|Year : 2019 | Volume
| Issue : 2 | Page : 101-106
Shear bond strength of metal and ceramic brackets using conventional acid etch/primer and self-etch primer
Chandrika Katti1, Girish Katti2, Syed Shahbaz2
1 Department of Orthodontics, Al-Badar Dental College and Hospital, Kalaburgi, Karnataka, India
2 Department of Oral Medicine & Radiology, Al-Badar Dental College and Hospital, Kalaburgi, Karnataka, India
|Date of Submission||22-Jan-2019|
|Date of Acceptance||09-Mar-2019|
|Date of Web Publication||30-Jul-2019|
Dr. Chandrika Katti
Department of Orthodontics, Al-Badar Dental College and Hospital, Naganhalli Road, Kalaburgi - 585 102, Karnataka
Source of Support: None, Conflict of Interest: None
Aims: The aim of this in vitro study is to evaluate shear bond strength (SBS) of metal and ceramic brackets using conventional acid etch/primer and self-etch primer (SEP) adhesive systems.
Methodology: Healthy, extracted 120 human premolar teeth were collected and were divided into group 1 – teeth bonded with metal brackets and group 2 – teeth bonded with ceramic brackets. These two groups were further subdivided: subgroup 1a – 30 metal brackets bonded using conventional acid etch/primer adhesive system, subgroup 1b – 30 metal brackets bonded using SEP, subgroup 2a – 30 ceramic brackets bonded using conventional acid etch/primer adhesive system, and subgroup 2b – 30 ceramic bracket bonded using SEP; brackets were debonded using a computerized universal Instron Testing Machine and the teeth were examined under ×10 magnification for adhesive remnants and scored according to modified adhesive remnant index (ARI).
Results: The mean SBS of metal and ceramic brackets bonded using conventional acid etch/primer adhesive system showed higher bond strength than those bonded using SEP. Bond strength ranged from 7.25 to 12.23 MPa which was in the acceptable clinical range. Modified ARI scores calculated showed varied results.
Conclusion: SBS values of all four subgroups exceeded the range of 6–8 MPa considered to be suitable for routine clinical use.
Keywords: Ceramic brackets, conventional acid etch/primer, metal brackets, self-etch primer, shear bond strength
|How to cite this article:|
Katti C, Katti G, Shahbaz S. Shear bond strength of metal and ceramic brackets using conventional acid etch/primer and self-etch primer. J NTR Univ Health Sci 2019;8:101-6
|How to cite this URL:|
Katti C, Katti G, Shahbaz S. Shear bond strength of metal and ceramic brackets using conventional acid etch/primer and self-etch primer. J NTR Univ Health Sci [serial online] 2019 [cited 2020 Apr 2];8:101-6. Available from: http://www.jdrntruhs.org/text.asp?2019/8/2/101/263629
| Introduction|| |
Orthodontic treatment for malaligned teeth using fixed appliances requires the proverbial handle to enable a force system to be applied to the teeth. The conventional bonding of orthodontic brackets to enamel has virtually discarded the custom-made bands which compromised esthetics and clinical time. This procedure requires three different agents: enamel conditioner, primer solution, and an adhesive resin. The field of fixed orthodontic treatment has been revolutionized by the advent of acid etching technique by Buonocore in 1955 using 85% phosphoric acid. 37% Phosphoric acid solution is the most widely used enamel conditioner for composite adhesive and has achieved good adhesive results. To simplify the procedure, self-etch primer (SEP) adhesive system (a sixth-generation adhesive) was introduced which combines acid and primer into a single solution, reducing the steps and time spent for orthodontic bonding.
Esthetics has always been important in the field of orthodontics. Patients preferred the appearance of the “bandless metal braces” made of stainless steel. These brackets rely on mechanical retention for bonding. To enhance patient's esthetics during treatment, ceramic brackets were introduced into clinical practice which is durable and resistant to staining.,
The stress released during debonding of the bonded brackets is measured in terms of shear bond strength (SBS). Optimal SBS ranges between 6 and 8 MPa. The unit of shear bond strength is Mega Pascals(Mpa), kg/cm 2, or Pounds per sq inch. The purpose of this study was to determine and compare the SBS of metal and ceramic brackets using conventional acid etch/primer and self-etching primer adhesive systems.
| Methodology|| |
This in vitro study was carried out on 120 healthy, extracted human maxillary and mandibular right and left premolar teeth. All teeth collected were with intact buccal enamel surface, with no restorations, caries, fissures, or cracks. Teeth subjected to previous application of chemical agents or orthodontic/endodontic treatments were excluded from the study.
The teeth were cleaned with periodontal curette, placed in thymol solution of 0.1%. The roots of the teeth were embedded in self-polymerizing acrylic resin at a sandy stage avoiding contact between resin and crown. The buccal surface of all teeth was cleaned and polished with oil-free pumice and a rubber prophylactic cup for 10 s, rinsed with water and dried using an oil and moisture-free air stream.
The metal brackets used in the study were Gemini MBT Premolar Brackets (Jamuna International 3M Unitek, Gemini MBT 022 slot brackets) with the bracket base area of 10.5 mm 2 [Figure 1]. The ceramic bracket used was Transcend 6000 series premolar brackets (3M Unitek) with a bracket base area of 8.25 mm 2 [Figure 1]. The SEP used in this study was Transbond Plus SEP (3M Unitek) which is in the form of a lollypop, consisting of etchant and primer [Figure 2]. The adhesive used was Transbond XT [Figure 3].
|Figure 3: (a) Transbond XT adhesive. (b) 37% phosphoric acid. (c) Transbond XT primer|
Click here to view
The samples were divided randomly into two groups:
Group 1: Teeth bonded with metal brackets
Group 2: Teeth bonded with ceramic brackets.
The two groups were further divided into four subgroups (number of sample, n = 30):
Subgroup 1a: 30 teeth bonded with metal bracket using conventional acid etching/primer adhesive system
Subgroup 1b: 30 teeth bonded with metal bracket using SEP adhesive system
Subgroup 2a: 30 teeth bonded with ceramic brackets using conventional acid etch/primer adhesive system
Subgroup 2b: 30 teeth bonded with ceramic brackets using SEP adhesive system.
Group 1: 60 teeth bonded with metal brackets
Subgroup 1a: The prepared enamel surfaces were etched with 37% phosphoric acid gel for 20 s, followed by thorough washing and drying, and then Transbond XT primer [Figure 2] was applied on the etched surfaces. The metal brackets were bonded on to the teeth surface using the adhesive Transbond XT (3M Unitek) according to the manufacturer's recommendation.
Subgroup 1b: SEP (Transbond Plus) was applied on the prepared enamel surface for 15 s and gently evaporated with air, according to the manufacturer's recommendation. For activation, the two components were squeezed together and the resulting mix was applied directly on the enamel surface. The active ingredient in Self etch primer is methacrylated phosphoric acid ester. The phosphate group dissolves calcium and removes it from hydroxyapatite lattice of enamel, which forms a complex with phosphate and incorporates into network when primer polymerizes. Etching and monomer penetration of exposed enamel rods are simultaneous. The metal brackets were then bonded onto the teeth using Transbond XT adhesive.
Group 2: 60 teeth bonded with ceramic brackets
Subgroup 2a: The enamel surfaces were acid-etched with 37% phosphoric acid gel (3M Unitek) for 20 s, followed by thorough washing and drying, and then Transbond XT primer was applied. The ceramic brackets were bonded onto the teeth using the adhesive Transbond XT according to the manufacturer's recommendations.
Subgroup 2b: SEP (Transbond Plus) was applied on the prepared tooth surface for 15 s and gently evaporated with air, according to the manufacturer's recommendations. For activation, the two components were squeezed together and the resulting mix was applied directly on the tooth surface. The ceramic brackets were then bonded onto the teeth using Transbond XT.
All bonding procedure was performed by a single operator. Excess bonding material was removed with an explorer before the resin was polymerized. A conventional halogen light source (3M ESPE 2500) was used to cure for 20 s from each of mesial and distal sides.
After the bonding procedure, the samples were stored in distilled water at 37°C for 24 h to simulate the oral conditions. Brackets were debonded using a Computerized Universal Instron Testing Machine (Unitek 9450, India) [Figure 4] at a crosshead speed of 1 mm/min. Before debonding, the embedded specimens were secured in a jig attached to the base plate of the universal testing machine. A chisel-edge plunger was mounted in the movable crosshead of the testing machine and was positioned so that the leading edge aimed at the enamel–bracket interface before being brought into contact at the crosshead speed of 1 mm/min [Figure 5]. The force required to dislodge the brackets was measured and recorded by the computer, connected electronically to the testing machine, in Newtons (N), and the SBS (1 MPa = 1 N/mm 2) was then calculated by dividing the force values by the bracket base area to convert the values into megapascal.
After debonding, the teeth and brackets were examined under ×10 magnification with a light microscope. Adhesive that remained on teeth after bracket removal was assessed and scored according to modified adhesive remnant index (ARI).
Descriptive statistics including mean and standard deviation (SD) were calculated for all the groups. Student's t-test was used to determine significant difference in the bond strength between the groups.
| Results|| |
The mean SBS and SDs of all the groups are shown in [Table 1] and [Graph 1]. The mean SBS varied between test groups. In ascending order, the lowest mean SBS was 7.25 MPa for group 1b, metal brackets bonded with SEP. The second lowest mean SBS was 9.66 MPa for group 1a, metal brackets bonded with conventional acid etch/primer. The mean SBS of ceramic brackets bonded with SEP was 10.32 MPa. Ceramic brackets bonded with conventional acid etching/primer had the highest mean SBS of 12.23 MPa.
The SDS for the data varied between groups; the highest was in group 2a, ceramic brackets bonded with conventional acid etch/primer and the lowest SD was in group 1a, metal brackets bonded with conventional acid etch/primer adhesive system.
The descriptive statistics for the SBS of the subgroups of group 1 and group 2 tested are presented in [Table 2]. The results of Student's t- test indicated that there was no statistically significant difference.
The modified ARI scores  calculated for each group are presented in [Graph 2]. Modified ARI scores range from 5 to 1, where, 5 = no adherence of composite on enamel, 4 = less than 10% of composite remaining on enamel surface, 3 = more than 10% but less than 90% of composite remaining on the enamel, 2 = more than 90% composite remaining on the enamel surface, and 1 = entire composite remaining on the tooth, with impression of the bracket base. The results of the adhesive remnant index scores showed that subgroup 1a, metal brackets bonded to teeth using conventional acid etch/primer adhesive system, had more adhesive remains on the tooth surface indicating more intact enamel surface during its use.
| Discussion|| |
The results of the present investigation showed that all the test groups had SBSs exceeding a long-acceptable clinically optimal level of 6–8 MPa, which is similar to previous studies.,,,,
The results of this in vitro study showed that metal and ceramic brackets bonded using conventional acid etch/primer adhesive systems had higher SBS than those bonded using self-etching primer. Traditional use of acid etchant followed by primer has been an essential part of the bonding procedure with composite adhesives to allow good wetting and penetration of sealants into the enamel surface because of the gross retentive structures that are produced by differential dissolution of the underlying enamel prisms., These results were consistent with previous studies.,
In this study, ceramic brackets exhibited significantly higher SBS when compared with stainless steel brackets, and modified ARI scores showed that ceramic brackets were more prone to enamel fracture. Because ceramic brackets will not bond chemically with adhesives, manufacturers must use mechanical undercuts, a coating of silica and a silane coupling agent, or both to bond these brackets to enamel. Either the mechanical or chemical process tends to increase bond strength compared with metal brackets, producing a greater likelihood of enamel damage during debonding. This finding is in corroboration with previous studies.,, Transcend 6000 Series brackets have a unique microcrystalline bonding surface which provides consistency, strength, and reliability of mechanical retention. Mechanical lock base provides reliable bond strength with all chemical and light cure bonding adhesive systems.
Hence, ceramic brackets offer a viable alternative to their metal counter part because they combine esthetics with a bond strength that is comparable to and as reliable as their metal counterpart which is in accordance with the results obtained by Gwinnett and Brook.
According to this study, ceramic bracket bonded using conventional acid etch primer adhesive system had higher SBS and showed more enamel loss during debonding of these brackets, than when bonded with SEP, so self-etching primer can be used along with ceramic brackets to reduce the chances of enamel loss during debonding. These findings are in consistent with the study.
The SBS of metal brackets bonded with Transbond plus SEP in the study was 7.25 ± 2.44 MPa, and a study done by Bishara et al. showed the SBS using Transbond plus SEP was 5.9 ± 2.7 MPa  and they have concluded that the results were in clinically acceptable range which corroborated with the findings of this study.
In contrast to the results of this study, a few studies in literature have also reported no difference in SBS of orthodontic metal brackets bonded either with self-etching primer or with conventional acid etching methods; one such study was previously reported.
In this study, the results showed lower SBS with self-etching primer which is in clinically acceptable range. On the contrary, a study showed that Transbond Plus was superior to the conditioning methods both in terms of SBS and the time required for application. With Transbond Plus self-etching primer, all the steps are combined into a single application and produce a highly porous surface on prismatic enamel. This is because in simultaneous etching and priming, the primer penetrates the entire depth of the etch ensuring an excellent mechanical interlock. Furthermore, variations in bond strengths, even though an identical adhesive system was applied in different studies, may be attributed to differences in operator technique and methodology.
Acid etching, rinsing, priming, and application of adhesive are thus combined in one step ultimately reducing the number of steps and saving chairside time. SEP showed maximum bond strength under both dry and wet conditions. A study appreciated that Transbond Plus is packaged for single patient use to avoid contamination, is fast to apply, and is cost-effective when used for full bonding.
Furthermore, adhesive remnants on the tooth surface were calculated and scored according to modified ARI, which revealed 8 of 30 teeth showed more than 90% of composite remaining on enamel surface indicating more intact enamel surface and enamel fracture is less likely to occur in subgroup 1a during debonding. These findings are in near approximation with another study.
The direct bonding of orthodontic brackets has enhanced and improved the clinical practice of orthodontics. This study evaluated the use of new SEP when compared with the conventional bonding procedure of ceramic and metal brackets indicating that the use of SEP to bond orthodontic brackets to the enamel surface provided lower but clinically acceptable SBS. However, this was an in vitro study and care should be taken in comparing the results with those that might be obtained in the oral environment. More research is needed to determine the SBS of these self-etching primers under in vivo conditions to further authenticate the results which might replace the conventional acid etching primer adhesive system in days to come.
| Conclusion|| |
Under the conditions of this in vitro study, the following conclusions were drawn:
- Metal and ceramic brackets bonded using conventional acid etch/primer adhesive systems had higher SBS than those bonded using SEP; however, the SBS values of all four subgroups exceeded the clinically acceptable range of 6–8 MPa, hence it can be concluded that SEP can be recommended for routine clinical use which has the advantage of reduced clinical time and increased convenience
- Ceramic bracket bonded with conventional acid etch/primer had higher bond strength and more prone for enamel fracture during debonding than ceramic brackets bonded with SEP as per modified ARI scores. Hence, self-etch primer can be recommended to be used with ceramic brackets to prevent enamel fracture. Furthermore, modified ARI scores showed that metal brackets bonded using conventional acid etch/primer adhesive system have minimal tendency for enamel fracture.
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]