Journal of Conservative Dentistry

ARTICLE
Year
: 2007  |  Volume : 10  |  Issue : 1  |  Page : 26--32

Effect of Rewetting agents on the shear bond strength of different bonding agents when applied on dry dentin


Abhishek Bansal, Vasundhara Shivanna 
 Department of Conservative and Endodontics, College of Dental Sciences, Davangere - Karnataka, India

Correspondence Address:
Abhishek Bansal
Department of Conservative and Endodontics, College of Dental Sciences, Davangere - Karnataka
India

Abstract

Background and Objectives: The objective of this study was to compare shear bond strength of the three bonding agents containing different concentrations of water when applied over the etched dentin surfaces under different conditions like dry, wet (control subgroup) or dry and rewetted with different rewetting agents like Aqua Prep and Gluma desensitizer. Methods: The study samples comprised of the buccal and lingual surfaces of 60 extracted human molars that were ground to expose the dentin. The teeth were randomly assigned to three groups depending upon the different bonding agents (Multipurpose Scotch bond, Single Bond, Prime and Bond NT)­Further each group was divided into four subgroups depending upon the different etched dentin surface conditions i.e. dry, wet (control subgroup), dry and rewetted with different rewetting agents that received the following treatment. In all the three groups, the dentin surface was etched with 35% phosphoric acid for 15 seconds and the treated surface was rinsed thoroughly with water followed by the application of respective bonding agents according to manufacturers instructions and light cured under different etched dentin surface condition like dry, wet or dry and rewetted with aquaprep and Gluma desensitizer. Each major group was further divided into 4 subgroups of 10 samples each depending upon different etched dentin surface conditions. The specimens were stored in distilled water at 37 o C for 24 hours and the shear bond strength was tested by lowering the knife edge chisel at a cross head speed of l mm/minute. The data was analysed with One way ANOVA test and post hoc Tukey test. Results: The highest mean shear bond strengths were obtained (in order) on dentin that was re-wetted with Gluma desensitizer, rewetted with Aquaprep or in wet dentin substrate condition, differences between these surface conditions were not statistically significant for either material. Interpretation and Conclusion: The use of dentin bonding agents containing different percentage of water should be considered according to different dentin substrate conditions i.e. dry or wet. Use of rewetting agents may be beneficial when dentin was over dried after acid etching and rinsing, and when less percentage of water concentration dentin bonding is used in such situation.



How to cite this article:
Bansal A, Shivanna V. Effect of Rewetting agents on the shear bond strength of different bonding agents when applied on dry dentin.J Conserv Dent 2007;10:26-32


How to cite this URL:
Bansal A, Shivanna V. Effect of Rewetting agents on the shear bond strength of different bonding agents when applied on dry dentin. J Conserv Dent [serial online] 2007 [cited 2019 Dec 5 ];10:26-32
Available from: http://www.jcd.org.in/text.asp?2007/10/1/26/42277


Full Text

 Introduction



A major research goal of dental materials during the past 20 years was to develop a filling material capable of forming a strong bond with the tooth structures. This has lead to various developments in the field of adhesive restorative dentistry.

Achieving predictable bonding to dentin has long been a goal and challenge in restorative dentistry. But adhesion of resin to enamel is highly predictable and durable due to micromechanical bond between the resin bonding agent and the highly inorganic substrate of enamel. However, bonding of composite resin to dentin is comparatively difficult due to the following reasons: Complex structure of dentin with a low inorganic content randomly arranged in an organic collagen matrix, presence of dentinal fluid, which is constantly flowing outwards and proximity of dentinto pulp.

Early dentin bonding agents attempted at bonding to either the inorganic or organic constituents of dentin .[1] The current basis for dentin bonding is the formation of a hybrid layer, resulting from resin penetration into the acid demineralized dentin. [6] Application of dentin bonding agent causes enmeshment of the exposed collagen fibrils, by hydrophilic resin monomers. This is the resin­-dentin 'hybrid layer' that is located between the dentin and the composite restorative material. [5]

Clinically, it is very difficult to either assess or standardize the ideal amount of moisture that should be left on dentin surface before application of adhesive system. Ideally water should form an uniform layer without over wetting or overdrying, Moreover when less or no water content adhesive or acetone, ethanol (water chaser) based adhesives were used or when situations like over drying of dentin substrate occurs, it causes collapse of the collagen network and prevents penetration of resin monomers thus leading to weaker bonds. In such situations it is essential to rewet the etched dentinal surface with the help of different rewetting agents before application of the adhesive. [8]

Rewetting agents are nothing but the aqueous solution containing 35-37% of HEMA (2­Hydroxyethyl methacrylate) water (H 2 O) or some solutions contains (NaF) sodium fluoride and glutaraldehyde also. HEMA plays an important role as a stiffening agent preventing any subsequent shrinkage and have a potential reaction (chemical) between the ester functional group of HEMA and dentin collagen, they also have the ability to promote dentin adhesion and help in facilitating diffusion of resin monomer and the formation of hybrid layer7Commonly available rewetting agents arc, Aquaprep (BISCO) which contains 35% HEMA and water, gluma desensitizer which contains 36.1% HEMA, 5.1% Glutaraldehyde and water itself also acts as a rewetting agent and has the tendency to re-expand the collapsed fibrils.

 Objective



The objective of this study was to compare the shear bond strength of three bonding agents containing different concentrations of water when applied over the etched dentin surfaces under different conditions like dry, wet or dry and rewetted

 Methodology



Materials used for the study:

1) Etchant used Is : 35% Phosphoric Acid Gel

2) Bonding agents

a) Scotch Bond Multipurpose (3M)

b) Single Bond (3M) Single Component System

c) Prime and Bond NT (Dentsply) (Single component System)

3) Rewetting agents used

a) Aquaprep (BISCO)

b) Gluma Desensitizer (Hereus Kulzer)

4) Composite resin (Z-100, 3M)

5) Etchant and bonding agent application brushes

6) Flour pumice

7) Polyester resin

8) Distilled water

 Procedure

:

All the experimental teeth were cleaned with scalers and flour pumice. The roots of all the 60 teeth were sectioned l mm below the cemento enamel junction and the crowns were sectioned in a mesio-distal direction. 120 samples thus obtained were mounted in a block of polyester resin, and flat dentinal areas were exposed, on the buccal and lingual surfaces by grinding them with a diamond disc.

 Grouping

:

The specimens were divided into three major groups of forty samples each depending upon the different bonding agents used.

GroupI :Scotch bond multipurpose dentin bonding agent

Group II :Single Bond Dentin Bonding Agent

Group III: Prime and Bond NT dentin bonding agent

In all the three groups, the dentin surface was etched with 35% phosphoric acid for 15 seconds and the treated surface was thoroughly rinsed with water followed by the application of the respective bonding agents according to manufacturers instructions and light cured under different dentin surface conditions like dry, wet or dry and rewetted with different rewetting agents (Aquaprep and Gluma Desensitizer according to respective grouping).

 Subgrouping

:

Further each major group were divided into four subgroups of 10 samples each depending upon different etched dentin surface conditions like dry, wet (control subgroup) or dry and rewetted with different rewetting agents.

Subgroup Ia:

After rinsing of the etched dentin surface, it was dried for 5 seconds with an air syringe positioned 2 cm from the dentin surface followed by the application of Scotchbond multipurpose with a disposable brush and light cured for 10 seconds (This was the dry subgroup).

Subgroup lb:

Samples were treated same as in subgroup Ia except that after rinsing, the etched dentin surfaces were blotted with blotting paper leaving the surface visibly wet, evidenced by a glistening appearance. Compressed air was not used. (This was the wet subgroup-Control subgroup).

Subgroup Ic:

Samples were treated same as in subgroup Ia but after air drying the dentin surface was re-wetted with a disposable brush tip saturated in Aquaprep (rewetting agent) prior to the application of Scotchbond multipurpose.

Subgroup Id:

Samples were treated as in subgroup Ia but after air drying the dentin surface was re-wetted with a disposable brush tip saturated in Gluma desensitizer (rewetting agent) prior to the application of Scotchbond multipurpose.

Subgroup IIa:

The samples were treated same as in subgroup Ia but the dentin bonding agent used was single bond (This was the dry subgroup).

SubgroupIIb:

The samples were treated same as in subgroup Ib but the dentin bonding agent used was single bond (This was the wet subgroup - control subgroup).

Subgroup IIc:

The samples were treated same as in subgroup Ic but the dentin bonding agent used was single bond.

Subgroup IId:

The samples were treated same as in subgroup Id but the dentin bonding agent used was single bond.

Subgroup IIIa:

The samples were treated same as in subgroup Ia but the dentin bonding agent used was Prime and Bond NT. (This was the dry subgroup).

Subgroup III b:

The samples were treated same as in subgroup Ib but the dentin bonding agent used was Prime and Bond NT. (This was the wet subgroup - Control subgroup).

Subgroup IIIc:

The samples were treated same as in subgroup Ic but the dentin bonding agent used was Prime and Bond NT.

Subgroup IIId:

The samples were treated same as in subgroup Ic but the dentin bonding agent used was Prime and Bond NT.

After the above mentioned steps, a Teflon mold with circular hole (3.5 mm diameter, height is 2.5 mm) was used on all the samples. A Z-100 (3M) resin composite was inserted into the circular hole of the Teflon mold, and light cured for 80 seconds and Teflon mold was removed after curing, by which a cylinder of resin composite was obtained.

 Results



The results were analysed by one way ANOVA for multiple comparison and pair-wise comparison were made using Post Hoc Tukey test for significance.

 Analysis of results



The shear bond strength values obtained from individual sample from all the groups are summarized in [Table 1].

In Group I (Scotchbond Multipurpose) Subgroup condition i.e.(dry), shear bond strength value ranged between 16.1-20.8 MPa.

In Group I (Scotchbond Multipurpose) Subgroup condition i.e. (wet control subgroup), shear bond strength value ranged between 3.3 - 5.7 M Pa.

In Group I (Scotchbond Multipurpose) Subgroup condition i.e. (treated with Aquaprep), shear bond strength value ranged between 4.2-8.1 MPa.

In Group I (Scotchbond Multipurpose) Subgroup condition i.e. (treated with Gluma desensitizer), shear bond strength value ranged between 5.2 - 9.2 MPa.

In Group II (Single Bond) Subgroup condition i.e. (dry), shear bond strength value ranged between 8.7 - 14.0 MPa.

In Group II (Single Bond) Subgroup condition i.e. (wet - control subgroup), shear bond strength value ranged between 20.1-25.0 MPa.

In Group II (Single Bond) Subgroup condition i.e. (treated with Aquaprep), shear bond strength value ranged between 20.8-25.7 MPa.

In Group 11 (Single Bond) Subgroup condition i.e. (treated with Gluma desensitizer), shear bond strength value ranged between 24.0-28.1 MPa.

In Group III (Prime & Bond NT) Subgroup condition i.e. (dry), shear bond strength value ranged between 4.2-7.8 MPa.

In Group III (Prime & Bond NT) Subgroup condition i.e. (wet - control subgroup), shear bond strength value ranged between 8.9-14.1 MPa.

In Group III (Prime & Bond NT) Subgroup condition i.e. (treated with Aquaprep), shear bond strength value ranged between 10.0-16.0 MPa.

In Group III (Prime & Bond NT) Subgroup condition i.e. (treated with Gluma desensitizer), shear bond strength value ranged between 10.5 - 16.6 MPa.

Shear bond strength values in 3 main groups and further sub groups were compared and related information in terms of mean and standard deviation are presented in [Table 1] and [Graph 1].

In Group I, subgroup condition i.e. (dry) mean shear bond strength values were 18.5, which was significantly higher when compared to all other groups (P [9] Here the dentin surface is left visibly moist (glistening) after etching and rinsing prior to application of the dentin bonding agent. It has been suggested that the inclusion of water in the adhesive may re-expand the collapsed fibrils and facilitate the infiltrations of etched dentin by the resin monomers. On the other hand, excess water in the etched dentin also can result in an inadequate bonding substrate. This so called "overwet" phenomenon is observed.

The water concentration may vary for different bonding agents like water based dentin bonding agents eg. Scotchbond Multipurpose (3M) which consist of 50% of water in it. Some dentin bonding agents comes with less water concentration eg. Single Bond (3M) which contains 5% of water, was an ethanol based dentin bonding agent. And some dentin bonding agents have 0% of water in it eg. Prime and Bond NJ So to over come this problem concept of rewetting agents comes into play. Rewetting agents are nothing but the solution containing a mixture of HEMA and water in it. Eg. Aquaprep (BISCO) contains 35% HEMAand water, Gluma desensitizer consists 36.1% HEMA; water and 5.1 % Glutaraldehyde.

Re-wetting following acid conditioning not only expands the demineralized collagen network but also increases the surface energy of the substrate, favoring the diffusion of the hydrophilic resin monomers into the etched zone. The amount of water in wet bonding might be a critical factor for some adhesive systems, on the other hand, the fact that the HEMA containing re-wetting agents elevated the mean shear bond strength values for the adhesive containing 0% of water eg. Prime and Bond NT.

According to the result obtained, Scotchbond multipurpose (Group I) showed the highest shear bond strength value in the dry subgroup condition, which was highly statistically significant to other dentin bonding agents whereas Prime and Bond NT showed the lowest bond strength value and differences were statistically significant when it was compared to other groups. In dentin adhesion for the shear bond strengths of systems containing water i.e. (Scotchbond Multipurpose) were higher than those containing acetone (Prime and Bond NT) when the dentin was dry. In addition, systems that contained acetone (Prime and Bond NT) exhibited greater adhesion under wet conditions.

The [2] bonding system which contained acetone as the solvent (Prime and Bond NT) had significantly lower bond strength when applied to dry dentin and same bonding agents shows better results when applied to moist dentin.

In a wet subgroup (Control) dentin substrate condition:

Single bond dentin bonding agent showed the highest shear bond strength values which was statistically significant to other dentin bonding agents used whereas Scotchbond multipurpose showed the lowest shear bond strength value and the difference was statistically significant.

Moist [3] bonding is only essential for particular bonding systems with a low water content of the primer such as All Bond-2 or Single bond which comprises only 5% of water in it. In contrast Primer with water content of 20% or more (Scotch bond Multipurpose) can be used in a dry dentin substrate condition due to their intrinsic rewetting capacity.

Application [10] of water containing primers (Scotchbond Multipurpose) to an already moist dentin surface results in an overwet phenomenon which results in formation of very thin hybrid layer which definitely hampers the bond strength when compared to other ethanol or acetone based primer adhesive systems. When comparison of single bond and Prime and Bond NT was done in wet subgroup conditions, both bonding agents had minimal or no water content so there was no question of "overwet phenomenon" in both the cases but single bond exhibits higher bond strength when compared it with Prime and Bond NT.

Single bond [7] (contains 5% water, ethanol based) shows higher shear bond strength when compared to Prime and Bond NT (contain 0% water, acetone based) used in wet dentin substrate condition. Single bond [7] (contain 5% water ethanol, based) shows higher shear bond strength when compared to Prime and Bond NT (contain 0% water, acetone based) used in condition like dry and rewetted with Aquaprep and Gluma desensitizer.

The Single bond showed the higher shear bond strength, the probable reasons were the same when used in case of wet subgroup condition.

Routinely blot dry dentin surface condition which shows the glistening appearance was the ideal dentin substrate condition for application of the primer adhesive system. Above all, the role of dentin bonding agents and rewetting agents which comprises different percentage of water in their constitutional composition should be taken into consideration for different etched dentin substrate conditions for better bond strength between the tooth and the restoration. However additional in-­vivo and in-vitro tests and clinical trial are desirable in order to elucidate the effectiveness of these dentin bonding agents.

 Conclusion



Following conclusions are drawn from this study;

The use of different dentin bonding agents having different percentage of water should be implicated according to the different etched dentin surface conditions eg. dry or wet. The use of rewetting agents have become mandatory in case of those dentin bonding agents which does not possess the intrinsic self rewetting capacity for mimicking the ideal dentin substrate condition.[Figure 1],[Figure 2],[Figure 3],[Figure 4]

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