Dowel pin positioning technique for fixed partial denture working casts

DENTAL TECHNOLOGY SECTION

EDITOR

DANIEL H. GEHL

Dowel pin positioning technique for fixed partial denture working casts Francis B. Robinson,

D. D.S.,* and Bob Block**

University

College

of Kentucky,

of Dentistry,

Lexington,

T

he dowel pin method of orienting dies produces the least amount of inaccuracy in a horizontal direction and the second lowest vertical deviation of four types of removable dies.’ However, the correct placement of the dowel pins is often a problem. If positioned inaccurately, they may impinge on the margins, weaken the die, or prevent it from being easily removed from the cast.? The following method of positioning dowel pins is simple and more accurate than most methods currently in use.

Ky.

3. Place bankers pins so that the flat head is centered mesiodistally and slightly to the buccal of the tooth impression by sighting down vertically into the impression (Fig. 2). 4. Place an additional strip of Mortite over the pins to secure their position (Fig. 3).

TECHNIQUE 1. Trim excess rubber get a relatively flat border 2. Place % inch to 1 (Mortell Co., KanKaKee, the tray and impression Mortite is 7 to 10 mm preparations (Fig. 1). *Assistant Professor, Department **Dental Student.

base of the impression to anterioposteriorly. inch of Mortite material Ill.) on the outer border of so that the top strip of above the margin of the

of Restorative

Dentistry.

Fig. 2. Bankers pins placed in impression.

Fig. 1. Mortite placed on outer border of impression.

0022-3913/81/080215

+ 02$00.20/08

1981 The C. V. Moshv Co.

Fig. 3. Additional their position.

Mortite

THE JOURNAL

placed over pins to secure

OF PROSTHETIC

DENTISTRY

215

ROBINSON

Fig. 4. Pour die stone, taking pins.

care not to cover heads of

Fig. 5. Dowel pins placed into stone contact flat head of bankers pin. 5. Pour die stone into the impression, taking care not to cover the heads of the banker pins (Fig. 4). 6. Place the dowel pins into the stone so that the flat side of the pin contacts the flat head of the bankers pin. This will aid in keeping the dowel pins upright. The knurled end of the dowel pin should be covered with stone, and the pins should be parallel to each other and to the desired path of draw on the dies (Fig. 5). 7. Allow the first pour of artificial stone to set. 8. Remove the bankers pins and Mortite. 9. Apply gypsum separator and make the second pour of stone (Fig. 6). DISCUSSION

AND

AND

BLOCK

Fig. 6. Bankers pins and Mortite have been removed, and gypsum separator has been applied.

cumbersome bobby pins, paper clips, anesthetic needles, and sticky wax. No pins are pushed into the impression material that might cause distortion. The method (1) allows the dental laboratory technician to place the dowel pins free hand after the impression has been poured and (2) does away with many problems associated with prepositioning the dowel and stabilizing it with sticky wax before pouring the impression. With this method, there is nothing to vibrate loose, and there is excellent vision and access for teasing stone into all recesses of the impression with a spatula or brush. The heavy body and sticky characteristic of Mortite ensures that the bankers pins will not be dislodged during vibration of stone, and the dowel pins can be precisely located. REFERENCES 1. Balshi, T. J., and Mingledorff, E. B.: Matches, clips, needles, or pins. J PROSTHET DENT 34:467, 1975. 2. Shillingburg, H. T., Hobo, S., and Whitsett, L. D.: Fundamentals of Fixed Pmsthodontics. Chicago, 1976, Quintessence Publishing, p 197. Reprint requeststo: DR. FRANCISB. ROBINSON UNIVERSITY OF COLORADO HEALTH SCIENCESCENTER SCHOOL OF DENTISTRY

4200 E. NINTH AVE. DENVER. CO 80262

SUMMARY

This simple, accurate technique of positioning dowel pins saves the time and effort of working with

216

AUGUST

1981

VOLUME

46

NUMBER

t