Written by Arnold J. Bender, DDS Tuesday, 30 April 2002 19:00
Imagine your patient arrives in your office for a three-unit bridge to be done while they wait. No more temporary bridges to be made, no more worries about the shade, contours, margins, fit, or communication to a technician you may not even know. This scenario sounds too good to be true, but today this is realistic because the dentist can be the technician, in total control of the entire procedure.
There are a number of recent products available that help to make this scenario a reality. I have constructed approximately 45 simple bridges and single units while my patients wait. Think about the fact that two appointments can be condensed into one. There is no temporary bridge that must be made, then cemented, and later removed, no clean-up of temporary cements, less local anesthetic, no time spent communicating to a third party, and generally less total stress on the patient and dentist. The feedback from patients has been overwhelmingly positive. Everyone really wants to get the job done as quickly and efficiently as possible. In addition, there are no costly laboratory bills, which will significantly improve profit margins. Still skeptical? I don’t blame you, because I was skeptical myself until I actually constructed my first three-unit bridge. Please follow along with me on a case involving a three-unit bridge from the maxillary right first molar to the maxillary right first bicuspid, replacing the maxillary right second bicuspid, and decide for yourself.
|Figures 1 and 2. A resin-bonded bridge will replace the missing tooth.|
|Figures 3 and 4. The entire buccal surface of tooth No. 3 was covered for aesthetic as well as structural considerations.|
The patient presented with failing amalgam restorations on teeth Nos. 3 and 5, with No. 4 missing. On consultation with the patient it was decided to place a resin-bonded bridge to replace the missing tooth (Figures 1 and 2). After administration of local anesthetic, preparation for an MO onlay was performed on tooth No. 3, and for tooth No. 5 a reverse three-quarter crown preparation. The entire buccal surface of tooth No. 3 was covered for aesthetic as well as structural considerations (Figures 3 and 4). Allowance of at least 1.5 to 2 mm of occlusal clearance was made for sufficient bulk of restorative material, and heavy chamfers were placed on all the margins.
|Figure 5. An impression was taken using alginate and reversible hydrocolloid.|
The prepared teeth were packed with No. 1 cords (Van-R), which were left in place until the final cementation. After 5 minutes, an impression was taken using alginate and reversible hydrocolloid injected around the teeth, which was removed within 90 seconds with a sharp snap (Figure 5). The hydrocolloid had been boiled and conditioned earlier in a unit called a dry processor made by Cadco, the entire process taking only one-half hour. A number of cartridges can be loaded into the unit and stored the entire week, ready for instant use. The combination of alginate and hydrocolloid provides a quick, accurate, and highly detailed impression of the prepared teeth. After the impression, the patient was dismissed into the reception area while the bridge was being constructed.
|Figure 6. Detail of the model.|
Immediately, a working model was made using Mach 2 polyvinylsiloxane die material (Parkell). This consists of a catalyst and base ejected from a gun through a mixing tip, and it sets very quickly. The tip should be placed at the very bottom of the impression in order to not trap air and should be dispensed rapidly before the material begins to polymerize. After placing this material into the impression, a base was made using Blu-Mousse bite registration (Parkell), also dispensed from a gun. After only 1 minute, the materials were set, the impression separated from the model, and the bridge was ready to be constructed. The detail of the model was excellent (Figure 6). The entire elapsed time for the preparation to be completed was less than 10 minutes. An opposing model could be made and both models mounted in an articulator; however, it appears to be ultimately faster and more efficient to work with only the one unmounted model and to make adjustments in the mouth.
The next step was to construct the bridge on the model using hybrid composite. Filtek Z250 (3M ESPE), which was used in this case, has excellent working characteristics as well as strong physical properties for this purpose, and it is recommended for indirect as well as direct restorations. The material is available in 15 shades, including an incisal blend, which allows accurate matching of the adjacent teeth. In addition to excellent aesthetics, two of the nicest features are that it doesn’t slump or stick to instruments. These are crucial factors when trying to build large amounts of composite to contour.
A small amount of material was placed on the gingival margins and cured. In order to gain strength for the pontic, it was necessary to use a reinforcing material attached to the abutments and passing through the middle of the pontic. Utilizing a material called Ribbond (Ribbond, Inc), which comes in different widths and thicknesses, the required length of material was cut in two strips from the stock of material with a special cutter supplied by the manufacturer in the starter kit. The two pieces of Ribbond were saturated with liquid bonding agent and adapted to the abutments either on the outer axial surface or the internal box, depending on the type of preparation. One strip was placed on the buccal of both preparations, and one strip was placed on the lingual. A small amount of composite was initially placed on the preparations to hold the strips in place and also between the strips in the pontic area where they were ultimately pinched closer together, forming a reinforced bar. Two 3-mm wide ribbons, which were well adapted to the preparations, were used in this case. Note that at the pontic area there should be sufficient room gingival and occlusal to the bar for enough bulk of composite yet to be placed.
It would be appropriate to mention a few words about Ribbond at this time, because this remarkable material is the key to this procedure. The fibers are made from the same material used to make bulletproof vests. The fibers are woven in a cross-link lock stitch leno weave, making them extremely tough and fracture resistant. Also, this prevents the Ribbond from splaying when cut and, when adapted against the teeth, distributes the applied forces throughout the fiber network, acts as a crack stopping mechanism, and minimizes composite polymerization shrinkage. Ribbond also bonds well to composite resin and has virtually no memory when it is adapted to the preparations. The material is very versatile and can be used to splint teeth for orthodontic or periodontal reasons as well as constructing endodontic posts. The key to the success of its use is ensuring that it is well adapted to the die and enough layers of correct width are used, strategically placed together for maximum strength. The booklet supplied with the introductory kit provides detailed instructions and illustrations covering a number of different situations that may be encountered. In addition to the various widths, there are currently two thicknesses available for various situations. There has been a definite but gentle learning curve for me using this material, however, the results have been most gratifying. A good reference may be found in Dental Clinics of North America, January 1999, by Rudo and Karbhari.1
|Figure 7. Framework is comparable to a PFM bridge.|
After curing, the framework was ready for the application of more composite and could be compared loosely to the metal structure of a PFM bridge (Figure 7). Composite was placed over the framework one tooth at a time to build out the contours, occlusion, and margins. Please note that it is important that this be done to only one tooth at a time to minimize distortion from shrinkage as the composite cures. Also, it is important that the light is directed in several directions as the composite cures, again to minimize distortion. After all the necessary composite was added, the entire bridge was easily removed from the elastic model and further cured from the under side. Next, the embrasures were opened up with a thin diamond disk, and the contours were trimmed with coarse sandpaper disks, going almost to the margins. Only preliminary contouring was done at this time.
|Figure 8. Stain placed in grooves provides a more realistic effect.|
The patient was called back into the treatment area, and the bridge was fitted to the preparations. Only slight relief to the internal aspects of the bridge was required in order for it to completely seat, as well as some adjustment to the contact areas. High-speed diamonds, burs, and finer disks were used to further adjust and refine the contours, embrasures, and margins both in and out of the mouth, as required. The luxury of being able to add composite if any areas are deficient by sandblasting and applying bonding agent is a great advantage. A Danville microetcher was used inside a micro-cab to contain the aluminum oxide particles. Next, the occlusion was adjusted with high-speed diamonds and burs, at the same time detailing the anatomy. Polishing the bridge out of the mouth using appropriately shaped composite finishers and diamond paste on a felt wheel followed this. Lastly, the gingival area of the pontic and the occlusal grooves were sandblasted and painted with bonding liquid. Stain was placed in the grooves for a more realistic effect, and the completed bridge was cured one last time out of the mouth (Figure 8).
|Figures 9 and 10. The final result after finishing and polishing.|
Before cementation, the internal aspects of the retainers were sandblasted, the abutments were etched for 15 seconds with 37% phosphoric acid gel and rinsed, and Gluma desensitizer was placed. Prime & Bond NT (DENTSPLY Caulk) mixed with dual-cure activator was applied to the abutments and the internal of the bridge, excess was blown off, and Rely X arc (3M ESPE) was used as a luting cement. One of the major advantages with this cement is that it reaches an intermediary stage, which allows for easy cleanup with instruments and floss. It was then light cured to its final set. Lastly, finishing burs and fine disks were used to smooth and polish the supra-gingival margins prior to polishing with diamond paste on a felt wheel (Figures 9 and 10). The final result was a strong prosthesis made of the composite and Ribbond to form a dental-restorative complex with the abutment teeth, which is not rigid and will bend, unlike a cast bridge. Because of this stress-breaking effect, there is less chance of the bridge debonding from the abutment teeth.
Initially, constructing a bridge with this technique may seem lengthy and complicated, but the total clinical time spent is really no longer than for a traditional laboratory-fabricated bridge. In fact, I find that it is somewhat simpler, because time and effort are completely directed at fabricating the final bridge. Equally important is the sense of control and satisfaction achieved when one can use innovative products and current available scientific information, all blended with artistic skill. The myriad of superior dental materials and techniques we are fortunate to have available allow us unprecedented creativity and diversity in how we can deliver cosmetic and adhesive dentistry to our patients. In fact, a true paradigm shift now exists in the way restorative dentistry can be viewed today.
1. Rudo DN, Karbhari VM. Physical behaviors of fiber reinforcement as applied to tooth stabilization. Dent Clin North Am. 1999;43:7-35.
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