A Three-Unit Bridge on a Bruxer

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This topic has 2 replies, 1 voice, and was last updated 10/11/2012 at 5:45 pm by DrAnil.

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10/11/2012 at 5:42 pm #11046

DrAnil

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Case Study

A 51-year-old male, who was a new patient with no relevant medical history, presented for replacement of a fractured porcelain-fused-to-metal FPD spanning teeth #29 to 31 (Fig. 2). His dental history was significant for bruxism, as was evidenced by the generalized moderate wear facets on the dentition. The existing FPD demonstrated considerable fracturing of porcelain and destruction of the metal substructure. Tooth #31 had a prior history of endodontic therapy that had required access through the occlusal surface of the FPD. This access had been sealed with a composite resin that now showed signs of marginal leakage and may also have contributed to the fracturing of the occlusal porcelain (Fig. 3). The patient was treatment planned for a full-contour zirconia bridge to prevent future porcelain fracture associated with his bruxism habit. Preliminary impressions and a bite registration were sent to the laboratory for the development of a wax-up. The FPD would be stained to incorporate the shade of the adjacent teeth in the same quadrant (A3) and the opposing dentition (A2).

At the treatment visit, while waiting for adequate anesthesia, a pre-operative impression was taken using a polydimethylsiloxane impression in a stock tray. This impression was set aside for later use during fabrication of the provisional bridge. The original bridge was carefully sectioned and removed so as to preserve remaining tooth structure. The composite resin filling the endodontic access on tooth #31 was removed and the remaining four walls of tooth structure were etched, bonded, and filled with a dual-cure, fluoride-releasing core buildup material. The preparations were completed with supragingival margins to aid hygiene, although had the tooth margins appeared in the esthetic zone, the margins would have been prepared equi-gingivally.

A custom tray was fabricated using light-cured material, for use during taking of the final impression to improve its accuracy (Fig. 4). A polyvinylsiloxane material was selected as adequate isolation and moisture control had been achieved. Application of a surfactant was performed to optimize flow of the impression material over the tooth surfaces and around preparation margins. A heavy body polyvinylsiloxane impression material was mixed into the custom tray while a light body polyvinylsiloxane impression material was loaded into a metal syringe. The cord was removed and the light body material was syringed into the sulcus, one prepared abutment at a time. After all surfaces of interest were covered, an air syringe was gently used to thin the impression material to reduce polymerization shrinkage. The full-arch tray of heavy body material was easily seated because it had been customized for the patient. After the setting time of five minutes had expired, the tray and impression material were removed and inspected for accuracy. The margins were shown to be fully captured with additional light body material well into the gingival sulcus (Fig. 5). The opposing arch was recorded with a polydimethylsiloxane impression material in a stock tray. This material demonstrates good dimensional stability and does not have to be poured in stone before transportation to the dental laboratory. An interocclusal record was recorded using rigid fast-set polyvinylsiloxane. This form of polyvinylsiloxane offers less resistance to biting forces and sets more quickly, reducing the chances for jaw movements to alter the record.

A provisional bridge was fabricated by dispensing a bis-acryl resin into the pre-operative impression (Fig. 6). The tray was reseated intraorally and allowed to cure for 90 seconds. After removal, a curing light was held over the provisional bridge for 20 seconds to expedite the curing process (Fig. 7). This step aids in removal of the provisional bridge from the pre-operative impression while avoiding distortion or fracture. The provisional bridge was trimmed with a thin flame diamond bur and checked intraorally for marginal integrity and occlusal harmony. An advantage of bis-acryl resin is its ability to easily bond with composite resin.

Since the original bridge had fractured porcelain, composite resin was added to the provisional bridge to improve strength, function and esthetics (Fig. 8). A non-eugenol zinc oxide cement was syringed into the internal surfaces of the abutments’ restorations and seated. As it was anticipated that a resin cement would be used for the final case, it was important to avoid the use of eugenol in the provisional cement. A sufficient amount of temporary cement was dispensed and the margins were carefully checked with an explorer. The impression and bite registration were disinfected and sent to the laboratory together with the lab prescription.

Shade Communication

Numerous digital color communication technologies have been introduced to the dental profession over the last 15 years. The most impactful device is the digital camera (Fig. 9). The use of 35 mm digital cameras to communicate color and characterization between the operatory and dental laboratory has dramatically reduced the most common reason for disappointment on delivery day—poor color matching.

10/11/2012 at 5:43 pm #16154

DrAnil

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Laboratory Technique

Provisional Restoration

A provisional bridge can also be fabricated in the laboratory using hybrid resin. The previously developed patient/clinician-approved diagnostic wax-up was first matrixed with silicone putty. A duplicate cast was minimally prepared and lubricated with petroleum jelly. An initial application of enamel shade hybrid resin material was placed into the matrix from the heated syringe, distributed appropriately with the electric spatula, and allowed to cool. The dentin shade was then syringed into the matrix and seated on the cast while it was ensured that the matrix was completely seated. After the material was allowed to cool for four minutes, the matrix was carefully removed by first carving carefully where significant undercuts existed, to prevent damaging the uncured wax-like material. (Voids from trapped air can be repaired, if necessary, using the electric spatula.) After the hybrid resin had cooled, it was carved to develop the desired final contours and anatomy, after which the occlusal and interproximal contacts were thoroughly checked. The glaze was then applied with a disposable brush and cured. Figure 10 shows the excellent results that can be achieved using this method for a provisional for the same case.

Fabricating the Definitive FPD

All ceramic materials and technologies have exhibited an exponential development over the previous 20 years for ceramic indirect restorative advancements. The workhorse porcelain-fused-to-metal restoration is slowly being replaced with high-strength CAD/CAM-developed ceramic materials. Development has moved through leucite-reinforced pressed ceramics to pressed or machined lithium disilicate ceramics. The use of YZ zirconium oxide as a substrate veneered with stacked ceramics has evolved into monolithic CAD/CAM-produced restorative systems. In this case, the FPD was created with full-contour zirconia, utilizing a digitally optimized fabrication technique. Upon completion of the master cast fabrication, the casts were articulated in a centric relation utilizing the provided occlusal registration.

The working cast was scanned and, utilizing the design software, the margins were identified at 100 times the actual size, thereby providing a level of accuracy that is impossible to achieve with traditional die trimming (Figs. 11-12). The virtual cement gap was determined specifically for each area of the restoration by establishing independent parameters for margins, axial walls, the occlusal surface, and line angles. The desired external contours were transferred from a scan of the approved diagnostic wax-up (Fig. 13-16). The .stl file was then e-mailed to the central manufacturing facility for milling of the restoration. Upon receipt of the file, the restoration was milled from a pre-sintered zirconium oxide disk. Next, the restoration was dipped in the appropriate stain to achieve the desired dentine shade of the completed restoration. Finally, the restoration was sintered in an oven at 1600 degrees Celsius, fusing the zirconia particles and shrinking them by approximately 30%. The sintering process transforms the zirconia into a more dense material with high strength. The restoration was then returned to the laboratory for confirmation of internal, occlusal, and interproximal adaptation. After minimal adjustments were accomplished, external characterization was applied for appropriate intra-oral esthetic matching. For optimal results, A-3 Dentine was applied to the areas of wear illustrated on the buccal cusp tips of teeth #29 and 30 (Fig. 17).

Placement of the FPD

The definitive restoration was tried in to assess marginal fit, adequate interproximal contact with the distal of tooth #28, and occlusion. A bitewing radiograph confirmed the visual inspection that marginal fit had been achieved (Fig. 18). Occlusal and interproximal contacts required no adjustment owing to an accurate impression, bite registration, and meticulous laboratory work. A dual-cure resin cement was used to retain the FPD. A resin cement will adhere to the abutment tooth structure for added retention. The patient was pleased with the improved function and high esthetics of the final result (Fig. 19). The selected shade was successful in blending the opposing dentition (shade A2) with the adjacent dentition (more A3).

Summary

Dentists today have a variety of materials at their disposal for each step in the fabrication of an FPD. The successful recording of preparations, manufacture of multi-unit restorations, and their delivery intraorally is aided by astute attention to material properties at each of these critical stages.

Case Study Introduction

Restoring teeth in the anterior region routinely presents with esthetic challenges. In this case, the patient, a 42-year-old female, was unhappy with her smile. Several composite restorations had been placed a number of years earlier due to decalcification of the facial surfaces of her anterior teeth and had discolored over time. In addition, the patient’s high lip line and significant gingival display presented a challenge that mandated meticulous planning. (Figure 1) The spacing and position of the teeth were otherwise ideal, allowing minimal preparation for 6 porcelain veneers. As increasing the length of the central incisors would result in more harmonious proportions, gingival recontouring prior to veneer preparation was recommended to the patient. Probing and sounding was completed to ensure that there was adequate room to perform soft tissue recontouring (Figure 2), and a CBCT scan was captured and studied.

At the first treatment appointment, a laser gingivectomy was performed to remove the gingival excess. Proper, consistent, and adequate reduction of the facial surfaces was facilitated through depth cuts on the facial surfaces of the anterior teeth. (Figure 3) After the depth cuts had been created, the preparations were completed and carried over the incisal edges. Preparation of the teeth on the centric stops was avoided by checking the occlusion before initiating the preparations and by recording the centric stops (in blue). (Figure 4)

Gingival retraction paste was used to achieve adequate retraction and hemostasis for optimal impression conditions. B4^® pre-impression surface optimizer (DENTSPLY Caulk) provided ideal wetness of the preparations for consistent coating with VPS impression material. An impression material with extended working time (Aquasil Ultra Xtra Smart Wetting^®, DENTSPLY Caulk) was used as there were several preparations in this case. Porcelain veneers were laboratory fabricated.

At the seat appointment, a total-etch bonding agent (XP Bond^®, DENTSPLY Caulk) was applied to ensure high bond strengths. The veneers were next cemented using the base portion, without catalyst, of an esthetic resin cement (Calibra^®, DENTSPLY Caulk), giving an extended working time during seating. Each restoration was placed, the margins cleaned, and the teeth flossed before an initial tack cure. Excess cement was then removed and a full cure was initiated. The central incisors were seated first, followed by the right and left lateral incisors and canines, and a final cure of 40 seconds on each restoration was accomplished (20 seconds on the facial surface and 20 seconds on the palatal surface). (Figures 5-8)

The veneers demonstrated a precise fit and smooth transition to natural tooth structure. The patient was very pleased with the esthetic results achieved. At 6-month recall, gingival health adjacent to the veneers, and esthetics, were excellent.
As demonstrated, proper planning of preparation style, material selection and patient communication are key to the success of anterior veneers.