Table of Contents

Continuing Education
Kois Center Case of Month
Research Update


September 2011, Volume 32, Issue 7
Published by AEGIS Communications

How to Increase the Durability of Resin-Dentin Bonds

David H. Pashley, DMD, PhD; Franklin R. Tay, BDSc (Hon), PhD; and Satoshi Imazato, DDS, PhD


Resin-dentin bonds are not as durable as was previously thought. Microtensile bond strengths often fall 30% to 40% in 6 to 12 months. The cause of this poor durability is a combination of the activation of matrix metalloproteinases (MMPs) by weak acids such as lactic acid released by caries-producing bacteria, and acid-etchants used in adhesive bonding systems. These acids uncover and activate matrix-bound MMPs. The other contributing factor is incomplete resin infiltration. If all exposed collagen fibrils were enveloped by resin, the MMPs would not have free access to water, an obligatory requirement of these enzymes. Recently, several inhibitors of MMPs have been added to adhesive primers. Examples include chlorhexidine (CHX), benzalkonium chloride (BAC), and MDPB, an antibacterial monomer used in a two-step self-etching primer adhesive. The advantage of MDPB over CHX and BAC is that it polymerizes with adhesive resins and cannot leach from the hybrid layer. This is an example of what can be termed a "therapeutic adhesive system" that provides anti-MMP activity along with antibacterial qualities.

Although the immediate resin-dentin bond strengths of contemporary adhesives are quite high, these values gradually fall with aging,1-3 decreasing 30% to 40% in 6 to 12 months. Strategies are, therefore, needed to increase the longevity of resin-dentin bonds. Bond durability is vital for the longevity of esthetic restorations because as adhesive strength falls, gaps form between teeth and restorative materials. The average service length for tooth-colored restorations is only 5.7 years.4 Replacements of these defective restorations cost about $5 billion annually in the United States alone.5 The development of new, more durable bonding systems would potentially save patients and governments a great deal of money. This article examines the problems that cause poor durability and explores possible solutions.


Historically, adhesion of resins to enamel or dentin has been accomplished via hybrid layer formation.6 That is, the hard tissues are acid-etched to remove smear layers and increase their permeability, and then infiltrated with resin to create hybrid layers. In dentin hybrid layers, collagen fibrils are the only continuous structure between underlying mineralized dentin and the overlying adhesive layer. Early investigations on the durability of resin-dentin bonds demonstrated that their bond strengths decreased over time.7,8 However, the mechanism of the decrease in bond strengths was not known until Armstrong et al9 published transmission electron micrographs (TEMs) of etch-and-rinse resin-dentin hybrid layers after nearly 4 years of water storage. Those TEMs showed that the cause of decreases in bond strength was degradation of the collagen fibrils in dentin hybrid layers.

Degradation Due to Host Collagenous

That same year, Pashley et al10 revealed that acid-etched dentin matrices spontaneously degraded over time in vitro when incubated in aqueous buffer, but not if the buffer contained protease inhibitors or 0.2% chlorhexidine (CHX), a known inhibitor of matrix metalloproteinases (MMPs)11, or were incubated in oil (ie, in the absence of water). Those authors concluded that the degradation of collagen fibrils in vitro was due to the presence of activated endogenous MMPs that are neutral hydrolases. That is, the enzymes add water across specific peptide bonds to cleave them at neutral pH. The loss of collagen fibrils within the hybrid layer causes a loss of continuity with underlying dentin and a weakening of the coupling of resin composites to dentin.

Nonpolymerizable MMP Inhibitors

Rapid research progress followed showing that CHX stabilized hybrid layers in vitro12,13 and in vivo.14-17 However, although CHX binds to demineralized dentin electrostatically,18 there is no covalent bonding. It is likely that MMP inhibitors that do not covalently bond with collagen or resins may leach from hybrid layers over the course of 1 to 2 years and will only delay but not stop collagen degradation.19

Self-etching adhesives are very hydrophilic because they must contain sufficient water (approximately 35% to 40%) to ionize the acidic monomers used for self-etching.20 Self-etching adhesives may absorb less water than two-step etch-and-rinse adhesives,21-23 but they still absorb significant amounts of water over time. Some of this water is taken up into adhesives where the water weakens the polymers. Water also reaches the MMPs bound to collagen where it can hydrolyze collagen peptides.

The mild self-etching adhesives usually remove the smear layer but leave smear plugs in the tubules.24-26 This tends to prevent convective and osmotic water movement from dentinal tubules into the bonded interface.27 However, most self-etching adhesives etch slightly deeper than they infiltrate,28-29 just like etch-and-rinse adhesives. Because the hybrid layers created by mild to moderately aggressive self-etching adhesives are only about 1-µm thick, the resin infiltration is more homogeneous than in hybrid layers created by etch-and-rinse adhesives.

The hybrid layers of self-etching adhesives degrade just like those of etch-and-rinse adhesives,2,30 but it is difficult to demonstrate this even using transmission electron microscopy because the layers are so thin. This is because self-etching adhesives generally have a pH between 1.6 to 2.9 and cannot etch very deeply into dentin. This pH is sufficiently low to demineralize dentin and uncover MMPs and activate them without denaturing them.31,32

Schematic drawings of mineralized dentin collagen fibrils are shown in Figure 1, Figure 2 and Figure 3. Prior to acid-etching, the MMPs bound to the collagen matrix are covered with apatite crystallites; about half of the crystals are outside the collagen fibrils and are called "extrafibrillar" crystallites, and the other half of the crystallites are located inside the collagen fibrils and are termed "intrafibrillar" (Figure 1). In this mineralized state, the MMPs are fossilized and inactive. When mineralized dentin is etched with mild self-etching adhesives, most of the extrafibrillar crystals are removed to provide space for resin infiltration (Figure 2). These acidic self-etching adhesives also remove some of the intrafibrillar crystallites, thereby uncovering MMP enzymes and activating them, allowing them to slowly attack the very collagen fibrils that are used to anchor resin composites to teeth.

Acid-etching dentin with 32% to 37% phosphoric acid removes both extra- and intrafibrillar crystallites (Figure 3), thereby uncovering even more matrix-bound MMPs and activating them, allowing them to slowly attack the hybrid layer, especially in regions that are poorly infiltrated with resin.

Nonspecific MMP inhibitors like CHX have been added to two-step self-etching primer adhesives33,34 and have prevented the usual degradation in bond strengths seen in CHX-free controls. Careful transmission electron microscopy of dentin bonded with mild self-etching primer adhesives showed that a significant amount of residual apatite crystallites remain in the hybrid layer.35 Indeed, nanoleakage studies reveal no silver uptake into collagen fibrils (unlike moderate silver uptake in collagen treated with etch-and-rinse adhesive systems), suggesting that self-etching primers may leave intrafibrillar apatite crystallites in place (Figure 2). The authors speculate that this retention of apatite crystallites prevents water permeation into the internal compartments of collagen fibrils where it could accelerate MMP-induced hydrolysis of collagen over time. The bond strengths of most self-etching adhesives decrease over time; this is presumably due to water uptake into extrafibrillar spaces, facilitating MMP hydrolysis of collagen fibrils from the outside only. This is in contrast to the presence of water in both extra- and intrafibrillar collagen compartments, which facilitates even more rapid collagen hydrolysis in etch-and-rinse adhesives (Figure 3).

Bonding to Bacterially Contaminated Dentin

Most direct esthetic restorations are placed in carious teeth. Whether due to primary or secondary caries, the bacteria-infected dentin must be removed without sacrificing normal dentin. This is not always possible. For instance, as the clinician excavates caries-infected dentin toward a pulp horn, a decision needs to be made; overly aggressive excavation of residual caries-infected dentin may not only cause a pulp exposure but also inadvertently result in forcing chips of bacterially infected dentin into the pulp chamber, requiring expensive endodontic treatment. What is needed is an antibacterial adhesive that would kill bacteria on contact. The pH of self-etching adhesive monomers ranges from 1.6 to 2.9. This is acidic enough to kill many bacteria. However, the pH of these adhesives rapidly rises as soon as it contacts dentin due to the strong buffer capacity of dentin.36,37 Thus, clinicians cannot rely on low pH to kill all residual bacteria.

In the mid-1990s, Imazato and his colleagues38-40 synthesized an antibacterial analog of a self-etching monomer from Kuraray Medical Inc., 10-methacryloyloxydecamethylene phosphoric acid (MDP), by substituting an antibacterial pyridinium group for the terminal phosphate group. The resulting antibacterial monomer, called 12-methacryloyloxydodecyl-pyridinium bromide, is usually identified by its abbreviation, MDPB. The company incorporated 5 wt% MDPB into its Clearfil™ SE Bond self-etching primer adhesive to create a new product, Clearfil™ Protect Bond. An updated version of that product is currently called Clearfil™ SE Protect. The antibacterial monomer MDPB is incorporated into the self-etching primer, not the adhesive. The product has been shown to have strong bacteriocidal activity while a liquid; as long as it is in liquid form it can diffuse into dentin. After photopolymerization, it copolymerizes with the adhesive, forming an antibacterial polymer that kills any bacteria that contact it.38-41

The antimicrobial properties of MDPB reside in its terminal pyridinium group. This group is a member of a broad class of antimicrobial agents termed quaternary ammonium compounds such as benzalkonium chloride (BAC).

Use of Polymerizable Inhibitors of Dentin MMPs

The authors screened a number of quaternary ammonium compounds, including BAC, for their ability to inhibit endogenous MMPs in dentin as well as for their antimicrobial activity.42,43 These matrix-bound MMPs are responsible for the degradation of hybrid layers over time. If they could be inhibited by anti-MMP compounds that contain polymerizable acrylate or methacrylate groups, they might remain in hybrid layers for many years. If their anti-MMP activity compounds remain effective for years, then the durability of the hybrid layers or resin-dentin bonds would likely be extended, thereby making resin-bonded composites more durable over time.

In a recent paper, the authors screened the anti-MMP activity of MDPB along with a number of other quaternary ammonium methacrylates.43 Among the quaternary ammonium methacrylates tested, 5 wt% MDPB showed the highest inhibition of soluble recombinant human MMP-9 (rhMMP-9) and matrix-bound MMPs compared to all others tested (Table 1). Thus, in addition to its antimicrobial activity, MDPB also has potent anti-MMP activity. This is highly desirable because the caries process involves demineralization of the dentin matrix by bacterially derived organic acids. These acids lower the pH of the matrix to around 4.5 to 5, which can both uncover and activate MMPs.44 Once activated, the MMPs can destroy the exposed collagen and deepen the lesion. The presence of MDPB in the self-etching primer of Clearfil SE Protect should inhibit the endogenous MMPs of dentin and prevent further progression of the lesion; however, this assumption is speculative, and future experiments must be designed to confirm these potential actions.

How Dentin MMPs are Activated

The dentin matrix contains MMPs-2, -8 and -9.45-52 These host-derived proteases contribute to the breakdown of collagen matrices in dental caries.44,53,54

The acid-etching step in bonding is thought to uncover and activate pro-MMPs trapped within mineralized dentin.10 However, 37% phosphoric acid is highly acidic (pH 0.4 to -1) and may denature exposed MMPs due to their low acidity. The acidic resin components of etch-and-rinse adhesives55 and self-etch adhesives31,32 have been shown to increase the gelatinolytic and collagenolytic activities of completely or partially demineralized dentin. A self-etching adhesive was also shown to increase the synthesis of MMP-2 in human odontoblasts,56 which may secrete MMP-2 into dentinal fluid and then into hybrid layers. Mildly acidic self-etching monomers seem to activate latent forms of MMPs (pro-MMPs) via the cysteine-switch mechanism that exposes the catalytic site of these enzymes that were blocked by propeptides.57 These same self-etching monomers may also activate dentin MMPs by displacing tissue inhibitors of metalloproteinases (TIMPs)58 in MMP-TIMP complexes.46,59 Solubilization of collagen from the hybrid layer can result in the loss of mechanical properties of the collagen matrix,42,60 and a loss in resin-dentin bond strength.15

Cysteine cathepsins are another class of endopeptidases that participate in intracellular proteolysis with the lyzosomal compartments of living cells.61 However, they are also trapped in the dentin matrix during dentinogenesis but are inactive because they are covered with mineral crystallites.62,63 During acid-etching, they become uncovered and active and can serve as proteases by cleaving to collagen in hybrid layers. Recent unpublished research has shown that chlorhexidine can inhibit cathepsins as well as it inhibits MMPs. Future studies are planned to determine if MDPB inhibits cathepsins as well as it inhibits MMPs.

Therapeutic Adhesives

In a recent review of three-step etch-and-rinse adhesives,27 the authors suggested that such adhesives provide a number of therapeutic opportunities to inhibit bacteria as well as dentin MMPs. Two-step primer adhesives provide similar therapeutic opportunities.

The incorporation of MDPB into the self-etching primer of a self-etching primer/adhesive product as described herein is an example of a so-called "therapeutic adhesive." In addition to simply bonding to dentin, this new class of dental adhesives provides specific, value-added therapeutic activity that kills residual bacteria in caries-infected dentin and inhibits any endogenous MMPs that are activated by the caries process or exposed and activated by the self-etching adhesive system. It is the authors' hope that the dental industry will emulate this innovative approach to product development.


This research was supported by a grant from the following companies: Kuraray Medical Inc., 3M ESPE, Bisco Inc., and DENTSPLY.


1. Breschi L, Mazzoni A, Ruggeri A, et al. Dental adhesion review: aging and stability of the bonded interface. Dent Mater. 2008;24(1):90-101.

2. Zhang SC, Kern M. The role of host-derived dentinal matrix metalloproteinases in reducing dentin bonding of resin adhesives. Int J Oral Sci. 2009;1(4):163-176.

3. Tam L, Jokstad A. The bond between resin composite restorations and dentin may degrade in the mouth over time. J Evid Based Dent Pract. 2010;10(1):21-22.

4. National Institute of Dental and Craniofacial Research (NIDCR) 2009-2013 Strategic Plan. Bethesda, MD: US Dept of Health and Human Services, National Institutes of Health, NIDCR; 2009. NIH publication 09-7362.

5. Jokstad A, Bayne S, Blunck U, et al. Quality of dental restorations. FDI Commission Project 2-95. Int Dent J. 2001;51(3):117-158.

6. Nakabayashi N, Pashley DH. Hybridization of Dental Hard Tissues. Chicago, IL: Quintessence Publishing; 1998.

7. Shono Y, Terashita M, Shimada J, et al. Durability of resin-dentin bonds. J Adhes Dent. 1999;1(3):211-218.

8. 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.

9. Armstrong SR, Vargas MA, Chung I, et al. Resin-dentin interfacial ultrastructure and microtensile dentin bond strength after five-year water storage. Oper Dent. 2004;29(6):705-712.

10. Pashley DH, Tay FR, Yiu C, et al. Collagen degradation by host-derived enzymes during aging. J Dent Res. 2004;83(3):216-221.

11. Gendron R, Grenier D, Sorsa T, Mayrand D. Inhibition of the activities of matrix metalloproteinases 2, 8, and 9 by chlorhexidine. Clin Diagn Lab Immunol. 1999;6(3):437-439.

12. Breschi L, Cammelli F, Visintini E, et al. Influence of chlorhexidine concentration on the durability of etch-and-rinse dentin bonds: a 12-month in vitro study. J Adhes Dent. 2009;11(3):191-198.

13. Breschi L, Mazzoni A, Nato F, et al. Chlorhexidine stabilizes the adhesive interface: a 2-year in vitro study. Dent Mater. 2010;26(4):320-325.

14. Hebling J, Pashley DH, Tjäderhane L, Tay FR. Chlorhexidine arrests subclinical degradation of dentin hybrid layers in vivo. J Dent Res. 2005;84(8):741-746.

15. Carrilho MR, Geraldeli S, Tay F, et al. In vivo preservation of the hybrid layer by chlorhexidine. J Dent Res. 2007;86(6):529-533.

16. Brackett WW, Tay FR, Brackett MG, et al. The effect of chlorhexidine on dentin hybrid layers in vivo. Oper Dent. 2007;32(2):107-111.

17. Brackett MG, Tay FR, Brackett WW, et al. In vivo chlorhexidine stabilization of hybrid layers of an acetone-based dentin adhesive. Oper Dent. 2009;34(4):379-383.

18. Kim J, Uchiyama T, Carrilho M, et al. Chlorhexidine binding to mineralized versus demineralized dentin powder. Dent Mater. 2010;26(8):771-778.

19. Sadek FT, Braga RR, Muench A, et al. Ethanol wet-bonding challenges current anti-degradation strategy. J Dent Res. 2010;89(12):1499-1504.

20. Hiraishi N, Nishiyama N, Ikemura K, et al. Water concentration in self-etching primers affects their aggressiveness and bonding efficacy to dentin. J Dent Res. 2005;84(7):653-658.

21. 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.

22. Malacarne J, Carvalho RM, de Goes MF, et al. Water sorption/solubility of dental adhesive resins. Dent Mater. 2006;22(10):973-980.

23. Hosaka K, Nakajima M, Takahashi M, et al. Relationship between mechanical properties of one-step self-etch adhesives and water sorption. Dent Mater. 2010;26(4):360-367.

24. Tay FR, Sano H, Carvalho RM, et al. An ultrastructural study of the influence of acidity of self-etching primers and smear layer thickness on bonding to intact dentin. J Adhes Dent. 2000;2(2):83-98.

25. Tay FR, Carvalho R, Sano H, Pashley DH. Effect of smear layers on the bonding of a self-etching primer to dentin. J Adhes Dent. 2000;2(2):99-116.

26. Tay FR, Pashley DH. Aggressiveness of contemporary self-etch adhesives systems. I: Depth of penetration beyond dentin smear layers. Dent Mater. 2001;17(4):296-308.

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

28. Tay FR, King NM, Chan KM, Pashley DH. How can nanoleakage occur in self-etching adhesive systems that demineralize and infiltrate simultaneously? J Adhes Dent. 2002;4(4):255-269.

29. Carvalho RM, Chersoni S, Frankenberger R, et al. A challenge to the conventional wisdom that simultaneously etching and resin infiltration always occurs in self-etch adhesives. Biomaterials. 2005;26(9):1035-1042.

30. Okuda M, Pereira PNR, Nakajima M, et al. Long-term durability of resin-dentin interface: nanoleakage vs. microtensile bond strength. Oper Dent. 2002;27(3):289-296.

31. Nishitani Y, Yoshiyama M, Wadgaonkar B, et al. Activation of gelatinolytic/collagenolytic activity in dentin by self-etching adhesives. Eur J Oral Sci. 2006;114(2):160-166.

32. Tay FR, Pashley DH, Loushine RJ, et al. Self-etching adhesives increase collagenolytic activity in radicular dentin. J Endod. 2006;32(9):862-868.

33. Zhou J, Tan J, Chen L, et al. The incorporation of chlorhexidine in a two-step self-etching adhesive preserves dentin bond in vitro. J Dent. 2009;37(10):807-812.

34. Zhou J, Tan J, Yang X, et al. Effect of chlorhexidine application in a self-etching adhesive on the immediate resin-dentin bond strength. J Adhes Dent. 2010;12(1):27-31.

35. Koshiro K, Sidhu SK, Inoue S, et al. New concept of resin-dentin interfacial adhesion: the nanointeraction zone. J Biomed Mater Res B Appl Biomater. 2006;77(2):401-408.

36. Camps J, Pashley DH. Buffering action of human dentin in vitro. J Adhes Dent. 2000;2(1):39-50.

37. Iwasa M, Tsubota K, Shimamura Y, et al. pH changes upon mixing of single-step, self-etching adhesives with powdered dentin. J Adhes Dent. 2011;13(3):207-212.

38. Imazato S, Torii M, Tsuchitani Y, et al. Incorporation of bacterial inhibitor into resin composite. J Dent Res. 1994;73(8):1437-1443.

39. Imazato S, Kinomoto Y, Tarumi H, et al. Incorporation of antibacterial monomer MDPB into dentin primer. J Dent Res. 1997;76(3):768-772.

40. Imazato S, Ebi N, Takahashi Y, et al. Antibacterial activity of bactericide-immobilized filler for resin-based restoratives. Biomaterials. 2003;24(20):3605-3609.

41. Imazato S. Bio-active restorative materials with antibacterial effects: new dimension of innovation in restorative dentistry. Dent Mater J. 2009;28(1):11-19.

42. Tezvergil-Mutluay A, Mutluay MM, Gu LS, et al. The anti-MMP activity of benzalkonium chloride. J Dent. 2011;39(1):57-64.

43. Tezvergil-Mutluay A, Agee KA, Uchiyama T, et al. The inhibitory effects of quaternary ammonium methacrylates on soluble and matrix-bound MMPs. J Dent Res. 2011;90(4):535-540.

44. Tjäderhane L, Larjava H, Sorsa T, et al. The activation and function of host matrix metalloproteinases in dentin matrix breakdown in caries lesions. J Dent Res. 1998;77(8):1622-1629.

45. Martin-De Las Heras S, Valenzuela A, Overall CM. The matrix metalloproteinase gelatinase A in human dentine. Arch Oral Biol. 2000;45(9):757-765.

46. Sulkala M, Larmas M, Sorsa T, et al. The localization of matrix metalloproteinase-20 (MMP-20, enamelysin) in mature human teeth. J Dent Res. 2002;81(9):603-607.

47. Sulkala M, Tervahartiala T, Sorsa T, et al. Matrix metalloproteinase-8 (MMP-8) is the major collagenase in human dentin. Arch Oral Biol. 2007;52(2):121-127.

48. Mazzoni A, Mannello F, Tay FR, et al. Zymographic analysis and characterization of MMP-2 and -9 forms in human sound dentin. J Dent Res. 2007;86(5):436-440.

49. Mazzoni A, Pashley DH, Tay FR, et al. Immunohistochemical identification of MMP-2 and MMP-9 in human dentin: correlative FEI-SEM/TEM analysis. J Biomed Mater Res A. 2009;88(3):697-703.

50. Boukpessi T, Menashi S, Camoin L, et al. The effect of stromelysin-1 (MMP-3) on non-collagenous extracellular matrix proteins of demineralized dentin and the adhesive properties of restorative resins. Biomaterials. 2008;29(33):4367-4373.

51. Santos J, Carrilho M, Tervahartiala T, et al. Determination of matrix metalloproteinases in human radicular dentin. J Endod. 2009; 35(5):686-689.

52. Toledano M, Nieto-Aguilar R, Osorio R, et al. Differential expression of matrix metalloproteinase-2 in human coronal and radicular sound and carious dentine. J Dent. 2010;38(8):635-640.

53. Van Strijp AJ, Jansen DC, DeGroot T, et al. Host-derived proteinases and degradation of dentin collagen in situ. Caries Res. 2003;37(1):58-65.

54. Chaussain-Miller C, Fioretti F, Goldberg M, Menashi S. The role of matrix metalloproteinases (MMPs) in human caries. J Dent Res. 2006;85(1):22-32.

55. Mazzoni A, Pashley DH, Nishitani Y, et al. Reactivation of inactivated endogenous proteolytic activities in phosphoric acid-etched dentine by etch-and-rinse adhesives. Biomaterials. 2006;27(25):4470-4476.

56. Lehmann N, Debret R, Roméas A, et al. Self-etching increases matrix metalloproteinase expression in the dentin-pulp complex. J Dent Res. 2009;88(1):77-82.

57. Tallant C, Marrero A, Gomis-Rüth FX. Matrix metalloproteinases: fold and function of their catalytic domains. Biochim Biophys Acta. 2010;1803(1):20-28.

58. Ishiguro K, Yamashita K, Nakagaki H, et al. Identification of tissue inhibitor of metalloproteinase-1 (TIMP-1) in human teeth and its distribution in cementum and dentine. Arch Oral Biol. 1994;39(4):345-349.

59. Sulkala M, Wahlgren J, Larmas M, et al. The effects of MMP inhibitors on human salivary MMP activity and caries progression in rats. J Dent Res. 2001;80(6):1545-1549.

60. Carrilho MR, Tay FR, Donnelly AM, et al. Host-derived loss of dentin stiffness associated with solubilization of collagen. J Biomed Mater Res Part B Appl Biomater. 2009;90(1):373-380.

61. Dickinson DP. Cysteine peptidases of mammals: their biological roles and potential effects in the oral cavity and other tissues in health and disease. Crit Rev Oral Biol Med. 2002;13(3):238-275.

62. Tersariol IL, Geraldeli S, Minciotti CL, et al. Cysteine cathepsins in human dentin-pulp complex. J Endod. 2010;36(3):475-481.

63. Nascimento FD, Minciotti CL, Geraldeli S, et al. Cysteine cathepsins in human carious dentin. J Dent Res. 2011;90(4):506-511.

About the Authors

David H. Pashley, DMD, PhD
Emeritus Regents' Professor of Oral Biology
Georgia Health Sciences University
School of Dental Medicin
Augusta, Georgia

Franklin R. Tay, BDSc (Hon), PhD
Associate Professor of Endodontics
Georgia Health Sciences University
School of Dental Medicine
Augusta, Georgia

Satoshi Imazato, DDS, PhD
Professor of Biomaterials Science
Osaka University Graduate School of Dentistry
Osaka, Japan