Re: Considerations When Restoring a Nonvital Tooth

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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.