COMPARISON OF SHEAR BOND STRENGTH OF NEW AND RECYCLED BRACKETS WITH DIFFERENT MESH DESIGNS

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1 COMPARISON OF SHEAR BOND STRENGTH OF NEW AND RECYCLED BRACKETS WITH DIFFERENT MESH DESIGNS Author: Dr.Pragati, M.D.S. 3 rd year student Department of Orthodontics, Co-Authors: Prof. Praveen Mehrotra, M.D.S. (Lko) Principle and Head, Department of Orthodontics, Prof. Sudhir Kapoor, M.D.S. (Lko) Professor, Department of Orthodontics, Dr. Harish Dattada, M.D.S Reader, Department of Orthodontics, Dr. Namrata Rastogi, M.D.S. Reader, Department of Orthodontics, Corresponding Author: Dr. Pragati, M.D.S. 3 rd year student Post Graduate Department of Orthodontics, Sardar Patel Institute Of Dental and Medical Sciences, Uthratia, Raebarielly Road, Lucknow (U.P.) PH: , navit32@rediffmail.com Abstract : This study was designed to compare shear bond strength of metallic orthodontic brackets, having bases with two different mesh designs i.e. double mesh and Microetched, when debonded at different intervals of 30 minutes and 24 hours before and after recycling. Materials and methods : Total 120 metal twin brackets (premolar) with Double and Micro-etched foil meshes were taken. Each group was further divided into three subgroups. Brackets were bonded and shear bond strength of half the sample under each subgroup was assessed after half an hour and after 24 hours of initial bonding. The specimens were tested on a universal testing machine. Brackets were then recycled by a portable sand blasting unit, re-bonded and subjected to the same testing process. Results and Observations : Bond strength values recorded at 24 hour interval were higher for both new and recycled brackets. This increase was however insignificant. Time had minimal effect on bond strength values. Bond strength of micro-etched brackets was higher than Double mesh brackets before and after recycling. Conclusion : Sandblasting should be considered as viable, time saving, and convenient method of recycling. Keywords : Bond strength, Double mesh base, Micro-etched mesh base, Sandblasting, Recycling. 52

2 INTRODUCTION: Over the past 50 years, the bonding of various adhesives to enamel and dentin has developed a niche in nearly all areas of dentistry, including orthodontics. Buonocore s acid-etch technique revolutionized the practice of orthodontics with the introduction of direct bonding of brackets to teeth thereby providing an esthetic alternative to orthodontic banding 1. To enhance the retention of the adhesive to the metal base of orthodontic brackets, various chemical and mechanical retentive designs have been suggested. Mechanical retention was enhanced by placing undercuts in the cast bracket bases or by welding different diameter mesh wires to the bracket base as well as incorporating different designs in the mesh itself. Other innovative approaches to improve retention included laser-structured bases, chemically etched bases, metal plasma-coated bracket bases, and fusing metallic or ceramic particles to the bases 2. The foil mesh type of base has been most widely used and provides tension & shear bond strengths which are adequate for clinical use. In spite of its obvious advantages, one of the most common problems associated with bonding is the accidental De-bonding of the brackets before the treatment is completed 3. Sometimes prior to the completion of orthodontic treatment, intentional debonding is required when brackets are incorrectly positioned, often necessitating repositioning 4. Thus bracket recycling has emerged concurrently with the direct bonding technique. One of the clinical implications of recycling brackets is the alteration which occurs in the bond strength 5. Previous research has been focused individually in evaluating the shear bond strength of orthodontic brackets with different base surface areas, base designs at different time periods. Literature is deficient of research reporting the comparison of the shear bond strength of double mesh and micro-etched bracket bases before and after recycling, at different time intervals. Also the effects of recycling on bond strength values with time, needs to be adequately investigated. The present study was undertaken with the following aims and objectives. (1) To determine the shear bond strength of metal brackets with Micro-etched and double foil meshes, 30minutes after bonding. (2) To evaluate and compare the same, 24 hours after bonding. (3) To assess the change in shear bond strength of the brackets after recycling. (4) To determine the best foil-mesh configuration for clinical usage before & after recycling. MATERIALS AND METHODS A total of 240 extracted maxillary and mandibular premolars were stored in 0.1% (wt/vol) thymol solution at room temperature 3,6. The teeth were embedded in chemically activated acrylic resin using PVC rings as moulds 3. Total 120 metal twin brackets (premolar) were taken. Half of the total sample (60 brackets) comprised of brackets with Double foil meshes and one half (60 brackets) with Micro-etched foil meshes. A) Group 1(60) - Double foil mesh bases This group comprised of 20 brackets each from three different manufacturers of brackets with double mesh bases. Group A 1: - Ultratrimm Brackets, Dentaurum, Germany Group A 2: - Minidiagonali Roth Brackets, Leone, Italy Group A 3: - Minidiamond Brackets, Ormco, Glendora, Calif B) Group 2(60) - Micro-etched bases This group comprised of 20 brackets each from three different manufacturers of brackets with micro-etched bases. Group B 1: - Gemini Twin metal Brackets, Unitek 3M Group B 2: -EliteOpti-Mim MiniTwin Brackets, Ortho- Organizer Group B 3: - Ovation metal Bracket series, GAC International, Bohemia. TOOTH SURFACE PREPARATION Prior to bonding an orthodontic attachment to the tooth surface, it was prepared with pumice and rubber prophylactic cups for 10 seconds using a slow speed handpiece, washed with abundant water spray and dried with air spray 3,7,8. BONDING PROCEDURE The enamel surface was then treated with an acid etchant 37% phosphoric acid gel (3M Etchant) to the buccal surface of each tooth for 15 seconds 3,9. The teeth were then rinsed with a continuous water spray for 30 seconds. After etching, the Transbond XT Primer was applied on the enamel and photopolymerized for ten seconds. A small layer of adhesive Transbond XT was applied to the bracket base and positioned on the pretreated crowns and was cured for 20 seconds with LED, applying the light from both interproximal sides of the brackets

3 SHEAR BOND STRENGTH TESTING Shear bond strength of half the sample under each subgroup was assessed after half an hour of initial bonding. The specimens were tested on a universal testing machine. An occlusogingival load was applied to the bracket, producing a shear force at the brackettooth interface. A blade was placed at the bracket baseenamel interface, at a crosshead speed of 0.5 mm/min until rupture of the bracket-tooth union 4, 11 (Fig.1). The other half of the sample was debonded after 24 hours. RECYCLING OF BRACKET BASES The entire samples of brackets were then recycled by a portable sand blasting unit (Fig: 2). The brackets were then re-bonded as before and subjected to the same testing process. Before rebonding, brackets were agitated in acetone for 20 seconds to ensure the removal of any debris 12. The bracket bases were examined and photographed at magnification of x18 and x100 using a scanning electron microscope at an operating voltage of 15 KV. The mesh base was evaluated before and after sandblasting (Fig: 3and4). The results were subjected to statistical analysis to determine the more effective foil mesh system with optional shear bond strength. Mean, standard deviation, Student t test and Analysis of variance (ANOVA) of each variable was calculated for both double mesh and micro-etched bracket bases. RESULTS A) Comparison of bracket types based on mesh design The result of our study shows that shear bond strength for micro-etched brackets was significantly higher (p=<0.001) than double mesh brackets when debonded after 30 minutes, [15.29±2.76Mpa>11.94±2.89Mpa] and after 24 hours of initial bonding [15.66±2.82Mpa>12.29±2.67Mpa](Table:I). However, Time as a factor appeared to have minimal effect on the bond strength for both the groups i.e. Double mesh and Micro-etched mesh bases, as bond strength values on debonding were insignificantly different at 30 minutes and 24 hours interval respectively. Ultratrimm brackets (Dentaurum) had maximum shear bond strength among brackets debonded after 30 minutes and 24 hours of initial bonding followed by Mini-diagonali brackets (Leone) and Mini-diamond brackets (Ormco). In micro-etched group Gemini metal brackets (Unitek 3M) had maximum shear bond strength followed by Elite Opti-mim brackets (Ortho- Organizers) and Ovation Roth brackets (GAC), when they were debonded after 30 minutes and 24 hours of initial bonding. Results of Shear Bond Strength of brackets in decreasing order are as follows:- Micro-etched brackets debonded after 24 hours > Double mesh brackets debonded after 24 hours > Micro-etched brackets debonded after 30minutes > Double mesh brackets debonded after 30 minutes. B) Comparative discussion of recycled bracket types based on mesh design. On doing comparative analysis of new brackets with recycled brackets at different time intervals, it was observed that new brackets had better shear bond strength than recycled brackets. There was no significant difference between new brackets and recycled brackets at 30 minutes of initial bonding and 24 hours of bonding for all six types of brackets. The results of our study shows that shear bond strength values for recycled micro-etched brackets were significantly higher (p=<0.001) than recycled double mesh brackets when debonded after 30 minutes [15.27±2.99Mpa>11.77±2.70Mpa] and after 24 hours of initial bonding [15.36±2.81Mpa>12.19±2.74Mpa] respectively(table II). Among the recycled brackets shear bond strength was observed to be maximum for Ultratrimm brackets followed by Mini-diagonali brackets and Mini-diamond bracket, at both time intervals of debonding. Similarly shear bond strength of recycled brackets was observed to be maximum for Gemini metal brackets (Unitek 3M) followed by Elite Opti-mim brackets (Ortho-Organizers) and Ovation Roth brackets (GAC) on debonding. Comparative analysis of new brackets with recycled brackets at different time intervals show that new brackets had better shear bond strength than recycled brackets, at both the time intervals i.e. 30 minutes and 24 hours of initial bonding, but the differences were insignificant. DISCUSSION Shear bond strength magnitude of brackets debonded after 30 min and 24 hour This study was conducted to compare the shear bond strength of double and micro-etched bracket bases before and after recycling. The results indicated that shear bond strength for micro-etched brackets was significantly higher than double mesh brackets when debonded after 30 minutes and after 24 hours of initial bonding. This increase in bond strength of micro-etched brackets is in agreement with the result of various other studies 11,12. According to these micro-etching of metal 54

4 bracket base increases the surface area of bracket base, which enhances bracket retention/adhesion. However, Time as a factor appeared to have minimal effect on the bond strength for both the groups i.e. Double mesh and Micro-etched mesh bases, as bond strength values on debonding were insignificantly different at 30 minutes and 24 hours interval respectively. These findings are in agreement with the views expressed by Chamda and Stein 13 (1996), who stated that bond strength of light cured composite resin Transbond XT continued to increase up to first 10 minutes and there were insignificant differences in bond strength at 1 hour and 24 hour intervals. In double mesh bracket group, Ultratrimm brackets (Dentaurum) had maximum shear bond strength followed by Minidiagonali brackets (Leone) and Mini-diamond brackets (Ormco), when debonded after 30 minutes and 24 hours of initial bonding. Adhesion of bracket is due to interlocking of resin with mesh. Mesh design and mesh spacing (number of opening per unit of area base) affect penetration of resin, the escape of air and interlocking, which in turn affects bonding strength 14. Although in this group all brackets have same type of mesh design i.e. double mesh, it is the mesh spacing which has attributed to the differences observed in bond strength of different bracket systems. Large mesh spacing was found in Dentaurum (5.1 x 10-2 mm 2 ) followed by Leone (3.1 x 10-2 mm 2 ), and finally Ormco (2.9 x 10-2 mm 2 ). In micro-etched group Gemini metal brackets (Unitek 3M) had maximum shear bond strength followed by Elite Opti-mim brackets (Ortho-Organizers) and Ovation Roth brackets (GAC), when they were debonded after 30 minutes and 24 hours of initial bonding. Student t test showed significant difference in bond strength between Gemini and Elite opti-mim mini twin (p<0.01). Elite opti-mim mini twin bracket is Ni-free bracket with micro-etched base that are contiguous with the bracket body (1 piece injection molded brackets) which result in a base with very shallow grooves 12. This decreases the interlocking and penetration of resin into the mesh base. On the other hand Gemini bracket had wider mesh, which allows more efficient and complete penetration of resin, than Elite opti-mim mini twin bracket, resulting in significant increase in shear bond strength. Similarly there is highly significant increase in shear bond strength of Gemini brackets over Ovation Roth brackets (p<0.001), which could be again due to the improper penetration of resin in the grooves and undercuts of Ovation Roth brackets. Ovation Roth brackets had 80 gauge layered on a 150 gauge microetched foil mesh which may have caused congestion of the mesh design of bracket base resulting in decreased mesh spacing. Shear bond strength magnitude of recycled brackets debonded after 30 min and 24 hour Recycling of micro-etched brackets and double mesh brackets had insignificant effect on shear bond strength after debonding at 30 minutes and 24 hours time interval respectively. It shows that time had a minimal effect on shear bond strength of recycled brackets. The bond strength of light cure resin seems to reach a peak soon after curing, and then remain at the same level without any appreciable increase in magnitude with time 13. Recycling had no effect on the polymerization of light cure resin and polymerization time was same for new and recycled brackets. Hence no difference in shear bond strength for both brackets was seen at both time intervals after recycling. An overview of both the bracket groups show that recycled Gemini brackets had maximum shear bond strength among micro-etched brackets and recycled Ultratrimm brackets had maximum bond strength among double mesh brackets when debonded after 30minutes and 24 hours of initial bonding. In our results, the mean bond strength of brackets of both groups was adequate, at 30 minutes (Double mesh brackets:-9.5mpa & Micro-etched mesh brackets:-13.4mpa) and 24 hours (Double mesh brackets:-10.1mpa & Micro-etched mesh brackets:-13.9mpa) after bonding as suggested by Reynold 15 ( Mpa) which is sufficient for clinical orthodontic needs. Further, it has been observed that high-speed stream of aluminum oxide particles propelled by compressed air increases the surface area of bracket base and enhance adhesion, leading to an increase in bond strength post recycling, the bond strength being essentially remaining the same as for non-recycled brackets. This conviction was further supported by Maccoll et al 16. (1996) who found an increase in bond strength and the survival time of recycled brackets over non-recycled brackets. CONCLUSION The following conclusions were drawn from the present study: 1) 3M Gemini (micro-etched) bracket system recorded highest shear bond strength values as compared to all other bracket system evaluated at 30 minutes and 24 hour interval both before and after recycling. 2) The order for mean shear bond strengths after 30 minutes and 24 hours of initial bonding before and after recycling for both systems were:- 55

5 a) Double mesh bases: Ultratrimm> Minidiagonali> Minidiamond b) Micro-etched mesh bases: Gemini>Elite opti-mim> Ovation Roth 3) Result suggests that bond strength acquired at 30 minutes post bonding of both new and recycled brackets is adequate enough to resist the stresses induced on the brackets during its clinical use. Though the bond strength values recorded at 24 hour interval were higher for both new and recycled brackets. This increase was insignificant. Hence time appeared to have minimal effect on bond strength values. 4) Sandblasting of metal brackets to remove composite residue, had insignificant effect on the shear bond strength. Hence sandblasting should be considered as viable, time saving, and convenient method of recycling. REFERENCES: 1. Newman G.V, Snyder W.H, Wilson C.E- Epoxy adhesives for orthodontics attachments: progress report, Am J Orthod 1968; 51: Bishara SE, Soliman MA, Oonsombat C, Laffoon JF, Ajlouni R- The effect of variation in mesh-base design on the shear bond strength of orthodontic brackets, Angle Orthod. 2003; 74:3: Tavares SW et.al -Shear bond strength of new and recycled brackets to enamel, Braz Dent J. 2006; 17: Cacciafesta V, Sfondrini M.F, Melsen B, Scribante A- A 12 month clinical study of bond failures of recycled versus new stainless steel orthodontic brackets, European Journal of orthodontics 2004; 26: Tavares S.W et.al- Evaluation in vitro of the shear bond strength of aluminum oxide recycled brackets, Braz J Oral Sci, 2003; 7: Montasser M.A, Drummond J.L, and Evans C.A- Rebonding of Orthodontic Brackets, Angle Orthodontist: 2008; 78: Northrup R.G, Berzins D.W, Bradley T.G, Schuckit W- Shear Bond Strength Comparison between Two Orthodontic Adhesives and Self-Ligating and Conventional brackets, Angle orthodontist 2007; 4: Regan D, van Noort R- Bond strength of two integral bracket base combinations: an in vitro comparison with foil-mesh, Eur J Orthod. 1989; 11: Nordenval K.J, Brannstrom M, Malmgren O- Etching of Deciduous Teeth and Young and old Permanent Teeth. A Comparison between 15 and 60 seconds of etching, American Journal of Orthodontics 1980; 78: Cozza P, Martucci L, Toffol L.D, Penco S.I- Shear bond strength of metal brackets on enamel, Angle Orthodontist 2005; 76: Maccoll GA, Rossouw PE, Titley KC, Yamin C- The relationship between bond strength and base surface area using conventional and micro-etched foil-mesh bases,am J Orthod Dentofacial Orthop 1996; 109: Sharma-Sayal SK, Rossouw PE, Kulkarni GV, Titley KC- The influence of orthodontic bracket base design on shear bond strength, Am J Orthod Dentofacial Orthop. 2003;124: Chamda RA, Stein E- Time-related bond strengths of light cured and chemically Cured bonding systems: An in vitro study, Am J Orthod Dentofacial Orthop 1996; 110: Wang W.N, Hsing C, Chou T.H, Wang D.D.H (1992)-Bond strength of various bracket base designs, American Journal of Orthodontics and Dentofacial Orthopedics, 2004; 125: Reynolds IR-A review of direct orthodontic bonding, Br J Orthod 1975; 2: Maccoll GA, Rossouw PE, Titley KC, Yamin C: The relationship between bond strength and base surface area using conventional and micro-etched foil-mesh bases. Am J Orthod Dentofacial Orthop 1996; 109: LEGENDS FOR FIGURES: Fig: 1: Universal testing machine with customized mounting jig Fig. 2: Sandblasting unit (Pencil Blaster) Fig: 3: a. Double foil mesh bracket base before recycling Fig: 3: b. Double foil mesh bracket base after recycling Fig: 4: a. Micro-etched bracket base before recycling Fig: 4: b. Micro-etched bracket base after recycling LEGENDS FOR TABLES: Table: I: New bracket debonded after 30 minute and 24 hours Table: II: Recycled bracket debonded after 30 minute and 24 hours 56

6 Fig. 3b Fig. 1 Fig. 4a Fig. 2 Fig. 4b Fig. 3a 57

7 Table 1: New brackets debonded after 30 min and 24 hour Double mesh base brackets Micro-etched base brackets Debonded after 30 min Debonded after 24 hour Debonded after 30 min Debonded after 24 hour Ultratrimm Mini- Mini- Ultratrimm Mini- Mini- Gemini Elite opti-min Ovation roth Gemini Elite opti-min Ovation roth brackets diagonali diamond brackets diagonali diamond brackets brackets brackets brackets brackets brackets brackets brackets brackets brackets N N 75.2 N 153.6N 127.6N 101.6N N N N 185.2N N 262.2N N N 78.4 N 120.9N 117.0N 110.4N N 148 N N N 138.6N 219.4N N N 64.8 N 117.1N 116N 75.2N N N N 154.8N 132.5N 146.2N N N 84.8 N 118N 134.6N 64.8N N N N 152.8N 164.8N 142.1N N 102 N 63.2 N 91.2N 110N 78.4N N N N 129.3N 170.1N 181N N 74.8 N 99.2 N 146.8N 103.8N 61.6N N N N 160.7N 161.7N 190.4N N N N 126.7N 78.3N 114.4N N N N 161.7N 129.1N 175.2N N N 60.8 N 166N 141.6N 77.6N N N N 201.8N N 227.7N N 95.9 N 54.4 N 138.2N 87.1N 52.8N N N N 220.5N 176.4N 187.6N N N 83.2 N 145.9N 138.1N 72.8N N N N 208.7N 153.3N 178N Mean N N 77.8 N 132.4N 115.4N 80.9N N N N 174.8N 158.5N 190.9N 13.4 Mpa 12.7 Mpa 9.73 Mpa 13.8Mpa 13.12Mpa 10.1Mpa 17.5 Mpa 14.8 Mpa 13.5 Mpa 17.8Mpa 15.1Mpa 13.9Mpa Table 2: Recycled brackets debonded after 30 min and 24 hour Double mesh base brackets Micro-etched base brackets Debonded after 30 min Debonded after 24 hour Debonded after 30 min Debonded after 24 hour Ultratrimm Mini- Mini- Ultratrimm Mini- Mini- Gemini Elite opti-min Ovation roth Gemini Elite opti-min Ovation roth brackets diagonali diamond brackets diagonali diamond brackets brackets brackets brackets brackets brackets brackets brackets brackets brackets N 103.8N 64N N 101.2N 69.6N 122.5N 152.2N 144.9N 184.2N 151.2N 242.8N N 93.2N 68N 108.4N 106.4N 84.6N N 117.6N 231.8N 118.5N 138.6N 198.7N N 146N 72.8N 138.2N 133.7N 110N 133.2N 164.8N 131.1N 161.7N 160.6N 189N N 129.3N 65.6N 120N 111.7N 76N 174.4N 135.4N 176.6N 170.5N 164.8N 158.7N 5 120N 135.5N 78.4N 158.4N 142.5N 84.8N 161.7N 149.1N 209.7N 148.9N 129.1N 146.2N N 97.68N 66.4N 145.9N 93.2N 63.2N 183.2N 165.9N 173.8N 185.2N 161.7N 172.5N 7 71N 95.9N 60.8N 145.9N 138.1N 83.2N 204.8N 131.2N 240.1N 193N 124.9N 190.4N N 102N 78.4N 159.3N 89.76N 49.6N N 196.3N 168.3N 161.7N 205.8N 215.2N N 89.76N 94.4N 100.8N 104.7N 109.6N 208.7N 169N 180.7N 208.7N 176.4N 184.9N N 115.2N 111.2N 126.7N 115.2N 60.8N 184.2N 161.7N 200.1N 192N 153.3N 178N Mean 126.9N 110.8N 76N 131.7N 113.6N 79.1N 169.7N 154.3N 185.7N 172.4N 156.6N 187.6N 13.23Mpa 12.6Mpa 9.5Mpa 13.7Mpa 12.9Mpa 9.9Mpa 17.32Mpa 14.7Mpa 13.46Mpa 17.6Mpa 14.9Mpa 13.6Mpa 58

Immediate versus Delayed Force Application after Orthodontic Bonding; An In Vitro Study

Journal of Dentistry, Tehran University of Medical Sciences Original Article Immediate versus Delayed Force Application after Orthodontic Bonding; An In Vitro Study M. Basafa 1, F. Farzanegan 2 1 Professor,