Adhesives: Changing Through the Generations

In most fields of modern technology, the latest version of a product is usually an improvement over the previous ones. For example, smartphones, hybrid cars, the Blu-Ray disk, and high-definition television represented significant advancements over their predecessors. So why is this continual advancement apparently not the case when it comes to dental adhesives? Over the last 25 years, dentistry has seen significant generational changes, new materials categories, new chemistries, and new clinical protocols with dental adhesives—much of it driven by an effort to simplify or to shorten the bonding procedure. However, not all of the newer materials have necessarily offered improvements to the patient or for the long-term viability/prognosis of the restorations placed. How does the clinician make a rational choice from among more than 65 adhesives still on the market today? Among the so-called fourth-, fifth-, sixth-, and seventh-generation adhesives—alternatively known as the “etch-and-rinse” and “self-etch bonding agents”—which system gives the most consistent, long-term clinical results and has the longest viable bond strength over time? Which system resists oral degradation and allows for the integration of new methodology to treat the hybrid layer for long-term stability while addressing the inevitability of the presence of bacteria and composite polymerization and functional stress?

The current resin-dentin bonding mechanism, whether using etch-and-rinse or self-etch systems, relies on the formation of a hybridized layer that couples adhesives/resin-composites with the underlying mineralized dentin. With the exception of resin tags, which extend down into the dentinal tubules, only the collagen fibers offer physical continuity between the hybrid layer¹ (as it is known after being infiltrated with resin) and the underlying mineralized dentin. The collagen fibers represent millions of fibril anchors, which emerge from the underlying mineralized dentin matrix into the demineralized layer.

In an excellent overview of factors that affect the bond strength of bonding agents, Powers et al² point out that the type of substrate (ie, superficial dentin, deep dentin, permanent/primary dentition, carious dentin), phosphoric acid/acidic primers, preparation by air abrasion and laser, moisture, contaminants, desensitizing agents, and self-cured/light-cured restorative materials all affect the bond strength; bond strength is reduced by more than 50% when bonding conditions are not ideal. Further, when lasers are used to prepare hard tissues, studies show that bonding to these surfaces may be more problematic than bonding to conventionally bur-prepared preparations.³ Rushing to complete such procedures by reducing the priming time from 20 to 5 seconds can cause a 17% reduction in mean bond strength.⁴ In contrast, using a 20-second application time to agitate a self-etch adhesive significantly improves the shear bond strength to dentin.⁵ In addition to agitation, rather than applying a single coat of adhesive resin on dentin, up to four additional coatings increase the bond strength and decrease nanoleakage.⁶ Multiple research reports attest to the existence of material incompatibilities that depend on formulation, and that bond strengths can be reduced by 45% to 90% or more when incompatible combinations are applied clinically.^7-9 Acetone-based adhesives show a high degree of technique sensitivity,¹⁰ and over- or under-drying the acid-etched dentin compromises the bond.¹¹ Simplification of the bonding procedure does not necessarily lead to improved bonding performance, especially in the long term.¹² Alex³ perhaps has stated it best: “The bottom line is, it is incumbent on every dentist to learn about their specific adhesive system, its idiosyncrasies, its strengths and weaknesses, and how to maximize its performance.”

Practitioners and their teams should be aware not only of the immediate bond strengths—whether shear or tensile (the immediate configuration factor [C-factor] polymerization shrinkage stress is about 24 MPa in a Class I cavity preparation)¹³ but also, the long-term performance or longevity (patency) of their bonding agent in actual clinical performance.¹⁴ Much of the bond testing has been done in a laboratory under ideal controlled conditions, which may not be possible to replicate in a clinical environment, and results may vary depending on the testing methods and devices used.¹⁵ Some studies test immediate or 24-hour bond strength only on dentin just below the enamel surface, where bonding is easiest and strongest; and most of these studies have been done in vitro on human or bovine teeth, without positive fluid flow or the positive pressure that exists clinically—both of which can drastically decrease long-term performance. A short, simplified overview of the systems and their clinical behavior follows.

Fourth-Generation Adhesives

Compared to current adhesives or bonding agents, those still considered to be the “gold standard” in long-term durability are fourth-generation adhesives (etch-rinse-prime-adhesive resin) or multi-bottle systems (eg, 3M™ ESPE™ Scotchbond™ MP Multi-Purpose Plus, 3M ESPE, www.3mespe.com; ALL-BOND 2® and ALL-BOND 3®, Bisco, Inc., www.bisco.com; Perma Quick, Ultradent Products, Inc., www.ultradent.com; and OptiBond FL®, Kerr Corporation, www.kerrdental.com).^16,17 These etch-and-rinse materials still provide the deepest, strongest, most predictable, and long-term bond to enamel.¹⁸ This strong layer resists microleakage and protects the dentin bond from water degradation, which may contribute to better long-term clinical performance.^19-23 Arrais²⁴ has reported that these three-step adhesives also form the thickest hybrid layer, followed by one-bottle adhesives, with the self-etching adhesives forming the thinnest hybrid layers. It must be noted that strict adherence to etching times is critical, as prolonged phosphoric acid-etching can form a deep demineralized dentin zone that may not be fully impregnated by the primer and adhesive, resulting in low bond strength.²⁵ These products, which bond well to dentinal substrates, have lost some of their popularity due to the fact that they are multi-bottle, multi-step systems, which require etch, rinse, and application of hydrophilic primers followed by a hydrophobic adhesive layer. As such, these systems can be very technique-sensitive, if the sequencing and timing is not exactly adhered to, with some having complicated instructions on how to bond to tooth structure and other dental materials. The so-called fourth-generation bonding agents have the major benefit of being effectively used with self-cure, dual-cure, and light-cured composites as well as indirect restorations without concern. Representative bonding strengths for products in this category are: OptiBond FL, 39 MPa to dentin,²⁶ and Scotchbond MP, 45.6 MPa to dentin.¹⁹

Fifth-Generation Adhesives

Fifth-generation adhesives (etch-and-rinse plus [primer and bond]) or the single-bottle systems, such as MPa™ (CLINICIAN’S CHOICE®, www.clinicianschoice.com); Sealbond Ultima (RTD, Clinical Research Dental, www.clinicalresearchdental.com); OptiBond® Solo Plus (Kerr); Adper™ Single Bond Plus (3M ESPE); Prime & Bond® NT™ (DENTSPLY Caulk, www.caulk.com); PQ1 and Peak™ (Ultradent Products); ExciTE® (Vivadent, www.ivoclarvivadent.com); and One Step Plus and ACE® ALL-BOND TE™ (Bisco), contain primers and adhesive in a single bottle. This simplifies the bonding technique by eliminating some of the variables regarding the number of bottles and steps required. This single-bottle, etch-and-rinse adhesive type shows the same effectiveness as the fourth-generation systems in terms of microleakage,²⁷ and shows good dentin bond strengths with excellent marginal seal in enamel.^28-30 However, not all fifth-generation adhesives are compatible with dual- and self-cure composites or core materials. The lower pH of the oxygen-inhibited layer, or the acidic monomers in some simplified products, are too acidic and thereby de-activate the tertiary amine in chemical-cured composites. This results in no bonding, or weak bonding, with a material such as Prime & Bond NT in its light-cured version showing a bond strength of 0 MPa.³¹ Some adhesive systems such as OptiBond Solo Plus require a dual-cure activator, which is a resin-free benzene sulphinic-acid/sodium salt solution, which will raise the acidic pH of the oxygen-inhibited layer in order to bond to self-cured/dual-cured products. However, this additional step lowers bond strengths because of the dilution of the adhesive and the inherent permeability of the polymerized adhesive.³² Other products, such as MPa, Sealbond Ultima, and One Step Plus, do not require the use of a dual-cure activator. With a self-cure composite, One Step Plus shows bond strength of 21.4 MPa³³ in one study and 19 MPa in another.³⁴ In the later study, MPa showed a bond strength of 18.5 MPa to the self- cure composite; however, when the oxygen-inhibited layer was removed with alcohol, the bond strength more than doubled to 38.9 MPa to the level obtained using light-cured composite.³⁴

The solvents in bonding agents can be either ethanol-based, a nonvolatile solvent, or acetone-based. Products such as Sealbond Ultima and One Step Plus contain acetone, a very volatile solvent that should never be pre-dispensed into a dappen dish before the actual clinical bonding procedure, because the evaporation of the solvent will drastically reduce the patency of the bonding agent. Products that use ethanol or acetone need the proper amount of moisture (a moist bonding protocol), to prevent the collapse of the exposed collagen network.³⁵ The amount of impregnation of the hybrid layer can be reduced by 50% if the dentin is over dried.³⁶ Ethanol-based adhesives contained in products such as MPa™, Peak™, and OptiBond Solo Plus generally are more forgiving in clinical application and show the highest microtensile bond strengths.^35,37,38 It must be noted here that the 3 to 5 seconds recommended by some manufacturers for the evaporation of solvents is generally not enough to remove even half of the solvent, and therefore extension of this time is recommended.³⁹

The clinician also needs to know whether they are using a filled or unfilled adhesive, as the inclusion of fillers changes the viscosity and thickness of the applied layer. As well, evidence in the literature supports the concept that filled resins provide stress relief at the tooth–restoration interface.⁴⁰ Not all fifth-generation adhesives are the same in regards to the number of applications (unfilled need more applications), so it is critical to follow the manufacturer’s directions. Some products, such as One Step Plus and Adper Single Bond Plus, require two coats of the adhesive, while others like MPa™ and PQ1 require only one.⁴¹ Of course a single coat saves material and time, because less of each is required for bonding the restoration. Representative dentin bond strengths reported in this category are 42 MPa to dentin for Adper Single Bond Plus²⁵ and 41 MPa for MPa™.³⁴

Postoperative sensitivity can be induced with the etch-and-rinse technique when exacting protocols are not followed. This is more prevalent in deeper dentin preparations and in high C-factor cavity preparations.⁴² Simplification by combining the primer and adhesive into one bottle, which also applies to the so-called seventh-generation or self-etch all-in-one adhesives, increases the hydrophilicity and permeability of the bond, making them more likely to undergo hydrolysis. This is especially true for the unfilled bonding agents, as they create a thinner hybrid layer.⁴³

Sixth-Generation Adhesives

The self-etch systems, or sixth-generation adhesives, are classified into two types. Type I adhesives, which are self-etch priming systems such as Clearfil™ SE Bond (Kuraray America, Inc. Dental, www.kuraraydental.com), Prelude SE (Danville Materials), and Ultradent Peak™ SE (Ultradent Products Inc.), use a self-etching primer followed by the application of an adhesive. These systems are gaining in popularity due to the fact they are not as clinically technique-sensitive, and are easy to use,⁴⁴ with less reported post-operative sensitivity. However, controlled clinical studies show no difference in postoperative sensitivity as compared with etch-and-rinse systems when proper clinical protocol is used.^45,46

With most of the self-etch systems, the clinician may sacrifice marginal seal and longevity.^47,48 In order for a self-etch system to provide a good enamel marginal seal, the pH must be lower than 1.5 to effectively condition uncut enamel, and prevent marginal leakage; however, some of these products are mildly acidic, having a pH as high as 3.3. The research literature is replete with studies showing that these self-etch adhesives have more marginal defects,⁴⁹ poor penetration with less adhesion,⁵⁰ and increased microleakage⁵¹ in enamel when compared to etch-and-rinse systems, with a somewhat better result with instrumented enamel.^52,53 This is worrisome because the enamel bond helps to protect the dentin bond from long-term degradation. Some clinicians still incorporate the use of a phosphoric acid on the enamel margins when using a self-etch product to enable increased bonding to the enamel.⁵⁴ Using this technique, the clinician achieves a more predictable bond on the enamel margin; however, depending on control of the phosphoric acid, this technique can lead to clinical variability, and/or more permeability of the bond and sensitivity. The reason self-etch systems tend to minimize postoperative sensitivity is that the smear layer on the dentin surface and smear plugs in the dentinal tubules are left intact. If the phosphoric acid migrates onto the dentin surface during placement or the washing step, it can remove the smear layer and plugs, which allows fluid movement within the tubule; this leads to decreased tensile bond strength and sensitivity.⁵⁵

If this is a preferred technique, the clinician may want to consider a phosphoric acid such as Ultra-Etch (Ultradent), which has the ideal viscosity for placement on vertical surfaces without migration. A recognized variable in the self-etch systems is the thickness of the smear layer, with diamond burs creating a thicker smear layer than carbide burs, resulting in less adhesion to dentin when the thick smear layer cannot be fully penetrated by the self-etch system.^56,57 The self-etching primers, which are not rinsed off, are an acidic monomer, which may not be fully neutralized; this creates a demineralized zone below the hybrid layer that can compromise bond strength.⁵⁸ A concern with self-etch systems is that they may not have resin penetration into or obturate the dentin tubules, thus allowing pulpal fluids to penetrate past the smear plug and into the hybrid layer.⁵⁹ “The higher the micropermeability, the higher the risk of defects at the resin–dentin interface, which may represent the pathway for hydrolytic and enzymatic degradation of the collagen and resin dentin bonds over time.”⁶⁰ This causes what is known as a “hydrolytic” or “water-tree” effect, which breaks downs the bond from the inside out, reducing both in-vivo and in-vitro bond strengths.⁶¹

As a general rule, self-etching systems are more ideally used in posterior restorations for prevention of sensitivity. In addition, due to a less predictable bond to enamel, which can lead to additional staining secondary to microleakage, these self-etch systems are not ideal for anterior restorations. When the level of enamel etching is of concern (ie, the pH is above 1.5), phosphoric-acid–etching may be indicated. However, some of these Type I adhesives, such as Peak SE, which has the highest bond strength in this category of 50 MPa to dentin,²⁶ has an adhesive, Peak™ LC Bond Resin (Ultradent), that can be used in the anterior dentition with an etch-and-rinse phosphoric-acid technique. Many of these products do have catalysts for use with dual-cured composites and can be compatible with self-cure.

Type II self-etch adhesive systems such as All-Bond SE® (BISCO, Inc.), Brush & Bond® (Parkell, www.parkell.com), Futurabond® NR (VOCO America, Inc., www.vocoamerica.com), Touch & Bond® (Parkell), Adper™ Prompt™ L Pop™ (3M ESPE), and Xeno III® (DENTSPLY Caulk), use a self-etch primer and adhesive that are mixed together prior to placement. These self-etching primer/adhesives should not be confused with the self-etching primers of Type I systems. Both Type I and Type II systems leave the smear layer intact before placement and thereby limit postoperative sensitivity. However, Type II systems have all of the same drawbacks as Type I, and can have 35% lower bond strength, because no hydrophobic adhesive layer is placed. As mentioned above, the hydrophobic resin layer helps to prevent water-induced interfacial changes.⁶² It is important to note that thermocycling, which is used to more closely mimic oral conditions, leads to further lowering of the bond strength of these hydrophilic systems.⁶³ The remaining acidity and permeability of these Type II products make them incompatible with self- or dual-cured composites and core materials. Touch & Bond, for instance, demonstrates extremely low bond strengths of 12 MPa to enamel and only 2 MPa to dentin.⁶⁴

Seventh-Generation Adhesives

Among the self-etch adhesives—also called “all-in-one” or seventh-generation adhesive systems—are G-Bond™ (GC America, www.gcamerica.com), iBond® (Heraeus Kulzer, www.heraeus-dental-us.com), Xeno® IV (DENTSPLY Caulk), Adper™ Easy Bond (3M ESPE), AdheSE® One (Ivoclar Vivadent), and Clearfil® S3 Bond (Kuraray). They are very similar to sixth-generation systems, with the biggest difference being that all the components are pre-mixed in one bottle. This one-bottle solution etches, primes, and bonds all at the same time. These self-etch adhesives are permeable membranes and are the most hydrophilic of the adhesive categories.65As such, water sorption by polymers (composites) causes plasticization and lowers mechanical properties.⁶⁶ Residual acidity causes an adverse reaction with chemically cured composites and core materials, creating a reduction in bond strength with permeability, also a further cause of bond strength reduction.⁶⁷ Swift states that for these single-step self-etch adhesives, the bond strength to chemical-cured composites can be enhanced with the adjunctive use of co-initiators, based on sodium salts of aromatic sulphinic acids, but he notes that it might not apply to all simplified adhesives.⁶⁸ This generation of self-etch adhesives also has the highest pH values which results in one-fifth the bond strength to enamel versus the three-step etch-and-rinse system,⁶⁹ and a higher percentage of leakage at the margins.⁷⁰ In general, the all-in-one seventh-generation bonding agents show lower bond strengths, with G-Bond having a bond strength of 12.5 MPa to dentin and 15.4 MPa to enamel.²⁶

Conclusion

Making a decision on a suitable dental adhesive is not easy, as there are many factors to consider. The driving factor should be choosing the product and/or procedure that will offer the best quality of care for patients, and deliver the most predictable long term-results. The predictability of fourth- and fifth-generation adhesives has been unmatched. Ongoing research may lead to advances in dental chemistry that result in stable, long-term attachment to both enamel and dentin.

Disclosure

Dr. Boksman was previously a part-time paid consultant to Clinician’s Choice and Clinical Research Dental, holding the title of Director of Clinical Affairs.

References

1. Nakaba Nakabayashi yashi N, Pashley DH. Hybridization of Dental Hard Tissues. Chicago, Illinois: Quintessence Publishing Co., Ltd; 1998.

2. Powers JM, O’Keefe KL, Pinzon LM. Factors affecting in vitro bond strength of bonding agents to human dentin. Odontology. 2003;91(1):1-6.

3. Alex G. Adhesive dentistry: the good, the bad, and the ugly. Compend Contin Educ Dent. 2009;30(8)553-568.

4. El-Badrawy W. Kozovski L, Nathan G, Roperto RC. 1490 Bond strength of dentin as a function of priming time Seq #180 Bond Strength of Composites to Enamel and Dentin—Application Technique [abstract]. IADR/AADR/CADR 85th General Session and Exhibition. March 21-24, 2007. Available at: http://iadr.confex.com/iadr/2007orleans/techprogram/abstract_89827.htm. Accessed October 11, 2011.

5. Velasquez LM, Sergent RS, Burgess JO, Mecante DE. Effect of placement agitation and placement time on the shear bond strength of 3 self-etching adhesives. Oper Dent. 2006;31(4):426-430.

6. Hashimoto M, Sano H, Yoshida E, et al. Effects of multiple adhesive coatings on dentin bonding. Oper Dent. 2004;29(4):416-423.

7. Hagge MS, Lindemuth JS. Shear bond strength of an auto-polymerizing core build-up composite bonded to dentin with 9 adhesive systems. J Prosthet Dent. 2001;86(6):620-623.

8. Jung H, Friedl KH, Hiller KA, Schmalz G. 0341 Bond strength of composite resins using a new one-step adhesive system [abstract]. Seq #49 Self-etching Adhesive Systems 3, Adhesion Composite Bond Strength Program. 81st General Session of the International Association for Dental Research. June 25-28, 2003. Available at: http://iadr.confex.com/iadr/2003Goteborg/techprogram/abstract_31644.htm. Accessed October 11, 2011.

9. Carvalho RM, Garcia FC, E Silva SM, et al. Critical appraisal: adhesive-composite incompatibility, part 1. J Esthet Restor Dent. 2005;17(2):131.

10. Van Meerbeek B, Vargas S, Inoue S, et al. Adhesives and cements to promote preservation dentistry. Oper Dent. 26;S119-S144.

11. Kanca J. Effect of resin primer solvents and surface wetness on resin composite bond strength to dentin. Am J Dent. 1992;5:213-215.

12. Shirai K, De Munck JD, Yoshida Y, et al. Effect of cavity configuration and aging on the bonding effectiveness of six adhesives to dentin. Dent Mat. 2005;21(2):110-124.

13. Asmussen E, Munksgaard EC. Adhesion of restorative resins to dentinal tissues. In: Vanherle G, Smith DC, eds. Posterior Composite Restorative Materials. Amsterdam: Peter Szule Publishing Co.; 1985:228.

14. Hashimoto M, Ohno H, Kaga M, et al. In vivo degradation
of resin-dentin bonds in humans over 1-3 years. J Dent Res. 2000:79(6):1385-1391.

15. Pecora N, Yaman P, Dennison J, Herrero A. Comparison of shear bond strength relative to two testing devices. J Prosthet Dent. 2002;88(5):511-515.

16. De Munck J, Van Landuyt K, Peumans M, et al. A critical review of the durability of adhesion to tooth tissue: Methods and results. J Dent Res. 2005;84(2):118-132.

17. Thunpithayakul C, Cobb DS, Denehy G, et al. 0346 In vitro microtensile dentin bond strength of adhesives by classification. Seq #70 Bond strength of composites to enamel and dentin with self-etching adhesives [abstract]. IADR/AADR/CADR 85th General session and exhibition. March 21-24, 2007. Available at: http://iadr.confex.com/iadr/2007orleans/techprogram/abstract_90534.htm. Accessed October 13, 2011.

18. Hashimoto M, Ohno H, Yoshida E, et al. Resin-enamel bonds made with self-etching primers on ground enamel. Eur J Oral Sci. 2003;111(5):447-453.

19. De Munck J, Van Meerbeek B, Yoshida Y, et al. Four year water degradation of total-etch adhesives bonded to dentin. J Dent Res. 2003;82(2):136-140.

20. May KN, Swift EJ, Wilder AD, Futrell SC. Effect of surface sealant on microleakage of Class V restorations. Am J Dent. 1996;9:133-136.

21. Abdalla AI, Feilzer AJ. Four year water storage of a total-etch and two self-etching adhesives bonded to dentin. J Dent. 2008;26:611-617.

22. Gamborgi GP, Loguercio A, Reis A. Influence of enamel border and regional variability on durability of resin-dentin bonds. J Dent. 2007;35(5):371-376.

23. Frankenberger R, Strobel WO, Lohbauer U, et al. The effect of six years of water storage on resin composite bonding to human dentin. J Biomed Mater Res B Appl Biomater. 2004;15;69(1):25-32.

24. Arrais CA, Giannini M. Morphology and thickness of the diffusion of resin through demineralized or unconditioned dentinal matrix. Pesqui. Odontol Bras. 2002;16(2):115-120.

25. Hashimoto M, Ohno H, Endo K, et al. The effect of hybrid layer thickness on bond strength: demineralized dentin zone of the hybrid layer. Dent Mater. 2000;16(6):406-411.

26. Christensen GJ. Bonding agents: Is convenience overriding strength? Clinician’s Report reprint from June 2010. Dental Economics. 2010;3(6):1-3.

27. Schmitt DC, Lee J. Microleakage of adhesive resin systems in the primary and permanent dentitions. Pediatr Dent. 2002;24(6):587-593.

28. Gallo JR, Comeaux R, Haines B, et al. Shear bond strength of four filled bonding systems. Oper Dent. 2001;26:44-47.

29. El-Kalla IH, Garcia-Godoy F. Saliva contamination and bond strength of single bottle adhesives to enamel and dentin. Am J Dent. 1997;10:83-87.

30. Castelnuovo J, Tjan AH, Liu P. Microleakage of multi-step and simplified-step bonding systems. Am J Dent. 1996;9:245-248.

31. O’Keefe KL, Powers JM. Adhesion of resin composite core materials to dentin. Int J Prosthodont. 2001;14(5):451-456.

32. Tay FR, Suh BI, Pashley DH, et al. Factors contributing to the incompatibility between simplified-step adhesives and self-cured or dual-cured composite. Part II. Single bottle total etch adhesive. J Adhes Dent. 2003;5(2):91-105.

33. Swift EJ Jr, Perdigão J, Combe EC, et al. Effects of restorative and adhesive curing methods on dentin bond strengths. Am J Dent. 2001;14(3):137-140.

34. Walter R, Swift EJ Jr., Ritter AV, et al. Dentin bonding of an etch-and-rinse adhesive using self-and light-cured composites. Am J Dent. 2009;22(4):215-218.

35. Lopes GC, Cardoso PC, Vieira LC, et al. Shear bond strength of acetone-based one-bottle adhesive systems. Br Dent J. 2006;17(1):39-43.

36. Hashimoto M, Ohno H, Kaga M, et al. The extent to which resin can infiltrate dentin by acetone-based adhesives. J Dent Res. 2002;81(1):74-78.

37. Nunes MF, Swift EJ, Perdigão J. Effects of adhesive composition on microtensile bond strength to human dentin. Am J Dent. 2001;14(6):340-343.

38. Cardoso Pde C, Lopes GC, Vieira LC, Baratieri LN. Effect of solvent type on microtensile bond strength of a total-etch one-bottle adhesive system to moist or dry dentin. Oper Dent. 2005;30(3):376-781.

39. Pashley DH, Tay FR, Breshi L, et al. State of the art etch-and-rinse adhesives. Dent Mater. 2011;27(1):1-16.

40. Swift EJ Jr, Vargas MA. Dentin/enamel adhesives: Their current status. Oral Health. 2009;12-22.

41. Montes MA, de Goes MF, da Cunha MR, Soares AB. A morphological and tensile bond strength evaluation of an unfilled adhesive with low-viscosity composited and a filled adhesive in one and two coats. J Dent. 2001;29(6):435-441.

42. Opdam NJ, Feilzer AJ, Roeters JJ, Smale I. Class I occlusal composite restorations: In vivo post-operative sensitivity, wall adaptation, and microleakage. Am J Dent. 1998;11(5):229-234.

43. Tay FR, Pashley DH. Have dentin adhesives become too hydrophilic? J Can Dent Assoc. 2003;69(11):726-731.

44. Loguercio AD, Bittencourt DD, Baratieri LN, Reis A. A 36-month evaluation of self-etch and etch-and-rinse adhesives in non-carious cervical lesions. J Am Dent Assoc. 2007;138(4):507-514.

45. Browning WD, Blalock JS, Callan RS, Brackett WW, et al. Postoperative sensitivity: a comparison of two bonding agents. Op Dent. 2007;32(2):112-117.

46. Casselli DS, Martins LR. Postoperative sensitivity in Class I composite resin restorations in vivo. J Adhes Dent. 2006;8:53-58.

47. Kanemura N, Sano H, Tagami J. Tensile bond strength to and SEM evaluation of ground and intact enamel surfaces. J Dent. 1999;27(7);523-530.

48. Pashley DH, Tay FR. Aggressiveness of contemporary self-etching adhesives. Part II: etching effects on un-ground enamel. Dental Mater. 2001;17(5):430-444.

49. Van Meebeek B, Kanumilli P, De Munck J, et al. A randomized controlled study evaluating the effectiveness of a two-step self-etch adhesive with and without phosphoric acid etching. Dent Mater. 2005;21(4):375-383.

50. Hashimoto M, Ohno H, Yoshida E, et al. Resin enamel bonds made with self-etching primers on ground enamel. Eur J Oral Sci. 2003;111(5):447-453.

51. Deliperi S, Bardwell DN, Wegley C. Restoration interface microleakage using one total-etch and three self-etch adhesives. Oper Dent. 2007;32(2):179-184.

52. Brackett WW, Ito S, Nishitani Y, et al. The microtensile bond strength of self-etching adhesives to ground enamel. Oper Dent. 2006;31(3):332-337.

53. Perdigao J, Geraldeli S. Bonding characteristics of self-etching adhesives to intact versus prepared enamel. J Esthet Restor Dent. 2003;15(1):32-42.

54. Van Meebeek B, Kanumilli P, De Munck J, et al. A randomized controlled study evaluating the effectiveness of a two-step self-etch adhesive with and without selective phosphoric etching of enamel. Dent Mater. 2005;21(4):375-383.

55. Torii Y, Itou K, Nishitani Y, et al. Effect of phosphoric acid etching prior to self-etching primer application on adhesion of resin composite to enamel and dentin. Am J Dent. 2002;15(5):305-308.

56. Ogata M, Harada N, Yamaguchi S, et al. Effects of different burs on dentin bond strengths of self-etching primer bonding systems. Oper Dent. 2001;26(4):375-382.

57. Kenshima S, Reis A, Uceda-Gomez N, et al. Effect of smear layer thickness and pH of self-etching adhesive systems on the bond strength and gap formation to dentin. J Adhes Dent. 2005;7(2):117-126.

58. Oliveira SS, Marshall SJ, Habelitz S, et al. The effect of a self-etching primer on the continuous demineralization of dentin. Eur J Oral Sci. 2004;112(4):376-383.

59. Radovic I, Vulicevic ZR, Garcia-Godoy F. Morphological evaluation of 2- and 1-step self-etching system interfaces with dentin. Op Dent. 2006;31(6):710-718.

60. Sauro S, Pashley DH, Mannocci F, et al. Micropermeability of current self-etching and etch-and-rinse adhesives bonded to deep dentine: a comparison study using a double-staining/confocal microscopy technique. Eur J Oral Sci. 2008;116(2):184-193.

61. Donmez N, Belli S, Pashley DH, Tay FR. Ultra-structural correlates of in vivo/in vitro bond degradation in self-etch adhesives. J Dent Res. 2005;84(4):355-359.

62. Carvalho RM, Pegoraro TA, Tay FR et al. Adhesive permeability affects coupling of resin cements that utilize self-etching primers to dentine. J Dent. 2004;32(1):55-65.

63. Kerby RE, Knowbloch LA, Clelland N, et al. Microtensile bond strengths of one-step and self-etching adhesive systems. Oper Dent. 2005;30(2):195-200.

64. Farah JW, Powers J. Bonding agents. The Dental Advisor. 2007;24(6):1-40.

65. Van Landuyt KL, Mine A, De Munck J, et al. Technique sensitivity of water-free one-step adhesives. Dent Mater. 2008;24(9):1258-1267.

66. Ito S, Hashimoto M, Wadgaonkar B, et al. Effects of resin hydrophilicity on water sorption and changes in modulus of elasticity. Biomaterials. 2005;26(33):6449-6459.

67. Tay FR, Pashley DH, Yiu CK, et al. Factors contributing to the incompatibility between simplified-step adhesives and chemical-cured or dual-cured composites. Part 1. Single-Step self-etch adhesive. J Adhes Dent. 2003;5(1):27-40.

68. Carvalho RM, Garcia FCP, e Silva SMA, et al. Adhesive-composite incompatibility, Part II. J Adhes Dent. 2005;17(3):191-195.

69. De Munck J, Van Meerbeek B, Satoshi I, et al. Microtensile bond strengths of one- and two-step self-etch adhesives to bur-cut enamel and dentin. Am J Dent. 2003;16(6):414-420.

70. Ernst CP, Cortain G, Spohn M, et al. Marginal integrity of different resin-based composites for posterior teeth: an in vitro dye-penetration study on eight resin-composite and compomer/adhesive combinations with a particular look at the additional use of flow-composites. Dent Mater. 2002;18(4):351-358.

About the Authors

Leendert (Len) Boksman, DDS, BSc, FADI, FICD
Retired from Private Practice
London, Ontario, Canada

Gregg Tousignant, CDT
Technical Support Manager
Clinical Research Dental
London, Ontario, Canada

Lee W. Boushell, DMD, MS
Assistant Professor
Department of Operative Dentistry
University of North Carolina School of Dentistry
Chapel Hill, North Carolina

Gildo Coelho Santos, Jr., DDS, MSc, PhD
Assistant Professor and Chair Division of Restorative Dentistry
Schulich School of Medicine and Dentistry
University of Western Ontario
London, Ontario, Canada
Private Practice
London, Ontario, Canada