COHEN AND WEINER

The recently introduced composite resin cements that possess increased compressive strength for post and core cementation are recommended.3

REFERENCES

1. Finger IM. Salvaging the restoration. Dent Clin North Am 1987;31:487- 503.

2. Gelbman J, Biber, CL. Salvaging the broken porcelain-fused-to-metal partial prosthesis. Clin Prev Dent 1986;8:22-3.

3. Assif D, Ferber A. Retention of dowels using a composite resin as a ce menting medium. J PROSTHET DENT 1982;48:292-4.

Reprint requests to: DR. BURTON COHEN NEW JERSEY DENTAL SCHOOL 110 BERGEN ST. NEWARK, NJ 07103

The laminar impression technique

Gary A. Schoenrock, D.D.S. Holland, Ohio

The laminar impression technique is a precise, rapid, and predictable alternative to traditional methods of impression-making in fixed prosthodontics. A preliminary impression is made using plastic “triple-arch” type trays and high-stiffness vinyl polysiloxane jaw relation registration material. After tooth preparation, tissue management, and retraction this registration can be used for provisional fabrica- tion. Two holes are then drilled through the facial wall of the tray into the region of the preparation. The tray is replaced in the mouth and light-bodied vinyl polysiloxane impression material is injected into the holes by using an “automix- ing” gun system. (J PROSTAET DENT 1989;62:392-6.)

T he unique advantages of “double-arch” impres- sion techniques have been well outlined in the literature and are widely used.le4 This article describes an impression technique for fixed prostheses (the laminar impression technique) that takes advantage of the desirable aspects of double-arch impressions with improvements in the tech- nique.

IMPRESSION TRAYS

The laminar impression technique uses double-arch plastic trays. The trays are produced by several manufac- turers, and the type or size selected depends on the loca- tion and type of prosthesis and the anatomic variations of the patient.

A tray should be selected that will allow closure of the teeth into maximum intercuspation without interference, The most common interference is with the high sidewalls of plastic trays. Bite registration trays that do not have high sidewalls are preferred by some dentists.

Fig. 1. Three posterior “triple-bite” type impression trays. Note variation in width.

Fig. 1 illustrates three different posterior trays showing variation in width. Such a selection accommodates most patients. Anterior and full-arch trays are available to accommodate almost any clinical condition.

TECHNIQUE

tray clears the distal aspect of the upper terminal molar and avoids interference with the mandibular dentition.

2. A vinyl polysiloxane registration material (Blu- Mousse, Parke11 Products, Farmingdale, N.Y. or Regisil, L. D. Caulk, Milford, Del.) is mixed and applied evenly to both sides of the tray.

1. Before tooth preparation, an appropriate tray is seated in the upper arch to ensure that the crossbar of the

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3. The tray is reseated and the patient instructed to close in maximum intercuspation. The occlusion should be verified on the contralateral side for correct closure (Fig. 2).

4. After polymerization of the registration material, the tray is removed from the mouth and set aside.

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LAMINAR IMPRESSION TECHNIQUE

Fig. 2. Impression tray positioned in mouth.

Fig. 3. Molar full-crown preparation.

The materials recommended for this technique have two main advantages. First, they mix to a fluid consistency, which allows easy closure of the teeth and minimizes the likelihood of inaccurate recording. Second, these materials set rigidly, which minimizes distortion from tray deforma- tion. Double-arch impression methods have been criticized for distortion of the plastic trays when impression materi- als of insufficient stiffness are used.

5. Preparation, tissue management, and retraction are carried out according to the preference of the dentist (Fig. 3).

6. Two holes are drilled through the plastic tray from the facial aspect (Fig. 4). The holes correspond to the mesial and distal interproximal “spikes” of the registration mate- rial mesial and distal to the preparation area. These holes should be approximately 2 mm in diameter and can be prepared with a suitable bur (No. 702 straight handpiece) of 3/32 inch twist drill.

7. A large round bur (No. 10) is used to relieve the reg- istration material (approximately 0.5 mm) in the cervical region of the preparation. This procedure ensures that the critical cervical interproximal margin will be reproduced in adequate thickness by the secondary impression.

Fig. 4. Holes prepared in preliminary registration with No. 702 straight bur. Holes should correspond to mesial and distal interproximal areas.

Fig. 5. Prepared tray ready for final impression proce- dure.

8. The tray is reseated in the mouth and the patient is instructed to close into the indentations of the registration material (Fig. 5). The contralateral occlusion is again ver- ified.

9. The secondary impression is produced with a Iow-vis- cosity vinyl polysiloxane impression material. My prefer- ence is for an automixing and dispensing system (Express, 3M Dental Products, St. Paul, Minn., or Extrude, Kerr Dental Products, Romulus, Mich.). These systems have the advantages of convenience, speed, and consistency of mix (Fig. 6).

10. A mixing tip with an intraoral tip attached (Fig. 7) is positioned on the cartridge and inserted into one of the holes previously drilled in the tray.

11. The wash material is injected into the tray. Injection continues until the material issues from the exit hole of the tray and runs clear of fluid contaminants such as blood and saliva. This “flushing” effect yields impressions of unusual sharpness and detail. The tip is withdrawn from the tray,

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SCHOENROCK

Fig. 6. Vinyl polysiloxane automixing delivery system.

Fig. 8. Intraoral tip placement in tray hole and injection of impression material. Excess extrudes from exit hole.

Fig. 7. Disposable plastic mixing tip and intraoral deliv- ery tip.

with injection continuing during withdrawal to prevent “sucking” of some wash material from within the impres- sion (Fig. 8).

12. After polymerization, the impression is removed and inspected (Fig. 9).

PROVISIONAL CONSTRUCTION

Excellent provisional restorations can be made when the laminar impression technique is used. After the prelimi- nary registration is obtained and after tooth preparation is complete, autopolymerizing tooth-colored acrylic resin or bis-acryl plastic (Pro-Temp, Premier Dental Products, Norristown, Pa.) is placed in the preparation part of the impression.

The tray is then replaced in the mouth over the lubri- cated preparation and the provisional material is allowed to cure. After removal of the provisional material from the impression, it is necessary to clean the impression with al- cohol to remove acrylic resin or bis-acryl plastic residue that may interfere with adherence of the impression mate- rial to the registration material.

VARIATIONS

This versatile technique can be used for both-anterior and posterior prostheses, multiple units, and short-span fixed partial prostheses.

Fig. 9. Final impression.

For fixed partial dentures, a section of the polymerized registration material between the two abutments is re- moved. This “trench” then becomes a connection that al- lows the injection of wash material to both abutments at once. Only two holes are drilled in the tray, one at the me- sial aspect of the mesial abutments and the other at the di- stal aspect of the distal abutment.

ADVANTAGES

When the laminar impression technique is used, the oc- clusal registration, opposing arch impression, and final im- pression are combined in one modular unit. By achieving multiple objectives, a significant time-saving is achieved over more traditional methods.

Precision injection of the wash material avoids waste of excessive impression material. In addition, injection into an open system does not generate compressive forces that can force impression material intramucosally and cause a foreign body reaction until removed.5-7

The flushing action of injecting a continuous flow of im- pression material aids in the removal of sulcular contam- inants and produces clear, detailed impressions of critical regions.

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LAMINARIMPRESSIONTECHNIQUE

SUMMARY

The laminar impression technique is an alternative to traditional impression methods. The simplicity, speed, predictability, economy, and precision in the impression procedure makes it a useful technique.

REFERENCES

1. Christensen G. A new simple double arch impression tray. Clin Res As- sac News1 1981;5:4.

2. Costello WJ. An efficient impression-articulation technique. Dent Surv 1977;53:44-5.

3. Wilson EG, Werrin SR. Double arch impressins for simplified restor- ative dentistry. J PROSTHET DENT 1983;49:198-202.

4. Douglass GD. The cast restoration-why is it high? J PROSTH~ DENT 1975;34:491-5.

5. O’Leary TJ, Standish SM, Bloomer RS. Severe pe~&bx~t.al destruction following Impression procedures. J Periodontol 1973;1:43-8.

6. Gullett CE, Caulder SL. Residual fragment of rubber-base material. Oper Dent 1978;3:131-2.

7. Clark SM. Rubber-base foreign body. J PROSTHET DENT 1974;31:439- 440.

Reprint requests to: DR.GARYA.SCHOENROCK 6924 SPRINGVALLEY DR.,STE. 201 HOLLAND,OH 43528

Interocclusal wax impressions for use in provisioltral a334S associated fixed prosthodontic proced&res

Jules M. Hoffman, D.D.S.,* and Marvin K. Rubin, D.D.S.** Columbia University, School of Dental and Oral Surgery, New York, N.Y.

A procedure is presented for the construction of a direct provisional acrylic resin restoration by means of an interocclusal wax impression. This technique requires no prepreparation or laboratory time and quickly results in a restoration that accurately covers all margins of the preparation and restores proper contact, contour, and occlusion. This procedure can also be used for large restorations, immediate fixed partial dentures, final impressions of preparations, provisional crowns to fit existing removable partial dentures. and some office emergencies. (J PROSTHET DENT 1989;62:395-400.)

A simple technique for constructing a provisional restoration from an interocclusal wax impression was described in 1958 by Rubin.’ It involved making a preop- erative wax impression of the operative quadrant by using an interocclusal gauze impression tray. Since that time other techniques have involved the use of aluminum shells,2 vacuum resin shells, 3-5 alginate (irreversible hy- drocolloid) impressions,@ laboratory fabrication,g and sil- icon putty impressions.

These methods have shortcomings ranging from inordi- nate time consumption and excessive occlusal adjustment to inadequate marginal adaptation and expense. These shortcomings can be overcome by the direct interocclusal wax impression procedure.

Provisional restoration is important in the efficient management of reconstructions for (1) protection and se- dation of the pulp, (2) evaluation of a path of withdrawal from prepared abutments, (3) prevention of tooth migra- tion, (4) stabilization of mobile teeth, (5) an aid in period- ontal therapy, (6) improvement of esthetics, (7) provision for immediate replacement of teeth, (8) a matrix for peri- odontal dressings, (9) aid in developing an occlusal scheme,

*Assistant Clinical Professor of Prosthodontics. **Former Professor, Operative Dentistry; private practice. 10/l/14824

THEJOURNAL OF PROSTHETIC DENTISTRY

(10) evaluation for a change in the vertical dimension of occlusion or prognosis for questionable teeth, and (11) provision of time for patient acceptance.rO

The interocclusal wax impression enables the dentist to reproduce the margins of the crown in acrylic resin while it hardens in centric occlusion position. Paradoxically the inability of the wax to render an accurate, gin&al impres- sion results advantageously in a thicker and sturdier acrylic resin margin, enabling the dentist to selectively trim and contour the emergence profile of the provisional crown. The use of irreversible hydrocolloid or other accurate elas- tic materials as a mold for provisional restorations often results in an acrylic resin margin that ia too thin at the gin- gival surface where the least amount of tooth reduction is made. Provisional restorations made in this manner re- quire relining and time-consuming adjustments.

BASIC TECHNIQUE

1. A sheet of Moyco hard Beauty Pink wax (Moyco In- dustries, Philadelphia, Pa.) the size of the operating field is warmed and folded over on itself and around a Bite Bite Tray (Temrex Div. of Interstate Dental Corp., Freeport, N.Y.) tray and then molded over the quadrant where the teeth are to be prepared. The patient is instructed to close in centric occlusion. This is verified on the opposite side of the mouth. The impression is chilled and removed.

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