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Research

Authors: Dr. Mayank Agrawal, Dr. Atul Singh, Dr. O.P Mehta

ABSTRACT

Objective: To test the null hypothesis that the deproteinizing agent does not increase the shear bond strength of light cure bonding material bonded with conventional, self-etching and moisture insensitive primers.
Material And Method: one hundred thirty five human premolars extracted for orthodontic purpose were used and divided into nine subgroups: A1) Teeth with conventional etching, conventional primer and bonding, A2) Teeth with self etch primer and bonding, A3) Teeth with conventional etching, moisture insensitive primer and bonding, B1) Teeth with deproteinizing agent, conventional etching, conventional primer and bonding B2) Teeth with deproteinizing agent, self etch primer and bonding, B3) Teeth with deproteinizing agent, conventional etching, moisture insensitive primer and bonding C1) Teeth with deproteinizing agent, conventional primer and bonding C2) Teeth with deproteinizing agent and bonding C3) Teeth with deproteinizing agent, moisture insensitive primer and bonding. After bonding, the mechanical tests were performed in a Universal mechanical test machine. The values obtained were submitted to an analysis of variance and afterward to the unpaired t test (P < .05).
Results: The shear bond strength results demonstrated that the mean shear bond strength values of subgroup A1 (9.84MPa), subgroup A3(9.35MPa), subgroup B1 (10.58MPa) and subgroup B3 (10.34MPa) were in the range of 9-10 MPa which has been higher than the clinically acceptable limit 8MPa but the difference among them is statistically insignificant.
Conclusions: SBS value obtained with the use of deproteinizing agent was comparatively higher as compared to conventional bonding method but statistically not very significant. Still, the use of 37% phosphoric acid for 15 seconds for conditioning of enamel remains the best method for pretreatment of enamel.
KEY WORDS: Shear Bond strength; Deproteinization; Etching;

INTRODUCTION:-

The cutting edge in dentistry at the end of the 20th century came with the advent of aesthetic and adhesive bonding materials. The developments of acid etch technique by Bunocore1 in 1955 led to the direct bonding of orthodontic brackets with epoxy resin by Newman2 in 1965. Etching of the enamel has been done to remove contaminants, to raise the surface energy of the enamel and to create micropores into which the resin may flow for micromechanical attachments. This increases the bond strength of resin to the enamel and reduces the marginal leakage 4. Human enamel usually contains 96 % of the inorganic substance and 4 % of organic substances with water. The protein present in the organic component in the mature enamel is amelogenin and enamelin. However, the action of phosphoric acid on enamel surface occurs mostly on its mineralized part and does not eliminate the organic contents completely7. Venezie et al9 introduced the concept of enamel deproteinization with sodium hypochlorite to enhance the bonding efficiency of hypocalcified amelogenesis imperfect enamel. Since sodium hypochlorite has been used to remove the organic contents from the root canal space, its role in removing the organic contents from the enamel surface may provide better results. Therefore, it has been recommended to be used as a deproteinizing agent before direct bonding of orthodontic attachments to the enamel surface. The aim of this study was to evaluate and compare the effects of deproteinizing agent sodium hypochlorite on the shear bond strength of metal brackets bonded with light cure adhesive using conventional, self-etch and moisture insensitive primers.

MATERIAL AND METHODS:-

One hundred thirty five human premolars extracted (for orthodontic purpose) collected and stored in 0.1 % thymol solution, were used. Customized steel rings of 25 mm length and 21 mm diameter were fabricated. The teeth were mounted within cold cure acrylic poured into the steel rings such that the long axis of acrylic block and the buccal and lingual surfaces were exposed for surface treatment and adhesive bonding.
Initially, prophylaxis of all the teeth was performed with a non fluoridated prophylactic paste followed by cleaning with water spray and air drying. After this the teeth were randomly divided into three groups(Group A, B and C) of fourty five teeth each and these three groups were further divided into nine subgroups (Three subgroups of each group n=15) treated as in the following:-
Subgroup A1 was etched with 37% phosphoric acid for 30 seconds, washed with water spray and air dried. Primer was applied with an applicator tip on the enamel surface and cured with LED light for 20 seconds. Stainless steel brackets with foil mesh bracket base design were placed on the enamel surface with the light cure bonding material and cured with LED light for fourty seconds.
Subgroup A2 was treated with self Etching Primer on the enamel surface with an applicator tip and lightly dried with oil and moisture free air for five seconds. Stainless steel brackets with foil mesh bracket base design were placed on the tooth surface with the light cure bonding material and cured with LED light for fourty seconds.
Subgroup A3 was etched with 37% phosphoric acid for 30 seconds, washed with water spray and air dried. The enamel surface was moistened with a thin coat of artificial saliva, brushed on buccal surface. A thin coat of moisture insensitive primer was applied with an applicator tip and air-thinned with a gentle burst of dry air for 5 seconds Stainless steel brackets with foil mesh bracket base design were placed on the tooth surface with the light cure bonding material and cured with LED light for fourty seconds.
Subgroup B1 was preconditioned with 5% sodium hypochlorite for 60 seconds, washed with water spray and air dried for 10 seconds. The enamel surface was then etched with 37% phosphoric acid for 30 seconds, washed with water spray and air dried. Primer was applied with an applicator tip on the enamel surface and cured with LED light for 20 seconds. Stainless steel brackets with foil mesh bracket base design were placed on the tooth surface with the light cure bonding material and cured with LED light for fourty seconds.
Subgroup B2 was preconditioned with 5% sodium hypochlorite for 60 seconds, washed with water spray and air dried for 10 seconds. Self Etching Primer was applied on the enamel surface with an applicator tip and lightly dried with oil and moisture free air for five seconds. Stainless steel brackets with foil mesh bracket base design were placed on the enamel surface with the light cure bonding material and cured with LED light for fourty seconds. Subgroup B3 was preconditioned with 5% sodium hypochlorite for 60 seconds, washed with water spray and air dried for 10 seconds followed by etching with 37% phosphoric acid for 30 seconds, washed with water spray and air dried. The enamel surface was moistened with a thin coat of artificial saliva, brushed on buccal surface.
A thin coat of moisture insensitive primer was applied and air-thinned with a gentle burst of dry air for 5 seconds. Stainless steel brackets with foil mesh bracket base design were placed on the tooth surface with the light cure bonding material and cured with LED light for fourty seconds. Subgroup C1 was preconditioned with 5% sodium hypochlorite for 60 seconds, washed with water spray and air dried for 10 seconds. Primer was applied with an applicator tip and cured with LED light for 20 seconds. Stainless steel brackets with foil mesh bracket base design were placed on the enamel surface with the light cure bonding material and cured with LED light for fourty seconds. Subgroup C2 was preconditioned with 5% sodium hypochlorite for 60 seconds, washed with water spray and air dried for 10 seconds. Stainless steel brackets with foil mesh bracket base design were placed on the enamel surface with the light cure bonding material and cured with UV light for fourty seconds.
Subgroup C3 was preconditioned with 5% sodium hypochlorite for 60 seconds, washed with water spray and air dried for 10 seconds. The enamel surface was moistened with a thin coat of artificial saliva, brushed on buccal surface. A thin coat of moisture insensitive primer was applied and air-thinned with a gentle burst of dry air for 5 seconds. Stainless steel brackets with foil mesh bracket base design were placed on the enamel surface with the light cure bonding material and cured with LED light for fourty seconds. The shear bond strength of the bonded teeth was determined using Universal Testing Machine at Spectro analytical labs Ltd. New Delhi.
The surface topography of debonded enamel surfaces was evaluated using scanning electron microscope. SEM Analysis was carried out at University Sophisticated Instrumentation Facility, Aligarh Muslim University, Aligarh. Statistical analysis The values obtained were submitted to an analysis of variance and afterward to the unpaired t test with level of significance 0.05 (P < .05).

RESULTS
 

SUBGROUPS

MEAN SBS (MPa)

SD(MPa)

SIGNIFICANCE (P < .05)

A1

9.84

1.045

A2 P = 0.001*
A3 P = 0.204
B1 P = 0.178
B2 P = 0.001 *
B3 P = 0.449
C1 P = 0.001 *
C2 P = 0.001 *
C3 P = 0.001*

A2

7.9

0.714

A3 P = 0.001*
B1 P = 0.001*
B2 P = 0.012
B3 P = 0.002 *
C1 P = 0.001 *
C2 P = 0.009 *
C3 P = 0.001*

A3

9.35

1.022

B1 P = 0.02*
B2 P = 0.001 *
B3 P = 0.013
C1 P = 0.001 *
C2 P = 0.001 *
C3 P = 0.001*

B1

10.58

1.795

B2 P = 0.001*
B3 P = 0.75
C1 P = 0.001 *
C2 P = 0.001 *
C3 P = 0.001*

B2

8.15

0.8744

B3 P = 0.001 *
C1 P = 0.001 *
C2 P = 0.009 *
C3 P = 0.001*

B3

10.34

2.30

C1 P = 0.001 *
C2 P = 0.001 *
C3 P = 0.001*

C1

6.70

0.364

C2 P = 0.001 *
C3 P = 0.078

C2

2.05

6.34

C3 P = 0.01*

C3

6.34

0.671

 


The shear bond strength results demonstrated that the mean shear bond strength values of subgroup A1 (9.84MPa), subgroup A3(9.35MPa), subgroup B1 (10.58MPa) and subgroup B3 (10.34MPa)were in the range of 9-10 MPa which has been higher than the clinically acceptable limit 8MPa but the difference among them is statistically insignificant. The mean SBS of subgroup A2 (7.9MPa) and B2 (8.158MPa) was lower than other subgroups and this difference was statistically significant. This suggested that Self-etching primer had lower shear bond strength as compared to conventional primer and moisture insensitive primer with or without deproteinizing agent.
The SEM study of group A (conventional bonding methods) and group B (deprotenizing agent, priming and bonding) revealed that subgroup A1, A3, B1 and B3 had minimal surface changes with evenly etched surfaces after debonding. While subgroup A2 and B2 had irregular etched surface. Thus, scanning electron microscope has revealed that there have been no significant changes in the surface characteristics with or without the use of deproteinizing agent.




DISCUSSION

The foundation for adhesive restorative and preventive dentistry was laid in 1955, when Buonocore1 proposed that acids could be used to alter the surface of enamel to “render it more receptive to adhesion”. His hypothesis was based on the common industrial use of phosphoric acids to improve adhesion of paints and acrylic coatings to metal surfaces. He found that acrylic resin could be bound to human enamel that was preconditioned with 85% phosphoric acid for 30 seconds.
Ever since the bonding procedure was introduced by Newman2 into orthodontic practice, there has been a constant endeavor to improve the quality of bonding materials. In the field of orthodontics ideally the bond strength needs to be optimum rather than too much or too less. Excessive bond strength increases the risk of enamel damage during debonding and too weak bond strength results in frequent bond failures during the course of treatment.
According to Reynolds81, the optimum bond strength should be in the range of 6MPa to 8MPa. Rapid strides in material science over the years have produced progressively advanced materials making the direct bonding procedure more precise, comfortable and time-effective31. Bonding of orthodontic brackets using acid etch technique has become a routine orthodontic procedure and it is clinically acceptable method provided all steps of enamel conditioning (acid etching, rinsing, drying and application of bonding agent) have been properly executed. However, some disadvantages in conventional technique have increased chair side time and uncontrolled demineralization of enamel surface.
In addition, other factors can potentially contribute to the strength of the bond between the enamel and the orthodontic bracket, including type of enamel conditioner, acid concentration, etching time, composition of the adhesive, bracket base design, bracket material, oral environment, and skill of the clinician82. The traditional three step acid etch produced has been used for years to successfully bond orthodontic brackets to the teeth. Generally the use of a phosphoric acid concentration between 30% and 45%, etching time of not less than 15 seconds and washing time for 5-10 seconds are recommended to achieve the most receptive enamel surface for bracket bonding83.
The bond strength between orthodontic accessories and the enamel may also be compromised by the presence of acquired pellicle, which covers the soft and hard tissues in the oral region, particularly the surface of tooth enamel. This membrane is a biofilm, free of bacterial colonization, and its most abundant components are proteins, glycoproteins, enzymes, and mucins or their derivatives. These organic elements make it difficult for the composite resin to adhere to the tooth enamel surface, diminishing its shear bond strength84. It is also advisable to think of removal of some organic matter, though, small in quantities, on the surface of the enamel which would obstruct the effectiveness of the phosphoric acid.
Dissolution of the collagen by deprotinization prior to adhesive bonding has been observed to produce excellent bonding efficacy. Sodium hypochloride has been a well known non specific proteolytic agent capable of removing organic material. It has been seen that the layer of collagen does not offer a direct quantitative contribution to the interfacial bond strength. With the purpose of eliminating the influence of the organic matrix on the adhesion of the composite to the enamel surface, Justus et al70 suggested the use of 5.25% sodium hypochlorite for 60 seconds as a deproteinizing agent before etching with 37% phosphoric acid to achieve higher shear bond strength.
Hence, the present study has been conducted with an aim to investigate the influence of the application of deproteinizing agent sodium hypochlorite on the shear bond strength of metal brackets bonded with light cure adhesive using conventional, self-etch and moisture insensitive primers. In the present study higher SBS have been observed with conventional and moisture insensitive primers. The SBS has further increased with the pre-conditionening of enamel surface with 5% sodium hypochlorite and conventional etching procedures. The difference in bond strength of these two groups has not been observed to be statistically significant. Suggesting thereby, that there is a considerable increase in SBS of enamel surface with the use of deproteinizing agent followed by etching procedure. Whereas the self-etching primer gives SBS slightly equivalent to clinically acceptable limit. And this difference in value in comparison to other primers was statistically significant.
The results reveal increase in SBS when enamel was preconditioned with 5% sodium hypochlorite with use of self etching primer as compared to group in which preconditioning was done with H3PO4 alone. And this difference in SBS was statistically insignificant. The results of the present study were similar to the previous study conducted by Harleen72 et al where enamel deproteinization using sodium hypochlorite before acid etching had no significant effect on the shear bond strength of AdperTM Single bond 2 adhesive and FiltekTM Z-350 XT composite resin.
Originally Silverstone6 et al gave three etching patterns. In type I etching pattern, H3PO4 dissolves the head of the prism, with the peripheral material or interprismatic substance remaining intact. In type II, the acid dilutes the peripheral zone of the prism, leaving prism head relatively intact. In type III surface change has no specific features but displays generally some superficial dissolution that does not alter the deeper strata where the enamel prism are located. Type I and type II etching patterns are ideal for good bonding.
In the present study, etching pattern of type I and II were observed on the enamel surface in the subgroups in which conventional primer and moisture insensitive primer were used irrespective of the application of deproteinizing agent or not. Whereas in the subgroups in which self etching primer was used irrespective of deproteinizing agent, shows some superficial dissolution with no specific feature of etching which resembles type III etching pattern. These finding corresponds with the results obtained in our study, the mean shear bond obtained in the self etching primer subgroups A2 and B2 was 7.9 ± 017 MPa, 8.158 ± 0.87 MPa respectively which was lower than other subgroups.
The study conducted by Espinosa10,11 et al in 2008 and further supported by their excellent study using resin replica in 2010, it was observed that enamel deproteinization before acid etching significantly enhanced the type I and type II etching patterns, but there was no enhancement in the shear bond strength of the samples. The results of the above study were somewhat similar to our study where no significant enhancement in bond strength was seen.
In the present study the SEM images have revealed higher irregular surface with areas of patches of etched surface with self etching primer as compared conventional primer and moisture insensitive primers were used. Scanning electron microscopic images further demonstrated that application of 5 % sodium hypochlorite did not revealed any significant changes on the enamel surface irrespective of the primer used for bonding. The SEM results of the current study were analogous with the preceding study conducted by Bhoomika et al8 where enamel deproteinization with 5.25 % sodium hypochlorite did not grossly alter the topographic features of enamel before acid etching and concluded that use of sodium hypochlorite doesn’t make significant difference to enamel pretreatment. In another study conducted by Gandhi et al76 it was observed that there was no significant difference in resin tags formation on application of 5% sodium hypochlorite as compared to control group (conventional technique).

CONCLUSION

In the present study, it has been revealed that SBS obtained with the use of deproteinizing agent was comparatively higher as compared to conventional bonding method but statistically not very significant. Therefore, the reliability of this study may be tested with a larger sample in the near future. Still, the use of 37% phosphoric acid for 15 seconds for conditioning of enamel remains the best method for pretreatment of enamel.

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