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Braz J Oral Sci. October/December 2003 - Vol. 2 - Number 7 Evaluation in vitro of the shear bond strenght of aluminun oxide recycled brackets Stenyo Wanderley Tavares1 Simonides Consani2 Darcy Flávio Nouer3 Maria Beatriz Borges de Araújo Magnani3 João Sarmento Pereira Neto3 Fábio Lourenço Romano4 1 DDS, MS, PhD student, Department of Orthodontics, University of Campinas – Piracicaba Dental School - Brazil 2 DDS, MS, PhD, Professor, Department of Dental Materials 3 DDS, MS, PhD, Professors, Department of Orthodontics, University of Campinas – Piracicaba Dental School - Brazil 4 MS student, Department of Orthodontics, University of Campinas – Piracicaba Dental School - Brazil Abstract The aim of this study was to evaluate the shear bond strength of recycled brackets with 90 and 50 µm aluminum oxide blasting. It was used 30 human bicuspids, whom it was accomplished brackets bonding with composite resin chemically activated. The teeth were separated in 3 groups (n = 10). In group I (Control) brackets bonded after enamel acid etching. In groups II and III brackets were rebonded after recycling, respectively, by 90 and 50 µm aluminum oxide blaster. Shear bond test was made in the Instron machine, with 0,5 mm/ minute speed and the results were submitted to ANOVA and Tukey’s test (5%). The results showed no significant statistical difference between recycled brackets by aluminum oxide and control group. Recycled brackets by 90 and 50 µm aluminum oxide showed no significant statistical difference. Key Words Recycling; aluminum oxide; shear bond strength Received for publication: June 16, 2003 Accepted: October 31, 2003 Correspondence to: Stenyo Wanderley TAVARES Rua Coronel Barbosa 333/44 São Judas - Piracicaba - SP CEP: 13416-120 e-mail: [email protected] 378 Braz J Oral Sci. 2(7): 378-381 Evaluation in vitro of the shear bond strenght of aluminun oxide recycled brackets Introduction The low retentiveness of certain bracket bases and the action of oclusal forces are also major factors causing brachet debonding. This fact is a frequent problem in Orthodontics practice causing stress and delays in Orthodontic treatment are also an economic disadvantage. Recycling consists basically in removal of the remnant bonding agent of the bracket basis, making the used bracket able to reutilization, without damages to retention mesh, keeping the retentive features1. Although clinical use can produce little distortion in brackets, the removal phase is responsible for most distortion and damages observed 2. Brackets recycling can be performed by the immediate method in the clinical practice, or by mediate method, that is performed by specialized companies, without alteration in the position of the “slots”3. Two methods are commonly used for bracket recycling: 1Heat application for adhesive burning, followed by electrolytic polishing for removal of oxide; 2- Use of chemical solvents for adhesive dissolution, combined with high frequency vibrations and electrochemical polishing4-7. The immediate debonded bracket recycling can be performed with Aluminum Oxide air abrasion. The increase of retentivity in bracket bonding to dental structure by Aluminum Oxide air abrasion occurs due to the micro-roughness production by the process in the base surface, increasing its union area to the composite, essentially mechanical union caused by bonding of the composite to the retention mesh and to existent micro-roughness. There is not an agreement in the literature, concerning the size particle used in recycled brackets by oxide aluminum. The 90 µm particle was used in the following studies 8-11. However other autors 12-13 recommended the use of 50 µm particle for brackets recycling. Although Aluminum Oxide air abrasion is a widely used method for recycling in private practice and research, the technique originally was devised to increase mechanical retention of new brackets14, facilitating the bracket bonding in restored teeth as well as conditioning enamel surface15. The aim of this work was to evaluate in vitro shear resistance of brackets bonded with chemically activated composite after recycled by 90 and 50 µm aluminum oxide air abrasion. Materials and Methods Thirty human premolar teeth were extracted for orthodontic reasons, in the Surgery Clinics of Piracicaba Dental School. Teeth were stored in 0,9% NaCl, at 4ºC for a maximum time of six months before use. All experimental procedures were according to the specification TR 11405 of the International Organization for Standardization (ISO)16. Teeth were individually fixed by the root in PVC tubes filled with chemically activated acrilic resin Vipi Flash (Dentalvipi, 379 Pirassununga, SP). Enamel conditioning was performed with 37% Concise gel of phosphoric acid (3M, Nova Odessa, SP), during 30 seconds. Enamel was then washed in water for 20 seconds and dried for 20 seconds with soft air jet. The bicuspid metal brackets (Dental Morelli, Sorocaba, SP) were fixed in the central region of the buccal aspect of the teeth. The chemically activated composite resin Concise Orthodontic (3M) was used for bonding. After bracket fixation, the samples were randomly separed in 3 experimental groups (n=10): Group I - Control : Brackets bonded by conventional technique. Group II – Aluminum Oxide air abrasion: Debonded brackets, etched with 90 µm Aluminum Oxide Bio-art (São Carlos, SP) and rebonded. Group III – Aluminum Oxide air abrasion: Debonded brackets, etched with 50 µm Aluminum Oxide Bio-art (São Carlos, SP) and rebonded. Bracket debonding of groups II and III was performed by using a nipper (Starlet). Then, the residual resin was removed from the tooth surface with multilaminated burs KG Sorensen 9114F with handpiece (Dabi Atlante) in low velocity17. Burs were changed by new ones after used in 5 teeth. The residual resin remotion from group II and III brackets were made with Aluminum Oxide air abrasion, with 90 µm and 50 µm particles, respectively, using the micro-etcher (BioArt) during 15 to 30 seconds, depending on the amount of residual resin, keeping a 10 mm distance of the bracket base 10-11 . The rebonding of both recycled brackets and new brackets was performed as descrebed in the initial fase of bonding. Teeth were stored in humid incubators at 37o C for 24 hours. Shear bond strengths were determined with an INSTRON universal machine (model 4411, Instron Corp., Canton, Mass.). Debonding was accomplished with crosshead speed of 0.5 mm/minute. The needed force for bracket debonding was measured in kgf. This value was divided by the bracket bonding surface (14.7 mm2) obtaining the shear bond strength in kgf/mm2. The bracket surfaces were observed in Scanning Electron Microscopy (LEO 435 VP, Cambridge, England) for mesh evaluation before (group I) and after debonding, as well as the recycled ones (groups II and III). The shear bond strength test results were submitted to Analysis of Variance and Tukey´s test, with 5% significance. Results The average shear bond strength, measured in kgf/mm2 of the groups and the test are summarized in Table I. That shows that there was no statistically significant differences in shear bond strength between Group I (Control) and Groups II and III (90 and 50 µm aluminum oxide). Braz J Oral Sci. 2(7): 378-381 Evaluation in vitro of the shear bond strenght of aluminun oxide recycled brackets Table 1 -Shear bond strength mean values GROUPS MEAN (SD) GROUP I (control) 0,5478 (± 0.237) a GROUP III (50mm) 0,3625 (± 0.126) a GROUP II (90mm) 0,3575 (± 0.144) a Average followed by distinct letters differ between themselves in significance level of P<0,05 (n=10) Discussion There are few articles regarding orthodontic brackets recycling and the comparison of our results with others is difficult, due to the several laboratorial proceedings addopted. Recycling debonded brackets is used to reduce the costs in reposition of Orthodontic accessories. Aluminum Oxide air brasion came as an option in brackets recycling, offering a simple and practical technique that can be performed in dental practice, avoiding time wasting, since brackets do not have to be sent for specialized companies13. The present study did not show statistically significant difference in shear bond strength between Group I (Control) and aluminum oxide air abrasion recycled brackets (Groups II and III) (table I). This is in agreement to previous studies 11, 10 and with the work of Sonis8 that used GAC brand bracket with base area of 9.9 mm2 and light cured resin. These authors concluded that there was no statistically significant difference in retention of jetted recycled brackets and new brackets. However, Willems 11 related that efficiency of sandblasting depends on bracket type. The improved mechanical retention of the bracket to tooth promoted by aluminum oxide air abrasion is due to the microroughness in the bracket base caused by this method (Fig. 2 and 3), when compared to control group (Fig.1). This increased the union area to the composite 13. Fig. 1 – Photomicrographic view (SEM) in 200x magnification, of new bracket base (Group I) Fig. 2 – Photomicrographic view (SEM) in 200x magnificcation of the bracket base recycled with Aluminum Oxide jet (Group II) Fig. 3 – Photomicrographic view (SEM) in 200x magnificcation of the bracket base recycled with Aluminum Oxide jet (Group III) The present study (table 1) showed that 90 µm and 50 µm particles (0.3575 kgf/mm2 and 0.3625 kgf/mm2 , respectively) of aluminum oxide sandblasting were effective in the recycle process, since no statistically significant difference was found for shear bond strength when compared to control group (0.5478 kgf/mm2). In a similar study, Penido et al.10 also verified no statistically significant difference between bracket recycled with 90 µm particles (0.4543 kgf/ mm2) aluminum oxide air abrasion and control group (0.3906 kgf/ mm2 ). For brackets recycling was recommended the use of 50 µm Aluminum Oxide particles, whom promoted increased brackets retention due to roughness formation12-13. However, Sonis 8; Penido et al. 10 and Tavares11, showed that the 90 micrometers particles also produced higher micro-roughness in the surface of the bracket base, increasing the disposable area for union with the composite. The use of Aluminum Oxide with either 90 or 50 µm particles for bracket recycling had similar efficacy, due to the absence of statistically significant difference between groups II and 380 Braz J Oral Sci. 2(7): 378-381 Evaluation in vitro of the shear bond strenght of aluminun oxide recycled brackets III (Table I). Consequently, the micro-roughness created by different sized aluminum oxide particles promotes similar bonding force between recycled brackets and Control (Table I). In this work, the time used for Aluminum Oxide jetting was 15 to 30 seconds, keeping a 10 mm distance of the bracket basis, what usually caused no damages to the accessory mesh (Fig. 2 and 3). The same time distance interaction was utilized by Penido et al.10 and Tavares11, showing results similar to our study, what corroborates the technique effectiveness. Millet et al.14 utilizing only 3 seconds for jet new brackets before bondage in tooth, obtained satisfactory results increasing roughness, without mesh damage. This work allowed to demonstrate that brackets recycling by means of aluminum oxide air abrasion (90 and 50 µm) is efficient and technically simple. The brackets reutilization in these conditions could reduce costs for clinician, and consequently, for the patient. References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 381 Maccoll GA et al. The relationship between bond strenght and base surface area using conventional and micro-etched foil-mesh bases. Am. J. Orthod. Dentofacial Orthop. 1996; 109: 338-9. Oliver RG, Pal AD. Distorcion of edgewise orthodontic brackets associated with methods of debonding. Am. J. Orthod. 1989; 71: 65-71. Hixson ME et al. Changes in brackets slot tolerance following recycling of direct-bond metallic orthodontic appliances. Am. J. Orthod. 1982 ; 81: 447-54. 4.Buchman DJL. Effets of recycling on metallic direct-bond orthodontics brackets. Am. J. Orthod. 1980; 77: 654-68. Mascia VE, Chen SR. Shearing strengths of recycled direct-bonding brackets. Am. J. Orthod. 1982; 82: 211-6. Maijer R, Smith DC. Corrosion of orthodontic brackets bases. Am. J. Orthod. 1982; 81: 43-8. Buchwald A. A three-cycle in vivo evaluation of reconditioned direct-bonding brackets. Am. J. Orthod. 1989; 95: 352-4. Sonis AL. Air abrasion of failed bonded metal brackets: a study of shear bond strength and surface characteristics as determined by scanning electron microscopy. Am.J.Orthod. Dentofacial Orthop. 1996; 110: 96-8. Willems G, Carels CEL, Verberke G. In vitro peel/shear bond strength evaluation of orthodontic brackets base design. J. Dent. 1997; 25: 271-8 Penido SMMO, et al. Avaliação da resistência ao ciasalhamento de bráquetes reciclados e novos recolados. Rev Dental Press Ortod Ortop Facial 1998; 3: 45-52. Tavares SW. Estudo in vitro da resistência ao cisalhamento de bráquetes reciclados e novos [Thesis]. Piracicaba: Faculdade de Odontologia de Piracicaba, Universidade de Campinas; 2002. Newman GV, et al. Update on bonding brackets: an in vitro survey. J. Clin. Orthod. 1994; 28: 396-402 Pinto AS, et al. A reciclagem de bráquetes na clínica ortodôntica. Ortodontia 1996; 29: 63-7 Millet D, Mccabe JF, Gordon PH. The role of sandblating on the retention of metallic brackets appllied with glass ionomer cemeut. Br. J. Orthod. 1993; 201: 117-22. Senay C, Iiken K, Ela A. The effect of enamel air abrasion on the retetion of bonded metallic orthodontic brackets. Am J Orthod Dentofacial Orthop. 2000; 117: 15-9. International Organization for Standardization – Guidance on testing of adhesion to tooth structure. ISO/TC106/SC 1 N236, Resolution 6 1. – CD 1994; TR 11405, trieste, October. 17. Gandini Junior LG, et al. Avaliação de diferentes métodos de remoção da resina remanescente ao esmalte dentário após descolagem de bráquetes ortodônticos. Ortodontia 1995; 28: 53-60.