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Removable partial denture design for the mandibular resection patient
Removable mandibular David
N. Firtell,
partial denture design for the resection patient D.D.S., M.A.,*
University of California,
and Thomas
A. Curtis, D.D.S.**
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 chemotherapy. 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 surgical management, prosthodontic treatment, speech therapy, 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 edentulous patients, it is also applicable to partially edentulous patients. A review of this classification will aid in understanding the physiologic and treatment needs of patients with resected mandibles. Presented Wash. *Professor **Associate
before
the Academy
of Denture
Prosthetics,
Seattle,
and Chairman, Removable Prosthodontics. Professor, Removable Prosthodontics.
0022-3913/82/100437
+ 07$W.70/0@
1982
The C. V. Mwby
Co.
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 hypoglossal 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 classification. While Class I patients have some anatomic and functional limitations, most function well with removable partial dentures. 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, deglutition, and mastication. When compared to the Class I patient, the Class II patient experiences additional sensory neural loss and further impairment of degiutition, taste, and saliva control If the lesion invades the posterior tongue, surgical resection may require removal of the hypoglossal nerve. The reauhant loss of motor innervation further complicates oral physiologic functions as well as the mechanical control of a prosthesis. The largest number of mandibular resection patients can be found in this classification. The Class III mandibular resection patient has had the mandible resected to the midline or possibly beyond
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
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F :RTELL
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CURTIS
Fig. 1. Edentulous mandibular resection patients are classified by remaining structures. A, ClassI, alveolar resection. B, ClassII, total resection distal to cuspid. C, ClassIII, total resection to midline or beyond. D, ClassIV, total resectionwith partial reconstructicIn. E,
ClassV, total anterior resection reconstructed surgically. (From Cantor, R., and C utis, T. A.: Prosthetic managementof 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 increasedproblemswith mandibular deviation, denture stability, saliva control, speech,and deglutition. The ClassIV mandibular resectionpatient hashad a lateral resection and a subsequentbone 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
438
more support for a prosthesis.A v~tibuloplasty may also be needed to improve tongue movement and increasethe supporting area for a l~osthesis. The Class V mandibular resecticuipatient has had an anterior resection that crossestl e midline, but the bilateral temporomandibular art& ulation has been maintained. There is sufficient mandibular structure remaining to reestablishfunctional :ontinuity by placing an autogenousbone graft (Fig. 1, E). Even with bony augmentation many of the functional deficits associatedwith resectionsof the ant :rior portion of the
OCTOBER
1982
VOL
JME
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NUMBER
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REMOVABLE
PARTIAL
DENTURE
DESIGN
Fig. 2. Class I partially edentulous mandibular resection 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 successfulprosthodontic rehabilitation, secondary surgical procedures are often indicated to increasethe amount of mandible available for support and to mobilize a restricted tongue or lower lip. The ClassVI mandibular resectionpatient is similar to a ClassV patient, but the continuity of the mandible has not been restored surgically. Becauseeach 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’ suggestthe 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 elementswithin physiologic limits; balanced hard and soft tissue support; and an environment conducive to proper oral hygiene. Although the application of theseprinciples in mandibular resection patients may vary due to the specificneedsof eachpatient, somegeneral recommendations can be made. Multiple rests are indicated to increase support and distribute stress. Altered cast impressionproceduresare essentialfor distal extension edentulousor surgically reducedridges. (The functional concept of impressionmaking may be beneficial in someareas.) If possible,the artificial teeth should be positioned to minimize occlusal forces on the resected
THE
IOURNAL
OF PROSTHETIC
DENTISTRY
Fig. 4. Class II mandibular resection patients have proximal surface of last tooth on resectedside accessible for placement of a retentive arm. Line A denotes primary fulcrum line around which prosthesis is expected to rotate. Line B denotesa secondary fulcrum line that becomesactive with excessiverotation.
sidewithout severely compromisingesthetics.Minimal but effective retention is suggestedbecausethe altered mandibular function of these patients may encourage excessiveretentive forces that may exceed the physiologic limits of the supporting structures. The designof removable partial dentures for ClassI mandibular resectionpatients (Fig. 2) should be similar to that for nonsurgical patients. However, proper tissue support in the resectedregion may be compromised. Scar bands, redundant tissue, lossof vestibular
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 passesthrough center of remaining teeth and rests. Retentive arm can be placed on mesial surface of anterior abutment. depth, and soft tissue attachments often prevent prosthesis extension and compromisethe occlusal scheme. Vestibuloplasty procedures may be indicated to increasesupport for the partial denture base. Class II mandibular resection patients have a distal extension space on the resected side, but absenceof bony support prevents useof a prosthesisin the region (Fig. 3). If other modification spacesexist, the length of
the space and condition of the at utment teeth will determine the need for a fixed or rei novableprosthesis. Tooth-supported removable partia dentures do not require special design consideratio:ls. When a distal extension baseis required on the ncnresectedside, the primary axis of rotation* centers a;,ound the fulcrum line connecting the most distal occlu! al rests bilaterally (Fig. 4). Mesial rests are recommendedon the most distal abutments bilaterally with mii .or connectorsand 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 toothborne side of a Kennedy Class II *emovablepartial denture. In both situations depressionof the distal extension base subjectsthe contrala era1 abutment to lateral torque. However, the dista. surface of this abutment is accessiblein 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 positioned 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 fulcrum line when the distal extension denture base is depressed.This position for an I-ba:. retainer allows function as suggestedby KroP and K .atochvil.7 When *The primary fulcrum which the prosthesis
and axis are the center s of rotation around is expected to function iuring normal use.
OCTOBER
1982
VOLUN
E 4.9
NUMBER
4
EMOVABLE
PARTIAL
DENTURE
DESIGN
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. 7. When a retentive arm is positioned on proximal 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 secondary 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 discussed 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.
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
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 precedenceas it is the primary functional area. The replacement teeth contained in the anterior extension are positioned for
441
FIRTELL
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 multiple occlusal rests are recommended, and flexible retentive arms are placed into minimal undercuts on the
442
AND
CURTIS
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
OCTOBER
19132
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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 acceptable 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.
REFERENCES 1.
2.
3.
4.
5.
6.
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 concepts of support, retention, and stability should be fulfilled.
ARTICLES
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 Rehabilitation: 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 hrmimandibulectomy. 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, physiologic, 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 DR.
reyue.sts to:
DAVID
Uimmsm Scfrtw~o~ SAN
N. FIRTELI. OP CALIFORNIA DEIVTISTRY
FRANUS~:O,
CX 94143
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 using conventional
of silicone rubber prosthetic materials fabrication processing techniques
Keith Kent, D.M.D., and Robert F. Ziegel, Ph.D.
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
443
N. Firtell,
partial denture design for the resection patient D.D.S., M.A.,*
University of California,
and Thomas
A. Curtis, D.D.S.**
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 chemotherapy. 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 surgical management, prosthodontic treatment, speech therapy, 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 edentulous patients, it is also applicable to partially edentulous patients. A review of this classification will aid in understanding the physiologic and treatment needs of patients with resected mandibles. Presented Wash. *Professor **Associate
before
the Academy
of Denture
Prosthetics,
Seattle,
and Chairman, Removable Prosthodontics. Professor, Removable Prosthodontics.
0022-3913/82/100437
+ 07$W.70/0@
1982
The C. V. Mwby
Co.
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 hypoglossal 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 classification. While Class I patients have some anatomic and functional limitations, most function well with removable partial dentures. 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, deglutition, and mastication. When compared to the Class I patient, the Class II patient experiences additional sensory neural loss and further impairment of degiutition, taste, and saliva control If the lesion invades the posterior tongue, surgical resection may require removal of the hypoglossal nerve. The reauhant loss of motor innervation further complicates oral physiologic functions as well as the mechanical control of a prosthesis. The largest number of mandibular resection patients can be found in this classification. The Class III mandibular resection patient has had the mandible resected to the midline or possibly beyond
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
437
F :RTELL
AND
CURTIS
Fig. 1. Edentulous mandibular resection patients are classified by remaining structures. A, ClassI, alveolar resection. B, ClassII, total resection distal to cuspid. C, ClassIII, total resection to midline or beyond. D, ClassIV, total resectionwith partial reconstructicIn. E,
ClassV, total anterior resection reconstructed surgically. (From Cantor, R., and C utis, T. A.: Prosthetic managementof 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 increasedproblemswith mandibular deviation, denture stability, saliva control, speech,and deglutition. The ClassIV mandibular resectionpatient hashad a lateral resection and a subsequentbone 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
438
more support for a prosthesis.A v~tibuloplasty may also be needed to improve tongue movement and increasethe supporting area for a l~osthesis. The Class V mandibular resecticuipatient has had an anterior resection that crossestl e midline, but the bilateral temporomandibular art& ulation has been maintained. There is sufficient mandibular structure remaining to reestablishfunctional :ontinuity by placing an autogenousbone graft (Fig. 1, E). Even with bony augmentation many of the functional deficits associatedwith resectionsof the ant :rior portion of the
OCTOBER
1982
VOL
JME
48
NUMBER
4
REMOVABLE
PARTIAL
DENTURE
DESIGN
Fig. 2. Class I partially edentulous mandibular resection 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 successfulprosthodontic rehabilitation, secondary surgical procedures are often indicated to increasethe amount of mandible available for support and to mobilize a restricted tongue or lower lip. The ClassVI mandibular resectionpatient is similar to a ClassV patient, but the continuity of the mandible has not been restored surgically. Becauseeach 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’ suggestthe 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 elementswithin physiologic limits; balanced hard and soft tissue support; and an environment conducive to proper oral hygiene. Although the application of theseprinciples in mandibular resection patients may vary due to the specificneedsof eachpatient, somegeneral recommendations can be made. Multiple rests are indicated to increase support and distribute stress. Altered cast impressionproceduresare essentialfor distal extension edentulousor surgically reducedridges. (The functional concept of impressionmaking may be beneficial in someareas.) If possible,the artificial teeth should be positioned to minimize occlusal forces on the resected
THE
IOURNAL
OF PROSTHETIC
DENTISTRY
Fig. 4. Class II mandibular resection patients have proximal surface of last tooth on resectedside accessible for placement of a retentive arm. Line A denotes primary fulcrum line around which prosthesis is expected to rotate. Line B denotesa secondary fulcrum line that becomesactive with excessiverotation.
sidewithout severely compromisingesthetics.Minimal but effective retention is suggestedbecausethe altered mandibular function of these patients may encourage excessiveretentive forces that may exceed the physiologic limits of the supporting structures. The designof removable partial dentures for ClassI mandibular resectionpatients (Fig. 2) should be similar to that for nonsurgical patients. However, proper tissue support in the resectedregion may be compromised. Scar bands, redundant tissue, lossof vestibular
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 passesthrough center of remaining teeth and rests. Retentive arm can be placed on mesial surface of anterior abutment. depth, and soft tissue attachments often prevent prosthesis extension and compromisethe occlusal scheme. Vestibuloplasty procedures may be indicated to increasesupport for the partial denture base. Class II mandibular resection patients have a distal extension space on the resected side, but absenceof bony support prevents useof a prosthesisin the region (Fig. 3). If other modification spacesexist, the length of
the space and condition of the at utment teeth will determine the need for a fixed or rei novableprosthesis. Tooth-supported removable partia dentures do not require special design consideratio:ls. When a distal extension baseis required on the ncnresectedside, the primary axis of rotation* centers a;,ound the fulcrum line connecting the most distal occlu! al rests bilaterally (Fig. 4). Mesial rests are recommendedon the most distal abutments bilaterally with mii .or connectorsand 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 toothborne side of a Kennedy Class II *emovablepartial denture. In both situations depressionof the distal extension base subjectsthe contrala era1 abutment to lateral torque. However, the dista. surface of this abutment is accessiblein 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 positioned 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 fulcrum line when the distal extension denture base is depressed.This position for an I-ba:. retainer allows function as suggestedby KroP and K .atochvil.7 When *The primary fulcrum which the prosthesis
and axis are the center s of rotation around is expected to function iuring normal use.
OCTOBER
1982
VOLUN
E 4.9
NUMBER
4
EMOVABLE
PARTIAL
DENTURE
DESIGN
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. 7. When a retentive arm is positioned on proximal 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 secondary 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 discussed 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.
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
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 precedenceas it is the primary functional area. The replacement teeth contained in the anterior extension are positioned for
441
FIRTELL
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 multiple occlusal rests are recommended, and flexible retentive arms are placed into minimal undercuts on the
442
AND
CURTIS
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
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 acceptable 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.
REFERENCES 1.
2.
3.
4.
5.
6.
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 concepts of support, retention, and stability should be fulfilled.
ARTICLES
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 Rehabilitation: 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 hrmimandibulectomy. 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, physiologic, 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 DR.
reyue.sts to:
DAVID
Uimmsm Scfrtw~o~ SAN
N. FIRTELI. OP CALIFORNIA DEIVTISTRY
FRANUS~:O,
CX 94143
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 using conventional
of silicone rubber prosthetic materials fabrication processing techniques
Keith Kent, D.M.D., and Robert F. Ziegel, Ph.D.
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
443