An implant-supported fixed-removable prosthesis with a milled tissue bar and Hader clip retention as a restorative option for the edentulous maxilla

Aria Davodi, DDS, a Russell Nishimura, DDS, b and John Beumer III, DDS, MS c University of Minnesota School of Dentistry, Minneapolis, Minn., and UCLA School of Dentistry, Los Angeles, Calif.

Restoration of the edentulous maxilla with implant retained and supported prosthesis is challeng- ing because of inherent anatomic limitations present after the loss of teeth. A fixed-removable prosthesis is one treatment choice for restoration o f the edentulous maxilla with implants. This prosthesis meets the requirements for esthetics, phonetics, comfort, and hygiene, as well as favor- able biomechanical stress distribution to the implants. This article presents a procedure for fabrica- tion of a fixed-removable prosthesis with a precision milled bar, Hader clip attachments, and a superstructure prosthesis. The criteria for patient selection and the advantages and disadvantages of this prosthesis are discussed. (J Prosthet Dent 1997;78:212-17.)

T h e restoration of the edentulous maxilla with osseointegrated implants is challenging. The quantity of the residual alveolar ridge, its corticocancellous com- position, resorptive patterns, presence of anatomic struc- tures such as the incisive foramen, nasal floor, and max- illary sinuses, as well as the maxillomandibular relation- ship, limit the number, length, and anterior-posterior spread o f implants . A pros thes is fabr ica ted on osseointegrated implants must be rigid, provide adequate lip support for esthetics, allow for proper phonetics, and facilitate oral hygiene procedures. Several treatment op- tions have been described for maxillary edentulous pa- tients with implants. 1-8 Prosthesis design is based on the amount of alveolar ridge resorption and fulfillment of prosthodontic criteria of support, stability, and reten- tion. When considering the anatomic limitations of an edentulous maxilla, the nccd for a properly designed prosthesis that results in favorable biomechanical stress distribution and fulfillment of patient needs, in regard to esthetics, phonetics , comfor t , and hygiene, an overdenture prosthesis is usually the prosthesis of choice.

Wicks 3 described the variables to be considered in de- termining implant prosthodontic support as number, length, location of implants, and nature ofmucosal sup- port. Typically, patients exhibit an adequate amount of bone in the premaxilla for placement of four implants and fabrication of an overdenture prosthesis supported anteriorly by implants and posteriorly by the residual alveolar ridge. Because of this dual nature of support, one must design an overdenture tissue bar that allows for rotation of the prosthesis along a fulcrum line and

~Associate Clinical Professor, Division of Prosthodontics, School of Dentistry, University of Minnesota.

bAssistant Professor, Section of Removable Prosthodontics, UCLA School of Dentistry.

cprofessor and Chairman, Section of Removable Prosthodontics, UCLA School of Dentistry.

seating of the overdenture base on denture bearing sur- faces in function. However, there are patients who have an adequate amount of bone for placement of six or more implants in a curvilinear arrangement that extends be- yond the premaxillary segment. A curvilinear arrange- ment of implants provides more prosthodontic support and stability than a linear arrangement. 9 In designing a prosthesis for these patients, an implant-supported pros- thesis that does not derive support from denture bear- ing tissue may be considered. Prosthodontic treatment options for these patients include a fixed bone anchor partial denture or porcelain fused to metal (PFM) res- toration. These prostheses are ideally suited for patients with minimal residual ridge resorption where proper es- thetics and phonetics can be achieved.

Another option, which has all the advantages of an overdenturc prosthesis in addition to support, stability, and retention characteristics similar to a fixed implant- supported prosthesis, is the hybrid or fixed-removable prosthesis. This concept of prosthesis design has been applied to implant prosthodontics. Lothigius et al. 1°-12 have described techniques for fabrication of a hybrid maxillary prosthesis by using attachments. Van RoekeP 3 has described a technique for using electrical discharge machining (spark erosion), which was devised by Sillard, 14 to fabricate a fixed-removable prosthesis.

The purpose of this article is to describe the criteria and a design used for fabrication of an implant-supported fixed-removable prosthesis with a milled tissue bar and Hader clip retention.

S E L E C T I O N C R I T E R I A

Careful clinical and radiographic evaluations are con- ducted to determine whether a patient is a candidate to receive a fixed-removable maxillary prosthesis. Clini- cal evaluation involves a preliminary diagnostic mount- ing of maxillary and mandibular casts in centric rela- tion at the proper vertical dimension of occlusion on a

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semiadjustable articulator with a face-bow transfer. For this purpose, the patient's existing denture or dentures can be duplicated if functionally and esthetically ac- ceptable, otherwise, a preliminary arrangement of ar- tificial teeth in wax may be necessary. Radiographic analysis of quantity, quality, and anatomic architecture of the residual bone should be performed with com- puter ized tomography (CT). On the basis of the patient 's needs and the diagnostic information ob- tained, a decision to fabricate a fixed-removable pros- thesis is made if the following criteria are met. Because support for this type of a prosthesis is derived prima- rily from implants, the placement of six or more im- plants is recommended. To design a restoration that is biomechanically sound, sufficient bone must exist for a curvilinear arrangement o f implants so that a 20 mm anterior-posterior spread of implants is present. Supe- rior biomechanical stress distribution patterns to the surrounding bone with greater anterior-posterior spread of implants has been repor ted) s 18 The length of the most distal implants bilaterally is important. Because of poor bone quality in the posterior maxilla and based on documentat ion of higher failure rates for shorter implants in the posterior maxilla, I9-21 a minimum im- plant length of 1 3 mm is recommended for the most distal implants. Distal cantilevers are best avoided or confined to a minimum length. 22-2a The determination of adequate interocclusal space is based on minimum prosthodontic requirements o f tissue bar height for ri- gidity, adequate thickness o f the superstructure cast- ing, and the necessary amount of acrylic resin to en- compass the artificial denture teeth and impart struc- tural integrity and strength.

C L I N I C A L P R O C E D U R E S

The clinical procedures involved in fabricating a fixed- removable prosthesis are similar to fabrication of an implant and tissue-supported overdenture. 1. Assess the gingival tissue height circumscribing the

implants at or after second stage implant surgery. Recontour any excessive gingival tissue that is coro- nal to the top of implants so that a maintainable peri- implant gingival pocket is established.

2. After soft tissue healing, make a preliminary impres- sion at the implant level with pick-up type impres- sion copings. Fabricate a master cast.

3. Make a face-bow transfer and an interocclusal record at the proper vertical dimension of occlusion and in centric relation. Mount the maxillary and mandibu- lar casts on a semiadjustable articulator.

4. Perform a wax try-in of the selected artificial teeth to ensure proper tooth position for lip support, esthet- ics, phonetics, and verification of the interocclusal record. Establish the position of the artificial teeth to allow for evaluation of the amount of space available for proper tissue bar fabrication.

Fig. 1. Mounted piaster index of arranged artificial teeth.

Fig. 2. Hader bar attachments positioned in between distal most implants bilaterally avoiding cantilevers.

L A B O R A T O R Y P R O C E D U R E S

1. Fabricate a plaster index incorporating the incisal edges and cusps of the artificial teeth. Mount the index to capture the spatial relationship of the arti- ficial teeth to the residual alveolar ridge (Fig. 1).

2. Remove the artificial teeth and lute them to the in- dex with sticky wax (Kerr Manufactur ing Co., Romulus, Mich.). Select the abutments and assemble on the master cast. [Typically, the UCLA abutment is selected because of its flexibility in solving angu- lation, proximity, and space problems. ]

3. Wax the tissue bar to proper contours, allowing for access to peri-implant tissue for hygiene and approxi- mation of the occlusal contacts of the artificial teeth along the long axis of the implants.

4. Survey the bar to determine a path of insertion of the superstructure and tripodize the master cast. In- corporate Hader bar (Lifecore Biomedical Inc., Chaska, Minn.) plastic patterns within the tissue bar in line with the determined path of insertion, con- necting the anterior most implants, and cantilever- ing distal to the posterior implants bilaterally. [If

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Fig. 3. A, Tissue bar placed on milling machine and circumferentially milled at 2-degree taper. B, Milled tissue bar, palatal contours. C, Milled tissue bar inserted.

sufficient space exists between the distal most im- plants, a cantilever segment is avoided by placing the Hader bar plastic patterns between the distal most implants parallel to the anterior Hader bar seg- ment (Fig. 2).]

5. Perform a preliminary milling of the waxed tissue bar to create parallel labial and palatal walls that coincide with the path of insertion of the superstruc- ture. Section, sprue, invest, and cast the wax pat- tern in a gold palladium alloy (250SL, Leach and Dillon, North Attleboro, Mass.).

6. Devest the casting, remove the sprues, and finish un- der magnification (10×) to remove any casting irregu- larities such as blebs, nicks, or flash. Try-in the tissue bar segments and examine the fit clinically and radio- graphically. Additional sectioning may be necessary to ensure passive and accurate seating of all segments.

7. Assemble the segments int raoral ly with autopolymerizing resin (GC Pattern Resin, GC Corp., Tokyo, Japan) and a type 2 piaster index (Kerr Manufacturing Corp.). Connect soldering analogs to the segments and fabricate an accurate soldering index with a type IV stone (Die Keen, Bayer Corp., South Bend, Ind.). Solder the sections together and verify the fit on the soldering index.

8. If any discrepancy or rocking exists, section and resolder the bar. When the soldered bar fits the sol- dering index accurately in all dimensions, perform a clinical try-in. Once satisfied with the accurate and passive fit of the tissue bar clinically and radiographi- cally, substitute guide pins for seating screws.

9. Fabricate a custom impression tray, properly mold the labial and buccal contours in compound, and make an impression in light body polysulfide im- pression material (Kerr Manufacturing Co. ) incor- porating the tissue bar. Connect laboratory analogs to the tissue bar and fabricate a master cast. Place the master cast tissue bar assembly on a milling machine (Degussa, Frankfurt, Germany) survey to the path of insertion of the superstructure casting and tripodize cast. Use a milling bur (Brassler USA, Savannah, Ca.) with a 2-degree taper to circumferentially mill the tissue bar on palatal and labial surfaces (Fig. 3, A through C).

10. Once the tissue bar contours are finalized on the master cast, fabricate a tissue bar retained record base and make a face-bow transfer record, using all previous reference points. Mount the master cast against the plaster index that incorporated the pre- viously arranged artificial teeth and assess the

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Fig. 4. Completed superstructure prosthesis housing plastic Hader clips.

amount of space available for superstructure fabri- cation.

11. Position the master cast tissue bar assembly on a tripod to the set marks, block out all undercuts and screw access channels in wax, and make an impres- sion in medium viscosity vinyl polysiloxane (Reprosil, Dentsply International Inc.) to provide a refractory cast for the development of the super- structure wax pattern.

12. Bead the refractory cast at the desired palatal exten- sions of the superstructure and complete the wax pattern. Incorporate wax beads (California Dental Products Inc., North Hollywood, Calif.) in the su- perstructure wax pattern to enhance mechanical re- tention for acrylic resin processing.

13. Sprue, invest, and cast the superstructure wax pat- tern in a metal similar to that of the tissue bar. Re- move all casting irregularities under magnification (10x) and fit the cast superstructure to the tissue bar with a disclosing medium (Fit Checker, GC Corp.).

14. Carefully adjust the cast Hader clip housings, in- corporated within the superstructure, to allow for easy placement and removal of the plastic Hader clips. Mount the master cast, tissue bar, superstruc- ture assembly on the articulator against the plaster index that incorporates the arranged artificial teeth.

15. Transfer the artificial teeth to the superstructure with extra-hard set-up wax (Bayer Corp.) and perform a final clinical try-in to assess esthetics, phonetics, and verify vertical dimension and maxillomandibular re- lationships.

16. Condition the superstructure casting with a metal primer (GC Corp.) and process the overdenture in heat-polymerizing acrylic resin (Lucitone, Dentsply International Inc.). [ Opaquing of the metal super- structure is often necessary and is performed before pacldng of the acrylic resin with an opaquing me- dium (Dentacolor Opaker, Heraeus Kulzer, Wehrheim, Germany). ]

17. After processing, perform a laboratory remount to

Fig. 5. A, Incorporation of amalgam centric stops to reduce occlusal wear. B, Superstructure casting designed with cus- tom metal occlusion to reduce occlusal wear.

correct processing errors. Complete all finishing and polishing procedures of the bar and overdenture, insert new plastic Hader clips, and deliver prosthe- sis to the patient (Fig. 4).

P R O S T H E S I S D E L I V E R Y

On delivery of the prosthesis, care is taken to prop- erly adjust the new plastic Hader clips to facilitate inser- tion and removal of the overdenture. The indirect re- tention provided by the engagement of the superstruc- ture casting and the milled tissue bar and the direct retention provided by the Hader clips may make pros- thesis insertion and removal difficult for some patients. Patients are asked to practice insertion and removal of the overdenture in the presence of the dentist. Patients are also given oral hygiene instructions for peri-implant plaque control and maintenance of the removable overdenture prosthesis. Patients are encouraged to re- move the prosthesis at bedtime and keep the prosthesis hydrated.

D I S C U S S I O N

Given the difficulties encountered in restoring the edentulous maxilla with an implant-supported prosthe- sis, a fixed-removable prosthesis with a precision milled

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bar has proven to be an efficient, cost-effective treat- ment. Currently, such a prosthesis is prescribed for pa- tients who meet the selection criteria described herein and for patients who have experienced severe bone loss in the maxillary arch where implant placement can only be accomplished after osseous grafting procedures.

There are several advantages to such a prosthesis. The intimate adaptation of the secondary casting to the milled bar provides added retention and stability not available in implant- and tissue-supported prostheses. The pros- thesis is rigid, it splints the implants, and is minimally cantilevered (or lacks cantilevering), which results in a favorable biomechanical design. Adequate esthetics and phonetics are achieved as a result of the ability to prop- erly form labial and palatal contours in moldable com- pound. Proper oral hygiene procedures can be performed by patients, and minimal soft tissue coverage by the su- perstructure promotes mucosal health. The plastic re- placeable clips can be removed and reinserted to pro- vide easy serviceability of the attachment system. The laboratory procedures involved in fabricating this type of a prosthesis do not differ substantially from conven- tional implant laboratory techniques. A local dental labo- ratory with a milling machine can perform the mechani- cal milling procedures making prosthesis fabrication practical and economical. By comparison, a fixed-remov- able implant prosthesis fabricated with electrical dis- charge machining technology requires special equip- ment, which is not available to most dental laboratories and is significantly more expensive.

The experience of the authors of this article has shown that this type of a prosthesis has been well-received by patients. The prosthesis function is similar to that of a fixed implant prosthesis because of its enhanced stabil- ity and retention and because the wear rate of the plastic Hader clips is significantly reduced, the need for pros- thesis maintenance has been minimal. Although there are many advantages to this prosthesis, proper execu- tion of all clinical and laboratory procedures requires lcnowledge of important laboratory techniques and clini- cal skills. The amount of tissue bar wear, as a result of engagement of the superstructure, must be critically in- vestigated; however, initial observations have not re- vealed significant wear. Finally, special attention must be paid to the occlusal materials and scheme used in designing a fixed-removable prosthesis. A fixed-remov- able prosthesis functions in a manner similar to a fixed implant-supported prosthesis. Accelerated wear of arti- ficial teeth has been observed when the prosthesis op- poses natural or restored dentitions. Occlusal wear can be reduced by placement of amalgam plugs in the artifi- cial teeth as centric stops, incorporation of custom metal occlusal surfaces on the superstructure, or use of porce- lain artificial teeth if sufficient space is available for pro- cessing of acrylic resin (Fig. 5, A and B). The occlusal scheme selected for a fixed-removable prosthesis is group

function. The lateral and protrusive paths of excrusion of artificial teeth must be in coordination with condylar paths of movement. This coordination is important in reducing the transfer ofnonaxial loads to implants, es- pecially when opposed by natural or restored dentition or fixed implant restorations. Hence, obtaining accu- rate condylar movement records, such as a stereographic recording, is recommended.

C O N C L U S I O N

The application of a fixed-removable implant pros- thesis with a milled tissue bar, Hader clip attachments, and a superstructure casting for treatment of complete maxillary edentulous jaw has been presented. Selection criteria, clinical and laboratory procedures, and advan- tages and disadvantages of this type of a prosthesis have been discussed. A fixed-removable prosthesis with a milled tissue bar and a superstructure casting can also be used for restoration of mandibular edentulous jaw, selected maxillofacial resection patients, and partially edentulous patients with proper patient selection and design criteria.

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Reprint requests to: DR. ARIA DAVODI 516 FIFTH ST. SE-#4 M]NNEAPOUS, MN 55414

Copyright © 1997 by The Editorial Council of The Journal of Prosthetic Den- tistry.

0022-3913/97/$5.00 + 0. 10/1/82807

The single unit, single retainer, cantilever resin-bonded bridge Briggs P, Dnnne S, Bishop K. Br DentJ 1996;81:373-9.

Purpose. Although resin-bonded bridges (RBBs) have become routinely used in clinical practice, several doubts remain about the long-term reliability of these restorations. These doubts include: clinical performance of RBBs is variable; "gray out" of metal wings are cosmetically unacceptable; unnoticed partial decementation can lead to dental caries; little agreement as to optimal RBB design; moisture control is difficult to achieve during cementation; temporization and occlusion is diffictflt to achieve; and the possibility exists of swallowing or inhaling a RBB if it debonds. This article describes the clinical function and the importance in clinical practice of the single abutment, single pontic cantilever resin-bonded bridge (CRRB) as an alternative to a fixed two abutment retained RBB. Material and Methods. Fifty-four single abutment, single pontic cantilever resin-bonded bridges (CRRB) were evaluated over time ranging from 1 to 82 months (mean 26.7 months). Forty-six (85%) where placed in the maxilla, while eight (15%) were placed in the mandible. Of the CRRB, 61% were cemented in the anterior region, 11% in the anterior/posterior region(canine/premo- lar), and 28% in the posterior region. Results. Eleven (20%) of the 54 CRRB debonded during the study period and the mean time before debond was 8 months. Of these debonds, eight (73%) were recemented and these restora- tions continued to be in clinical service to the end of the study. The remaining debonded CRRBs required remake or retreatment planning. Of the debonds, 91% (10) occurred in the maxillae and 9% (1) in the mandible. Discussion. The clinical performance of CRRBs in this study is comparable to other studies of RBBs, in that they tended to perform better than fixed two abutment retained RBBs. The authors discuss the factors affecting the clinical performance of the CRBB that included retainer design, abutment preparation, pontic features, occlusion, metal preparation and cementation, periodontal factors, and creation of sufficient interocclusal distance. Conclusions. This study highlights the good clinical potential for using the single unit, single abutment CRRB in dental practice. Results support other clinical studies. The authors stress the need for further clinical studies to compare the clinical performance of this design with other RBB designs and to evaluate the role of the full coverage retainer in terms of clinical performance of the CRRB. 28 references.--RPRenner

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