statistical analysis of two group comparisons, the t-test was used. When comparing more than two groups, the analysis of variance was employed. If that analysis showed significant differences between groups, multiple comparisons were performed using the Newman-Keul sequential range test. The 5 per cent level of confidence was used to indicate statistical significance. Long full crown. The data for the marginal adaptation of long complete crown castings produced by the 5 investments are shown in Table I. The analysis of variance shows that there was no significant difference between the various investments (P < 0.10) in the fit of the castings. Short full crown. Table I also shows the marginal adaptation of the short complete crown castings. The analysis of variance shows that castings made from Lustercast, Ceramigold, and Beauty-Cast investments had significantly smaller marginal discrepancies than those made with Cristobalite and Hygrotrol (P < 0.005). However, the differences in the fit of castings made from Hygrotrol and Lustercast were not significant. MO inlay. Table II shows the marginal discrepancy between the die and MO castings made with the 5 investments measured in 4 areas. (The discrepancy for castings produced with Beauty-Cast was so large that only Area 1 was measured.) The summary of the statistical analysis of these data is shown in Table III. An analysis of variance comparing the 5 investments for Area 1 showed a significant difference between Beauty-Cast and the other investments (P < 0.01). The Newman-K&l test confirmed that the marginal discrepancy for castings produced from the Beauty-Cast investment was significantly greater than that for castings made with the other 4 investments. While the analysis shows there were no significant differences between those 4 investments, there was a significant difference in the fit of castings at the 4 areas (P < 0.005). No multiple comparisons were performed for differences between the areas. MOD inlay. The marginal discrepancies of MOD castings are seen in Table II, with the statistical analysis shown in Table IV. The analysis of variance produced an F-ratio that indicated no significant differences in the fit of castings made with the various investments. However, significant F-ratios were noted between the fit of castings in various areas (P < 0.005) and for the interaction between investments and areas (P < 0.05). In other words, the differences between investments were not constant for the 4 areas measured. Therefore, even though the F-ratio between investments was not significant, the investments were compared for each of the areas measured. There were no significant differences between castings made from the investments in Areas 1 and 2. For Area 3, the castings from Lustercast had a significantly larger discrepancy than those made with Ceramigold and Hygrotrol. For Area 4, Lustercast and Beauty-Cast produced castings having significantIy smaller discrepancies than those produced by Hygrotrol.

VoIume 25 Number 2


Table I. Mean marginal discrepancies which castings fail to seat cervically




and standard deviations by

in millimeters



of inlay




Long full crown

0.096 (0.076)

0.036 (0.025)

0.033 (0.012)

0.012 (0.009)

0.010 (0.010)

Short full crown

0.070 (0.026)

0.053 (0.021)

0.030 (0.010)

0.013 (0.006)

0.010 (0.010)

The mean values joined by an underline are not significantly different.


II. Mean



in millimeters

by which castings failed to seat

at selected reference points (see Fig. 2) Patterns




Area 2

Area 3

Area 4


Ceramigold Cristobalite Hygrotrol Lustercast Beauty-Cast

0.030 0.050 0.047 0.033 0.103

0.027 0.027 0.010 0.023 -

0.023 0.013 0.013 0.040 -

0.017 0.010 0.007 0.013 -


Ceramigold Cristobalite Hygrotrol Lustercast Beauty-Cast

0.023 0.053 0.050 0.017 0.043

0.020 0.023 0.013 0.030 0.023

0.037 0.053 0.023 0.073 0.043

0.037 0.037 0.063 0.013 0.027

Three-quarter crown

Ceramigold Cristobalite Hygrotrol Lustercast Beauty-Cast

0.020 0.040 0.117 0.030 0.010

0.063 0.070 0.150 0.030 0.047


Ill. Analysis for MO inlay from data in Table II

Areas I, 2, 3, and 4. Comparison for 4 investments,

Beauty-Cast (2 = 0.103)

Cristobalite (5 = 0.050)


Hygrotrol (X = 0.047)


Lustercast (X = 0.033)

Ceramigold (X = 0.030)

The mean values joined by underline are not significantly different. Areas 1,2, 3, and 4. Comparison Source of variation

Between investments Betieen areas Interaction

for 4 investments,

excluding Beauty-Cast*


0.62 (n.s.) 6.92 1.21 (n.s.)


P > 0.50 P < 0.005 P < 0.50

The four investments do not show any significant difference. *Beauty-Cast was excluded because measurements could be obtained only for Area 1.


Jenkins and Phillips

J. Prostb. Dent. February, 1971

Table IV. Analysis for MOD inlay from data in Table II Source of variation


Between investments Between areas Interaction


1.04 (n.s.) 5.92 3.64

P < 0.50 P < 0.005 P < 0.05

Areas 1 and 2.

Show no significant differences between the 5 investments. Area 3.

Lustercast (X = 0.073)

Cristobalite (X = 0.053)

Beauty-Cast (it = 0.043)

Ceramigold (Z = 0.037)

Hygrotrol (X = 0.023)

Ceramigold (sz = 0.037)

Cristobalite (X = 0.037)

Beauty-Cast (ii =0.027)

Lustercast (ii = 8.013)

Area 4.

Hygrotrol (si = 0.063)

The mean values joined by an underline are not significantly different.

Table V. Analysis for three-quarter crown from data in Table II Source of variation

Hygrotrol (ii = 0.133)



Betkeen investments Between areas Interaction

P < 0.001 P < 0.005 P > 0.50

23.31 12.57 0.86 (n.s.) Cristobalite (X = 0.055)

Ceramigold (X = 0.042)

Lustercast (X = 0.030)

Beauty-Cast (Ti = 0.028)

The mean values joined by underline are not significantly different.

Three-quarter crown. The marginal adaptation at 2 areas for three-quarter crowns is seen in Table II with the statistical analysis in Table V. An Analysis of Variance shows significant differences between the investments (P < 0.001). The Newman-Keul test shows that Hygrotrol produced castings with marginal discrepancies significantly larger than those for castings made from the other investments. The differences in marginal discrepancies between areas were also significant (P < 0.005). Representative castings produced from the various investments are shown in Figs. 3 to 7. They are illustrative of the data shown in the tables. DISCUSSION On the basis of the results of this study, it would be difficult to determine which of the investments is superior over the entire clinical range of castings employed, especially as there is no widely accepted criterion for the satisfactory fit of cast restorations. However, the investigation has clearly substantiated the previously established concept that no one level of investment expansion will satisfy all of the types of clinical small castings encountered in a typical dental practice. On occasion, it may


of inlay investing techniques

Fig. 3. Representative castings produced from Kerr’s Cristobalite Note that the full crown castings fail to seat completely.

Fig. 4. Representative

castings produced

from Lustercast.

Fig. 5. Representative

castings produced

from Hygrotrol.

for the five clinical-type




Jenkins and Phillijs

J. Prosth. Dent. February, 1971

Fig. 6. Representative castings produced from Ceramigold.

Fig. 7. Representative castings produced from Beauty-Cast. Note that the MO casting fails to seat completely.

be necessary to reduce or increase the expansion by various procedures, such as altering the powder&ater.ratio of the investment. Applying the value of 0.05 mm. as the maximum discrepancy that might be considered as being clinically acceptable, the following observations might be made. Castings made from Hygrotrol exceeded this value for the three-quarter crown preparation (0.133 mm.) and the short full crown preparation (0.053 mm.). Beauty-Cast investment was unsatisfactory for the two-surface casting. Lustercast and Ceramigold investments produced castings for all 5 of the preparations that had mean value discrepancies of less than 0.05 mm. However, it should be noted that with Lustercast the MOD castings showed ,a mean discrepancy of 0.073 mm. in Area 3, which is on the occlusal keyway. No explanation is offered for the deficiency in this one area, especially since it was not reflected in the results attained from the other intracoronal preparation. Cristobalite investment exceeded the 0.05 mm. value when used to make castings for the long full crown (0.096 mm.), the short full crown (0.070 mm.), and the

Volume 25 Number2


of inlay investing techniques


three-quarter crown (0.055 mm.). Thus, that investment might be considered unsatisfactory for extracoronal types of castings unless the normal expansion can be augmented in some manner. The combined setting and thermal expansion of that investment is stated by the manufacturer to be 1.5 per cent at 1,290’ F. This is considerably less than the combined thermal and setting expansion of Lustercast, the value of which is given as 1.75 to 1.9 per cent at that temperature. These figures would seem to verify the finding of this study, namely, that the normal expansion of Cristobalite is not adequate for a critical extracoronal casting. It is somewhat difficult to conceive that an investment as widely used as Kerr’s Cristobalite would not produce satisfactory castings for all three types of extracoronal preparations. However, this finding does confirm the subjective opinion of clinicians who have occasionally experienced difficulty in seating this type of casting when made with that investment. The use of stripping or etching techniques may, of course, compensate for the somewhat undersized casting that results when such an investment is used. Furthermore, it must be remembered that the castings used in this study were made by the direct technique. Thus, the effects induced by the additional steps involved in the indirect technique have been ignored in these considerations. For example, the size of the die upon which the pattern is constructed does influence the fit of the casting produced. If the die is slightly oversize, such as is the case of a stone die, the castings made from an extracoronal preparation would seat more completely than if a direct technique were used. Thus, it is possible that, in the typical indirect technique, an extracoronal casting invested with Cristobalite often may be acceptable. Beauty-Cast would be considered an acceptable investment if the dentist were prepared to adjust his technique for certain preparations, e.g., the two-surface inlay. Similarly, Hygrotrol could be used if the expansion were, in some manner, altered for certain types of restorations. One of the interesting findings derived from the statistical analysis of the data was that there was a significant difference in the fit of castings in different areas even when fabricated with a given investment and technique. For example, the discrepancy at one margin of a three-quarter crown may be markedly greater, or smaller, than in other areas of that same restoration. A more detailed study of this anomalous behavior would seem to be warranted. The phenomenon may simply be a reflection of specimen size or could be related to factors such as the influence which the geometry of the pattern may play in altering the setting expansion of the investment.

SUMMARY AND CONCLUSIONS An investigation was made of the comparative marginal discrepancy of 183 castings produced by 5 different investments for a series of typical cavity preparations. The results were analyzed statistically. The criterion used to assess the maximum acceptable marginal discrepancy of the castings was that the over-all mean value for all of the areas measured should not exceed 0.05 mm. On the basis of this arbitrarily selected value, Kerr’s Cristobalite investment produced unacceptable castings for all of the extracoronal cavity preparations when a single standard investing technique was employed. Castings



J. Prorth. Dent. February, 1971

and Phillips

made from Hygrotrol were unacceptable with the short full crown and three-quarter crown disc, while Beauty-Cast castings made for the two-surface inlay did not meet this standard. In general, Lustercast and Ceramigold able castings for all five crown and cavity preparations investing procedure.

investments produced acceptwithout any alteration of the

These results should not be construed as a recommendation for any given investment,

but rather

they should


that, with



one realm


expansion may not produce an acceptable fit of castings over the entire range of types of cavity preparations encountered in general practice. In such situations, the procedure may be altered to attain the desired mold size. The statistical analysis of the data revealed that there was a significant difference in the fit of castings when measured at different tion of this facet of the study is suggested.

areas on the die. Further


The authors wish to acknowledge the assistance of Dr. Rosario Potter for designing the statistical analyses of the data. References 1. Taylor, N. D., and Paffenbarger, G. C.: A Survey of Current Inlay Casting Technics, J. Amer. Dent. Ass. 17: 2058, 1930. 2. Suffert, L. W., and Mahler, D. B.: Reproducibility of Gold Castings Made by Present Day Casting Technics, J. Amer. Dent. Ass. 50: 1, 1955. 3. Snyder, J. W., and Shell, J. S.: Determination of the Effect of Variables in the Casting Technic Employing Tapered Dies, I. A. D. R. 34: 88, 1956 (Abst.). 4. Hollenback, G. M., and Rhoads, J. E.: A Study of the Behaviour of Pattern Wax. Part I, J. S. Calif. Dent. Ass. 27: 298, 1959. 5. Sahs, E. A., and Wick, F. H.: Determining the Accuracy of Inlays by Mercury Micromeasurement, Dent. Prog. 1: 164, 1961. 6. Teternck, W. R., and Mumford, G.: The Fit of Certain Dental Casting Alloys Using Different Investing Materials and Techniques, J. PROSTH. DENT. 16: 910, 1966. 7. Bjorndal, A. M., and Sahs, E. A.: Comparative Microphotographic Study of Marginal Adaptation of Amalgam and Gold Inlay Restorations, Iowa Dent. J. 46: 12, 1960. 8. Christensen, G. J.: Long Lasting Cast Gold Restorations, J, Kentucky Dent. Ass. 20: 29, 1968. 9. Christensen, G. J., and Brown, T. A.: Accuracy of Fit of Direct Fired Porcelain Inlays, I. A. D. R. 46: 198, 1968 (Abst.). 10. Christensen, G. J.: Marginal Fit of Gold Inlay Castings, J. PROSTH. DENT. 16: 297, 1966. 11. Jorgensen, K. D., and Wakumoto, S.: Occlusal Amalgam Fillings: Marginal Defects and Secondary Caries, Odont. T. 76: 43, 1968. 12. Teteruck, W. R.: A Study of the Fit of Certain Dental Casting Alloys Using Different Investing


and Technics,




13. Custer, F., and Desalvo, J. C.: The Accuracy of Castings ments, J. PROSTH. DENT. 19: 273, 1968. 14, Jenkins, C. B. G., and Phillips, R. W.: Unpublished data. MR. JENKINS : UNIVERSITY OF BRISTOL BRISTOL, ENGLAND DR. PHILLIPS : INDIANA UNIVERSITY SCHOOL OF DENTISTRY 1121 W. MICHIGAN ST. INDIANAPOLIS, IND. 46202

School of Dentistry, 1963. Produced by Various Invest-