Shear Bond Strength of Different Adhesive Materials used for Bonding Orthodontic Brackets : A Comparative in vitro Study

Introduction: Bond strength is an important property and determines the amount of force delivered and treatment duration in orthodontics. Many light-cured bonding materials are being used; but it is required to determine the most efficient one with desired bond strength. Objective: To determine and compare the shear bond strength of three visible light-cured composites (Transbond XT, Heliosit and Enlight) and two self-cured composites (Rely-a-bond and Concise). Materials & Method: 100 extracted premolars were collected and randomly divided into 5 test groups of different adhesives. Brackets were bonded to the teeth in each test group with the respective adhesive according to the manufacturer’s instructions. Each specimen was debonded using Universal Testing Machine and the shear bond strength for each specimen was calculated. All the groups were compared by ANOVA one-way test. Results: There were statistically significant differences among the five groups (P<0.05). The shear bond strength of Enlight (13.92 ± 3.92) is similar to Transbond XT (14.30 ± 4.35). Conclusion: Light cure composites showed higher bond strength than self cure composites.


INTRODUCTION
Transbond XT is a conventional light-cured BISGMAbased (Bis Phenol A Glycidyl dimethacrylate) composite resin popularly used as orthodontic adhesive agent with optimal bond strength. 4 It consists of BISGMA resin (monomer) matrix and TEGDMA (Triethylene glycal dimethacrylate) as diluents. It also contains filler particles like ground glass or silica and silane coupling agent to provide bond between inorganic and organic resin matrix. Camphoroquinone is used as a photo initiator for the polymerization of monomer.
The quest to overcome the shortcomings of conventional filled composites has led to the development of "flowable Composites". 5 Flowable composites achieved great attention due to their clinical handling characteristics like non-stickiness, fluid injectability, adequate working time and short cure time. They are especially useful during indirect bonding of attachments. Heliosit, a flowable composite although initially intended for bonding of brackets, its application as a bonding agent for bonding lingual retainers, and even as a luting cement for prosthesis has been tested. Heliosit as a bonding agent of brackets has been scarcely studied. Heliosit composition includes Bis-GMA (50-100%), UDMA (10-25%) and Deca Methyl endi methacrylate (10-25%). 4 Enlight composition includes Dimethacrylate monomer 20-30%, silicate filler 70-80%, other supplements 4%, among them camphoroquinone is the activator.
Self-curing resins, for a long time were the only option for dental restorative and orthodontic bonding procedures.

MATERIALS AND METHOD
A total of one hundred freshly extracted maxillary premolar teeth and 100 pre-adjusted edgewise upper premolar stainless steel brackets (Ormco Mini 2000 series) were used in the study.
The teeth used were anatomically and morphologically sound and non-carious. Ethical clearance was obtained from the Institution for the use of natural teeth in the study.
The freshly extracted teeth were cleaned to remove blood or any tissue debris and were stored in 0.1% thymol solution to prevent bacterial contamination and dehydration. The teeth were then mounted on self-cured, acrylic blocks of dimensions 25x10x10 mm such that the roots were completely embedded into the acrylic block up to cemento-enamel junction. The buccal surface of crown was perpendicular to the base of the block. The acrylic blocks were numbered from 1 to 100 to differentiate between different groups.
The teeth samples were divided into five following groups: console. This force was expressed in Newtons. To evaluate the shear bond strength in MPa from the force value, the following formula was used: Area of the bracket base (sq mm) The area of the bracket base was measured as 9.63mm 2 by using digital Vernier calipers.

RESULT
The result of the shear bond strength of the five adhesives: Group I-Transbond XT, Group II-Heliosit, Group III-Rely-abond, Group IV-Enlight and Group V-Concise with their interpretation are presented in Table 1 and Table 2, and graphically represented in Graph 1.
Descriptive statistics like mean and standard deviation were calculated for every group. Group differences were analyzed with one-way analysis of variance (ANOVA) ( Table 2).

DISCUSSION
Manufacturers are continuously introducing new adhesive systems to the dental profession that are claimed to be more reliable, stronger, adhere better to enamel and dentin, less liable to leak at the margins and easy to handle.
In the present study five different adhesive materials: Transbond XT, Heliosit, Rely-a-bond, Enlight and Concise were assessed. The Light cure composites used in the present study were Transbond XT, Heliosit and Enlight. Transbond XT is a commercially available (3M Unitek, California) light-cured Bis-GMA based composite resin and is a popularly used orthodontic adhesive agent. It has been extensively evaluated for its bond strength and found to have optimal bond strength. In the present study, when the shear bond strength of