Evaluation of the Effect of Tooth Surface Wetting and Bond Strength of Composite-an In vitro Study

Singh Yashpal^* and Saini Monika

Qassim Private College, Saudi Arabia

Corresponding Author:

Dr. Yashpal Singh
Associate professor
Head of Oral and maxillofacial rehabilitation
Qassim private college, Saudi Arabia
Tel: 966-538921650
E-mail: dryashpal.singh@gmail.com

Received Date: November 30, 2013; Accepted Date: January 24, 2014; Published Date: January 27, 2014

Citation: Yashpal S, Monika S (2014) Evaluation of the Effect of Tooth Surface Wetting and Bond Strength of Composite-an In vitro Study. J Interdiscipl Med Dent Sci 2:111. doi: 10.4172/2376-032X.1000111

Copyright: © 2014 Yashpal S, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

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Abstract

Adhesive restorations have become integral part of routine dental treatment. To achieve clinical success with such restorations, it is of clinical importance to ensure good bonding between this restoration and tooth surface. Bonding to dentin is far more challenging. Bond between dentin and dentin bonding adhesives is greatly influenced by: (1) Surface condition of dentin (moist/dry); (2) Chemical nature of dentin bonding agents. The present study has been designed: (i) to study the effect of various conditions (moist/dry) of dentin on bonding with dentin bonding agents; (ii) to compare the strength achieved by dentin, bonding agent of different systems (water/acetone based). This study was conducted to evaluate the effect of tooth surface wetting on shear bond strength of composite. Freshly extracted central incisors were taken. Cavities were prepared in middle 1/3 of teeth. Teeth were divided in groups A,B,C depending on their surface treatment (wet, semi dry, dry surface) and again in to sub groups depending on whether they are treated water based or acetone based dentin bonding agents(scotch bond, prime bond NT, clear fil SE) . All the cavities in samples were filled with composite and light cured. Composite was debonded from teeth by Instron machine. Debonded samples were scanned and micro graphed under SEM. From the observations made, statistically analyzed and duly discussed, following conclusions are drawn: 1. Optimal water content is necessary for achieving good bonding between dentin and composite. 2. Water based dentin bonding agents, show maximum shear bond strength with dentin in dry conditions. 3. Acetone based dentin bonding agents show maximum shear bond strength with dentin in wet conditions. Overview of the results shows that moisture plays a vital role in bonding of composite with dentin. Optimal water should be present for better bonding of dentin with composite. If dentin is in dry stage, then water based dentin-bonding agents should be used as they produce best results in dry conditions and if dentin is in wet state then acetone based dentin-bonding agents should be used as they produce best results in wet conditions.

Introduction

Adhesive restorations become a very important part while doing full mouth rehabilitation case. To achieve clinical success with such restorations, it is of clinical importance to ensure good bonding between this restoration and tooth surface.

Speaking about adhesion to tooth substances, we need to distinguish the difference between enamel and dentin. Enamel is mainly composed of hydroxyapatite crystals and bond between enamel and resin has been one of the strongest bonds achieved within tooth substance.

Bonding to dentin is far more challenging as it is composed of apatite crystals embedded in collagen matrix. Lower bond strengths to dentin are the result of a number of factors:

1. Dentin contains less mineralized tooth structure and more water than does the enamel.

2. The presence of smear layer makes wetting of dentin by the adhesive more difficult. Even when good wetting occur, stress cause by polymerisation shrinkage of resin can pull the resin away from tooth structure causing microporosity1. Bonding between dentin and composite resin is not strong enough to overcome the stress of polymerization shrinkage.

3. Fluid in dentin tubules reduces the stability of composite resin to dentin bond.

It is widely accepted that bonding to dentin relies on penetration of adhesives in to the collagen fibers and encapsulation of irregular hydroxyapatite crystals at the bottom of decalcified area, which created the resin reinforced interdiffusion zone called hybrid layer [1,2].

Bond between dentin and dentin bonding adhesives is greatly influenced by:

(1) Surface condition of dentin (moist/dry) [3,4].

(2) Chemical nature of dentin bonding agents [5,6].

The present study was designed: (i) to study the effect of various conditions (moist/dry) of dentin on bonding with dentin bonding agents; (ii) to compare the strength achieved by dentin bonding agent of different systems (water/acetone based) under different conditions of dentin. Structure of samples was also studied under SEM after it was debonded from composite.

Materials and Methods

Materials used for holding sample

1. Freshly extracted non carious central incisors¹

2. Physiologic saline → was taken to store the teeth.

3. Brassdie of 15 mm × 20 mm → was prepared to hold the sample in self polymerising resin.

4. Self polymerising resin² Dappen Dish

5. Mixing spatula

Equipment used for preparing the cavity

1. Airotor hand piece³

2. 3 No. 245 bur⁴ III- Etchant and different Bonding agents used

3. [35% Phosphoric acid] Etchant [7]

4. Prime bond NT

5. Scotch bond

6. Clearfil SE bond

Material and Equipment used for application of bonding agent, etchant and drying the cavity

1. Paint brush – was used to apply bonding agent on cavity in sample tooth

2. Three way syringe

3. Timer⁵

Composite used and material used for its application and curing

1. Z-100 composite²

2. Teflon coated spatula

3. Visible light curing unit³

Instruments used for testing the bond strength of composite

Instron⁴: An instron machine was used for testing the bond strength of composite to the sample tooth sample. Instron machine had different calibrations. Cross head speed of the machine was 1140mm/minute.

Instrument used for Micrography

1. Supper coater: Used to deposit a uniform gold coat on sample.

2. Scanning electron microscope was used to take pictures of sample after debonding.

Methodology

I. Non carious upper/lower central/lateral incisors were selected and stored in physiologic saline solution

II. Each tooth was held in 15 mm x 20 mm mold of acrylic resin

III. A cavity was prepared on middle third of labial surface of tooth to reach sound dentin structure

IV. Samples were divided in three major groups on the basis of treatment of cavity surface Diagram 1 [8].

V. Cavity in each sample was filled with composite (Z100) and cured for 40 seconds with visible light curing unit

VI. Shear bond strength of composite in each sample was measured with the help of the Instron machine.

VII. All samples were scanned under and then photographed.

Diagram 1: Methodology.

One-way ANOVA and level of significance at p<0.05 were used for Statistical analysis (Table 1).

Table 1: Showing Groupwise Distribution of Samples.

Table 2 shows that mean shear bond strength of subgroup A₁ is 11.518 MPa with a standard deviation of 1.9228. Mean shear bond strength of subgroup A₂ is 12.064 MPa with standard deviation of 1.19. Mean shear bond strength of subgroup A₃ is 25.10 MPa with standard deviation of 3.7108. Mean shear bond strength of subgroup B₁ is 13.378 MPa with standard deviation of 1.8175. Mean shear bond strength of subgroup B₂ is 10.226 MPa with standard deviation of 0.7162. Mean shear bond strength of subgroup B₃ is 30.966 MPa with standard deviation of 1.0805. Mean shear bond strength of subgroup C₁ is 20.92 MPa with standard deviation of 0.9550. Mean shear bond strength of subgroup C₂ is 6.13 MPa with standard deviation of 0.7418. Mean shear bond strength of C₃ is 31.06 MPa with standard deviation 1.5962.

Table 2: Showing mean shear bond strength with standard deviation and standard error of samples of Group A, B and C.

Table 3 shows the intergroup comparison of mean shear bond strength, standard deviation and standard error for Subgroup 1 (samples treated with Scotch Bond). It was seen that the mean shear bond strength was highest for Subgroup C₁ followed by Subgroup B₁ and then Subgroup A₁ (Diagram 2). The standard deviation was maximum in Subgroup A₁ followed by Subgroup B₁ and then Subgroup C₁. The standard error was maximum in Subgroup A₁ followed by Subgroup B₁ and then Subgroup C₁.

Diagram 2: Shear bond strength pattern for the subgroup 1 (treated with Scotch bond) in different groups: Subgroup C₁>Subgroup B₁>Subgroup A₁.

Table 3: Showing Intergroup Comparison of Shear Bond Strength in Subgroup 1 (Treated with Scotch Bond).

Since ‘F’ is significant, hence shear bond strength differs significantly in subgroups. It is maximum in Subgroup C₁ and minimum in A₁ (Tables 4 and 5)

Table 4: Showing Analysis of Variance of Shear Bond Strength in Subgroup 1 (Treated with Scotch Bond).

Table 5: Showing Intergroup Comparison of Shear Bond Strength in Subgroup 1 (Treated with Scotch Bond).

On comparing the mean shear bond strength of subgroup A₁ to subgroup B₁, the mean shear bond strength was higher in subgroup B₁ but it was not significant statistically (p=0.15, NS). However, when subgroup A₁ was compared with subgroup C₁, the mean shear bond strength for subgroup C₁ was found to be significantly higher than subgroup A₁ (p<0.001). On comparing the subgroup B₁ with subgroup C₁, once again the mean shear bond strength for subgroup C₁ was found to be significantly higher than subgroup B₁ (p<0.001).

The above analysis shows the following shear bond strength pattern for the subgroup 1 (treated with Scotch bond) in different groups (Diagram 2):

Subgroup C₁>Subgroup B₁>Subgroup A₁

Table 6 shows the intergroup comparison of mean shear bond strength, standard deviation and standard error for Subgroup 2 (samples treated with Prime Bond NT). It was seen that the mean shear bond strength was highest for Subgroup A₂ followed by Subgroup B₂ and then Subgroup C₂ (Diagram 3). The standard deviation was maximum in Subgroup A₂ followed by Subgroup C₂ and then Subgroup B_1/2. The standard error was maximum in Subgroup A₂ followed by Subgroup C₂ and then Subgroup B₂.

Diagram 3: Shear bond strength pattern for the subgroup 2 (treated with Prime Bond NT) in different groups: Subgroup A₂>Subgroup B₂>Subgroup C₂.

Table 6: Showing Intergroup Comparison of Shear Bond Strength in Subgroup 2 (Treated with Prime Bond NT).

Since ‘F’ is significant, hence shear bond strength differs significantly in subgroups. It is maximum in Subgroup A₂ and minimum in C₂ (Table 7).

Table 7: Showing Analysis of Variance of Shear Bond Strength in Subgroup 2 (Treated with Prime Bond NT).

On comparing the mean shear bond strength of subgroup A₂ to subgroup B₂, the mean shear bond strength was significantly higher in subgroup A₂ (p<0.01). When subgroup A₂ was compared with subgroup C₂, once again the mean shear bond strength for subgroup A₂ was found to be significantly higher than subgroup C₂ (p<0.01). On comparing the subgroup B₂ with subgroup C₂, the mean shear bond strength for subgroup B₂ was found to be significantly higher than subgroup C₂ (p<0.001) (Table 8).

Table 8: Showing Intergroup Comparison of Shear Bond Strength in Subgroup 2 (Treated with Prime Bond NT).

The above analysis shows the following shear bond strength pattern for the subgroup 2 (treated with Prime Bond NT) in different groups (Diagram 3):

Subgroup A₂>Subgroup B₂>Subgroup C₂

Table 9 shows the intergroup comparison of mean shear bond strength, standard deviation and standard error for Subgroup 3 (samples treated with Clearfil SE Bond). It was seen that the mean shear bond strength was highest for Subgroup C₃ followed by Subgroup B₃ and then Subgroup A₃ (Diagram 4). The standard deviation was maximum in Subgroup A₃ followed by Subgroup C₃ and then Subgroup B₃. The standard error was maximum in Subgroup A₃ followed by Subgroup C₃ and then Subgroup B₃.

Diagram 4: shear bond strength pattern for the subgroup 3 (treated with Clearfil SE Bond) in different groups: Subgroup C₃>Subgroup B₃>Subgroup A₃.

Table 9: Intergroup Comparison of Shear Bond Strength in Subgroup 3 (Treated with Clearfil SE Bond).

It was observed in SEM of debonded samples that subgroups A₃, B₃, C₃ show cohesive failure in composite. Micrograph of A₃, B₃, C₃ show presence of some composite in debonded area. None of the sample in A₁, B₁, C₁ and A₂, B₂, C₂ show times of cohesive failure. They show adhesive failure. There is no sign of composite in debonded area.

Since ‘F’ is significant, hence shear bond strength differs significantly in subgroups. It is maximum in Subgroup C₃ and minimum in A₃ (Table 10).

Table 10: Showing Analysis of Variance of Shear Bond Strength in Subgroup 3 (Treated with Clearfil SE Bond).

On comparing the mean shear bond strength of subgroup A₃ to subgroup B₃, the mean shear bond strength was significantly higher in subgroup B₃ (p<0.01). When subgroup A₃ was compared with subgroup C₃, the mean shear bond strength for subgroup C₃ was found to be significantly higher than subgroup A₃ (p<0.01). On comparing the subgroup B₃ with subgroup C₃, the mean shear bond strength for subgroup B₃ was found to be higher than subgroup C₃ but it was not significant statistically (p=0.91, NS) (Tables 11-13).

Table 11: Showing Intergroup Comparison of Shear Bond Strength in Subgroup 3 (Treated with Clearfil SE Bond).

Table 12: Showing Comparison of Shear Bond Strength in Group A.

Table 13: Showing Analysis of Variance of Shear Bond Strength in Group A.

The above analysis shows the following shear bond strength pattern for the subgroup 3 (treated with Clearfil SE Bond) in different groups (Diagram 4):

Subgroup C₃>Subgroup B₃>Subgroup A₃

Table 14 shows the comparison between mean shear bond strength, standard deviation and standard error for Group A. It was seen that the mean shear bond strength was highest for Subgroup A₃ followed by Subgroup A₂ and then Subgroup A₁. The standard deviation was also maximum in Subgroup A₃ followed by Subgroup A₁ and then Subgroup A₂. The standard error was maximum in Subgroup A₃ followed by Subgroup A₂ and then Subgroup A₂.

Table 14: Showing Comparison of Shear Bond Strength among the three subgroups of Group A.

Since ‘F’ is significant, hence shear bond strength differs significantly in subgroups. It is maximum in Subgroup A₂ and minimum in A₂.

On comparing the mean shear bond strength of subgroup A₁ to subgroup A₂, the differences were found to be statistically nonsignificant. However, when subgroup A₂ was compared with subgroup A₃, the mean shear bond strength for subgroup A₃ was found to be significantly higher than subgroup A₁ (p<0.001). On comparing the subgroup A₂ with subgroup A₃, once again the mean shear bond strength for subgroup A₃ was found to be significantly higher than subgroup A₂ (p<0.001) (Tables 15 and 16).

Table 15: Showing Comparison of Shear Bond Strength in Group B.

Table 16: Showing Analysis of Variance of Shear Bond Strength in Group B.

The above analysis shows the following shear bond strength pattern for the three subgroups of Group A:

Subgroup A₃>Subgroup A₂>Subgroup A₁

Table 15 shows the comparison between mean shear bond strength, standard deviation and standard error for Group B. It was seen that the mean shear bond strength was highest for Subgroup B₃ followed by Subgroup B₁ and then Subgroup B₂. The standard deviation was maximum in Subgroup B₁ followed by Subgroup B₃ and then Subgroup B₂. The standard error was maximum in Subgroup B₁ followed by Subgroup B₃ and then Subgroup B₂.

Since ‘F’ is significant, hence shear bond strength differs significantly in subgroups. It is maximum in Subgroup B₃ and minimum in B₂.

On comparing the mean shear bond strength of subgroup B₁ to subgroup B₂, the mean shear bond strength was significantly higher in subgroup B₁ at 99% level of confidence (p<0.01). However, when subgroup B₁ was compared with subgroup B₃, the mean shear bond strength for subgroup B₃ was found to be significantly higher than subgroup B₁ (p<0.001). On comparing the subgroup B₂ with subgroup B₃, once again the mean shear bond strength for subgroup B₃ was found to be significantly higher than subgroup B₂ (p<0.001) (Tables 17-19).

Table 17: Showing Comparison of Shear Bond Strength among the three subgroups of Group B.

Table 19: Analysis of Variance of Shear Bond Strength in Group C.

The above analysis shows the following shear bond strength pattern for the three subgroups of Group B:

Subgroup B₃>Subgroup B₁>Subgroup B₂

Table 20 shows the comparison between mean shear bond strength, standard deviation and standard error for Group C. It was seen that the mean shear bond strength was highest for Subgroup C₃ followed by Subgroup C₁ and then Subgroup C₂. The standard deviation was maximum in Subgroup C₃ followed by Subgroup C₁ and then Subgroup C₂. The standard error was maximum in Subgroup C₃ followed by Subgroup C₁ and then Subgroup C₂.

Table 20: Comparison of Shear Bond Strength among the three subgroups of Group C.

Since ‘F’ is significant, hence shear bond strength differs significantly in subgroups. It is maximum in Subgroup C₃ and minimum in C₂.

Table 20 Comparison of Shear Bond Strength among the three subgroups of Group C.

On comparing the mean shear bond strength of subgroup C₁ to subgroup C₂, the mean shear bond strength was significantly higher in subgroup C₁ (p<0.001). However, when subgroup C₁ was compared with subgroup C₃, the mean shear bond strength for subgroup C₃ was found to be significantly higher than subgroup C₁ (p<0.001). On comparing the subgroup C₂ with subgroup C₃, once again the mean shear bond strength for subgroup C₃ was found to be significantly higher than subgroup C₂ (p<0.001).

The above analysis shows the following shear bond strength pattern for the three subgroups of Group C:

Subgroup C₃>Subgroup C₁>Subgroup C₂

Debonded samples were studied under SEM. It was observed in SEM of debonded samples that a few samples in subgroups A₃, B₃, C₃ show cohesive failure in composite. Micrograph of A₃, B₃, C₃ show presence of some composite in debonded area.

None of the sample in A₁, B₁ C₁ and A₂, B₂, C₂ show signs of cohesive failure. They show adhesive failure. There is no sign of composite in debonded area.

Discussion

Adhesive restorations have become the inseparable part of dentistry. For, success of these restorations bonding between restoration and tooth surface is of utmost importance. Bonding with dentin is far more complex process. The dynamic variable nature of dentin poses significant challenges to bonding between adhesive restoration and dentin.

The purpose of this study was to evaluate the effect of various conditions (moist/ dry) of dentin on bonding with dentin bonding agent and to compare the strength achieved by dentin bonding agent of various systems (acetone/water) under different conditions of dentin (moist/dry). Structure of dentin was also studied under SEM after it was debonded from composite.

Several factors complicate the process of bonding of adhesive resins to dentin. Brannstrom in 1993 showed dentinal fluid under positive pressure from pulp may affect diffusion of monomers in to etched dentin. Structural variability of dentin must also be considered. Intertubular dentin which is ideal for formation of Hybrid layer occupies 96% of dentin surface at DEJ and only 12% near pulp [4,9]. Thickness and tenacity of smear layer attachment to underlying dentin surface also affects bonding. Role of moisture is of utmost importance in dentin bonding with adhesive resins [5].

The central incisors were selected for the study as the use of composite restorations is largely done for esthetically purposes. So it will be relevant to study the behavior of dentin-bonding under various conditions (wet, semi-dry, dry) in central incisors which bear utmost esthetic value.

Teeth were held in resin mold of 15 mm x 20 mm [as specified for Instron machine]. A cavity was prepared in middle third of labial surface of tooth for the ease of testing shear bond strength with Instron machine.

No. 245 bur was used to prepare the cavity and was penetrated till 1/3rd to 1/2 of the length of the bur head. This will place the cavity margins within 0.2 mm of dentin and the chances of pulp exposure were minimized.

Now the samples were divided in three groups. Cavities in group A samples were treated by wet surface treatment before applying dentin bonding agent by swabbing the cavity with wet cotton pellet. It was done to observe the effect of bonding of dentin with dentin bonding agent in wet conditions.

Cavities in Group B samples were treated by semi-dried surface treatment before applying dentin bonding agent by drying the cavity for 3 seconds. It was done to observe the effect of bonding of dentin with dentin bonding agent in semi-dried conditions.

Similarly, cavities in Group C samples were treated by dry surface treatment by drying the cavities by 15 minutes to observe the effect of bonding of dentin with dentin bonding agent in dried condition. Cavities in Group C were dried for 15 seconds because when several teeth were dried and time for complete drying of the teeth was observed then the mean time of the drying of the teeth was found to be 15 seconds.

Now Groups A, B and C were further subdivided into subgroups A₁, A₂, A₃, B₁, B₂, B₃, C₁, C₂ and C₃.

In subgroups A₁, B₁, C₁ Scotch bond was used to line the cavity surface as it has water-based primer so it could be observed that in what conditions of dentin, dentin-bonding agents with water based primers show maximum shear bond strength 2, 3, 4.

In Subgroups A₂, B₂, C₂ Prime-bond NT was used to line the cavity surface as it is acetone based. So it could be observed that in what conditions of dentin acetone-based dentin-bonding agents show maximum shear bond strength.

In Subgroups A₃ A₃, B₃, C₃ Clearfil-SE was used to line the cavity surface. Clearfil-SE is also water based but has self-etching primer. Clearfil-SE is placed in sixth generation of dentin-bonding agents. So it can be observed what effect does self-etching primer containing dentin-bonding agent has on shear bond strength with dentin under various conditions.

The choice of dentin-bonding agents served the purpose of the study as it was aimed to observe the effect of various conditions (wet, dry and semi-dry) of dentin on bonding with dentin-bonding agents and comparisons of strengths achieved by various dentin-bonding agents of different systems (water/acetone based) under different conditions of dentin.

After treating the samples by wet, semi-dry or dry surface treatments cavity was filled with Z-100 composite and was light cured. Shear bond strength of all samples were tested using Instron machine.

As shown in Table 5, mean shear bond strength of C₁ was highest followed by B₁ and A₁. It can be explained by the study of Iwami et al. proved that when the water on the dentin surface is less before application of dentin bonding agent, collagen fibers in dentin surface might shrink [8]. Shrinkage of collagen fibers inhibits the infiltration of resin monomers in to dentin and optimal amount of water is necessary to inhibit the shrinkage of collagen fibers. In contrast, excessive water on dentin surface prevents infiltration of resin monomers into the dentin because the concentration of resin monomer in dentin bonding agent decreases. Therefore, optimal water on dentin surface is necessary for the formation of adequate bond strength between resin composite and dentin.

Scotch-bond has water based primer. In wet conditions, it actually over wets the dentin that in turn prevents the infiltration of resin monomers in dentin because the concentration of resin monomers in primer decreases.

In dry condition, Scotch-bond wets the dentin and prevents the shrinkage of collagen fibers, thus helping in better infiltration of resin monomers in dentin.

Table 8 shows that mean shear bond strength of A₂ was highest followed by B₂ and then C₂. It can be explained by the study of Kanca et al. [10,11], which showed that acetone containing dentin bonding agents work well in wet conditions. Acetone present in primer apparently acts as water chasers. Acetone spreads the primer over water coated dentin surface in carried the resin monomer present in primer in to dentin. In addition acetone containing primer on contact with wet dentin surface raise the boiling point of acetone and lower the boiling point of water such that this may enhance removing water in the collagen matrix which in turn exchanges for acetone and finally for the adhesive resins.

Prime-bond NT is acetone based. In wet conditions acetone spreads the dentin bonding agent over water coated dentin surface in carrying resin monomer in dentin.

In dry condition acetone in Prime bond dentin over dries the dentin as acetone is water chaser. So, it causes shrinkage of collagen fibers in dentin and thus minimizes the infiltration of resin monomer in dentin which in turn causes weak bond between dentin and composite.

Table 11 shows that mean shear bond of C₃ was highest followed by B₃ and A₃. It can be explained, as in case of Table 5, as Clearfil-SE is also water-based dentin bonding agent.

High mean shear bond strength [12-14] of A₃, B₃, C₃ as compared to A₁, B₁, C₁ and A₂, B₂, C₂ can be explained by the fact that Clearfil-SE is sixth generation dentin bonding agent whereas Scotch-bond is placed in fourth generation and Prime-bond NT is placed in fifth generation.

These results were in confirmation of earlier studies which prove that optimal amount of water is necessary for dentin for good bonding with composite. Over wetting or over drying both decreases the strength of bond between dentin and composite.

It could be observed from the study that out of subgroups A₁, B₁, C₁, subgroup C₁ showed maximum shear bond strength followed by B₁ and A₁ as Scotch-bond has water based primer and worked best in dry conditions. Of subgroups A₂, B₂, C₂ mean shear bond strength of A₂ was highest followed by B₂ and C₂ as Prime-bond NT is acetone based bonding agent and worked best in wet conditions. Of subgroups A₃, B₃, C₃ mean shear bond strength of C₃ was highest followed by B₃ B₃ and A₃ as Clearfil SE is water-based bonding agent and worked best in dry conditions.

So the water-based dentin-bonding agents work well in dry conditions and acetone based dentin-bonding agents work well in wet conditions.

All the bonded samples were scanned under SEM. A few samples of subgroups A₃, B₃, C₃ showed cohesive failure in composite (Figures 7-9). This shows that the fracture occurred within the composite which proves good bonding between dentin and composite. None of the sample showed cohesive failure in composite in subgroups A₁, B₁, C₁ (Figure 1-3) and A₂, B₂, C₂ (Figures 4-6) which show adhesive failures.

Figure 1: SEM micrograph of subgroup A₁ after debonding.

Figure 2: SEM micrograph of subgroup B₁ after debonding.

Figure 3: SEM micrograph of subgroup C₁ after debonding.

Figure 4: SEM micrograph of subgroup A₂ after debonding.

Figure 5: SEM micrograph of subgroup B₂ after debonding.

Figure 6: SEM micrograph of subgroup C₂ after debonding.

Figure 7: SEM micrograph of subgroup A₃ after debonding.

Figure 8: SEM micrograph of subgroup B₃ after debonding.

Figure 9: SEM micrograph of subgroup C₃ after debonding.

This can be explained as the greater strength of the bond formed in sixth generation dentin bonding agent as compared to fourth and fifth generation dentin bonding agents.

Overview of the results shows that moisture plays a vital role in bonding of composite with dentin. Optimal water should be present for better bonding of dentin with composite. If dentin is in dry stage, then water based dentin-bonding agents should be used as they produce best results in dry conditions and if dentin is in wet state then acetone based dentin-bonding agents should be used as they produce best results in wet condition.

Conclusion

From the observations made, statistically analyzed and duly discussed, following conclusions are drawn:

1 Optimal water content is necessary for achieving good bonding between dentin and composite.

2 Water based dentin bonding agents, show maximum shear bond strength with dentin in dry conditions.

3 Acetone based dentin bonding agents show maximum shear bond strength with dentin in wet conditions.

Acknowledgements

This original work is attributed to Department of Prosthodontics, U.P. King George's University of Dental Sciences, Lucknow in collaboration with Central Drug Research Institute, Lucknow.

¹Kurary Dental, Japan

²3M Dental Products

³Dentsply International Inc

⁴Instron 1140 (HAL)

⁵Racer, Kadio, Japan

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