Farah Final.doc J Bagh College Dentistry Vol. 26(3), September 2014 Frictional resistance Orthodontics, Pedodontics and Preventive Dentistry 118 Frictional resistance of aesthetic brackets Farah Gh. Agha, B.D.S. (1) Mushriq F. Al-Janabi, B.D.S., M.Sc. (2) ABSTRACT Background: The aim of this study was to evaluate and compare the static frictional forces produced by monocrystalline ceramic (sapphire) bracket and polycrystalline ceramic bracket. Materials and methods: one hindered twenty brackets/segment of archwire combinations were used, each bracket/segment of archwire combination was tested 10 times. The tests were performed in a universal testing Instron machine. The data was submitted to in depended t-test. Results: The independent sample t-tests showed a highly significant difference in the static frictional forces between monocrystalline ceramic (sapphire) bracket and polycrystalline ceramic bracket. Conclusion: According to the biomechanical result gained from the present study, the monocrystalline ceramic (sapphire) brackets produced lower static friction level than polycrystalline ceramic bracket. Keywords: Frictional resistance, aesthetic brackets. (J Bagh Coll Dentistry 2014; 26(3):118-121). INTRODUCTION The demand for esthetic orthodontic appliances is increasing, and the development of materials that present acceptable esthetics for the patients and an adequate clinical performance for clinicians is needed (1). This problem has been partially solved by the introduction of esthetic brackets made of ceramic or composite, which are becoming more popular (2). The ceramic brackets available nowadays are made of alumina either in polycrystalline or monocrystalline forms (3). Ceramic brackets currently represent an esthetic alternative, although their use is limited. They abrade the enamel, and fracture more easily, and they have a higher coefficient of friction, increasing resistance to sliding (4). The manufacturing process of monocrystalline brackets results in a purer structure, a smoother surface, and a considerably harder substance than the fabrication of polycrystalline brackets (5). During mechano-therapy involving movement of the bracket relative to the wire, friction at the bracket-wire interface may prevent the attainment of optimal force levels in the supporting tissues (6). Therefore, a decrease in frictional resistance tends to benefit the hard and soft tissue response (7). It has been proposed that approximately 50% of the force applied to slide a tooth is used to overcome friction (8). Up to 60% of the force applied for dental movement can be lost as the result of ceramic bracket resistance to sliding, leading to a longer treatment period (9,10). MATERIALS AND METHODS For this study the materials listed in Table 1 were used A 120 bracket were used divided to 60 monocrystalline ceramic brackets and 60 poly- (1) M.Sc. Student. Department of Orthodontics, College of Dentistry, University of Baghdad (2) Assistant Professor. Department of Orthodontics, College of Dentistry, University of Baghdad crystalline brackets each bracket was ligated to two size of aesthetic coated archwires with three types of coating (Teflon, epoxy and polymer). Experimental models were especially designed for this study to assess the friction in the Instron testing machine. The experimental model consisted of: 1. the bracket bonded to an acrylic block. 2. The orthodontic wire, along which the bracket could slide, fixed to the load cell of the testing machine. 3. The ligation method, consisting of coated ligature wire. Preparation of the acrylic blocks by using Cold-cured acrylic Size of acrylic block: 1.8cm height x 1.8cm width x 3cm length. Retentive holes of 2mm diameter and 2mm depth were drilled corresponding to the positions of the brackets (11). A total of 120 sections of aesthetic coated wires were prepared with length 35mm. Friction generated by the experimental model consisting of upper right 1st premolar bracket fixed on the acrylic block (12,13) 0.5mm away from the end of the block, the archwire and the bracket was tested on the Instron H50KT Tinius Olsen testing machinewith a loadcell of 10 N, and speed of 6 mm/minute (14, 15). Each testing archwire was seated in the slot of the bracketand ligated with the coated ligature wire twisted until taut then untwisted a quarter turn until become slackened and to allow the archwire to slide freely, and then cut the access leaving a small part of it (15, 16).Then the free end ofthe coated aesthetic tested archwire(0.014″ NiTi , 0.019″ x 0.025″ SS) was clamped by the load cell of Instron machine and the same then the bottom of the acrylic block was clamped by the lower fixed crosshead of the Instron machine (12),a computer connected to the testing machine displayed a graph showing peak force variation and recording the frictional resistance force generated on every 0.01mm distance of the tested wire in addition to the maximum frictional J Bagh College Dentistry Vol. 26(3), September 2014 Frictional resistance Orthodontics, Pedodontics and Preventive Dentistry 119 resistance force generated in Newton, which then converted to grams, each of the 12 bracket/wire combinations, was tested 10 times, with new tested archwire, bracket and ligation method on each trial. For every traction test over a distance of 12mm at a speed of 6 mm/min, the maximum force needed to move the wire along the bracket (static friction) were recorded. RESULTS The independent sample t-test was used for comparison among monocrystalline ceramic brackets and polycrystalline ceramic brackets with 14”NiTi teflon coated archwire, and showed significant differencesp-level of < 0.05, as shown in table 2, and shown a highly significant differencesp-level of < 0.01, when coupled with 14”NiTi epoxy coated archwire as shown in table 3, and shown a highly significant differencesp- level of < 0.01, when coupled with 14”NiTi polymer coated archwire as shown in table 4,and shown a highly significant differencesp-level of < 0.01, when coupled with 19” x25” SS Teflon coated archwire as shown in table 5,and shown a highly significant differencesp-level of < 0.01, when coupled with 19” x25” SS epoxy coated archwire as shown in table 6,and shown a highly significant differencesp-level of < 0.01, when coupled with 19” x25” SS epoxy coated archwire as shown in table 7. Table1: Materials used for this study No. Materials Manufacturer 1 Polycrystalline ceramic bracket for the upper right 1st premolar Ortho Technology reflection, USA 2 Monocrystallineceramic bracket for the upper right 1st premolar Ortho Technology reflection, USA 3 Epoxy coated(14” NiTi,19”x 25” SS) archwire Ortho Technology reflection, USA 4 Polymer coated(14” NiTi,19”x 25” SS) archwire G&H Wire Company, USA 5 Teflon coated(14” NiTi,19”x 25” SS) archwire HUBIT, KOREA Table 2: The independent t-test between monocrystalline and polycrystalline ceramic brackets used 14” Niti teflon coated archwire Groups Sample size Mean S.D t-test P-value Monocrystalline,teflon 10 83.97 6.73 2.75 0.013* Polycrystalline , teflon 10 94.98 10.75 **Highly Significant at level P < 0.01,* Significant at level 0.05 ≥ p > 0.01 Table 3: The independent t-test between monocrystalline and polycrystalline ceramic brackets used 14” Niti epoxy coated archwire Groups Sample size Mean S.D t-test P-value Monocrystalline, epoxy 10 79.92 5.72 8.09 0.000** Polycrystalline, epoxy 10 100.33 5.55 Table 4: The independent t-test between monocrystalline and polycrystalline ceramic brackets used 14” Niti polymer coated archwire Table 5: The independent t-test between monocrystalline and polycrystalline ceramic brackets used 19” x25” SS teflon coated archwire Groups Sample size Mean S.D t-test P-value Monocrystalline, teflon 10 149.53 10.90 11.41 0.000** Polycrystalline, teflon 10 191.81 4.32 Table 6: The independent t-test between monocrystalline and polycrystalline ceramic brackets used 19” x25” SS epoxy coated archwire Groups Sample size Mean S.D t-test P-value Monocrystalline, epoxy 10 178.22 9.22 5.58 0.000** polycrystalline, epoxy 10 199.43 7.71 Groups Sample size Mean S.D t-test P-value Monocrystalline, polymer 10 64.65 8.78 6.13 0.000** Polycrystalline, polymer 10 86.21 6.82 J Bagh College Dentistry Vol. 26(3), September 2014 Frictional resistance Orthodontics, Pedodontics and Preventive Dentistry 120 Table 7: The independent t-test between monocrystalline and polycrystalline ceramic brackets used 19” x25” SS polymer coated archwire Groups Sample size Mean S.D t-test P-value Monocrystalline, polymer 10 132.51 7.15 6.13 0.000** polycrystalline, polymer 10 173.98 7.98 DISCUSSION The results of the present study revealed that, there was a wide range of variation in the mean values of static forces between sapphire and ceramic brackets when coupled with both 0.014″ NiTi and 0.019″ x 0.025″ SS coated (teflon, epoxy, polymer) aesthetic archwire, with the sapphire bracket (monocrystalline brackets) has the lowest mean value of static friction generated than ceramic brackets (polycrystalline brackets)this could be contributed to the fact that Polycrystalline brackets have a higher coefficient of friction than monocrystalline ceramic brackets. This is due to their rougher and more porous surface (17).Slot surfaces of polycrystalline brackets have a coarser surface texture and more prominent surface irregularities than slot surfaces of the stainless-steel or single-crystal brackets (18).Higher frictional values of polycrystalline brackets could be produced by sharp and hard edges created at the intersection of the base and walls of the slot with the external surface of the bracket (19).These results fully agree with those of previous studies (2,20,21),but did not agree with (22,23), other study did not find any significant advantage of monocrystalline brackets over polycrystalline ceramic brackets with regards to their frictional characteristics (24). Also this could be contributed to the round slot of monocrystalline ceramic bracket (sapphire) than sharp, rectangular slot of polycrystalline bracket (ceramic), development of ceramic brackets with round smoother slot surfaces and slot base will reduce frictional resistance (25). According to the biomechanical result gained from the present study, the monocrystalline ceramic bracket (sapphire) produced lower static friction level when coupled with all type of coated archwire (Teflon, epoxy, polymer). REFERENCES 1. Elayyan F, Silikas N, Bearn D. Mechanical properties of coated superelastic archwires in conventional and self-ligating orthodontic brackets. Am J Orthod Dentofacial Orthop 2010; 137(2): 213–7. 2. Russell JS. Current products and practice aesthetic orthodontic brackets. J Orthod 2005; 32(2): 146–63. 3. Reicheneder CA, Baumert U, Gedrange T, Proff P, Faltermeier A, Muessig D. Frictional properties of aesthetic brackets. Eur J Orthod 2007; 29(4): 359-65. 4. Ghafari J. Problems associated with ceramic brackets suggest limiting use to selected teeth. Angle Orthod 1992; 62(2):145-52. (IVSL). 5. Reicheneder CA, Baumert U, Gedrange T, Proff P , Faltermeier A, Muessig D. Frictional properties of aesthetic brackets. Eur J Orthod 2007; 29(4): 359-65. 6. Ogata RH, Nanda RS, Duncanson MG, Sinha PK, Currier GF. Friction resistances in stainless steel bracket-wire combinations with effect of vertical deflections. Am J Orthd Dentofac Orthop 1996; 109(5): 535-42. 7. Shivapuja PK, Berger J. A comparative study of conventional ligation and self-ligation bracket systems. Am J Orthod Dentofac Orthop 1994; 106(5): 472-80. 8. Kusy RP, Whitley JQ, Prewitt MJ. Comparison of the frictional coefficients for selected archwire-bracket slot combinations in the dry and wet states. Angle Orthod 1991; 61(4): 293-302. (IVSL). 9. Holt MH, Nanda RS, Duncanson MG. Fracture resistance of ceramic brackets during archwire torsion. Am J Orthod Dentofacial Orthop 1991; 99(4): 287-93. 10. Vaughan JL, Duncanson MG, Nanda RS, Currier GF.Relativekinetic frictional forces between sintered stainless steelbrackets and orthodontic wires.Am J Orthod Dentofacial Orthop 1995; 107(1): 20-7. 11. Mohammed AA. Evaluation and comparison of frictional forces generated by three different ligation methods (An in vitro study). A master thesis, College of Dentistry, University of Baghdad, 2010. 12. Dilip S, Krishnaraj R, Rajasecar, Duraisamy S, Poornima R. A comparative study of frictional resistance of stainless steel, nickel titanium, TMA, timolium and CAN archwire with stainless steel brackets- an in vitro study. SRM University J Dent Sci 2010; 1(1): 63-7. 13. Cunha AC, Marquezan M, Freitas AOA, Nojima LI. Frictional resistance of orthodontic wires tied with 3 types of elastomeric ligatures. Braz Oral Res 2011; 25(6): 526-30. 14. Baccetti T, Franchi L, Camporesi M. Forces in the presence of ceramic versus stainless steel brackets with unconventional vs. conventional ligatures. Angle Orthod 2008; 78(1): 120-4. (IVSL). 15. Gandini P, Orsi L, Bertoncini C, Massironi S, Franchi L. In vitro frictional forces generated by three different ligation methods. Angle Orthod 2008; 78(5): 917-21. 16. Jassim ES. The Effect of Bracket Ligation Methods on Canine Retraction. A master thesis, College of Dentistry, University of Baghdad, 2006. 17. Jena AK, Duggal R, Mehrotra AK. Physical properties and clinical characteristics of ceramic brackets: A comprehensive review. Trends Biomater Artif Organs 2007; 20(2): 101-15. 18. Gill JR. Friction in sliding orthodontic mechanics in ceramic brackets, teflon-coated wires, and comparative resistances. A master thesis, College of Dentistry, University of Saint Louis, 1989. J Bagh College Dentistry Vol. 26(3), September 2014 Frictional resistance Orthodontics, Pedodontics and Preventive Dentistry 121 19. Saunders CR, Kusy RP. Surface topography and frictional characteristics of ceramic brackets. Am J Orthod Dentofacial Orthop 1994; 106(1):76-87. 20. Franco D, Spiller RE, Fraunhofer JAV. Frictional resistances using Teflon-coated ligatures with various bracket-archwire combinations. Angle Orthod 1995; 65(1): 63-74. (IVSL). 21. Khambay B, Millett D, McHugh S. Archwire seating forces produced by different ligation methods and their effect on frictional resistance. Eur J Orthod 2005; 27(3): 302-8. 22. Guerrero AP, GuarizaFilho O, Tanaka O, Camargo ES, Vieira S. Evaluation of frictional forces between ceramic brackets and archwires of different alloys compared with metal Brackets. Braz Oral Res 2010; 24(1): 40-5. 23. Pimentel RF, Oliveira RS, Chaves MG, Elias CN, Gravina MA. Evaluation of the friction force generated by monocristalyne and policristalyne ceramic brackets in sliding mechanics. Dental Press J Orthod 2013; 18 (1): 121-7. 24. Keith O, Kusy RP, Whitley JQ. Zirconia brackets: An evaluation of morphology and coefficients of friction. Am J Orthod Dentofac Orthop 1994; 106(6): 605-14. 25. Gautam P, ValiathanA. Ceramic Brackets: In search of an ideal, Trends Biomater Artif Organs 2007; 120(2): 1-6.