Foundational Core Build-Up Materials for Full-Coverage Restorations
Core-Flo™ DC Lite is an exceptional core build-up solution
Fred H. Peck, DDS, AAACD
Single-unit crown restorations are one of the most common procedures in a general dental practice. According to recent statistics from Glidewell Laboratories, there were 53.5 million crowns produced in the United States in 2013 (data on file). Further investigation shows that roughly 88% of cases received in labs are 1- to 2-unit cases. They may be a standalone restoration, part of a fixed bridge, or an integral part of a more complex restorative plan. A crown is often used because the underlying tooth is structurally compromised. Many of these teeth are being restored to replace fractured teeth and existing crowns or large fillings that have failed. The core build-up is often necessary to support the final restoration and must have the integrity to ultimately support the occlusal forces placed upon it. A core material may also be used in conjunction with a post in an endodontically treated tooth.
Core materials are available in multiple options. One option is amalgam, which often requires the use of pins to retain the material. However, it often leaves the tooth permanently discolored and many patients today wish to have an alternative to metal in their mouth. In the author’s opinion, one should consider removing existing filling materials prior to placement of a new crown if there is any doubt that secondary decay could be present. Yip and colleagues have written about the toxicity to human health of mercury in dental amalgam,1 continuing the controversy of this material for use in dentistry. Other materials have come and gone from the dental marketplace, leaving composite resins as the current standard.
When considering which composite resin to use, several factors must be considered. A core material should foremost withstand occlusal forces and have high bond strength.2 With the prevalence of today’s all-ceramic restorations, the underlying resin of the newer core build-up materials must blend with the final ceramic color to avoid show-through of a dark core and should also help to mask a dark, discolored tooth.3 Lastly, the core material must be easy to dispense, fill the missing tooth structure completely, and not induce sensitivity to the underlying pulp. Dentists are looking for easier techniques with strong reliable dental materials to accomplish these tasks.
BISCO, Inc. (www.bisco.com) developed Core-Flo™ DC Lite, a new formulation of core build-up material that is a self-leveling, lower-viscosity, dual-cure resin. This product uses traditional composite restoration techniques, such as acid etching with phosphoric acid, placement of a bonding agent, and final placement of the restorative component, which can be light- or dual-cured.
For surface restorations that require a core build-up, clinicians have their choice of materials. In cases where visual confirmation can ensure that no air pockets were created when the resin was placed, the author uses BISCO’s Core-Flo DC. For deeper restorations more prone to air pockets or where visual confirmation is not possible, such as over an endodontic access opening, cementing a post, and those that require a matrix band to create a proper form, Core-Flo DC Lite is an excellent solution when combined with BISCO’s Universal Primer™ dual-cure adhesive. The advantage of a dual-cure primer/bonding agent is that the adhesive will set when used with a dual- or self-cured restorative material.4
A patient presented with recurrent decay under an existing porcelain-fused-to-metal crown on tooth No. 3. The crown was originally placed in 1989. The crown, existing build-up material, and all decay were removed down to the level of the gutta-percha from the previous endodontic therapy (Figure 1). A retraction cord infiltrated with aluminum chloride was placed in the sulcus to control hemorrhage and allow for proper retraction of the gingival tissue to facilitate removal of the marginal decay and the final impression.
After removal of the existing decay and previous filling material, the tooth was sandblasted with 27-micron aluminum oxide to increase bond strength.5 The next step was etching the enamel with phosphoric acid. A selective-etch technique reduces dentinal sensitivity when the tooth is vital. A complete-etch technique can be used on non-vital teeth. BISCO’s Select HV® Etch was applied to the enamel surfaces for 15 seconds and then thoroughly rinsed. Removal of excess water was accomplished with 1 to 2 seconds of evaporation via high-speed suction, leaving the tooth slightly moist.
Application of the adhesive followed. In cases where light curing is unpredictable and incomplete, it is beneficial to use a dual-cure adhesive, such as Universal Primer, which comes in a 2-part system. In this case, Universal Primer was then applied in two separate coats with a microbrush, scrubbing the tooth preparation for 10 to 15 seconds per coat. No light curing was done between coats. Moderate to strong air drying with an air-water syringe for at least 10 seconds removed excess solvent. There should be no visible movement of the adhesive and the surface should have a uniform glossy appearance. Light curing the adhesive for 10 seconds is optional.
Core-Flo DC Lite was then injected into the deepest parts of the tooth overlaying the gutta-percha and filled about three quarters towards the occlusal surface. A brief 2- to 3-second cure was performed to help hold the existing resin in place, though this is not required. A final layer of Core-Flo DC Lite was placed (Figure 2) to bring the tooth prep to full contour (Figure 3). If the tooth had a post being placed, this material could serve as the cement for the post as well as the core material. The crown preparation was then completed, with the contouring of Core-Flo DC Lite with a diamond bur. The material cuts very smoothly.
A final impression was then taken and a provisional restoration was placed until the final crown was cemented. The crown was seated a few weeks later (Figure 4).
A patient presented to the office with the lingual cusp on tooth No. 13 completely fractured off from trauma, though the tooth remained vital (Figure 5). Although the patient was scheduled for a crown preparation, the remaining filling was lost during the interval between appointments. The tooth was prepared for the crown, and the clinician noticed the lingual fracture ended at the level of the bone. A crown placed at this level would have resulted in a biologic width invasion.6 A hard tissue laser, Waterlase MDX (Biolase, www.biolase.com), was utilized to remove the gingival tissue and underlying bone to gain a proper biologic width.7 No bleeding resulted and no sutures were required. The procedure to condition the tooth and apply the bonding agent was performed as listed in case 1. Special care was given to not desiccate the tooth after acid etching. The dentin was left moist and Universal Primer was the adhesive of choice to use prior to the build-up of the Core-Flo DC Lite. Core-Flo DC Lite was used to build up the tooth to help support the eventual crown (Figure 6). The tooth preparation was finalized and a final impression was taken for a lithium disilicate crown. The crown was seated a few weeks later (Figure 7).
There are a variety of resin core build-up materials to choose from when restoring a tooth. The lower viscosity of Core-Flo DC Lite works ideally in the cases discussed. The material was needed to flow into a deep preparation where margins were subgingival and hard to visualize. The material self-levels, leaves no voids, and is an excellent dentin replacement. In the author’s opinion, the flexural strength of up to 129 MPa and compressive strength up to 266 MPa helps ensure success in the restorative dental procedures that patients expect.
About the author
Fred H. Peck, DDS, AAACD
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