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The effect of surface pre-treatment on bond strength of orthodontic brackets to aged composite restorations using a universal adhesive Introduction: Back in the days when Angle first introduced his orthodontic appliance system, the edgewise brackets were soldered to bands which were custom made for each tooth. 1 The entire process was extremely time consuming. The advent of direct bonding of the orthodontic bracket to the tooth surface has been declared the most significant advance in the second half of the 20th century.2 For the first time it was possible to position the orthodontic bracket with precision on the desired location on the tooth. Ever since the introduction of the acid etch method to dentistry by Bounocore 3, there has been an ongoing effort to enhance tooth surface preparation prior to the bonding of composite resins. Many studies have focused on the replacement of the conventional acid etching method with other surface treatment procedures including air abrasion 4, 5 and laser treatment 6, 7 while others have been focusing on improvement of the original method. The time necessary for the application of the 3 step bonding procedure has been a particular field of interest. Many generations of bonding agents were developed, each aiming for a reduction in clinical chair time and addressing the limitations of its predecessors. A fairly successful development was the self-etching primer (SEP), which eliminated the need for a separate etching and rinsing.8 The SEPs were assessed and quickly gained wide-spread acceptance in restorative dentistry.8 The substitution of the conventional etch and rinse bonding agents with SEPs in orthodontic bracket bonding to enamel surfaces has been the subject of several studies.9-11 The results in these studies are contradictory, and while some authors recommended the use of the SEPs, others reported an inferior performance regarding bond strength.10 Disregarding the label on the SEPs, a few studies investigated the bond strength obtained by these systems after enamel etching and demonstrated an improvement in performance.12, 13 The most recent universal or multi-mode bonding systems can be used in a range of clinical situations. 14, 15 This means that they can be applied with or without a separate etching step without alteration of their properties or performance.16 While bonding to enamel surfaces is continuously improved through the evolution of adhesives, a new challenge has presented itself; bonding to composite surfaces. Composite resins have replaced the conventional amalgam restorations especially in the buccal surface of anterior teeth. Therefore many patients undergoing orthodontic treatment will require bracket attachment to a composite restoration. Both the etch/rinse method and the SEPs have been demonstrated as being inferior in providing bond strength with composite resins 17, 18 Authors have investigated the effect of adding adjunctive treatment including sandblasting, HF etching, bur roughening and laser treatment in the shear bond strength of adhesives to composite surfaces. 17-19 Eliasson et. al demonstrated that the addition of a silane layer can significantly improve bonding to composite resin restorations.20 The recent universal bonding systems contain silane agents and can therefore provide better bond strengths compared to conventional adhesives, furthermore they have to potential to eliminate the need for an additional stage of silane application prior to bracket bonding. Furthermore the presence of MDP in the chemical composition of universal bonding agents may provide an additional enhancement in the chemical adhesion to stainless steel brackets. In the present study we aim to investigate the bond strength provided by a universal adhesive (Scotchbond™) to aged composite surfaces. We will compare the shear bond strength of this procedure with conventional means of bonding to composite resins. Moreover, we will assess the addition of laser (Er: YAG) treatment prior to bonding to demonstrate any potential improvements in the bond strength on orthodontic brackets. Materials and methods: Preparing the composite discs A total of 144 composite resin discs, 6mm in diameter with a thickness of 3mm will be made from a nano-hybrid resin composite (Filtek Z250, 3M ESPE, St Paul, Minnesota, USA). For the purpose of obtaining a flat smooth surface, a glass layer will be placed upon the composite before curing with an intensity of 950 mW/cm2 for 20 seconds. Initial thermocycling To simulate the effect of intraoral aging on resin composite restorations, we will be subjecting the discs to a thermocycling procedure. Following the preparation of the discs, they will be placed in distilled water at 37 °C for a day. Subsequently thermocycling will be carried out at 6000 cycles between 5 °C and 55 °C with a dwelling time of 30 seconds between each cycle. Treatment of the composite surfaces The 144 composite discs will be divided randomly to 6 groups (n=24) each receiving a different method of preparation. The treatment groups will be as follows: Group A: Treatment: Etching with 37% phosphoric acid, rinsing with water and drying with air. Application of a silane agent. Bonding agent: Transbond™ XT primer Group B: Treatment: Sandblasted with 50µm Al2O3 particles at a pressure of 3.5 to 4.5 bar using a micro-etcher for 7 seconds at a distance of 10mm. Application of a silane agent. Bonding agent: Transbond™ XT primer Group C: Treatment: Treated using an Er:YAG laser working at a wavelength of 2940 nm and a power of 75mJ-1.1W with an angle of 90 degrees. Application of a silane agent. Bonding agent: Transbond™ XT primer Group D: Treatment: No surface treatment. Bonding agent: Scotchbond™ Universal Adhesive Group E: Treatment: Etching with 37% phosphoric acid, rinsing with water and drying with air. Bonding agent: Scotchbond™ Universal Adhesive Group F: Treatment: Treated using an Er:YAG laser working at a wavelength of 2940 nm and a power of 75mJ-1.1W with an angle of 90 degrees. Application of a silane agent. Bonding agent: Scotchbond™ Universal Adhesive Bonding of the orthodontic brackets All 144 discs will be bonded using right upper incisor brackets (Mini Master Series; American Orthodontics, Sheboygan, Wisconsin, USA) with a bracket base area of 10.88 mm2. The light-cure adhesive system which will be used for bonding of the brackets will be Transbond™ XT (3M Unitek, Monrovia, California, USA). Before application of the adhesive a thin layer of the same bonding agent used during surface treatment will be added to the bracket base. Second thermocycling: To recreate the oral environment and fatigue the resin composite the bonded samples will be stored in 37° C distilled water for a day and then subjected to 3000 cycles between 5 °C and 55 °C with a dwelling time of 30 seconds between each cycle. Shear bond strength testing For the shear bond strength testing each sample will be placed in a universal testing machine in a manner that ensures parallel positioning of the bracket base with the loading rod. Shear load will be applied to the composite bracket interface at a speed of 0.5 mm/min until fracture. The results will be recorded in Newtons and subsequently converted to Megapascals. Half of the brackets in each group (n=12) will be debonded at 30 minutes post-bonding and before the second thermocycling to measure the initial bond strength which is significant clinically as it represents the initial insertion of the archwire. Adhesive remnant index and SEM evaluation Following the debonding of the brackets from the composite discs, they will be subjected to microscopic evaluation (×40) to be categorized according to the adhesive remnant index (ARI) system based on the amount of adhesive material remaining on the composite discs. One sample from each group will be selected randomly and sent for SEM evaluation (×1000). References: 1. Dewel BF. The clinical application of the edgewise appliance in orthodontic treatment. Am J Orthod 1956;42: 4-28. 2. Wahl N. Orthodontics in 3 millennia. Chapter 16: Late 20th-century fixed appliances. Am J Orthod Dentofacial Orthop 2008;134: 827-30. 3. Bounocore M. A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. J Dent Res 1955;34: 849-853. 4. Olsen ME, Bishara SE, Damon P, Jakobsen JR. Comparison of shear bond strength and surface structure between conventional acid etching and airabrasion of human enamel. Am J Orthod Dentofacial Orthop 1997; 112(5):502-6. 5. Roeder LB, Berry EA, You C, Powers JM. Bond strength of composite to air-abraded enamel and dentin. Oper Dent 1995;20(5): 186-90. 6. Basaran G, Ozer T, Berk N and Hamamci O. Etching Enamel for Orthodontics with an Erbium, Chromium:Yttrium-Scandium-GalliumGarnet Laser System. Ang Orthod 2007;77: 117-123. 7. Ozer T, Basaran G, Berk N. Laser etching of enamel for orthodontic bonding. Am J Orthod Dentofacial Orthop 2008;134: 193–197. 8. Lopes GC, Baratieri LN, de Andrada MA, Vieira LC. Dental adhesion: present state of the art and future perspectives. Quintessence Int. 2002;33: 213-24. 9. Elekdag-Turk S, Cakmak F, Isci D, Turk T. 12-month self-ligating bracket failure rate with a self-etching primer. The Angle Orthodontist 2008;78(6):1095-100. 10.Ireland AJ, Knight H, Sherriff M. An in vivo investigation into bond failure rates with a new self-etching primer system. Am J Orthod Dentofacial Orthop 2004;124: 323-6. 11. Manning N, Chadwick SM, Plunkett D, Macfarlane TV. A randomized clinical trial comparing 'one-step' and 'two-step' orthodontic bonding systems. Journal of Orthodontics 2006;33: 276-83. 12.Rotta M, Bresciani P, Moura SK, Grande RH, Hilgert LA, Baratieri LN, et al. Effects of phosphoric acid pretreatment and substitution of bonding resin on bonding effectiveness of self-etching systems to enamel. J Adhes Dent. 2007;9: 537-45. 13.Frankenberger R, Lohbauer U, Roggendorf MJ, Naumann M, Taschner M. Selective enamel etching reconsidered: better than etch-and-rinse and selfetch? J Adhes Dent. 2008;10(5):339-44. 14.Hanabusa M, Mine A, Kuboki T, Momoi Y, Van Ende A, Van Meerbeek B, et al. Bonding effectiveness of a new 'multi-mode' adhesive to enamel and dentine. J Dent. 2012;40(6):475-84. 15.Munoz MA, Sezinando A, Luque-Martinez I, Szesz AL, Reis A, Loguercio AD, et al. Influence of a hydrophobic resin coating on the bonding efficacy of three universal adhesives. J Dent. 2014;42(5):595-602. 16.Wagner A, Wendler M, Petschelt A, Belli R, Lohbauer U. Bonding performance of universal adhesives in different etching modes. J Dent. 2014;42(7):800-7. 17.Bayram M, Yesilyurt C, Kusgoz A, Ulker M, Nur M. Shear bond strength of orthodontic brackets to aged resin composite surfaces: effect of surface conditioning. Eur J Orthod 2010; 3: 174-179. 18.Jafarzadeh Kashi TS, Erfan M, Rakhshan V, Aghabaigi N, Tabatabaei FS. An in vitro assessment of the effects of three surface treatments on repair bond strength of aged composites. 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