Removable partial denture design for the mandibular resection patient

David N. Firtell, D.D.S., M.A.,* and Thomas A. Curtis, D.D.S.** University of California, School of Dentistry, San Francisco, Calif.

S quamous cell carcinoma of the lateral border of the tongue and the floor of the mouth may be treated by a combination of surgery, radiation therapy, and chemo- therapy. Surgical resection of this tumor often includes a partial mandibular resection, a partial glossectomy, a partial resection of the floor of the mouth, and a radical neck dissection. The extent of surgery and the effects of radiation therapy and chemotherapy determine the amount of rehabilitation needed by a given patient.

Rehabilitation efforts may include secondary surgi- cal management, prosthodontic treatment, speech ther- apy, and psychologic care. Acceptable fabrication and use of a prosthesis will be dependent on the coordinated efforts of the rehabilitative team as well as on the extent and location of the defect. The presence or absence of natural teeth in a resected mandible often determines the approach to prosthodontic rehabilitation.

Several authors have described the rationale for the prosthodontic management of mandibular guidance, the need for altered palatal contours to accommodate restricted tongues, and the prosthodontic rehabilitation of edentulous mandibular resection patients.lm3 The literature, however, contains few references to the rehabilitation of partially edentulous mandibular resection patients.’ This article will discuss the design of removable prostheses for these patients based on a classification suggested by Cantor and Curtis.’

Cantor and Curtis classified edentulous mandibular resection patients by the amount of mandible that remains after resection and surgical reconstruction. Although the classification was suggested for edentu- lous patients, it is also applicable to partially edentu- lous patients. A review of this classification will aid in understanding the physiologic and treatment needs of patients with resected mandibles.

Presented before the Academy of Denture Prosthetics, Seattle,

Wash.

In the Class II mandibular resection patient the total mandible has been resected distal to the canine (Fig. 1, B). The condyle, ramus, and posterior portion of the body of the mandible have been removed and the function of the attached muscles has been lost, resulting in deviation of the remaining mandible toward the surgical defect. A portion of the tongue has been resected or used for closure of the surgical wound. Loss of condylar control of the mandibie and muscular control of the tongue and mandible introduces major functional problems associated with speech, degluti- tion, and mastication. When compared to the Class I patient, the Class II patient experiences additional sensory neural loss and further impairment of degiuti- tion, taste, and saliva control If the lesion invades the posterior tongue, surgical resection may require remov- al of the hypoglossal nerve. The reauhant loss of motor innervation further complicates oral physiologic func- tions as well as the mechanical control of a prosthesis. The largest number of mandibular resection patients can be found in this classification.

*Professor and Chairman, Removable Prosthodontics. The Class III mandibular resection patient has had **Associate Professor, Removable Prosthodontics. the mandible resected to the midline or possibly beyond

REVIEW OF CLASSIFICATlON

The Class I mandibular resection patient has had a radical alveolar resection, but the continuity of the mandible has been preserved (Fig. 1, A). The inferior border of the mandible, the muscles of mastication, and most of the tongue and contiguous soft tissues have been retained. Scar contracture and wound closure limit the mobility of the tongue and Boor of the mouth. There may also be a sensory neural loss to regions supplied by branches of the mandibular and hypoglos- sal nerves if they have been resected or traumatized. A patient with a lateral discontinuity defect of the body of the mandible who subsequently has continuity restored with a bone graft is also considered in this classifica- tion. While Class I patients have some anatomic and functional limitations, most function well with remov- able partial dentures.

0022-3913/82/100437 + 07$W.70/0@ 1982 The C. V. Mwby Co. THE JOURNAL OF PROSTHETIC DENTISTRY 437

F :RTELL AND CURTIS

Fig. 1. Edentulous mandibular resection patients are classified by remaining structures. A, Class I, alveolar resection. B, Class II, total resection distal to cuspid. C, Class III, total resection to midline or beyond. D, Class IV, total resection with partial reconstructic In. E, Class V, total anterior resection reconstructed surgically. (From Cantor, R., and C utis, T. A.: Prosthetic management of edentulous mandibulectomy patients. Part I: Anatc lmic, physiologic, and psychologic considerations. J PROSTHET DENT 25446, 1971.)

(Fig. 1, C). In addition to the structures removed in the Class II patient, the anterior portion of the mandible and its associated muscles are resected, causing increased problems with mandibular deviation, denture stability, saliva control, speech, and deglutition.

The Class IV mandibular resection patient has had a lateral resection and a subsequent bone augmentation to form a “pseudoarticulation” of bone and soft tissue in the region of the ascending ramus (Fig. 1, D). Articulation with the temporal bone has not been restored, but there is less mandibular deviation and

more support for a prosthesis. A v~tibuloplasty may also be needed to improve tongue movement and increase the supporting area for a l~osthesis.

The Class V mandibular resecticui patient has had an anterior resection that crosses tl e midline, but the bilateral temporomandibular art& ulation has been maintained. There is sufficient mandibular structure remaining to reestablish functional :ontinuity by plac- ing an autogenous bone graft (Fig. 1, E). Even with bony augmentation many of the functional deficits associated with resections of the ant :rior portion of the

438 OCTOBER 1982 VOL JME 48 NUMBER 4

REMOVABLE PARTIAL DENTURE DESIGN

Fig. 2. Class I partially edentulous mandibular resec- tion patients have adequate remaining structures for prosthesis support.

Fig. 3. Class II mandibular resection patients have diminished or no bony support on resected side. Arrows denote area of total mandibular resection.

mandible remain. For successful prosthodontic rehabil- itation, secondary surgical procedures are often indi- cated to increase the amount of mandible available for support and to mobilize a restricted tongue or lower lip.

The Class VI mandibular resection patient is similar to a Class V patient, but the continuity of the mandible has not been restored surgically. Because each lateral fragment moves independently, the prognosis for a removable prosthesis is poor and fabrication is not recommended.

PROSTHESIS DESIGN CONSIDERATIONS

The principles of partial denture design should be followed when planning a removable partial denture for the mandibular resection patient. Henderson and SteffeJs Krol,’ and Kratochvil’ suggest the need for rigid connectors, guide planes, and proximal plates for stability; occlusal forces being directed along the long axis of the teeth; bracing and retentive elements within physiologic limits; balanced hard and soft tissue sup- port; and an environment conducive to proper oral hygiene. Although the application of these principles in mandibular resection patients may vary due to the specific needs of each patient, some general recommen- dations can be made. Multiple rests are indicated to increase support and distribute stress. Altered cast impression procedures are essential for distal extension edentulous or surgically reduced ridges. (The function- al concept of impression making may be beneficial in some areas.) If possible, the artificial teeth should be positioned to minimize occlusal forces on the resected

Fig. 4. Class II mandibular resection patients have proximal surface of last tooth on resected side accessi- ble for placement of a retentive arm. Line A denotes primary fulcrum line around which prosthesis is expected to rotate. Line B denotes a secondary fulcrum line that becomes active with excessive rotation.

side without severely compromising esthetics. Minimal but effective retention is suggested because the altered mandibular function of these patients may encourage excessive retentive forces that may exceed the physio- logic limits of the supporting structures.

The design of removable partial dentures for Class I mandibular resection patients (Fig. 2) should be simi- lar to that for nonsurgical patients. However, proper tissue support in the resected region may be compro- mised. Scar bands, redundant tissue, loss of vestibular

THE IOURNAL OF PROSTHETIC DENTISTRY 439

FIRTELL AND CURTIS

Fig. 5. A, Occlusal view of occlusal rest. B, Proximal view of occlusal rest. SI’ecial contours are necessary for occlusal rests when engaging proximal undercut.; for retention. Extending an occlusal rest to facial surface of abutment can provide a br; :cing component as suggested by Swenson and Terkla. * Rest areas are rounded i:l all configurations to allow functional movements. This contour becomes more important when a tooth is tipped lingually, as occurs with many mandibular resection patient: (see Fig. 11). -- -

Fig. 6. When a Class II mandibular resection patient has no teeth on resected side, primary fulcrum line fAJ passes through center of remaining teeth and rests. Retentive arm can be placed on mesial surface of anterior abutment.

depth, and soft tissue attachments often prevent pros- thesis extension and compromise the occlusal scheme. Vestibuloplasty procedures may be indicated to increase support for the partial denture base.

Class II mandibular resection patients have a distal extension space on the resected side, but absence of bony support prevents use of a prosthesis in the region (Fig. 3). If other modification spaces exist, the length of

the space and condition of the at utment teeth will determine the need for a fixed or rei novable prosthesis. Tooth-supported removable partia dentures do not require special design consideratio:ls. When a distal extension base is required on the ncnresected side, the primary axis of rotation* centers a;,ound the fulcrum line connecting the most distal occlu! al rests bilaterally (Fig. 4). Mesial rests are recommended on the most distal abutments bilaterally with mii .or connectors and rests placed for proper bracing an1 reciprocation to prevent migration (Fig. 5). The retainer on the defect side is comparable to the anterior c asp on the tooth- borne side of a Kennedy Class II *emovable partial denture. In both situations depression of the distal extension base subjects the contrala era1 abutment to lateral torque. However, the dista. surface of this abutment is accessible in the mandibular resection patient, and an infrabulge area into which a retentive arm may be placed is often present.

The retentive arm on the defect I ide can be posi- tioned to accomplish two objectives. First, placing an I-bar retainer on the distal surfacc will provide a passive retentive arm in relation to :he primary ful- crum line when the distal extension denture base is depressed. This position for an I-ba:. retainer allows function as suggested by KroP and K .atochvil.7 When

*The primary fulcrum and axis are the center s of rotation around which the prosthesis is expected to function iuring normal use.

OCTOBER 1982 VOLUN E 4.9 NUMBER 4

EMOVABLE PARTIAL DENTURE DESIGN

Fig. 7. When a retentive arm is positioned on proxi- mal surface of a tooth, there should be no contact with resin base to allow clasp flexibility and proper hygiene. A, Buccal view. B, Lingual view.

the prosthesis is displaced occlusally, the retentive arm becomes active. Second, on excessive rotation a second- ary fulcrum* line becomes effective with the center of rotation on the defect side transfering to the retentive arm (Fig. 4). The distal retentive arm may force the tooth mesially, but this force will be resisted by other teeth in the arch. This is in contrast to the Kennedy Class II anterior abutment, where the retentive tip cannot be placed on the distal surface.

When a Class II mandibular resection patient has no abutments on the resected side (Fig. 6), the primary fulcrum line is parallel or nearly parallel to the linear arrangement of the remaining teeth. The retentive arm can be placed into the mesial undercut of the most anterior abutment with the same favorable functional result as placing the retentive arm into the distal undercut of the Class II distal extension design dis- cussed previously. The retentive arm is passive with rotation around the primary fulcrum line and active against occlusal displacement. The adjacent teeth resist distal forces on the anterior abutment. To facilitate

*?‘hr secondary fulcrum and axis are the centers of rotation around which the prosthesis may function under normal or abnormal use as movement of the prosthesis occurs and the fulcrum shifts.

Fig. 8. Class II mandibular resection patients with distal and anterior extensions will have a fulcrum line for distal extension CA’) and a different fulcrum line for anterior extension (AZ). Retentive arms must be placed to reduce leverage around both fulcrums.

Fig. 9. Class III mandibular resection patients have reduced bony support.

flexion of the retentive arm and hygiene, the acrylic resin base in proximity to the abutment should be relieved. The relief should be wide enough to allow cleaning with a small brush (Fig. 7).

A Class II mandibular resection patient may have both a distal extension and an anterior extension (Fig. 8). The distal extension should take precedence as it is the primary functional area. The replacement teeth contained in the anterior extension are positioned for

THE JOURNAL OF PROSTHETIC DENTISTRY 441

FIRTELL AND CURTIS

Fig. 10. Class IV mandibular resection patients have had a bone graft, which may be used for additional support. Note skin graft placed to release tongue and permit extension of prosthesis (arrows).

Fig. 11. Class V mandibular resection patients have reduced support for placement of a prosthesis. Note lingual tipping of teeth, which requires modification of rest configurations as suggested in Fig. 5.

esthetics with minimal function, and the patient is cautioned to minimize anterior functional contacts. The mesial undercut on the anterior abutment cannot be used in this situation as this retentive arm would be in direct conflict with rotation of the distal extension around the primary fulcrum line. The mesial retentive arm would become active as the distal extension denture base was depressed. For these patients multi- ple occlusal rests are recommended, and flexible reten- tive arms are placed into minimal undercuts on the

Fig. 12. Bilateral buccal and lingual occlusal rests and bracing elements establish a ful:rum line (A) and direct occlusal forces. Retentive ilrms are placed on mesial surface of anterior abutmen s and are passive in function.

lingual surface to reduce the leve ‘age created by the anterior extension; but the undera t used should be as close as possible to the fulcrum line.

The Class III mandibular resection patient (Fig. 9) is comparable to Class II mandibul u- resection patients whose abutments are present only on the nonresected side. The design of the removable partial denture is similar to that described for the C.ass II patient with both a distal extension base and ar anterior extension base. The major difference is th.: amount of bony support available for the anterior extension. The replacement teeth are often position Ed for esthetics, and speech in an area where there is mc cosal support only. Kratochvil’ refers to this extension as the “outrigger” because of the lack of bony suppor:.

The Class IV mandibular resectic n patient (Fig. 10) is also similar to the Class II mandibular resection patient. Unlike the Class III patien: , however, there is increased support for a removabl,: prosthesis. This support should be recorded with fun ztional altered cast procedures so that both esthetics ar d function can be enhanced.

The Class V mandibular resectior patient resembles a Kennedy Class IV removable part al denture patient because the resection crosses the :nidline. Posterior teeth are often present on both sides of the arch, but there is only a narrow area of bony idge available for support in the area of the defec (Fig. 11). The remaining teeth often have a lingual inclination with little if any retentive undercut on the buccal surfaces. Bilateral lingual and buccal occlusal rests and bracing

442 OCTOBER 19132 VOLUME 48 NUMBER 4

REMOVABLE PARTIAL DENTURE DESIGN

elements can establish a fulcrum line and direct occlusal forces in the long axis of abutment teeth (Fig. 12). Ribbon rests, suggested by Kratochvil,’ are accept- able but require preparations that compromise tooth structure. If a restoration must be placed under such an extensive rest, sufficient tooth structure must be removed to permit adequate contour of rest seats and prevent fracture of the restoration.

Retentive arms are placed on the mesial surface of the most anterior teeth. These retentive arms are passive when the prosthesis is placed in function and active when a dislodging force is applied to the prosthesis. When the abutments have questionable periodontal support, the retentive arm may be replaced by a guide plane to increase stability in place of retention.

SUMMARY

Design of removable partial dentures for patients who have had mandibular surgical resections varies from partial denture design for patients with intact mandibles. The extent of the surgical resection and the location and quality of the remaining structures will dictate the need to alter some basic principles of partial denture design. Suggestions for variations of design for different degrees of resections have been discussed. Even though the application of basic principles may vary in mandibular resection patients, the basic con- cepts of support, retention, and stability should be fulfilled.

REFERENCES

1.

2.

3.

4.

5.

6.

Beumer, J., and Curtis, T. A.: Acquired defects of the mandible: Etiology, treatment, and rehabilitation. h Beumer, J., Curtis, T. A., and Firtell, D. N.: Maxillofacial Rehabilita-

tion: Prosthodontic and Surgical Considerations. St. Louis, 1979. The C. V. Mosby Co.

Robinson, J. E., and Rubright, W. C.: Use of a guide plane for maintaining the residual fragment in partial or hrmimandibu-

lectomy. J PROSTHET DENT 14~992, 1964.

Cantor, R., Curtis, T. A., Shipp, T., Beumer III, J.$ and Vogel,

B. S.: Maxillary speech prostheses for mandibular surgical defects. J PROSTHET DEKT 22~2.53, 1969.

Cantor, R., and Curtis, T. A.: Prosthetic management of

edentulous mandibulectomy patients. Part I: Anatomic, physi- ologic, and psychologic considerations. J PROSWET DENT

25~446. 197 1. Henderson. D., and Steffel, V. I,.: McCracken’s Removable

Partial Prosthodontics, ed 6. St. Louis, 198 I, The C. V. Mosby

(h. I&l, A. J.: Removable Partial Denture Design: Outline

Syllabus. University of the Pacific, School of Dentistry, November 1972. Kratochvil, F. J.: Sections on partial denture design. In

Beumer, J.~ (Curtis. T. A., and Firtell, I). N : &lraxillofacial

Rehabilitation: Prosthodontic and Surgical Considerations. St. Louis, 1979, The C. V. Mosby Co.

Swenson. M. G., and Terkla, L. G.: Partial Denwrrs, ed 2. St. I.ouis. 1959, The C. \‘. Mosby Co.

Keprmt reyue.sts to:

DR. DAVID N. FIRTELI.

Uimmsm OP CALIFORNIA Scfrtw~o~ DEIVTISTRY

SAN FRANUS~:O, CX 94143

ARTICLES TO APPEAR IN FUTURE ISSUES

A contemporary review of the factors involved in complete denture retention, stability, and support. Part I: Retention T. E. Jacobson, D.D.S., and A. J. Krol, D.D.S.

A qualitative comparison of various record base materials John D. Jones, D.D.S.

A replacement technique for a broken occlusal rest Altug Kazanoglu, D.M.D., MS., and Edwin H. Smith, D.D.S., M.Sc.D.

Surface topography of silicone rubber prosthetic materials fabrication using conventional processing techniques Keith Kent, D.M.D., and Robert F. Ziegel, Ph.D.

THE JOURNAL OF PROSTHETIC DENTISTRY 443