|Year : 2017 | Volume
| Issue : 3 | Page : 170-175
A comparison of the shear bond strength of conventional acid etching, self-etching primer, and single bottle self-adhesive - An In vitro study
Aman Sachdeva1, Shweta Raghav2, Munish Goel3, Namita Raghav4, Sudhanshu Tiwari2
1 Department of Orthodontics, Bhojia Dental College and Hospital, Baddi, Himachal Pradesh, India
2 Department of Orthodontics, College of Dental Sciences and Hospital, Rau, Indore, Madhya Pradesh, India
3 Department of Conservative Dentistry, Himachal Dental College, Sundernagar, India
4 Department of Oral Medicine and Radiology, KD Dental College and Hospital, Mathura, Uttar Pradesh, India
|Date of Web Publication||7-Aug-2017|
Department of Orthodontics, Bhojia Dental College and Hospital, Baddi, Himachal Pradesh
Source of Support: None, Conflict of Interest: None
Background: Bonding of brackets to enamel has been a critical issue in orthodontic research since the significance of achieving a stable bond between the tooth and its bracket was obvious from the onset. This study aimed to determine the shear bond strength (SBS) of self-adhesive system, to compare SBS of conventional etchant, self-etching prime and self-adhesive system under dry condition, and to estimate the chair-side time saved for the application of the bonding agents.
Keywords: Orthodontic adhesives, self-etching primer, shear bond strength
|How to cite this article:|
Sachdeva A, Raghav S, Goel M, Raghav N, Tiwari S. A comparison of the shear bond strength of conventional acid etching, self-etching primer, and single bottle self-adhesive - An In vitro study. Indian J Dent Sci 2017;9:170-5
|How to cite this URL:|
Sachdeva A, Raghav S, Goel M, Raghav N, Tiwari S. A comparison of the shear bond strength of conventional acid etching, self-etching primer, and single bottle self-adhesive - An In vitro study. Indian J Dent Sci [serial online] 2017 [cited 2023 Mar 23];9:170-5. Available from: http://www.ijds.in/text.asp?2017/9/3/170/212401
| Introduction|| |
Genesis of acid-etching technique and subsequent adaptation of direct bonding in orthodontics has revolutionized the placement of orthodontic appliances. Rapid strides in material science over the years have produced progressively advanced material making the direct bonding procedure more precise, comfortable, and time effective.
Since Buonocore  introduced the concept of acid-etching technique and Newman  introduced the bonding of orthodontic brackets various bonding adhesives were developed. The first and most popular bonding resins were chemical curing bonding systems. Later, self-cure adhesive systems came into use. Although the inability to manipulate the setting time of the composite resin was a major drawback.
Tavas and Watts  first described the use of light-cured materials in vitro for orthodontic bonding . In the direct bonding technique, the material is cured under metal-based brackets by direct illumination from different sides and by transillumination because the tooth structure transmits visible light. Rapid polymerization occurs when visible light is applied, producing a “command set” that is of great advantage; such setting “on demand” results in a nearly unlimited working time, allowing more accurate bracket placement.
Newer self-etching adhesive materials have been introduced recently in orthodontics to simplify the bonding process by reducing the bonding steps and eliminating the need for etching and priming, thus lessening the risk of contamination and reducing the bonding time. These self-etching primers combine the conditioning and priming agents into one acidic solution and have shown advantages such as reduced loss of enamel, prevention of saliva contamination, and less chair time. Self-etching was recently reported to save 10.2 s per tooth, for a total of 204 s when bonding 20 teeth. The benefits of fewer bonding steps and less chair time should be weighted against the increasing cost of self-etching primer.
Shear bond strength (SBS) is the main factor, which has to be concerned in the evolution of bonding materials. The bond strength of the orthodontic bracket must be able to withstand the forces applied during the orthodontic treatment. Reynolds  stated that 5.9–7.8 MPa resistances are sufficient to withstand masticatory forces. Bishara et al. compared bond strengths of an acidic primer and composite resin with a conventional adhesive system and found mean bond strengths of 10.4 and 11.8 MPa, respectively. The SBSs of self-etching primers can vary widely, ranging from 2.8–16.6 MPa.
An ideal orthodontic adhesive should have adequate bond strength while maintaining unblemished enamel after debonding. Therefore, researchers have been working hard to achieve the best quality and gentlest procedures for bonding orthodontic brackets. A gentler etch pattern has been obtained with self-etching primers, and scanning electron microscope (SEM) studies have shown that these conditioners yield shorter resin tags. In the study by Hosein et al., they found that the least enamel loss occurs when a self-etching primer is used for conditioning and the enamel is cleaned up with a slow-speed tungsten carbide bur.
Dental adhesive systems have evolved through several generations with changes in chemistry, mechanism, number of bottles, application technique, and clinical effectiveness. The trend in the latest generation of dental bonding systems is to reduce the number of component and clinical placement steps. The introduction of a single bottle dental adhesive system is the new generation material and combines etchant, adhesive, and desensitizer in one component.
The purpose of this study was to evaluate and compare the SBS of orthodontic brackets bonded with three different orthodontic adhesives.
| Materials and Methods|| |
This study was conducted in the department of orthodontics and dentofacial orthopedics, 150 newly extracted premolars were collected and stored in a solution of 0.1% (wt/vol) thymol. The premolars were obtained from a group of patients who underwent therapeutic extractions, before orthodontic therapy. Only morphologically well-defined teeth with no caries, fractures, structural defects, or any restorations were included in the study. The teeth were cleansed and pumiced using a rubber cup with fluoride-free paste for 10 s, thoroughly washed with water, and air-dried.
Stainless steel edgewise premolar brackets with bondable bases were used, with the 0.022 slot. The surface area of bracket base was 11.15 mm 2 and the mesh size was 80 gauge.
The teeth were randomly divided equally into three groups based on the adhesive system used as follows [Table 1].
- Group I, the teeth were etched (37% phosphoric acid for 15 s), washed with water, and dried to a chalky white appearance. An adhesive primer was applied to the etched surface; the bracket was placed on the tooth and bonded with Transbond XT (3M Unitek, CA, USA) [Figure 1]
- Group II, the teeth were conditioned with Transbond Plus self-etching primer (3M Unitek, CA, USA) which uses a lollipop system with two compartments: One that contains methacrylated phosphoric acid esters, initiators, and stabilizers; and the other contains water, fluoride complex, and stabilizers. Both compartments are squeezed out to activate the product, and the contents of each compartment are mixed. The resulting mix is then applied by continuously rubbing the self-etching primer on the enamel surface. The primer was applied for 20 s, lightly dried with compressed air for 1–2 s, and then brackets were bonded with Transbond XT
- Group III, the teeth were conditioned with 7th generation light-cure self-etching primer (G-BOND (G.C. Corporation, Japan). It is a light-curing, self-etching, one-component adhesive. According to the manufacturer's recommendations it was was brushed gently using a soft disposable brush onto the enamel surface and left undisturbed for 30 seconds. Then a moisture free air was used to deliver a gentle burst of air until no movement of the adhesive was noticed and light cured for 20 seconds then adhesive paste was applied to the base of the bracket. The metal brackets, with the help of a bracket holding tweezer, were pressed gently for bonding at midpoint “A” to ensure uniformity in the bracket seating. Subsequently, the excess adhesive was removed from the margins of the bracket with the help of an explorer. The brackets to be bonded were light cured for 20 seconds on each side of the brackets (i.e. mesial and distal) by exposing it to a light from the light curing unit.
In all groups, the brackets were light-cured (377–490 nm of wavelength, Smartlite, Dentsply, Milford, DE, USA) for a total of 20 s, with the light beam directed for 10 s at each of the mesial and distal faces. A vertical line is drawn passing through the long axis of the tooth and a horizontal line that divides the tooth into two equal portions. The point of intersection of the two lines is taken as the midpoint “A” which was used as a guideline for correct positioning of bracket. These bonded teeth were fixed in acrylic resin blocks [Figure 2] and were subjected to thermo cycling using PCR machine with 50C to 550C for 1000 cycles with 30 sec dwell time in each bath. After completion of thermal cycling the bonded samples were then stored in distilled water at room temperature in sealed containers in a beaker for 6 weeks before debonding. An occluso-gingival load was applied to produce a shear force at the bracket-tooth interface. This was accomplished with the flattened end of a steel rod attached to the crosshead of a universal testing machine LLOYDS (Instron Corp., Canton, Mass, USA) [Figure 3]. The SBS testing was carried out in the Material & Metallurgy wing of the Indian Institute Of Technology, Kanpur. A mounting jig was used to align the facial surface of the tooth to be parallel to the force during the SBS test. The bond strengths were measured at a crosshead speed of 1 mm/min, and the load applied at the time of fracture was recorded in Newton and then calculated by dividing the debonding force by the bracket base surface area yielding megapascals (MPa) as a unit. The LLYOD unit was attached to an electronic console that displayed the debonding forces acting on the bracket tooth interface. Thus, the exact force at which the bracket debonded was noted from the console. This force was expressed in Mega Pascal's (MPa). Selected surfaces of each group were also examined under SEM (ZEISS DSM 950, Germany) to observe enamel surface after debonding [Figure 4].
The mean SBS of the three groups was compared by one-way analysis of variance (ANOVA) and the significance of the mean difference between the groups was done by paired t-test.
| Results|| |
The SBS values (in MPA) was calculated for each group [Graph 1],[Graph 2],[Graph 3] and descriptive statistics for all groups are shown in [Table 2]. One-way ANOVA revealed statistically significant (F = 13.73, P < 0.001) differences in SBS among various groups. Therefore, pair-wise comparison between the groups was done by paired t-test. SBS was compared and assessed in three different groups:
Comparison of shear bond strength between same groups [Table 3] and [Figure 5]
The mean SBS with bonding of each group was compared to mean SBS of other two and analyzed by paired t-test. The mean SBS with bonding was observed to be 16.31 ± 3.96 MPa for Group I which was compared to mean SBS of Group II and Group III. The mean SBS with bonding was observed to be 12.04 ± 3.29 MPa which was compared to mean of Group I and Group III. The mean SBS with bonding was observed to be 15.54 ± 4.16 MPa which was compared to mean of Group I and Group II. This difference was statistically significant (P < 0.05) as confirmed by paired t-test.
Comparison of shear bond strength between different groups [Table 4]
Group I had the highest initial SBS of 16.31 ± 3.96 MPa followed by group III with 15.54 ± 4.16 MPa and Group II had the lowest mean bond strength of 12.04 ± 3.29 MPa. One-way ANOVA test revealed statistically significant difference between three groups with bonding.
Difference in mean shear bond strength in three groups [Table 3]
Group I and Group II differ significantly. Group I has better SBS than Group II. Group I and Group III is nonsignificant, that is, Group I and Group III are equally effected to each other, whereas Group III is significant with Group II. As revealed by the one-way ANOVA test.
| Discussion|| |
The direct bonding of orthodontic brackets has revolutionized and advanced the clinical practice of orthodontics. Nowadays, bonding makes use of acid etchants followed by primer materials as an essential part of the bonding procedure to allow good wetting and penetration of the sealant that bond the bracket to the enamel surface  improvements continue through the introduction of new materials. These improvements minimize enamel loss, reduce chair-side time, simplify the bonding procedure, and make it more predictable.,,,,
Dentistry has witnessed introduction of several bonding agents starting with Buonocore's first generation through the sixth generation of bonding system. The latest entrant is the seventh-generation bonding agent. The elimination of steps with this new bonding agent minimizes the probability of contamination because the etchant and sealant are applied simultaneously without an intermediary step of washing and drying the tooth between these two applications. To the best of our knowledge, there are no studies that have evaluated the use of seventh generation bonding agents for orthodontic purposes.
This study, we therefore undertook which, compared three bonding systems, a conventional system in which the etching, priming, and adhesive placement on the brackets were done in separate steps during the bonding procedure, second we took self-etching primer in which etching and priming are done in a single step with mixing them together and third a new system (G-BOND) in which the etching and priming were combined into one step (single bottle) and is the seventh-generation bonding system. This study was undertaken to determine whether it is applicable in the orthodontic bonding procedures the newly introduced self-adhesive (G-BOND) had clinically acceptable SBS values and to further compare the bond strength of this material with that of conventional acid etching (Transbond XT) and with self-etching primer (Transbond SEP).
In this study, mean SBS of Transbond XT was 16.31 Mpa, which was the highest among all groups and correlates with other studies. Pickett et al. and Arnold et al. who reported SBSs of 11.2 and 9.7 MPa, for conventional acid-etch adhesive and Transbond XT, respectively. However, Scougall Vilchis et al. compared Transbond XT (control group) with Transbond Plus and other three self-etching adhesives and found that the SBS of Transbond XT was highest (19.0 MPa), followed by Transbond Plus (16.6 MPa) and three other self-etching adhesives.
The mean value of the SBS of self-etching primer (Transbond SEP) was found to be 12.04 MPa which was less compared to conventional acid etching (Transbond XT) and newly introduced single bottle, no mix, self-adhesive (G-BOND, SBS 15.54 MPa). The findings indicated that the use of a self-etching primer to bond orthodontic brackets to the enamel surface provided lower, but clinically acceptable, shear bond forces as reported in previous studies.,,
Although low bond strength of SEPs has been reported, some recent studies showed no significant differences of bond strengths between SEPs and conventional etching agents., From a clinical standpoint, the use of SEPs can be desirable because they reduce clinical steps, save chair time, prevent saliva contamination, improve adhesive procedures, and reduce the risk of decalcification or white spot formation. The SEP used in this study (Transbond Plus) has been shown to provide lower bond strength than Transbond XT, but it is clinically acceptable. It seems to fulfill the requirements for clinical efficiency and is potentially adequate for orthodontic bonding needs.
The findings indicated that the use of this single bottle, no mix self-adhesive (G-BOND) to bond orthodontic brackets to the enamel surface can provide comparable and clinically acceptable SBS values. This class of adhesives is based on the concept of hybridization and relies on wet-bonding technique. It differs from self-etching primers and conventional acid etching in that it uses one component resin, that is, after conditioning of enamel, the steps of etching and priming are combined so that bonding is achieved with single component formula. Although these systems have reduced the number of components, it may require multiple applications of the adhesive to ensure optimal penetration of resin. Various studies have evaluated the SBSs of conventional bonding systems on contaminated enamel. They reported that the success of bonding to enamel was negatively affected by contamination with oral fluids such as blood and plasma. There was a reduction of approximately 50% in the mean SBSs when the resin composite adhesive was bonded to contaminated etched enamel surfaces compared with the uncontaminated etched enamel surfaces. Possibly, the self-etching primer usage would have been a blessing in certain clinical situations such as with surgically exposed impacted/unerupted teeth or bleeding from inflamed and hypertrophied gingiva where the chair-side time and keeping the field dry is critical. That is why many studies are undertaken for evaluating the self-etching primer system in compromised conditions. Bishara et al. evaluated the use of self-etching primer system on contaminated enamel conditions and found that the uncontaminated control group had a significantly stronger SBS than the groups that had blood contamination, regardless of whether this occurred before after, or before and after the application of the self-etch primer, that is, blood contamination at any stage of the bonding procedure results in a significant and drastic drop in the SBS of orthodontic brackets. Although conventional acid etching (Transbond XT) is a clinically efficient material as again confirmed from this study, single bottle, no mix self-adhesive (G-BOND) if its bond strength values are further improved, it can be considered as an alternative bonding system. Considering the in vitro nature of the present study, the findings should be interpreted with caution while applying it for clinical application. The efficacy of the self-adhesive (G-BOND) as a bonding agent, needs in vivo and clinical assessment through a survival analysis. Preliminary evaluation done in this study however will be a valuable guide for the future in clinical use.
On performing ANOVA, an F-ratio of 13.73 which is found to be statistically significant. Thus, the difference among the groups is find to be statistically significant (P < 0.001). Intergroup comparison using Student's t-test for Transbond XT and Transbond SEP shows that Transbond XT shows significantly higher SBS as compared to Transbond SEP (P < 0.001). Transbond SEP shows significantly lower SBS as compared to G-BOND. Thus, Transbond XT and G-BOND do not show significance difference in their SBSs.
Although Transbond XT is the ideal material for light cured direct bonding of orthodontic attachments to teeth. G-BOND no mix, self-adhesive material may be an alternative material for bonding orthodontic attachments to teeth. The prime disadvantage with seventh-generation bonding agent (G-BOND) is in its storage. When exposed to air, there is variation in viscosity and generally thickens in the form of gel. Hence, it is mandatory to close the lid tightly immediately after dispensing. G-BOND when not in use it should be refrigerated at 40-100 C. Clinicians should remember that this was an in vitro study and the results may not necessarily be the same as those that would be obtained in the oral environment. Therefore, more research is needed to prove the clinical reliability of G-BOND.
| Conclusions|| |
Based on this study, the highest SBS was observed in Transbond XT, followed by G-BOND with and lowest in Transbond Plus. Single bottle, no mix, self-adhesive (G-BOND) has a mean SBS value of 15.54 MPa. Its SBS value is lower compared to conventional acid etching (Transbond XT) with value of 16.31 MPa and higher compared to self-etching primer (Transbond SEP) with value of 12.04 MPa. All the three adhesives exhibited clinically acceptable bond strength values. The latest generation self-etching primer G-BOND showed clinically acceptable SBS and less amount of residual adhesive left on the enamel surface after debonding. Thus, the future research needs to be focused toward the biocompatibility, bond strength, and viscosity for self-adhesive (G-BOND) to be used as routine orthodontic adhesive.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3], [Table 4]
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