A simple paralleling template for precision attachments

Fixed partial prosthodontics

A simple Robert

H. W.

paralleling Brodbelt,

template L.D.S. (Liverpool),

for

precision

L.D.S.,

attachments

R.C.S. (England)*

Northwestern University, Chicago, Ill.

lh e preparation of abutment teeth for the reception of precision attachments on the dovetail principle must include proximal boxes large enough to accommodate the female parts of the attachments within the coronal contour of the teeth. This is greatly facilitated by first preparing the proximal box to accommodate the attachment accurately, and then completing the preparation. Cutting all of the proximal boxes for the female parts of the attachments at one time enhances the opportunity of providing the necessary degree of parallelism to assure the proper seating of the removable partial denture with its male attachments. It is advisable that the path of insertion of the individual tooth restorations differs from that of the precision attachment to assure the retention of the abutment cr0wns.l Precision attachments are very retentive and, therefore, are more likely to dislodge the individual restoration that carries them, if both have the same path of withdrawal. The size of the attachment often requires considerable loss of healthy tooth tissues2 Intraoral and extraoral parallelometers can simplify the preparation of proximal boxes but they are expensive and time consuming for straight-forward procedures. Freehand paralleling is very difficult and frequently lacks the precision required when aligning boxes on both sides of the dental arch. It is the purpose of this article to describe a simple paralleling template to achieve the following objectives : (1) minimal tooth destruction, (2) ease of use with little strain on the dentist, and (3) simple and inexpensive to make with a surveyor. TECHNIQUE After thorough examination of the patient, the articulated casts, and the diagnostic radiographs, the type of attachment is chosen for the prosthesis (Fig. 1) . The largest attachments with the most frictional surface area contact that can be included intracoronally are selected, since they will be stronger and more retentive.3 The length of the attachment is also critical, because it is directly proportional to its retention. Since the female part of the attachment is soldered into the abutment casting, it is necessary to have a thin wall behind the attachment for its support5 This will require the proximal box to be cut larger than the attachment. The size of the selected attachment, plus a further 0.5 mm. of space for the backing, needs to be *Present

address:

See p. 288.

285

286

Brodbelt

Fig.

1. Diagrammatic

Fig. 2. Diagram Fig. 3. Diagram

J. Pro&et. Dent. March, 1972

representation

of the maxillary

showing

sites for proximal

showing

the outline

of a template

Fig.

4. An acrylic

resin

template

Fig.

5. The

insert

and paralleling

metal

occlusal

surface.

boxes.

and embedded

and metal

metal

insert.

inserts.

“lug.”

transposed to each tooth so that the proximal box is a suitable length, width, and depth. The depth is related to a radiograph of the tooth to avoid pulpal damage. This is now drawn on the cast (Fig. 2). To guide the dentist’s handpiece, metal inserts are used (Fig. 3). These inserts of the are ground from squares of student’s alloy (K- metal). The inner dimensions inserts are ground with stones to precisely match the areas drawn on the cast. Thus, while these proximal boxes are prepared, the inserts will limit the width and depth of the box. Also, a lug is cut on the lingual arm of the insert away from the area of the box. The excess metal around the inserts is trimmed to make the plate less bulky. The inserts are now positioned on the cast and held with sticky wax. Next, coldcuring acrylic resin is molded over the metal inserts and over the palate, cusps, and incisal edges of the remaining teeth. This gives the template maximum stability on the teeth and tissues and holds the inserts rigidly (Fig. 4). The acrylic resin must be of sufficient thickness gingival to the inserts. Next, using a surveyor, the lug can be extended into the acrylic resin parallel to that designed for the box and to the desired length for the attachment (Fig. 5). F inally, the acrylic resin template is smoothed and polished, ready for its clinical use.

Paralleling

template

for

precision

attachments

207

Fig. 6. The modification of a proximal box for preparations in which the path of withdrawal differs from the line of insertion of the precision attachment. TOOTH

PREPARATION

The template should fit firmly on the remaining teeth and not exhibit any mobility when rocked by hand. A stationary fissure bur is placed in the lug, and the bur alignment is transposed to the tooth. Next, using the sides of the metal inserts as guides for depth and width and the lug for length, the box can be cut to the planned size. To recheck the parallelism, the bur must be stopped before replacing it in the lug. The preparation of the tooth is then completed. If the path for withdrawal from the cavity differs from the line of insertion of the precision attachment, modifications to that wall will be necessary to eliminate the potential undercut (Fig. 6). Then, only final finishing of the preparation is required. ADVANTAGES (A) (B) paralleling (C) used. (D) (E) abutment

The template can be both tooth and tissue borne for maximum stability. The template has little effect on access to the teeth. This is unlike many devices and can be easily put in and taken out of the mouth. Metal inserts can be copied when several of the same attachments are being Metal inserts can be reused with another template. The plates can be combined with bushings for paralleling pinholes for other teeth and are especially useful when several teeth are to be splinted.

SUMMARY A simple inexpensive to guide the preparation

acrylic resin plate with of teeth for the proximal

prefabricated metal inserts is used boxes that receive the female parts

208

.I. Prosthet. Dent. March. 1972

Brodbelt

of precision attachments. This length of the proximal boxes.

guide

is for planned

I wish to thank Dr. C. H. Miller for his help in preparing instructor-technician, for his help and patience in perfecting Mr. S. J. Bailey, Miss J. Holmer, Mr. B. Wylie, and Mr. sistance.

paralklism,

depth.

Jvidth.

anti

this article; Mr. D. Stananoupht, the laboratory procedures; and One for their photographic a+

References 1. 2. 3. 4. 5.

Stern Technical Reports, Stern Dental Company, Inc., Mt. Vernon, N. Y. Ray, G. E.: “Precision Attachments,” Dental Practitioner Handbook, Bristol, 1969, John Wright & Sons, Ltd. Preiskel, H. W.: “Precision Attachments for Free-end Saddle Prosthesis.” Br. Dent. J. 127: 462-468, 1968. Preiskel, H. W.: “Precision Attachments in Dentistry,” London, 1969, Henry Kimpton. Tylman, S. D., Blumfield, R. C., Moulton, G. H., and Tylman, S. G.: “Theory and Practice of Crown and Bridge Prosthodontics,” ed. 5, St. Louis, 1965, The C. V. Mosby Company. pp. 88 l-885. DENTAL GUY’S LONDON ENGLAND

DEPARTMENT HOSPITAL BRIDGE,

S.E.l