The fixed-removable partial denture

The fixed-removable partial denture

REMOVABLE SECTION PROSTHODONTICS EDITORS LOUIS BLATTERFEIN S. HOWARD PAYNE The fixed-removable GEORGE A. ZARB partial denture John E. Rhoads,...

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REMOVABLE SECTION

PROSTHODONTICS

EDITORS

LOUIS BLATTERFEIN

S. HOWARD

PAYNE

The fixed-removable

GEORGE A. ZARB

partial denture

John E. Rhoads, D.D.S. Monterey, Calif.

T

he replacement of missing teeth and restoration of alveolar contour has always presented a problem in those patients who have suffered traumatic injury to the anterior dentition and alveolar processes. Many of these injuries are of moderate severity and, except for excessive loss of or damage to the residual ridge, would be scheduled for restoration with a fixed partial denture. The loss of the residual ridge, however, precludes or makes extremely difficult an esthetic and hygienic restoration with a conventional fixed prosthesis (Fig. 1). Due to the constraints of fixed pontics in relation to the residual ridge, the use of this modality is virtually eliminated as a successful means of restoring such defects. It remains, then, for the replacement to be predicated on the use of a removable prosthesis to supply missing tissue contour and provide a means of positioning the replacement teeth in their natural relationships. The use of a conventional removable partial denture of necessity incorporates coverage of soft tissue by major connectors and other necessary elements of the prosthesis and involves several of the teeth as suitable abutments for stabilization. An approach to the treatment of such problems was conceived whereby a removable pontic section could be supported directly by adjacent abutment teeth in a manner similar to that of a fixed prosthesis (Fig. 2). In this way a replacement or pontic section (Fig. 3) could be used that (1) would cover a minimum of soft tissue, (2) could afford a means of replacement of teeth with optimum esthetic arrangement, (3) could compensate for soft tissue defects, and (4) could be removed by the patient for easy day-to-day hygiene (Fig. 4). BACKGROUND

INFORMATION

The particular approach to be described was first brought to my attention about 25 years ago by Downs,*

Presented before the Academy of Denture Prosthetics, Wash *Ihvtls, 8 M.: Prrsottal communication, 1955.

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who in turn had become familiar with the technique through contact with Steiger and Boitel.’ The merit of the modality was obvious, and it has been used in appropriate situations for many years. So versatile is it that little modification of the technical procedure has been made during its many years of application. The concept of removable pontic sections supported by abutment teeth certainly is not new. Evidence that illustrates attempts to develop and employ such a modality is presented in textbooks and periodical literature dating at least to the early 1900s. An approach by Fossume using a round bar attached to abutment crowns that supported a suprastructure appears to be one of the first attempts to construct a fixed-removable partial denture (Fig. S).l,’ Undoubtedly further perusal of the literature would disclose even earlier attempts at this modality. Other variations that employ;:d the “bar and clip” concept for retention and relied on extended tissue coverage for rotational stability were presented by Dolder’ and more recently by Baker, Hader (Fig. 6), and Andrews (Fig. 7). The first attempt to use a precision or semiprecision bar-and-sleeve assembly that provided for rotational stability gained directly through the substructure bar and abutment teeth that has been discovered was the approach by Bennett-the so-called Bennett blade (Fig. 8). Although precise information has not been found, the modality was probably developed between lOI 5 and 1920. It appears to be the ancestor of the technique that is being described. In recent years many variations of this concept have been developed by the laboratory craft and precious metals manufacturers but do not appear in the dental literature. Their introduction has been through advertisement in trade literature. The origin and history of many of these techniques is difficult to trace, although some have been illustrated by Schwartz.? The Bennett blade is illustrated by Steiger and Boitel,’ who describe a refined modification of the modality applicable to a variety of situations (Fig. 9). Although the concept of the fixed-removable partial denture is sufficiently flexible in principle to allow adaptation to both anterior and posterior replacements,

FIXED-REMOVABLE

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Fig. 1. Excessive loss of or damage to residual ridge makes esthetic and hygienic restoration difficult. Due to constraints of fixed pontics in relation to residual ridge, use of fixed partial denture is contraindicated.

Fig. 3. A, Removable suprastructure ponttc mated to substructure provides support for replacement teeth. 8, Underside of suprastructure showing broad frictional surfaces and retentive pins that m&r to corresponding contours of substructure. Fig. 2. Fixed substructure bar attached to abutment teeth provides support and stabilization for removable suprastructure. the discussion and technique description will be limited to its application to the restoration of defects in the anterior region of the mouth. DESCRIPTION The fixed-removable prosthesis to be described consists of a milled substructure bar (designed for the specific contours of the problem being treated) that is rigidly attached to abutment castings (Fig. 2). The bar is specifically designed and fabricated to the contours of the residual ridge. A matching suprastructure to which the replacement teeth are attached is fabricated and fitted accurately to the substructure (Fig. 3, B) The irregularly arcuate contour provides exceptional retention and resistance to rotational forces for the suprastructure (Fig. 4). FABRICATION OF THE BAR SUBSTRUCTURE Determination of path of placement. The path of placement, although essentially vertical in direction, THE JOURNAL

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Fig. 4. Replacement teeth are placed for optimum function and esthetics, and missing tissur contours are restored. should allow the suprastructure to be placed from the labial aspect toward the lingual to minimize the embrasures between the abutment teeth and replacement teeth (Fig. 10). The working cast should be mounted on a suitable platform that will allow easy removal and replacement on the milling apparatus without loss of the plane of orientation. 123

Fig. 5. Early attempt in development of fixed-removable concept was presented by Fossume. Device employed round bar attached to abutment crowns that supported suprastructure.

Fig. 7. Development by Andrews consisted of prefabricated arch bar and matching sleeve to which replacement teeth and other suprastructure elements were attached.

Fig. 8. Bennett blade appears to be first attempt to use precision or semiprecision bar-and-sleeve assembly that provided for rotational stability to be gained directly through substructure bar and abutment teeth. Fig. 6. Variations in “bar and clip” concept for retention were developed by Dolder (left), Hader (top), and Baker (right). These concepts relied on extended tissue coverage for rotational stability.

Positioning of substructure bar. The position of the substructure bar is determined largely by the position of the replacement teeth. It should be placed immediately lingual to these teeth so that excessive bulk in the lingual contour of the suprastructure can be avoided or minimized. Positioning of retentive pins. The position of the retentive pins should be determined after the replacement teeth have been oriented and stabilized with a removable plaster core (Fig. 11). The most advantageous pin placement is opposite the interproximal embrasure space of adjacent replacement teeth. Such placement allows the increased thickness of metal in the substructure bar that is necessary for reinforcement around the pins. After pin positions have been selected, holes of a size

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comparable to the pins (0.7 mm) are drilled parallel into the respective ridge areas of the working cast to a depth of approximately 2 mm. These holes will accept and stabilize stainless steel pins in a parallel relationship during the subsequent fabrication of the substructure bar. Fabrication of substructure bar. The substructure bar is developed in wax around the prepositioned stainless steel pins (Fig. 12). The bar is carved to approximate dimension to minimize the milling of metal in the subsequent step. The sides of the wax substructure bar should be carved parallel to each other with a suitable carving mandrel affixed to the surveyor spindle or modeling arm of the milling apparatus. The wax bar is removed, invested, and cast in type IV partial denture gold alloy. The stainless steel pins are maintained in the wax pattern to be removed from the casting at a later point in the procedure. After casting, the bar is reoriented into alignment with the path of insertion and joined to the abutment castings by soldering.

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Fig. 10. Path of placement of suprastructure, while essentially vertical in direction, should provide for insertion from a labial direction toward lingual to allow minimizing of embrasures between abutment teeth and replacement teeth.

Fig. 9. A, Refined approach to blade concept has been presented by Steiger and Boitel. It is applicable to a variety of situations. B, Modifications of blade concept as presented by Steiger and Boitel.

The stainless steel pins are removed from the cast bar by tapping to loosen them and drawing them out with pliers. The holes are cleaned and reamed with spiral drills or jeweler’s broaches of appropriate size. The assembled substructure is returned to the working cast and placed on the milling apparatus for refining of the lateral surfaces (Fig. 13). These surfaces are milled parallel to each other with provision being made for adequate bulk of metal in the immediate area of the retentive holes. The parallel-milled surfaces are smoothed with cylindric milling and finishing burs and then polished to a fine finish. FABRICATION

OF THE SUPRASTRUCTURE

New stainless steel pins are inserted into the retentive holes in the substructure bar (the pins should have a light frictional fit). The plaster core supporting the replacement teeth is repositioned, and pattern resin (Duralay, Reliance Dental Mfg. Co., Worth, Ill.) is

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Fig. 11. Retentive pin replacement teeth have with removable plaster tion is in interproximal

position is determined after been positioned and stabilized core. Most advantageous posispacing.

applied in small increments to the lubricated substructure bar. After the initial veneer layer of the pattern resin has been applied to the bar, the remainder of the suprastructure is built to the desired contour with additional pattern resin or inlay wax (Fig. 14). The suprastructure pattern is removed from the substructure, examined for completeness, invested, and cast in an appropriate gold alloy. After casting, the stainless steel pins are removed and the inner surface of the casting carefully finished with cylindric finishing burs to produce an accurate frictional fit on the substructure. After finishing and polishing of the internal portion of the suprastructure, the final precious metal retentive pins are oriented and affixed by soldering. lifter final wax-up the replacement teeth are

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Fig. 12. A, Substructure bar is developed in wax around prepositioned stainless steel pins. It is carved to approximate dimension to minimize subsequent milling procedures. B, Waxed bar is invested and cast in type IV partial denture gold alloy. Stainless steel pins are maintained in wax pattern as it is invested and are removed from casting later in fabrication procedure.

attached to the suprastructure with suitable denture base acrylic resin to the desired facial contour (Fig. 15). EVALUATION

OF THE MODALITY

Although precise data relative to abutment response, tissue response, design and structural problems encountered, maintenance factors, and number of prostheses placed have not been maintained, evaluation resulting from approximately 25 years of clinical experience with the modality is summarized. Advantages Flexibility of design. The basic elements of the system lend themselves to a variety of applications to meet the requirements of any particular situation. Being custom made to the contours and alignment of each individual mouth, the substructure affords oppor-

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Fig. 13. A, Lateral surfaces of bar art’ milled parallel to predetermined path of placement. Provision is made for adequate bulk of metal in areas immediately adjacent to retentive holes. B, Substructure bar assembly is finished to high polish to assure smooth mating surfaces of suprastructure to be developed. [unity for wide variation in design, placement, contour, and retentive capability. Oral hygiene. The fixed substructure’s narrowness in its contact with the underlying tissue permits optimum hygiene of abutment teeth and adjacent tissue (Fig. 16). The removal of the suprastructure permits easy cleaning of the underlying tissues, which are habitual problems associated with conventional fixed partial dentures. Minimal tissue coverage. Being greater only where loss of contour of the residual ridge has occurred. the tissue contact and coverage can approximate that of the fixed partial denture. It is unnecessary to cover extensive areas of palatal OF lingual tissue with the prosthesis (major connectors) and to involve a number of teeth with clasp retainers as is necessary with a conventional removable partial denture. The bulk of the prosthesis that essentially replaces the contour of missing dental structures (and only that) affords greater acceptance by the patient. Durability. Experience has shown this approach to

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Fig. 14. Initial layer of inlay pattern resin is applied to lubricated substructure bar. Remainder of suprastructure is built to desired contour with additional pattern resin or inlay wax.

be most durable and to have presented few maintenance problems. Breakage and major repair have been found to be infrequent. Esthetic results. The wide selection of replacement teeth and restorative materials that can be used allows optimum esthetic results to be obtained even in patients in whom considerable deformity exists (Fig. 17). Ease of adjustment. The broad frictional areas presented by the lateral surfaces of the mating parts enable an inherently stable prosthesis to be developed. The wear of the frictional surfaces, which occurs with time, is distributed over a large surface with relatively little effect on the retentive character of the suprastructure. The retentive pins of the suprastructure that traverse the corresponding holes in the substructure can be adjusted easily to provide adequate frictional retention as the necessity arises.

Fig. 15. A, Replacement structure, and simulated oped to final contour. attached to suprastructure base acrylic resin.

are arranged on supragingival tissues are develB, Replacement teeth are frame with suitable denture

teeth

Limitations In general the limitations associated with use of the fixed-removable prosthesis are similar to those encountered in conventional fixed partial dentures. Abutment requirements. The abutment requirements for the fixed-removable partial denture are identical to those of the fixed partial denture. Both derive their entire support from the abutment teeth, none from the ridge. Common path of placement. All abutment teeth are tied or splinted together through the rigid connection to the substructure bar, a condition comparable to that in the fixed partial denture when the abutments are affixed to one another through the interposed pontic section. Accordingly the path of placement and

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Fig. 16. Substructure assembly in position removal of the retentive elements of the abutment preparations must be in directional harmony with each other. Long axes of the teeth that are to serve as abutments must be sufficiently harmonious so that the preparation of the teeth may present the required degree of parallelism and occlusogingival length to provide adequate retention and stabilitv. ;“\n even more

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Fig. 17. A, Suprastructure is in position and replaces missing teeth and alveolar process lost as result of automobile accident. B, Suprastructure in position. Unsightly triangular embrasure between central incisor teeth has been minimized by favorable path of insertion. critical relationship exists in those instances wherein multiple abutments are used. The feasibility of placing a fixed or fixed removable prosthesis can be severely compromised if serious misalignment of the abutment teeth is encountered. Crown-to-root ratio. The bony support of the abutment teeth as influenced by root morphology and length, amount and character of supporting bone, and ratio of root length embedded in bone to tooth length coronal to the alveolar crest is vital to the success and longevity of any fixed prosthesis. With due consideration to the reported results of recent investigations on periodontal-prosthetic rehabilitation3,’ the prosthodontist is limited in the planning of treatment by the conditions of the abutment teeth and their alveolar support. Span length. The length of the pontic space between abutments presents the same requirements for the fixed-removable partial denture as for the conventional fixed prosthesis. If excessively long spans are encoun-

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tered, the use of multiple abutments may be required. The use of the modality may be contraindicated for patients with exceedingly long spans and inadequate abutment support. Rotational forces. The axiom of geometry stating that “the shortest distance between two points is a straight line” can be applied to fixed prosthodontics when the relationships of abutments and pontic area are considered. The forces of occlusion applied to the pontic are best resisted by the abutments when all members are in comparative alignment.’ The more arcuate the pontic in its configuration, the greater the rotational moment that is reflected to and must be resisted by the abutment teeth. The length of span and curvature of the pontic from axial alignment of the abutment teeth are limiting factors to use of the modality.” Interocclusal space requirements. A minimum occlusogingival height of 3 to 4 mm is necessary for proper function of the prosthesis. Accordingly the interocclusal space available between the residual ridge and opposing teeth is a determining factor in the decision to use the fixed-removable concept. From a practical standpoint, however, there is usually more than adequate occlusogingival space available since most patients under consideration present damaged ridges and lost alveolar process.

Disadvantages Gingival response to fixed substructure. When a fixed part of a prosthesis is in continuous contact with soft tissue, patient hygiene of the region becomes a potential problem. This is true with fixed partial dentures and also with the substructure of the fixedremovable partial denture. Being of narrow dimension (1.5 to 2 mm in width) and rounded labiolingually where tissue contact is made, the fixed substructure presents a minimum contact area that can be easily cleaned by the patient with toothbrush and dental floss. Although a distinct possibility, tissue proliferation in the region of contact of bar and ridge has been rarely observed. Precise technical procedures. A limiting factor in the decision to use the fixed-removable partial denture as a treatment modality is the availability of personnel familiar with and trained in the technique. Although the technique is not extremely difficult to carry through, a certain degree of fine craftsmanship is necessary. Technicians trained in the use of precision attachments, milled crowns, and other precision or semiprecision elements should experience little difficulty in fabrication. The technique is more time consum-

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ing than either a removable partial denture or conventional fixed partial denture. CONCLUSION

OF PROSTHETIC

1. 7.

The concept of the fixed-removable partial denture as it has been presented provides a combination of some of the best attributes of both fixed and removable partial dentures. It minimizes many of the shortcomings of each modality. It has proved to be a useful method of restoring moderate-size defects in the anterior region of both jaws. It has also proved to be a comparatively troublefree treatment modality with a service expectancy of many years. Repairs of the suprastructure can be made with ease. Failure of the substructure assembly has been found to be infrequent. When such failure has occurred, however, it has required major modifications similar to those experienced with corresponding failure of a fixed partial denture. The concept is one that lends itself to a variety of treatment variations. It can be a most useful part of a dentist’s armamentarium for treatment of defects in the anterior region of the mouth.

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REFERENCES

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