Minimizing prosthesis movement in a midfacial defect: a clinical report

Herman B. Dumbrigue, DDMfl and Ann Fyler b College of Dentistry, University of Florida, Gainesville, Fla., and University of Iowa Hospitals and Clinics, Iowa City, Iowa

M . idfacial defects are acquired defects that in- volve the middle third of the face, which communicate with intraoral defects. 1 Retention of prostheses in the midface has traditionally been accomplished with ana- tomic undercuts, adhesives, eyeglass frames, and attach- ment to maxillary obturators. Problems commonly en- countered with these methods of retention have been reported. 2-8 Respiratory epithelium is easily traumatized by frictional contact with prostheses and limits the use of anatomic undercuts. 2 Soft tissue around midfacial defects may not always be ideal for adhesive retention, because movement that occurs during smiling and gri- macing compromises adaptation of prostheses margins. 3,9 Without the benefit ofosseointegratcd implants, attach- mcnt ofextraoral prostheses to maxillary obmrators may be the preferred method of retention.

Nadeau 4 first described the use of combination extraoral-intraoral prostheses connected by magnets. Connecting extraoral and intraoral prostheses often re- suits in the movement of the extraoral prosthesis during mastication, s-s This movement is particularly problem- atic in edentulous patients with maxillary defects be- cause of compromised retention, support, and stability of the intraoral prosthesis.

This clinical report describes a method for minimiz- ing the movement of a midfacial prosthesis attached to a maxillary obturator by using an acrylic resin substruc- ture that moves with some degree of independence rela- tive to the midfacial prosthesis. The substructure is at- tached to the base of the interior portion of the midfacial prosthesis with a silicone pedicle. Vertical movement of the maxillary obturator results in flexure of the silicone pedicle, which minimizes transmission of movement to the midfacial prosthesis.

CLINICAL REPORT

A 64-year-old man with extensive history of head and neck cancer and with a midfacial defect was examined for prosthodontic treatment. The patient underwent a total laryngectomy with postoperative radiation therapy in 1964 for well-differentiated squamous cell carcinoma

aAssistant Professor, Department of Prosthodontics, College of Den- tistry, University of Florida.

UAnaplastologist, Department of Otolaryngology, Head and Neck Surgery, University of Iowa Hospitals and Clinics.

J Prosthet Dent 1997;78:341-45.

Fig. 1. Midfacial defect with obturator in place.

(SCCA) of the larynx. In April 1995, the patient under- went rhinectomy and anterior maxillectomy for nasopha- ryngeal cancer and surgical resection of a right tempo- ral SCCA, followed by radiation therapy.

At initial presentation, it was noted that the patient was edentulous with a moderately resorbed maxillary ridge that exhibited an anterior maxillary defect. The mandibular ridge was severely resorbed and skin around the lower two thirds of the midfacial defect moved sig- nificantly during smiling and grimacing. Previous sur- gery had resulted in superior retraction and shortening of the upper lip and an absent nasal spine (Fig. 1). There was lack ofkeratinized tissue in the anterior walls of the nasal cavity, limiting use of anatomic undercuts. Because anatomic undercuts could not be used and adhesive re- tention of the cxtraoral prosthesis would be unsatisfac- tory because of the tissue mobility, the extraoral pros- thesis was attached to the maxillary obturator with mag- nets. It was anticipated that stability of the maxillary obturator would be compromised, thus a method for minimizing movement of the extraoral prosthesis dur- ing mastication was devised.

P R O C E D U R E

Intraoral prostheses were first fabricated to establish desired lip support. Despite a shortened upper lip, the patient was able to maintain lip competency with lower lip movement (Fig. 2). Two Teflon-coated samarium cobalt magnets (Dexter Magnets, Elk Grove, Ill.) were embedded on the maxillary obturator section (Fig. 1). A keyway was developed between the two magnets (Fig.

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Fig. 2. A, Patient at physiologic rest position. B, Patient applying interocclusal pressure. Move- ment of acrylic resin connector in upward direction is noted.

Fig. 3. Connector attached to obturator by magnets.

1) to facilitate proper alignment of an acrylic resin in- terconnecting piece (connector). The connector was fab- ricated freehand with autocure orthodontic resin (Caulk Dentsply, Milford, Del.). The undersurface of the con- nector contains two magnets and articulates with the maxillary obturator section in two planes (Fig. 3). Mag- nets in the anterior portion of the connector were ori- ented vertically and embedded in planes perpendicular to each other to provide positive articulation with the

midfacial prosthesis (Fig. 3). An acrylic resin substruc- ture was then fabricated containing magnets that articu- late with the anterior portion of the connector (Fig. 4, A). The intraoral prostheses were inserted, the connec- tor attached to the obturator section through the midfacial defect, and the acrylic resin substructure at- tached to the connector.

Before making a facial impression, the patient was asked to apply interocclusal pressure to ensure complete seating of the maxillary obturator. This was also done to capture the superior-most displacement of the obtura- tot-connector (Fig. 2). A facial impression was then made with light-body polyvinyl siloxane (Caulk Dentsply). Two wooden sticks were attached with sticky wax across the acrylic resin substructure and connected to the fa- cial impression on both sides. This captured the rela- tionship of the anterior portion of the connector with facial tissues. Polyvinyl siloxane is the material of choice because its flow is easily controlled and it may be used at room temperature to minimize facial grimacing while the impression material is applied to skin. While the impression material was setting, polyester mesh was par- tially embedded to form a scaffold for the plaster back- ing. A thin layer of quick-set plaster was then carefully applied against the impression material to prevent com-

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Fig. 5. Bottom half of mold, incorporating substructure, shown before processing. Orientation of plaster core (right) in mold is preserved by keys in mold around substructure.

Fig. 4. A, Acrylic resin substructure that will articulate with connector (shown with plaster core). B, Substructure is incor- porated in processed silicone, mechanically attached at its lower portion.

pression or distortion of underlying tissues. After the plaster backing had set, plaster bandages (Johnson and Johnson, New Brunswick, N.J.) were placed over the entire impression to provide rigidity and support for the impression. The impression was then removed, inspected for accuracy, and poured in dental stone. A connector analog, consisting of two magnets embedded in acrylic resin, was attached to the substructure (picked up in the impression) and became incorporated in the master cast.

A 0.020-inch clear splint material (Zahn Dental Co., Melville, N.Y.) was vacuuformed over the cast to gener- ate a template. The template was trimmed and fitted to the patient to verify accuracy of the impression. The tem- plate was then modified so that it rested on stable tissue surrounding the midfacial defect. The modified template then served as a backing for the wax sculpture. In this manner, shards of wax that inadvertently get incorpo- rated on the tissue surface of the wax sculpture can be easily detected. A wax sculpture replacing missing facial anatomy was then completed to incorporate the acrylic resin substructure. This acrylic resin substructure, ini- tially used in the impression, will be engaged by a sili- cone pedicle in the final prosthesis (Fig. 4, B).

The wax sculpture was hollowed out on the interior

portion to reduce weight and to provide space for move- ment of the acrylic resin substructure. Plastcr was poured into the hollowed-out portion of thc wax sculpture to produce a plaster corc. Kcyways were then placed in the plastcr core (Figs. 4, A, and 5). The plaster core was used to maintain the space within thc prosthcsis during subsequent investing and proccssing procedures. The mastcr cast was then modified by removal of its central portion, corresponding to the midfacial defcct. Thc con- nector analog was also rcmovcd in this process. The wax sculpturc, with its acrylic resin substructure and plaster core, was then sealed to thc mastcr cast. Dental stone was backpourcd through the channel in the undersurface of the master cast created by removal of its ccntral por- tion. The mastcr cast was thcn flaskcd and invested in an appropriately sized polyvinyl pipe. Figure 5 illustrates the bottom half of thc mold after rcmoval of thc wax sculpturc. The acrylic resin substructure thus rcmains in the mold during processing of the silicone and be- comes incorporated in the final prosthesis (Fig. 4, B).

Thc prosthcsis was proccsscd in silicone (1 part MDX4-4210 and 4 parts Silastic 891 mcdical adhcsivc Type A, Dow Coming Corp.), colored with oil pigments, and polymerized in a moist heat oven at 16I ° F for 3 hours. Aftcr proccssing, thc prosthcsis was trimmed and b o n d c d to a po lyurc thanc l ining (Fig. 6). l°aI A 0.005-inch polyurethane sheet (Factor II, Lakeside, Ariz.) was sccurcd on a vacuuform machine (Buffalo Manufacturing, Syosset, N.Y.) and clcancd on both sur- faccs with rcagcnt-grade acetone. Under a flow hood, 1205 primer (Dow Corning Corp.) was applied to the top surface and allowcd to dry for 1 minute. The poly- urethane shect was then heated until it began to sag bencath the framc (approximately 2 minutes) and adapted, under vacuum, to thc tissue side of a perfo- ratcd duplicatc cast prcviously made. The technique for fabrication of perforatcd duplicate casts has been re-

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Fig. 6. Prosthesis bonded to polyurethane lining. Fig. 8. Relationship of extraoral prosthesis to connector and obturator.

Fig. 7. Patient with intraoral and extraoral prostheses in place.

ported elsewhere? ° The silicone prosthesis was painted with Silastic 891 medical adhesive Type A on its tissue surface and adapted to the polyurethane lining on the duplicate cast, while still under vacuum. Excess medical adhesive was then removed.

The prosthesis, while still on the duplicate cast, was placed in a moist heat oven for 30 minutes. Incomplete removal of excess medical adhesive will render a grayish tint on the transparent polyurethane on curing. The

polyurethane lining increases tear-resistance of prosthe- sis margins, provides compatibility with non-silicone based adhesives, and provides an effective method of masking the margins, m l The polyurethane lining was trimmed, and the prosthesis was fitted on the patient and extrinsically colored (Fig. 7).

D I S C U S S I O N

Connection of extraoral prostheses to intraoral pros- theses should be avoided when intraoral prostheses have compromised retention, support, or stabifity. The move- ment that occurs with the extraoral prosthesis during mastication is potentially embarrassing for the patient. However, this situation may be unavoidable if other means of retention for the extraoral prosthesis cannot be used.

Figure 2 illustrates the amount of upward movement that occurs with the obturator as the patient applies interocclusal pressure. At maximum interocclusal sepa- ration, the obturator loses peripheral seal, which results in downward displacement. Movement of the maxillary obturator will translate to movement of the midfacial prosthesis. To minimize this occurrence, an acrylic resin substructure can be incorporated within the midfacial prosthesis that articulates with the connector. The sub- structure is then attached to the base of the interior por- tion of the midfacial prosthesis by a silicone pedicle. Vertical movement of the maxillary obturator results in flexure of the silicone pedicle, which minimizes trans- mission of movement to the midfacial prosthesis. In ad- dition, the substructure supports the weight of the sili- cone midfacial prosthesis, moves the center of gravity internally thus reducing the effect of gravity on the pro- jecting nose, maintains the prosthesis in position, and allows reduced contact of the midfacial prosthesis with skin, minimizing dermal irritation. Figure 8 shows the relationship between obturator, connector, and midfacial prosthesis. The midfacial prosthesis is thus retained by magnetic attachment to the maxillary obturator and by

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Fig, 9. M idsag i t t a l sec t i on o f prosthes is . Ver t i ca l m o v e m e n t o f

c o n n e c t o r (A) causes f l e x u r e o f s i l i cone p e d i c l e (B), w h i c h

resul ts in m o v e m e n t o f subs t ruc tu re (C) w i t h i n prosthes is .

adhesive retention on skin overlying and inferior-lateral to the nasion.

The flexibility o f the silicone pedicle retaining the acrylic resin substructure allows limited independent movement of the substructure within the midfacial pros- thesis, and thus minimizes movement of the midfacial prosthesis during mastication (Fig. 9). The amount of movemen t o f the acrylic resin substructure may be con-

trolled by altering the length and thickness of the sili- cone pedicle that connects the subst ructure to the midfacial prosthesis.

I thank Dr. Michael R. Arcuri and Dr. William E. kaVel[e, my men- tors and friends, for their invaluable advice and assistance.

REFERENCES

1. Marunick MT, Harrison R, Beumer J 3d. Prosthodontic rehabilitation of midfacial defects. J Prosthet Dent 1985;54:553-60.

2. Udagama A, King GE. Mechanically retained facial prostheses: helpful or harmful? J Prosthet Dent 1983;49:85-6.

3. Shifman A. Selective-pressure impression technique for nasal prostheses. J Prosthet Dent 1987;58:349-51.

4. Nadeau J. Maxillofacial prosthesis with magnetic stabilizers. J Prosthet Dent 1956;6:114-9.

5. Nadeau J. Special prostheses. J Prosthet Dent 1968;20:62-76. 6. Javid N. The use of magnets in a maxillofacial prosthesis. J Prosthet Dent

1971;25:334-41. 7. Scannell JB. Practical considerations in the dental treatment of patients

with head and neck cancer. J Prosthet Dent 1965;15:764-9. 8. Birnbach S, Herman GL Coordinated intraoral and extraoral prostheses in

the rehabilitation of the orofacial cancer patient. J Prosthet Dent 1987;58:343-8.

9. Martone AL. Anatomy of facial expression and its prosthodontic signifi- cance. J Prosthet Dent 1962; 12:1020-42.

10. Udagama A. Urethane-lined silicone facial prostheses. J Prosthet Dent 1987;58:351-4.

11. Lemon JC, Martin JW, King GE. Modified technique for preparing a poly- urethane lining for facial prostheses. J Prosthet Dent 1992;67:228-9.

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Copyright © 1997 by The Editorial Council of The Journal of Prosthetic Dentisty.

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