SECTION EDITOR A procedure for making fixed prosthodontic impressions with the use of preformed crown shells M. R. Dimashkieh, DDS, MSc, a and Steven M. Morgano, DMD b King Saud University, College of Dentistry, Riyadh, Saudi Arabia; and Harvard School of Dental Medicine, Boston, Mass. Void-free impressions of tooth preparations for fixed prosthodontics are essential for accurately fitting restorations; however, commonly used impression methods are arduous and time-consuming. A procedure has been developed in which an impression is made in a preformed temporary crown shell for each tooth prepara- tion and then a final over impression is made. The result is an atraumatic and uncomplicated complete-arch impression that incorporates an accurate impression of each prepared tooth. (J PROSTHET DENT 1995;73:95-6.) Accurate impressions of tooth preparations with intracrevicular margins are essential for fixed prosthodon- tic restorations. Commonly, gingival displacement cord that has been impregnated with a hemostatic agent is in- serted in the gingival sulcus. The cord is allowed to remain undisturbed for a period of time to control crevicular seep- age and displace the gingival margin. 1The cord is removed, and the impression material is injected in the gingival crevice and over the prepared tooth. Although this proce- dure is the most popular approach, it is time-consuming and requires the use of chemicals that can cause local tis- sue damage or systemic effects. 2 As the number of abut- ments increases, the difficulty in obt~aining an acceptable impression increases exponentially because tissue fluids and saliva must be controlled while a free-flowing impres- sion material is simultaneously injected. Other procedures for making subgingival impressions have been reported. Electrosurgical soft tissue dilation can be used to expose the finish line, create a space for adequate bulk of impression material, and ensure hemostasis. 3 How- ever, electrosurgery is not recommended when the gingival tissue is thin and friable because of the potential for tissue damage or recession and is contraindicated for patients with cardiac pacemakers. 4 Copper band impressions were popular before the intro- duction of elastomeric impression materials in the 1960s. Control of tissue fluids and gingival displacement are facil- itated with the copper band procedure, and this approach may be less damaging to soft tissue than other methods. 5 aprofessor and Chairman, Department of Restorative Dental Sci- ences, and Director, Division of Fixed Prosthodontics, College of Dentistry, King Saud University. bDirector of Postdoctoral Prosthodontics Program, Harvard School of Dental Medicine. Copyright 9 1995 by the Editorial Council of THE JOURNAL OF PROSTHETIC DENTISTRY. 0022-3913/95/$3.00 + 0 10/1/59112 Nevertheless, the procedure of trimming and fitting the copper band is arduous, and impressions made in copper bands require a coping transfer at a second patient visit to make a cast that relates the individual dies to the dental arch. Hoffman6 suggested a procedure that was a refinement of a method reported by Cannistraci. 7 This procedure used a custom-made acrylic resin provisional crown to make an intracrevicular impression for a complete crown prepara- tion, which was followed by an over impression at the same patient visit to make a working cast. This approach elim- inated the need for displacement cord but was time- consuming because the dentist made a provisional crown for each tooth preparation before making the impression. A procedure has been developed in which an impression is made in a preformed temporary crown shell for each tooth preparation and in which a final over impression is then made. The result is a complete-arch impression incorporating an accurate impression of each prepared tooth that includes the gingival terminations. PROCEDURE 1. Select a preformed polycarbonate crown (Ion Polycar- bonate Temporary Crowns, Dental Products/3M, St. Paul, Minn.) and adjust the gingival margin to extend slightly apical to the finish line of the preparation. The crown should fit loosely over the tooth. Adjust the prox- imal contacts to avoid binding on contiguous teeth. Do not remove the tab. 2. Coat the internal and external surfaces of the provi- sional crown shell with the adhesive recommended by the manufacturer for the planned impression material. 3. Mix a regular-body elastomeric impression material and fill the provisional crown shell. Avoid air entrapment when the crown is filled. 4. Seat the shell crown, filled with impression material, over the tooth preparation to cover the finish line (Fig. 1). 5. Allow the impression material to set, and remove the tab with scissors. JANUARY 1995 THE JOURNAL OF PROSTHETIC DENTISTRY 95