Comparison of Shear Bond Strength of Two Commercially Available Bondable Molar Tubes

Introduction: Direct and indirect bonding has revolutionized clinical orthodontics by reducing chair-side time and enhancing patient comfort. Clinicians often hesitate to bond molars due to ambiguity on shear bond strength. This study was conducted to compare shear bond strengths of two commercially available bondable molar tubes. And asses mesh if the mesh design had a role to play in differences in shear bond strength. Materials & Method: 30 extracted maxillary molars were divided into Group I and II (n=15).Group I bonded with Victory series MBT (3M Unitek). And Group II bonded with Ortho classic proprietary PadLok (Navy orthodontics). Teeth were mounted on a jig and Shear Bond Strength was evaluated on an Instron universal testing machine at a cross head speed of 1mm/minute. They were also subjected to scanning microscopic examination to check the base pattern. Result: Shear bond strength of navy orthodontic tubes were (18.0675+/4.0187 MPa) was significantly higher than 3M victory series (8.93 +/2.493MPa). Unpaired T-test shows a higher significant difference in SBS between two groups at 1% of significance. SME showed that navy orthodontic tube base was pad-lock mesh design, while 3M was a single mesh base design. Conclusion: 3M victory series molar tube exhibited a near ideal while other sample showed far higher shear bond strength than recommended. Higher values may result in enamel fracture.


INTRODUCTION
Direct and indirect bonding of orthodontic attachments has revolutionized clinical orthodontics by reducing chair-side time and enhancing patient comfort. But at the same time band failure of attachments tends to retard treatment leading to more time, material and patient inconvenience. Therefore clinician often hesitates to bond molars. But rather use the orthodox method of banding molars.
Manufacturers have decreased the size of the tube without sacrificing bond strength. [1][2][3] Possible due to Refinement of base design and Improved Adhesive systems. [4][5] Placing undercuts in cast bracket bases or by welding different diameter mesh wires to the bracket base as well as incorporating different designs in the mesh itself mechanical retention has been enhanced. Other innovative approaches to improve retention included using laser-structured bases, 1 using metal plasma-Refinement of base design is possible by undercuts in bases, Different design mesh Sandblasting, Laserstructured bases, Chemical treatment, Fusing metallic or ceramic particles.
It has been reported that mesh based brackets with larger mesh spaces (apertures) provide a greater shear bond strength than do bases with smaller mesh apertures. 4 The number of openings per unit of area of the bracket base is determined by the wire diameter and the mesh spacing. For resin to penetrate the base effectively air needs to be able to escape and this is determined by the free volume between the mesh and the bracket base. 3,5 It has been reported that mesh based brackets with larger mesh spaces (apertures) provide a greater shear bond strength than do bases with smaller mesh apertures. 4 The number of openings per unit of area of the bracket base is determined by the wire diameter and the mesh spacing. For resin to penetrate the base effectively air needs to be able to escape and this is determined by the free volume between the mesh and the bracket base. 3,5 As far as the mesh design is concerned, Matasa 4 claimed that the mesh number and the wire diameter of the mesh are the most important influencing factors. The two areas in which improvements have taken place are in the design of the mesh as well as the use of bond enhancing metal surface treatments applied to the mesh. 4,5 The various types of treatment applied to bracket bases have entailed micro-etching, sandblasting, polymer coating or a spray with fine particles of molten metal1.The current trend is for a less dense mesh to be used so as to ensure a larger aperture or open area in the base. 9 Areas of Improvement in adhesive system are seen in Adhesive materials, Primers and Bond enhancers.
The aim of this study was to compare the shear bond strengths of two commercially available bondable molar tubes. And asses the mesh if the mesh design had a role to play in differences in the Shear Bond Strength (SBS) values. Also to assess the Adhesive Remnant Index(ARI).

MATERIALS AND METHOD
The study was conducted in the Department of Orthodontics and Dentofacial Orthopedics of Kathmandu Medical College, Duwakot, Bhaktapur. The ethical clearance of the study was obtained from the ethical committee of the institute on 20th April, 2018 before starting the study Institutional Review Committee KMCTH (Ref no:1004201816). The study was conducted from May 2018 to November 2018.
Simple random sample consisted of 30 extracted human molar teeth with intact buccal surface without caries and fluorosis were included in the study.
• Molar tubes will be bonded using Transbond XT, primer and adhesive.
The teeth were debrided and cleansed under running water and stored in distilled water. The teeth were randomly divided into Group I and II (n=15) (Figure 1).
Molar tubes from Victory Series MBT (3M Unitek) were bonded in Group I using Transbond XT, primer and adhesive as per the manufacturer's instructions after acid etching with 37% phosphoric acid for 15 seconds.
Group 2 had molar tubes from X company bonded using Transbond XT, primer and adhesive as per the manufacturer's instructions after acid etching as per protocol.
The test samples were stored in distilled water in separate containers for 24 hrs prior to testing.