In recent years, a number of reports have proposedprocedures for registering jaw relation and making thealtered-cast impression during the same visit as theframework try-in.1,2 By minimizing the number of vis-its, such an approach reduces both the cost of the treat-ment and inconvenience to the patient.

To make an altered-cast impression3 correctlyrequires that the framework remain in exactly the sameposition as during the try-in. Problems often arisebecause the impression material placed between frame-work and mucosa may cause the framework to lift awayfrom the mucosa; subsequently, during flasking, theframework will depress again, producing inaccuracies inthe prosthesis. An attempt can be made to counter thisproblem by pressing down on the framework with thefingers while making the impression; however, this maynot give acceptable results, because it is difficult tojudge how much pressure to exert; in addition, the actof pressing down may itself cause slight displacements.An alternative approach is to take the altered-castimpression first, and then to obtain a jaw relationrecord in silicone.2 This procedure has 2 major disad-vantages: (1) It is difficult to ensure that the frameworkwill remain in the correct position, and (2) the impres-sion material used for obtaining the jaw relation recordmay be displaced slightly, leading to inaccuracies in thefinal structure. Another possibility is to use the frame-work as record base3,4; however, this procedure is alsosometimes inaccurate.

This article describes an accurate procedure for reg-istering the jaw relation and making the altered-castimpression during the same session as the frameworktry-in for the removable partial denture (RPD).

PROCEDURE

A patient who needed a bilateral distal-extensionRPD and a maxillary complete denture was selected toillustrate this procedure.

After the framework is completed in the laboratory,make RPD bases5 (Figs. 1 and 2). These may be oflight-cured acrylic resin tray material as shown, or alter-natively of modeling impression compound or thermo-plastic baseplate material. With the framework andRPD bases seated on the cast, mark the frameworkthrough the holes in the denture bases (Fig. 1). Tomake certain that the framework is seated correctly, itmust be tried in and fitted in the mouth to ensure thatit is in the same position every time it is seated.6 Thisdepends on a passive fit, and the absence of occlusalinterferences.

Any defects in the framework should be corrected at

An accurate method for occlusal registration and altered-cast impression forremovable partial dentures during the same visit as the framework try-in

U. Santana-Penín, MD, PhD,a and J. Gil Lozano, MD, PhDb

Faculty of Medicine and Odontology, University of Santiago de Compostela,Santiago de Compostela, Spain

Preparation of mandibular distal-extension removable partial dentures usually requires a secondaryimpression (the altered-cast impression) to improve the stability of the prosthesis. A potential prob-lem with conventional altered-cast impression procedures is incorrect or incomplete seating of theframework in the mouth or on the cast. This article describes a procedure for obtaining the interjawrelationship and an accurate altered-cast impression in a single appointment (that of the frameworktry-in). (J Prosthet Dent 1998;80:615-8.)

aProfessor, Department of Occlusion and Prosthodontics.bProfessor, Department of Prosthodontics, Faculty of Medicine and

Odontology, University of the Basque Country EHU, Leioa, Viz-caya, Spain.

NOVEMBER 1998 THE JOURNAL OF PROSTHETIC DENTISTRY 615

Fig. 1. Light-cured acrylic resin tray formed over edentulousridge portion of framework. Holes are made in tray to allowresin columns to be built up through it. Position of holes canbe marked with pencil so that it is clear where to locatebases of columns (arrows).

DENTAL TECHNOLOGY Kenneth D. Rudd

this stage. The tissue stops on the intaglio surface of theresin-retention part of the framework should toucthe soft tissue but should not exert pressure against it

(the purpose of the stops is to touch the cast and pre-vent the distal end of the framework from depressingduring the packing process).7 After the framework hasbeen fitted to the mouth, complete the following steps.

1. Build a 1⁄4-inch diameter column of light-curedresin on the resin-retention part of the frameworkin the position corresponding to the hole in theacrylic resin impression tray (Fig. 3), and extendthis column up to the opposing occlusion in thecorrect jaw relation position. (The tripoding effectestablished by the column of resin on each distal-extension framework and the anterior teeth of thedenture ensures that the framework is seated in thesame way each time the patient closes in the estab-lished jaw relation position.)

2. Remove the framework with the columns of resinattached, seat it on the master cast, and mount it

on an articulator with an opposing cast. In addi-tion, a stone index may be prepared below the lin-gual major connector, facilitating and improvingpositioning when the framework is reseated on thealtered master cast.8 If necessary, enlarge the holesin the laboratory-made removable denture bases sothat they fit correctly over the resin columns. Seatthe bases over the framework (Fig. 4), then heatthem and adapt them to the framework, makingcertain they are firmly attached to it.

3. Place the framework with attached bases in themouth and relieve any overextensions and/or pres-sure spots, then apply low-heat-softened com-pound to the borders of the denture bases andborder-mold it.

4. Remove the framework-plus-tray, apply impressionwax into the tray, then reinsert the whole structureand maintain it in the mouth while the wax adapts

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Fig. 2. Acrylic resin trays (with holes for resin columns)detached from framework.

Fig. 3. Framework in mouth showing 1 resin column built upas jaw relation index.

Fig. 4. Acrylic resin tray in position on framework afterbuilding up resin column (a) that acts as jaw relation index.In addition, stone index beneath major connector (b) willfacilitate accurate repositioning of framework on alteredcast.

Fig. 5. Completed impression seated on cast from whichedentulous ridges have been removed.

to the edentulous ridge. Ask the patient to makemolding movements. At this stage, the occlusalindex serves to maintain the framework in the cor-rect position.

5. Remove the edentulous ridges from the cast, bymaking 2 cuts, the first longitudinally, the secondat right angles to the longitudinal axis of the ridge,1 mm distal to the abutment (Fig. 5).

6. Score the cut surfaces with a knife or bur to ensuregood attachment of the new stone to the old.

7. Position the framework-impression assembly onthe cast with the edentulous ridges removed andmake certain that the framework is seated correct-ly on the teeth and in the index for the bar (Fig. 5).If there is any chance that it will change positionsduring the boxing procedure, wax it securely inplace with sticky wax.

8. Bead the impression with beading wax or plasticineand wrap the cast with boxing wax. Seal the bor-ders with more wax so unset stone will not leakthrough when it is poured (Fig. 6).

9. Pour a mix of stone into the boxing and allow it toset.

10. Remove the blockout and boxing material fromthe cast (Fig. 7) but do not separate the frame-work-impression assembly from the cast at thistime.

11. Mount the mandibular cast in the articulator afterensuring that the resin columns are correctly posi-tioned against the previously mounted maxillarycast (Fig. 8).

12. Remove the framework-impression assembly anddo the necessary procedures to complete the RPD.

DISCUSSION

It is our opinion that the use of altered-cast tech-niques during the preparation of distal-extensionRPDs3,6 is highly recommendable, because it is easy toperform and gives predictable results. Such techniques

were considered to be routinely used in clinical prac-tice, and they are included in basic training.

An apparent disadvantage of such procedures is thatthey are time-consuming and require a specific visit.However, they often save time that would otherwise bespent on final modifications of the denture. Further-more, altered-cast procedures produce a better denturebase that not only withstands occlusal forces moreeffectively but also improves stability and retention (inother words comfort for the patient); these are strongarguments for making the extra effort involved inpreparing an altered cast. Although to the best of ourknowledge there have been no controlled studies, itseems reasonable to assume that a better adapted andmore stable base will reduce the risk of failure of theabutments.

The correct execution of an altered-cast impressionrequires the framework to be perfectly seated andmaintained in position while the impression material

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NOVEMBER 1998 617

Fig. 6. Impression is boxed, in this case with plasticine. Fig. 7. Finished altered master cast, with impression and jawrelation indexes (arrows) in place.

Fig. 8. Resin columns (Figs. 3 to 5 and 7) are used to relatemandibular cast to previously mounted maxillary cast, andare attached to lower arm of articulator with stone.

hardens.3 However, this may be difficult in certain clin-ical situations (for example, when the edentulous ridgeis long). In such situations, the framework may lift upslightly or the dentist may press down too hard on theretentive grid and push it too far down. Furthermore,the patient must keep his mouth open while the dentistmakes molding movements by pressing in the impres-sion-tray zone with his fingers; again, the dentist mayapply too much or too little pressure. Subsequently, thepressure is released so that the patient can close hismouth to allow the wax impression to be taken, andthis may mean that the framework lifts up (particularlyif the patient is asked to make molding movementswith the mouth closed).

These problems can be overcome by building anindex consisting of a rigid column that arises from theretentive grid and terminates against the occlusal sur-face of the opposing teeth or dentures. An index of thistype ensures that the framework remains in the correctposition throughout the impression procedure, inde-pendently of pressure applied by the dentist. The indexalso acts as a jaw relation record to facilitate subsequentpositioning of the cast in the articulator. The photo-chemically cured index described in this article can bemade in a short time (seconds) and in the desired inter-maxillary position. The technique by Lay et al., 2 formaking a jaw relation record during the same visit asthe framework try-in, has the disadvantage that theindex is elastic and does not remain joined to theimpression. The result of this technique is that it maynot always adopt exactly the same position as duringthe try-in. In our opinion, the procedure described inthis article is more reliable, and probably reduces thelikelihood of error when the cast is positioned in thearticulator.

A minor disadvantage of the procedure described inthis article arises when the antagonist is itself a mucosa-supported complete denture. In such cases, clenchingcan cause slight displacement of the opposing prosthe-sis, because the pressure exerted by the natural incisorsmay cause rotation and detachment of the posteriorpart of the denture. To avoid such problems, thepatient should be instructed not to clench tightly, butsimply to bring the maxillary and mandibular archestogether. The dentist should be able to detect excessiveclenching by monitoring the position of the frameworkstop with respect to the impression surface. If excessive

clenching is detected, a new layer of wax should beapplied and the impression should be obtained again toensure that the patient does not clench excessively.

SUMMARY

The procedure described in this article presents sev-eral advantages: (1) The patient can make moldingmovements with the mouth closed to ensure that theframework remains immobile in its initial position; (2)the procedure requires little time; (3) the procedurecan be performed in the clinic, without new jaw rela-tion trays; (4) the procedure obviates the fourth stagein conventional preparation of a removable partial den-ture (establishment of functional and harmoniousocclusion3); and (5) the jaw relation index obtained isstable and rigid, eliminating possible errors associatedwith the fitting of provisional indices during the labo-ratory phase.

REFERENCES

1. Kakar A. Simplified one-step procedure for making impressions and jawrelation records of implant-supported reconstruction. J Prosthet Dent1995;74:314-5.

2. Lay LS, Lai WH, Wu CT. Making the framework try-in, altered-cast impres-sion, and occlusal registration in one appointment. J Prosthet Dent1996;75:446-8.

3. McGivney GP, Castleberry DJ, editors. McCracken’s removable partialprosthodontics. 8th ed. St Louis: CV Mosby; 1989. p. 327-37,339-60.

4. Warren K, Capp N. A review of principles and techniques for makinginterocclusal records for mounting working casts. Int J Prosthodont1990;3:341-8.

5. Lund PS, Aquilino SA. Prefabricated custom impression trays for thealtered cast technique. J Prosthet Dent 1991;66:782-3.

6. Stewart KL, Rudd KD, Kuebker WA. Clinical removable partial prostho-dontics. St Louis: Ishiyaku EuroAmerica; 1992. p. 45-6.

7. Rudd KD, Morrow RM, Rhoads JE. Dental laboratory procedures. Vol III:removable partial dentures. 2nd ed. St Louis: CV Mosby; 1986. p. 30-57,187-208.

8. Shifman A. Index to reposition the metal framework accurately on thealtered cast. J Prosthet Dent 1992;68:979-81.

Reprint requests to:DR U. SANTANA-PENIN

DEPARTMENT OF OCCLUSION AND PROSTHODONTICS

FACULTY OF MEDICINE AND ODONTOLOGY

UNIVERSITY OF SANTIAGO DE COMPOSTELA

ENTRERRIOS, S/N15705 SANTIAGO DE COMPOSTELA

SPAIN

Copyright © 1998 by The Editorial Council of The Journal of ProstheticDentistry.

0022-3913/98/$5.00 + 0. 10/1/92494

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