Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Journal of Orthodontics, Vol. 37, 2010, 37–42 SCIENTIFIC SECTION Shear bond strengths of orthodontic brackets with a new LED cluster curing light Mariana Marquezan, Thiago Lau, Carina Rodrigues, Eduardo Sant’Anna, Antônio Ruellas Department of Pedodontics and Orthodontics, Federal University of Rio de Janeiro (UFRJ), Brazil Marcela Marquezan Federal University of Santa Maria (UFSM), Brazil Carlos Elias Militar Engeneering Institute (IME), Rio de Janeiro, Brazil Objective: To evaluate the shear bond strength of orthodontic brackets bonded to bovine enamel using a new curing appliance composed of an LED cluster. Design: In vitro, laboratory study. Materials and methods: Standard edgewise maxillary central incisor metal brackets (0.0220 slot) were bonded to 60 bovine incisors which were arranged in a parabola, simulating the dental arch. The arches were randomly allocated to one of five groups: three experimental groups in which a half arch was cured using the Whitening Lase Ortho LED Cluster light for 10, 20 and 40 s (EG10s, EG20s, EG40s) and two control groups. Control group 1 (CGH) were cured using a halogen light for 20 s and control group 2 (CGL) were cured using a conventional LED light for 20 s per tooth. A shear debond test was performed using an EMIC machine and the results were analyzed by ANOVA and post hoc Tukey multiple comparisons. The Adhesive Remnant Index (ARI) was determined at 106 magnification. Results: The one-way ANOVA showed a statistically significant difference between the groups (P,0.001). The post hoc Tukey comparison showed that the bond strength for group EG10s was significantly lower than both the control groups CGH (P,0.001) and CGL (P,0.001). There was no significant difference between the bond strengths for groups EG10s and EG20s (P50.100). Neither were there any statistically significant differences detected between groups EG20s, EG40s, CGL and CGH (P.0.05).The ARI analysis revealed a higher frequency of score 2 for groups CGL, EG10s, EG20s, a higher frequency of score 0 and 1 for the CGH group and a score of 1 was most frequent for the EG40s group. Conclusion: The Whitening Lase Ortho LED Cluster light shows promise when bonding a half dental arch with a curing time of 40 s. Key words: Light-polymerization, LED/halogen, Shear bond strength, Orthodontic brackets Received 10th December 2008; accepted 27th October 2009 Introduction Light-polymerized orthodontic composites allow the ease of bracket placement and removal of excess resin.1,2 Most dental photoinitiator systems use camphoroquinone as the diketone absorber, with a peak of absorption at a wavelength of approximately 470 nanometres (nm).3 This is the region of the visible light spectrum, which includes the quartztungsten-halogen light, light-emitting diodes (LED), the argon laser and the xenon plasma arc light. According to most manufacturers of composite resins conventional halogen curing lamps need at least 20 s per Address for correspondence: Dr Antônio Carlos Oliveira Ruellas, Federal University of Rio de Janeiro, Brazil. E-mail: [email protected] # 2010 British Orthodontic Society bracket to achieve sufficient bond strength.4 The plasma arc and laser have a reduced polymerization time, but the cost of the equipment remains high. Light-emitting diode systems were proposed as an alternative curing system in 1994.5 They are now well accepted by clinicians and have a cost comparable with that of conventional halogen lights. The advantages of LEDs are: a lifetime of over 10,000 h with relatively little degradation; they require little power to operate; they are resistant to shock and vibration; and require no filters to produce blue light.6,7 Undoubtedly, LED systems are an excellent alternative to conventional halogen lamps. DOI 10.1179/146531207225022329 38 Marquezan et al. Figure 1 Scientific Section The specimens arranged in a parabola A new generation of high-intensity LED units has been introduced into the market.2,8 These consist of multiple LEDs9 or LEDs with larger emission areas to reduce the time needed to bond orthodontic attachments and to optimize the bonding procedure. The aim of this study was to evaluate the shear bond strength of orthodontic brackets bonded to bovine enamel using a new polymerization appliance composed of an LED cluster (Whitening Lase Ortho DMC Equipamentos, São Carlos, São Paulo, Brazil). The null hypothesis was that there were no differences in the force required to debond brackets between the new LED cluster light and two other light curing systems tested. Methods A total of 60 extracted bovine incisors without any visible defects were stored in 0.1% thymol solution at Table 1 JO March 2010 room temperature. The crowns were individually embedded in auto polymerizing acrylic resin (JET, Clássico Artigos Odontológicos, São Paulo, Brazil) with the labial surface touching a glass plate. After polymerization, this surface was abraded until an enamel area of approximately 664 mm2 was exposed, using abrasive paper 180 and then polished with abrasive papers 400 and 600 (40 to 50 movements along the X and Y axes). Each abrasive paper was divided into four parts and each part used for only five teeth. The specimens were embedded in plaster stone, in groups of 6, forming a parabola to simulate the shape of the dental arch (Figure 1). A square was used to check whether the labial surface was perpendicular to the floor. The specimens were randomly divided into five groups according to Table 1. Before bonding, the enamel was cleaned with a mixture of water and pumice, rinsed with water and dried with oilfree air. At this time, the surface was etched with 37% phosphoric acid gel for 30 s, rinsed with a water/spray combination for 30 s, and dried until a characteristic frosty white etched area was observed. The Transbond adhesive primer (3M Unitek, Monrovia, CA, USA) was applied, as recommended by the manufacturer, and polymerized for 20 s. The surface was prepared to receive the brackets. Standard edgewise maxillary central incisor metal brackets (Dental Morelli Ltda, Sorocaba, São Paulo, Brazil), slot 0.0220, were used. Composite resin Transbond XT (3M Unitek, Monrovia, CA, USA) was applied to each bracket base by a single operator. Then the bracket was positioned on the tooth and lightly pressed into the desired position using a Hollenback carver. Excess adhesive was removed with a probe. Distribution of specimens in the experimental and control groups according curing time and appliance. Group Number of specimens Polymerization appliance Curing time CGH CGL EG10s EG20s EG40s 12 12 12 12 12 OrthoLux XT (3M Unitek) Ultra Blue IS 600 mW (DMC Equipamentos) Whitening Lase Ortho (DMC Equipamentos) Whitening Lase Ortho (DMC Equipamentos) Whitening Lase Ortho (DMC Equipamentos) 20 20 10 20 40 Table 2 s s s s s per per per per per teeth teeth half arch half arch half arch Technical characteristics of the light curing units investigated in this study. Curing unit OrthoLux XT (3M Unitek) Ultra Blue IS 600 mW (DMC Equipamentos) Whitening Lase Ortho (DMC Equipamentos) *According to the literature.12,20,21 **According to the manufacturer. Type Halogen LED LED Light source out put 75 W 0,6 W 2,1 W (per cluster) Tip dimensions (area) 2 0.5 cm 0.5 cm2 7.5 cm2 Light intensity Wavelength 2 400–505 nm 400–480 nm 400–480 nm .400 mW/cm * 1200 mW/cm2** 280 mW/cm2** JO March 2010 Scientific Section The effect of LED cluster on bond strength 39 Figure 4 Polymerization in the experimental groups Figure 2 The Whitening Lase Ortho LED Cluster light (DMC Equipamentos, São Carlos, São Paulo, Brazil) The composite was polymerized using one of three curing lights allocated to that group of teeth (Table 1). The technical details of the lights are presented in Table 2. Experimental groups: a Whitening Lase Ortho (DMC Equipamentos, São Carlos, São Paulo, Brazil) (Figure 2) curing light was used to polymerize the composite. This is composed of an LED cluster (460–480 nm) disposed in a half moon (Figure 3). The manufacturer recommends a single shot to polymerize half a dental arch, therefore three bovine teeth were arranged in a half parabola, measuring 40 mm or approximately equivalent to the distance between a maxillary central incisor and second premolar in a human dental arch. The experimental group was divided into three groups with polymerization times of 10 s (EG10s), 20 s (EG20s) and 40 s (EG40s) for half the arch (Figure 4). Control groups: There were two control groups. One group of teeth (CGH) was cured using a conventional halogen light (OrthoLux XT, 3M Unitek, Monrovia, CA, USA) and the second control group (CGL) was cured using a conventional LED light (Ultra Blue IS 600 mW, DMC Equipamentos, São Carlos, São Paulo, Brazil). The cure time for both the groups was 20 s per tooth (10 s for the mesial and 10 s for the distal of the bracket). After bonding, the specimens were kept in distilled water for 24 h before the shear test. The mechanical test was performed using a universal mechanical testing machine (EMIC DL2000, Curitiba, Paraná, Brazil). Each specimen was then stressed at the junction of the bracket and adhesive in an occlusogingival direction with a 50 kg load cell at a crosshead speed of 0.5 mm/ min until the brackets were debonded. Statistical analysis A sample size calculation was undertaken using previous data from the literature.2,10 It was determined that 12 teeth were required to identify a significant difference of 3 MPa in shear bond strength of orthodontic brackets with a significance level of 5% and power of 80% (SD 3 MPa). A one-way analysis of variance with post hoc Tukey multiple comparisons was undertaken in order to detect a significant difference in the shear bond strengths between the groups. The adhesive remnant index (ARI) was recorded according to the four-point scale introduced by Årtun:11 0, no adhesive left on the tooth; 1, less than half the adhesive left on the tooth; 2, more than half the adhesive left on the tooth; 3, all the adhesive left on the tooth with a distinct impression of the bracket mesh. The teeth were examined independently by two judges at 106 magnification (binocular optic microscopy Nikon Eclipse E600, Nikon Corporation, Tokio, Japan). The degree of agreement was assessed using a weighted kappa statistic and was considered good (0.91). Statistical analyses were performed using SPSS Statistical Package (SPSS 13, SPSS Inc., Chicago, IL, USA) and Quick Calcs (GraphPad Software Inc., San Diego, CA, USA). Statistical significance was set at P,0.05. Results Figure 3 The LED cluster arranged in a half moon The results of the one-way ANOVA are presented in Table 3. This showed that there was a statistically 40 Marquezan et al. Scientific Section significant difference in the shear bond strength between the groups (P,0.001). The descriptive statistics are given in Table 4. The post hoc Tukey comparison showed that the bond strength for group EG10s was significantly lower than both the control groups CGH (P,0.001) and CGL (P,0.001). There was no significant difference between the bond strengths for groups EG10s and EG20s (P50.100). Neither were there any statistically significant differences detected between groups EG20s, EG40s, CGL and CGH (P.0.05). The microscopic evaluation of the bond failure site showed that the majority of failures were of a cohesive nature (ARI scores 1 and 2). The ARI scores for groups CGL, EG10s, EG20s were mainly 2, whereas the scores for CGH were mainly 0 and 1 and for EG40s was score 1 (Table 5). The numbers were too small for statistical analysis. Table 3 Frequency distribution of the adhesive remnant index. Table 5 ARI EG10s count % within group EG20s count % within group EG40s count % within group CGH count % within group CGL count % within group 0 1 2 3 0 0% 0 0% 2 16.7% 4 33.3% 1 8.3% 1 8.3% 2 16.7% 7 58.3% 4 33.3% 2 16.7% 10 83.3% 10 83.3% 3 25% 3 25% 9 75% 1 8.3% 0 0% 0 0% 1 8.3% 0 0% One-way ANOVA for shear bond strengths. Between groups Within groups Total Table 4 JO March 2010 Sum of squares df Mean square F P value 57.808 100.288 158.097 4 55 59 14.452 1.823 7.926 ,0.001 Descriptive statistics of shear bond strengths. 95% confidence interval Group Mean (MPa) Standard deviation Group of comparison Lower bound Upper bound P value CGH 4.9 2.0 CGL 4.9 1.1 EG10s 2.2 0.8 EG20s 3.6 1.3 EG40s 4.0 1.4 CGL EG10s EG20s EG40s CGH EG10s EG20s EG40s CGH CGL EG20s EG40s CGH CGL EG10s EG40s CGH CGL EG10s EG20s 21.5 1.1 20.3 20.6 21.6 1.1 20.3 20.6 24.2 24.2 22.9 23.3 22.8 22.8 20.2 21.9 22.5 22.5 0.7 21.2 1.6 4.2 2.8 2.5 1.5 4.2 2.8 2.5 21.1 21.1 0.2 20.2 0.3 0.3 2.9 1.2 0.6 0.6 3.3 1.9 1.000 ,0.001 0.156 0.437 1.000 ,0.001 0.167 0.458 ,0.001 ,0.001 0.100 0.023 0.156 0.167 0.100 0.974 0.437 0.458 0.023 0.974 *Groups with different letters are statistically different at a,0.05%. JO March 2010 Scientific Section Discussion This in vitro study found that the shear bond strength of brackets bonded to bovine enamel using the new Whitening Lase Ortho LED cluster light was comparable after 40 s for half an arch with those obtained using a conventional halogen lamp for 20 s per bracket. When the appliance was used for only 10 s, the values were significantly lower. This could lead to a potential saving of 60 s curing time per halfarch. The literature supports the use of LED curing lights for the polymerization of orthodontic composites.3,4,6,7,9,12–14 The results of this study suggest that the Whitening Lase Ortho LED curing light may be a useful adjunct to reduce the time necessary to bond an orthodontic appliance to a dental arch with light-polymerized composites. Composed of an LED cluster, the manufacturers claim that the light can cover an area of 40 mm, which should be sufficient for half an arch. The appliance has a light intensity of 280 mW/cm2, which is lower than the 400 mW/cm2 suggested by Rueggeberg et al.15 for the polymerization of dental resin composites. Our results concur with Usumez et al.7 who found comparable shear bond strength values when curing with an LED source for 20 and 40 s and lower values when cured for 10 s, although there was no statistically significant difference between EG10s and EG20s. The ARI scores from this study differed among groups that used different LED sources and different polymerization times. This is contrary to the findings of Usumez et al.7 and Swanson12 who found no difference in the ARI scores when varying time-polymerization and LED sources. The experimental group that was cured for 10 s had similar results to those of Thind et al.,16 who tested an LED source with a 10 s polymerization time and found ARI scores of mainly 2 and 3. The ARI scores for the 20 s and 40 s cure times are in agreement with Usumez et al.7 who found a higher frequency of score 1. The conventional LED scores in our study were similar to Swanson et al.12 who found a higher frequency of score 2. The ideal tooth to use for bonding studies is the human maxillary central incisor. It has a nearly flat bonding surface that is usually consistent from incisor to incisor without the concern of fitting a bracket base to a varying curved surface. However, it is increasingly difficult to get non-carious, sound human incisors for studies. Some studies have advocated the use of premolars to standardize results.17 They are more easily obtainable than other teeth as they are commonly extracted for orthodontic treatment, but premolars vary in the curvature of their labial surface and therefore provide an additional variable of the bracket base not The effect of LED cluster on bond strength 41 closely fitting the tooth.18 Bovine lower incisors are easily obtainable and therefore are an inexpensive substitute for human incisors. They have been used in a number of previous studies.18 Although bovine enamel acts in a similar way to human enamel, the strength of the bond to bovine enamel is lower than to human enamel, probably due to differences in formation, leading to larger crystal grains, and more lattice defects.18 The actual shear bond strength values in this study were lower than those found in other studies. This might be due to differences in the bonding protocol adopted. To facilitate the inclusion of the teeth, in a group of six, in the same base filled with plaster stone, the crowns of the teeth were included in acrylic resin and then the labial surfaces were flattened to allow them to be located perpendicular to the floor. This procedure has not been used extensively in the literature limiting the comparison of nominal values.19 Among the experimental groups there were increasing bond strengths with increasing curing times, which concurs with previous studies;4,12 although these were not statistically significant between EG10s and EG20s or between EG20s and EG40s. This increasing bond strength is due to the higher conversion rate of monomer to polymer with increasing polymerization times.12 The statistically non-significant results can be explained either by the fact that there is no true difference between the samples or alternatively that our sample was not large enough to detect a significant difference. Using data from our study we are able to determine that we would require a sample size of 47 specimens in order to detect a significant difference of 1 MPa between the EG40s and CGH or 21 specimens to detect the same difference between EG10s and EG20s (power of 80% and significance level P,0.05). The advantage of an in vitro experiment is that it allows the number of variables to be minimized. Laboratory studies are a valuable screening tool, but clinical evaluation is necessary before validation of any product or technique. Further studies are also necessary to evaluate the compatibility and physical characteristic of various orthodontic adhesive when submitted to this LED cluster polymerization procedure. Conclusions N There were no significant differences in the bond strengths when using the new Whitening Lase Ortho curing light for 40 s for a half arch compared with conventional halogen and LED curing lights used for 20 s per tooth. This could lead to a potential saving of 60 s curing time per halfarch. 42 N Marquezan et al. Scientific Section Differences were observed for ARI scores when light sources and polymerization time changed. Acknowledgements The authors would like to thanks Morelli Ortodontia for the donation of the brackets and DMC Equipamentos for lending the Whitening Lase Ortho for this study. Contributors Mariana Marquezan, Carina Rodrigues, Thiago Lau and Antônio Carlos Ruellas were responsible for the study design. Carlos Elias provided the technical support for the shear debonding test. Marcela and Mariana Marquezan performed the statistical tests and data interpretation. Critical revision and final approval of the article were undertaken by Eduardo Sant’Anna and Antônio Carlos Ruellas. Mariana Marquezan and Antônio Carlos Ruellas are the guarantors. References 1. Bishara SE, Gordan VV, VonWald L, Jakobsen JR. Shear bond strength of composite, glass ionomer, and acidic primer adhesive systems. Am J Orthod Dentofacial Orthop 1999; 115: 24–28. 2. Mavropoulos A, Staudt CB, Kiliaridis S, Krejci I. Light curing time reduction: in vitro evaluation of new intensive lightemitting diode curing units. Eur J Orthod 2005; 27: 408–12. 3. Dunn WJ, Taloumis LJ. Polymerization of orthodontic resin cement with light-emitting diode curing units. Am J Orthod Dentofacial Orthop 2002; 122: 236–41. 4. Silta YT, Dunn WJ, Peters CB. Effect of shorter polymerization times when using the latest generation of light-emitting diodes. Am J Orthod Dentofacial Orthop 2005; 128: 744–48. 5. Nakamura S, Mukai T and Senoh M. Candela-class high brightness InGaN/AlGaN double heterostructure bluelight-emitting diodes. Appl Phys Lett 1994; 64: 1687–89. 6. Turkkahraman H, Kucukesmen HC. Orthodontic bracket shear bond strengths produced by two high-power light-emitting diode modes and halogen light. Angle Orthod 2005; 75: 854–57. 7. Usumez S, Buyukyilmaz T, Karaman AI. Effect of lightemitting diode on bond strength of orthodontic brackets. Angle Orthod 2004; 74: 259–63. JO March 2010 8. Pandis N, Strigou S, Eliades T. Long-term failure rate of brackets bonded with plasma and high-intensity lightemitting diode curing lights: a clinical assessment. Angle Orthod 2007; 77: 707–10. 9. Bishara SE, Ajlouni R, Oonsombat C. Evaluation of a new curing light on the shear bond strength of orthodontic brackets. Angle Orthod 2003; 73: 431–35. 10. Ip TB, Rock WP. A comparison of three light curing units for bonding adhesive pre-coated brackets. J Orthod 2004; 31: 243–47; discussion 02-3. 11. Artun J, Bergland S. Clinical trials with crystal growth conditioning as an alternative to acid-etch enamel pretreatment. Am J Orthod 1984; 85: 333–40. 12. Swanson T, Dunn WJ, Childers DE, Taloumis LJ. Shear bond strength of orthodontic brackets bonded with lightemitting diode curing units at various polymerization times. Am J Orthod Dentofacial Orthop 2004; 125: 337–41. 13. Krishnaswamy NR, Sunitha C. Light-emitting diode vs halogen light curing of orthodontic brackets: a 15-month clinical study of bond failures. Am J Orthod Dentofacial Orthop 2007; 132: 518–23. 14. Mirabella D, Spena R, Scognamiglio G, Luca L, Gracco A, Siciliani G. LED vs halogen light-curing of adhesiveprecoated brackets. Angle Orthodontist 2008; 78: 935–40. 15. Rueggeberg FA, Caughman WF, Curtis JW, Jr. Effect of light intensity and exposure duration on cure of resin composite. Oper Dent 1994; 19: 26–32. 16. Thind BS, Stirrups DR, Lloyd CH. A comparison of tungsten-quartz-halogen, plasma arc and light-emitting diode light sources for the polymerization of an orthodontic adhesive. Eur J Orthod 2006; 28: 78–82. 17. Fox NA, McCabe JF, Buckley JG. A critique of bond strength testing in orthodontics. Br J Orthod 1994; 21: 33–43. 18. Oesterle LJ, Shellhart WC, Belanger GK. The use of bovine enamel in bonding studies. Am J Orthod Dentofacial Orthop 1998; 114: 514–19. 19. Lalani N, Foley TF, Voth R, Banting D, Mamandras A. Polymerization with the argon laser: curing time and shear bond strength. Angle Orthodontist 2000; 70: 28–33. 20. Sfondrini MF, Cacciafesta V, Pistorio A, Sfondrini G. Effects of Convetional and High Intensity Light-Curing on Enamel Shear Bond Strength of Composite reson and resin modified glass-inoment. Am J Orthod Dentofacial Orthop 2001; 119: 30–5. 21. Signorelli MD, Kao E, Ngan PW, Gladwin MA, Comparison of Bond Strength between Orthodontic Brackets Bonded with Halogen and Plasma Arc Curing Lights: an invitro and in-vivo study. Am J Orthod Dentofacial Orthop 2006; 129: 277–82.