|Year : 2021 | Volume
| Issue : 3 | Page : 155-160
An In Vitro Study to Compare the Shear Bond Strength of Orthodontic Brackets Bonded to Permanent Teeth by Using Conventional Acid-Etching and Self-Etching Primers
Department of Orthodontics & Pediatric Dentistry, Faculty of Dentistry, Qassim University, Kingdom of Saudi Arabia
|Date of Submission||10-Feb-2021|
|Date of Decision||15-May-2021|
|Date of Acceptance||10-Oct-2021|
|Date of Web Publication||2-Nov-2021|
Department of Orthodontics & Pediatric Dentistry, College of Dentistry, Qassim University
Kingdom of Saudi Arabia
Source of Support: None, Conflict of Interest: None
Objectives: The objective of the present study was to evaluate and compare the bond strength of orthodontic brackets bonded to permanent teeth with a conventional acid-etching and self-etching primer systems. Also, the study aims to evaluate the mode of bond failure after debonding the brackets. Materials and Methods: It was an experimental study. Fifty extracted permanent premolars were collected, checked, and cleaned. Teeth were split equally into two groups, group A and B. Orthodontic brackets were bonded using conventional acid-etching and self-etching primer systems for group A and B, respectively. Shear bond strength (SBS) was measured with a universal testing machine, and the mode of bracket-adhesive failure was determined by using adhesive remnant index (ARI). Data were analyzed with a statistical software. Independent sample t-test was used to compare the SBS and Mann–Whitney U test was used to assess whether there is a significant difference of ARI score between the groups. Results: Although the SBS with self-etching primer was within clinically acceptable range, the overall mean SBS for group A (14.71 MPa) was significantly greater than group B (9.24 MPa) (P = 0.024). There was no significant difference in ARI scores between conventional acid-etching and self-etching groups (P = 0.801). Conclusion: The SBS of the conventional acid-etching was significantly higher than the self-etching primer. The SBS of self-etch was within the acceptable range to withstand the forces of mastication. The majority of the brackets recorded ARI score of 1 indicating a cohesive failure with no significant difference between acid-etch and self-etch groups.
Keywords: Adhesive remnant index, conventional acid-etching, dentistry, self-etching primer, orthodontics, shear bond strength, universal testing machine
|How to cite this article:|
Bilal R. An In Vitro Study to Compare the Shear Bond Strength of Orthodontic Brackets Bonded to Permanent Teeth by Using Conventional Acid-Etching and Self-Etching Primers. Dent Hypotheses 2021;12:155-60
|How to cite this URL:|
Bilal R. An In Vitro Study to Compare the Shear Bond Strength of Orthodontic Brackets Bonded to Permanent Teeth by Using Conventional Acid-Etching and Self-Etching Primers. Dent Hypotheses [serial online] 2021 [cited 2022 Nov 27];12:155-60. Available from: http://www.dentalhypotheses.com/text.asp?2021/12/3/155/329762
| Introduction|| |
The success of orthodontic treatment majorly depends on the correct application of sustained forces applied to teeth via orthodontic appliances. Direct bonding of brackets can be achieved by the micromechanical adhesion of a resin-based material to etched tooth surface. Bonding materials should penetrate into the enamel porosities and have simple manipulation and dimensional stability.
To achieve a successful bond between enamel and bracket, its strength should be adequate to endure the forces of mastication and stresses applied through arch wires. But there are multiple dynamics at play that contribute to this success. This includes the type of primer, acid concentration, span of etching time, configuration of the adhesive, bracket material, bracket base design, oral environment, and expertise of the clinician. Since re-bonding of brackets could be time-consuming and hazardous to enamel surface, achieving appropriate bond strength is an imperative clinical objective.
Shear bond strength (SBS) is the key aspect that is always fundamental in the evaluation of bonding materials. An ideal orthodontic adhesive must have sufficient bond strength while maintaining untarnished enamel after debonding. Hence, orthodontists have always been on a look out to discover the products that are of best quality as well as least damaging to the hard tissues of the oral cavity.
According to Rossouw, acid-etching is a routine process to eliminate smear layer for effective bonding. The main problem with this technique is demineralization near or around the bracket edges, damage of surface enamel, and subsurface enamel wear. This can lead to weakening or crack of enamel surface during debonding attributed to strong acidic conditioning or prolonged etching. Newer self-etching adhesive systems have been introduced that merge acid and primer and abridge the bonding procedure into a simple single step technique. This lessens chair time, is less technique sensitive, and reduces risk of saliva contamination while maintaining similar rates of etching depth and primer penetration., Literature supports that self-etching primer (SEP) produces a gentler etch configuration than 37% phosphoric acid. It not only saves time, but also reduction in the stages of bonding process could lead to a decline in technical and clinician related errors.,,
The aim of this study was to evaluate and compare the bond strength of orthodontic brackets bonded to permanent teeth with a conventional acid-etching and self-etching primer system and to evaluate the mode of bond failure of these two primer systems by determining the residual adhesives on the permanent teeth after debonding the brackets through adhesive remnant index (ARI).
| Materials and Methods|| |
The study received the approval from the dental ethical committee of college of dentistry, Qassim University, code number: EA/6006/2018. It was an experimental study. Fifty permanent premolars that were extracted for therapeutic purpose were collected. The sample was chosen by random convenience sampling depending upon the availability of teeth that were extracted for therapeutic purpose. All other permanent and deciduous teeth, chemically treated teeth, teeth damaged from extraction procedure, hypoplastic enamel, and carious lesion or cavitation on the buccal surface were excluded from the study. All teeth were checked for an intact buccal structure; calculus was removed by using a piezoelectric ultrasonic scaler (Woodpecker ultrasonic scaler UDS-J2, Zhengzhou, China) with stainless steel scaling tip (G2). Teeth were washed and stored in distilled water until they were used in this study. Finally, teeth were embedded in the specimen holder box made up of self-curing acrylic resin.
Teeth were divided into two groups of 25 each (group A and B). There were uniform numbers of maxillary and mandibular first and second premolars in both the groups, using acid-etching primer system Meta P&Bond® primer (META BIOMED, Chungcheongbuk-do, Republic of Korea) for bonding the brackets for the group A and self-etching primer system (DENSPLY prime & bond® York, PA, USA) for the group B.
The standard edgewise brackets with 0.022-inch slot (Mini-Twin Brackets, BioMIM, Ortho Classic, Sylmar, CA, USA) were used in the study. The manufactures instructions were followed to bond the teeth to the enamel. The acid-etching primer system was applied to group A and the self-etching primer system to groups B. In group A, each tooth was washed with a water spray for 10 seconds and parched with an airstream. The facial surface of enamel was etched with 37% phosphoric acid gel (Meta Etchant, META BIOMED, Chungcheongbuk-do, Republic of Korea) for 15 seconds, thoroughly rinsed for 20 seconds, and subsequently dried with moist cotton pellet as per the manufacturer’s instruction. Frosty look of the surface enamel was an indication of the effective etching process. An even thin layer of Meta P & Bond® primer (META BIOMED, Chungcheongbuk-do, Republic of Korea) was applied to the etched enamel surface using a micro brush, gently air dried for 5 seconds, and finally light-cured for 10 seconds. For bonding the bracket to the enamel surface, Filtekz250 bonding adhesive (3M ESPE, St, Paul, Minnesota, USA) was applied to the base of the bracket. The bracket was positioned firmly on the buccal surface of the tooth with bracket placing plier (3M Unitek, Monrovia, CA, USA). Any excessive adhesive along the margins of the bracket base was removed with the back end of the plier. Then, the bracket was light-cured with a Starlight pro polymerization lamp, light emitting diode (LED) curing light having voltage of 3.7 V 1100 mAh (Mectron Dental Bengaluru, Karnataka, India Pvt. Ltd.) for 10 seconds (5 seconds each on mesial and distal surface), as per manufacturer’s instructions.
In group B, the buccal surface of crown of each tooth was cleansed and rinsed as in group A. DENSPLY prime &bond® (York, PA, USA) was applied sufficiently wetting all the buccal enamel surface uniformly for 20 seconds, evaporated with a moderate stream for 5 seconds, and finally light-cured for 10 seconds, as per manufacturer’s instructions. The brackets were then bonded with Filtek z250 (3M ESPE, St, Paul, Minnesota, USA) adhesive. The LED curing light (Mectron Dental Bengaluru, Karnataka, India Pvt. Ltd.) was used to light cure as in group A.
A universal testing machine (INSTRON® 3300 Dual Column Universal Testing System, Norwood, MA, Canada) was used to determine SBS. The specimen holder was placed in the machine and load was applied to the bracket with a force in the occluso-gingival direction parallel to the buccal enamel surface. The force required to shear off the bracket was recorded in newton (N) at a crosshead speed of 0.5 mm per minute. The SBS was calculated by dividing the force in newton by the bracket base area.
After testing the SBS, ARI was used to evaluate the amount of remnant adhesive on the enamel surface of the teeth by one investigator with naked eye. The ARI score ranged from 0 to 3 [Table 1].
The data was analyzed using Statistical Package for Social Sciences (SPSS) version 21.0 (IBM Corp., Armonk, NY, USA). Descriptive statistics including mean bond strengths, standard deviations, and ranges were calculated. Independent sample t-test was used to compare the SBS of two primer systems. Mann–Whitney test was used to test any significant differences between groups with regard to ARI. The significance level (P value) was set at 0.05.
| Results|| |
Sample dropout rate was 16%. The dropout was attributed to fractured and broken teeth during the debonding procedure by universal testing machine. The descriptive statistics of SBS and ARI score of each tooth sample in both group A and B are shown in [Figure 1] and [Figure 2], respectively.
|Figure 1 SBS and ARI score of each tooth in group A. ARI, adhesive remnant index; SBS, shear bond strength.|
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|Figure 2 SBS and ARI score of each tooth in group B. ARI, adhesive remnant index; SBS, shear bond strength.|
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Means, standard deviations, and range of the SBS of each group are shown in [Table 2]. The results of independent sample t-test [Table 2] showed significant difference in SBS between acid-etching and self-etching primer systems. The overall mean of SBS for group A (14.71 MPa) was significantly greater than group B (9.24 MPa) (P = 0.024). [Table 2] shows the mean SBS of brackets bonded with conventional and self-etching primers and the comparison between the SBS of both the groups. Significance is set at 95% confidence interval with P value (P < 0.05).
Mann–Whitney test showed no significant differences in ARI scores between group A and B (P = 0.801). The distribution of ARI scores for each group showed that majority of both groups scored 1 [Table 3].
| Discussion|| |
In the literature, there are no clear guidelines about shear force limits. A good orthodontic biomaterial should allow good adhesion in order to sustain masticatory forces with a minimum bond strength of 5 to 10 MPa. On the other hand, adhesion forces should not be too strong in order to avoid enamel loss after debonding (40–50 MPa). Therefore, the ideal orthodontic biomaterial should have bonding forces included in the interval of 5 to 50 MPa, even if these limits are mostly theoretical.
Literature supports the use of 37% phosphoric acid for 15 seconds enhances the bond strength. However, if the etching time is changed for various lengths of time, it can have a negative effect on surface roughness and enamel hardness, and the subsequent bond strength can be weakened. In our study, the conventional acid-etching group (group A) showed significantly higher value of SBS. The mean SBS was 14.71 MPa, while in the self-etching primer group (group B) mean SBS was 9.24 MPa.
Hitmi et al. reported that SBS of acid-etched group was greater than self-etch. A study by Zope et al. compared the conventional acid-etching with four different types of self-etching primers. The results showed statistically significant difference of mean SBS with highest values of SBS in acid-etching group.
Several other studies also reported that there was significant reduction in the bond strengths when self-etching primer systems were used on clean dry enamel surfaces than when acid-etching primer systems were used.,,,, On the contrary, Bishara et al. compared two adhesive systems and found no significant difference between SBS of the two; however, acid-etch system showed superior results. Several other studies conducted between 2003 and 2005 reported that SBS of self-etch primers were significantly lesser than or equal to those bonded with a conventional etching process.,,,
In addition, other studies showed that in presence of liquid contamination (water, blood, and saliva), the self-etching system exhibited superior bonding properties than the acid-etching system. This can be evocative of the fact that self-etching primers may be a suitable bonding option in obstinate children in their mixed dentition.,
Although in this study the SBS with the self-etching primer was significantly lesser than the acid-etch system, the mean SBS of self-etch (9.24 MPa) was within acceptable clinical range, that is, more than 8 MPa, and can successfully withstand the occlusal loads and forces of mastication. We can safely use it especially in the posterior region where saliva control can be a challenge as well as in uncooperative and juvenile patients. Furthermore, it can reduce the chairside time as compared to the acid-etch primer system. This can be time and cost-effective in busy practices and teaching institutes, where the adjustment of patient’s appointment can be a challenge at times.
The universal testing machines are necessary testing equipment for material mechanical property and strength quality. They have been used extensively to determine the tensile and biaxial flexural strength of various dental materials in general and SBS of orthodontic brackets in particular.,
In orthodontics, bond failure at the enamel surface can cause enamel fracture; it occurs when the bond between bracket and adhesive is excessively strong. Artun and Bergland used an ARI system to assess the amount of adhesive left on the tooth after debonding. This index is universally used for assessing the characteristics of bond between the composite and tooth and between composite and bracket base.,
Bonding of orthodontic bracket to the tooth surface is a short-term phenomenon; the bracket is taken off at the end of orthodontic treatment. Hence, debonding techniques, residual adhesive on the enamel surface, etching process, and cleaning of enamel after debonding can mutilate it. Ideal SBS decreases the adhesive left over after debonding and minimizes the requirement of aggressive cleaning of enamel. At the same time, very high SBS can also result in no adhesive left on tooth, which can predispose enamel cracks and subsequent fracture.
In this study, there was no significant difference in ARI scores between the acid-etch and self-etch groups. The majority of the sample recorded score 1 that depicts less than half of the adhesive remaining on the tooth and a cohesive bond failure. The benefit of reduced amounts of adhesive on the enamel is a reduction in polishing time; however, it can accelerate the chances of cracks., In general, bonding and debonding should result in minimal enamel damage, but the literature shows higher enamel loss using an acid-etch primer in comparison to a self-etch primer. The slight enamel loss with self-etching primers can be described with less residual adhesive on the teeth after debonding and thus less polishing requirements subsequently. This shows that self-etching can be safely used to bond the bracket to a tooth by withstanding the loads with solid enamel-adhesive bond, yet the strength of bond is least damaging to the enamel surface.
The present report evaluated adhesive type on SBS. Other variables could alter the results of the present report. Composite type has been demonstrated to have a significant effect on in vitro and clinical adhesion efficacy. Additionally, sandblasting,  cyclic fatigue, remineralizing pretreatment, and aging could have a significant effect on adhesion efficacy. Therefore, further reports are needed in order to match the present results with other unexplored conditions.
This study had some limitations. One was unavailability of scanning electron microscope (SEM) to view the surface topography and fractured teeth during the debonding procedure. Also, the in vitro studies cannot extrapolate the exact condition of oral cavity, and so all the factors could not be taken into account. Other factors, as mentioned above, were also not evaluated, which might have affected the result of this report.
The results of this study determine that self-etch primer can be safely used to bond the brackets to enamel surface with least damaging mode of bond failure, hence making it a viable choice for clinicians in the clinical orthodontic setup. We recommend in vivo studies to deduce the exact effects of oral cavity on the SBS of orthodontic brackets when bonded with self-etch primers. Also, the use of SEM and fractographic analysis should be encouraged to study the surface changes. Also, latest biomaterials with nanoparticles should also be explored to recognize their effects on SBS.
| Conclusion|| |
The SBS of both the groups was higher than the clinically adequate range of 6 to 8 MPa. SBS of group A (37% phosphoric acid) was significantly higher than group B (self-etch primer). Most of the ARI scores showed less than half of the adhesive remaining on the tooth surface (score 1) indicating a cohesive failure with no significant difference between acid-etch and self-etch groups. Self-etching primer system can be an acceptable choice to condition the enamel for bracket bonding as it can withstand occlusal forces and produces minimum need of invasive enamel cleaning procedures, thereby preserving the enamel structure and architect. It can also reduce chair time and contamination.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]