Indian Journal of Dental Research

ORIGINAL RESEARCH
Year
: 2014  |  Volume : 25  |  Issue : 4  |  Page : 470--474

Evaluation of shear bond strength with different enamel pretreatments: An in vitro study


Anila Charles1, RS Senkutvan1, RS Ramya1, Sanjay Jacob2,  
1 Department of Orthodontics, Madha Dental College, Kundrathur, India
2 Saveetha Dental College, Chennai, Tamil Nadu, India

Correspondence Address:
Anila Charles
Department of Orthodontics, Madha Dental College, Kundrathur
India

Abstract

Context: Bonding procedures are time consuming and debonding of brackets is a common problem encountered in orthodontics. Aims: The purpose of this in vitro study was to evaluate the shear bond strength (SBS) with different enamel pretreatment (acid etching, air abrasion, and bur abrasion) to enhance the bonding performance. Subjects and Methods: A total of 60 extracted premolars for orthodontic purposes were randomly assigned to three groups based on conditioning method: Group I - conventional etching with 37% phosphoric acid; Group II - air abrasion with 50 μm aluminum oxide; and Group III - bur abrasion with diamond fissure (#330, MANI, Dia-Burs, New Jersey, USA). After storing the specimens for 24 h in distilled water at 37°C, SBS was measured with Universal testing machine (Lloyd Universal testing machine-Model No. L.R 100K, UK). The shear force at a crosshead speed of 1 mm/min was transmitted to brackets. The adhesive remnant index (ARIs) scores were recorded after bracket failure. Statistical Analysis Used: Descriptive statistics, multiple comparisons of the SBS of different groups, were performed by analysis of variance. The Tukey«SQ»s test was used to evaluate differences in ARI scores between groups. All statistical evaluations were calculated using the Statistical Package for Social Sciences Windows, release 10.0.0 (SPSS Inc., Chicago, Illinois, USA). Results: The analysis of SBS variance (P < 0.01) and Chi-square test of ARIs scores (P < 0.01) revealed significant differences among three groups tested. The SBS in Group I (mean: 8.822 ± 0.92 MPa) and Group III (mean: 6.015 ± 0.87 MPa) was significantly higher than Group II (mean: 3.824 ± 0.57 MPa). The ARI was used to evaluate the residual adhesive on the enamel after bracket removal. The Tukey«SQ»s test was used to evaluate differences in the ARI scores among the groups. Conclusions: The current findings indicate that enamel surface preparation using bur abrasion results in a significant higher than air abrasion; within the limitations of this study recommend bur abrasion as a viable alternative to acid etching.



How to cite this article:
Charles A, Senkutvan R, Ramya R S, Jacob S. Evaluation of shear bond strength with different enamel pretreatments: An in vitro study.Indian J Dent Res 2014;25:470-474


How to cite this URL:
Charles A, Senkutvan R, Ramya R S, Jacob S. Evaluation of shear bond strength with different enamel pretreatments: An in vitro study. Indian J Dent Res [serial online] 2014 [cited 2020 Jul 4 ];25:470-474
Available from: http://www.ijdr.in/text.asp?2014/25/4/470/142537


Full Text

Innovation of materials and bonding technique was widely accepted due to its simplicity, efficacy and provided more esthetic qualities in the late nineteenth century. [1] The technology has resulted in significant treatment improvements, including more esthetic and hygienic appliance, elimination of post treatment band space, easier caries detection and treatment, less soft tissue irritation, and decreased possibility of enamel decalcification. Acid etching the enamel surface in orthodontic bonding is a routine practice. The primary effect of enamel etching is to increase the surface area and thereby change the surface from a low-energy hydrophobic surface to high-energy hydrophilic surface. [2] To obtain good bond strength enamel must be etched with 35-40% phosphoric acid for 15-60s. [3]

Another novel technology had introduced before acid etch bonding was by Robert Black in the 1940s. Its popularity declined as it effect was viewed as a disadvantage in the late 1950s in restorative dentistry. [4] Today it is viewed as an advantage in terms of protecting the oral soft tissues with typical tooth surface preparation times ranging from 0.5 to 3 s without the additional step of rinsing in orthodontic bonding. Air abrasion technique uses the kinetic energy of Al oxide particles for cutting and abrading tooth surface.

In recent years, in addition to conventional acid etch and air abrasion technique bur abrasive techniques has been used for preparation of enamel surfaces. As surface roughness created by diamond burs causes an increased surface area, the mechanical retention is increased. Since various techniques are available to enhance the bonding performance the most reliable technique was evaluated by this in vitro study. Scanning electron microscopic observations were also conducted.

 SUBJECTS AND METHODS



Sixty (maxillary and mandibular premolars) freshly extracted teeth for orthodontic purpose were used in the present investigation. All the teeth used in this study were extracted over the course of 3 months. They had undamaged buccal enamel with no caries, cracks and no pretreatment by any chemicals. Following extraction, residue on the teeth was removed and washed away with tap water. They were then stored in normal saline at room temperature to prevent dehydration and changed weekly to prevent bacterial growth.

To mount the teeth in universal testing machine (Lloyd Universal testing machine-Model No. L.R 100K, UK) they were fixed in a self-cure acrylic blocks with dimension by 35 mm Χ 9 mm. The teeth were mounted on acrylic blocks such that the roots were completely embedded into the acrylic up to the cemento-enamel junction leaving the crown exposed. The teeth were randomly divided into three groups. The blocks were color coded for easy identification. Prior to the bonding procedure, the enamel surface was polished with oil and fluoride free fine pumice, using a brush and a slow-speed hand piece, rinsed again and dried with an air syringe. The method specified for each experimental group was then followed.

Sixty premolar brackets (0.022 inch PEA Roth brackets, Gemini series, 3M Unitek, Germany) with a base surface area of 9.806 mm 2 were used for this study.

For the acid etching procedure (Group I) the enamel surfaces were etched with 37% phosphoric acid gel for 20 s as shown in [Figure 1] rinsed with air-water spray for 15 s, and dried to a chalky-white appearance. Conventional Transbond adhesive primer and adhesive 3M Unitek, Monrovia, California was applied on the enamel surface, excess was removed using a probe and was cured using A 3M ESPE, Elipar 2500, (Satelec and Sopro Companies, North America)-Halogen -curing unit emitting light at wavelength of 480 nm was used for polymerization for 40 s.{Figure 1}

For air abrasion procedure (Group II) the enamel surfaces were air blasted for 5 s with 50 μm Al 2 O 3 particles at 80 psi. It was accomplished at a distance of approximately 2 mm using the KCP 2000 unit (Dentsply, Brazil) and at an angle of 45°. The application of the aluminium oxide jet was accomplished inside a closed transparent acrylic box, to avoid the particle aspiration by the operator as shown in ion [Figure 2] after the blasting; oil-free compressed air was used to clean the surface. On it a thin film of bonding agent was applied, and bonding was done as per manufacturers' manufactures instruction.{Figure 2}

For bur abrasion procedure (Group III) the enamel surface was abraded mechanically using a thin diamond fissure bur slightly (#330, MANI, Dia-Burs, Japan). Air and water spray from the hand piece was adjusted to a level of 85% air and 85% water for 2 W. During abrasion procedure the bur was placed parallel to the buccal surface of teeth as shown in [Figure 3]. The tooth surface was dried, and bonding agent was applied and the bracket was secured with adhesive on the buccal surface and cured. The bonding of all the brackets was performed by the same operator.{Figure 3}

After storing the specimens for 24 h in distilled water at 37°C, shear bond strength (SBS) was measured with universal testing machine (Lloyd Universal testing machine-Model No. L.R 100K, UK). The specimen mounted in its acrylic block was secured to the lower grip of the machine. To maintain a consistent debonding force a loop was embedded on to an acrylic block was fixed in the movable head and positioned in such a way that it touches the bracket as shown in [Figure 4].{Figure 4}

A cross-head speed of one mm/min was used. The computer recorded the force to debond the bracket in Newtons (N) and converted into megapascals using the formula

[INLINE:1]

Results were recorded and analyzed using Statistical Package for Social Sciences Windows, release 10.0.0 (SPSS Inc., Chicago, Illinois, USA).

Adhesive remnant index

The sheared surfaces were further investigated with a stereomicroscope (Olympus, SZX9, Tokyo, Japan) at Χ20 magnifications to assess the adhesive remnants on the specimen surface. The adhesive remnant index (ARI) as described by Artun and Bergland [5] was used and recorded for this assessment. ARI scores were used as a means of defining the sites of bond failure between the enamel, resin (adhesive), and the bracket base. The ARI (the substrate ARI score or ARIs) was scored 0-3, as follows:

0 - no adhesive left on the tooth

1 - less than half of the adhesive left on the tooth

2 - more than half of the adhesive left on the tooth

3 - all the adhesive left on the tooth with the mesh pattern visible.

 RESULTS



The descriptive statistics for SBS of the various groups tested are presented in [Table 1] and [Table 2] described the results of the analysis of variance (ANOVA). There was a significant difference among the groups at 5% confidence level was used. The SBS among the three groups tested were Group I (8.82 ± 0.92) Mpa, Group II (3.82 ± 0.57) Mpa, and Group III (6.01 ± 0.87) Mpa. From the obtained statistical results, we observed a significant difference among the groups (P < 0.0001).{Table 1}{Table 2}

Based on individual 95% confidence intervals, the Group I showed significant higher SBS (8.82 ± 0.92 Mpa) than Group II and Group III. The Group III SBS values were higher than Group II.

The ARI scores are listed in [Table 3]. Air abrasion and bur abrasion produced adhesive failures, whereas cohesive failures were seen with acid etching and bur abrasion.{Table 3}

Where N is the sample size, X shows the mean of each group, SD denotes the standard deviation and min denotes the minimum value and max denotes the maximum value of the data. The observed F = 192.06, which is higher than the expected value of F distribution at (2, 17) degrees of freedom at 5% level of significance.

P value shows that there is a significant difference among the three groups and hence the three groups' effects have significant change in their contribution.

 DISCUSSION



The present study assessed the SBS between three groups. A key factor that influences bond strength is the nature of enamel preparation. The bond strength attachment must be able to withstand the forces applied during orthodontic treatment. Enamel preparation has traditionally been done with phosphoric acid where the organic matter and inorganic components are altered. The process involves a form of micro etching [6] were selective dissolution of prism cores, with resultant micro porosity into which resin can flow and can be polymerized to form a mechanical bond to the enamel. This procedure practically eliminated micro leakage at the tooth/restoration interface. [7] Etching of enamel with H 3 PO 4 for 60 s result in superficial etched zone and sub-surface quantitative and qualitative porous zone. The enamel from the superficial etch zone is permanently lost but the porous zones establishes a mechanical bond to etched enamel. [8] Despite the acid etching technique being simple and clinically expedient, inherent limitations such as loss of enamel structure, toxicity of acid to oral soft tissue and time required lead to explore alternative methods.

Surface roughness created by diamond burs are directly related to the size of diamond particles used on the bur. Surface roughness creates an increased surface area. There by enhancing mechanical retention. In many study evaluating bonding to enamel tissue, outer enamel layer has been removed by use of diamond bur in clinical conditions. These range from <10 μm to about 100 μm [9] Sengun et al., compared two bonding system with two different abrading technique, Their findings indicate that enamel surface preparation using air abrasion and bur abrasion were close to each other. Since the bur abrasion technique is faster and avoids damage to soft tissue it could be consider as in alternate method of enamel preparation for direct bonding procedure. However a thorough knowledge, with clinical experience is indicated while roughening the enamel surface.

In recent years, in addition to conventional bur abrasive techniques, air abrasion technique has been used for preparation of enamel surfaces. Due to the advent of the high and low speed rotations, which were considerably less expensive, the air abrasion technique was not widespread later air abrasion was reintroduced, focused on clinical procedures and it requires only 0.5-3 s time to prepare enamel surface and with minimal oral soft tissue damage. [10],[11] Chung et al. in a study promoted sandblasting procedure as it produce similar degrees of surface irregularity and types of etch pattern favorable for boding. [6]

In this study sandblasting produced lower SBS than clinically acceptable limits and the main disadvantage was the particle size of aluminum oxide. Inherent drawbacks of air abrasion procedure like its inability to use in respiratory disease. Such patient may not be an ideal choice for orthodontic treatment. [12]

In the present study, Group I (acid etch) show higher bond strength than the air and bur abrasion, suggesting that the acid etch treatment of enamel is more favorable than the air abrasion method, and bur abrasion method in providing better bond strength. The depth of etched enamel surface created by phosphoric acid may be a contributing factor to the higher SBS.

In Group II (50 μm Al 2 O 3 ) and Group III (bur abrasion) mean SBS values were reduces as Group II (50 μm Al 2 O 3 ) showed decrease in bond strength than Group III (bur abrasion), this was due to the finer aluminum particles size that cause a smoother surface, and result in less mechanical retention. According to our findings, bur abrasion produced optimal bond strength suggested by Reynolds [2] to withstand normal orthodontic forces.

In this study bur abrasion required no rinsing and a gain in chair side time of 15 s for each tooth was obtained. The time used for bur abrasion, and the sandblasting procedure was an advantage though the enamel lost is not well determined. The increased bond strength in the phosphoric acid group when compared to the air abraded group as observed in this study was in conformity with previous work done by Reisner et al. [13]

The amount of residual adhesive on the enamel surface as evaluated by the ARIs scores indicated that there was significant differences among three surface treatment groups bond failure at the bracket adhesive interface was highest in acid etch, approximately in two thirds of the teeth no adhesive was left on the tooth surface treatments with acid etch. Whereas in air and bur abrasion most of the adhesive remained on the tooth and showed higher frequency of bond failure at enamel adhesive interface.

 CONCLUSIONS



The surface treatment with a diamond bur and acid etching equally produced the highest SBS and the lowest SBS was observed in air abrasion.

Though conventional etching of enamel surfaces with phosphoric acid was found to be preferable procedure conventional bur preparing was considered favorable for bonding procedures as they are less time consuming and cost effective.

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