Direct Fiber-Reinforced Composite Bridges

The use of nonmetallic, fiber-reinforced, resin-based composite dentistry for human tooth replacement is detailed for anterior and posterior indirect procedures. The use of fiber reinforcing increases the flexural strength of present day materials.1-21 The techniques covered in this paper are direct, chairside, single sitting techniques for placing fiber-reinforced bridges. The most practical situations for these devices are the adolescent with congenitally missing lateral incisors, the geriatric problem, or any number of similar situations that demand a more conservative and less invasive approach than that required by most laboratory-created prostheses.

BACKGROUND

Someday it will likely be possible to culture a few cells from a patient, and use them to grow a new tooth to replace one they have lost. Until then, dentists are faced with using various artificial replacements for lost and missing teeth. Implants and a variety of bridge techniques have been well proven, and are serving us very well. Unfortunately, multiple appointments, provisional restorations, and laboratory costs put these procedures well beyond the resources of many of our patients.

Fiber-reinforced composite (FRC) technology is well proven in industrial applications. In dentistry, it dates back to the 1960s, and was first proposed for reinforcing denture base acrylic.1,12 Today, FRC is most commonly used in prefabricated form for endodontic posts. There are also a number of laboratory processed systems available for bridge fabrication. Unfortunately, these systems offer few advantages over PFM technology. In terms of cost to the patient there is no advantage.

Enter the direct FRC bridge. For about half the cost of a PFM bridge, the dentist can fabricate a replacement for a missing tooth directly in the mouth in less than 2 hours. A number of variations on the technique have been published in the literature in the last 20 years,22-29,30 and no less than five manufacturers make the materials available. Still, the technique has failed to gain widespread acceptance. Perhaps it just seems a little too good to be true. The authors have placed or participated in the placement of hundreds of these bridges over the years, and have found the longevity to be comparable with other direct composite restorations. They are certainly more conservative and cost-effective than PFM bridges.

Case selection for FRC bridges is important, as it is for all treatment procedures. The authors have seen the technique used to replace virtually every tooth in the mouth at one time or another. The technique is most predicable when used to replace missing incisors or bicuspids. When replacing bicuspids, every effort should be made to limit the occlusal forces on the pontic, particularly torquing forces on the bridge. The limitations on fiber orientation created by fabrication of the bridge directly in the mouth limit the ability of the prosthesis to resist torsional forces.31 The ideal indication for a direct FRC bridge restoration is probably a single missing lower incisor, a situation for which a PFM bridge with full-coverage retainers often produces less than satisfactory results.

Several techniques have been developed for the direct intraoral fabrication of FRC bridges. The authors present just two of them here, one for posterior bridges, and one for anterior bridges. The key to all contemporary techniques is the fabrication of a “pontic button.” This is the portion of the pontic in contact with the edentulous ridge. It is fabricated such that it can be removed from the mouth, trimmed and polished, and then incorporated into the bridge structure during assembly. This allows the operator control over the design and finish of this all-important aspect of the bridge.

Figure 1. Gingival defect due to failed endodontic treatment and subsequent extraction.

In the illustrated example, a direct FRC bridge was selected as the best treatment to achieve all the goals of treatment. The patient was given the option of an implant or a conventional PFM fixed bridge. Ideally, a ridge augmentation procedure would be required to correct the gingival defect left by a failed endodontic treatment and the subsequent extraction (Figure 1). The patient was reluctant to undergo further surgery and wanted an economical solution that would be conservative of abutment tooth structure.

Preparation

The patient was anesthetized and the teeth were scaled and polished thoroughly. A rubber dam was placed primarily to control the cheeks and tongue. Usually a slit dam technique is preferable, as it allows for exposure of the edentulous ridge.

Figure 2. Proximal box preparations made on abutment teeth.

Preparation of the teeth begins with removal of any existing restorations. Proximal box preparations are made on the abutment teeth adjacent to the edentulous space to allow the fibers to pass from the occlusal portion of the preparations to the gingival portion of the pontic (Figure 2). The proximal box preparations should have an overall square shape with rounded internal angles. This will resist torquing forces on the pontic. The fibers should be located toward the gingival part of the pontic in a three-unit bridge, because this is where the tensile forces are concentrated. The occlusal cavo-surface margins are treated with a 1/4-round groove created with a No. 2 round bur in a high-speed handpiece. This exposes the ends of the enamel rods for improved bonding, maintains bulk of composite at the margins, and helps to break up light transmission at the margins so they blend invisibly with the tooth structure. Proximal cavo-surface margins are created with a long bevel using a fine finishing diamond.

Creating the Pontic Button

Figure 3. Steps in the proximal boxes serve as positive stops to assist in positioning the pontic button.

Once the preparations are complete, the pontic button is fabricated. Microfill or micro-hybrid composite of the appropriate color is used to ensure a highly polished surface in contact with the soft tissue. In this case, Gingifill (Cosmedent) gingival-colored composite was used to simulate the missing gingiva. A shade is selected that is slightly darker than the actual gingival color, because the intense color of the gingival composite tends to fade with time. A quantity of gingival composite is rolled into a ball, pressed into place in the edentulous space, and cured. This is followed with a small amount of tooth-colored composite. The pontic button is shaped with the composite-forming instrument of choice, or with the G2 ceramist’s brush (Ivoclar Vivadent). The pontic button should extend to the gingival outline of the pontic and slightly into the proximal boxes of the abutment teeth. These small “steps” in the proximal boxes will serve as positive stops, which will assist in positioning the pontic button as the bridge is assembled (Figure 3).

Figure 4. Peripheral areas were treated to a heavy chamfered finishing line.

The pontic button is then trimmed and polished. The tissue contact surface is created by the tissue of the edentulous ridge and needs to be adjusted to the desired design. Any irregularities that will make hygiene difficult should be removed, and the tissue contact surface should be polished to a high shine. The peripheral areas are treated to a heavy chamfered finishing line to which the composite forming the rest of the pontic can be finished (Figure 4). The completed pontic button should be as thin as practical, highly polished on the underside, and should seat positively into position using the rests in the proximal boxes of the abutment teeth. The completed pontic button is set aside to await preparation of the fibers.

Fiber System Planning

Figure 5. Fibers were impregnated with unfilled resin and the filled low-viscosity composite.

The length for the fibers is selected by measuring the prepared teeth. In this case, Construct fibers (Kerr) were selected for their convenience and ease of handling. The fibers should extend the full length of the bridge, from the mesial part of the mesial-most prepared tooth to the distal extent of the distal-most prepared tooth. A dental floss pattern can be used to determine the exact length of fibers required. A Boley gauge or Miltex springbow divider (Miltex Instrument Co) can also be used for establishing this measurement. The fibers are cut to length using serrated scissors designed for the purpose. A sharp scalpel can also be used. The fibers are then placed on a sheet of tinfoil (Buffalo Dental Mfg), impregnated with unfilled resin and then the filled low-viscosity composite (Figure 5). The foil is then folded over to protect the impregnated fibers from ambient light, and set aside to await preparation of the teeth for bonding.

Assembly

Figure 6. Positive contact was established with a composite contact former instrument.

The teeth are then prepared for bonding. They are cleaned and disinfected with 5% sodium hypochlorite, rinsed, etched with 35% phosphoric acid, rinsed, and the dentin adhesive applied. Because the bicuspid abutment was also missing the mesial marginal ridge, this portion of the tooth was restored at this time. A contoured matrix band (Contact Molar Bands, Ivoclar Vivadent) was placed, and the mesial box was restored with Tetric Ceram composite (Ivoclar Vivadent). Positive contact was established using a  composite contact former instrument (American Eagle) (Figure 6).

Figure 7. Flowable composite was light cured to maintain the position of the pontic button.

Once the teeth are prepared for bonding, the pontic button is carried to place, and a small drop of flowable composite is placed where the pontic button contacts the abutment teeth. This step is a little like soldering. The flowable will flow to fill the gap between the pontic button and the abutment teeth. Care should be taken to avoid excess flowable, which will compromise the contour of the embrasures. Any excess flowable can be removed using a small No. 1 or No. 2 artist’s brush or the G2 ceramist’s brush. The flowable composite is then light cured to maintain the pontic button in position while the rest of the bridge is completed (Figure 7).

The fibers are recovered from the tinfoil and placed in the prepared teeth and over the pontic button. They should be thoroughly wetted with flowable composite. More flowable can be added at this stage if there are any voids or bubbles. As much fiber as possible should be incorporated into the bridge. For convenience, the structure can be cured in increments as construction progresses. Hybrid composite is applied over the fiber and shaped until it is as close to the final contour as possible. There should be enough hybrid composite over the fibers to prevent exposure of the fibers when adjusting the occlusion. The final shape of the pontic and the abutment teeth is created in composite, and the entire structure is cured thoroughly. The lingual cusps of the pontic should be small, and the occlusal table should be narrow to minimize functional stresses.

Finish and Final Polish

The completed bridge is trimmed and polished to a high shine. Occlusion is adjusted for light centric contact on the pontic and normal occlusion on the abutment teeth. Contact in lateral excursions is to be avoided. The finished prosthesis displays contours harmonious with the adjacent teeth as well as good color match. The use of the gingival-colored composite, while not required in every case, avoids the development of an unaesthetic “long pontic” or a “black hole” under the bridge (Figures 8 and 9).

This section presents the steps for the placement of an anterior direct FRC bridge, created at the chair in the patient’s mouth. The authors and many other practicing dentists who have learned the technique and are placing these bridges in hundreds of patients worldwide can assure their patients that the technique has been used successfully for at least 20 years. The first bridges from 1982, many in the mouths of professional ice hockey players, are still in function.

The authors’ staff schedules 1 hour for replacing one anterior tooth, and 2 hours  for replacing two anterior teeth. The fee is the same as that charged for Maryland bridges.

Figure 10. The missing lateral incisor was replaced with a FRC bridge.

During the treatment planning stage, determine the area of opposing tooth contact so that the proper positioning of the intra-enamel preparations can be made later and the occlusion will not interfere with the placement of the reinforcing fiber band. This can best be accomplished by sitting the patient upright and using red marking paper, having the patient close in all functional excursions. In this case, the missing lateral incisor (Figure 10) was replaced with a FRC bridge by attaching a fiber band into very shallow preparations placed into the lingual enamel of the central and the canine. Do not make any preparations until the initial step in creating the pontic has been accomplished.

Creating the Pontic Button

Using powder-free or cleaned fingertips that have been moistened with bond resin (Heliobond, Ivoclar Vivadent), roll a small ball of a microfill resin composite (Heliomolar, Ivoclar Vivadent) composite and press it onto the air-dried gingival tissue. The bond resin prevents the composite from sticking to the gloved fingers after the application of the composite onto the dried gingival tissue. The choice of a microfill ensures that the tissue-contacting surface of the pontic can be highly polished. By holding the ball in a position that will spread the ridge-lap portion onto the tissue so that the incisal portion becomes a sharp line, the tissue portion will spread from labial to lingual onto the ridge-lap area. Keep the index finger of the placing hand on the lingual portion of the pontic button as the initial shaping with a suitable instrument begins. Shape the interproximal surfaces as you would like to see in the finished product. Do not allow the soft composite to fill the undercut embrasures of the adjacent teeth. Create an opening just large enough so that a floss threader and floss can be passed through after the bridge is completed.

Figure 11. Indentations made with cotton pliers indicate the labial and lingual surfaces of the pontic button.	Figure 12. Trial placement of the pontic button.

Press the jaws of a cotton plier into the labial and lingual surfaces of the unpolymerized pontic button (Figure 11). These indentations will indicate labial and lingual later and give more support to the gripping jaws of the cotton plier after the composite is cured. There will be a grinding and shaping step to finalize the fit of the pontic button into the space later, and these grooves will facilitate safe holding. Polymerize the pontic button thoroughly and remove it from the mouth. Begin the shaping and polishing of the pontic button. The goal is to polish all of those surfaces that will be inaccessible once the pontic is incorporated into the structure. These include the tissue contacting the ridge, the interproximal surfaces, and the transition from the ridge-lap onto the labial and the lingual surfaces. Remove a portion of the labial, interproximal, and lingual areas of the pontic button after polishing, creating a finishing line. This finishing line will enable the placement of the balance of the labial, lingual, and interproximal composite of the pontic structure, eliminating the requirement of shaping and polishing close to the tissues and the abutment teeth after the pontic is cured in place. After these steps, trial place the pontic button for a final fit to be sure that the height of contour of the pontic button will match the gingival height of the central and the canine (Figure 12). Set the pontic button aside in a safe place.

Tooth Preparation

Figure 13. Lingual intra-enamel preparations in areas of nonocclusal contact.

Prepare lingual intra-enamel preparations in those areas of no occlusal contact, if possible (Figure 13). When this is not possible, a deeper preparation must be made. With today’s excellent dentin adhesives, this is not a major concern. The dimensions of the preparations should be 1 mm greater inciso-gingivally than the width of the fiber band chosen. Always choose the widest band that can be safely used. The determining factors will be the opposing contacts and the length of the abutment teeth. Most post-orthodontic cases have excellent lingual clearance. It has been the authors’ experience that 2-mm bands are the norm. The preparations should cover two thirds of the MD dimension of the lingual aspect of the abutment teeth.

Fiber System Planning

Figure 14. Trial pattern prior to cutting the actual fiber band.

Using a piece of waxed dental floss or dental tape, cut a trial pattern so that it can be fitted into the preparations prior to cutting the actual fiber band (Connect, Kerr) (Figure 14). This band should fit loosely into the preparations to prevent the possibility of fibers not fitting completely into the preparations during the bonding step. After cutting the fibers to the proper length, try them into the preparations. When satisfied that the band will fall into place where intended, saturate the fibers with a filled light-curable resin, following the instructions for the specific fiber system that is to be used.

Prepare the preparations for attaching the fiber band by cleaning thoroughly with 5.25% sodium hypochlorite (Clorox), etch as usual, and seal with a dentin/enamel adhesive. Polymerize as per manufacturer’s instructions.

Assembly

Figure 15. Curing the fiber band into one preparation.	Figure 16. Opposite end of the fiber band is attached to the other abutment.

An efficient method of placing the fiber band into the preparations utilizes a piece of flat matrix material cut to match the gingival contour of the lingual aspect of the central incisor, and another to match the lingual of the canine. These matrices do not need to be the exact shape of the gingival contours, merely rounded to prevent a squared corner of the matrix from resisting being positioned correctly as the fiber band is cured into the abutment preparation. A small volume (too little is better than too much) of a heavy viscosity microhybrid is injected onto the matrix strip as a patty, positioned so that when mated into the lingual aspect of one of the abutment teeth, the composite will press into the preparation area. One end of the saturated fiber band is pressed into this patty. The matrix is then carried to the mouth with a cotton plier and pressed into the acid-etched, dentin adhesive sealed preparation. The low-viscosity filled resin that is used to saturate the fiber band is forced into the preparation by the heavy viscosity patty on the matrix. This is held with a finger, and the curing energy is transmitted through the labial aspect to cure the fiber band into one preparation (Figure 15). The other end of the band is treated in the same manner to attach it to the other abutment (Figure 16).

Figure 17. Band should be positioned more labially than lingually.

The band is positioned so there will be sufficient space between the ridge and the fiber band, so the pontic button can be slipped between the band and the tissue. If this is not sufficient, while holding the matrix with the index finger, pull the band toward the incisal with an explorer, then polymerize the first abutment. Aim the light guide so that the energy is directed away from the pontic area of the fiber band if at all possible. This will result in that portion of the pontic area remaining uncured, making placement of the pontic button more efficient. Be aware of the labio-lingual position of the band, as it should be more labially positioned than lingually (Figure 17). If it is more to the labial, there is no possibility of exposing fibers while adjusting the occlusion.

Try the pontic button in the space. Usually some reduction of the pontic button will be necessary to enable the polished ridge-lap portion to be positioned in the optimum position for aesthetic results. Once this has been accomplished, clean all surfaces of the pontic button with 5.25% sodium hypochlorite (Clorox), rinse, dry, and apply the same dentin/enamel adhesive used in the preparation to create an adhesive surface on the pontic button.

Figure 18. Pontic button held firmly in place by polymerizing the flowable composite.

Holding the pontic button in the proper position with a light ridge-lap pressure, inject a flowable composite resin between the fiber band and the closest surfaces of the pontic button, and polymerize the flowable so that the pontic button is now held firmly in place (Figure 18). Inject a microhybrid (Tetric Ceram, Ivoclar Vivadent) onto the lingual aspect of the pontic button, and shape with suitable instruments. Polymerize lightly, ie, cure enough so that the composite can no longer be moved, then inject onto the labial surface with a microfill, shape, and now cure both labial and lingual thoroughly.

Final Finish

Final shaping and trimming is accomplished with spiral bladed finishing burs, number H48L-010 (labial) and H379-0243 (lingual) from Axis or Brasseler. Final polishing of the labial and lingual surfaces is accomplished by using abrasive impregnated silicone rubber cups of the finest grit available (Astropol, Ivoclar Vivadent) (Figures 19 and 20). These are used dry with light pressure, using the highest speed the slow-speed handpiece will deliver.

CONCLUSION

More time-efficient and cost-effective dental procedures must be developed and clinically proven for the contemporary dentist to serve today’s educated patient. The use of fiber-reinforced resin systems are found in many devices that we use daily. Industry can implement more expanded uses of this technology without the concerns of human response to the chemistry of the resins which they incorporate. Clinical observations, evidence-based designs, and proven restorative methods have been combined to allow the dentist to use this methodology to restore missing teeth in selected situations. The limited history of dental devices created through the use of fibers and resin has been mostly anecdotal, but with the advent of advanced dental resin-based composites, user-friendly fiber systems, and ever increasing literature support, direct FRC bridges are entering the realm of routine treatment. All that is now required is for contemporary dentists to avail themselves of the opportunities presented by these techniques.

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