An impression and cast construction technique for implant-retained auricular prostheses

An impression implant-retained

and cast construction technique auricular prostheses

for

John F. Wolfaardt, BDS, MDent, PhD,a and Philip Coss, RDTb Misericordia Hospital, Caritas Health Group, Edmonton, Alta., Canada Implant-retained auricular prostheses present a challenge with regard to the esthetic placement of the margins of the prosthesis. A technique for the impression and master cast fabrication to produce an implant-retained auricular prosthesis is described. This technique allows control of the esthetic margin, fabrication of a durable master cast with planned blockout, and inclusion of a replica of the retentive bar, which allows processing duplicate prostheses without returning the retentive bar to the mold. CJ

PROSTHET DENT 199%75:45-9.)

I

mplant-retained auricular prostheses provide a challenge with regard to adaptation ofvisible margins that may adversely influence the esthetic result of the prosthesis. Movement of the mandibular condyle and soft tissues associated with changes in head position can result in the loss of contact of the anterior margin of the silicone prosthesis with the underlying skin. The exposed anterior margin of the implant retained auricular prosthesis must maintain skin contact at all times if the esthetic value of the prosthesis is to be preserved. The design of the fitting surface should only allow for prosthesis-skin contact at the anterior and conchal margins and the posterior conchal margin must include an aeration channel. The goal of this technique is to maintain skin contact of the anterior silicone margin. With the exception of the superior and inferior perimeters, the remainder of the fitting surface of the prosthesis is designed to provide 1 to 3 mm of clearance for aeration of the skin under the prosthesis. The goals of the technique are (1) to make an impression that allows continuous skin contact by the anterior silicone margin, (2) to construct a master cast that provides adequate planned spacing under the completed prosthesis, and (3) to construct a master cast that does not require the retentive bar to be returned to the mold for prosthesis processing. A review of articles on craniofacial implant prosthesis construction did not address how the preceding goals could be achieved.re4 Common practice, as described by Thomas,5 is to add stone or wax to the surface of the master cast to create space. The anterior margin is usually managed by scraping the master cast and then smoothing the area with

Fig.

1. Retentive

bar with

outline

of ear position.

Fig. 2. Locating indices (5.0 mm diameter acrylic resin rods) on acrylic resin tray and resin substructure (arrows). aDirector, Craniofacial Osseointegration and Maxillofacial Prosthetic Rehabilitation Unit (COMPRU). bAnaplastologist, COMPRU. Copyright 0 1996 by The Editorial Council of THE JOURNAL OF PROSTHETIC DENTISTRY. 0022-3913/96/$5.00 + 0.

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abrasive paper; however, these methods are unpredictable. Indirect techniques described in the literature require that the retentive bar be returned to the mold for processing. ‘a ’ This is inconvenient for the patient and

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Fig. 5. Recording of impression with mouth prop holding jaw open and head in predetermined position. Confirmation of relationship between custom tray, acrylic resin substructure, and retentive bar through cutout in custom tray. Fig. 3. Window in custom tray that allows visualization of retentive bar through clear acrylic resin substructure.

Fig. 4. Uncatalyzed

silicone putty is syringed around base of acrylic resin substructure. Excess uncatalyzed silicone putty is trimmed away.

risks damage to the bar. This technique address these problems.

was developed

Fig. 6. Recovered impression with silicone putty removed. Photocopy (on transparent sheet1 of normal ear is reversed and used to demarcate anterior margin, internal spacing, and aeration channel.

to

PROCEDURE 1. Make a preliminary impression that incorporates the implant impression copings. 2. Fabricate the retentive bar and clip retained resin substructure according to prescribed techniques.3, 4 Space the acrylic resin substructure to provide 1 to 3 mm of clearance from the skin (Fig. 1). 3. Fabricate an autopolymerizing acrylic resin custom tray and index it to the resin substructure (Fig. 2). (The custom tray must provide for clear visualization of the retentive bar through the resin substructure through a window in the tray [Fig. 31.)

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Fig. 7. Rotary instrument impression surface.

used to cut area of spacing into

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Fig. 8. Completed trimming rugh posterior margin.

Fig. 9. Stainless steel wire tentive bar bent to replicate

of diameter bar.

of impression

that matches

re-

4. Assess the movement of the condyle of the mandible under the preauricular skin to determine the point of maximum skin depression. Also assess head movement for maximum skin depression and record the impression in these positions. (The mandible can be held open in the desired position with a mouth prop.) 5. Mark the desired position of the prosthesis on the skin. (This position may be determined by biometric guides on the face or transferred from the surgical template used during implant installation. 6. Load uncatalyzed silicone putty (Rapidsoft, Coltene, Altstatten, Switzerland) into a disposable syringe (#412, Monoject, St. Louis, MO.) with its tip cut off. Place the acrylic resin substructure in position on the retentive bar and syringe the silicone putty around the margin

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surface shows aeration

channel

(arrows)

QF PIZOSTHETIC

DENTISTFtY

tho-

Fig. 10. Completed cast shows stainless steel wire replica of retentive bar, blockout around margin of the resin substructure, soft tissue spacing, and soft tissue recording for anterior margin of silicone prosthesis.

of the acrylic resin substructure. Use a plastic instrument to remove the excess silicone putty (Fig. 4). 7. Paint the custom impression tray with adhesive (polyether adhesive, Espe-Premier, Norristown, Penn.) and load the tray with polyether impression material (Permadyne/Impregum, Espe, Seefeld, Germany). Select the viscosity accordmg to skin mobility. Position the tray over the substructure and seat it to engage the indices. Verify that the relationship with the retentive bar has not been altered, by viewing the acrylic resin substructure through the cutout in the tray, and confirm the relationship between the tray and substructure (Fig. 5). (Tb.e positioning of the tray, the head, and

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Fig. 11. Fitting surface of two prostheses processed out of same mold show planned spacing for aeration (arrows).

Fig. 13. Anterior esthetic tains skin contact during ments.

Fig. 12. Completed prosthesis margin along anterior border.

shows contact

of silicone

margin of prosthesis extreme mandibular

mainmove-

9. Reduce the impression surface in the marked area in step 3 with tungsten carbide rotary instruments (F’ig, 7). Assess the depth of spacing with a periodontal probe. To provide a defined margin, trim the impression material margin around the resin substructure. The impression surface posterior to the resin substructure can be reduced to create the opening for the aeration chamber under the ear prosthesis (Fig. 8). 10. Bend a stainless steel wire of diameter that matches the retentive bar to replicate the bar. (This is introduced into the clips in the resin substructure.) Box and pour the impression (Fig. 9). 12. Incorporate the replica of the bar, soft tissue spacing, and anterior soft tissue recording into the completed cast (Figs. 10 and 11) to provide an esthetic margin (Figs. 12 and 13). SUMMARY

the jaw held in the predetermined open position with a mouth prop are shown in Fig. 5.) 8. Recover the impression and mark the area of soft tissue that is not to have tissue contact anterior to the acrylic resin substructure on the impression surface (Fig. 6). Use a photocopy (on a transparency sheet) of the normal ear to help demarcate the anterior margin, internal spacing, and aeration channel.

483

This technique (1) allows processing of the prosthesis without using the retentive bar in the mold, (2) allows multiple processing on duplicate resin substructures, and (3) incorporates required blockout and spacing for subprosthesis dermal aeration. Of importance, the technique provides a well-adapted prosthesis anterior margin that does not depend on arbitrary reduction of the cast.

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REFERENCES

5. Thomas KF. Prosthetic 1994169-98.

1. TjellstrGm A. Osseointegrated implants for replacement of absent or defective ears. Clin Plast Surg 1990;1’7:355-66. 2. Pare1 SM, Halt R, Brinemark PI, Tjellstrtim A. Osseointegration and facial prosthetics. Int J Oral Maxillofac Implant 1986;1:27-9. 3. Bergstr6m K. Prosthetic techniqtxes for orbital defects. Bone anchored applications. In: Williams E, ed. Nobelpharma International Updates. Gdteborg: Nobelpharma, 1993;2(93.2):5-8. 4. Tjellstrtim A, Jansson K, Br&xmark PI. Craniofacial defects. In: Worthington P, Br&nemark PI, Carol Stream, eds. Advanced osseointegration surgery. Chicago: Quintessence Pub1 Co, 1992:293-312.

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