Full Mandibular Reconstruction Using The Branemark System
The first application for the implant-supported prosthesis or tissue-integrated prosthesis (TIP) was the fully edentulous mandible. This has become known as the traditional Branemark System fixed removable bridge.
Clinical implant studies conducted by Branemark et aLl and Adell et aU have indicated the effectiveness and long-term success of this restoration. The first edentulous patient was successfully treated in 1965 by closely following the established osseointegration principles.3 The patient showed excellent dentate function, as well as soft and hard tissue conditions after a 15-year follow-up was completed. A 25-year follow-up study indicated equally encouraging results. By combining extensive documentation of biological research analysis with their equally thorough proven methods of prosthodontic reconstruction, the Swedish researchers have truly given the world an invaluable resource.
The authors' modification of the original Toronto design by Zarb et al. 4 has produced over 550 bridges with only three fractures. These failures have been attributed to inadequate thickness of the metal surrounding the terminal abutment cylinder in conjunction with severe bruxism and/or extremely strong masticatory forces.
As stated earlier, the need for proper treatment planning cannot be emphasized enough. Radiographs, study casts, and any information available should be used to construct a surgical guidestent for the placement of the fixtures.
There are several types of prosthetic teeth that have been successfully used in the denture bridge format. These include Ivoclar (Ivoclar); Bioblend, Bioform (Dentsply); Myerson (Nobelpharma); and Vita (Vita Zahnfabrik).
The results can be outstanding if care is taken in the selection of shade and mold.
The hardware for the Branemark System includes the titanium implant fixture, the titanium abutment and abutment screw. The prosthetic components at the top are the gold cylinder and gold screw. The Branemark System prosthetic gold cylinder has a melting temperature of 2350° F. The alloy selected for the frame must have a melting temperature well below this figure.
This is a cross-sectional view of the assembled hardware without the gold cylinder.
The metal of choice is widely accepted to be a Class IV gold alloy. A successful lowercost metal is a palladium-based alloy with Class IV properties.
The authors strongly recommend a heat-cured acrylic for use in the final denture bridge prosthesis. Good results have been obtained by the high impact Lucitone 199 (Dentsply).
In cases of restricted vertical dimensions where mechanical retention is limited, it is necessary to use a metal treatment to attain retention. Such treatments include: Lee Metal Primer (Lee Pharmaceutical); the Silicoater (Kulzer); and 4-Meta (Parkel).
The rest of the chapter will show in detail the fabrication procedures of the traditional denture bridge from the impression to final insertion.
Following second stage surgery, the correct abutments are placed.
The clinician takes a full arch impression of the fixture abutments and all edentulous areas. Soft tissue anatomical landmarks should be reproduced for diagnostic evaluation. The preliminary cast is fabricated from the impression.
Square impression copings are positioned on each fixture site and secured with sticky wax. This will indicate the proper height and width necessary for the window portion of the custom tray.
Impression copings are blocked out with utility wax facilitating an easy removal from the custom tray.
A heavy body acrylic tray is heated and vacuum formed over the entire cast. The tray is separated from the cast and finished to proper dimensions. An access window is cut into the top of the coping block out until all screws have clearance.
Impression copings are screwed into place with guidepins; a light wrap of dental floss or similar material is adapted to all copings intraorally. The coping/floss bridge is luted together with small amounts of Dura Lay until the entire pattern is complete. This technique stabilizes the copings within the impression, increasing the accuracy of the pickup.
The tray is tried in the mouth to determine the fit over the copings and DuraLay bridge. Impression material is loaded into a syringe and a custom tray. The fixture area is adapted first, using the syringe, then the impression is taken following normal protocol. Screw access holes should be identified and exposed. The guidepins are unscrewed and the impression removed and inspected. All coping surfaces engaging the fixture must be cleaned. Impression material covering any metal margin indicates inaccurate component contact and the impression should be retaken.
After the impression is deemed accurate, guidepins are used to secure brass replicas into place.
Impressions are poured in improved die stone and occlusal rims are fabricated. The mandibular rim is implant-supported using at least two cut down impression copings (a square impression coping as shown on patient's right is cut in half as shown at left). This is done routinely, since the vertical height of the coping is usually taller than the occlusal plane to be registered.
Copings are blocked out with wax from the tissue up to the underside of the square portion of this cylinder-like component. All subsequent brass replicas are covered with wax up to the height of the coping block-out. The cast is then lubricated. Triad light-cured material or cold cure acrylic is adapted around the square copings. Any area distal to the last replica is given tissue contact up to the retromolar pad; giving better support in those areas not stabilized by the impression coping. After curing, finish and lightly polish with pumice. Wax is then luted to the base at the recommended heights (18 mm anteriorly and half way up the retromolar pad posteriorly).
Gold screws, or guide pins that have been cut down below the occlusal height, can be used to secure this intraorally.
The fully edentulous casts are mounted on a semi-adjustable articulator using the occlusal rims.
Using the information from the occlusal rims, denture teeth (Bioblend, Dentsply) are set and verified intraorally. A verification jig is fabricated to check the accuracy of the impression. Gold cylinders are mounted and secured with guide pins. The cylinders are blocked out up to the concavity, and at least 6 mm of DuraLay is built on top of this. After the DuraLay has cured, the jig is checked for passive fit on the model. When this has been satisfied, the verification jig is tried intraorally. There must be a perfect passive fit of each cylinder to each abutment. If the jig is inaccurate, the offending cylinder must be located and sectioned. It is then re-DuraLayed in the mouth. At this time, the altered cast technique must be performed (see Figures 3-44 and 3-45) .
The authors strongly recommend setting all fully edentulous restorations in a full-balanced occlusion. This will prevent premature wear of teeth, but, more importantly, will prevent the "popping off" of teeth which usually occurs in the maxillary if this is not done. This important step can save hours of future chair time.
Figure 3-17 shows the balancing side with all the lingual cusps of the upper in contact with the buccal cusps of the lower. Incisal edges of the upper and lower are also in contact.
When fit, function and esthetics are verified, the lower cast is keyed in preparation to receive a matrix.
The cast is lubricated and the plaster matrix is formed. Plaster is placed around the buccal and labial of the wax-up, engaging the keys on the cast and the occlusal surface of the posterior and incisal edges of anterior teeth.
After the plaster has set, wax is boiled away and the light-cured base is removed. The matrix with teeth in place is returned to the keyed cast. The frame is now ready to be built within this master cast, matrix, and tooth configuration. Red lines on the cast indicate a 15 mmcantilever. Since the second molars go beyond this mark, they will be omitted.
The gold cylinders are placed on the brass replicas and secured with guide pins. Red utility wax is used to block out the bottom portion of cylinder up to the point where the cylinder has its concavity. There is also a slight block out of the ridge of the cast distal to last cylinder. Blue rope wax is then used to outline the red block out wax. This will act as a trough to contain the wet DuraLay and prevent it from spilling onto the cast.
This is a lingual view of screw-retained cylinders with trough and block-out.
Using the brush method, the trough is filled with DuraLay. Screws can be lightly coated with petroleum jelly to aid in easy removal.
When the DuraLay has set, all wax is steamed off. The overbuilt frame is now ready for contour.
Using a variety of burs, the DuraLay frame is shaped and smoothed. A lingual wall of at least 4 mm and bucco-lingual width of 3 mm is essential for strength. Since the terminal cylinders bilaterally are extreme stress points, it is recommended that 5-6 mm in height be built circumferentially in this immediate area.
The plaster matrix is fitted to the master cast. The relationship of teeth to frame is checked for proper support. The transition from frame to teeth should be as smooth as possible to eliminate any discrepancies or irregularities that might irritate the tongue.
Because of the uncontrollable stresses of large or even small amounts of DuraLay, it is necessary to cut every section between each cylinder. This will allow each cylinder to sit perfectly on each brass replica.
Exploded view of sectioned frame.
Each section is waxed to fill any voids, and a finish line is incorporated. Careful attention should be given to the cylinders. No wax or debris should be in or around the gold component from the double ring configuration to at least .5 mm up On the outer circumference.
A nylon bristle brush is used as a final check for clearing any wax or DuraLay from the inner portion of the cylinder.
To insure equal tightei1-ing force, the Nobelpharma electronic torque driver is used for all subsequent steps. This guarantees that all cylinders are tightened to 10 N cm.
Each wax and DuraLay section is secured to the master cast with guide pins in their proper positions. Small increments of DuraLay are then used to lute the sections together.
After the resin has set, a carbide bar is used to cut a bezel finish line around the buccal and lingual of the frame. This will act as a retentive device to grab the processed acrylic and eliminate any separating of the acrylic at the metal-acrylic junction. It is recommended that the resin frame set overnight to relieve all stresses and insure a proper fit.
Loops are added to the frame for acrylic retention. Eighteen gauge rope wax is wrapped around a straight-shanked instrument, then slid off. Each ring which touches the frame should be luted with sticky wax. This not only retains the acrylic, but adds overall strength to the frame.
The matrix is fitted to the master cast, and any teeth that contact the loops of the frame must be reduced.
This is the buccal view of the finished wax-up. Beads (Veneer Lock, Taub Products Co.) have been added to further increase the acrylic retention.
This is the lingual view showing the smooth finish for ease in casting and polishing.
Twelve gauge sprue wax is luted to the tip of the lingual walls between each cylinder. A wax bar is connected to the terminal end of each cantilever, with two extra sprues added vertically. NOTE: Sprue wax should not be placed directly behind gold cylinders.
The DuraLay frame is invested following manufacturer directions (Beauty Cast, Whip Mix Co.). Care should be taken that the investment comes from the underside and pushes its way through the top. This will insure against air being trapped in the cylinder.
The ring should be bench set for one hour. It is then placed in a cold burn-out oven and burned out at 5000 F for one hour. The temperature is then raised to 11500 F, held for 30 minutes, and the ring is then cast in a type IV gold alloy (T-IV-L, Nobelpharma). After bench cooling, the ring is carefully broken out and the casting is cleaned. DO NOT sand blast the gold cylinders.
This;, shows the cast gold framework with sprues cut off. The bar at the distal of the cantilevers is left attached until final processing of the restoration is complete. This will help to prevent warpage during lab procedures, especially during packing and breakout.
The underside of the frame must be highly polished and as smooth as possible. This will prevent plaque and other debris from collecting in these areas.
When finishing and polishing the underside of the frame, brass replicas or a protective cap should be used to avoid marring or nicking the metal interface surface of the gold cylinder.
This shows the highly polished finished gold frame.
Even though the frame fit the master cast, it proved inaccurate when brought to the mouth. It is sectioned at the offending site and DuraLayed in the mouth for the correct position. NOTE: If a verification jig had been used, these soldering steps would not have been necessary. The jig would have pointed out the impression inaccuracy and a new impression could have been taken before the laboratory procedures were started.
Since the frame was sectioned and DuraLayed, it will now not fit the master cast. Locate the offending area and carefully remove the brass replica from the cast; connect a new one to the frame by a guide pin. When the frame is placed on the cast, the new replica must sit passively in the bored-out area. There should be no stone touching any part of the new replica. When the frame will seat in this fashion, it is secured by all guide pins and stone is used to secure the new replica. This will produce the new altered master cast. The frame can now be soldered.
Using the plaster matrix as a guide, the denture teeth are waxed to the gold frame. Occlusion and esthetics are checked, and it is recommended that a final intraoral check be done.
After final verification, brass replicas are attached to the frame using guide pins.
A small plaster model is fabricated. This will aid greatly in the breakout procedure.
The restoration is now half-flasked in the usual manner. It may be necessary to relieve protruding guide pins with wax or a silicone-type material so that they will not bind and prevent the flask halves from separating.
The second half of the flask is prepared in the conventional manner.
The flask is placed in boiling water and all wax is eliminated. Extra retentive cuts can be made in the denture teeth. Paint both sides of the flask with a separating medium (AI-Cote, Densply).
This is the opposite side of the flask, showing the gold framework.
The Silicoater (Kulzer) is used for increased acrylic-to-metal bond.
Since the gold frame has a tendency to show through the pink acrylic, it is necessary to opaque the metal.
Tooth-colored acrylic (Jet, Lang Dental Mfg.) is mixed, applied to the screw access holes, and the flask is closed. This prevents pink acrylic from appearing on the occlusal surfaces of the teeth. The flask is immediately opened and any flash material is trimmed away.
Lucitone 199 acrylic (Dentsply) is formed into a roll and placed on both sides of the flask. Separating cellophane is placed between the two halves and the entire flask is closed and pressed at 3500 PSI. The flask is opened, the cellophane is removed, and all flash acrylic is removed. New cellophane is applied and the flask is pressed again. This procedure is continued until all flash material is eliminated.
Before final closure, remove the cellophane and apply a light coat of monomer to the acrylic surfaces, close the flask, press, and cure at 1650 F for nine hours.
After the curing cycle is complete, the flask is separated, and the processing model with prosthesis is carefully removed.
A lingual view of the processed TIP.
It is sometimes necessary to use pliers in removing guide pins from the processed acrylic.
An alternate method of removing guide pins is to use a punch on the threaded end of the guide pin. This punch could be fabricated from a standard laboratory steel-shanked bur. A concavity is formed on one end using a #8 bur.
The concavity holds the punch on the screw, preventing the bur from sliding and marring the gold cylinder.
The distal stabilizing bar IS removed.
The processed upper and TIP lower are remounted on the articulator and processing errors are removed. It is important to recheck the balanced occlusion at this time.
The upper and lower are finished, polished, and ready for insertion.
This intraoral view of the TIP shows good framework fit, hygiene access areas, and esthetics.
Prosthodontic rehabilitation is complete.