Facially-Retained Maryland Bridges
An alternative approach to the resin-bonded, fixed partial denture
Gregg A. Helvey, DDS, MAGD, CDT
Anterior restorative dentistry can be simple, such as in the replacement of a fractured incisal edge, or complex, such as in cases requiring the combination of several techniques to achieve a desired esthetic effect while providing a balanced, functional occlusion. Clinicians encounter a multitude of restorative scenarios that oftentimes require imaginative and creative treatment planning to be successful. For these cases, collaboration with a dental technician is paramount in exploring different restorative possibilities. One particular restorative need that clinicians are presented with is the replacement of congenitally missing maxillary lateral incisors.
This article will describe a variation of an existing restorative option that has been used for decades-the Maryland bridge. However, in this modified technique, the engineering is reversed, placing the retainers on the facial surface in the form of laminate veneers while providing connectors to support a pontic.
Case Report
A 23-year-old female patient presented with a debonded porcelain-fused-to-metal Maryland bridge that was replacing both the left and right maxillary lateral incisors. The bridge was a 6-unit, fixed restoration spanning from canine to canine (Figure 1 and Figure 2). She expressed her displeasure with this restoration. After completion of orthodontic therapy years before, she was informed that the 6-unit Maryland bridge would be placed in lieu of implants because the space between her adjacent teeth (ie, the canines and central incisors) was insufficient for the proper placement of implants. Unfortunately, after the fixed bridge was placed, the patient was never happy with the esthetics. Specifically, she related that the metal retainers that were located on the back sides of both of her central incisors and canines created a greying effect that made these teeth appear darker. The opaqueness of the replacement teeth (ie, pontics) was also displeasing to her (Figure 3 and Figure 4). In addition to being unhappy with the fact that the bridge had debonded several times, she was also dissatisfied by the fact that, even after years of orthodontic therapy, she still had a space between her two front teeth, and that when closely viewed, the metal framework behind the space was visible. With all of these concerns, she wanted to know what her treatment options were to remedy the problems.
Diagnostic records were made, including mounted study models. The alginate impressions were double poured to preserve an original set of models while the second set was used for a mock-up. Initial observations of the study models revealed that the axial inclination of both canines was distally oriented. This root orientation placed the apices of the canines too close to the apices of the central incisors, which curtailed using implant therapy as a treatment alternative in replacing the missing lateral incisors. According to Misch, the amount of bone width in an edentulous area between two teeth should be at least 2 mm greater than the diameter at the implant insertion.1
Canine guidance was not present on either the left or right side, which could be attributed to the position of both her maxillary and mandibular canines. Without the presence of canine guidance, the lateral incisor pontics of the fixed bridge were contributing to posterior disocclusion in eccentric movements. This was most likely responsible for the multiple debonding episodes of the existing bridge.
In the laboratory, a mock-up was created on the second study model that extended the length of the canines to provide posterior disocclusion in lateral movements. The increased length of the canines would also eliminate the eccentric occlusal force on the pontics. In addition, the width of the two central incisors would be increased to eliminate the diastema. These treatment goals would be achieved by placing laminate veneers on both central incisors and canines, which would also serve as retainers supporting pontics in the lateral incisor positions. In other words, the final restorations were reversed versions of a Maryland bridge for which the retainers were located on the facial surface. This conservative treatment concept involving a resin-bonded, fixed dental prosthesis was first introduced in the mid-1980s.2 At that time, the material used for the prosthetic framework was a base metal alloy, which was due to the higher rigidity and hardness of base metals when compared with noble metals. This was important to provide less bulky retainers.3 However, since then, the advent of newer materials has provided other options. Materials such as glass-infiltrated alumina ceramic,4 fiber-reinforced resin composite,5 zirconia,6 and lithium disilicate7,8 have all been used with reported success.
After the existing fixed bridge was removed (Figure 5), the greyish effect on the abutment teeth immediately disappeared (Figure 6). All four abutment teeth were prepared for porcelain laminate veneers (Figure 7 and Figure 8). The preparation in the proximal areas, where the connectors would be located, was designed to allow for 4 mm of height and 3 mm of facial-lingual depth in order to maintain the required dimensions for all-ceramic connectors.9
The shade was selected utilizing a custom shade guide made from lithium disilicate (IPS e.max®, Ivoclar Vivadent) (Figure 9). After moistening the facial surface of the tooth with water, the shade tab was placed in contact with the tooth. This allowed the clinician to view the amount of influence that the stump shade would have on the final shade and then relay that information to the laboratory.
After two impressions were completed and a bite registration was taken, provisional restorations were placed. The method of placement involved utilizing a vacuum stent made from the mock-up model. Once the solid 6-unit provisional was placed using a spot etching and spot bonding technique, the occlusion was refined in all excursive movements (Figure 10). After the occlusion was finalized, a new alginate impression was made that would be used by the laboratory for a wax injection technique to duplicate the patient's provisional restorations.10
Laboratory Fabrication
In the laboratory, two working models were made: one with individual dies that would be used for refining the margins and a second solid model for the wax injection technique. On the solid model, two coats of die spacer were applied followed by an application of mineral oil to be used as a wax separator. A silicone matrix was then made from the provisional model. Next, holes were cut through the incisal edges of the two maxillary canine teeth for the hot, melted wax to be injected through. The matrix was then placed on the lubricated, solid working model, and using a jeweler's wax injection unit, melted wax was injected into one of the access holes with 5 lbs of pressure until it could be seen coming out of the other access hole. After the wax was allowed to dry, the matrix was removed, revealing an exact copy of the provisional model in wax.
Next, the excess wax was removed, leaving a solid 6-unit restoration. The contours were further enhanced in the wax. Using a silicone incisal matrix made from the provisional model, the incisal length was verified. The waxed restoration was then separated between the two central incisors, and each 3-unit bridge was placed on the multi-die working model for margin refinement. After this step was completed, both restorations were placed back on the solid model (Figure 11 and Figure 12), which was then mounted on a semi-adjustable articulator with the opposing model to finalize the occlusion. Finally, the bridges were sprued and invested for hot ceramic pressing using lithium disilicate ceramic.
Following the pressing cycle, the two restorations were divested from the pressing investment and the sprues were removed. After they were placed on the individual dies to verify the marginal integrity, they were placed on the solid model to verify complete seating. Once the seating was verified, a cutback and layering technique was employed to provide characterization to the incisal third of the restorations.
In this technique, a series of vertical notches were place along the incisal edges of the restorations to create the mamelon shapes. Longer notches were placed in the mesial areas, followed by ones that were shorter in length as they approached the distal areas. In addition, the width of the notches were varied in relation to their length. Between the notches, a series of more translucent incisal porcelains were placed and fired. Next, to obtain a "halo effect," a whiter incisal porcelain was applied to the incisal edge. This produced a frame around the translucent areas that were created between the mamelon shapes.
After final contour, a cervical stain (ie, khaki shade) was applied to the gingival areas. The stain was then thinned and extended into the interproximal areas to enhance the visual illusion of separation between the teeth (Figure 13). The restorations were then glazed, polished with a rubber wheel, and further polished with a stiff bristle wheel (Bristle Brushes, Abbott-Robinson®) using polishing paste (Zircon-Brite, Dental Ventures of America, Inc.) (Figure 14 and Figure 15).
Clinical Insertion
Under local anesthesia, the provisional restorations were removed. The prepared tooth surfaces were then lightly cleaned with a slow-moving, tapered diamond bur to create a clean bonding surface. Next, the two reverse-style Maryland bridges were moistened with water on the intaglio surface and tried in for fit. Once the patient approved the restorations for permanent seating, they were removed and conditioned for placement. The intaglio surfaces were etched with 5% hydrofluoric acid for 20 seconds. After rinsing and drying, an MDP-containing ceramic primer (CLEARFIL™ Ceramic Primer, Kuraray) was applied and then dried. An MDP-containing dentin adhesive (CLEARFIL™ Universal Bond Quick, Kuraray) was then applied to the intaglio surfaces, air-thinned, and followed with an application of a highly-filled, flowable resin composite (CLEARFIL MAJESTY™ Flow, Kuraray). Both restorations were then isolated from any light sources.
Returning to the patient, the teeth were isolated, etched with 37% phosphoric acid, rinsed, and dried. An application of the same MDP-containing dentin adhesive was then applied to all of the prepared tooth surfaces and air-thinned to remove the solvent. The adhesive layer was not light-cured at this time. Both of the bridges that were preloaded with flowable resin composite were then inserted, and the excess cement was removed with cotton rolls and microbrushes. While holding the restorations in place, the facial and lingual surfaces of the abutments were light-cured for 5 seconds each. Next, additional excess cement was removed followed by further light curing. After the bulk of the cement was removed in this manner, the final light curing was completed. Composite saw strips and sanding strips were used to finish the surfaces between the central incisors and the distal interproximals of the canine teeth. Following the verification of occlusion in all lateral excursions to validate the anterior and canine guidance, final polishing was completed with the polishing paste (Figure 16).
To facilitate the fabrication of a nightguard appliance that would also serve as a retentive device, alginate impressions were taken with the final restorations in place. The patient returned after two weeks for appliance delivery and final treatment photographs (Figure 17).
Conclusion
A combination of restorative procedures featuring the use of porcelain laminate veneers in a resin-bonded Maryland bridge concept satisfied the patient's esthetic concerns while providing a functional occlusion. Lengthening the canines to distribute the excursive occlusal loads removed the stress from the pontics. The balanced occlusion achieved will likely contribute to the long-term adhesive success of the bonded restorations.
Note: All of the laboratory work for this case was performed by the author.
References
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