Considerations When Restoring a Nonvital Tooth

[Anonymous]

tooth. First, once the tooth has been treated with endodontic therapy, in most cases in the posterior, cuspal coverage is indicated to reduce the risk of the tooth fracturing.1 Then, the extent of the decay must be considered in relation to several factors. Regarding the biologic width, is there sufficient distance from the floor of the preparation to the bone for a healthy periodontal structure? Next, is there enough tooth structure to allow the placement of an adequate ferrule of 1.5 mm to 2 mm over natural tooth structure during the preparation? Finally, will the remaining tooth structure, or lack thereof, require the use of a post in addition to the core material to retain the crown restoration on the tooth?
Additional considerations include restoration type (all-ceramic, metal-ceramic, etc), provisionalization versus same-day restoration, and preferences in treatment protocol, such as preparation techniques, hemostasis, and tissue retraction. During the procedure, the most critical factors impacting the final impression and the quality of the resulting restoration are the use of a rubber dam, effective hemostasis, and tissue retraction. If the preparation is not clear of debris, blood, and other fluids, acquiring the highest quality impression is not possible. Additionally, adequate soft-tissue retraction must be accomplished without damaging the sulcus or connective tissues. When loss of tooth structure to decay places the margin subgingivally to a significant extent, as in the case included in this article, these issues become all the morecritical.

        

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INTRODUCTION
Multiple factors must be considered when deciding how to restore an endodontically treated tooth. First, once the tooth has been treated with endodontic therapy, in most cases in the posterior, cuspal coverage is indicated to reduce the risk of the tooth fracturing.1 Then, the extent of the decay must be considered in relation to several factors. Regarding the biologic width, is there sufficient distance from the floor of the preparation to the bone for a healthy periodontal structure? Next, is there enough tooth structure to allow the placement of an adequate ferrule of 1.5 mm to 2 mm over natural tooth structure during the preparation?1,2 Finally, will the remaining tooth structure, or lack thereof, require the use of a post in addition to the core material to retain the crown restoration on the tooth?3

Additional considerations include restoration type (all-ceramic, metal-ceramic, etc), provisionalization versus same-day restoration, and preferences in treatment protocol, such as preparation techniques, hemostasis, and tissue retraction. During the procedure, the most critical factors impacting the final impression and the quality of the resulting restoration are the use of a rubber dam, effective hemostasis, and tissue retraction. If the preparation is not clear of debris, blood, and other fluids, acquiring the highest quality impression is not possible. Additionally, adequate soft-tissue retraction must be accomplished without damaging the sulcus or connective tissues. When loss of tooth structure to decay places the margin subgingivally to a significant extent, as in the case included in this article, these issues become all the more critical. This article describes the use of a new hemostatic-paste retraction system during a complex post-and-core preparation where significant tooth structure had been lost.

CASE REPORT
Diagnosis and Treatment Planning
A 32-year-old woman presented with a fractured upper right second premolar (tooth No. 4). Significant caries was present and a bite-wing radiograph showed a carious pulpal exposure (Figure 1).

Her medical history included high blood pressure, diabetes controlled with oral medications, and fibromyalgia.

A variety of restorative options were discussed with the patient, including extraction and implant placement, extraction and insertion of a 3-unit bridge, or preservation of the tooth with endodontic therapy and crown placement. The patient elected to maintain the natural tooth, choosing endodontic therapy and an all-ceramic crown for aesthetic reasons.

Clinical Procedures Begin
The tooth was prepared, the caries removed, endodontic therapy was performed, and a temporary filling was placed (Figures 2a and 2b).

Approximately 3 weeks after endodontic therapy, the patient returned, and after placing a rubber dam, the temporary restoration was removed to prepare the post space (Figure 3). Creating the post space requires removing enough of the restorative material and as little tooth structure as possible to achieve clean canal walls, typically at least half to no more than two thirds of the way down the root length.1,4 The appropriate size post is chosen after evaluating the size of the canal, which also determines drill size. After removal of the restorative and endodontic filling materials, the largest size post-preparation drill that would fill the canal space without removing excessive tooth structure was selected. If in doubt, always choose a smaller post drill. If it does not create a clean canal, move to the next size larger post drill. Once the post space was prepared, a 1.2-mm glass fiber post was chosen and tried-in to confirm proper size and seating (Figure 4). After confirming the post size, excess length can be removed from the occlusal end of the post with a diamond or carbide bur.

Current research supports the use of glass fiber posts, and favors the glass fiber post over titanium and ceramic posts.4-7 Glass fibers have a high level of light transmission and are therefore considered cure-through or light curable. Being able to light-cure through the post enables more complete polymerization of cement surrounding and down the length of the post. It has been shown that glass fiber posts have higher fracture strength and elasticity than posts made of other types of materials,3,8 which helps make the root/restoration stronger and more resilient. Ideally, the elastic modulus and flexural strength should be close to that of natural tooth structure (e-modulus 52 GPa/flexural strength 1,650 MPa). Ceramic posts that are not reinforced with glass fibers tend to debond more quickly. The Cure-Thru IntegraPost (Premier Dental Products) was chosen in this case for both strength and aesthetic reasons. This post incorporates zirconia-rich glass fibers within a composite matrix. The fibers are factory-silanated to enhance bonding with both the resin cement and the composite core build-up material. It has been demonstrated that the addition of zirconia fibers provides exceptional strength. The white color of this cure-through post eliminates any gray shadow showing through the tooth, especially important in the aesthetic zone. The posts are also color coded to match the company’s system of drills, which facilitates efficient use of the clinician’s time.

After verifying post selection, in terms of size and length, the tooth was prepared for cementation of the post and the subsequent placement of the core buildup. A clear matrix and a sycamore wedge were placed to establish a good gingival seal, control the flow of the composite material, and to minimize excess. The tooth and canal space were etched for 15 seconds with a self-etching primer. The preparation was thoroughly rinsed and dried, first with light air flow and completely with paper points. In this case IntegraBond Universal Bonding Agent (Premier Dental Products) and Auto-Cure Activator (Premier Dental Products) was used, equal drops of each placed into a mixing well and mixed for 2 seconds. The tooth surface should be thoroughly wet and left undisturbed for 15 seconds. After this time, the preparation was thoroughly dried with air for 15 seconds to remove all solvent. IntegraCem Dual Cure Resin Cement (Premier Dental Products) was dispensed onto a mixing pad in equal amounts and mixed for 20 seconds. The cement was carried into the canal with a paper point (Figure 5). Additional cement was applied directly to the post, which was then seated fully into the prepared space and light-cured for 20 seconds.

Core Buildup and Chamfer Preparation
The core buildup was completed using a nanofilled, dual-cure core build-up material (CompCore AF Stack [Premier Dental Products]) (Figure 6). This material has been shown to have excellent radiopacity, a low exothermic reaction, high compressive strength, and to release fluoride, deemed important in this particular high-caries-risk case. After light-curing for 20 seconds, the core build-up material was allowed to continue self-curing for 4 minutes (Figure 7). After complete setting, the matrix was removed and the crown preparation was started.

Initial occlusal reduction of the preparation was accomplished using a 2004.5 Two Striper TS2000 spiral football diamond (Premier Dental Products) (Figure 8). Prepping to the depth of this type of diamond, which at its widest is 2.5 mm in diameter, ensures adequate occlusal reduction. Axial reduction was accomplished with a 770.8C chamfer diamond (Premier Dental Products) providing adequate reduction for the chamfer preparation (Figure 9). The extensive decay present in the tooth originally required the placement of subgingival margins to meet the mechanical requirements of the tooth.

Once the chamfer preparation was completed, the rubber dam was removed and the preparation was rinsed and air-dried.

Soft-Tissue and Fluid Control: Taking the Impression
Obtaining a good impression requires adequate tissue retraction and hemostasis. To adequately capture the margins without distortion, the preparation must be free of blood, saliva, and other fluids (Figure 10). A variety of hemostatic products is available on the market, with the newest type being a "paste" that can be used to accomplish retraction and hemostasis simultaneously. There are 2 very good products currently available with these properties: Expasyl (Kerr) and the new Traxodent Hemodent (Premier Dental Products) paste retraction system, which I chose to use for the case presented here. Both are viscous pastes that contain aluminum chloride.

As an alternative to retraction cord, which requires packing and can put pressure on as well as tear gingival tissue, Traxodent was extruded into the sulcus via a bendable syringe tip. This paste is delivered via an ergonomic disposable syringe, and the angulation of the syringe tip can be adjusted chairside for optimal access. This material may be used for retraction and hemostasis before both digital and traditional impression techniques, seating restorations, and placing restorations in Class II, III, and V cavities. Traxodent can also be used in conjunction with traditional retraction cord in cases where deeper retraction is needed. In my experience, the process in combination with the impression caps can be less technique-sensitive than placing cord.

The syringe tip was placed at an angle to the gingival sulcus without penetrating the sulcus (Figure 11). This facilitates the placement of the material slightly into the sulcus, which is important for adequate hemostasis. The paste provides gentle pressure on the sulcus, absorbing excess crevicular fluid while the aluminum chloride creates an astringent effect. In Figure 11, it can be seen that the Traxodent is completely covered with blood after initial placement.

        

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Next, a size 3 anatomically-formed retraction cap was carefully placed over the preparation with the scalloping on the working or preparation end, facing mesial distal (Figure 12). Proper selection and placement of the retraction cap is important to ensure that the hemostatic paste is gently guided into the sulcus and stays in place during the waiting period. The patient was asked to gently bite down on the cap for 4 minutes. Combined with proper placement of the hemostatic retraction paste into the sulcus, the retraction cap provides essential hydrostatic pressure on the tissue to help accomplish the necessary hemostasis and retraction for accurate impressions.

After 4 minutes, the retraction cap was removed. Figure 13 shows the excellent hemostasis and retention of the Traxodent that was achieved in and around the tooth. Next, the hemostatic retraction paste was thoroughly rinsed using an air-water syringe and a suction tip, leaving an open, retracted sulcus (Figure 14).

Before making the impression, the preparation margins were evaluated to ensure there was access for the impression material to all the margin areas. In this case, a posterior T-LOC Triple Tray (Premier Dental Products) was selected for making the impression. This type of tray is wide enough to ensure that it does not impinge on the alveolar process. Its thin, flexible mesh allows adequate closing into occlusion without distortion, and it has retentive features built into the tray rim to stabilize and retain the impression material.

A heavy-body impression material (Imprint 3 Penta Heavy Body [3M ESPE]) was chosen because it offers adequate working time in addition to a short setting time, which minimizes the time the material needs to be in the mouth, adding to patient comfort. The light-body material (Imprint 3 Quick Step Light Body Impression Material [3M ESPE]) was extruded around the prepared tooth and margin areas, while the heavy-body material was loaded into the tray. The heavy body material was "overloaded" on both sides of the tray. The tray was then placed in the mouth, and the patient was instructed to close into her maximum interocclusal position for 2.5 minutes.

Upon removal, the impression was evaluated to verify all of the margins could be identified (Figure 15). With the use of the dual-arch tray, the preparation, the opposing arch, and the bite registration were captured simultaneously, saving time and improving patient comfort. At this point, if the restoration is slated to be fabricated by a dental laboratory, the impression is disinfected and sent to the lab.

A temporary crown was fabricated using a bis-acryl, light-cured, temporary composite material placed inside a putty impression matrix of the unprepared tooth. After trimming the margins, adjusting the occlusion, and polishing, the temporary was seated and cemented with a noneugenol temporary cement.

Because in this case the treatment plan included the in-office fabrication of the permanent restoration and the patient had opted for 2 shorter appointments, the impression was taken in order to create a physical model to use for creating the restoration between visits.

In-Office CAD/CAM System to Fabricate the Final Restoration
In my practice, I like to take advantage of new technology to enhance patient outcomes, comfort, and convenience. Using chairside CAD/CAM allows us to utilize new adhesive and ceramic technologies and provide high-strength aesthetic restorations in a single visit, while preserving natural tooth structure. It also enables the use of preparations that are more defect-oriented than material-oriented. I have used chairside CAD/CAM since 1998 in various forms, and the E4D (D4D Technologies) clinically as a beta tester since 2007.

The E4D system is designed for same-day delivery of restorations as well as for cases where there may be a need to separate the procedure into 2 visits. The E4D system can be used to scan, design, and mill all-ceramic restorations. Virtual models are used to create the appropriate crowns, veneers, inlays, onlays, and laboratory fabricated ceramic bridges, while incorporating the opposing dentition, a wax-up, or scans of a provisional or preoperative condition. With E4D, clinicians can scan both hard and soft tissue, pre- or post-preparation, and record bite registrations. The E4D is the only digital CAD/CAM system with the ability to scan in the mouth, directly on the impression, or on a model without using contrast agents or opaquing mediums. As of the writing of this article, the E4D (launched in 2008) cannot be used to fabricate bridge restorations, but soon, digital scanning (impression making) and sending a virtual restoration to the laboratory will be possible.

The final restoration for this case was fabricated using a lithium disilicate block (IPS e.max CAD; HT block, shade A2 [Ivoclar Vivadent]) (Figure 16). The preparation side of the dual-arch impression was directly scanned. Then the dual-arch impression was poured up and articulated according to the bite recorded in the triple tray. After the stone had set up, a bite registration was recorded from the model and scanned into the E4D system. The restoration was designed utilizing the bite information from the neighboring teeth and the occlusion, ensuring a highly accurate restoration.

After milling, the ceramic CAD glass block, or "blue block," was tried on the model and adjustments were made. IPS e.max stains and glaze were applied, and then the restoration was subsequently crystallized to its final hardness. The chameleon effect and higher strength of the lithium disilicate material provides excellent aesthetics while providing adequate strength and resistance to functional forces.

Final Restoration Delivery
When the patient returned for final delivery of the restoration, the temporary was removed and the preparation was pumiced to remove any temporary cement residue for optimal bonding. After try-in of the milled restoration to check for shade, fit, contacts, and proper occlusion, any necessary adjustments were made with fine diamonds at medium speed before it was polished. A rubber dam (Ivory brand 6×6 latex rubber dam [Heraeus Kulzer]) was applied to ensure an absolutely dry field. If there is any seepage in the marginal tissue, Traxodent can be applied for 2 minutes.

Before final seating, the restoration was etched with 5% hydrofluoric acid (IPS Ceramic etching gel [Ivoclar Vivadent]) for 20 seconds, then rinsed and dried thoroughly. Next, a universal primer (MonoBond-S [Ivoclar Vivadent]) (conventional silane can also be used on lithium disilicate) was applied to the internal surfaces of the crown to promote adhesion of the composite resin cement to the restoration. After being left to react for 60 seconds, the universal primer was air-dried.

The restoration was seated using a transparent shade of a universal self-etching luting composite (MultiLink [Ivoclar Vivadent]). This dual-cure material is designed to be used with a wide variety of indirect restoration materials, sets quickly, and has demonstrated high-strength bond strength values and long-term stability. After mixing the enamel-dentin A/B primer in a 1:1 ratio in a mixing well, it was applied to the tooth surface with a microbrush and scrubbed vigorously for 15 seconds. The tooth surface was then gently air-dried. Using the Multilink automix syringe with tip in place, the material was expressed directly into the crown. After ensuring the crown was fully seated, the material was light-cured for only 2 seconds at each line angle to achieve a gel state. Excess cement was immediately removed with an explorer. Contacts were flossed to remove excess cement interproximally. Polymerization of the cement was then completed by curing the tooth for 20 seconds each from the buccal, lingual, and occlusal.
After using finishing and polishing strips in the proximal regions to ensure that all the cement was removed, and after final confirmation of proper occlusion, the patient was dismissed with postoperative instructions. The patient was pleased with the final result and the excellent aesthetics achieved (Figures 17 and 18).

CLOSING COMMENTS
Two of the most critical factors impacting the quality of an impression and the resulting restoration are accomplishing the hemostasis and retraction necessary to accurately record the preparation margins. With the excellent new materials available to the practitioner, excellent hemostasis and tissue retraction can be accomplished in a few minutes, while minimizing patient discomfort. Clinical excellence and predictability, ensured by using reliable products and techniques, will ensure success of your final outcome.

        

[drmittal]

refer the document below for figures..

        

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