attachments for fixed ovds

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Attachment fixation

for overdentures. Part

I 367

BASIC PROSTHETIC DESIGN

Use of attachments introduces another factor in prosthetic design, i.e., need for a

critical attachment-prosthesis relationship. The requirements for each type of attach-

ment dif fer with the availability or desirability of resiliency and the adaptation of the

denture base over denture-supporting tissues. A displacement wash in the final im-

pression minimizes the differential of displaceability between abutments and denture-

supporting tissues.

Use of attachment fixation does not overcome failures related to complete den-

tures; adherence to basic principles remains essential. Failure of overdentures with

attachment fixation does not result from use of attachments. The true causes are im-

proper selection of attachments, failure to develop proper denture base extension and

border seal, and, for mandibular bases, failure to cover the retromolar pad. Improper

occlusal records can produce the same damaging results to the few remaining teeth

when making an overdenture as they can when making conventional removable par-

tial dentures.

Availability of proprioceptive elements in an attachment-retained overdenture

permits the use of gnathologic procedures. In some instances, this approach makes it

possible to use anterior teeth along with relevant instrumentation to dischrde the

posterior teeth.

MANAGEMENT OF ABUTMENTS

Except for the telescope crown overdenture, the teeth are treated endodontically

to permit maximum crown reduction and improved crown-root ratios. Nonattach-

ment overdenture abutments are usually 3 to 8 mm. high depending upon root length

and form, bone support, and presence of multiple abutments. In planning an attach-

ment, the crown is reduced to the level of the residual ridge to improve the crown-

root ratio and, thereby, allow space for both attachment and overlying tooth.

Periodontal therapy should be completed prior to final preparation of the teeth.

Surgical intervention in advance of preparation of copings increases the mechanical

advantage of the improved crown-root ratio and reduces the soft-hard tissue displace-

ability differential. Excess soft tissue can be surgically removed or repositioned over

the residual ridge and bone defects filled with a matrix of osseous coagulum to im-

prove stabilization. The need for this procedure can be established by digital exam-

ination of the mucosa for displaceability, periodontal probing for pocket depth, and

radiographic study for cratering or angular defects.

TOOTH PREPARATION

Tooth preparation varies with the type of retention and support. If no attach-

ments are planned, the teeth can be minimally restored with an occlusal amalgam or

a composite resin. The teeth and restorations are finished and polished; they may be

prepared later to receive a telescope crown or coping. It is essential to parallel the

preparations and make a definite finish line at the gingiva when using telescope

crowns. Because of its length and parallelism, the telescope crown gives more reten-

tion for the overdenture than the polished clinical crown. Selection of a telescope

crown

or a coping depends upon the mechanical factors, caries index, oral hygiene,

and ability of the patient to pay for this treatment plan.


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368 Mensor

J. Prosthet. Dent.

April, 1977

Fig. 1. Lack of bulk at attachment/dowel coping interphase can cause fracture or opening of

the copin g (right). A proper inlay seat help s pos ition the copin g, prevents rotation, and pro-

vides necessary bulk (left). (F

rom Gerber, A. A.: Reten tions Zylinder, Reten tions Puffer, Biel.

Switzerland, 1964, Cendres & Metaux, S.A.)

Tooth preparation for a dowel coping to carry an attachment requires

more than

reshaping of the root to the alveolar crest. The preparation must provide both re-

tention and seal for the coping by using a parallel chamfer preparation. A tent-

shaped preparation (two thirds to the facial and one third to the lingual side) pre

vents rotation of the coping (Fig. 1) . Additional orientation of the coping is accom-

plished by developing an inlay seat that also provides additional bulk to join the

coping with the dowel and attachment. The length of the dowel varies with the type

used. Most dowels should be no less than 8 mm. below the coping, with the excep-

tion of parallel-wall dowels which can be as short as 4 mm. when they support an at-

tachment-retained overdenture.

IMPRESSION TECHNIQUE

Impression methods and materials vary according to personal preference. Rubber

and silicone elastic materials or individual modeling compound impressions permit

the use of silver-plated or artificial stone dies. However, hydrocolloid impressions pro-

vide only artificial stone dies. Impressions of dowel preparations can be complicated.

for lack of parallelism can result in tearing or distortion upon separation. Several

impressions should be made with the dowels in place for transfer. Then the dowel

copings are fabricated, and these castings are related with a second master impres-

sion. An alternate method requires individual or ful l impressions of preparations.

joining dowels to copings with resin, transferring and soldering dowels to copings, and

preparing casts and dowel copings for subsequent positioning of the attachment and

fabrication of the overdenture.


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Attachment fixation for overdentures. Part I 369

LABORATORY PROCEDURES

The coping is waxed to an occlusal thickness of at least 1 mm. The coping should

have a marginal bulge to protect the gingival tissues. The occlusal surface is modified

to accept the attachment, which is soldered to the coping after casting and rough

finishing.

Orientation of most attachments is established with a parallelometer. The Zest

anchor* and Gintat and Rothermann * attachments do not require precise parallelism.

Other exceptions are plastic pattern types of attachments, such as the QuinlivanS

Snapper and the Hader bar, which are incorporated directly in the wax-up. Gen-

erally, attachment-coping orientation is determined by the position of the denture

tooth and the availability of space.

DOWEL SELECTION

Customized cast dowels. Waxed dowels, which require bulk for adaptation, usu-

ally are too short to give adequate retention. Close tolerance and diff iculties in con-

trolling expansion of alloys are important considerations when waxing both dowel

and coping and when casting them as a unit. The discrepancies are similar when an

inlay and a crown are made in the same casting. I f expansion for the coping is ade-

quate, the dowel is oversized and the coping cannot seat. The oversized dowel can

fracture the root during try-in or cementation because of the wedge effect of the

dowel and the hydraulic pressure of the cement. This problem can be minimized by

preparing a cement release groove along the long axis of the dowel. An undersized

dowel permits the coping to seat properly; however, the dowel retention is compro-

mised.

The diameter of a cast dowel must be larger than that of a prefabricated metal

dowel for equivalent strength. Cast dowels usually are shorter and more tapered.

When fabricated to a length of less than 8 mm., they do not retain attachment

bearing copings. When the attachment functions, the coping separates from the tooth.

Prefabricated resin patterns. Prefabricated dowel patterns have a matched set

of burs for preparing the dowel space. Plastic dowel patterns minimize technical

problems associated with customized dowel copings because of differences in expan-

sion of the wax pattern and the dowel and need for only one casting. The cross-sec-

tional strength of a pattern dowel is considerably less than that of a prefabricated,

high-fusing alloy dowel of the same size. Cast dowels are also subject to porosity and

resultant fracture. Of the many dowel patterns available, those requiring impression

pins with copper band impressions give the best results.

A promising new system is the cylindrical tapered dowel system.* It consists of a

series of color-coded cylindrical tapered burs and a matched set of burnable dowels,

impression dowels, and stainless steel/precious metal dowels. This system satisfies the

mechanical requirements for a retention dowel system using precision-fitted resin

and prefabricated metal dowels.

*APM-Sterngold, San Mateo, Calif.

twhaleden t Internationa l, New York, N. Y.

Quinlivan, J.: Personal Communication, Buffalo, N. Y., Oct., 1973.

, Ultratek Attachments and Technology, Inc., Concord, Calif.


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370 Mensor

J. Prosthet. Dent.

April, 1977i

Fig. 2. Schenker step pivot dowels come in two configurations,

one

for small

canals

and the

other for large ca nals. The step comp ensa tes for root taper, and para llel wa lls afford maximum

retention in the canal.

Fig. 3. V. K.

screw

cap affords the most rigid m echanical fixation. of the coping and is self-

tapping.

Fig. 4. V.K. double screw (UTTOW) can be used for fixed removable partial dentures and as a

base for fixation of superstructure s.

Prefabricated metal dowels. Prefabricated metal dowels have several advantages.

Their precise fit and excellent strength require only minimal canal enlargement,

thereby strengthening rather than weakening the tooth. As with resin pattern dowels,

matched sets of burs are included. The dowels are machined from high-fusing

wrought metal that is alloyed especially for the purpose. Most dowels have cement re-

lease grooves which reduce the risk of incomplete seating or root fracture during

cementation.

Parallel-walled dowels, such as the Schenker step pivot (Fig. 2), ef fect ively resist

dislodgment for their full length. Dowels of this type, 4 mm. in length, have been

used successful ly to retain attachment bearing copings,

The normal dowel coping preparation previously described is ideal for the pre-

fabricated metal dowel. A champfer margin and an occlusal inlay seat prevent rota-

tion of the coping and give bulk for the metallurgic bond between dowel and coping.

Prefabricated metal dowels can be transferred in the initial impression and incor-

porated in the laboratory wax-up. They also can be luted with wax or resin to the

coping during the try-in and soldered after transfer from the mouth. Dowels are

notched in the coping area to serve as a mechanical lock during casting or soldering.

Threaded dowels. Threaded dowels provide mechanical fixation in addition to

cementation. The threading of the V.K.* and Kurert systems affords excellent reten-

tion. The V.K. system uses a simple positional method with bar attachments when

teeth are markedly divergent (Figs. 3 and 4). ;\nother advantage of the threaded

APM-Sterngold, San Mateo, Calif.

TUnion Broach Company, Long Island, N. Y .


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Volume 37

Number 4

Attachment fixation

for

overdentures. Purt I 371

dowel is that it facil itates cementation of the coping in the absence of opposing teeth

to serve this purpose. A disadvantage of threaded dowels is that use of a screw too

large for the cross section of the tooth

can

cause a fracture during final cementation.

During the past 18 years, I have experienced failures with various dowel systems

for supporting attachments. I have seen no mechanical failures in the 10 years that

I have used the Schenker step pivot. + Therefore I recommend this dowel system for

coping bearing attachments and a threaded dowel system for copings carrying bars on

divergent teeth.

COMPARING BAR TO STUD FIXATION

Splinting of two or more teeth with a bar gives stability similar to that obtained

with a rigid stud-type attachment when the overdenture is in place. The only dif-

ference between the results in these two methods of splinting is that the stud pros-

thesis allows independent movement. If one tooth is especially weak, the strong

tooth can serve as the fulcrum point for movement of the weaker tooth in the

prosthesis.

The bar often splints in more than one plane. Instead of the bar prosthesis mov-

ing one tooth, all or none of the teeth moves under a functional load. A stronger and

a weaker tooth can be splinted with the result that the stronger tooth strengthens the

weaker tooth and the weaker tooth weakens the stronger tooth.

SUMMARY

Scientific evidence of both constructive and destructive movements of teeth has

influenced the design and selection of attachments for overdentures. Dowel designs

that would be acceptable for normal copings must be reconsidered in view of the

mechanical effect iveness of parallel-walled dowels and screws. Coping designs for

attachment overdentures must provide retention, resistance to rotation, and bulk

when joined with the dowel and attachment, without negating the advantage of

the reduced crown-root ratio. Splinting with a bar-type attachment ( 1) has ad-

vantages over splinting with a stud-type attachment that outweigh the disadvantages

of bulk and (2) provides ease of replacement when one of several remaining teeth is

excessively mobile.

Part II will consider the various types of bar, stud, and auxiliary attachments for

the overdenture.


References

1. Gerber, A. A.: Reten tions Zylinder Reten tions Puffer, Biel, Switzerland, 1964, Cendres &

Metaux, S. A., pp. 7,

8, 19.

2. Fenner,

W., Gerber, A. A., and Miihlemann, H. R.: Too th Mob ility Chan ges During Treat-

ment With Partial Denture Prosthesis, J. PROSTHE T. DENT. 6: 520-525, 1956.

3. Mensor, M. C.: The Rationale of Resilient Hinge-Action Stressbreakers, J. PROSTH ET.

DENT. 20: 204-215, 1968.

4. Dolder, E. J.: The Bar Joint Mandibular Denture, J. PROSTH ET. DENT. 11: 689-707, 1961.


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372 Mensor

.I. lrostttet. Drnt.

April, 1977

.5. Dolder, E. J.: Steg-Prothetik, Heidelberg, 1966, Alfred Hiithig.

6. Robinson, R. E.: Osseous Coagulum for Boric Induction, .J. Periodontal. 40: 50%5111, 1969.

100. S. ELLSWORTH, ST E. No. 509

SAN MA TEO , CALIF. 94401

DISCUSSION

Henry E. Ebel, D&S., MS.*

The continuous pattern of alveolar bone loss, once the teeth have been removed, has been

well documented by such researchers as Olsen,t Tallgren,z

and Atwoo d.:, .t Bone resorption

is so predictab le in most patients that every effort shou ld be made to preserve root and

alveolar bone. It is a sad state of affairs when so much time is spent constructing dentures to

flat edentulous ridges when it is possible to prevent such conditions of minimum denture

support.

The article by Dr. Mensor demo nstrates several ways to preserve the roots of periodonta lly

weakened den titions. The reduced crown-root ratio has heen an important adjun ct for the

treatment of weakened or hop eless den titions. Tooth-supp orted overdentures are far superior

in many w ays to the conven tional denture as they enha nce denture base stability, provide posi-

tive retention of alveolar bone, aid in proprioception and ma stication , and strongly strengthen

the psychologic factors of the patient.

Some overdenture retention attachm ents have been design ed to function within the en-

larged root cana l. Others are design ed with various retention stud s that are place d in retained

roots above the crest of the ridge. Dr. Mensor has concen trated on the latter. I felt this was a

wise selection, as there are several inherent dangers in trying to embed such attachments as the

CEKAt within the limited and weakened root canal areas.

From the material presented, one can observe the injured periodon tal structures even after

thorough overdenture cons truction. Protecting the collar of the gingival crevice from injury

must be a prime concern for root preservation. Inflamm ation and proliferation are frequently

observed in the periodon tal tissu es that approximate the retained roots, even though the root

casting is well contoured and oral hygiene is acceptable.

Retained roots frequently have minimu m root length in the alveolar bone. They are on the

ropes, so to speak, and present a doub tful progn osis. I que stion the widespread use of over-

denture stud attachment devices because of the horizontal and dislodging stress loads that

would be imparted to the roots I)y the overdenture. A careful asse ssm ent of the denture sup-

port areas and the number and quality of the retained roots must he undertaken before su b-

jecting these weakened roots to the added loads of mecha nical retention.

I recommen d that the root not he reduced to the depth of the gum crevice whenever poa-

sible. Redu ction of the crown root to a minimum of 1 mm. above the gingival crevice inflicts

no mec han ical injury to the periodon tal fibers, preserves the integrity of the anato mic root, and

sim plifie s periodon tal care and mainten ance. Of course, where esth etics dema nd, further ex-

tension into the gingival crevice cannot be avoided.

Stud ies by Lord and Tee1 5 show promising results for the treatment of roots that are used

for the support of overdentures. No castin g or attachm ents are place d on the reduced roots.

The endodontically treated canals are sealed with amalgam or compo sites and highly polished.

Patien ts are instructed in good oral hygiene. Added protection is provided by the daily appli-

cation of minimum amounts of flouride jel to the internal root recesses of the overdenture.

Their success rate for this procedure used in patients treated since 1965 has been unusually

high. Reline procedures of these all-acrylic resin overdentures are simplified, because no cast-

ings or attachm ents are embedd ed or cemen ted to the dentures or roots.

*Chief of Dentistry, Fairlane Center, Sate llite of Henry Ford Hos pital, Dearborn, Mich.

tCEKA , p.v.b.a., North Wa les, Pa.


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Volume 37

Number 4

Attachment fixation

for

overdentures. Part I 373

One of the most frustrating and time-con suming procedures has been the servicing of at-

tachments in the mouth. Although seemingly ideal in principle and design, maintenance and

repairs may prove costly. I strongly advocate that simp licity of desig n as describe d by Lord

and Tee1.s

When a root has been retained for overdenture treatment, a facial-lin gua l bony undercut

may exist. Some clinician s have recommended resilient denture material in these sites. The use

of this type of retention system wo uld seem to minimize the need for attachme nt locking de-

vices and, thereby, to simp lify the overdenture procedure.

Dr. Mensor mention ed that he experienced no failures with the Schenker step pivot* in

IO years. T his dowe l system appears to be most promising and far superior to those that I have

used in the past, and I shall add it to my armamentarium.

Crack lines induced by mecha nical stress will probably occur when using screw pins or

screw-type posts in roots. Studies have been reported on the microscopic stress lines that result

even when using the small T.M.S. pins.t

In my hand s, the bar-type attachm ents have been most sucre ssful. They are usua lly u sed

to provide cross-arch stabilization , and yet they allow vertical movement and hinging of the

denture base.

The various attachme nt system s have been organized in a comp endium by Dr. Mensor

known as the E. M. Selector. It represents 30 points o f information about each attachme nt

and can be found in Kornfelds book, Mouth Rehabilitation.~

Dr. Mensors stud ies and persona l conta cts with Prieskel, Gerber, Dolder, Steiger, and

Boite l add support to his authoritative references.

Dr. Mensor, we thank you for your contribu tions to this mee ting.


twhaleden t Internationa l, New York, N. Y.

Bell International Inc., Burlingame, Calif.

References

1. Olsen, E. S.: Vertica l Dime nsion of the Face, Dent. Clin. North Am. 13: 611-622, 1964.

2. Tallgren, A.: Changes in Adult Face Height Due to Aging, Wear and Loss of Teeth and

Prosthetic Treatment, Acta Odontol. Stand. 15: l-122, 1957.

3. Atwood, D. A.: Some Clinical Factors Related to Rate of Resorption of Residual Ridges,

J. PROSTHET. DENT. 12: 441-450, 1962.

4. Atwood, D. A.: Red uction of Res idual Ridge s: A Major Oral Disea se Entity, J. PROSTHET.

DENT. 26: 266-279, 1971.

5. Lord, J. L., and Teel, S .: The Overdenture: Patient Selection, Use of Copings, and Follow-

Up Evaluation, J. PROSTHET. DENT. 32: 41-51, 1974.

6. Moffa, J. P., and Razzano, M. R.: In Courtade, G. L., and Timm erman s, J. J., editors:

Pin s in Restorative Dentistry, St. Lou is, 1971, The C. V. Mosby Company, pp. 10-11.

7. Kornfeld, M.: Mouth Reh abilitation, St. Lou is, 1974, The C. V. Mosby C ompany, pp.

802-808.

FAIRLANE CENTER

19401 HUBBARD DR.

DEARBORN, MICH.

48126

attachments for fixed ovds

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