Experimental overlay and pin partial denture

Experimental

overCay and pin partial

Jack M. Knodle, D.D.S.* of Nebraska, The University

College

of Dentistry,

denture

Lincoln,

Neb.

U

nusual clinical situations in which several posterior teeth have been lost early in life create opportunity for drifting of the remaining posterior teeth into various malpositions that cause many problems in the design of removable partial dentures. Such factors as complexity, function, practicability, and potential hazard to remaining natural teeth are all adversely affected by these problems. Three basic approaches to clinical problems are possible. First, a conventional clasp removable partial denture could be constructed. Second, the malpositioned teeth could be extracted and more ideally aligned abutment teeth used, with clasps and free-end denture bases. Third, an experimental type of restoration with pins that fit into corresponding holes in cast crowns for the abutment teeth could be used. A study was conducted to measure the force necessary to dislodge these types of restorations. This article reports the findings of these tests. DENTOFORM

DESIGN

A Dentoform model was constructed for this study with the mandibular second bicuspids and first molars missing. The molars were inclined mesiolingually and the bicuspids distolingually (Figs. 1 and 2). The maxillary teeth were set somewhat irregularly but none was missing, and elongation was minimal. The arrangement of the teeth in the Dentoform model was examined by the Department of Fixed Prosthodontics in order to verify the contraindications for fixed partial dentures. CROWN but The that not

CONSTRUCTION

Crowns that had a path of insertion parallel not necessarily with each other, were made for preparations were conservative in all respects, obtained a clearance of 1.0 to 1.5 mm.’ The less than 0.5 mm. from contact with opposing

This project was supported by Research Grant States Public Health Service. *Associate Professor, Department of Prosthodontics.

472

with the long axis of the tooth, each of the four abutment teeth. except for an occlusal reduction wax patterns were carved to be teeth (Fig. 3). Thus, the mesial No.

W4603-24.4

from

the

United

Volume Number

17 5

Experimental

overlay

and pin partial

denture

473

Fig. 1 The test model. The first mandibular bicuspid is inclined distally, and the second mandibular molar mesially on the Dentoform model. Fig. 2 The abutment teeth of the Dentoform cedures.

model were inclined lingually

for the testing pro-

Fig. 3 The finished casting allows at least 0.5 mm. of space between the occlusal surfaces and teeth. Fig. 4 The completed framework of the overlay and pin retained partial denture is in place on the abutment castings. Note the form of the occlusal surfaces that has been developed to occlude with the maxillary teeth.

half of the occlusal surfaces of mandibular second molars, and the distal half of the mandibular first bicuspids were thicker than usual. The overlay was at least 0.5 mm. in thickness, in order to provide necessary strength and permit occlusal modifications after fabrication (Figs. 4 and 5). The anatomy of the carving was simple, with a basic angular form (Fig. 7). After the crowns had been cast, adapted, and polished, a dimple was cut into their occlusal surfaces at the locations for the pin holes. As many pins as possible were used, but they were spaced to avoid weakening the crowns. The crown thickness at the site of each starting dimple was measured and recorded, The Dentoform model with the teeth and crowns in position was attached

474

Knodle

Fig. 5 The overlays

intercuspate

properly

with

the opposing

terth.

Fig. 6 The Dentoform model is mountcxd on an adjuqtablc holes parallel to and at the desired angle.

drilling

table

in ordcl

11) drill

111~

Fig. 7 The pin holes have been drilled in the cast crowns with a No. $ round location and number of holes in the crowns. Note that the occlusal contour is simple, and basically angular in form.

bur. Note th(< of the crowns

Fig. 8 The finished mrnt crowns.

overlay and pin-retained partial dcntute It restores the proper occlusal anatomy.

framework

is in placcl on the ahlIt-

to an adjustable drilling table and a path of insertion established. By means of a No. vp round bur and a porcelain facing drill, the holes were completed to the maximum depth possible without perforating the crowns (Figs. 6 and 7 ‘j . The holes were drilled in all of the abutment crowns at the same angle. CASTING The originally

THE PIN-TYPE

RESTORATION

overlay and pin type of construction proved thought that the overlay and pin framework

to be challenging. It was could be cast as one unit.

Volume Number

17 5

Experimental

overlay

and pin partial

denture

475

Fig. IO

Fig.

Fig. 9 The pins are extensions on the overlays that fit into the pin holes in the abutment crowns.

Fig. 10 The pins are of varying length. Some of the shorter pins contribute little to retention. However, this method proved to be unsatisfactory, and separate overlay and pin units were cast for each crown, and then soldered to the gold framework (Figs. 8 and 9). The overlay and pin patterns could be removed, checked for accuracy and completeness, and occlusal adjustments made. The framework was cast in G3 Ney Gold,” and the crowns, overlays, and pins were cast in Firmi1ay.t Baker solder (570 fine) $ was used to join the umts.2 Some of the pin holes were extremely short, and appeared to be of questionable value in resisting vertical dislodging forces (Fig. 10). Tapered holes and pins probably could have been used to facilitate construction without sacrificing retention.

FRICTIONAL SURFACE AREA Typical precision attachments involve external and internal parts that dovetail together and depend upon friction for retention.3 These attachments have a much larger frictional surface area than do a few pins; by using a large number of pins, the total frictional surface area of the pins may be comparable, or even greater. The pins were cast with nylon bristles of 0.028 inch diameter used as patterns, and a No. r/z round bur was used to make the pin holes. The fit of the pins in the holes was acceptable. Comparisons between the ready-made attachments and the pins indicated that four precision attachments of approximately 4 mm. in length had a frictional surface area of 0.1788 square inch, The frictional surface area of the pins on the experimental partial denture was 0.123 1 square inch. This is a difference of 0.0557 square inch. For comparison, the experimental partial denture demonstrated 68.84 per cent as much frictional surface area as four precision attachments. *J. M. Ney Co., Bloomfield, Corm. +J. F. Jelenko & Co., Inc., New Rochelle, N. Y. $Baker Dental Division, Engelhard Industries, Inc., East Newark, N. J.

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Knodle

REMOVABLE

PARTIAL

DENTURE

WITH

CLASPS

The clasp partial denture was designed with an average 0.015 inch undercut at the retentive tips (Figs. 11 and 12) :’ A chrome-cobalt alloy* was used for the partial denture casting and no problems were encountered. RESULTS OF TESTS FOR RETENTION After the two removable partial dentures had been completed, their retentive qualities were measured. The direction of the dislodging force was kept as constant and uniform as possible. A Fisher Scientific balance scalef was used to measure the amount of dislodging force (Fig. 13). Weights were added until the test partial *Ticonium t2-022

No. 50, Ticonium Division, CMP Industries, Inc., Albany,

balance,

heavy

duty,

triple

beam; Fisher

Scientific

Company,

N. Y. Springfield,

X. J.

- .-.. Fig.

11

The complrted

framework

of the clasp-retained

partial

denture

is one of basic design.

Fig. 12 The removable partial denture framework has bar-type clasps.

.-.., Fig.

” ._.. ,-.,

^. . ..._._.

13

A Fisher Scientific balance lodge the test dentures.

scale was used to measure

the amount

of force

requirrd

to dis-

Fig. 14 A plastic disc was used to apply equal dislodging force on the test frameworks with either a two- or three-wire

connection.

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Experimental

overlay and pin partial denture

477

dentures were completely dislodged from the model, usually with a sudden quick release. Five measurements of the dislodging force were recorded for each abutment tooth, and the mean was computed (Table I). The mean dislodging force for the four abutment teeth were grouped as a unit, and a mean was established for each trial denture. The results indicated that the overlay pin partial denture required a mean of 312.68 Gm. more force to dislodge it from the model than was necessary to dislodge the clasp partial denture. With a plastic disc arrangement used to maintain equal force to all parts of the denture frame, the overlay pin partial denture required 509.55 Gm. more force to dislodge it than did the clasp partial denture (Fig. 14). With a similar three-wire force application, one to each denture base and one to the midline of the lingual bar, the overlay pin partial denture frame required 381.15 Gm. more force to dislodge it than did the clasp partial denture frame. DISCUSSION The mean dislodging force measurements of the retention of the individual abutment teeth was greater than the force required when either a two- or three-wire arrangement was used for applying the force. This was true for both types of partial dentures, and it may indicate a slight inaccuracy in the measurements of the retention of the attachments to the individual abutment teeth. However, the retention of one abutment tooth is influenced by the wedging and frictional resistance afforded by the other attachments. The results of this study were surprising. The tests showed that adequate retention of removable partial dentures could be attained by using the overlay pin principle. However, the procedure is complicated, and its use must be selective. SUMMARY A series of tests was made to compare the retention of a removable partial denture by overlay pins with a similar removable partial denture that was retained by clasps. The results indicate that greater retention was attained with overlay pins than with clasps. This design for partial denture retention is difficult to construct, but it can be useful for some patients.

Table I Grams of force needed to dislodge removable

We of denture Clasp partial denture Overlay and pin partial denture

Lower

Lower

left

left

bicuspid (Cm.)

partial

dentures

molar (Cm.)

Lower right molar (Cm.)

Lower right bicuspid (Cm.)

Mean (Gm.)

1051.01

586.85

1541.81

1965.15

1286.21

2087.64

906.43

917.2

2484.31

1598.89

Two wire pull with disc, one to each denture base (Gm.) 981.25

1490.8

Three wire pull with disc, one to each denture base and lingual bar (Gm.) 1054.65

1435.8

478

Knodle

I would like to thank Drs. L. M. Lynn, R. I-I. Steinacher, Haack for their advice and consultations during the project. technical assistance.

J. Pros. lknt. May, 1967

R. M. Stemm: and Mr. D. (1. and Mr. ,J. D. Hayes for his

References 1. Tylman, S. D.: Theory and Practice of Crown and Bridge Prosthesis, ed. 2, St. Louis: 1947, The Cl. V. Mosby Company, p. 572-583. 2. Skinner, E. W.: The Science of Dental Materials, ed. 3, Philadelphia and London. 1946, W. B. Saunders Company, p. 277. 3. McCracken, W. L.: Partial Denture Construction, Principles and Techniques, St. Louis. 1960, The C. V. Mosby Company, p. 151. 4. Applegate, 0. C.: Essentials of Removable Partial Denture Prosthesis, ed. 2. Philadelphia, 1960, W. B. Saunders Company, p. 139-181. UNIVERSITY OF NEBRASKA COLLEGE OF DENTISTRY 14~~ AND T STREETS IJNCOLN, NER. 68508