A Conservative Aesthetic Solution for a Single Anterior Edentulous Space: The Fiber Reinforced Resin Fixed Partial Denture
Written by Dino S. Javaheri, DMD Sunday, 31 August 2003 19:00
There is an increased patient demand for conservative dental treatment, improved aesthetics, and reduced expense. These requirements have lead to the development of new materials and techniques. Adhesive procedures and fiber- reinforced resin systems now allow clinicians to respond to different clinical situations, including replacement of a missing tooth. This article illustrates a restorative technique used for the treatment of a patient with a missing anterior tooth.
The functional replacement of a missing tooth may be accomplished in a variety of ways. It is recognized, however, that the aesthetic replacement of a missing tooth can be a challenge for the clinician. Selection of the appropriate treatment modality is dependent on the evaluation of many objective and subjective factors, including aesthetics, occlusion, osseous and soft-tissue architecture, condition of the proximal teeth, and patient expectations. While the materials and techniques utilized in the fabrication of a restoration will directly influence the treatment outcome, proper planning and communication between the patient, restorative dentist, dental specialists, and laboratory technician are crucial to success.
The treating dentist and patient must consider other nonclinical factors to define the optimal treatment plan, including the treatment time, patient motivation and expectation, anticipated longevity of the restoration, possibility of complications, and cost.1 The selection of the most appropriate treatment plan is not always simple and should be guided by the desires of the patient and the professional expertise of the treating clinician.
One of the treatment options available for the replacement of a missing tooth is an adhesive, fiber-reinforced resin fixed partial denture (FPD).1,2 This is very similar to the established “Maryland” bridge technique but with a fiber-reinforced resin material. Traditionally, Maryland bridges use metal retaining wings to maintain a pontic, but these metal wings have been shown to be associated with long-term problems such as retention and discoloration of the abutment teeth.3-5 Although the fiber-reinforced resin FPD is a recent development, the preparation and fabrication guidelines are established. Preliminary investigations support the clinical application of this technique.2,6
These FPDs can be utilized in a variety of situations. One indication is when a patient expresses a desire for a conservative, nonmetal restoration. Other indications are primarily clinical, and include the following: (1) minimally restored abutment teeth ; (2) the pontic space is short (ie, 11 mm or less in the anterior maxilla or mandible); (3) placement of a full-coverage fixed partial denture would be unnecessarily aggressive; (4) patient age, osseous support, medical status, or acceptance precludes an implant option; (5) isolation and control of moisture, saliva, or blood can be achieved; and (6) an absence of heavy occlusal contacts or a severe parafuntional habit.7-10 In situations where these conditions do not exist, other restorative options must be considered.
Contraindications for a fiber-reinforced resin FPD are cases where sufficient tooth reduction is not possible to allow for proper fabrication of the restoration, mobile teeth (> class 1 mobility), and short clinical crowns (< 5 mm incisal to gingival distance).11,12
The first indirect resin systems, which were introduced in the 1980s, had several limitations, including color instability and a tendency to fracture when subjected to significant occlusal stress.13 Contemporary formulations have improved the mechanical characteristics of indirect resin systems.14,15 Polymerization shrinkage has been reduced, while flexural and tensile strength, the resistance to abrasion and fracture, and color stability have been improved. These indirect resin systems have been classified as CEROMERs (CERamic Optimized polyMERs), polyglass, or polymerceramic material.16 The preceding terms do not signify a new category of materials, but are marketing terms designed to give the impressions that these indirect resin systems are similar to porcelain systems.
Rather, these indirect resins should be considered as laboratory-processed microhybrid composites. They contain a combination of inorganic fillers and an organic polymer matrix in a 2:1 ratio.17 The filler is the primary determinant of the clinical and physiochemical properties of a composite resin. The submicron filler particles provide for surface characteristics such as good aesthetics, polishability, and wear resistance.
The use of fiber reinforcement increases the flexural strength of resin systems.18-20 The fiber can resist stress in different directions and also allows the restoration to retain flexibility so that the material does not become too brittle.21 This adds both flexural strength and fracture resistance to the restoration. The mechanical strength provided by fiber reinforcement is generated by the material’s ability to dissipate the tension lines and internal microfissures that would cause complete fracture of a more rigid material.22,23 Specifically, the fact that the fibers are not arranged longitudinally or in parallel but are instead woven in an alternating pattern increases the dispersion of the internal tension lines and thus provides fracture resistance.24 Also, when subjected to functional stress, the material exhibits a deformation capacity that is similar to that of a natural tooth, which also reduces the tendency to fracture at the interface between the restoration and tooth.25
Laboratory-processed, fiber-reinforced resin systems offer strong yet conservative restorations when compared to traditional ceramic and resin restorations. These systems provide the advantages of both direct composite resins and indirect porcelain restorations without being confined by the inherent disadvantages of either restoration alone.26 Resin systems alone do not have the strength for a multiple unit restoration. Porcelain wings are brittle and can fracture. Fiber reinforcement of a resin system provides both the strength and flexibility necessary for a restoration.
|Figure 1. Patient presented with complaint of loose central incisor crown.||Figure 2. The central incisor was deemed unrestorable due to caries, periodontal disease, and internal resorption.|
A 30-year-old female patient presented with a loose crown on the maxillary right central incisor (Figure 1). The gingiva had receded and was inflamed, and the porcelain fused-to-metal crown was mobile. After removal of the crown, only a small post with subgingival tooth structure remained (Figure 2). There was caries on the remaining root structure. In addition, internal resorption was noted on the radiograph. The tooth was deemed unrestorable due to the caries, internal resorption, and poor crown-to-root ratio. Other than the unrestorable central incisor, all other teeth were in excellent condition. Occlusion was noncontributory since the patient had an anterior open bite.
The first consideration was the osseous support for the failing tooth. It is not uncommon to find significant bone loss associated with the failing tooth but not with the adjacent teeth. If the failing tooth is extracted, the bone level will be significantly more apical than what is observed for the adjacent teeth. This creates a very difficult aesthetic situation. One solution is to delay the extraction of the failing tooth so it can be orthodontically extruded. As this is accomplished over several months, the attachment apparatus of the unrestorable tooth is positioned coronally to a level matching the adjacent teeth. In this scenario, the aesthetic outcome will be improved.
|Figure 3. A large, threaded post was placed as an anchor for orthodontic extrusion.|
|Figure 4. Composite buildup of the central incisor.|
|Figure 5. Orthodontic extrusion was completed to improve osseous and soft-tissue contour prior to extraction.|
In the case presented here, the gingival margin on the buccal surface of the unrestorable tooth had receded, and extrusion was deemed necessary. To prepare the unrestorable tooth for extrusion, the existing post was removed and a large, threaded post was placed (Figure 3). A composite buildup was then placed around the post (Figure 4). The patient was referred to an orthodontist for extrusion of the unrestorable tooth. As the tooth was orthodontically extruded, the composite buildup was trimmed (Figure 5). Ultimately, the tooth was overextruded to allow for tissue retraction associated with extraction of the hopeless tooth. Upon completion of the orthodontic phase, the tooth was extracted.
A provisional restoration should be placed to extend into the socket to support the papillae form and to shape the soft tissue. This can be accomplished with either a temporary partial denture (also known as a stayplate or flipper) or a fixed bridge. A temporary partial denture is not as reliable, since it’s movement can adversely infringe on the papilla. In this case, after the extraction, a temporary fixed bridge was fabricated by using the preoperative model. Block-out material was added to the lingual surfaces of the adjacent teeth to create room for the retaining wings. In this case, no tooth reduction was necessary, since the patient had an anterior open bite.
A triple-tray vinyl polysiloxane impression was taken of the modified stone model. This impression was used as a stent to fabricate a provisional bridge. A chemically cured, bis-acryl composite material was placed into the stent and fitted onto the patient’s teeth. After 3 minutes, the impression stent and provisional bridge were removed. The provisional restoration was contoured, trimmed, and polished (Figure 6).
|Figure 6. The temporary restoration was shaped to adapt tissue to ideal contour.||Figure 7. An ovate pontic was shaped for aesthetic pontic emergence.|
After healing of the extraction site, a diode laser was used to shape an ovate pontic site (Figure 7). This presents the illusion that the pontic is emerging from the tissue as would a natural tooth, with at least 1 mm of soft tissue remaining above the osseous crest.
Tooth preparation that provides adequate clearance for the retainer wings can require removal of 1.5 mm of tooth structure on 80% or more of the lingual surface area of the abutment teeth, with extension to the proximal surface adjacent to the pontic site. The finish lines on the lingual surface are extended to within 1 mm of the proximal line angle and the incisal edge. Cervically, the finish line should be 1 mm short of the cementoenamel junction or the free gingival margin, whichever is encountered first. For this patient, due to the open bite, no lingual reduction was necessary to provide room for the retaining wings. A 0.5-mm horizontal groove was placed in the middle of the lingual surface of the abutment teeth to assist in confirming a positive seat of the final restoration. In addition, a 0.5-mm-deep proximal box was placed just lingual to the proximal height of contour of the edentulous space to add strength at the connector site. The preparation was designed to allow seating of the bridge from the lingual.
A vinyl polysiloxane impression was taken and sent to the laboratory along with photographs, opposing models, and a bite registration.
|Figure 8. Final soft-tissue contour prior to placement of the restoration.|
Upon delivery of the final restoration from the laboratory, the FPD was evaluated on the die segment for proper fit. At the cementation visit, the patient was anesthetized, and the provisional restoration was removed (Figure 8). The teeth were cleansed with a 2% chlorhexidine gluconate solution, and the restoration was tried in with a water soluble try-in paste to verify marginal fit and the aesthetic results. The occlusion was not verified during try-in to avoid stress on the restoration. The patient was shown the restoration and gave final consent.
To prepare the restoration for bonding, it was cleansed by applying a 35% phosphoric acid gel for 10 seconds. The acid was rinsed away, and the internal surfaces of the restoration were coated with silane ceramic primer for 60 seconds. A warm-air dryer was used to evaporate the excess liquid. One coat of a one-bottle adhesive system was applied to the internal surfaces of the FPD. The adhesive was air-thinned but not cured. A light-cured resin cement was applied to the wings of the FPD, which was then placed in a light-sealed container.
The tooth preparations were acid-etched with 35% phosphoric acid for 15 seconds. After rinsing the teeth, excess water was blotted dry, leaving a moist preparation. Three coats of the bonding agent were applied to each preparation. A warm-air dryer was used to evaporate the solvent and to avoid pooling of adhesive. The FPD was seated and held in place, and excess cement was removed with a brush. The restoration was spot-tacked on the lingual aspect with a 2-mm curing tip, and any remaining excess cement was removed. Glycerin gel was applied to all marginal areas to eliminate an uncured, oxygen-inhibited layer. Light activation was applied to polymerize the resin cement. The final cure was achieved with a plasma arc light applied for 10 seconds to the facial, incisal, and lingual surfaces of each abutment tooth.
|Figure 9. The final fiber-reinforced resin bridge.||Figure 10. Lingual view showing the retaining wings.|
Excess composite resin in the interproximal region was removed with a No. 12 blade. A bur should not be used as this may create a ledge. The final polishing was achieved with composite polishing points and diamond polishing paste (Figures 9 and 10). Since the patient had an anterior open bite, no occlusal adjustment was required.
The evolution of aesthetic materials and restorative techniques enables clinicians to respond to patient demands for conservative restorations, satisfactory aesthetics, and reduced expense. The fiber-reinforced resin FPD technique should be considered as a treatment option for replacement of a missing tooth.
The author would like to thank Juan Gutierrez, CDT, of Terra Ceramics, San Ramon, Calif; Robert Cuenin, DDS (orthodontist), Danville, Calif; and Ali Alijanian, DDS (oral surgeon), Walnut Creek, Calif, for their contributions to this case.
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