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ORIGINAL RESEARCH Table of Contents   
Year : 2008  |  Volume : 19  |  Issue : 2  |  Page : 129-133
Evaluation of microtensile bond strength of total-etch, self-etch, and glass ionomer adhesive to human dentin: An in vitro study


Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College and Hospital, Alapakkam Main Road, Maduravoyal, Chennai - 600 095, Tamil Nadu, India

Click here for correspondence address and email

Date of Submission05-Dec-2006
Date of Decision26-Jul-2007
Date of Acceptance27-Jul-2007
 

   Abstract 

Aim: To evaluate the microtensile bond strength of Single Bond, AdheSE, and Fuji Bond LC to human dentin. Fifteen non-carious third molars were selected for the study. The teeth were randomly divided into three groups of five teeth each. Each group was given a different bonding treatment. Group I was treated with Single Bond (3M, ESPE), group II with AdheSE (Ivoclar, Vivadent), and group III was treated with Fuji Bond LC (GC America). A T-band metal matrix was placed and composite resin bonded on to the tooth surface using appropriate bonding agents. The composite resin was packed in increments and light cured. Each tooth was sectioned to obtain 1 mm × 1 mm beams of dentin-resin samples. Tensile bond testing was done using a universal testing machine (Instron) at a cross-head speed of 0.5 mm/min.
Results: The mean bond strength of Single Bond (35.5 MPa) was significantly higher than that of AdheSE (32.8 MPa) and Fuji Bond LC (32.6 MPa). The difference between the microtensile bond strength values of AdheSE and Fuji Bond LC was statistically insignificant.
Inference: Though the bond strength of AdheSE and Fuji Bond LC was above 30 MPa, it was less than that of Single Bond as evaluated by testing of microtensile bond strength.

Keywords: Etching dentin, glass ionomer adhesive, microtensile bond strength

How to cite this article:
Neelima L, Sathish ES, Kandaswamy D, Bupesh. Evaluation of microtensile bond strength of total-etch, self-etch, and glass ionomer adhesive to human dentin: An in vitro study. Indian J Dent Res 2008;19:129-33

How to cite this URL:
Neelima L, Sathish ES, Kandaswamy D, Bupesh. Evaluation of microtensile bond strength of total-etch, self-etch, and glass ionomer adhesive to human dentin: An in vitro study. Indian J Dent Res [serial online] 2008 [cited 2014 Aug 28];19:129-33. Available from: http://www.ijdr.in/text.asp?2008/19/2/129/40467
Dentistry has witnessed many rapid advances in the last century. Over this period, there have been marked changes in restorative procedures. The concepts in restorative dentistry have been continually changing over the last four decades and adhesive dentistry has steadily gained in importance. The concept of adhesive restoration has been, essentially, the most noteworthy development in this ever-progressing science.

In 1955, Buonocore proposed the idea of chemically treating enamel with acid solution to alter the enamel surface in order to promote adhesion of resin. [1] However, due to some specific properties of human dentin, such as the tubular structure and its intrinsic wetness, bonding to dentin is more difficult to achieve than bonding to enamel. This challenge led to the development of many types of bonding agents.

Since 1950, several types of resin bonding systems have evolved. Dentin bonding agents can thus be classified on this basis. The first generation of adhesive systems treated the enamel surface, but they were able to achieve a bond strength of only 2-3 MPa. [2] While second-generation and third-generations products were also deficient with regard to bond strength, the fourth generation consisted of a three-step total-etch technique, which included acid etching, priming, and bonding steps; this increased the micromechanical retention and the bond strength of the adhesive system to the tooth substrate. [3] Simplified adhesive systems were later developed in order to reduce the number of steps during the bonding procedure. Subsequently, the fifth generation was developed, which consisted of a two-step total-etch technique, where etching was followed by priming and bonding, with the primer and bonding agent supplied in one bottle. The most recent development is that of self-etch adhesives - the sixth generation - which is also called the 'No rinse' technique. It may consist of two steps, with conditioning and priming combined into one step and followed by bonding agent application, or it may consist of only one step, where a single application of a liquid containing conditioner, primer, and bonding agent (supplied in one bottle) is done. Self-etching primer simultaneously etches and primes both enamel and dentin. It penetrates, dissolves, and incorporates the smear layer into the adhesive process, resulting in a one-step procedure.

Another way of classifying dentin bonding agents is as etch-and-rinse bonding agents, self-etching dentin bonding agents, and glass ionomer-based bonding agents.

Glass ionomer cements, with their advantage of chemical adhesion, were modified by the incorporation of resin component to act as a glass ionomer adhesive for composite (Fuji Bond LC). [4]

The purpose of the present study was to evaluate the quality of the adhesion created by three different techniques: total-etch technique [Single Bond (3M)], self-etching technique [AdheSE (Ivoclar)], and glass ionomer-based adhesive [Fuji Bond LC (GC)], using the nontrimming variety [5] of the microtensile bond strength testing technique.


   Materials and Methods Top


Fifteen non-carious unrestored human third molars were selected for the study. All the selected teeth were used within a month of extraction. Adequate care was taken to avoid fracture of the teeth during extraction procedures. Following extraction, the collection, storage, and handling of teeth was done as per the recommendations of Occupational Safety and Health Administration (OSHA) and the Center for Disease Control and Prevention (CDC). The surfaces of all the teeth were examined under a visible light-curing unit and teeth with cracks and structural defects were discarded.

The occlusal enamel of 15 teeth was removed perpendicular to the long axis of each tooth, using a slow-speed diamond disk with water coolant. The exposed dentinal surfaces were ground flat with 800-grit silica carbide sandpaper under adequate water cooling, thus reducing the dentin thickness by 1 mm and exposing the mid-dentin.

The composite resin used in this study was Filtek P60 (3M ESPE).

The selected teeth were randomly divided into three groups, each consisting of five teeth. The bonding agents used in each group were as follows:

Group         Bonding agent

I                  Single Bond (3M)

II                AdheSE (Ivoclar Vivadent)

III              Fuji Bond LC (GC)

All the adhesive systems were used according to the manufacturers' recommendations.

Group I - Single Bond (3M)

Etching was done using 37% phosphoric acid for 15 s; following this the tooth was rinsed for 15 s and then blot dried. It was brushed with two consecutive coats of priming resin, air dried gently for 2-5 s and light cured for 10 s.

Group II - AdheSE (Ivoclar Vivadent)

Primer was applied for 15 s; the tooth was then air dried and the bonding agent was applied and light cured for 10 s.

Group III - Fuji Bond LC (GC)

Conditioning was done with 20% polyacrylic acid for 10 s using a cotton pellet; after this the tooth was rinsed thoroughly with water and gently dried. Two drops of liquid and one spoon of powder were mixed for 10 s in a mixing well and light cured for 20 s.

Following the application of adhesive systems, a T-band metal matrix was used; the band was made to surround the entire circumference of the tooth sample. A composite resin block was built on the bonding surface, sequential application of 1-mm-thick layers of material (up to 4 mm) was done, and each specimen was cured for 40 s.

The completed specimens were stored in distilled water for 24 h. The teeth were then individually fixed to a sectioning block using acrylic resin. The block was mounted on the hard-tissue microtome and each tooth was serially sectioned in the occlusogingival direction, producing 1.0-mm-thick slabs. The block was then rotated 90 degrees and the serial sectioning was repeated. The tooth was removed from the block and the resulting specimens were sectioned free from the root. These specimens are termed as beams and have cross-sectional areas of 1.0 × 0.1 mm. [6] These beams consist of resin composite in the upper half and dentin in the lower half. A total of 20 to 30 dentin-composite specimens were obtained from each group of five teeth [Figure - 1].

Microtensile bond strength test

Specimen dimensions were measured with 0.01 mm precision at the adhesive interface using an electronic caliper (CIPET, Chennai). The beams were then attached to a custom-made jig using screws and cyanoacrylate glue and this jig was attached to the Instron universal testing machine (Mechanical Department, CIPET, Chennai). [Figure - 2]. A tensile load was applied at a cross-head speed of 0.5 mm/min until the beam fractured. The tensile load at which the fracture occurred was recorded. The microtensile bond strength values were recorded in units of megapascals (MPa). The results were tabulated and the mean tensile strength values were evaluated for group I (Single Bond), group II (AdheSE), and group III (Fuji Bond LC).


   Results Top


Inference [Table - 1]

Mean bond strength in group I (35.5 ± 1.1) is significantly higher than the mean bond strength in group II (32.8 ± 0.5) and group III (32.6 ± 1.0) ( P < 0.05). However there is no significant difference in mean values between group II and group III.

Statistical analysis

Means and standard deviations were estimated from the samples for each study group. Mean values were compared by one-way analysis of variance (ANOVA). The multiple range test by Tukey's HSD procedure was employed to identify the significance at 5% level if the P-value by one-way ANOVA was significant.

In the present study, P < 0.05 was considered as indicating statistical significance.


   Discussion Top


Simultaneous etching of enamel and dentin is the basis for most fourth-generation and fifth-generation dentin and enamel adhesives used today. This is known as the total-etch technique. Development of the total-etch technique concomitantly gave rise to hybridization of dentin, a molecular level mixture of adhesive polymers and dental hard tissues. The method has proved to be successful both in vitro and in vivo. [3] Bond strengths of these bonding agents to dentin is claimed to be between 17 MPa and 30 MPa, which is very close to the values obtained in enamel; hence, Single Bond was selected in this study.

The most recent development is the self-etching primer that combines the processes of etching and priming. In addition to simplifying the bonding technique, the elimination of the rinsing and drying steps reduces the possibility of over-wetting or over-drying, which possibly deteriorates the adhesive phenomena. [1] Self-etching primers containing acidic monomers like phenyl-p infiltrate through the smear layer into the underlying mineralized dentin matrix to create a special hybrid layer. Thus, it simultaneously demineralizes the dentin and infiltrates it with monomers, which are polymerized in situ, resulting in an improved marginal seal and adhesion to dentin - all achieved with a simplified bonding procedure. [1] In this study, AdheSE (Ivoclar) self-etching primer was taken to evaluate the bond strength on human dentin.

Another legend in the bonding arena is the glass ionomer-based adhesive which was employed in the present study.

The conventional bond strength tests have disadvantages, such as eccentric stress distribution, that often results in cohesive failures within the tooth substrate.

Sano et al . introduced the microtensile bond testing technique [7],[8] (Nakajima et al . 1995, Yoshiyama et al . 1996).This microtensile test allows for the assessment of bond strengths even with bonded surfaces with a cross-sectional area in the range of only 1-1.5 mm 2 .

There are several advantages of microtensile bond strength testing over conventional bond strength testing methods; the advantages of microtensile bond strength testing include the following: [3]

  1. Permits the use of only one tooth to fabricate several bonded dentin-resin rods.
  2. Allows for testing substrates of clinical significance, such as carious dentin, cervical dentin, and enamel.
  3. Results in fewer defects occurring in the small-area specimens; this is reflected in higher bond strengths.
  4. Allows for the testing of regional differences in bond strengths within the same tooth.


According to Sano et al . there is an inverse relationship between bond strength and bond area: the smaller the area, the greater is the bond strength. [8] A small surface area improves the specimen in terms of stress distribution and in having a reduced number of internal defects, since smaller surface area, it generally resulted in only adhesive failures. Larger specimens have a greater number of defects than smaller specimens; adhesive bonding is not uniform microscopically; there may be small flaws or defects in bonded interphases, such as air bubbles, water blisters, surface roughness, or regions of resin/solvent phase separations, which can serve as stress concentrations during bonding. Hence, smaller specimens have higher bond strength values. [7]

The original 'trimming version' of the microtensile test utilized dumbbell or hourglass specimens that allowed tensile stress to be more uniformly directed toward the weakest interfacial region. The disadvantage is that cohesive substrate failures are more liable to occur during testing of assemblies with high bond strength.

The present study utilized a modified version of the microtensile bond strength test, in which tensile stress is applied to a composite dentin beam that has a small but uniform cross-sectional area throughout the entire length of beam - 'non-trimming version.' [5] It apparently places stress on the adhesive interface during specimen preparation and handling. Compared to other methods, this modified testing method will allow study of materials producing relatively low bond strengths.

The results of the present study show that the bond strength of total-etch (Single Bond; group I) resulted in higher bond strength values than self-etch adhesive (AdheSE; group II) and glass ionomer adhesive (Fuji Bond LC; group III). On the other hand, the differences between group II and group III were found to be statistically insignificant.

Group I: Single Bond is a fifth-generation bonding agent that has two steps in application. The tooth is etched and this is followed by application of the bonding agent, which contains both primer and adhesive in a single bottle. Etched dentin should not be dried and the moisture should be preserved to prevent the collapse of the collagen meshwork maintaining the perifibrillar spaces that facilitate the diffusion of monomer. [9] Hence, in this study, the moist bonding technique was followed.

On application of 37% phosphoric acid, the smear layer and superficial dentin are demineralized and the collagen fibers of superficially demineralized dentin are exposed. The exposed collagen may provide reactive groups that can chemically interact with bonding primers. [6] The ethanol solvent of Single Bond, due to its high vapor pressure, competes with moisture, replacing it and promoting infiltration of monomer through the nano-spaces of the exposed collagen network. This serves as a framework for the creation of a resin-demineralized dentin hybrid layer, resulting in a strong micromechanical interlocking between resin and the superficially demineralized dentin. This could probably account for the higher bond strength values showed by group I (Single Bond showed 35.5 MPa) compared to all the other groups.

Group II: Self-etching primer or smear layer-modifying adhesive (AdheSE) has a self-etching primer and an adhesive in a single bottle. The primer of this system contains a bis-acrylamide compound, which dissolves in water as well as organic solvents. The amide group binds with collagen and the resin with the monomer. The phosphonic acid in the self-etching primer creates channels through the smear layer and aids in the penetration of the primer, which coats the surface and binds the monomer. AdheSE, with a pH of 1.4, can be classified as a mild self-etching adhesive. [10]

Self-etching priming systems combine the etching and priming steps, where the primer is not rinsed but only air dried. This results in the calcium and phosphate ions being solubilized from the apatite crystals, which are suspended in alcohol and water solvents in the primer. When these volatile solvents are evaporated, the concentration of calcium and phosphate may exceed the solubility product constants for calcium phosphate, resulting in its precipitation within the primer. This limits the ability of adhesives to penetrate the primed surface, presumably due to the buffering capacity of dentin and due to the common high ion concentrations of calcium and phosphate. This results in a lesser depth of penetration in dentin (only up to 1 μm).[11] The above factors contribute to the lower microtensile bond strength values of group II (32.8 MPa) as compared to that of group I.

Group III: According to a classification based on the number of clinical steps and the underlying mechanism of bonding to tooth substrate, the glass ionomer adhesive should be regarded as belonging to a separate category, next to that of 'etch and rinse' and 'self-etch' resin-based adhesives. [12]

Fuji Bond LC is a diluted version of the restorative resin-modified glass-ionomer cement (RMGIC). Glass ionomer adhesives have been documented to produce a hybrid layer with a thickness of about 0.5-1 μm.[12] This hybrid layer is formed upon the partial demineralization achieved through the use of 20% polyalkenoic acid conditioner. This conditioner 'cleans' the dentin surface (removes smear debris) without completely unplugging the dentinal tubules. Within the hybrid layer, the hydroxyapatite crystals are not completely removed from collagen. Consequently, these hydroxyapatite-coated collagen fibrils offer not only micromechanical retention sites for hybridization but also serve as receptors for primary chemical bonding with the carboxyl groups of polyalkenoic acid. Thus, a two-fold micromechanical and chemical bonding mechanism is seen. Fuji Bond LC also contains Hydroxy Ethyl Methacrylate. in its composition, similar to the fifth-generation and sixth-generation bonding agents, which provide for good wetting of dentin surface. [14] It is also a mild etchant, with a pH of 2, and thus resembles a self-etching agent. These could be the reasons for its having bond strength values similar to that of group II.

Further studies to check the thickness of the hybrid layer will highlight the clinical importance of correct selection of bonding systems.


   Conclusion Top


Though the microtensile bond strengths of AdheSe and Fuji Bond LC proved to be relatively high, they were significantly lower than that of the Single Bond system. The main reason for this high bond strength of Single Bond is the proper resin infiltration into dentin, which leads to strong micromechanical interlocking (formation of a hybrid layer).

 
   References Top

1.Nakabayashi NF. Hybirdization of dental hard tissues, charecterization of the hybrid layer. Quintessence Publication: p. 57-83.   Back to cited text no. 1    
2.Miguez PA, Castro PS, Nunes MF, Walter R, Pereira PN. Effect of acid-etching on the enamel bond of two self-etching systems. J Adhes Dent 2003;5:107-12.  Back to cited text no. 2  [PUBMED]  
3.Sturdevants. Art and science of operative dentistry, 4 th ed. Fundamental concepts of enamel and dentin adhesion. St.Louis Mosby; 2002. p. 237-68.  Back to cited text no. 3    
4.Schwartz B. Summitt-fundamentals of operative dentistry: A contemporary approach, 2 nd ed, Enamel and Dentin Adhesion. Quintessence Book: p. 178-235.  Back to cited text no. 4    
5.Shono H, Ogawa T, Terashita M, Carvalho RM, Pashley EL, Pashley DH. Regional measurement of resin-dentin bonding as an array. J Dent Res 1999;78:699-705.  Back to cited text no. 5    
6.Inokoshi S, Hosoda H, Harnirattisai C, Shimada Y. Interfacial structure between dentin and seven dentin bonding systems revealed using argon ion beam etching. Oper Dent 1993;18:8-16.  Back to cited text no. 6  [PUBMED]  
7.Pashley DH, Sano H, Ciucchi B, Yoshiyama M, Carvalho RM. Adhesion testing of dentin bonding agents: A review. Dent Mater 1995;11:117-25.  Back to cited text no. 7  [PUBMED]  
8.Sano H, Shono T, Sonoda H, Takatsu T, Ciucchi B, Carvalho R, et al. Relationship between surface area for adhesion and tensile bond strength-evaluation of a microtensile bond test. Dent Mater 1994;10:236-40.  Back to cited text no. 8  [PUBMED]  
9.Miyazaki M, Platt JA, Onose H, Moore BK. Influence of dentin primer application methods on dentin bond strength. Oper Dent 1996;21:167-72.  Back to cited text no. 9  [PUBMED]  
10.Yoshiyama M, Tay FR, Doi J, Nishitani Y, Yamada T, Itou K, et al. Bonding of self-etch adhesives to carious dentin. J Dent Res 2002;81:556-60.  Back to cited text no. 10  [PUBMED]  [FULLTEXT]
11.Van Meerbeek B, De Munck J, Yoshida Y, Inoue S, Vargas M, Vijay P, et al. Adhesion to enamel and dentin: Current status and future challenges. Oper Dent 2003;28:215-35.  Back to cited text no. 11    
12.Van Meerbeek, Vargas M, Inoue S. Adhesives and cements to promote preservation dentistry. Operat Dent Suppl 2001;6:119-44.  Back to cited text no. 12    
13.Inoue S, Abe Y, Yoshida Y, De Munck J, Sano H, Suzuki K, et al. Effect of conditioner on bond strength of glass-ionomer adhesive to dentin/enamel with and without smear layer interposition. Oper Dent 2004;29:685-92.  Back to cited text no. 13  [PUBMED]  
14.Palma-Dibb RG, de Castro CG, Ramos RP, Chimello DT, Chinelatti MA. Bond strength of glass ionomer cements to caries affected dentin. J Adhes Dent 2003;5:57-62.  Back to cited text no. 14  [PUBMED]  

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Correspondence Address:
Emmanuel S Sathish
Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College and Hospital, Alapakkam Main Road, Maduravoyal, Chennai - 600 095, Tamil Nadu
India
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DOI: 10.4103/0970-9290.40467

PMID: 18445930

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