Caries Removal Using Polymer Burs
Dentin-safe, self-limiting, medical-grade burs can help preserve healthy tissue during caries excavation.
Howard E. Strassler, DMD
The diagnosis and treatment of caries has been changing in recent years. The accurate diagnosis of the extent of pit-and-fissure caries has become more difficult.1,2 The increased use of fluoride has led to a change in the traditional characteristics of demineralization and the visual appearance of enamel opacities in the initiating lesion. In some cases, the dentin is carious without the appearance of caries in the adjacent pit or fissure. This presence of caries within the dentin adjacent to pits and fissures that appear sound has been referred to as “hidden caries,” “fluoride syndrome,” 3 “covert caries,” 4 and “occult caries.” 5 These lesions tend to be minimal in size in the enamel surface but, within the dentin, they spread along the dentino-enamel junction as a larger, more invasive lesion. One of the major goals of conservative dentistry is to develop a method for removing caries-infected dentin while preserving caries-unaffected dentin.
Over the years, several different approaches to removing these larger carious lesions while attempting to preserve sound dentin have been described. Traditionally, caries has been removed with sharp caries-excavator hand instruments and round carbide metal burs in a slow-speed handpiece.6 The drawback to using round carbide metal burs when removing bulk caries is the removal of sound tooth structure at the same time.7 Also, using these burs could lead to potential adverse effects to the pulp and there is a need for local anesthesia.8,9 A chemo-mechanical approach to caries removal has also been described. A solution is placed on the caries to soften it and allow for scraping the caries from the cavity preparation.9-11 These solutions, while effective, only softened carious dentin and increased the time of tooth preparation significantly; in some cases, special devices for their use were required.
In recent years, burs made from polymers and ceramics have been introduced and described as “dentin safe,” meaning that when removing carious dentin, they will be self-limiting when the bur reaches sound, healthy dentin. Concerns have been expressed that ceramic burs described as being “dentin safe” are as invasive as metal burs in caries removal and will remove healthy dentin if care is not taken.12 The use of polymer burs have been shown to be effective in caries removal.13-19 These reports and studies also demonstrated that polymer burs preserved healthy dentin.
Evaluation of Rotary Burs to Protect Healthy Dentin
How safe is safe when it comes to sound dentin and burs? In order to evaluate the “dentin safe” claims of polymer and ceramic burs, a research protocol to compare these burs was done. The goal of this study19 was to evaluate whether a new generation of caries removal burs (ceramic and polymer) is safe to sound, healthy dentin. Three same-sized round burs (#6) recommended for caries removal were evaluated: carbide metal, ceramic, and polymer (Figure 1). Extracted third molars were mounted in acrylic resin and sectioned with a saw to expose dentin. The dentin was sanded with 600-grit sandpaper. Five burs of each type were used to prepare sound dentin using a electric handpiece running at 4,000 rpm with a 50% torque for 2 seconds with the carbide metal bur and ceramic bur and 10 seconds with the polymer bur. Replicas were made of the prepared surfaces using a regular body PVS. Replicas were sectioned in half and measured for depth of dentin penetration and preparation. Depth of preparation was measured in millimeters using a digital micrometer.
Photographs of the specimens revealed significant removal of dentin with the carbide metal bur and ceramic bur, when compared to no sound dentin removal with the polymer bur (Figure 2, Figure 3, Figure 4, Figure 5, Figure 6, Figure 7). The depth of penetration of the sound dentin (in mm) was recorded with each type of bur. Microscopic evaluation at 8X with a stereomicroscope of all three burs demonstrated that after the use cycle, the bur integrity was equivalent from start to finish.
A major concern of clinicians when preparing teeth with carbide metal burs with deep carious lesions is the potential for a carious or mechanical pulpal exposure (Figure 8 and Figure 9). For teeth that are planned for laboratory-fabricated restorations, it is usually not recommended that indirect pulp-capping procedures be done. Both direct and indirect pulp capping have demonstrated some clinical success.20-22 It has been shown that the use of a polymer bur for caries removal provides a safety net to not overprepare the dentin when removing caries.18,22 The first-generation polymer bur SMARTPREP (SS White Burs, www.sswhiteburs.com) provided the first dentin-safe rotary bur. Unfortunately, the plastic used was not durable when run at rotary speeds above 1,000 rpm. The introduction of SmartBur II provides significant changes in design and materials used in the fabrication of the bur allowing for use at 4,000 rpm without damage to the bur’s integrity. The cutting surface of the bur is made from a medical-grade polymer that has a hardness less than that of healthy enamel and dentin but harder than carious dentin. As shown in the research study, this unique aspect of the bur allows it to be used to selectively remove carious tooth structure without unnecessarily removing or damaging healthy tooth structure. In some cases, caries can be removed without the need for local anesthesia.18 During cavity preparation, a polymer bur can be used to safely and effectively remove carious dentin (Figure 10 and Figure 11) without removing sound, healthy dentin.
A unique, medical-grade polymer bur, SmartBur II is a self-limiting caries removal bur for use in a slow-speed handpiece operating at up to 4,000 rpm. Research demonstrates that when compared to a carbide metal bur and ceramic bur, the polymer bur is truly dentin safe and will not cut sound, healthy dentin. Using the SmartBur II allows for preservation of sound, healthy tooth structure and can protect against unnecessary pulp exposures. In this author’s experience, some patients have not had the need for local anesthesia for caries removal in Class I and Class V preparations.
Dr. Strassler has received grant research support from SS White, and is an Advisory Board Member for the company.
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About the Author
Howard E. Strassler, DMD
Professor, Division of Operative Dentistry
Department of Endodontics, Prosthodontics, and Operative Dentistry
University of Maryland Dental School