REMOVABLE PROSTHODONTICS SECTION EDITORS

LOUIS BLATTERFElN S. HOWARD PAYNE (;EORGE A, ZARB

A loading impression technique for semiprecision and precision removable partial dentures

Louis Blatterfein, D.D.S.,* Ira E. Klein, D.D.S.,** and Joseph C. Miglino, D.D.S.*** New York University, College of Dentistry, New York, N. Y.

R e&ration of ridge contour under a load is generally accepted as desirable for ridge support of the base of a distal-extension removable partial denture.le6 The importance of this concept is accen- tuated when semiprecision or precision retainers are used.7 They transmit functional forces to abutment teeth which can result in cantilever action.

RATIONALE OF DESIGN

Semiprecision retainers for distal-extension remov- able partial dentures can be designed to minimize the dangers of cantilever action.8~‘z However, when prefabricated semiprecision or precision retainers which do not allow. prosthesis rotation are used, supplementary procedures are necessary to prevent

torque on the abutment tooth. Stress breakers and the registration of ridge contour in a loaded form are effective in minimizing torque.

Stress breakers (stress equalizers) have been used with varying degrees of success. Controversy exists as to the validity of their rationale and their ideal designs if the validity is accepted. Stress breakers are complicated, costly, and prone to disorientation and breakage. A strict regimen of patient recall and maintenance is mandatory to provide patients with

proper service. These factors limit the use of stress breakers as a broad-based treatment plan for patients of limited financial means.

An alternative treatment would be to use semipre- cision or precision rests designed to allow for varying amounts of prosthesis rotation. These can be coupled with a denture base fitted to ridges registered in a

Presented to the Greater New York Academy of Prosthodontics,

New York, N. Y.

*Professor Emeritus, Department of Removable Prosthodontics.

**Professor, Department of Graduate Removable Prosthodon- tics.

***Clinical Associate Professor, Department of Removable Pros-

thodontics.

0022-3913/80/010009 + 06$00.60/O 0 1980 The C. V. Moshy Co.

loaded form. This will minimize prosthesis rotation during function and result in less torque to abutment teeth. Also, the wear of rests and rest-seat compo- nents will be reduced.

The registration of ridge contour in a loaded form has been described by many authors.‘3-‘7 Their techniques are generally effective; however, they use primarily shallow rest and clasp removable partial dentures. When semiprecision and precision retain- ers are used, these techniques are not applicable because they do not provide firm seating for the abutment castings that are to be placed in the impression. The loading impression techniques that use rebasing concepts”’ I8 also have limitations when used for a semiprecision or precision removable partial denture. The repeated seatings required with the framework are difficult and unwieldy when the abutment castings are uncemented. If the technique is done after cementation, repeated seatings are difficult because of the frictional resistance that is usually present in newly placed deep rest retainer removable partial dentures.

EXISTING DEEP REST IMPRESSION TECHNIQUES

Impression techniques that are used to “pick up” or provide firm seats for deep rest abutment castings are effective in providing these seats. However they may fail to accomplish proper extension of the borders of the base and loading of the ridge muco- sa.

The all-plaster technique”‘. ” provides a highly accurate method of relating abutment castings to one another and to the ridges. However, the tech- nique fails to provide accurate border extension for the denture base, while loading of the ridge mucosa is minimal or nonexistent.

Techniques that combine mercaptan rubber,8 sili- cone, or polyether impression materials in a spaced

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BLATTERFEIN, KLEIN, AND MIGLINO

Fig. 1. The preliminary irreversible hydrocolloid im- pression (alginate) has been made with the abutment castings in position on the teeth.

Fig. 2. Cast poured from the preliminary impression.

custom tray in conjunction with plaster seats for the abutment castings overcome the problem of uncon- trolled border extension of the denture base. Correct border extension can be attained by using a stiff- bodied elastomer impression material’ in a slightly underextended custom impression tray or by border molding an underextended impression tray with modeling composition before applying a lighter bodied elastomer impression material. Both ap- proaches register the ridges in a passive, anatomic form and fail to provide the ridge loading that is desired. Some impression techniques register only the ridges in an unspaced custom tray and then relate this base impression to the abutment castings and remaining natural teeth with an overall impres- sion of plaster or similar material. The resulting final impression does not provide much ridge loading. Special steps such as biting pressure, finger pressure,

Fig. 3. A layer of baseplate wax has been placed over the teeth on the cast.

Fig. 4. A second layer of baseplate wax has been placed over the spaced and unspaced parts of the cast.

and tray pressure on occlusion rims are often incor- porated into these techniques to provide ridge load- ing.” When these adjuncts are used, the result becomes unpredictable and prone to error because of uneven pressure and malrelation of the parts of the impression.

IMPRESSION TECHNIQUE

The limitations of existing techniques for deep rest distal-extension removable partial dentures can be overcome by using a specially prepared custom tray in conjunction with modeling composition, activated acrylic resin, and a polyether gel impression materi- al. This technique will provide a final impression that has firm seats for the abutment castings, correct border extension of the denture base, and ridge loading.

After the abutment castings have been properly

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LOADING IMPRESSION TECHNIQUE

Fig. 5. Windows have been cut in the spacing wax to provide stops for a custom impression tray. Two stops are on the ridges, two are on the abutment castings, and one is on part of the incisal edges of the central incisors.

Fig. 6. An activated acrylic resin impression tray has been fabricated over the prepared cast.

fitted to the prepared teeth, an irreversible hydrocol- loid (alginate) impression is made of the jaw with the abutment castings in position (Fig. 1). A cast is

poured in artificial stone for the purpose of fabricat- ing an activated acrylic resin impression tray (Fig. 2). The planned impression tray is to be spaced from the remaining teeth, abutment castings, and ridges. A

layer of baseplate wax is first adapted only around the remaining natural teeth and abutment teeth (Fig. 3). The purpose of the initial spacing is to allow

for a greater thickness of the final polyether impres- sion material in this part of the tray. The set polyether has little yield when confined to a slightly spaced tray, and the teeth of the poured cast may be fractured during separation.

A second layer of baseplate wax is then adapted

Fig. 7. A view of the inner surface of th13 impression tray that shows the five elevated stops.

Fig. 8. Modeling composition has been placed in the ridge parts of the tray. A firm seat has been established for the tray against the ridges. Borders have been molded for proper height and width.

over the spaced and unspaced parts of the cast (Fig.

4). This creates space for the impression materials that will be used to establish the border limits of the

denture base and provide ridge loading. For the purposes of positioning and orienting this

spaced tray, reference contacts (stops) for the oral structures and abutment castings are needed. These

contacts (stops) are provided by cutting out small windows in selected parts of the spacing wax (Fig. 5). Three windows are cut for stops that will provide a

stable seat for the impression tray and two more windows are cut in the spacing wax over the abut- ment castings for seating stops. Windows for the tray-stabilizing stops on the ridges are usually cut over the horizontal parts or buccal. shelves of the ridges midway between their anterior-posterior

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BLATTERFEIN, KLEIN, AND MIGLINO

Fig. 9. Duralay is applied to the stops on the abutment castings and incisors to reestablish firm contact on them.

Fig. 11. Impression has been completed with a polyether gel. Abutment castings have been “picked up” in the impression and have a firm unyielding seat in the impres- sion. There is a thin lining of the gel over the modeling composition registration of the ridges.

Fig. 10. View of the inner surface of the tray showing the three stops corrected in relation to the modeling compo- sition basing that has been established on the ridges. ’

limits. The windows for natural tooth contacts are

cut over the mesial halves of the incisal edges of the central incisors.

An activated acrylic resin tray is fabricated over

the prepared cast (Fig. 6). The inner surface of the tray will show five well-defined teeth, abutment casting, and ridge stops (Fig. 7). The tray is then

trimmed so that its borders are about 2 mm short of the reflection of the tissues of the mucobuccal and mucolingual folds. Sufficient reduction of the edges is necessary to allow for the bulk of the basing

material necessary for proper border molding. Modeling composition is placed on the ridge parts

of the impression tray, thoroughly heated and tempered, and the tray is then positioned in the mouth. This step is repeated until a uniform and detailed seating has been obtained. The borders of

Fig. 12. Duralay with dowel inserts have been placed in the abutment castings. Borders of the impression have been protected by rimming ‘before final boxing and pouring.

the resulting impression are then heated, tempered, returned to the mouth, and molded to register the correct height and width that is available for support

of the denture base (Fig. 8). The modeling composition places the mucosa of

the ridge. It registers a form that the mucosa will

assume when functional forces are applied to the completed prosthesis. A firmer seat will be available for the removable partial denture and less stress will be transmitted to the abutments. The potential for overloading and trauma is reduced.

After completing the basing of the ridge sections of the impression tray, the relationship of the tray stops to the abutment castings and natural teeth must be

12 JANUARY 1980 VOLUME 43 NUMBER 1

LOADING IMPRESSION TECHNIQUE

Fig. 13. Anterior section of the impression tray has been cut away after pouring to avoid breaking the teeth of the cast during separation. The extra layer of spacing wax that was used facilitates this step.

Fig. 14. Completed final cast with abutment castings related to the remaining natural teeth and ridges in a loaded form.

accurately reestablished. Varying thicknesses of the basing material will change the original relation of the stops to remaining teeth and abutment castings.

A correction is effected by applying Duralay* to the three anterior stops (Fig. 9) and then firmly reseating

the tray. A hard unyielding seat is now provided for the abutment castings when the impression tray with the final impression material is placed in position

(Fig. 10). A polyether impression material is used for the

final impression. This material has good flow when

mixed, and it has adequate firmness when set. The good flow allows it to correct any unevenness of the modeling composition basing and still retain its loading effect. Its adherence to the modeling

composition and tray in a thin film is assured by using the adhesive supplied with the material (Fig. 11).

The firmness of the material stabilizes the abut- ment castings against horizontal displacement. The

Duralay occlusal stops stabilize the abutment cast- ings against vertical displacement in the combina-

tion final impression. Seats for the abutment castings on the final cast

can be provided by placing Duralay or pouring low-fusing metal in the properly prepared internal

surfaces of the abutment castings. Dowels are placed in the poured material to provide for their anchorage to the final artificial stone cast.

The impression can be easily rimmed and boxed to preserve the borders that have been established (Fig. 12). Direct separation of the impression from

*Reliance Dental Mfg. Co., Worth, I11

the poured cast is hazardous. The stiffness of the set polyether gel will usually cause the teeth of the

poured cast to break away. The acrylic resin impression tray should be cut

away in the region of the teeth (Fig. 13). This

procedure is facilitated by the extra thickness of polyether gel that was produced by the double-wax spacing of the preliminary cast prior to the fabrica-

tion of the impression tray. The casts that result from this impression tech-

nique will have an accurate relation of the abutment

castings to one another and to the ridges (Fig. 14). The ridges will be registered in a form that they assume when functional forces are applied to the

artificial teeth of the completed removable partial denture. This provides a favorable environment and

foundation for a bilateral distal-extension removable partial denture and minimizes the potential for

trauma and overloading of the abutrnent teeth.

SUMMARY

The rationale of designing a semiprecision or precision distal-extension removable partial denture and the justification of ridge loading in distal-

extension ridge impression techniques have been presented. The effectiveness of existing impression techniques in securing firm seats for abutment cast-

ings, accurate border extension of the denture base, and loading of the ridge mucosa has been evalu- ated.

A technique has been described that overcomes the limitations of existing impression techniques for

semiprecision and precision distal-exl:ension remov- able partial dentures.

THE JOURNAL OF PROSTHETIC DENTISTRY 13

BLATTERFEIN, KLEIN, AND MIGLINO

REFERENCES 13.

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

Cummer, W. E.: Impressions in partial denture service. Dent

Cosmos 70:272, 1928. McLean, D. W.: The partial denture as a vehicle for

function. J Am Dent Assoc 23:1272, 1936.

Singer, F.: Functional impression and interocclusal records for removable partial dentures. J PROSTHET DENT 12:536,

1962.

Hindels, G. W.: Load distribution in extension saddle partial

dentures. J PROSTHET DENT 2:92, 1952. Applegate, 0. C.: Essentials of Removable Partial Denture

Prosthesis, ed 3. Philadelphia, 1965, W. B. Saunders Co., pp 253-270.

Henderson, D., and Steffel, V. 0.: McCracken’s Removable

Partial Prosthodontics, ed 4. St. Louis, 1973, The C. V.

Mosby Co., pp 261-268.

Preiskel, H. W.: Impression techniques for attachment-

detained distal-extension removable partial dentures. J PROS- THET DENT 25:620, 197 1.

Blatterfein, L.: The use of the semiprecision rest in remov- able partial dentures. J PROSTHET DENT 22:307, 1969.

Thompson, M. J.: Reversible hydrocolloid impression mate-

rial: Its treatment and use in operative and prosthetic

dentistry. J Am Dent Assoc 39:708, 1949. Harris, F. N.: The precision dowel rest attachment. J

PROSTHET DENT 5:43, 1955. Morrison, M. L.: Internal precision attachment retainers for

partial dentures. J Am Dent Assoc 64:209, 1962. Koper, A.: An intracoronal semiprecision retainer for remov-

able partial denture-the Thompson dowel. J PROSTHET

DENT 30:759, 1973.

14.

15.

16.

17.

18.

19.

20.

21.

22.

Applegate, 0. C.: The partial denture base. J PROSTHET

DENT 5:636, 1955. Kramer, H. M.: Impression technique for removable partial

dentures. J PROSTHET DENT 11:84, 1961.

Holmes, J. B.: Influences of impression procedures and occlusal loading on partial denture movement. J PROSTHET

DENT 15:474, 1965.

Leupold, P. J., and Kratochvil, F. J.: An altered-cast

procedure to improve support for removable partial den-

tures. J PROSTHET DENT 15:672, 1965. Rapuano, J. A.: Single-tray dual-impression technique for

distal-extension partial dentures. J PROSTHET DENT 24:41,

1970. Wilson, J. H. L.: Partial dentures-relining the saddle

supported by the mucosa and alveolar’bone. J PROSTHET

DENT 3:807, 1953.

Steffel, V. L.: Relining removable partial dentures for fit and

function. J PROSTHET DENT 4:496, 1954.

Prothero, J. H.: Prosthetic Dentistry, ed 2. Chicago, 1916,

Medico-Dental Publishing Co., pp 506-516.

Nichols, I. G.: Prosthetic Dentistry. St. Louis, 1930, The C. V. Mosby Co., pp 567-575.

Leff, A.: Precision attachment Dentures. J PROSTHE? DENT

2:84, 1952.

Re+zt requests to:

DR. LOUIS BLATTERFEIN

1 HANSON PLACE

BROOKLYN, N. Y. 11243

ARTICLES TO APPEAR IN FUTURE ISSUES

Cementation, of cast complete crown retainers Jacob Abelson, D.D.S.

The combined reversible-hydrocolloid/irreversible-hydrocolloid impression system David C. Appleby, D.M.D., M.Sc.D., Cornelis H. Pameijer, D.M.D., M.Sc.D., DSc., and Joseph Boffa, D.D.S., M.P.H.

Glass-mounted composite-slide fabrication Isaac E. Appleton, D.D.S., M.S.

A review of the submerged-root concept David M. Casey, D.D.S., and Frank R. Lauciello, D.D.S.

Reliability of the fovea palatini for determining the posterior border of the maxillary denture Ming-Sheh Chen, B.D.M., M.Sc.

JANUARY 1980 VOLUME 43 NUMBER 1