|Year : 2019 | Volume
| Issue : 7 | Page : 515-522
A comparative study of shear bond strength of direct bonding system with and without a liquid primer: An in vitro study
Ashok Babu Devatha1, M Narasimha Lakshmi2, Naresh B Kumar3, Srikanth Erukala4, Rathna Valluri5, Kranti Kiran Reddy Ealla6
1 Department of Orthodontics, GITAM Dental College and Hospital, Visakhapatnam, Andhra Pradesh, India
2 Department of Orthodontics and Dentofacial Orthopedics, Government Dental College and Hospital, Hyderabad, Telangana, India
3 Department of Orthodontics and Dentofacial Orthopedics, Government Medical College, Mahabubanagar, Telangana, India
4 Department of Orthodontics, Meghana Institute of Dental Sciences, Nizamabad, Telangana, India
5 Department of General Dentistry, Malla Reddy Institute of Dental Sciences, Hyderabad, Telangana, India
6 Department of Oral and Maxillofacial Pathology, Malla Reddy Institute of Dental Sciences, Quthbullapur, Hyderabad, Telangana, India
|Date of Web Publication||14-Nov-2019|
Dr. Kranti Kiran Reddy Ealla
Department of Oral and Maxillofacial Pathology, Malla Reddy Institute of Dental Sciences, Quthbullapur, Hyderabad, Telangana - 500055, Ph: +91-9849409070
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: A primer in dental bonding agents enhances the bond between the adhesive and the tooth by way of deriding the tooth surface of moisture and creating a hydrophobic surface for the adhesive to bond and by facilitating the flow of the adhesive into the etched tooth surface. In the orthodontic context, however, there have been debatable results in the published literature as to how significantly the use of primer affects the bond strength between the bracket and the tooth surface. Aims: This study aimed to evaluate and compare the shear bond strength of two commercially available direct bonding systems with and without using liquid primer and to record their adhesive remnant index scores. Settings and Design: A total of 100 natural human teeth, extracted for orthodontic therapies, had been selected as specimens for the study. They were equally divided into four categories. Two commercially available products were used to bond metallic orthodontic brackets to the teeth, both with the use of and without the use of a primer to test the shear bond strengths of the four types of adhesive-tooth complexes created. Shear bond strength was measured using universal testing machine, and Student’s t-test was applied for the comparison of the results. Materials and Methods: A total of 100 extracted human premolar teeth were divided into two groups: Group I and Group II, each of which contained two subgroups (with one subgroup pretreated with a primer and the other, not pretreated with the primer). All the teeth were divided equally among the subgroups and were mounted on color-coded acrylic blocks to aid in identification. Group I was bonded with Transbond XT Light Cure Adhesive (3M Unitek Orthodontic Products, Monrovia, California) and Group II was bonded using Phase II two-paste system (Reliance Orthodontic Products, Itasca, Illinois). The shear bond strength of Transbond XT Light Cure Adhesive used with Transbond XT primer and Phase II orthodontic two-paste system used with liquid primer was compared with that of those used without a liquid primer, respectively. The shear bond strength was evaluated using universal testing machine and the adhesive remnant scores were evaluated subsequently. The Student’s t-test was applied for comparison of the two groups. Statistical Analysis: Descriptive statistics, such as mean, standard deviation, and a standard error, were calculated for Transbond XT used with and without primer and for Phase II two-paste system used with and without a liquid resin. The Student’s t-test was applied for comparison of the two groups. Results: In Group I, the mean bond strength of Transbond XT without primer (12.5272MPa, 95% CI: 11.76–13.68) was compared to that of Transbond XT with XT primer (13.2028MPa, 95% CI: 12.39–14.06). In Group II, the mean shear bond strength of Phase II two-paste system without primer (10.66MPa, 95% CI: 10.13–11.18) was compared to that of Phase II two-paste system with primer (10.66MPa, 95% CI: 10.13–11.18), and the values were statistically insignificant. Conclusion: The shear bond strength of the brackets bonded with Transbond XT and Phase II without using the liquid primer was sufficient enough to withstand the masticatory forces, which implies the elimination of liquid primer during bonding. Clinical Significance: The development of the acid-etch technique and Bisphenol A-glycidyl methacrylate-based liquid resin has changed the practice of orthodontics over the years more than any other single principle formulated. Despite its wide popularity, the cytotoxicity, which stems from the use of liquid primer, needs attention.
Keywords: Adhesive remnant index, bonding system, direct bonding, primer, shear bond strength
|How to cite this article:|
Devatha AB, Lakshmi M N, Kumar NB, Erukala S, Valluri R, Ealla KK. A comparative study of shear bond strength of direct bonding system with and without a liquid primer: An in vitro study. J Pharm Bioall Sci 2019;11, Suppl S3:515-22
|How to cite this URL:|
Devatha AB, Lakshmi M N, Kumar NB, Erukala S, Valluri R, Ealla KK. A comparative study of shear bond strength of direct bonding system with and without a liquid primer: An in vitro study. J Pharm Bioall Sci [serial online] 2019 [cited 2020 May 29];11, Suppl S3:515-22. Available from: http://www.jpbsonline.org/text.asp?2019/11/7/515/270896
| Introduction|| |
The introduction of the acid-etch bonding technique had led to dramatic changes in the practice of orthodontics. The procedure of acid etching and bonding had come to stay in orthodontics; this had indeed been endorsed by clinicians worldwide. Today, most orthodontists either directly or indirectly bond attachments to the teeth; these are the most aesthetically superior options. The advantages and disadvantages of bonding versus those of banding of different teeth must be weighed according to practitioner’s preferences, skill, and experience. Probably, the most important of these advantages of bonding are the improved appearance and hygiene, the decreased discomfort of the patient, and the ease of application for the clinician.
The development of acid-etch technique by Buonocore in 1955 led to the direct bonding of orthodontic brackets with composite resin. This development resulted in an improvement in orthodontic treatment that included greater comfort for the patient, elimination of pretreatment separation, decreased gingival irritation, easier oral hygiene maintenance, improved aesthetics, reduced chairside time, absence of posttreatment band spaces, facilitation of application of attachments to partially erupted teeth, minimized danger of decalcification with loose bands, and easier detection and treatment of caries. The development of acid-etch technique over years has changed the practice of dentistry more than any other single principle formulated.
Fully polymerized resins produce no harmful biological effects. Orthodontic staff working with these chemical agents had seen an increased risk of developing skin allergy on their hands. The prevalence of dermatosis in this occupational group was 40%–43%, whereas skin problem was recorded in only 21% of periodontists who handled resins less often in their daily practice. Occasional mucosal reactions related to resin restorations in teeth are also reported in patients. In a review by Löfroth et al., it was discussed that by curtailing contact with uncured dental resins, the risk of exposure to Bisphenol A (BPA) might be reduced. It was also mentioned that due to the structural similarity, BPA potentially acts as a xenoestrogen that binds to various nuclear receptors and elicits unruly effects.
The main focus of this study was to evaluate the shear bond strengths (SBSs) of two commercially available composites. Both are compared with and without the use of liquid resins. If they have the potential for obtaining clinically acceptable bond strength even without the liquid resin pretreatment, the liquid resin should be eliminated.
| Materials and Methods|| |
The SBS of Transbond XT Light Cure Adhesive (3M Unitek Orthodontic Products, Monrovia, California) used with Transbond XT primer (3M Unitek Orthodontic Products) [Figure 1] and Phase II orthodontic two-paste system (Reliance Orthodontic Products, Itasca, Illinois) used with liquid primer [Figure 3] was compared with that of those used without a liquid primer [Figure 2], respectively., ,
A total of 100 freshly extracted human healthy premolars, taken out for therapeutic purposes, were cleared of all soft tissue debris and stored in normal saline at room temperature until needed.
These samples were divided into two groups: Group I and Group II with each group being in turn subdivided into two subgroups. Groups I and II contained 50 samples each and they were equally divided among the subgroups. All the samples were mounted in color-coded acrylic blocks with the long axis of the tooth vertical to permit subsequent identification. All the teeth were first cleared of any soft tissue, washed with water, dried, and etched for 60s with viscous 37% phosphoric acid gel. After the specified time, the teeth were rinsed for 20s with water and then allowed to dry. Meshed, pre-contoured stainless steel brackets were used for bonding. Similar bonding procedures were used for each material. The only difference was in the application of the primer as shown below.
The brackets were then bonded. The total time per bracket with Transbond XT with XT Primer was 50s. After all the specimens were bonded, the entire block was allowed to stand in air for 10min before being put into water stored at room temperature for 48h, until the time of debonding. After 48h of storage, the SBS was tested with universal testing machine Model - AFS-X, 10 kN, Shimadzu, Columbia, Maryland 21046, USA [Figure 4].
| Results|| |
Descriptive statistics, such as mean, standard deviation (SD), and standard error, were calculated for Transbond XT [Table 1] used with and without primer and for Phase II two-paste system [Table 2] used with and without a liquid resin.
|Table 1: Statistical Analysis of Specimens bonded with Transbond XT (Group I)|
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|Table 2: Statistical Analysis of Specimens bonded with Phase II (Group II)|
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The changes in the SBS were tested with the help of universal testing machine. The results of this study was computed and analyzed with a computer. The Student’s t-test was applied for comparison of the two groups.
Group I: specimens bonded with Transbond XT
- The subgroup treated with primer [Figure 5]: The mean bond strength was found to be 13.20MPa, 95% CI: 12.39–14.06.
- The subgroup not treated with primer [Figure 6]: The mean bond strength was found to be 12.52MPa, 95% CI: 11.76–13.28.
Group II: Specimens bonded with Phase II two paste adhesive
- The subgroup treated with primer [Figure 7]: The mean bond strength was found to be 10.66MPa, 95% CI: 10.13–11.18.
- The subgroup not treated with primer [Figure 8]: The mean bond strength was found to be 10.66MPa, 95% CI: 10.13–11.18.
Comparison between the subgroups of Group I and Group II
Group I: In this group, the mean bond strength of Transbond XT without primer (12.52MPa, 95% CI: 11.76–13.28) was compared with that of Transbond XT with primer (13.20MPa, 95% CI: 12.39–14.06). The Student’s t-test was used for the comparison and it revealed the t value as 1.25 and P value > 0.05 (P = 0.214). So, these values showed statistically no significance [Table 1].
Group II: In this group, the mean bond strength of Phase II two-paste system without primer (10.66MPa, 95% CI: 10.13–11.18) was compared with that of Phase II two-paste system with primer (10.66MPa, 95% CI: 10.13–11.18). The Student’s t-test was used for the comparison and the resulting t value was 0.61 and P value > 0.05 level (P = 0.486) [Table 2]. Thus, the result was statistically not significant.
| Discussion|| |
Group I and Group II showed bond strengths that were close to or equal to the minimal requirement. In this study, under ideal conditions, for Group I, the mean SBS required for bond failure for specimens treated with XT primer and without XT primer were 13.20 and 12.52MPa, respectively. Transbond XT when used with XT primer had slightly higher mean SBS but it was not statistically significant. Previous studies with Transbond XT composite have reported bond strength ranging from 10.4 to 19.6MPa.
In Group II, the mean SBS required for bond failure for specimens bonded with Phase II two-paste system along with primer and for those bonded without primer was 10.90 and 10.66MPa, respectively. Phase II two-paste system when used without primer showed marginal decrease in mean SBS but it was not statistically significant.
A study conducted by Tang et al. aimed at assessing the adequacy of the early SBS acquired by the enamel-composite-bracket adhesion when the brackets were bonded by the use of composites (Transbond XT and Phase II composites) only and not their respective liquid resins. In the test groups, extracted premolars were bonded with orthodontic brackets on their buccal surfaces using the aforementioned composites without their liquid resins, and in the control group, the specimens were bonded with the same composites but with the use of their respective liquid resins. The specimens were stored underwater at 37°C for 24h and were subsequently tested for their SBSs. The results of this study implied that the SBSs of the control group and the test group specimens did not show a statistically significant difference. It was discussed that even without the use of liquid primer and with the absence of formation of resin tags, adequate SBS was attained by the specimens in the test group, which was similar to the control group. It was suggested that the success of this liquid-primer-free technique could be attributed to the fact that the etched enamel that has a higher surface tension is stabilized by the close adaptation of the composites. It was concluded from their study that the mechanical retention derived from the resin tags, formed from the use of a liquid primer, may not be the lone significant mechanism by which adequate SBSs are achieved.
The present findings clearly indicate that in Group I (specimens bonded with Transbond XT—with and without primer), the weakest point was located between the tooth surface and the composite.
In Group II (specimens bonded with Phase II two-paste system), for those bonded with liquid resin, the bond failure occurred at the composite bracket interfaces. In the other subgroup, the bond failure occurs between the tooth surface and the composite.
The results from present findings indicate that composite resins have adequate bond strengths, but their high adhesive remnant index (ARI) scores are disadvantageous as the cleanup of the residue mechanically will damage the enamel surface by producing cracks and scratches.
A limitation of this study is not taking into account “the material and the retentive design” factor of the orthodontic brackets when comparing the SBSs. In a study by Hofmann et al., it was discussed that depending on the type of bracket used, the retentive properties of the bracket, the adhesive used, the shear bonding, and bond-failure characteristics vary.
Pham et al., in an in vitro study, evaluated the influence of the orthodontic bracket base shape on SBS and ARI and concluded that SBS indeed varied depending on the differences in bracket base shape. There was higher SBS for bracket shapes that allowed even stress distribution.
Other factors that influence the bond strength between the metal bracket and tooth surface include different surface treatments, polymerization protocols, and the degree of conversion of the bonding agents. This has been discussed in a study performed by Sena et al., where they have used different surface treatments on enamel and concluded that both the bond/adhesive strength and the degree of conversion are affected by different surface treatments and polymerization protocols.
The differences in pressure exerted on the orthodontic bracket during its bonding to the tooth bring variations on the SBS by bringing about changes in the thickness of the adhesive. This has been concluded in a study conducted by Mohammadi et al., where 420 brackets were placed on bovine teeth using three types of adhesives using seven levels of force magnitudes. To achieve a higher bond strength, application of a higher force was advised.
The SBS also seems to vary between new and rebonded orthodontic brackets. Debonded brackets (cleaned and sandblasted) were concluded to have more SBS in a study conducted by Salama et al. on rebonding.
An in vitro study by Shaik et al. that included 100 extracted premolars, divided into four groups, compared the SBSs of orthodontic brackets bonded using Transbond Plus hydrophilic resin and hydrophobic Transbond XT resin under two conditions each: under salivary contamination and under no salivary contamination. The results showed that Transbond Plus hydrophilic resin had greater SBS under both the conditions than Transbond XT.
In a study by Valiollah et al., where 120 extracted human maxillary-premolar teeth were divided into four groups (metallic bracket/conventional bonding agent, metallic bracket/Transbond self-etching primer, ceramic bracket/conventional bonding agent, and ceramic bracket/Transbond self-etching primer), it was concluded that the bond strengths shown by metallic brackets were higher than those of ceramic brackets. So the use of the adhesive alone without the use of primer for bonding might not be justified for ceramic brackets.
In a study performed by Behnaz et al., 120 extracted human premolars were divided into four groups. First two groups were bonded with Transbond XT, one with and one without TiO2. The other two groups were bonded with Resilience light-cured composite, one with and one without TiO2. Each of these groups was in turn divided into three subgroups of 10 each and incubated at 37°C, for one day, one month, or three months. It was concluded that the SBS of Transbond XT was higher than that of Resilience and that no significant differences were noted in ARI scores based on the type of composite or addition of TiO2.
In a study conducted by Tayebi et al., the effect of surface preparation such as sandblasting and roughening with diamond bur in conjunction with the use of one of the three primers (Transbond XT, Assure Plus, and Composite Primer) on SBS of metal orthodontic brackets to aged composite was assessed. On the basis of the results, it was concluded that all combinations of primers and surface modifications provided adequate SBS, and when ARI scores were considered, it was concluded that surface preparation by bur was superior to sandblasting.
Oz et al. conducted a study to assess the role of an antibacterial-monomer-containing primer in preventing white spot lesions during fixed orthodontic therapy. In one group, brackets were bonded using antibacterial-monomer-containing primer and in the other group, brackets were bonded using a conventional primer (Transbond XT primer). The results of this study indicated no significant difference among the two groups in their ability to reduce the demineralization through the length of the treatment.
In an in vitro study by Cumerlato et al., the effects of grinding, drilling, sandblasting on the SBS of orthodontic brackets as well as the effects of surface modifications on the ARI were assessed. A total of 192 prefabricated teeth (PfT) were divided into four groups (one group had no surface modification and each of the rest of the three groups was either modified with a cylindrical diamond bur by grinding or with a spherical diamond bur by making two drillings or sandblasted with 50-µm aluminum oxide). Brackets were bonded using Transbond XT. Universal testing machine was used to measure the SBSs. It was concluded that the surface treatment on PfT had a positive effect in enhancing the SBS to brackets. Sandblasting and drilling seemed to achieve superior SBS than grinding.
In a study conducted by Ghadirian et al., the effect of quaternary ammonium salt (QAS) on SBS of orthodontic brackets to enamel was evaluated. QAS was added to Transbond XT primer in the concentrations of 0%, 10%, 20%, and 30%. Using these four combinations of QAS–primer mixture, brackets were bonded to 60 premolar teeth and SBSs were measured. The results concluded that the addition of QAS did not show any adverse effect on the SBSs of the brackets to enamel.
In a study conducted by Webster et al., SBS of Transbond XT used with Transbond primer was tested and compared with two other bonding agents (Transbond XT with Moisture intensive primer and Assure) that supposedly had qualities that let them be used over moisture/saliva-contaminated surfaces. Four different kinds of surface preparations were assessed, which included surfaces that were etched and dried, etched and dampened with saliva, etched-primed and dampened with saliva, and etched-primed-dampened and re-primed. It was concluded from the results that uncontaminated surface had the highest bond strengths with hydrophilic and hydrophobic systems.
In 2004, Rajagopal et al. concluded that moisture-insensitive primer and self-etching primer offered adequate bond strength under contaminated conditions. Self-etch primer displayed considerably superior performance under dry condition compared to that under contaminated condition.
In 2017, Sachdeva et al. concluded that highest SBS was observed in Transbond XT followed by G-Bond. Single bottle self-adhesive (G-Bond) has SBS of 15.54MPa. Its SBS is lower compared to conventional acid etching (Transbond XT) with a value of 16.31 MPa, which is higher compared to self-etching primer (Transbond SEP) with a value of 12.04 MPa.
In 2018, Tahir et al. concluded that there is no statistically significant difference in the SBS of orthodontic brackets cured with moisture-insensitive primer or with conventional primer.
| Conclusion|| |
In the first group, Transbond XT Light Cure Adhesive with XT primer and Transbond XT adhesive without XT primer were compared for in vitro SBS and location of site of adhesive failure. These were divided into two groups and each group was subjected to same enamel treatment.
It was observed that Transbond XT without XT primer under same enamel surface treatment had bond strength slightly lower than Transbond XT with XT primer, though not statistically significant.
In the second group, a different kind of material was used, which was the Phase II two-paste system with and without the use of liquid primer. Phase II two-paste adhesive used without liquid primer had bond strength that was marginally lower than that of the one used with liquid primer though not statistically significant.
Hence, it is clear that even without using the liquid primer, we could get sufficient bond strength. So bonding can be achieved satisfactorily even after eliminating the liquid primer. In conclusion, our data suggest that Transbond XT and Phase II might have enough SBS to resist masticatory forces even without the use of a primer. This might imply that mechanical interlocking between the etched enamel prisms and resin tags is probably not the only important mechanism for secure enamel adhesion. The clinical application of orthodontic bonding without liquid resin is yet to be supported by clinical trials.
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], [Figure 6], [Figure 7], [Figure 8]
[Table 1], [Table 2]