Clinical Communication

The dual-arch impressionIzchak Barzilay, D.D.S.* / Michael L. Myers, D.M.D.**

Introduction also be used for multiple restorations! or fixed partialdentures up to four units. However, if the most poste-rior tooth in the arch is prepared for a fixed partialdenture, the patient may close at a decreased verticaldimension of occlusion, which would result in a signifi-cant negative occlusal error.

Care must be excercised when this type of impressiontray is used. Before the impression is made the tray mustbe placed in the mouth to ensure that the impression willinclude a sufficient number of teeth to provide a definiteocclusal relationship of the casts. Ideally, there shouldbe at least two teeth in the same quadrant which havecontact with the opposing arch. Sufficient room behindthe most distal tooth in the quadrant is needed to accom-modate the posterior bar of the tray when the mouth iscompletely closed. If not, the patient can occlude on thebar, resulting in an increased occlusal vertical dimen-sion.

Previous literature, however, does not mention theimportance of h()rizontal clearance between the verticalrim of the tray and the alveolar ridges. If the bucco-lingu~l width of the alveolar ridge is wider than thewidth of the tray, the plastic outer rims will be wedgedapart when the patient closes into the impressionmaterial (Fig. 1). The tray will be expanded during theset of the impression material, and upon tray removal,the outer rim will return to its original shape and distortthe impression. Once poured, the resulting die will besmaller than (or of different configuration from) thetooth preparation, yielding a casting that is too small. Ifthis situation occurs, a new tray may be modified bycutting the mesh and spreading the tray several milli-meters. This prevents hard contact between the outerrims and the soft tissue during the impression procedure(Fig. 2). The remainder of this article will present a clini-cal situation in which this problem occurred.

Dual-arch impressions and trays have been used formany years. This technique saves time because it elimi-nates several procedures. It enables the dentist to makesimultaneous impressions of both the maxillary andmandibular arches, or segments thereof, and record theocclusal relationship. The technique also reducespatient discomfort and can reduce gagging. The majoradvantage of this technique is that it can reduce errorsand the need for occlusal adjustment which result from:1. Inaccuracies produced by the flexion of the mandible

during the wide opening required for conventional

impression techniques2. Errors that may occur during articulation of casts

either with or without interocclusal records3. Discrepancies in opposing casts which are made from

irreversible hydrocolloidThe impression tray can also be used for interocclusal

records, in provisional crown fabrication, or as a trans-fer impression for fixed partial dentures.

Currently, trays are available in both anterior andposterior designs and consist of an outer rim that isspanned by a mesh fabric. Both plastic and metaldesigns are produced. Any elastic impression materialcan be used, but more rigid-bodied materials are pre-ferred.1Trays have also been developed to be used withreversible hydrocolloid impression materials.

The dual-arch tray may be used to make impressionsfor single-unit crowns where a well-established inter-cuspal position is present and 1ateral contacts are not afactor (anterior guided occlusion). The technique may

Case report

. Postdoctoral Fellow, Department of Prosthodontics, Eastman

Dental Center, 625 Elmwood Avenue, Rochester, New York14620.

.. Assistant Chairman, Department of Prosthodontics, Eastman

Dental Center, 625 Elmwood Avenue, Rochester, New York14620.

A 39-year-old man in good health came to the prostho-dontic department of th~ Eastman Dental Center with a

293Quintessence International Volume 18, Number 4/1987

Clinical Communication

Fig. 1 The tray must not contact alveolar ridge tissues withpressure when it is seated because the tray may be wedgedapart (arrows), causing a distorted impression.

Fig. 2 The tray is modified by cutting the mesh and ex-panding the tray to accommodate a wide ridge.

Fig. 4 Perforated area of the tray (arrow) indicates contactbetween the tray and ridge tissues leading to wedging of the

tray.

Fig. 5 Measurements of buccolingual and mesiodistalwidths indicated differences in the two dies.

294 Quintessence International Volume 18, Number 4/1987

Clinical Communication

mean widths from the measurements showed that therewas a difference in the buccolingual dimension of 0.8 to0.9 mm and little difference in the mesiodistal width(Fig. 5). This discrepancy would be expected, consider-ing the direction of pressure placed on the tray by thealveolar ridge tissue.

Summary

The dual-arch impression is a very useful technique infixed prosthodontics. It is inexpensive, can save timeand impression material, can reduce gagging, and is use-ful when a sectional impression is needed. It can resultin fewer occlusal adjustments during insertion of therestoration. However, it must be used only when indi-cated and with the proper technique in order to achievegood results.

References

1. Wilson, E. G., and Werrin, S. R. Double arch impressions forsimplified restorative dentistry. J Prosthet Dent 49(2):198-202,1983. 0

severely broken down maxillary first molar. The toothwas prepared to receive a complete cast restoration. ATriple Tray impression (Premier Dental Products Co.)was made using a polyether impression material, and acomplete cast gold crown was fabricated. At the inser-tion appointment it was observed that the crown wouldnot seat completely, and after the use of a disclosingmedium, it was apparent that the casting was signifi-cantly undersized in the buccolingual dimension (Fig.3). Upon closer evaluation of the impression, it wasnoted that in certain areas the impression material hadbeen perforated to the plastic tray by the tissues of thealveolar ridge. These areas indicated contact betweenthe tray and the ridge tissue which caused the tray to be

wedged apart (Fig. 4).Another impression was made using the Triple Tray

and a polyether impression material; however, the traywas modified by cutting the mesh and expanding thetray. This impression showed no perforation of, theimpression material by the alveolar ridge soft tissues,and the restoration fabricated on this die fit accuratelyon the prepared tooth.

Measurement of the two dies with a measuringmicroscope was accomplished by two examiners. The

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295Quintessence International Volume 18. Number 4/1987

Second EditionHerbert ~ Shillingburg, Jr., D.D.S., Sumiya Hobo,D.D.S., Lowell D. Whitsett, D.D.S.The classic used in virtually all U.S. dental schools.

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Operative Dentistry