Year : 2008 | Volume
: 26 | Issue : 7 | Page : 104--108
Comparative evaluation of shear bond strength of different bracket base designs in dry and wet environments
OP Mehta, S Saini, A Dahiya
Department of Orthodontics, MMCDSR, Mullana (Ambala), India
O P Mehta
231- Navsansad Vihar, Plot No. 4, Sector 22, Dwarka, New Delhi
One hundred and thirty five extracted premolars were selected and bonded with three types of brackets with different bracket base designs viz. Gemini (foil mesh), Miniature twin (Laser etched) and Mini Dynalocks (Integral base). These brackets were bonded with Transbond XT adhesive using two types of primers viz. Conventional Transbond XT in dry conditions and M.I.P in dry and wet environments. The specimens were tested for SBS using Instron machine at C.I.P.E.T. (Amritsar), Punjab. Results were statistically analyzed.
Results and Discussion: The Miniature twin brackets revealed higher SBS values as compared to Gemini and Mini Dynalock in dry and wet conditions. All the groups showed higher SBS values in dry conditions as compared to wet conditions respectively. The Gemini and Mini Dynalock brackets showed very little difference of SBS values.
Conclusion: Miniature twin brackets with laser etched bracket base in dry and wet environments have revealed the highest SBS values. All the groups have revealed clinically acceptable SBS value of above 8 MPa in moist conditions.
|How to cite this article:|
Mehta O P, Saini S, Dahiya A. Comparative evaluation of shear bond strength of different bracket base designs in dry and wet environments.J Indian Soc Pedod Prev Dent 2008;26:104-108
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Mehta O P, Saini S, Dahiya A. Comparative evaluation of shear bond strength of different bracket base designs in dry and wet environments. J Indian Soc Pedod Prev Dent [serial online] 2008 [cited 2020 Aug 13 ];26:104-108
Available from: http://www.jisppd.com/text.asp?2008/26/7/104/44837
The introduction of acid etch technique by Buonocore in 1955 heralded a new era in adhesive dentistry. Direct bonding of orthodontic appliances to enamel with composite resin was first performed by Newman, in 1965 and even to date, it is the most accepted and widely used method by orthodontists all over the world. In orthodontics, bonding systems have been a continuous innovation with latest entrants being moisture insensitive primers and self-etching primers. These new primers have been claimed to be a blessing for orthodontists with bonding in moist conditions.
Bonding is a technique sensitive procedure and moisture is cited as one of the most common causes of bond failure. The effectiveness of mechanical bond of the conventional composite resin adhesive to enamel requires the enamel to remain completely dry after the etching to allow the penetration of hydrophobic primer for adequate retention. Contamination causes the plugging of porosities caused by acid etching and a reduction in surface energy, therefore penetration of resin is impaired and micro-mechanical retention is compromised.
Brackets in the oral cavity are subjected to variety of forces. Bond strength is influenced by various factors like the surface area, conditioning procedures, type of adhesive used, bracket base design, the treatment of the bracket base and protocol followed during bonding. Ideally, an orthodontic bracket must be able to deliver an optimal orthodontic force, must be able to withstand the masticatory loads and should be easily removed at the end of the treatment with minimal damage to the tooth surface. With increasing demand for esthetic appliances, there is decrease in the size of the brackets, thereby requiring alternative means of increasing the retentive capability of the bracket base.
Studies have indicated that bond failure in enamel bonded metal brackets occurs at the resin bracket base interface, within the resin itself or between the resin and enamel. However, there have been relatively more bond failures between the resin and bracket base because of the stress concentration and defects in the resin film. A bracket with good retentive bonding between the resin and metal base is needed. Therefore, it is essential to choose a good bracket base design to achieve the adequate bond strength of the attachment.
Sorel et al. in their study have revealed that laser structured bracket base has higher bond strength than that of simple foil mesh, is equally safe and does not induce any significant enamel surface loss. This study was conducted to investigate the influence of various bracket base designs on the shear bond strength of light cure adhesive (Transbond XT) used with Transbond XT – Primer and Transbond Moisture Insensitive Primer in dry and wet environments.
Materials and Methods
One hundred thirty-five extracted premolar teeth were selected with intact buccal enamel with no cracks, caries or developmental defects. The teeth were mounted on dental stone blocks and were then segregated into 9 groups, consisting of 15 teeth in each group.
Group IA, IB and IC comprised 45 teeth and Gemini, Miniature twin and Mini Dynalock brackets were used. The enamel surface was polished, etched with 37% phosphoric acid, rinsed with water and dried. A thin coat of Transbond XT conventional primer was applied to the enamel surface and air rinsed with a gentle burst of air for 2 seconds. The brackets were bonded with light cure Transbond XT adhesive and cured for 15 seconds. Group IIA, IIB and IIC comprised 45 teeth and Gemini, Miniature twin, Mini Dynalock brackets were used. The enamel surface was polished, etched with 37% phosphoric acid, rinsed with water and dried. A thin coat of Transbond Moisture Insensitive Primer was applied to the enamel surface and air thinned with a gentle burst of dry air for 2 seconds. The brackets were bonded with light cure Transbond XT adhesive and cured for 15 seconds.Group IIIA, IIIB and IIIC comprised 45 teeth and Gemini, Miniature twin and Mini Dynalock brackets were used. The enamel surface was polished, etched with 37% phosphoric acid, rinsed with water and dried. The teeth were moistened with a thin coat of artificial saliva, brushed on the buccal surface and primed with Moisture Insensitive Primer and air thinned for 2 seconds. The brackets were bonded with light cure Transbond XT adhesive and cured for 15 seconds.
The shear bond strength of the bonded teeth were determined using INSTRON testing machine (Universal Testing Machine LLOYD) at Central Institute of Plastics Engineering and Technology, Amritsar, Punjab.[Table 1]
Result and Discussion
Direct bonding has revolutionized the clinical practice of orthodontics. Wertz has emphasized that poor control of moisture seems to be the number one enemy of bonding. Improvements have continued through the introduction of different types of brackets with different bases. The latest invention is a new type of laser structured base design. They are produced by metal injection molding of stainless steel (AISI 316 L) and sintering to theoretical density. The smooth surface of bracket base is then treated with a sufficiently powerful NdYAG laser to create retentions for the adhesive. The laser beam is scanned over the base surface, melting and evaporating the metal and burning hole-shaped retentions in the base.
In this study, an in vitro bond strength characterization was chosen due to the relative simplicity, increased reliability of simulating debonding techniques and mode of application of shear force. Shear bond strength was tested because most masticatory forces are of a shearing nature.
Mean values of Group IA, IB and IC revealed that Group IB comprising Miniature twin brackets bonded with conventional Transbond XT primer in dry conditions has the highest shear bond strength (15.24±0.39 MPa.) as compared to Group IA (10.24±0.45 MPa.) comprising Gemini brackets (foil mesh base) and Group IC (9.95±0.25MPa.) comprising Mini Dynalock brackets (integral base). There is comparatively insignificant difference of shear bond strength between Group IA and IC [Graph 1]-[SUPPORTING:1].
Smith and Reynolds concluded that both fine mesh A Company (14.8±1.7KgF) and coarse mesh brackets Dentaurum (10.4±0.7 KgF) showed significantly greater bond strength as compared to an undercut integral base Dynalock (7.7±0.7KgF).
Mean values of Group IIA, IIB and IIC revealed that Group II B comprising Miniature twin brackets bonded with Transbond MIP in dry conditions has the highest shear bond strength (14.88±0.46 MPa.) as compared to Group IIA (10.24±0.31 MPa.) comprising Gemini brackets (foil mesh base) and Group IIC (9.72±0.35 MPa.) comprising Mini Dynalock brackets (integral base) [Graph 2]-[SUPPORTING:2].
Mean values of Group IIIA, IIIB and IIIC revealed that Group III B comprising Miniature twin brackets bonded with Transbond MIP in wet conditions has the highest shear bond strength (10.23±0.23 MPa.) as compared to Group IIIA (8.58±0.11 MPa.) comprising Gemini brackets (foil mesh base) and Group IIIC (8.48±0.31 MPa.) comprising Mini Dynalock brackets (integral base) [Graph 3]-[SUPPORTING:3].
Mean values of Group IA, IIA and IIIA revealed that Group IIIA comprising Gemini brackets (foil mesh base) bonded with Transbond Moisture Insensitive Primer in wet conditions has the lowest shear bond strength (8.58±0.11 MPa.) as compared to Group IA (10.24±0.45 MPa) and Group IIA (I0.24±0.31 M Pa) [Graph 4]-[SUPPORTING:4].
In a study on bond strength comparison of moisture-insensitive primers, Schaneveldt and Foley showed the shear bond strength with Transbond XT (14.82 ±2.62MPa) and MIP after saliva contamination (12.23 ±2.53MPa).
Mean values of Group IB, IIB and IIIB revealed that Group IIIB comprising Miniature twin brackets (laser structured bracket base) bonded with Transbond Moisture Insensitive Primer in wet conditions has the lowest shear bond strength (10.23±0.23 MPa.) as compared to Group IB (15.24±0.39 MPa.) and Group IIB (14.88±0.46 MPa) [Graph 5]-[SUPPORTING:5].
Zeppiere et al. in their study on effect of saliva on shear bond strength of an orthodontic adhesive used with moisture-insensitive and self-etching primers revealed that when the brackets were bonded with Transbond XT adhesive the control group: etch, dry, Transbond XT primer had the highest mean shear bond strength (21.3±6.8 MPa), followed by MIP group in a dry field (20.7±5.0 MPa). No significant difference was found between these two groups. Saliva contamination significantly lowers the bond strength of Transbond MIP (15±3.0 MPa) but it is clinically acceptable.
Mean values of Group IC, IIC and IIIC revealed that Group III C comprising Dynalock brackets (integral base) bonded with Transbond Moisture Insensitive Primer in wet conditions has the lowest shear bond strength (8.48±0.31 MPa.) as compared to Group IC (9.95±0.24 MPa.) and Group IIC (9.72±0.35 MPa.) in dry conditions [Graph 6]-[SUPPORTING:6].
The data in this study revealed that Transbond XT adhesive used with Moisture Insensitive Primer had significant lower shear bond strength in moisture contaminated field (Group IIIA, IIIB, IIIC) than under dry testing conditions. This finding is similar to those of Webster et al. and Hobson et al. But all these findings have confirmed that use of MIP in moist condition has given adequate SBS of above 8 MPa and is clinically acceptable.
As revealed by a study done at Rajiv Gandhi University, the shear bond strength of the sample bonded with conventional primer in wet condition was 4.51MPa, which is less than the optimal value. Thus it is advocated to use Moisture Insensitive Primer in wet condition showing the shear bond strength of 11.8 MPa instead of using conventional hydrophobic primer in moist conditions.
Miniature twin brackets have revealed comparatively higher SBS values as compared to Gemini and Mini Dynalock brackets in dry and wet conditions.Use of conventional Transbond XT Primer and MIP has revealed comparatively higher SBS value in dry conditions as compared to M.I.P in wet conditions.Use of conventional Transbond XT Primer and M.I.P in dry conditions has revealed comparatively similar SBS values in all the bracket base designs respectively.M.I.P in wet conditions has revealed clinically acceptable SBS value (above 8 MPa) and can be recommended for the purpose of orthodontic bonding in moist conditions.
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