Self-Etching Adhesives in the World of DBS
Dentists have many factors to consider when evaluating dentinal bonding systems.
By David S. Alleman, DDS
Clinicians who understand the proper use of self-etching dentinal bonding systems (DBS) in conjunction with stress-reducing restorative techniques have experienced success with the systems for more than 10 years (Figure 1). The same can be said for total-etching DBS. Newer, “simplified” self-etch and total-etch systems have fewer steps, but do not necessarily perform better (Figure 2). Therefore, individual dentists must evaluate their choices of DBS based on knowledge of the system’s respective strengths and weaknesses. The benefits of properly using DBS are the conservation of tooth structure and the ability to maintain pulpal vitality. Therefore, it is in patients’ best interest that dentists become experts in the proper use of the DBS.
Dozens of companies have brought hundreds of systems to market since the introduction of the CLEARFIL® (Kuraray Co Ltd, www.kuraraydental.com) total-etch dentinal bonding agent in 1978. Self-etching dentinal bonding systems have been available since 1993. Today, a dentist can order any one of 64 different DBS from 19 different manufacturers. How can a dentist evaluate the different categories of DBS, and the individual systems within each category? Understanding the worlds of scientific dental research, competitive commercial manufacturing, and post-doctoral continuing education can help a dentist understand which system or systems work best for his or her particular type of dentistry.
There are six major categories of DBS:
1. Etch-and-rinse three-step systems
2. Etch-and-rinse two-step systems
3. Self-etch two-step systems
4. Self-etch one-step systems
5. Non-resin-modified glass-ionomer systems
6. Resin-modified glass-ionomer systems
Systems in categories 2, 4, and 6 are considered “simplified” because of the decreased number of steps that the dentist performs. Of the 64 DBS referred to in the last paragraph, 22 are classified in the non-simplified categories 1, 3, and 5. The other 42 fall under the “simplified” categories. Of those 42, 17 are self-etch one-step systems. In testing, these self-etching one-step systems were found to have the lowest bond strengths and are the most prone to long-term degradation.1
Some dentists may buy low-performing systems out of concern about lower bond strengths to enamel. Bonding to unprepared enamel requires a lower pH conditioning to maximize the bond. These simplified systems etch the enamel deeper, but the dentinal bonding shortcomings of these systems far outweigh that benefit. One DBS, Prelude (Danville Materials, www.danvillematerials.com) has a two-step self-etch mode (for preparations with mostly dentin), and a two-step total-etch mode (for preparations mostly in enamel). This is a very good strategy.
Properly used in conjunction with stress-reducing techniques, DBS can facilitate long-term success for adhesive restorations. Long-term clinical success is best demonstrated in controlled clinical trials that standardize the materials used, and the protocols by which the materials are applied. These controlled trials are logistically and economically burdensome, and are rarely conducted.
A few individual dentists or groups of dentists have conducted practice-based research networks (PBRN) that test long-term adhesive restorations. PBRN clinical trials conducted by Dr. Simone Deliperi in Sardinia, Italy, are now into their eighth year. Dr. Niek Opdam just published a 12-year PBRN retrospective study that shows better survival rates for DBS-retained composites than with mechanically retained amalgams.2 These trials are proof that large-sized adhesive restorations are very successful in the long-term using adhesive retention instead of mechanical retention.
Short-term (up to 1 year) in vitro and in vivo experiments also provide a scientific basis to clinical protocols. Understanding of these experiments comes from academic research centers and private manufacturers. Products tested in university settings usually come from private companies who hold the proprietary and/or patented formulas of the DBS. Different methods are used to perform tests on the DBS. Each testing method involves different equipment costs and levels of technical expertise.
Every manufacturer hopes that their proprietary DBS will “beat the competition,” allowing salespeople to market their product as being better than competing products. The integrity of the academic research center is proven through consistent testing and unbiased analysis that usually comes in the form of peer-reviewed published literature. Each manufacturer also does its own testing, but usually not with the sophistication and diversity of major research centers. The greater number and variety of tests creates a better scientific database. This volume, variety, and independence cannot come from one laboratory. Because of this limitation, research from manufacturers is usually not published in the most important peer-reviewed journals.
There are dozens of universities around the world—University of Iowa, Tokyo Medical and Dental University, ACTA at the University of Amsterdam, for example—that are doing good and important research on dentinal bonding. There are also a number of journals, such as the Journal of Dental Research, the American Journal of Dentistry, and the Journal of Esthetic and Restorative Dentistry, that report the results of these researchers. The information a dentist uses to evaluate dentinal bonding systems should come from such respected sources. Dental professionals pursuing continuing education opportunities should also consider whether an educator is affiliated with any of these sources of scientific information. Of course, commercial dental salespeople can also access scientific data to help the dentist make a decision on a DBS.
To answer questions about the success and usefulness of self-etching DBS, dentists have to either read published literature or receive information from another source. Dr. Jan De Munck at the Catholic University in Leuven, Belgium, for example, has done original testing of DBS and has performed an extensive literature review. He has evaluated more than 1,000 studies published between 2004 and 2009. Dr. De Munck has concluded that, “simplified bonding procedures do not necessarily improve bonding performance, especially in the long-term.”1
Especially disturbing is the fact that many of the simplified DBS tests had a high number of pre-testing failures (PTFs), indicating the loss of all bond strength before the sample is even tested. The problems with these systems are related to solvent types used (acetone is more technique-sensitive than ethanol or water),3 the amount of solvents, and the difficulty of removing the solvents before photo-initiation of the adhesive monomers. In 2007, a German study concluded that, “evaporation of primer solvent remains a critical step ... and consequently has to be carried out thoroughly.”4
Of the non-simplified DBS systems, the three-step total-etch systems and the two-step self-etch systems are, on average, 2 to 3 times stronger than glass-ionomer adhesives when submitted to micro-tensile bond strength testing (mTBS) and micro-shear fatigue resistance testing (mSFR)5. This finding is attributed to the low cohesive strength of the glass-ionomer material itself, which is due to the material failing internally rather than debonding from the tooth surface.6
For this reason, the glass-ionomer DBS is best-suited for short-term adhesive applications such as pedodontic restoration, or as an atraumatic restorative treatment (ART) in less than ideal socio-economic circumstances. In permanent teeth, glass-ionomer dentinal bonding systems have been shown to have a nearly 20% higher failure rate over the course of a 9-year trial.7 The two systems judged to be the “gold standards” were the total-etch three-step system OptiBond FL® (Kerr Corporation, www.kerrdental.com)8 and the self-etch two-step system CLEARFIL® SE BOND (Kuraray Co, Ltd).9 In the total-etch two- step category, PQ1 (Ultradent Products Inc., www.ultradent.com) has also tested well.10 A desire to understand the stability of the DBS has led researchers to examine the role of the endogenous enzymes called matrix metalloproteinases (MMP). The application of chlorhexidine to deactivate these enzymes has been proven to keep the dentin bonds from degrading during the first year.11
One product that has proven to be stable is a modified version of CLEARFIL SE Bond (Kuraray Co Ltd). Originally marketed under the name Protect Bond, it is now sold under the name CLEARFIL® SE PROTECT. The proprietary monomer MDPB is bactericidal during placement, and is bacteriostatic in service. An added benefit is that the pyridinium bromide molecule chemically promotes a cross linkage of collagen fibrils in and under the hybrid layer. This creates an acid base resistant zone (ABRZ) 2 µm thick, termed “super dentin” by Junji Tagami.12 Other mild self-etch DBS with pH between 1.9 and 2.7 have been shown to create “super dentin.” Total-etch systems and low pH self-etch systems (pH < 1) do not form this ABRZ. It has also been shown that these mild self-etching DBS form ionic bonds with the hydroxyapatite of dentin.13
The thickness of the DBS adhesive layer is important to high mTBS and the ability to secure the seal on the dentin.14 As such, placing a 0.5-mm “resin coating” of flowable composite over DBS that have thin (< 40 µm) adhesive thicknesses is recommended.
This “elastic cavity wall concept”15 also helps to counteract the stress of polymerization shrinkage in higher C-factor cavities. The C-factor is the ratio of bonded to unbonded surfaces. If the C-factor is increased, all DBS have lower mTBS immediately. These weakened bonds also lose strength during function. In contrast, bonds developed under low C-factor conditions resist fatigue during function.16 One experiment in high C-factor preparations compared the gold standard total-etch three-step DBS OptiBond FL (Kerr), the two-step mild self-etching CLEARFIL Protect Bond and the simplified one-step self-etching iBond® (Heraeus, www.heraeus-ibond.com). After a year in water storage and 20,000 thermocycles, the two gold-standard DBS (with thicker adhesive layers not corrupted by excess solvents) had double the mTBS of the simplified DBS without “resin coating.” The specimens from the simplified one-step DBS also had 50% PTF with complete loss of mTBS.8
The performance of any DBS will also be affected by the amount and type of decay (outer/infected or inner/affected) left in the preparation17,18 and the depths of the preparation.19,20 Stress reduction of the layers on top of the DBS is absolutely necessary to maximize the strength of the adhesive bonds. Selection of an indirect or semi-direct restoration instead of a non-stress–reduced direct composite is the most important decision to ensure a sealed restoration.21
The immediate dentin sealing (IDS) technique greatly increases the bond strength in these sealed restorations.22,23 If the decision is made to use a direct composite technique, high bond strengths can be achieved with a stress-reduced direct composite (SRDC) technique using multiple horizontal layers,24 slow start/pulse-activated light polymerization protocols,25 and fiber net placements.26 These stress-reducing techniques allow the bonds to mature and attain maximum strength. Deliperi reported no failure on direct anterior restorations after 5 years of clinical service.27 He reported the same result on direct cusp-replacing posterior restorations.28 Both anterior and posterior restorations were performed on structurally compromised teeth.
Using these techniques have allowed the dentists who use them to see long-term success with self-etching DBS in all sizes of restorations. By being able to mimic the tensile strength of the DEJ region (around 45 MPa), new restorative principals have evolved that have eliminated the need for mechanical retention or resistance forms like boxes, grooves, slots, pins, and posts.29 Many progressive dentists have used these principles over the last decade to eliminate the need for new full-coverage crowns in their practices. Low-stressed and highly bonded restorations mimic the natural micro-movements of the natural tooth when chewing. They also can avoid catastrophic failures from masticatory crushing forces. These restorations remain uninfected with no developing cracks or gaps into dentin, which would cause symptoms of pain and sensitivity. This kind of dentistry is referred to as “biomimetic” because it is “lifelike.”30 Self-etching DBS can be a part of successful biomimetic dentistry.
References
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2. Opdam NJ, Bronkhorst EM, Loomans BA, et al. 12-year survival of composite vs. amalgam restorations. J Dent Res. 2010;89(10):1063-1067.
3. Armstrong, Jessop JL, Winn E, et al. Effects of polar solvents and adhesive resin on the denaturation temperatures of demineralised dentin. J Dent. 2008;36:8-14.
4. Balkenhol M, Huang J, Wostmann B, et al. Influence of solvent type in experimental dentin primer on the marginal adaptation of Class V restorations. J Dent. 2007;35:836-844.
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9. De Munck. An in vitro and in vivo study on the durability of biomaterial-tooth bonds. PhD dissertation. 2004; Catholic University, Leuven, Belgium.
10. Purk JH, Healy M, Dusevich V, et al. In vitro microtensile bond strength of four adhesives tested at the gingival and pulpal walls of Class II restorations. J Am Dent Assoc. 2006;137:1414-1418.
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18. Say EC, Nakajima M, Senawongse P, et al. Bonding to sound vs caries-affected dentin using photo- and dual-cure adhesives. Oper Dent. 2005;30(1):90-98.
19. Yoshikawa T, Sano H, Burrow MF, et al. Effects of dentin depth and cavity configuration on bond strength. J Dent Res. 1999;78(4):898-905.
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21. Iida K. Interfacial gaps following ceramic inlay cementation vs direct composites. Oper Dent. 2003;12(8):727-732.
22. Magne P, Kim TH, Cascione D, et al. Immediate dentin sealing improves bond strength of indirect restorations. J Prosthet Dent. 2005; 94:511-519.
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27. Deliperi S. Clinical evaluation of non-vital tooth whitening and composite resin restorations: five-year results. Eur J Esthet Dent. 2008; 3:148-159.
28 Deliperi S. Four-year clinical evaluation of direct cusp-replacing composite resin restorations. 42nd CED/IADR meeting (Thessaloniki, Greece; September 26-29, 2007).
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About the Author
David S. Alleman, DDS
Co-Director
Alleman-Deliperi Centers for Biomimetic Dentistry
South Jordan, Utah & Sardinia, Italy
