The Impact of Er,Cr:YSGG Laser Recycling on Shear Bond Strength (SBS) of Stainless Steel Orthodontic Brackets

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1 European International Journal of Science and Technology Vol. 3 No. 7 September, 2014 The Impact of Er,Cr:YSGG Laser Recycling on Shear Bond Strength (SBS) of Stainless Steel Orthodontic Brackets Faisal Ismail Bahnasi 1 ; Aida Nur Ashikin Abd Rahman 2* ; Mohamed Ibrahim Abu Hassan 3 1 PhD Candidate, Centre of Studies of Paediatric Dentistry and Orthodontic, Faculty of Dentistry, Universiti Teknologi MARA, Shah Alam, Selangor, Malaysia. 2 Senior Lecturer, Centre of Studies of Paediatric Dentistry and Orthodontic, Faculty of Dentistry, Universiti Teknologi MARA, Shah Alam, Selangor, Malaysia. 3 Dean, Professor, Centre of Studies in Restorative Dentistry, Faculty of Dentistry, Universiti Teknologi MARA, Shah Alam, Selangor, Malaysia. Corresponding Author: *Dr. Aida Nur Ashikin Abd Rahman Address: Faculty of Dentistry, Universiti Teknologi MARA, Shah Alam, Selangor, Malaysia. aida_nurashikin@salam.uitm.edu.my Sponsoring information: This study was supported by UITM Research Intensive Faculty UiTM Grant 600-RMI/DANA 5/3/RIF (572/2012). Abstract Objectives: to assess Er,Cr:YSGG laser method of recycling brackets, to evaluate SBS of new, recycled and repeated-recycled brackets with/without bracket base primer. Methods: 120-extracted teeth/brackets were randomly divided into six-groups. Er,Cr:YSGG laser was used in four-groups while the last two-groups were control. Repeated recycling was done in two-groups and primer was applied on brackets bases for two-groups. Brackets were subjected to shear force until debond and SBS was measured. Results: There was no significant difference between mean SBS of the new and recycled brackets using laser. Brackets with primer showed slightly higher SBS compared to those without bonding agent. While repeated recycled brackets showed slightly lower SBS compared to new and recycled brackets. Conclusion: Recycling brackets using laser can be used as an alternative to new brackets. It is recommended to apply bonding agent on the bracket-base to provide greater bond strength in case of higher bond strength is needed. Keywords: Er,Cr:YSGG laser; Recycling; SBS; Stainless Steel Orthodontic Brackets 1

2 European International Journal of Science and Technology ISSN: Introduction Development of modern adhesive materials has led to the widespread use of bonded attachment in fixed appliances. Composite resin is the most popular orthodontic adhesive because of good bond strength (Sunna & Rock, 1999). These adhesives are used currently in orthodontic treatment to bond brackets to teeth surfaces. There are different types of orthodontic brackets present in the market. Orthodontic brackets could be manufactured from stainless steel or aesthetic material as: ceramic or plastic. Metal brackets are cheaper than ceramic and easy to be recycled to reuse it again in case of bond failure or repositioning of brackets. Orthodontic bracket bond failure is common during orthodontic treatment. It could be due to salivary contamination during bonding procedure, heavy occlusal force especially in case of deep bite or traumatic occlusion, defect in bonding technique or inadequate polymerization of adhesive material. In addition to iatrogenic bond failure; brackets repositioning could be done by the clinician when they want to reposition brackets as in rotated tooth when bracket bonded more mesial or distal, or during finishing stage for proper detailing. To decrease the cost of orthodontic treatment; any debonded bracket can be recycled by different methods to provide a second alternative to new brackets (Wendl, Muchitsch, Pichelmayer, Droschl, & Kern, 2011). Cost effectiveness will be especially when use good quality expensive orthodontic brackets. The previous adhesive material can be removed from bracket mesh by different methods such as: sandblasting, grinding, thermal and chemical; or using laser as a new method of recycling. If SBS of recycled orthodontic bracket is not enough to withstand the occlusal force, bond failure will take place. Multiple orthodontic visits for rebonding of recycled brackets are time and material consuming; this may cost more than replacing the failed bracket with a new one. The main advantage of reused orthodontic brackets is cost saving. However there are a number of disadvantages such as: possibility of bracket distortion due to high occlusal force or during debonding process in case of brackets repositioning (Matasa, 1989); method of recycling process is time consuming; and lower SBS of recycled brackets in certain methods as direct flame (Quick, Harris, & Joseph, 2005). Various techniques have been employed for recycling metal orthodontic brackets. Different methods of reconditioning and removing adhesive remnants from stainless steel brackets bases orthodontic brackets were done. Green stone or dental bur grinding is a simple method of recycling, however, others evaluated that it may provide insufficient SBS rates (Basudan & Al-Emran, 2001; Quick et al., 2005). Direct flame was recommended as a simple and effective method of recycling brackets (Basudan & Al-Emran, 2001). However, Quick et al evaluated that direct flame had a low SBS (Quick et al., 2005). Aluminum oxide sandblasting is the most popular method. Different studies indicated that the sandblasting method of recycling achieved enough SBS when compared to new brackets (Basudan & Al-Emran, 2001; Faltermeier & Behr, 2009; Khosravanifard, Nemati-Anaraki, Nili, & Rakhshan, 2011; Lunardi et al., 2008; Sonis, 1996; Tavares et al., 2006). Laser has dental and medical applications. It can be used as a new method of recycling orthodontic brackets. Ishida et al used Er,Cr:YSGG laser and he concluded that it was an efficient method in removing adhesive from bracket bases, so the brackets can be used again, with good SBS (Ishida, Endo, Shinkai, & Katoh, 2011). Ahrari et al used Er,Cr:YSGG Laser in reconditioning metal orthodontic brackets, and he evaluated that Er,Cr:YSGG laser was efficient in removing adhesive from bracket bases, and resulted in significantly higher bond strength than for new brackets (Ahrari, Basafa, Fekrazad, Mokarram, & Akbari, 2012). It was evaluated that the SBS of ceramic orthodontic brackets after reconditioning with an Er, Cr: YSGG laser was efficient in removing adhesive from bases of debonded 2

3 European International Journal of Science and Technology Vol. 3 No. 7 September, 2014 ceramic brackets as it produced comparable bond strengths to new brackets (Ahrari, Fekrazad, Kalhori, & Ramtin, 2013). Reusing loose brackets after reconditioning is common; however, in case of second bracket bond failure to the same bracket, the clinician may prefer to use a new one instead of reusing the old one for a second time because they scared of distortion of bracket s base after repeating the procedure of reconditioning. This study was focused on the SBS of new, recycled and repeated recycled stainless steel orthodontic brackets to enamel surfaces using Er,Cr:YSGG laser; and the effect of bonding agent application to bracket base on the SBS of new, recycled and repeated recycle stainless steel orthodontic brackets. 2. Material and methods A total number of 120 extracted human premolar teeth were collected and all blood and adherent tissues were removed from the teeth. Teeth selected should be sound and free from any visible defects or restorations. 120 new stainless steel upper premolar orthodontic brackets (Unitek Gemini Bracket, Micro- Etch Base, 3M Unitek orthodontic products, USA) were used. The total number of 120 orthodontic brackets and 120 extracted human premolar teeth were randomly divided into six Groups (I-VI). The description of the groups was in Table 1. Bonding agent (Light Cure Orthodontic Adhesive Primer, 3M Unitek, USA) was applied to paper pad. Composite resin (3M Unitek Transbond XT Light Cure Composite, USA) was applied on 80 brackets. Brackets were positioned on the paper with gentle pressure and excess adhesive was removed with explorer. Polymerization was carried out using Light-emitting diode (LED) (SDI radii- cal) for 20s (10s for each side mesial and distal). The bonded brackets were separated from the paper pad using tweezers with light pressure. All 80 brackets were stored for distilled water for 24h at 37 C, and then they were subjected to the thermocycling using Automatic Thermocycling Dipping Machine (ATDM T6PD, Zecttron Sdn. Bhd.) for 500 cycles in distilled water between 5 C and 55 C. The exposure to each bath will be 20s and the transfer time between baths will be 5s (ISO/TS 11405:2003 E/ ). 2.1 Laser method of recycling The 80 brackets were recycled using Waterlase MD TM laser method (Waterlase, Biolase Technology, Irvine, CA, USA) to remove composite adhesive from the brackets bases. Waterlase laser uses a combination of Er,Cr3+:YSGG laser energy and water. It has a wavelength of 2780 nm. Removing of composite adhesive was done from a distance of 1mm away from the tip using 40 % water and 55 % air spray. The repetition rate was 30 Hz, and the power was 4 W. the duration of cleaning was for 20-30s depend on the amount of adhesive remaining. The procedure was followed until bonding resin was totally removed from the bracket base and was no longer visible to the naked eye. 2.2 Scanning electron microscopy (SEM) evaluation The orthodontic brackets bases were examined using scanning electron microscope (SEM) (Carl Zeiss SMT model: SUPRA 40 VP) at magnification 100X and 300X to compare the distortion after recycling procedure with the new brackets base. 2.3 Repeated recycled procedure The 40 brackets were recycled twice with the above method using the same ways of bonding and debonding, to evaluate the effect of repeated recycled brackets on SBS of orthodontic brackets. 3

4 European International Journal of Science and Technology ISSN: Bracket mesh bonding agent To evaluate the effect of adding bonding agent on on SBS of orthodontic brackets, light cure orthodontic adhesive primer was applied to the half of the all orthodontic brackets bases. 2.5 Teeth sample preparation The teeth were embedded horizontally in die stone in a plastic ring. The teeth were etched with 35% phosphoric acid gel for 15s (Unitek Etching Gel Syringe Delivery System 35% phosphoric acid by weight, 3M Unitek orthodontic products, USA), were thoroughly rinsed with water for 15s and the surfaces were thoroughly dried with a light/brief of air (oil and water free). Adhesive Primer was applied to the buccal surface of each tooth, thinned with gentle stream of air. Composite resin was applied to all bracket bases. The brackets were then firmly pressed to teeth surfaces with a plastic instrument and the excess adhesive was removed with an explorer before curing. Polymerization was carried out using LED light, and both mesial and distal sides were cured for 10s each. The light intensity of LED is 1800 Mw/cm². The power of device was calibrated before every cure using a dose meter device (SDI radiometer). 2.6 SBS determination After photo polymerization, the sample were subjected to a shear force within 30 minutes to simulate the clinical situation with a universal testing machine (Shimadzu Trapezium X, Shimadzu Corporation, Kyoto-Japan) until the bracket debonds with a crosshead speed of 1mm/min. The force in Newton (N) was recorded, and the stress was calculated by dividing the force in Newton/surface area and calculated in MPa. The surface area of the premolar bracket was measured mm². The teeth were examined by SEM at magnification 30X using SEM (HITACHI TM3000). Any remaining adhesive were assessed with the Adhesive Remnant Index (ARI) scores according to Artun and Bergland (Årtun & Bergland, 1984), with criteria illustrated in Table 2. σ = F/A = N/mm² Where: σ = Stress F= Force in Newton A= Surface area in mm² 2.7 Data analysis for Groups I-VI The mean SBS, standard deviation, and range were calculated for each of the six groups, and the data was subjected to statistical analysis to identify significant differences in means SBS between sub-groups. The statistical analyses were performed using the SPSS program (SPSS, Chicago, Illinois, USA). ANOVA was used; the level of significance was established at P < Results It can be observed that Group 4 had the highest mean (12.1) with SD 3.59 which means that the Laser method with bonding agent applied greater SBS (Figure 1). One of the assumptions of the one-way ANOVA is that the variances between the groups are similar. The Test of Homogeneity of Variances showed the result of Levene's Test of Homogeneity of Variance. It can be observed that the Levene's F Statistic had a significance value of (p <.05) which indicated that the assumption of homogeneity of variance had not been met. The Robust Tests of Equality of Means was done to test the homogeneity of variance. 4

5 European International Journal of Science and Technology Vol. 3 No. 7 September, 2014 Since the p-value as highlighted in grey is less than.05, there were significant differences between the 6 groups. To be able to determine which specific groups differed, the multiple comparisons table was done which showed only significance difference between groups 4 and 5 ( p = 0.049). 3.1 Adding bonding agent: o The mean SBS for Group 2, 4 and 6 were higher but not significantly different from Group 1, 3 and 5 respectively. 3.2 Repeated recycling: o The mean SBS for Group 3 and 4 were higher but not significantly different from Group 5 and 6 respectively. 3.3 SEM and ARI evaluation Figure 2 showed the evaluation of the orthodontic brackets bases (new, laser, and repeated laser recycling method) under the scanning electron microscope at magnification 100X and 300X. To calculate the percentage of the area occupied with composite remnant on the tooth surface after debonding; the area of composite covering the bracket base was subtracted from 100%. Table 3 showed the ARI off all groups. 4. Discussion The mean SBS of all sub-groups were more than that recommended by Reynolds in 1975; (for brackets bonded to teeth to overcome intraoral and orthodontic forces, SBS in the range of 5.9 to 7.8 MPa was required) (Reynolds, 1975). No significant difference was noted in the mean SBS between the new and Er,Cr3+:YSGG laser recycled brackets; although the recycled one showed slightly higher bond strenght. This result was in agreement with (Ishida et al., 2011). However the findings of this study were not in agreement with that of (Ahrari et al., 2012); as he evaluated that Er,Cr:YSGG laser was resulted in significantly higher bond strength than for new brackets. 4.1 Adding bonding agent: The means SBS for Groups 2, 4 and 6 (with bonding agent) were slightly higher but not significantly different from Groups 1, 3 and 5 (without bonding agent) respectively. Even though the brackets recycled twice using Er,Cr:YSGG laser, but showed greater SBS than that for the new brackets (groups 1 and 2) after adding bonding agent to their bases. Adding bonding agent to the brackets bases gave greater bond strength between brackets and enamel teeth surfaces than without bonding agent. 4.2 Repeated recycling: The means SBS for Groups 3 and 4 (Laser method of recycling) were slightly higher but not significantly different from Groups 5 and 6 (Repeated Laser method of recycling) respectively. There was no significant difference between repeated Laser and the new brackets. Previous study showed significant difference between new brackets and brackets recycled using 50 mm aluminum oxide powder sandblasting (Bahnasi, Rahman, & Abu-Hassan, 2012). 5. Conclusion It can be concluded that: The mean SBS of all groups were more than that recommended by Reynolds (1975). Bracket recycling using Er,Cr3+:YSGG laser did not affect the SBS of stainless steel brackets and can be used as an alternative to new brackets. This could certainly cut cost. 5

6 European International Journal of Science and Technology ISSN: Repeated recycled brackets using Er,Cr3+:YSGG laser was not significantly different with the new brackets and can also be used instead of using a new one. Brackets with bonding agents applied to its bases showed higher but no significantly different from the brackets without bonding agent. It is recommend applying bonding agent on the bracket-base to provide greater bond strength in case of higher bond strength is needed. 6. Acknowledgement This study was supported by UITM Research Intensive Faculty UiTM Grant 600-RMI/DANA 5/3/RIF (572/2012). 7. References Ahrari, F., Basafa, M., Fekrazad, R., Mokarram, M., & Akbari, M. (2012). The efficacy of Er, Cr: YSGG laser in reconditioning of metallic orthodontic brackets. Photomedicine and Laser Surgery, 30(1), Ahrari, F., Fekrazad, R., Kalhori, K. A., & Ramtin, M. (2013). Reconditioning of ceramic orthodontic brackets with an Er, Cr: YSGG laser. Lasers in Medical Science, 28(1), Årtun, J., & Bergland, S. (1984). Clinical trials with crystal growth conditioning as an alternative to acidetch enamel pretreatment. American Journal of Orthodontics, 85(4), Bahnasi, F. I., Rahman, A. N. A. A., & Abu-Hassan, M. I. (2012). The impact of recycling and repeated recycling on shear bond strength of stainless steel orthodontic brackets. Orthodontic Waves. Basudan, A. M., & Al-Emran, S. E. (2001). The effects of in-office reconditioning on the morphology of slots and bases of stainless steel brackets and on the shear/peel bond strength. Journal of Orthodontics, 28(3), Faltermeier, A., & Behr, M. (2009). Effect of bracket base conditioning. American journal of orthodontics and dentofacial orthopedics, 135(1), 12. e e15. Ishida, K., Endo, T., Shinkai, K., & Katoh, Y. (2011). Shear bond strength of rebonded brackets after removal of adhesives with Er, Cr: YSGG laser. Odontology, 1-6. Khosravanifard, B., Nemati-Anaraki, S., Nili, S., & Rakhshan, V. (2011). Assessing the effects of three resin removal methods and bracket sandblasting on shear bond strength of metallic orthodontic brackets and enamel surface. Orthodontic Waves, 70(1), Lunardi, N., Gameiro, G. H., Magnani, M. B. B. A., Nouer, D. F., de Siqueira, V. C. V., Consani, S., & Pereira-Neto, J. S. (2008). The effect of repeated bracket recycling on the shear bond strength of different orthodontic adhesives. Brazilian Journal of Oral Sciences, 7(27), Matasa, C. G. (1989). Pros and cons of the reuse of direct-bonded appliances. American journal of orthodontics and dentofacial orthopedics: official publication of the American Association of Orthodontists, its constituent societies, and the American Board of Orthodontics, 96(1), 72. Quick, A. N., Harris, A. M. P., & Joseph, V. P. (2005). Office reconditioning of stainless steel orthodontic attachments. The European Journal of Orthodontics, 27(3), Reynolds, I. (1975). A review of direct orthodontic bonding. Br J Orthodont, 2, Sonis, A. L. (1996). Air abrasion of failed bonded metal brackets: a study of shear bond strength and surface characteristics as determined by scanning electron microscopy. American journal of orthodontics and dentofacial orthopedics, 110(1), Sunna, S., & Rock, W. (1999). An ex vivo investigation into the bond strength of orthodontic brackets and adhesive systems. Journal of Orthodontics, 26(1),

7 European International Journal of Science and Technology Vol. 3 No. 7 September, 2014 Tavares, S. W., Consani, S., Nouer, D. F., Magnani, M., Nouer, P. R. A., & Martins, L. M. (2006). Shear bond strength of new and recycled brackets to enamel. Brazilian Dental Journal, 17(1), 44. Wendl, B., Muchitsch, P., Pichelmayer, M., Droschl, H., & Kern, W. (2011). Comparative bond strength of new and reconditioned brackets and assessment of residual adhesive by light and electron microscopy. The European Journal of Orthodontics, 33(3), Tables Table 1: The total six group s description Group Description Group 1 New orthodontic brackets (without bonding agent) (Control) Group 2 New orthodontic brackets (with bonding agent) (Control) Group 3 Laser recycling method (without bonding agent) Group 4 Laser recycling method (with bonding agent) Group 5 Repeated Laser recycling method (without bonding agent) Group 6 Repeated Laser recycling method (with bonding agent) Table 2: Adhesive Remnant Index (ARI) scores according to Artun and Bergland (1984) as he scaled in four points Point Description 0 No adhesive left on the tooth 1 less than half of the adhesive left on the tooth 2 more than half of the adhesive left on the tooth 3 All adhesive left on the tooth with distinct impression of the bracket mesh Table 3: Frequency of percentage distribution of the ARI scores in the study groups. The percentage of the area occupied with composite remnant on the tooth surface after debonding was calculated as the area of composite covering the bracket base was subtracted from 100%. Group ARI = 0, No. (%) ARI = 1, No. (%) ARI = 2, No. (%) ARI = 3, No. (%) Group 1 0 (0.0) 7 (35.0) 11 (55.0) 2 (10.0) Group 2 0 (0.0) 5 (25.0) 13 (65.0) 2 (10.0) Group 3 1 (5.0) 10 (50.0) 9 (45.0) 0 (0.0) Group 4 2 (10.0) 12 (60.0) 6 (30.0) 0 (0.0) Group 5 0 (0.0) 4 (20.0) 13 (65.0) 3 (15.0) Group 3 0 (0.0) 8 (40.0) 12 (60.0) 0 (0.0) 7

8 European International Journal of Scien ence and Technology ISSN: Figures G 1 (New orthodontic dontic b brackets without bondingg agent) G 2 (New orthodontic dontic b brackets with bonding agent) G 3 (Laser recycling cling met method without bondingg agent) 6 4 G 4 (Laser recycling cling met method with bonding agent) gent) 2 G 5 (Repeated Laser recycling rec method withoutt bondin bonding agent) 0 G 6 (Repeated Laser recycling rec method with bonding onding aagent) Fig 1: Mean SBS (MPa) and Standard Deviation D (SD) for all groups. The mean SBS for or Group 2, 4 and 6 were higher but not significantly differen rent from Group 1, 3 and 5 respectively. The mean an SBS for Group 3 and 4 were higher but not significantly different d from Group 5 and 6 respectively. ia ii a iiii a ib ii b iiii b SEM) evaluation of the metal orthodontic bracket et bases of: new at Fig 2: Scanning electron microscopy (SE 100X (i.a) and 300X (i.b), laser recyclin ling method at 100X (ii.a) and 300X (ii.b), repeate ated laser recycling method at 100X (iii.a) and 300X (iii.b) 8

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