* denotes required field

Your Name: *

FIRST NAME

 LAST NAME

Gender: *

Personal Email: *

This will be your username

Password: *

Display Name: *

This will be what others see in social areas of the site.

Address: *

STREET ADDRESS (LINE 1) *

 

STREET ADDRESS (LINE 2)

 

CITY *

STATE *

ZIP *

 

 

Phone Number:

School/University: *

Graduation Date: *

Date of Birth: *

ASDA Membership No:



ABOUT SSL CERTIFICATES

Username

 

Password

Hi returning User! please login with Facebook credentials where Facebook Username is same as THENEXTDDS Username.

Username

 

Password

 
Article
Comments (0)

Etching of Dental Substrates and Dental Adhesive Concepts

Etching the dental tissues with an acidic solution is a standard clinical procedure that results in the demineralization of the superficial layer of enamel and dentin. Different acids have been proposed over the years: phosphoric acid (from 10% to 50%), fluoridated phosphoric acid, pyruvic acid, citric acid, maleic acid, oxalic acid, tannic acid, EDTA, trichloracetic acid, and polyacrylic acid, among others.1-6

Recent studies have shown that the pH and the pKa of the acid solution are important parameters that influence the aggressiveness of the acids and their ability to demineralize the surface.7,8 The physical status of the solution (either gel or liquid) is an important parameter. The gel type etching agent is easier to apply on the enamel surface than the liquid form, and it is reported to produce a wider and deeper enamel penetration.8 As to methods of application, a continuous brushing technique may be useful when applying an acid-etching gel to obtain a more defined etched pattern for an improved marginal adaptation of the composite resin restoration.9

Etching of the enamel results in 3 types of patterns.10 A preferential removal of prism core material, leaving the periphery intact, constitutes the Type I etching pattern (Figure 1B). Type II is defined as a preferential removal of periphery core material, leaving the prism core relatively unaffected (Figure 1A). The Type III pattern represents a more random etching morphology in which adjacent areas of the tooth surface correspond to Types I and II, mixed with regions in which the pattern could not be related to prism morphology (Figure 2).

The consequences of etching dentin are different from etching enamel. Acids remove the superficial mineral dentin to expose the organic matrix, in particular, the collagen dentin network. The characteristic collagen banding is formed by a longitudinal overlapping of the molecules that involve approximately one quarter of the length of the fibril monomer, leaving a space between the extremity of one collagen triple helix and the beginning of the next.11 This “hole” has been considered a site for accumulation of hydroxyapatite crystals inside the collagen molecule.33 Collagen banding has been also reported in the peritubular region.12 The lack of collagen banding in some areas of etched dentin may be caused by the aggressiveness of the etchant, since dentin collagen, after demineralization, is susceptible to proteolytic degradation.13

In spite of assumptions that etching dentin results in collagen denaturation and precludes the establishment of durable bonding, it has never been validated, nor has it been proven that changes in collagen ultrastructure are detrimental for the performance of dentin adhesives. The results from a recent immunocytochemical study provided additional evidence that application of phosphoric acid for 15 seconds results in a mineral dissolution of the crystals, enveloping the superficial collagen fibers without damaging the collagen ultrastructure.14  

Other molecules of the dentin matrix that might have an important role in adhesion are the proteoglycans (PG). The complex molecular conformation of the collagen fibrils network that is exposed by the etching agent involves the presence of lateral chains of proteoglycans that have a fundamental role in stabilizing the fibrillar arrangement.15 Proteoglycans are important components of the extracellular matrix of all human connective tissues; keratan sulfate (KS) and chondroitin sulfate (C4-S and C6-S) are present in predentin, dentin, and cement.15,16 Due to the ability of PG to bind water molecules,17 PG regulate the biophysical properties of the collagen fibrils and are able to imbibe a great amount of water. This peculiarity is transferred to the nonmineralized connective tissues as a high resistance to a load force.18 On the other hand, the presence of the collagen fiber in the connective dentin matrix gives the typical high resistance to traction forces. Collagen fibers and PG interact closely, creating a complex network of fibrillar structures that act as the scaffold of the dentin matrix and react with the adhesive agent during infiltration.19 The role of proteoglycans is crucial, as water is fundamental in preventing collagen collapse after etching.

(Continued from page 1 )

DENTAL ADHESIVES: CURRENT CONCEPTS

A group of simplified dentin adhesive systems has been recently developed and received considerable attention from clinicians, due to a simplified clinical application. In these one-bottle dental adhesive systems, enamel and dentin are etched with phosphoric acid simultaneously, followed by the application of a single solution that combines primer and adhesive resin from the early generation. These simplified systems contain hydrophilic (ie, HEMA, PENTA, BPDM, or PMDM) and hydrophobic resins (ie, BisGMA, UDMA), dissolved in high vapor pressure solvents, such as acetone and ethanol. The solvents may be able to displace water from the dentin surface and from the moist collagen network and allow the monomers to intermingle with the filigree of collagen fibers to form a “hybrid layer” (Figure 3).20,21 However, the idea that organic solvents lead the monomers into direct contact with the moist collagen fibers and prevent their collapse has never been substantiated. In fact, some organic solvents may actually cause shrinkage of moist demineralized dentin and interfere with the penetration of resin monomers into dentin.22

The demineralized dentin matrix collapses when dentin is air dried following etching.23 When the “wet-bonding” technique24 was first considered as a standard procedure associated with total-etch, the moist dentin surface was deemed as the ideal bonding substrate, and most manufacturers recommend it.25 The concept behind it is to obtain high bond strengths in vitro, supporting the idea that moist dentin provides a porous collagen network that allows infiltration of adhesives into the nanospaces between adjoining collagen fibers(Figures 4 and 5).26-28 The immediate high-bond strengths obtained, decrease when the specimens are stored in aqueous environments.29,30

The demineralized dentin matrix collapses easily in vitro when it is air-dried after being rinsed with water.23,31-33 After dissolution of the hydroxyapatite crystals by the acid, it is essential to keep dentin moist, so that air-drying and consequent collapse of the fibrillar structure of the collagen scaffold is prevented, in vitro.27,28,30-33  

Air-drying of etched preparations was taught in dental schools as a method to check for etched aspect of enamel. Some clinicians still dry the preparation after rinsing the etching gel. As a result of air-drying enamel, dentin is also dried, which causes dentin collagen to collapse resulting in the closing of the pores in intertubular collagen in vitro. Re-wetting dried dentin with water raises the collapsed collagen to a level compared to a “wet bonding” technique and restores the bond strengths when dentin is re-wet for twice as long as the time spent with drying.27,34,35  

Data obtained from in vitro studies focused on different degrees of moisture have not been corroborated by clinical findings. As opposed to laboratory conditions, dentin is an inherently hydrated tissue in vivo, penetrated by a system of 1.0 to 2.5 mm diameter fluid-filled dentin tubules. Flow of fluid from the pulp to the dentin-enamel junction is a result of a slight, but constant, pulpal pressure,36 which has a magnitude of 25 mm to 30 mm Hg or 34 mm to 40 cm H2O.37,38 Six-month results of a clinical trial of two dentin adhesives, applied on moist versus dry dentin, have shown that the moisture level of the substrate may not be as important clinically as it is under laboratory conditions.39 In this study, an ethanol- and water-based adhesive and an acetone-based adhesive, were applied in non-carious, non-beveled, Class V lesions, either after removing the excess of water with a damp cotton pellet, or after drying enamel and dentin with air for 2 to 3 seconds. Retention rates for both adhesives applied on dried dentin were 100% at 6 months, which challenges the clinical relevance of the in vitro findings and the experimental setup of current laboratory experiments.

 

References:

 

 

  1. Garcia-Godoy F, Dodge WW, Donohue M, O’Quinn JA. Effect of a fluoridated etchant on the shear bond strength of a composite resin to enamel. Int J Paediatr Dent 1992;2(1):25-30.
  2. Sharma A, Chandra S, Jaiswal JN, Bajpai VK. Effect of conditioning the enamel surface of primary teeth with citric acid: A SEM study. J Clin Pediatr Dent 1992;16(3):207-212.
  3. Breschi L, Gobbi P, Mazzotti G, et al. High resolution SEM evaluation of dentin etched with maleic and citric acid. Dent Mater 2002;18(1):26-35.
  4. Prati C, Pashley DH, Chersoni S, Mongiorgi R. Marginal hybrid layer in Class V restorations. Oper Dent 2000;25(3):228-233.
  5. Bitter NC. The effect of 25% tannic acid on prepared dentin: A scanning electron microscope-methylene blue dye study. J Prosthet Dent 1990;64(1):12-16.
  6. Prati C, Montanari G, Biagini G, et al. Effects of dentin surface treatments on the shear bond strength of Vitrabond. Dent Mater 1992;8(1):21-26.  
  7. Misra DN. Interaction of citric acid with hydroxyapatite surface: exchange of ions and precipitation of calcium citrate. J Dent Res 1996;75(6):1418-1425.
  8. Baharav H, Cardash HS, Pilo R, Helft M. The efficacy of liquid and gel acid etchants. J Prosthet Dent 1988;60(5):545-547.
  9. Ben-Amar A, Baharav H, Liberman R, Nordenberg D. Continuous brushing acid-etch technique and microleakage of class V composite restorations. J Prosthet Dent 1988;59(5):573-576.
  10. Silverstone LM, Saxton CA, Dogon IL, Fejerskov O. Variation in the pattern of acid etching of human dental enamel examined by scanning electron microscopy. Caries Res 1975;9(5):373-387.
  11. Prockop DJ, Kivirikko KI, Tuderman L, Guzman NA. The biosynthesis of collagen and its disorders (first of two parts). N Engl J Med 1979;301(1):13-23.
  12. Perdigão J, Lambrechts P, van Meerbeek B, et al. Morphological field emission-SEM study of the effect of six phosphoric acid etching agents on human dentin. Dent Mater 1996;12(4):262-271.
  13. Okamoto Y, Heeley JD, Dogon IL, Shintani H. Effects of phosphoric acid and tannic acid on dentine collagen. J Oral Rehabil 1991;18(6):507-512.
  14. Breschi L, Perdigão J, Gobbi P, et al. Immunocytochemical identification of type I collagen in acid-etched dentin. J Biomed Mater Res A 2003;66(4):764-769.
  15. Goldberg M, Takagi M. Dentine proteoglycans: Composition, ultrastructure and functions. Histochem J 1993;25(11):781-806.
  16. Cheng H, Caterson B, Yamauchi M. Identification and immunolocalization of chondroitin sulfate proteoglycans in tooth cementum. Connect Tissue Res 1999;40(1):37-47.
  17. Scott JE. Proteoglycan: Collagen interactions and subfibrillar structure in collagen fibrils. Implications in the development and ageing of connective tissues. J Anat 1990;169:23-35.
  18. Ruoslahti E. Structure and biology of proteoglycans. Annu Rev Cell Biol 1988;4:229-255.
  19. Breschi L, Gobbi P, Lopes M, et al. Immunocytochemical analysis of dentin: A double-labeling technique. J Biomed Mater Res A 2003;67(1):11-17.
  20. Eick JD, Gwinnett AJ, Pashley DH, Robinson SJ. Current concepts on adhesion to dentin. Crit Rev Oral Biol Med 1997;8(3):306-335.
  21. Jacobsen T, Söderhold KJ. Some effects of water on dentin bonding. Dent Mater 1995;11(2):132-136.
  22. Nakajima M, Okuda M, Pereira PN, et al. Dimensional changes and ultimate tensile strengths of wet decalcified dentin applied with one-bottle adhesives. Dent Mater 2002;18(8):603-608.
  23. Pashley DH, Horner JA, Brewer PD. Interactions of conditioners on the dentin surface. Oper Dent 1992;Suppl 5:137-150.
  24. Kanca J. Resin bonding to wet substrate. 1. Bonding to dentin. Quintessence Int 1992;23(1):39-41.
  25. Kanca J. Effect of resin primer solvents and surface wetness on resin composite bond strength to dentin. Am J Dent 1992;5(4):213-215.
  26. Tam LE, Pilliar RM. Fracture surface characterization of dentin-bonded interfacial fracture toughness specimens. J Dent Res 1994;73(3):607-619.
  27. Gwinnett AJ. Dentin bond strength after air drying and rewetting. Am J Dent 1994;7(3):144-148.
  28. Kanca J 3rd. Improving bond strength through acid etching of dentin and bonding to wet dentin surfaces. J Am Dent Assoc 1992;123(9):235-243.
  29. Hashimoto M, Ohno H, Sano H, et al. Micromorphological changes in resin-dentin bonds after 1 year of water storage. J Biomed Mat Res 2002;63(3):306-311.
  30. 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.
  31. Perdigão J, Frankenberger R, Rosa BT, Breschi L. New trends in dentin/enamel adhesion. Am J Dent 2000;13(Spec No):25D-30D.
  32. Kato G, Nakabayashi N. Effect of phosphoric acid concentration on wet-bonding to etched dentin. Dent Mater 1996;12(4):250-255.
  33. Tay FR, Gwinnett JA, Wei SH. Micromorphological spectrum from overdrying to overwetting acid-conditioned dentin in water-free, acetone-based, single-bottle primer/adhesives. Dent Mater 1996;12(4):236-244.
  34. Perdigão J, Frankenberger R. Effect of solvent and rewetting time on dentin adhesion. Quintessence Int 2001;32(5):385-390.
  35. Tay FR, Gwinnett AJ, Wei SH. Ultrastructure of the resin-dentin interface following reversible and irreversible rewetting. Am J Dent 1997;10(2):77-82.
  36. Brännström M, Linden LA, Johnson G. Movement of dentinal and pulpal fluid caused by clinical procedures. J Dent Res 1968;47(5):679-682.
  37. Terkla LG, Brown AC, Hainisch AP, Mitchem JC. Testing sealing properties of restorative materials against moist dentin. J Dent Res 1987;66(12):1758-1764.
  38. Van Hassel HJ. Physiology of the human dental pulp. Oral Surg Oral Med Oral Pathol 1971;32(1):126-134.
  39. Perdigão J, Carmo AR, Geraldeli S, et al. Six-month clinical evaluation of two dentin adhesives applied on dry vs. moist dentin. J Adhes Dent 2001;3(4):343-352.

 

 

Sorry, your current access level does not permit you to view this page.