Polymer Preparation Instruments New Paradigm in Selective Dentin Removal

The purpose of dentistry is the ongoing development of the skills required to differentiate between diseased and healthy tooth structures. The armamentarium of dentistry includes the tools that are needed to remove decay and to restore the cleaned preparation1,2 (Figure 1). There have been many innovations over the past century that have facilitated this process: radiographs, low-speed and high-speed handpieces (first foot driven, then air driven, and now electrically powered) (Figure 2), improved lighting and magnification (Figure 3), and improved restorative materials, among many others. These innovations have made dental treatment better, faster, and easier for both the dentist and the patient, enhancing the overall level of dental health among the population in general and offering access to more individuals than ever before.

Figure 1. Cutting tools in dentistry: stainless steel, diamond, carbide, polymer. Figure 2. Electrically powered handpieces from KaVo and Sirona.
Figure 3. Magnification (Surgitel) and illumination (High Q).

However, one area has witnessed little development over the past century or so. The basic preparation (cutting) tool of the dentist is very similar to what it was generations ago. While the profession today has more bur shapes and sizes than previously—and a choice between stainless steel, carbide, and diamond abrasive surfaces—these instruments all function in the same manner: they are placed into direct contact with tooth structure, where the rotational speed and the abrasive surfaces of the bur indiscriminately remove tooth structure. While the dentist’s primary focus is the removal of carious dentin and enamel,3 traditional burs cannot differentiate between unhealthy and healthy structures. This means that in any preparation procedure, after sufficient enamel has been removed for access to the decay, traditional burs (stainless steel, carbide, and diamond) are likely to remove various amounts of perfectly healthy dentinal material. This inadvertent sacrifice of sound structures stands in the way of the profession achieving truly “conservative” dentistry wherein the preservation of healthy dentin is maximized.

Dentists have long recognized the tactile differences between decayed dentin (soft) and healthy dentin (hard). In fact, this is the single most common diagnostic tool that is employed by practitioners in the determination of which structures to remove. The presumption that healthy dentin is “harder” has been documented in extensive research.4,5 Because there is a difference in the hardness of healthy and unhealthy dentinal tissues, it would seem appropriate to use this qualitative difference both as a diagnostic and a treatment tool. An instrument that can selectively remove “soft” diseased dentin and yet leave “hard” sound dentin intact is a more conservative tool that combines on-site diagnosis and preparation into a single efficient step.

POLYMER PREPARATION INSTRUMENTS

Figure 4. SmartPrep instrument in a
sectioned tooth.

The first polymer preparation instrument to be introduced is the SmartPrep instrument (SS White Burs Inc), which is composed of a set of polymer instruments (Nos. 2, 4, and 6) that are used in the slow-speed handpiece in the same fashion as conventional round burs (Figure 4). The limited hardness of the polymer takes advantage of the dentin hardness differential, having been developed to be harder than “soft” decayed dentin, yet less hard than healthy dentin. Thus, it functions selectively to remove diseased tissue while leaving healthy dentin intact.6 The dentist can apply the SmartPrep instrument to the dentinal surface with confidence that only decayed tooth structure will be removed. This feature maximizes the conservation of healthy dentin and can virtually eliminate the risk of inadvertent carious pulp exposure.

One area of concern is the intermediate dentin (the areas that have been affected by the caries process, but are not infected). These areas of dentin are often discolored (another diagnostic parameter for diseased dentin), but are hard. There is ample evidence that these areas of discolored, affected dentin can be left in the tooth and will not compromise the tooth-restorative complex.7-9 Other studies indicate that bonding strength to affected dentin is not significantly reduced.10 Affected dentin can and should be left intact in the tooth. The SmartPrep instrument has been designed to be softer than affected dentin, and thus, it is a self-limiting tool that will not remove affected dentin.

While the vast majority of people understand the need for regular dental care and dental restorations, it is estimated that only approximately half the population actually visit dental offices at the recommended intervals, even when cost is not a factor. The most commonly cited reasons for this conscious neglect include fear of pain and fear of (anesthetic) injections. It is ironic that the agent of relief (the anesthetic injection) is sometimes more stressful

than the operative discomfort itself. Over the past 20 years, there have been numerous technique developments that have lessened or eliminated the causes underlying these attitudes. However, it is always incumbent on the profession to provide more comfort and encouragement to better dental health.

Operative sensitivity can occur during and after the tooth preparation process. One of the causes of this discomfort is thought to be the mechanical instrumentation and exposure of healthy dentinal tubules, altering the fluid permeability, and thus the pressure on the odontoblast within the tubule.11 This inadvertent manipulation of healthy tubules occurs where metal or diamond preparation instruments rapidly remove healthy dentin along with the decayed debris. This is why local dental anesthetic is such an important component of routine dental restorative treatment. Techniques that do not involve mechanical manipulation and/or exposure of the dentinal tubules are less likely to cause operative discomfort and thus less likely to require local anesthesia.12-15

When the polymer instrument contacts diseased dentin, the damaged dentin is abraded away. When this contact is with healthy dentin, it is the instrument surface that is selectively abraded rather than the healthy tooth. Thus, the self-limiting polymer is unlikely to mechanically expose dentinal tubules and unlikely to cause patient discomfort. In many cases, no local anesthesia is required for patient comfort. It is this factor that is most likely to capture the patient’s attention. The issue of enamel access to the decayed dentin is less of a problem; the microcrystalline structure of enamel does not have vital components that can cause discomfort and can therefore be instrumented without any anesthetic. The decreased need for local anesthetic also permits more multi-quadrant appointments.

TECHNIQUE

Figure 5. Decay is visible on the distal.

Prior to using polymer preparation instruments, the decayed area is identified visually, tactilely, and/or radiographically (Figure 5). In the case example presented, the distal surface of the lower left first bicuspid exhibits decay interproximally. The patient is advised that the SmartPrep technique will be utilized, and at least initially no local anesthetic is recommended. There is a standing order throughout the entire procedure that, if at any time the patient requests local anesthetic, it will be administered immediately.

Figure 6. Enamel access using a Fissurotomy bur.

Access is gained through the intact enamel using a Fissurotomy bur (SS White Burs Inc) (Figure 6). Because the length of the Fissurotomy bur assists in limiting its penetration to the depth of the enamel, it is unlikely that this step will cause any patient discomfort. In some cases, such as this example, no rubber dam is used. While the advantages and benefits of rubber dam isolation are universally recognized and recommended, the prospect of placing a rubber dam clamp on or adjacent to unanesthetized gingiva is less than pleasant. For small- to medium-size restorations, careful cotton roll isolation and efficient 4-handed dentistry may be just as effective as rubber dam isolation.16 The SmartPrep instrument cannot be used to remove enamel. Because the enamel is much harder, the instrument will simply lose its edges.

Figure 7. The conservative access opening for SmartPrep preparation.

The access opening must be large enough to permit the entry of the appropriate SmartPrep instrument (Figure 7). Because the proposed restoration will be a bonded composite resin, the preparation involves only the decayed portions of the tooth. There is no extension for retention (not necessary), and no extension for prevention (as with amalgam restorations). The access opening must also provide visibility to ensure that no decay has been left in the tooth.

Figure 8. SmartPrep No. 4 removing decay without the need for local anesthetic.

The SmartPrep instrument is used to remove any remaining dentinal decay (Figure 8). While the practitioner’s visual access into the preparation is severely limited in this case, there is no question that only decayed dentin is being removed from the depths of the cavity. The self-limiting hardness of the SmartPrep instrument can cut neither enamel nor healthy or affected dentin.

Figure 9. The completed preparation; all decay removed.

The cavity preparation is complete (Figure 9). The remaining dentin is checked for hardness with the explorer or spoon excavator. The patient is still in total comfort.

Figure 10. Omnimatrix and Flexi Wedge.

The preparation is isolated with a disposable matrix (Omnimatrix, Ultradent Products Inc), which in turn is stabilized with a Flexi Wedge (Common Sense Dental Products) (Figure 10). The preparation is then rinsed and the excess water is removed. The Flexi Wedge is designed to minimize interproximal gingival composite overhangs.

Figure 11. iBond seventh-generation adhesive application.

The 1-bottle, 1-step, seventh-generation adhesive iBond (Heraeus Kulzer Inc) is applied to the preparation, agitated on the preparation surface as directed, and then light cured for 10 seconds (Figure 11). Note that there are no separate etching, conditioning, priming, or desensitizing steps. Seventh-generation adhesives incorporate all the necessary chemistry and technique into a single application of one adhesive. iBond is not moisture sensitive; the tooth surface may be dry, moist, or even wet, as long as there is no puddling of the water.

Figure 12. Shaping Venus microhybrid with
the “duckhead.”

A shade-matched composite is applied into the adhesive-covered preparation. Venus (Heraeus Kulzer Inc) is a color-adaptive microhybrid composite resin that is available in a multitude of shades and comes with a cookbook-style 2-component shade guide. (Select the appropriate shade, and the cookbook tells you which colors to use to arrive at that precise result.) The surface layers are shaped to anatomy with the “duckhead” instrument from Hu-Friedy in order to minimize the time and effort required for final polishing after polymerization (Figure 12). The composite is light cured.

Figure 13. The complete restoration.

The completed restoration is functionally designed and aesthetically acceptable (Figure 13). The entire process was accomplished without the need for local anesthesia and with confidence that all the decay—and only the decay—was removed from within the cavity preparation.

CONCLUSION

The use of a selective dentin removal technique as described in this article brings new levels of comfort to the patient and confidence to the dentist. The SmartPrep instrument is both a diagnostic tool and an operative tool and avoids the problem of indiscriminant removal of healthy dentin along with decayed tooth structure.


References

1. Fusayma T. Two layers of carious dentin; diagnosis and treatment. Oper Dent. 1979;4:63-70.

2. Beetly LA, Yip HK, Steventson AG. Chemomechanical caries removal; a review of the techniques and latest developments. Br Dent J. 2000;188:427-430.

3. Roberson TM, Lundeen TF, Cariology: The lesion, etiology, prevention and control. In: Roberson TM, Heymann HO, Swift EJ (eds). Sturdevant’s Art and Science of Operative Dentistry. 4th ed. St. Louis, Mo: Mosby; 2002:99.

4. Hosoya Y, Marshall SJ, Watanabc LG, et al. Microhardness of carious deciduous dentin. Oper Dent. 2000;25:81-89.

5. Meredith N, Sherriff DJ, Swanson SAV. Measurment of the microhardness and Youngs’s modulus of human enamel and dentin using an indentation technique. Arch Oral Biol. 1996;41:539-545.

6. Gomez M, Silva NRFA, Gonzalez C, Thompson VP. I.A.D.R; San Anton 0226; 2003.

7. Fusayama T, Okuse K, Hosada H. Relationship between hardness, discoloration and microbial invasion in carious dentin. J Dent Res. 1966;45:1033-1046.

8. Terashima S, Watanabe M, Kurosaki N, et al. Hardness of dentin remaining after clinical excavation of soft dentin. Japanese J Conserv Dent. 1969;11:115-120.

9. Fusayama T, Okuse K, Hosada H. Relationship between hardness, discoloration and microbial invasion in carious dentin. J Dent Res. 1966;45:1033-1046.

10. Silva NRFA, Thompson VP. I.A.D.R.; San Anton 0227; 2003.

11. Yamada T, Nakamura K, Iwaku M, et al. The extent of the odontoblast process in normal and carious human dentin. J Dent Res. 1983;62:798-802.

12. Fusayama T. A Simple Pain-Free Adhesive Restorative System By Minimal Reduction and Total Etching. Tokyo, Japan: Ishiyaku EuroAmerica, Inc; 1993:2, 56.

13. Ericson D, Zimmerman M, Raber H, et al. Clinical evaluation of efficancy and safety of a new method for chemo-mechanical removal of caries. Caries Res. 1999;33:171-177.

14. Kutsch VK, Everett M. Process for the removal of soft tooth decay using a unique abrasive fluid stream. United States Patent 5,601,430. United Stated Patent and Trademark Office, issued February 11,1997.

15. Anusavice KJ, Kincheloe JE. Comparision of pain associated with mechanical and chemomechanical removal of caries. J Dent Res. 1987;66:1680-1683.

16. Knight GT, Barghi N, Conn LJ. I.A.D.R. Abstract No. 234, 1993.



Dr. Freedman is a past president of the American Academy of Cosmetic Dentistry and currently associate director of the Esthetic Dental Education Center at the State University of New York at Buffalo. He is also director of postgraduate programs in aesthetic dentistry at the University of Florida, University of California at San Francisco, University of Missouri (Kansas City), Eastman Dental Center (Rochester), university programs in Seoul, South Korea; London, England; and Schaan, Liechtenstein, and scientific chairman of the World Aesthetic Congress (London, England). Dr. Freedman is the author of 7 textbooks, more than 170 dental articles, and numerous CDs and video and audiotapes. A diplomate of the American Board of Aesthetic Dentistry, he lectures internationally on dental aesthetics, dental technology, and photography. Dr. Freedman maintains a private practice limited to aesthetic dentistry in Toronto, Canada, and can be reached at (905) 513-9191.

Dr. Goldstep is on faculty at the postgraduate programs in aesthetic dentistry at SUNY Buffalo, New York and the University of Florida. An ADA Seminar Series featured speaker, she is a fellow of the Academy of Dentistry International and the Academy of Dental-Facial Esthetics. Dr Goldstep has published more than 15 articles and textbook sections and has lectured nationally and internationally on dental health issues and office design. Dr. Goldstep is a consultant to a number of dental companies and maintains a private practice in Toronto, Canada. She can be reached at (905) 513-9191.

Disclosure: Dr. Freedman serves as a consultant for a number of dental manufactures and retailers, including some/or all of the
companies mentioned in this article.

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