A direct technique for fabrication of posts and cores

DENTAL DANIEL

TECHNOLOGY

H. GEHL,

Section editor

A direct

technique

Haushang

Shadman,

National

University

for D.D.S.,*

of

Iran,

fabrication and

E&n,

Parviz

Tehran,

of Azarmehr,

posts

and

cores

D.D.S.**

Iran

F

ollowing successful endodontic treatment, loss of tooth structure and a change in the patient’s metabolism occur; thus the tooth becomes brittle and vulnerable to fracture.’ This situation calls for some kind of reinforcement of tooth structure. For posterior teeth, an MOD onlay is the minimum required restoration. The onlay covers the entire occlusal surface of the tooth, and by holding the buccal and lingual cusps together, it prevents fracture of the tooth. In anterior teeth, two situations may be encountered. If adequate coronal structure remains so that sufficiently long axial walls may be prepared, the tooth may be reinforced by means of a cast post without a core. However, mutilation and loss of tooth structure are often so severe that a post and core is indicated for retention of the future restoration as well as reinforcement of the existing tooth (Figs. 1 and 2). The biophysical requirements of posts and cores have been described in detail.* For gaining maximum resistance, a segment of the cemented post should be supported in the canal by the alveolar bone. This portion should be at least half way between the apex of the root and the alveolar crest of the supporting bone.” Therefore, short roots with inadequate bone support, due to advanced periodontal disease, apicoectomy, or external root resorption, are not ideal for posts and cores. PREPARATION

OF

THE

TOOTH

( 1) Complete the endodontic treatment (2) Remove a sufficient amount of the (3) Prepare the root canal to sufficient rigid and unyielding. All undercuts must wax pattern. (4) Prepare a definite seat in the root *Senior

Lecturer,

**Head

of the

Department Department

of Crown of Prosthetic

and

in the usual manner. root filling material to the desired depth.3 size so that the fabricated post will be be removed to allow easy removal of the face. This Bridge

seat may be in the form

of an

Prosthetics.

Dentistry.

463

464

Fig.

Shadman

1. The

anterior

teeth

with

Fig. 2. View of endodontically of tooth structure.

Fig.

3. A barbed

Fig.

4. The

Fig.

5. The

Fig.

6. The

barbed

core

J. Prosthet. October.

and Azarmehr

broach

is placed

broach

adequate

is removed

teeth

on a piece

has been

of the tooth

excess wax

(A) treated

structure

(A)

with

when the pattern

the

and

adequate

of cotton

wrapped

is formed and

coronal with

after

(B) loss of tooth

coronal

spreading

structure

Dent. 1975

structure.

and

(B)

loss

the fibers.

cotton.

pattern cleaned

of the of debris.

post

has the desired

shape.

Volume Number

34 4

Fabrication

of

posts and cores

465

Fig. 7. The pattern is cast in hard dental gold alloy. Fig. 8. The try-in of the castings in canal. oval-shaped well,” a wedge,2 or a groove (Fig. 1, B) . This will prevent root fracture and allow accurate placement of the post at the time of cementation. (5) Remove all coronal undercuts, unsupported enamel, previously placed coronal restorations, and carious surfaces. (6) Shape the remaining portion of the crown into two labial and lingual inclined planes to prevent rotation of the post. In other instances, this is accomplished by making the coronal portion of the canal void in cross section or by providing it with a wedge-shaped notch, or a groove. (7) Prepare a conventional finishing line for the future restoration.

FABRICATION OF THE WAX PATTERN Various techniques of direct and indirect fabrication of wax patterns for posts and cores have been described. Many of these techniques employ extensive and special armamentarium. The main advantage of this method is that all required instruments and materials are routinely present in most dental offices. ( 1) Wash and clean the canal of debris, and then dry it. (2) Carry a lubricant to the canal with a narrow camel-hair brush; then dry it. (3) Spread cotton fibers in the shape of a thin square, with the sides about 5 inch in length. (4) Place a barbed broach on the cotton (Fig. 3)) and wrap the fibers around the broach (Fig. 4). Care should be taken not to leave the cotton unsupported. The barbs prevent sliding of the cotton fibers. (5) Pour molten blue inlay wax over the cotton to form a cone. (6) Carry the softened wax into the canal, and firmly press the extra wax to the root face. (7) Remove the wax pattern, and check for possible imperfections. (8) Correct voids by adding inlay wax. Reseat the pattern. When the pattern of the post has the desired shape, the core is formed as if to prepare the crown of the tooth for a restoration (Fig. 5). A warmed plastic instrument can be especially helpful for this purpose. Excess wax is removed, and the pattern is cleaned of debris (Fig. 6).

466

Shadman

CASTING

and Azarmehr

J. I’rosthet. Octobrr.

Dent. 1975

THE PATTERN

(1) Cut off the handle of the broach with a wirecutter, and place the broach on a sprue former with a narrow hemostat. (2) Add red counter wax around the broach to increase the diameter of the sprue. (3) Place a ring lined with a layer of wet asbestos on the sprue former, and invest in the usual manner. (4) Pull the barbed broach out of the investment at the burn-out stage. (5) Cast with a hard dental gold alloy of type C or D (Fig. 7) or a rigid nonprecious metal.5 (6) Finish the casting in the usual manner, and try it in the canal (Fig. 8). The post and core should have adequate retention. (7) A radiograph is made to verify the proper apical extension of the post. Although the casting should seat accurately in place, there is no need for sealed margins. The final restoration will cover the core as well as the remaining portion of the crown, and that will provide the marginal seal. SUMMARY A barbed broach covered by cotton fibers is used as a matrix to carry blue inlay wax into the canal prepared for a post. This simple, direct technique of post fabrication lends itself to various clinical situations. The technique requires no special armamentarium. References 1. Frank, A. L.: In Ingle, J. I.: Endodontics, Philadelphia, 1965, Lea & Febiger, Publishers, p. 614. 2. Stern, N., and Hirshfeld, Z.: Principles of Preparing Endodontically Treated Teeth for Dowel and Core Restorations, J. PROSTHET. DENT. 30: 162-165, 1973. 3. Sheets, C. E.: Dowel and Core Foundations, J. PROSTHET. DENT. 23: 58-65, 1970. 4. Bassett, R. W., Ingraham, R., and Koser, J, R.: An Atlas of Cast Gold Procedures, Buena Park, Calif., 1964, Uni-Tro College Press, p. 8 1. 5. Pinkley, V. A., and Morris, D. R.: Use of Nonprecious Metal for Cast Dowel and Core, J. PROSTHET. DENT. 32: 78-79, 1974. NATIONAL EVIN,

UNIVERSITY TEHRAN,

IRAN

OF IRAN