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International Journal of Contemporary Orthodontics doi: 10.1013/IJCO/1701-0008 Original Research Comparison of shear bond strength of orthodontic brackets using three different bonding techniques and two different light cure sources. Ishan Sojitra1, Anand Sabane2, Siddhart Shinde2, Vinit Swami2, Amol Patil2 1 Postgraduate, Department of Orthodontics, Bharati Vidyapeeth University Dental College and Hospital, Pune, India 2 Faculty, Department of Orthodontics, Bharati Vidyapeeth University Dental College and Hospital, Pune, India Abstract Aim of the study was to measure and compare shear bond strengths and evaluate the composite adhesive remnant on the tooth surface using combination of different bonding methods as well as two different light sources.120 maxillary premolar teeth were divided into three groups of 40 teeth and each group then subdivided in to two groups of 20 teeth (A1,A2,B1,B2,C1,C2). An Instron universal testing machine was used to measure the shear bond strength. Following debonding of brackets ARI was noted. ANOVA was done using Paired T-test. There were statistically significant difference between group A1 (10.98 ± 3.47 MPa) and C1 (8.79 ± 3.23 MPa), as p value was 0.046(<0.05). Between B1 (11.37 ± 3.42 MPa) and C1 (8.79 ± 3.23 MPa), there was statistically significant difference, as p value was 0.019(<0.05). Between A2 (9.84 ± 3.10 MPa) and C2 (7.92 ± 2.85 MPa), there was statistically significant difference, as p value was 0.049(<0.05). Between B2 (10.25 ± 4.06 MPa) and C2 (7.92 ± 2.85 MPa), there was statistically significant difference, as p value was 0.043(<0.05). 30-35% of the samples in group A had a “0” ARI score and 30-50% of the samples in group B had a “0” ARI score. 15% of the samples in group C had a “0” ARI score. Maximum shear bond strength and minimum adhesive remaining on the tooth surface was seen in the group in which primer was not applied on the bracket base. And minimum shear bond strength and minimum adhesive remaining on the tooth surface was seen in group where primer applied on the bracket base and cured. Keywords: Shear bond strength, LED, Halogen, bonding material.1 Introduction Bond strength of orthodontic brackets is an important c onsideration in orthodontics. Shear bond strength depends on various factors, including the adhesive properties of the bonding materials, the attachment at the different interphases like the tooth to composite interphase and the composite to bracket interphase, as well as the polymerization of the composite Correspondence: Dr Anand Sabane Bharati Vidyapeeth University Pune Email [email protected] The method of attachment should allow the delivery of orthodontic forces and should be sufficient to withstand masticatory loads. In direct bonding of orthodontic brackets, current bonding systems involve etching the enamel surface, flowing an unfilled or lightly filled liquid resin into the etched surface, and then using a filled resin on the bracket base to form the final bond between the bracket and the tooth before selfcuring or light-curing the adhesive2. Currently clinicians use various methods for bonding orthodontic brackets on teeth i.e. application of primer only on the tooth surface as well as the bracket bases. However there is variation in the bonding methods used by clinicians. Sabane et al. In addition, the attachments should easily be removed at the end of orthodontic treatment, and result in minimal enamel damage during the procedure. While a strong and durable bond is required, the problem of removing the bracket without damaging the labial enamel must not be overlooked. The ideal bonding material sandwich should fail during debonding by the clean separation of the resin from the etched enamel. Vol. 1 Issue 1 example, Group A1 samples numbered as A1-1 to A1-20 and in the other groups as well, i.e. A2-1 to A2-20, B1-1 to B1-20, B21 to B2-20, C1-1 to C1-20, C2-1 to C2-20) 1. 2. This study was designed to measure and compare shear bond strengths and evaluate the composite adhesive remnant on the tooth surface using combination of different bonding methods as well as two different light sources i.e. LED and halogen light. The outcome of this study will provide information about which of the combinations produces a higher shear bond strength and lower composite adhesive remnant on the tooth surface. 3. 4. MATERIAL AND METHODS The present study was aimed at measuring and comparing the shear bond strength using combinations of three different bonding methods and two different light cure sources. One hundred and twenty (120) premolar teeth extracted for the purpose of orthodontic therapy were used in this study. First and second maxillary premolar teeth were used from patients who underwent therapeutic extractions of teeth as part of orthodontic treatment. Teeth with caries, restoration and fracture lines were excluded from the samples. The collected extracted teeth were washed, dried and stored in 0.9% w/v normal saline to prevent dehydration. Dental stone blocks (size:- 2” x 2” x 2.5”) were used to mount the tooth for testing the shear bond strength. The dental stone blocks were prepared such that the tooth was centred in the block with the long axis of the teeth perpendicular to the base of the block and embedded in the stone till cement enamel junction and the entire crown was kept exposed for bonding the bracket. A total of 120 dental stone blocks which were prepared by the above mentioned method were later stored in normal saline at room temperature before subjecting them to shear bond strength test. The mounted teeth were cleaned with ultrasonic scaler to remove any left over tissue tags and calculus. The buccal surfaces were polished with oil-free pumice slurry using rubber cup mounted on a slow speed hand piece. They were washed by using distilled water and then dried using oil free compressed air. The sample of 120 teeth was divided into three groups of forty (40) teeth each and each group then subdivided in to two groups of twenty (20) each as shown in table below. These samples were then numbered in a sequential manner. (For 2 5. First, the buccal surfaces of the teeth on the stone blocks were cleaned using pumice and with the help of polishing cup at slow speed. The cleaned tooth surfaces were washed with distilled water and were dried with dry compressed air. The area to be etched was marked on the buccal surface by using a pencil of 0.5 mm B and a bracket marker. The long axis of the crown was marked and also the horizontal marking was done at 4 mm from the incisal edges. This marking was done by leaving approximately equal distance to the base area of the bracket. Application of the etchant: After the tooth marking, the etchant was gently applied on buccal surface by using an applicator brush. Two coats were applied, once horizontally and once vertically. After 15 seconds, the etchant applied on buccal surface was washed for 10 seconds and dried with air using a compressed air syringe. After the brackets were bonded, the teeth with blocks were stored again in fresh distilled water at 37 ̊ C for 40 hours (±2 hours) to simulate oral conditions prior to shear bond testing procedure. A storage time of 40 hours was chosen so that the bonding strength could be maximized. An Instron universal testing machine was used to measure the shear bond strength. The experiments were conducted at room temperature of 25 ̊C. Each specimen (tooth mounted on plaster block) was positioned on the Instron machine platform in such a way that the upper jaw of instron machine was directed parallel to the long axis of the tooth and contact was made as close as possible to the junction of the tooth surface and the bracket base edge. When the testing started, a progressive load was applied at a crosshead speed of 3 mm/min. The load at which the first sign of bracket debonding occured was recorded. This data was subsequently added to a formula to calculate the shear bond strength in mega Pascals. Following the debonding of the brackets, the tooth surface where the bracket was placed, was analysed under a optical stereomicroscope using external illumination at 10X magnification and given a score according to the adhesive remnant index (ARI) given by Artun J and Berglund S3. Analysis of Variance (ANOVA): One-way analysis of variance was done using Paired T-test for multiple group comparison. International Journal of Contemporary Orthodontics Vol. 1 Issue 1 . Sabane et al. Table 2. The shear bond strength of maximum, minimum, mean and standard deviation for each group. Table 1. Group segregation of the sample and light source used The statistically significant level was set at p < 0.05 level and p values 0.000 and 0.001 were considered to be highly significant. Mean values and standard deviations for each measured variable were calculated. RESULTS AND DISCUSSION The mean shear bond strengths for brackets cured with LED light source, i.e. group A1, group B1 and group C1 were 10.98 ± 3.47 MPa, 11.37 ± 3.42 MPa and 8.79 ± 3.23 MPa respectively. When mean shear bond strengths were compared between group A1 (10.98 ± 3.47 MPa) and group B1 (11.37 ± 3.42 MPa), there was no statistically significant difference, as p value was 0.721(>0.05). When mean shear bond strengths were compared between group A1 (10.98 ± 3.47 MPa) and group C1 (8.79 ± 3.23 MPa), there was statistically significant difference, as p value was 0.046(<0.05). When mean shear bond strengths were compared between group B1 (11.37 ± 3.42 MPa) and group C1 (8.79 ± 3.23 MPa), there was statistically significant difference, as p value was 0.019(<0.05). The mean shear bond strengths for brackets cured with Halogen light source, i.e. group A2, group B2 and group C2 were 9.84 ± 3.10 MPa, 10.25 ± 4.06 MPa and 7.92 ± 2.85 MPa respectively. When mean shear bond strengths were compared between group A2 (9.84 ± 3.10 MPa) and group B2 (10.25 ± 4.06 MPa), there was no statistically significant difference, as p value was 0.725(>0.05). When mean shear bond strengths were compared between group A2 (9.84 ± 3.10 MPa) and group C2 (7.92 ± 2.85 MPa), there was statistically significant difference, as p value was 0.049(<0.05). International Journal of Contemporary Orthodontics When mean shear bond strengths were compared between group B2 (10.25 ± 4.06 MPa) and group C2 (7.92 ± 2.85 MPa), there was statistically significant difference, as p value was 0.043(<0.05). The mean shear bond strengths for brackets cured with both light sources (LED and Halogen), i.e. group A1, group A2, group B1, group B2, group C1 and group C2 were 10.98 ± 3.47 MPa, 9.84 ± 3.10 MPa, 11.37 ± 3.42, 10.25 ± 4.06 MPa, 8.79 ± 3.23 MPa and 7.92 ± 2.85 MPa respectively. When mean shear bond strengths were compared between group A1 (10.98 ± 3.47 MPa) and group A2 (9.84 ± 3.10 MPa), there was no statistically significant difference, as p value was 0.281(>0.05). When mean shear bond strengths were compared between group B1 (11.37 ± 3.42 MPa) and group B2 (10.25 ± 4.06 MPa), there was no statistically significant difference, as p value was 0.349(>0.05). When mean shear bond strengths were compared between group C1 (8.79 ± 3.23 MPa) and group C2 (7.92 ± 2.85 MPa), there was no statistically significant difference, as p value was 0.371(>0.05). The adhesive remnant index showed that group A and group B has minimal adhesive remaining on to the tooth surface when brackets were debonded. 30-35% of the samples in group A had a “0” score and 30-50% of the samples in group B had a “0” score. Group C shows maximum adhesive remaining on to the tooth surface when brackets were debonded. 15% of the samples in group C had a “0” score. This study was designed to measure and compare shear bond strengths and evaluate the composite adhesive remnant on the tooth surface using combination of different bonding methods as well as two different light sources i.e. LED and halogen light. The outcome of this study will provide information about which 3 Sabane et al. Table 3. Statistical significance values (p-values) when comparing two groups of the combinations produces a higher shear bond strength and lower composite adhesive remnant on the tooth surface. The sample size of this study was 120 extracted maxillary first and second premolars. After extraction they all were stored in 0.9% w/v normal saline till the samples were tested. Linklater et al4 (2001) found that premolar teeth exhibited significantly higher shear bond strength compared to incisors and canines. Previous investigators5,6,7 found that saline solution as a storage medium produces comparable bond strength. Thus, saline was chosen as a storage media in this present study. Various authors6-21 found that etching time between 10 to 30 seconds did not affect bond strength or location of failure site where as etching for 0 to 5 seconds reduced bond strength significantly (<3 MPa). Hence, 15 seconds of etching time was chosen in this present study. According to previous researchers8-11,13,15,17-20,22-24 curing time of 40 seconds had significantly higher bond strength values. Hence, 40 seconds (10 seconds each side of the bracket) of curing time was chosen in this present study. It is known in the literature that shear bond strength achieved with the light cured/dual cure resin increased with time. This increase is either due to a dual cure system in the formulation of the resin or due to the polymerization of the resin under the bracket base after the diffusion of free radicals. Various studies813,15,16-20,24-35 done to evaluate shear bond strength have storage time for 24 to 48 hours. Thus, in the present study, the storage time chosen was 40 hours (± 2 hours). To produce “pure shear” force vector, and eliminating other undesirable force components, Brantley and Eliades method as cited by Akhoundi et al36 was used where force applied to an area near the base of the bracket or at the bracket-adhesive 4 Vol. 1 Issue 1 interface via a rod attached to the crosshead of a testing machine. The moving crosshead of the testing machine is the component that applies the required force to the specimens. It has been recommended to keep the crosshead speed of the testing machine as low as possible. Various studies9,11-13,16,20,22,26,34,36, have recommended crosshead speed of 0.1 mm/min. The fundamental concept may be that a lower crosshead speed results in more accuracy. However such slow and precise force application rarely occurs in the oral environment. This means that using slow crosshead speeds might not be suitable for stimulation of the forces acting in the oral cavity. Most bond failures are caused by a much higher velocity. Versluis et al37 also have demonstrated that when higher crosshead speeds are used, the incidence of cohesive failure in the tooth substrate decreases significantly thus, 3 mm/min of crosshead speed was chosen in this present study. ` After testing 120 samples the data was subjected to statistical analysis and results have been tabulated from table-3 to table-7. For the purpose of better understanding, the discussion is categorized according to the various groups tested. Groups A- primer not applied on the bracket base In group A1, where brackets were cured with LED light, as depicted in table-3, the mean shear bond strength is observed to be 10.39 ± 3.47 MPa. This finding is in agreement to the shear bond strength found by Chamada et al25 (1996) (11.46 ± 2.49 MPa), Sharma et al12 (2014) (15.49 ± 2.55 MPa), Di Nicolo et al34 (2010) (15.88 ± 5.49 MPa) and Cerekja et al18 (2011) (15.01 ± 3.57 MPa). Results of some investigations14,20,32 are in disagreement with the finding of the present study. Niepraschk et al32 (2007) found significantly higher shear bond strength (46.16 ± 1.92 MPa) compared to findings of this present study. The higher shear bond strength could probably be due to variation in adhesive used by Niepraschk et al32 (2007) (Eagle Spectrum, American Orthodontics). Bishara et al14 (2009) and Carvalho et al20 (2013) found significantly lower shear bond strength 6.0 ± 3.1 MPa and 5.53 ± 2.28 MPa respectively, compared to the finding of this present study. The difference in mean shear bond strength found by Bishara et al14 (2009) and Carvalho et al20 (2013) probably could be due to low intensity of curing light used in their investigation. i.e 400 mW/cm2 and 700 mW/cm2 respectively. In Group A2, where brackets were cured with halogen light, as depicted in table-3, the mean shear bond strength is observed to be 9.84 ± 3.10 MPa. This finding is in agreement to the shear bond strength found by Dunn et al13 (2002) (8.8 ± 1.0 MPa), Banerjee et al17 (2011) (12.47 MPa) and Carvalho et al20 (2013) (6.21 ± 1.74 MPa). Finding of the present study is not in International Journal of Contemporary Orthodontics Vol. 1 Issue 1 . Sabane et al. agreement with studied by Bishara et al14 (2003) (5.1 ± 2.5 MPa), Niepraschk et al32 (2007) (48.35 ± 1.87 MPa) and Penido et al33 (2009) (4.21 ± 1.18 MPa). The variation could be due to low intensity light cure used by Bishara et al14 (2003) (400 mW/cm2) and Penido et al33 (2009) (500 mW/cm2). The higher shear bond found by Niepraschk et al32 (2007) probably could be due to variation in adhesive used (Eagle Spectrum, American Orthodontics). between the mean shear bond strengths with use of LED or Halogen curing light as p values are greater than 0.05 (A1 vs A2-p=0.281, B1 vs B2-p=0.349 and C1 vs C2-p=0.371). These findings are in agreement with Di Nicolo et al34 (2008), Penido et al33 (2009), Carvalho et al20 (2013) and Niepraschk et al32 (2007). This means that the shear bond strength may not be significantly affected by use of either LED or Halogen light sources. Groups B- Primer applied on the bracket base but not cured Adhesive remnant index In group B1, where brackets were cured with LED light, as depicted in table-3, the mean shear bond strength is observed to be 11.37 ± 3.42 MPa. In group B2, where brackets were cured with halogen light, as depicted in table-3, the mean shear bond strength is observed to be 10.25 ± 4.06 MPa. These results could not be compared to other studies as a similar method of bonding was not found in the literature. Groups C- Primer applied on the bracket base and cured In group C1, where brackets were cured with LED light, as depicted in table-3, the mean shear bond strength is observed to be 8.79 ± 3.23 MPa. Tukkarahraman et al15 (2005) found higher shear bond strength (23.86 ± 6.20 MPa) when primer was precured on the bracket base and brackets were cured with LED light. These findings are in discordance with present study. In group C2, where brackets were cured with halogen light, as depicted in table-3, the mean shear bond strength is observed to be 7.92 ± 2.85 MPa. Turkkahraman et al15 (2005) found higher shear bond strength (17.38 ± 5.41 MPa) when primer was precured on the bracket base and brackets were cured with halogen light. This finding is in disagreement with the finding of the present study probably due to low cross head speed of 0.5 mm/min used by Turkkahraman et al15 (2005). Table 7 depicts that, the samples in group A and group B had minimal adhesive remaining on to the tooth surface when brackets were debonded by using the ARI index described by Artun et al3 (1984). 30-35% of the samples in group A had a “0” score and 30-50% of the samples in group B had a “0” score. “0” score in ARI is when no residual adhesive remnant is found on the tooth surface after the bracket is debonded. Group C showed maximum adhesive remaining on to the tooth surface when brackets were debonded. 15% of the samples in group c had a “0” score. In the present study, it was found that samples in group A, where brackets were bonded without application of primer, showed maximum shear bond strength and minimal adhesive remaining on the tooth surface. It meant that bond failure occurred at enamel adhesive interface rather than adhesive bracket interface which was found out in the group C. These findings are in agreement with previous investigation9,18,22,26 where they found minimal adhesive remaining on the tooth surface when brackets were cured without application of primer on the bracket base. In group C, brackets were bonded with application of primer and curing. It also showed maximum adhesive remaining on the tooth surface after bracket debonding. This means that the bond strength between adhesive & tooth was stronger than bracket & adhesive. According to findings of the present study, it can be hypothesised that, to improve mechanical interlocking of adhesive and bracket mesh it is necessary that the adhesive should enter in between interlocking pattern of the bracket mesh. When primer is cured on the bracket base, it probably blocked the meshwork on the bracket bases, there by interfering with the mechanical interlocking of the adhesive in the meshwork and lowering the shear bond strength. Currently, research is on, to develop time-conserving and step reducing methods for bonding of orthodontic brackets. As is observed in the present study, curing of primer on the bracket base increases chair side time while bonding and debonding during removal of adhesive from the tooth surface which may possibly also damage enamel surface. This method has also shown to produce reduced shear bond strength. So, this method may not be as effective and efficient as the conventional bonding method. Comparison between the two different light sources CONCLUSION Table 6 depicts the comparison of the mean shear bond strength of groups where brackets were cured with LED and Halogen light sources. No statistically significant difference was found International Journal of Contemporary Orthodontics 1. The results of this study showed maximum shear bond strength and minimum adhesive remaining on the tooth 5 Sabane et al. surface in the group in which primer was not applied on the bracket base. 2. Primer applied on the bracket base and cured resulted in minimum shear bond strength and minimum adhesive remaining on the tooth surface. 3. The mean shear bond strengths observed in samples cured with LED are marginally higher than the mean shear bond strengths observed in samples cured with halogen light source. However the difference in shear bond strengths do not show statistical significance. Vol. 1 Issue 1 10. 11. 12. 13. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 6 Banerjee S, Banerjee R. A comparative evaluation of the shear bond strength of five different orthodontic bonding agents polymerized using halogen and lightemitting diode curing lights: An in vitro investigation. Ind J Dent Res. 2011;22(5):731-2. Sharma S, Tandon P, Nagar A, Singh GP, Singh A, Chugh VK. Comparison of shear bond strength of orthodontic brackets bonded with four different orthodontic adhesive. J Orthod Sci. 2014;3(2):29-33. Artun J, Berglund S. 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