Relative accuracy of four removable die systems

Michael Myers, D.M.D.,* and John H. Hembree, Jr., D.D.S.** hiedical l’nivrrsity of South Carolina, College of Dental Medicine, Charleston, S.C.

E lastic impression materials and indirect techniques Numerous articles in the literature describe tech- have greatly aided the making of inlays, crowns, and niques fur the making of dies*-” and the accuracy of fixed partial dentures. This has decreased chair time, various techniques.“-” In this study, the relative accu- simplified laboratory phases, and decreased the num- racy of four die techniques, including three techniques ber of adjustments at delivery. However, to maximize not previously reported, will be described. clinical success, an accurate cast is needed. The remov- able dies should be made of a hard, dense material. They should seat in the master cast accurately, posi- tively, and solidly. The dies shollld be able to be removed easily and replaced in the master cast.’ These dies should also be accurately related to adjacent teeth and should remain so during the course of the labora- tory procedures.

MATERIAL AND METHODS

The procedure used in this study was originally designed by Dilts et al.” We have made minor modifi- cations. Four die systems were studied: the brass dowel pin (J. M. Ney Co., Bloomfield, Corm.). the Plastipin (J. M. Ney Co.), the J-pin (J-Pin Co., Mountain View, Calif.), and Logix Model System (,J. F. Jelenko, New Rochelle, N.Y.) (Fig. 1).

Vinyl polysiloxane (Reflect, Kerr Mfg. Co., Romu- lus. Mich.) impressions were made of a standardized brass model and poured in a suitabk die material

Fig. 1. Die systems tested in study: a, brass dowel pin; b, Plastipin; c, J-Pin; and d, Logix Model System.

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MYERS AND tIFMBRt~E

aa Vertical Displacement

0 Horizontal Displacement

.150

.125

.lOO

.075

.050

.025

0 h3s

Dowel Pin Plastipin J-Pin Logix

Fig. 2. Reference points a to d for measuring vertical and horizontal shift in die.

Fig. 3. Graph representing vertical and horizontal shift in die systems.

Table I. Vertical and horizontal shift in die systems (in millimeters) -- _.__ -..--.-

Models

System 1 2 3 4 5 6 7 8 9 10 Mean

Brass dowel pin Vertical shift Horizontal shift

Plastipin Vertical shift Horizontal shift

J-Pin Vertical shift Horizontal shift

Logix Model System Vertical shift Horizontal shift

+0.28 0.17

0

0.03

+0.14 0.07

+0.07 0

-0.01

0

+0.1i3 0.04

+0.05 0.07

+0.17 to.16 -0.03 to.14 0.11 0.14 0.13 0.03

0 +0.14 +0.28 +0.25 +0.15 +0.14 -0.14 to.05 0.144 0.07 0.16 0.01 0.03 0.09 0.09 0.14 0.13 0.089

+o.ols +0.05 -0.07 f0.16 -0.03 to.11 +0.1: -0.07 0.092 0.10 0.11 0.11 0.3 0.1 0 0.04 0.02 0.058

to.23 to.17 to.03 +0.17 +0.14 +0.07 to.10 +0.16 0.126 0 0.07 0.04 0.02 0.07 0.10 0.06 0 0.05

(Silky Rock, Whip-Mix Corp., Louisville, KY.). Ten working casts were made with each of the four die systems, carefully following the technique described by the manufacturers to reduce the variables.

Measurements in the study were made with a stereoscopic microscope (Unitron Instrument Co., Newton Highlands, Mass.) with a widefield filar micrometer graduated to 0.01 mm. Reference points a and b were used to determine vertical shift, and points c and d were used to determine horizontal shift of the dies (Fig. 2).

Original measurements were made and recorded before the dies were sectioned. The dies were then removed and replaced 30 times. All dies and casts were cleaned and reassembled prior to final measuring. Final measurements were made and recorded from the same reference points, and the differences between the

-0.03 to.17 0 +0.14 -0.1 0.101 0.07 0.09 0.07 0.07 0 13 0.084

original measurement and the final measurements were then determined and recorded.

RESULTS

Table I indicates the amounts of vertical and hori- zontal shift found in the various die systems. A plus value in vertical shift indicates that the die did not seat fully; a negative value indicates that the die was submerged from the initial position. A plus value in the horizontal shift indicates the die had shifted to the right; a negative value indicates a shift to the left (Fig. 3).

DISCUSSION

The horizontal shift of the dies was inconsistent among the various types. Some of the dies shifted to the left, and some shifted to the right. Most of the vertical

164 AUGUST 1982 VOLUME 48 NUMBER 2

4CCURACb OF REMOVABI t DIE SYSTEMS

shift observed was in a positive (occlusal) direction. The Logix Model System was more difficult to use,

as the dies fit very tightly in the master cast and required much more effort to remove and replace. However, this did not seem to affect the accuracy as compared to the other dies.

The arithmetic means were calculated for the hori- zontal and vertical movements of each die type without regard to direction of movement. The Plastipin exhib- ited the least amount of horizontal shift. The brass dowel pin exhibited the greatest shift in both directions. A statistical analysis was performed on the data. There was no statistical significance between the various die systems. The mean movement of all types studied was 0.07 mm in the horizontal direction and 0.116 mm in the vertical direction. In clinical and laboratory use, this amount of shift would probably result in an adequate restoration.

SUMMARY

Four removable die systems were studied: brass dowel pins, the Plastipin, the J-Pin, and the Logix Model System. Results of measurements made of 10 working casts to determine the amount and type of vertical and horizontal shift revealed no statistical significance between various dies.

REFERENCES

I Rudd. K. 1). Strunk. P. R., and ~lorrow, R. Xl.: Removable

cIw\ for cm\ ns. inky ml lkd parrial dentures. J PROSTHET

11~x1 23:W. 1070

2 Henrlicld, J. W.. and J,yon\, G. V.: Precision dies from elastic

impre\Gons. ,J PROS~HFX DEW 12:757, 1962.

3. Saunders, Al.: The orientation of dies in restorative dentiswy.

131, I)cnt J 117:137. 1964,

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