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The impact of recycling and repeated recycling on shear bond strength of stainless steel orthodontic brackets
orthodontic waves 72 (2013) 16–22
Available online at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/odw
Research paper
The impact of recycling and repeated recycling on shear bond strength of stainless steel orthodontic brackets Faisal Ismail Bahnasi a,*, Aida Nur Ashikin Abd Rahman a, Mohamed Ibrahim Abu-Hassan b a b
Centre of Studies of Paediatric Dentistry and Orthodontic, Faculty of Dentistry, Universiti Teknologi MARA, Malaysia Centre of Studies in Restorative Dentistry, Faculty of Dentistry, Universiti Teknologi MARA, Malaysia
article info
abstract
Article history:
Purpose: To compare Shear Bond Strength (SBS) of new, recycled and repeated recycled
Received 29 June 2012
stainless steel orthodontic brackets with and without bracket base primer.
Received in revised form
Materials and methods: 120 extracted human premolar teeth and 120 premolar stainless steel
24 September 2012
orthodontic brackets were divided into six groups for 20 teeth each. Orthodontic brackets of
Accepted 4 October 2012
four groups were sandblasted with 50 mm aluminum oxide powder and half of them were
Published on line 24 November 2012
recycled for second time. Light cure orthodontic adhesive primer was applied for half of total brackets. Light cure composite was applied for all brackets and polymerization was carried
Keywords:
out. Groups 1–6 were subjected to a shear force within half hour to simulate as done clinically
Recycled bracket
with a universal testing machine (Shimadzu Trapezium X) until the bracket debond.
SBS
Results: The results of this study demonstrated that the mean SBS of all groups were more
Sandblasting
than that recommended by Reynolds in 1975, there was no significant difference between
Stainless steel orthodontic bracket
new and recycled brackets. Only one group (repeated recycled without bond) has significantly lower SBS. Conclusion: It can be concluded that: sandblasted recycled orthodontic brackets can be used as an alternative to new brackets which might provide cost reduction and in case of using repeated recycled brackets, better to apply bonding agent on bracket base for more bond strength. # 2012 Elsevier Ltd and the Japanese Orthodontic Society. All rights reserved.
1.
Introduction
1.1.
Adhesives
Early bonding systems consist of brackets welded onto bands bonded to enamel with zinc phosphate cement. Currently, it is easier to bond bracket to tooth surface using different adhesive materials. Efforts have been made to improve mechanical retention with various designs as mechanical
undercut into which the orthodontic adhesive extends before polymerization [1]. 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 [2]. According to Owens and Miller [3] ‘‘if bond strength is the primary consideration for choosing an adhesive, the composite resin should be utilized’’. These adhesives are used currently in orthodontic treatment to bond brackets to teeth
* Corresponding author at: Centre of Studies of Paediatric Dentistry and Orthodontic, Faculty of Dentistry, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia. Tel.: +60 17 3457096; fax: +60 3 55435803. E-mail address: [email protected] (F.I. Bahnasi). 1344-0241/$ – see front matter # 2012 Elsevier Ltd and the Japanese Orthodontic Society. All rights reserved. http://dx.doi.org/10.1016/j.odw.2012.10.001
orthodontic waves 72 (2013) 16–22
surfaces. To achieve the complex tooth movements during orthodontic therapy, clinician requires a reliable method of attachment to tooth tissue. The method of attachment should allow the delivery of orthodontic forces and should be sufficient to withstand masticatory loads. In addition, the attachment should be easily removed at the end of treatment, and result in minimal hard and soft tissue damage during application [1].
1.2.
Orthodontic brackets
There are different types of orthodontic brackets present in the market. Orthodontic brackets could be manufactured from stainless steel or esthetic material as: ceramic or plastic. Austenitic stainless steel alloy – used for bracket manufacturing – contains: 16–18% chromium, 10–14% nickel, 2–3% molybdenum and 0.03% carbon (value in wt.%) [4]. Stainless steel alloy shows some corrosion which may be identified at underlying adhesive layer in the form of discoloration. This discoloration is due to diffusion of corrosion products to the adhesive layer from the orthodontic bracket base [5]. Metal brackets are cheaper than ceramic and easy to be recycled to reuse it again in case of bond failure or repositioning of brackets. The mechanism of retention between teeth and brackets’ surfaces depends mainly on the undercuts in bracket mesh which facilitate adhesive to flow into the undercuts. Also bonding agent has a chemical bonding which acts together with the mechanical type of retention to avoid bond failure.
1.3.
Bracket recycling
Orthodontic bracket bond failure is common during orthodontic treatment. To decrease the cost of orthodontic treatment; any debonded bracket can be recycled to provide a second alternative to new brackets [6]. 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 that they are cheaper. However there are a number of disadvantages: Possibility of bracket distortion due to high occlusal force, or during debonding process in case of brackets repositioning [7]. Method of recycling process is time consuming. Lower SBS of recycled brackets in some methods such as using direct flame [8]. Aluminum oxide sandblasting is most popular method; different studies indicated that sandblasting method of recycling achieved enough SBS in comparison to new brackets [9–14].
1.4.
Repeated recycling
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
17
reusing the old one for a second time. Lunardi et al. [11] evaluated the effect of repeated recycling procedures on the SBS of different orthodontic adhesives. He used four types of adhesive materials, and he concluded that repeated bracket recycling using 50 mm aluminum oxide particle air abrasion had no effect on the SBS of metallic brackets bonded with different adhesive materials [11]. Summary of reviewed articles related to recycled stainless steel orthodontic brackets by sandblasting method was in Table 1. This study was focused on the SBS of new, recycled and repeated recycled stainless steel orthodontic brackets to enamel surfaces using sandblasting method; and the effect of bonding agent application to bracket base on the SBS of new, recycled and repeated recycle brackets.
2.
Materials and methods
120 extracted human premolars teeth were collected and all blood and adherent tissues were removed from the teeth. Teeth with caries or other visible defects or restorations were excluded. The teeth were then placed in distilled water in a refrigerator (i.e. nominal 4 8C). Storage medium was replaced periodically every one week to minimize deterioration (ISO/TS 11405:2003 E). 120 new stainless steel upper premolar orthodontic brackets (UnitekTM Gemini Bracket, Micro-Etch Base, 3M Unitek orthodontic products, Monorovia, CA, USA) were used. Bonding agent (Light Cure Orthodontic Adhesive Primer, 3M Unitek, Monorovia, CA, USA) was applied to paper pad, and then light cure was done for 10 s using Light-emitting diode (LED) (SDI radii-cal). Composite resin (3M Unitek TransbondTM XT Light Cure Composite, Monorovia, CA, USA) was applied on 80 of them. Brackets were positioned on the paper pad with gentle pressure and excess adhesive were removed with explorer. Polymerization was carried out using LED light for 20 s (10 s for each side mesial and distal). The light intensity of LED was 1800 MW/cm2. The power of device was calibrated before every cure using a dose meter device (SDI radiometer). The bonded brackets were separated from the paper pad using tweezers with light pressure. All 80 brackets were stored in distilled water for 24 h at 37 8C, and then subjected to the thermocycling test using Automatic Thermocycling Dipping Machine (ATDM T6PD, ZecttronSdn. Bhd.) for 500 cycles in distilled water between 5 8C and 55 8C. The exposure to each bath was 20 s and the transfer time between baths was 5 s (ISO/TS 11405:2003 E/5.2.4.5). After that these brackets were sandblasted with 50 mm aluminum oxide particle powder from a distance of 10 mm away from the nozzle of Microetcher (MicroEtcherTM Intraoral Sandblaster, Danville Materials, Innovative Dental Products, San Ramon, CA, USA) under the air pressure of 90 PSI for 20– 30 s depend on the amount of adhesive remaining. Procedure was done until bonding resin was totally removed from the bracket base and no longer visible to the naked eye. Repeat bonding, debonding, thermocycling and sandblasting were carried out for half of these brackets (i.e.: 40). The orthodontic brackets’ mesh were examined using scanning electron microscope (SEM) (Carl Zeiss SMT model: SUPRATM 40 VP) at magnification 100, 300 and 1000 to detect any distortion
18
Table 1 – Summary of reviewed articles related to recycled stainless steel orthodontic brackets. No.
Author
Year
Type of study
Aim
Methods and methodology Sample/ group
Khosravanifard et al.
2011
Vitro
To evaluate the effect of three resin-removal methods on the SBS of OB.
10
2
Faltermeiera and Behrb
2009
Vitro
20
3
Lunardi et al.
2008
Vitro
To compare the effect of a silicoating system, the influence of sandblasting, and the effect of a silane-coupling agent after sandblasting on the SBS of stainless steel foil-mesh OB. To evaluate the effect of two consecutive recycling procedures on the SBS of different orthodontic adhesives.
10
Edgewise standard OB with foil-meshed bases (Dentaurum) Ormesh OB (Ormco)
Edgewise OB (Dentaurum, Germany)
Method of recycling
Adhesive
L.C.U
Test machine
1. Tungsten carbide bur (TCB) using a highspeed hand piece 2. TCB using low speed 3. Aluminum oxide sandblasting 1. Aluminum oxide sandblasting 2. Silane-coupling agent + sandblasted base 3. Sandblasting + tribochemical coating + Silanecoupling agent Aluminum oxide sandblasting
No-Mix orthodontic bonding system (Dentaurum)
Chemical-cured
Zwick test machine (GmbH & Co. KG, Ulm, German)
Leo, #440, UK
Using recycledsandblasted brackets may provide sufficient RBS rates.
Transbond XT (3M Unitek, USA)
Ortholux LED L.C.U (3M Unitek, USA) for 20 s
1446, Zwick, Germany
Not used
Sandblasting and tribochemical treatment of stainless steel brackets improves SBS of recycled brackets.
Concise Orthodontic (3M Dental Products, USA) Transbond XT (3M Unitek, USA) Fuji Ortho LC (Gc Corporation, Japan) Smart Bond adhesive system (Sweden) Concise Orthodontic (3M Dental Products, USA)
Chemical-cured
Instron Corp., Canton, Mass
LEO 435 VP, Leo Electron Microscopy Ltd., England
Chemical-cured
Instron machine (Instron Corp., Canton, MA, USA)
LEO 435 VP; Leo Electron Microscopy Ltd., Cambridge, England
Two pastes of Ortho-Concise
Chemical-cured
Instron Corp., Canton, USA
Stereoscopic microscope
Repeated bracket recycling using 50mm aluminum oxide particle air abrasion did not affect the SBS of metallic brackets bonded with different orthodontic adhesives. The bracket recycling using 90microm aluminum oxide particle airabrasion was efficient and technically simple, and might provide cost reduction for orthodontists and patients alike. Attachments that had only been flamed had the lowest bond strength, followed by those that had been roughened with a greenstone.
4
Tavares et al.
2006
Vitro
To evaluate in vitro the SBS of [2_TD$IF]recycled OB.
10
S2CO3Z OB (Dental Morelli, Brazil)
1. Aluminum oxide sandblasting 2. Silicon carbide stone grinding using low speed 3. Cleaning by a specialized recycling contractor company (unknown technique)
5
Quick et al.
2005
Vitro
To determine a simple, effective method for reconditioning stainless steel OB.
14
Mini Diamond Twin (Ormco, USA)
-Flamed + Ultrasonic -Ground with greenstone -Flamed + Ultrasonic + Siliane -Flamed + Aluminum oxide sandblasting
SEM
Halogen L.C.U (3M Unitek, [19_TD$IF]Brazil) for 40 s Chemical-cured
orthodontic waves 72 (2013) 16–22
1
S/S OB type
Conclusion
Stereoscopic microscope (Swift Institute)
JOEL SEM (Model T200, JOEL Corp., Tokyo, Japan)
Instron, Model 8500 Plus Dynamic Testing System, USA
Instron universal testing machine (Model 4301, Instron Corp., Canton, MA, USA)
Not mentioned
Opitux 400 curing unit (Demetron Research Corp., Danbury, Conn.) for 40 s Rely-a-bond (Reliance, Inc., Itasca, Ill.) 1. Aluminum oxide sandblasting GAC microarch mandibular premolar OB (GAC) To compare the in vitro SBS of previously failed bonded metal brackets subjected to air abrasion with new untreated brackets. Vitro Sonis A.L. 7
1996
30
Transbond XT (3M Unitek, USA) 1. Green stone grinding 2. Aluminum oxide sandblasting 3. Direct flame 4. BigJane method 5. Buchman method Diamond standard edgewise twin OB (Ormco, USA) To compare the effect of five in-office OB reconditioning methods on SBS. Vitro Basudan and Al-Emran
2001
22
Adhesive Method of recycling S/S OB type Sample/ group
6
Author No.
Table 1 (Continued )
Aim Type of study Year
Methods and methodology
SEM Test machine L.C.U
Conclusion
Reconditioning with a green stone was not effective. Sandblasting method and direct flaming are recommended because of simplicity and time-saving advantages. This simple technique should allow for the immediate reuse of previously failed bonded metal brackets.
orthodontic waves 72 (2013) 16–22
19
during recycling procedure and compared the result with the new brackets (Fig. 1). Light cure orthodontic adhesive primer was added to half of total number of brackets. 120 extracted human premolars teeth and 120 orthodontic brackets were divided into six groups: Group 1 : New orthodontic bracket with bracket base bonding agent; Group 2 : New orthodontic bracket without bracket base bonding agent; Group 3 : Recycled orthodontic bracket with bracket base bonding agent; Group 4 : Recycled orthodontic bracket without bracket base bonding agent; Group 5 : Repeated recycled orthodontic bracket with bracket base bonding agent; Group 6 : Repeated recycled orthodontic bracket without bracket base bonding agent. The teeth were embedded horizontally in die stone in a plastic ring. The buccal surface of the teeth were be cleaned with a non-fluoridated prophylaxis powder (pumice stone) with a rubber cup at low speed hand piece for 15 s, then were rinsed with water for 10 s, and were dried with a light/brief stream of oil-free compressed air. The teeth were etched with 35% phosphoric acid gel for 15 s (UnitekTM Etching Gel Syringe Delivery System 35%, 3M Unitek orthodontic products, Monorovia, CA, USA), were thoroughly rinsed with water for 15 s 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, was thinned with gentle stream of air and was cured for 10 s according to the manufacturer’s recommendations and cured for 10 s. Primer was added to half of total number of brackets, cured for 10 s. Composite resin was placed to all bracket bases. The brackets were then firmly pressed to teeth surfaces with a plastic instrument and the excess adhesive were removed with an explorer before curing. Polymerization was carried out using LED light, and both mesial and distal sides were cured for 10 s each. After photo polymerization, Groups 1–6 were subjected to a shear force within half hour to simulate as done clinically with a universal testing machine (Shimadzu Trapezium X, Shimadzu Corporation, Kyoto, Japan) until the bracket debond as in Fig. 2A. The block with the tooth was placed vertically and the slot of the bracket was parallel to the jig blade (Fig. 2B). The sample were loaded till debond with a crosshead speed of 1 mm/min. The force in Newton (N) was recorded. The stress were calculated by dividing the force in Newton/surface area and calculated in MPa. F s ¼ ¼ N=mm2 A where s = stress, F = force in Newton, A = surface area in mm2. The teeth were examined by SEM at magnification 30 using SEM (HITACHI TM3000). Any remaining adhesive were assessed with the Adhesive Remnant Index (ARI) scores according to Artun and Bergland [12] with criteria illustrated in Table 2. Data were subjected to statistical analysis to identify differences in mean SBS between Groups 1 and 6. The analysis was carried out using the SPSS program (SPSS, Chicago, IL, USA). For group comparison, the single factor
20
orthodontic waves 72 (2013) 16–22
[(Fig._1)TD$IG]
Fig. 1 – Scanning electron microscopy (SEM) evaluation (100T, 300T, and 1000T) of the surfaces of new (I), recycled (II) and repeated recycled (III) metal orthodontic bracket bases. I A: SEM evaluation 100T of the surface of new bracket base. II A: SEM evaluation 100T of the surface of recycled bracket base. III A: SEM evaluation 100T of the surface of repeated recycled bracket base. I B: SEM evaluation 300T of the surface of new bracket base. II B: SEM evaluation 300T of the surface of recycled bracket base. III B: SEM evaluation 300T of the surface of repeated recycled bracket base. I C: SEM evaluation 1000T of the surface of new bracket base. II C: SEM evaluation 1000T of the surface of recycled bracket base. III C: SEM evaluation 1000T of the surface of repeated recycled bracket base.
variance analysis (ANOVA) was used. The level of significance was established at p < 0.05.
3.
Results
Mean and standard deviation for all groups were recorded in Table 3. Statistical analysis was performed using one-way ANOVA test, p < 0.05. Thus, at least one pair of means differ
significantly. The test of homogeneity of variances gave a pvalue of 0.858. Hence equality of variance assumption was met. Based on the Tukey’s post hoc test: the mean for the G1 (new with bond) was significantly higher compared to the G6 (repeated recycle without Bond).
Table 3 – One-way ANOVA for groups (1–6). Group
Table 2 – ARI Point Scale. Point 0 1 2 3
Description No adhesive left on the tooth. Less than half of the adhesive left on the tooth. More than half of the adhesive left on the tooth. All adhesive left on the tooth with distinct impression of the bracket mesh.
G1: G2: G3: G4: G5:
New with bond New without bond Recycle with bond Recycle without bond Repeated recycle with bond G6: Repeated recycle without bond
Mean
Std. Deviation
F
9.41 9.15 8.98 8.77 8.29
2.11 2.33 2.36 2.22 1.98
2.74
7.19
1.96
p-Value 0.023
21
orthodontic waves 72 (2013) 16–22
[(Fig._2)TD$IG]
Fig. 2 – (A) Shimadzu Precision Universal Testing Machine (Shimadzu Trapezium X, Shimadzu Corporation, Kyoto, Japan). (B) The Specimen with the Jig: the teeth were embedded horizontally in die stone in a plastic ring. The block with the tooth was placed vertically and the slot of the bracket was parallel to the jig blade (B).
Table 4 – Independent Samples t-test for sub-group 1 and sub-group 2.
Table 6 – Independent Samples t-test for sub-group 5 and sub-group 6.
Group
p-Value
Group
0.714
G5: Repeated recycle with bond G6: Repeated recycle without bond
G1: New with bond G2: New without bond
Mean
Std. Deviation
t
9.41 9.15
2.11 2.33
0.37
Mean
Std. Deviation
t
p-Value
8.29
1.98
1.78
7.19
1.96
0.084
Table 5 – Independent Samples t-test for sub-group 3 and sub-group 4. Group G3: Recycle with bond G4: Recycle without bond
Mean
Std. Deviation
t
8.98 8.77
2.36 2.22
0.28
p-Value
Table 7 – Independent Samples t-test for Group 4 with Groups 2 and 6, respectively.
0.779
Group
The Independent Samples t-test was used to compare between each categories’ groups 1 & 2, 3 & 4 and 5 & 6, there were not significantly different in the mean of the each two groups (Tables 4–6). Based on the Independent Samples t-test, the mean for the G6 (repeated recycled without bond) was significantly different compared to the mean for the G2 (new without bond) and G4 (recycled without bond). The G6 had significantly lower strength than both G2 and G4 (Table 7).
G6: Repeated recycled without bond G2: New without bond G4: Recycled without bond
Mean
Std. Deviation
t
p-Value
7.19
1.96
–
–
9.15 8.77
2.33 2.22
2.88 2.40
0.006 0.022
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 8).
Table 8 – Frequency of percentage distribution of the ARI scores in the study groups. Group G1: G2: G3: G4: G5: G6:
New with bond New without bond Recycle with bond Recycle without bond Repeated recycle with bond Repeated recycle without bond
ARI = 0, No. (%) 2 1 0 0 0 0
(10.0) (5.0) (0.0) (0.0) (0.0) (0.0)
ARI = 1, No. (%) 12 10 8 7 5 4
(60.0) (50.0) (40.0) (35.0) (25.0) (20.0)
ARI = 2, No. (%) 6 9 12 11 13 13
(30.0) (45.0) (60.0) (55.0) (65.0) (65.0)
ARI = 3, No. (%) 0 0 0 2 2 3
(0.0) (0.0) (0.0) (10.0) (10.0) (15.0)
22
orthodontic waves 72 (2013) 16–22
references
4.
Discussion
The present study measured the SBS of rebonded brackets that were recycled one and two times by sandblasting. The mean SBS of all groups were more than that recommended by Reynolds in 1975, as he stated that for brackets bonded to teeth to overcome intraoral and orthodontic forces, SBS in the range of 5.9–7.8 MPa was required [15]. Although G6 (repeated recycle without bond) showed lowest mean SBS, but still enough according to Reynolds [15]. The mean SBS of new bracket groups were slightly higher than recycled groups which also were slightly higher than repeated recycled groups. There was no significantly different between G2 and G4, while there was significantly different between G2 & G6 and G4 & G6. The G6 had significantly lower strength than the G2 and G4. The current study showed that using recycled-sandblasted brackets may provide a sufficient SBS rate which was in agreement with other studies [9,10,13,14,16], so sandblasted recycled bracket can be used instead of new one in case of bond failure for cost saving. However, in case of second bracket bond failure to the same bracket, clinician may prefer to use a new one instead of reuse it for second time. According to Lunardi et al. [11] repeated bracket recycling using sandblasting method did not affect the SBS of metallic brackets. While in the current study the SBS of repeated bracket recycling was less than SBS of new and recycled bracket, unless bonding agent was applied which showed enough SBS. The mean SBS of new, recycled and repeated recycled with bonding agent applied to bracket base were slightly higher but not significantly different from the mean SBS of the same groups without bonding agent. From this study, it can be concluded that: Sandblasted recycled orthodontic brackets can be used as an alternative to new brackets which might provide cost reduction. In case of using repeated recycled brackets, better to apply bonding agent on bracket base for more bond strength.
Acknowledgment This work was supported by Faculty of Dentistry, UITM, Malaysia.
[1] Knox J, Hubsch P, Jones ML, Middleton J. The influence of bracket base design on the strength of the bracket–cement interface. Br J Orthod 2000;27:249–54. [2] Sunna S, Rock WP. An ex vivo investigation into the bond strength of orthodontic brackets and adhesive system. Br J Orthod 1999;26:47–50. [3] Owens SE, Miller BH. A comparison of shear bond strengths of three visible light-cured orthodontic adhesives. Angle Orthod 2000;5:352–6. [4] Brantly WA, Eliades T. Orthodontic materials: scientific and clinical aspect. New York, USA: New York Press; 2001. p. 146. [5] Maijer R, Smith DC. Corrosion of orthodontic bracket bases. Am J Orthod Dentofacial Orthop 1982;81:43–8. [6] Wendl B, Muchitsch P, Pichelmayer M, Droschl H, Kern W. Comparative bond strength of new and reconditioned brackets and assessment of residual adhesive by light and electron microscopy. Eur J Orthod 2001;33:288–92. [7] Matasa GC. Pros and cons of the reuse of direct-bonded appliances. Am J Orthod Dentofacial Orthop 1989;96:72–6. [8] Quick AN, Harris AM, Joseph VP. Office reconditioning of stainless steel orthodontic attachments. Eur J Orthod 2005;27:231–6. [9] Khosravanifard B, Nemati-Anaraki S, Nili S, Rakhshan V. Assessing the effects of three resin removal methods and bracket sandblasting on shear bond strength of metallic orthodontic brackets and enamel surface. Orthod Waves 2011;70:27–38. [10] Faltermeiera A, Behrb M. Effect of bracket base conditioning. Am J Orthod Dentofacial Orthop 2009;1 . 12.e1–12.e5. [11] Lunardi N, Gameiro GH, Borges MB, Nouer DF, Vieira VC, Consani S, et al. The effect of repeated bracket recycling on the shear bond strength of different orthodontic adhesives. Braz J Oral Sci 2008;7:1648–52. [12] Artun A, Zachrisson B. Improving the handling properties of a composite resin. Am J Orthod Dentofacial Orthop 1982;81:269–76. [13] Tavares SW, Consani S, Nouer DF, Magnani MB, Nouer PR, Martins LM. Shear bond strength of new and recycled brackets to enamel. Braz Dent J 2006;17:44–8. [14] Basudan AM, Al-Emran SE. The effects of in-office reconditioning on the morphology of slots and bases of stainless steel brackets and on the shear/peel bond strength. J Orthod 2001;28:231–6. [15] Reynolds IR. A review of direct orthodontic bonding. Br J Orthod 1975;2:171–8. [16] 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.
Available online at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/odw
Research paper
The impact of recycling and repeated recycling on shear bond strength of stainless steel orthodontic brackets Faisal Ismail Bahnasi a,*, Aida Nur Ashikin Abd Rahman a, Mohamed Ibrahim Abu-Hassan b a b
Centre of Studies of Paediatric Dentistry and Orthodontic, Faculty of Dentistry, Universiti Teknologi MARA, Malaysia Centre of Studies in Restorative Dentistry, Faculty of Dentistry, Universiti Teknologi MARA, Malaysia
article info
abstract
Article history:
Purpose: To compare Shear Bond Strength (SBS) of new, recycled and repeated recycled
Received 29 June 2012
stainless steel orthodontic brackets with and without bracket base primer.
Received in revised form
Materials and methods: 120 extracted human premolar teeth and 120 premolar stainless steel
24 September 2012
orthodontic brackets were divided into six groups for 20 teeth each. Orthodontic brackets of
Accepted 4 October 2012
four groups were sandblasted with 50 mm aluminum oxide powder and half of them were
Published on line 24 November 2012
recycled for second time. Light cure orthodontic adhesive primer was applied for half of total brackets. Light cure composite was applied for all brackets and polymerization was carried
Keywords:
out. Groups 1–6 were subjected to a shear force within half hour to simulate as done clinically
Recycled bracket
with a universal testing machine (Shimadzu Trapezium X) until the bracket debond.
SBS
Results: The results of this study demonstrated that the mean SBS of all groups were more
Sandblasting
than that recommended by Reynolds in 1975, there was no significant difference between
Stainless steel orthodontic bracket
new and recycled brackets. Only one group (repeated recycled without bond) has significantly lower SBS. Conclusion: It can be concluded that: sandblasted recycled orthodontic brackets can be used as an alternative to new brackets which might provide cost reduction and in case of using repeated recycled brackets, better to apply bonding agent on bracket base for more bond strength. # 2012 Elsevier Ltd and the Japanese Orthodontic Society. All rights reserved.
1.
Introduction
1.1.
Adhesives
Early bonding systems consist of brackets welded onto bands bonded to enamel with zinc phosphate cement. Currently, it is easier to bond bracket to tooth surface using different adhesive materials. Efforts have been made to improve mechanical retention with various designs as mechanical
undercut into which the orthodontic adhesive extends before polymerization [1]. 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 [2]. According to Owens and Miller [3] ‘‘if bond strength is the primary consideration for choosing an adhesive, the composite resin should be utilized’’. These adhesives are used currently in orthodontic treatment to bond brackets to teeth
* Corresponding author at: Centre of Studies of Paediatric Dentistry and Orthodontic, Faculty of Dentistry, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia. Tel.: +60 17 3457096; fax: +60 3 55435803. E-mail address: [email protected] (F.I. Bahnasi). 1344-0241/$ – see front matter # 2012 Elsevier Ltd and the Japanese Orthodontic Society. All rights reserved. http://dx.doi.org/10.1016/j.odw.2012.10.001
orthodontic waves 72 (2013) 16–22
surfaces. To achieve the complex tooth movements during orthodontic therapy, clinician requires a reliable method of attachment to tooth tissue. The method of attachment should allow the delivery of orthodontic forces and should be sufficient to withstand masticatory loads. In addition, the attachment should be easily removed at the end of treatment, and result in minimal hard and soft tissue damage during application [1].
1.2.
Orthodontic brackets
There are different types of orthodontic brackets present in the market. Orthodontic brackets could be manufactured from stainless steel or esthetic material as: ceramic or plastic. Austenitic stainless steel alloy – used for bracket manufacturing – contains: 16–18% chromium, 10–14% nickel, 2–3% molybdenum and 0.03% carbon (value in wt.%) [4]. Stainless steel alloy shows some corrosion which may be identified at underlying adhesive layer in the form of discoloration. This discoloration is due to diffusion of corrosion products to the adhesive layer from the orthodontic bracket base [5]. Metal brackets are cheaper than ceramic and easy to be recycled to reuse it again in case of bond failure or repositioning of brackets. The mechanism of retention between teeth and brackets’ surfaces depends mainly on the undercuts in bracket mesh which facilitate adhesive to flow into the undercuts. Also bonding agent has a chemical bonding which acts together with the mechanical type of retention to avoid bond failure.
1.3.
Bracket recycling
Orthodontic bracket bond failure is common during orthodontic treatment. To decrease the cost of orthodontic treatment; any debonded bracket can be recycled to provide a second alternative to new brackets [6]. 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 that they are cheaper. However there are a number of disadvantages: Possibility of bracket distortion due to high occlusal force, or during debonding process in case of brackets repositioning [7]. Method of recycling process is time consuming. Lower SBS of recycled brackets in some methods such as using direct flame [8]. Aluminum oxide sandblasting is most popular method; different studies indicated that sandblasting method of recycling achieved enough SBS in comparison to new brackets [9–14].
1.4.
Repeated recycling
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
17
reusing the old one for a second time. Lunardi et al. [11] evaluated the effect of repeated recycling procedures on the SBS of different orthodontic adhesives. He used four types of adhesive materials, and he concluded that repeated bracket recycling using 50 mm aluminum oxide particle air abrasion had no effect on the SBS of metallic brackets bonded with different adhesive materials [11]. Summary of reviewed articles related to recycled stainless steel orthodontic brackets by sandblasting method was in Table 1. This study was focused on the SBS of new, recycled and repeated recycled stainless steel orthodontic brackets to enamel surfaces using sandblasting method; and the effect of bonding agent application to bracket base on the SBS of new, recycled and repeated recycle brackets.
2.
Materials and methods
120 extracted human premolars teeth were collected and all blood and adherent tissues were removed from the teeth. Teeth with caries or other visible defects or restorations were excluded. The teeth were then placed in distilled water in a refrigerator (i.e. nominal 4 8C). Storage medium was replaced periodically every one week to minimize deterioration (ISO/TS 11405:2003 E). 120 new stainless steel upper premolar orthodontic brackets (UnitekTM Gemini Bracket, Micro-Etch Base, 3M Unitek orthodontic products, Monorovia, CA, USA) were used. Bonding agent (Light Cure Orthodontic Adhesive Primer, 3M Unitek, Monorovia, CA, USA) was applied to paper pad, and then light cure was done for 10 s using Light-emitting diode (LED) (SDI radii-cal). Composite resin (3M Unitek TransbondTM XT Light Cure Composite, Monorovia, CA, USA) was applied on 80 of them. Brackets were positioned on the paper pad with gentle pressure and excess adhesive were removed with explorer. Polymerization was carried out using LED light for 20 s (10 s for each side mesial and distal). The light intensity of LED was 1800 MW/cm2. The power of device was calibrated before every cure using a dose meter device (SDI radiometer). The bonded brackets were separated from the paper pad using tweezers with light pressure. All 80 brackets were stored in distilled water for 24 h at 37 8C, and then subjected to the thermocycling test using Automatic Thermocycling Dipping Machine (ATDM T6PD, ZecttronSdn. Bhd.) for 500 cycles in distilled water between 5 8C and 55 8C. The exposure to each bath was 20 s and the transfer time between baths was 5 s (ISO/TS 11405:2003 E/5.2.4.5). After that these brackets were sandblasted with 50 mm aluminum oxide particle powder from a distance of 10 mm away from the nozzle of Microetcher (MicroEtcherTM Intraoral Sandblaster, Danville Materials, Innovative Dental Products, San Ramon, CA, USA) under the air pressure of 90 PSI for 20– 30 s depend on the amount of adhesive remaining. Procedure was done until bonding resin was totally removed from the bracket base and no longer visible to the naked eye. Repeat bonding, debonding, thermocycling and sandblasting were carried out for half of these brackets (i.e.: 40). The orthodontic brackets’ mesh were examined using scanning electron microscope (SEM) (Carl Zeiss SMT model: SUPRATM 40 VP) at magnification 100, 300 and 1000 to detect any distortion
18
Table 1 – Summary of reviewed articles related to recycled stainless steel orthodontic brackets. No.
Author
Year
Type of study
Aim
Methods and methodology Sample/ group
Khosravanifard et al.
2011
Vitro
To evaluate the effect of three resin-removal methods on the SBS of OB.
10
2
Faltermeiera and Behrb
2009
Vitro
20
3
Lunardi et al.
2008
Vitro
To compare the effect of a silicoating system, the influence of sandblasting, and the effect of a silane-coupling agent after sandblasting on the SBS of stainless steel foil-mesh OB. To evaluate the effect of two consecutive recycling procedures on the SBS of different orthodontic adhesives.
10
Edgewise standard OB with foil-meshed bases (Dentaurum) Ormesh OB (Ormco)
Edgewise OB (Dentaurum, Germany)
Method of recycling
Adhesive
L.C.U
Test machine
1. Tungsten carbide bur (TCB) using a highspeed hand piece 2. TCB using low speed 3. Aluminum oxide sandblasting 1. Aluminum oxide sandblasting 2. Silane-coupling agent + sandblasted base 3. Sandblasting + tribochemical coating + Silanecoupling agent Aluminum oxide sandblasting
No-Mix orthodontic bonding system (Dentaurum)
Chemical-cured
Zwick test machine (GmbH & Co. KG, Ulm, German)
Leo, #440, UK
Using recycledsandblasted brackets may provide sufficient RBS rates.
Transbond XT (3M Unitek, USA)
Ortholux LED L.C.U (3M Unitek, USA) for 20 s
1446, Zwick, Germany
Not used
Sandblasting and tribochemical treatment of stainless steel brackets improves SBS of recycled brackets.
Concise Orthodontic (3M Dental Products, USA) Transbond XT (3M Unitek, USA) Fuji Ortho LC (Gc Corporation, Japan) Smart Bond adhesive system (Sweden) Concise Orthodontic (3M Dental Products, USA)
Chemical-cured
Instron Corp., Canton, Mass
LEO 435 VP, Leo Electron Microscopy Ltd., England
Chemical-cured
Instron machine (Instron Corp., Canton, MA, USA)
LEO 435 VP; Leo Electron Microscopy Ltd., Cambridge, England
Two pastes of Ortho-Concise
Chemical-cured
Instron Corp., Canton, USA
Stereoscopic microscope
Repeated bracket recycling using 50mm aluminum oxide particle air abrasion did not affect the SBS of metallic brackets bonded with different orthodontic adhesives. The bracket recycling using 90microm aluminum oxide particle airabrasion was efficient and technically simple, and might provide cost reduction for orthodontists and patients alike. Attachments that had only been flamed had the lowest bond strength, followed by those that had been roughened with a greenstone.
4
Tavares et al.
2006
Vitro
To evaluate in vitro the SBS of [2_TD$IF]recycled OB.
10
S2CO3Z OB (Dental Morelli, Brazil)
1. Aluminum oxide sandblasting 2. Silicon carbide stone grinding using low speed 3. Cleaning by a specialized recycling contractor company (unknown technique)
5
Quick et al.
2005
Vitro
To determine a simple, effective method for reconditioning stainless steel OB.
14
Mini Diamond Twin (Ormco, USA)
-Flamed + Ultrasonic -Ground with greenstone -Flamed + Ultrasonic + Siliane -Flamed + Aluminum oxide sandblasting
SEM
Halogen L.C.U (3M Unitek, [19_TD$IF]Brazil) for 40 s Chemical-cured
orthodontic waves 72 (2013) 16–22
1
S/S OB type
Conclusion
Stereoscopic microscope (Swift Institute)
JOEL SEM (Model T200, JOEL Corp., Tokyo, Japan)
Instron, Model 8500 Plus Dynamic Testing System, USA
Instron universal testing machine (Model 4301, Instron Corp., Canton, MA, USA)
Not mentioned
Opitux 400 curing unit (Demetron Research Corp., Danbury, Conn.) for 40 s Rely-a-bond (Reliance, Inc., Itasca, Ill.) 1. Aluminum oxide sandblasting GAC microarch mandibular premolar OB (GAC) To compare the in vitro SBS of previously failed bonded metal brackets subjected to air abrasion with new untreated brackets. Vitro Sonis A.L. 7
1996
30
Transbond XT (3M Unitek, USA) 1. Green stone grinding 2. Aluminum oxide sandblasting 3. Direct flame 4. BigJane method 5. Buchman method Diamond standard edgewise twin OB (Ormco, USA) To compare the effect of five in-office OB reconditioning methods on SBS. Vitro Basudan and Al-Emran
2001
22
Adhesive Method of recycling S/S OB type Sample/ group
6
Author No.
Table 1 (Continued )
Aim Type of study Year
Methods and methodology
SEM Test machine L.C.U
Conclusion
Reconditioning with a green stone was not effective. Sandblasting method and direct flaming are recommended because of simplicity and time-saving advantages. This simple technique should allow for the immediate reuse of previously failed bonded metal brackets.
orthodontic waves 72 (2013) 16–22
19
during recycling procedure and compared the result with the new brackets (Fig. 1). Light cure orthodontic adhesive primer was added to half of total number of brackets. 120 extracted human premolars teeth and 120 orthodontic brackets were divided into six groups: Group 1 : New orthodontic bracket with bracket base bonding agent; Group 2 : New orthodontic bracket without bracket base bonding agent; Group 3 : Recycled orthodontic bracket with bracket base bonding agent; Group 4 : Recycled orthodontic bracket without bracket base bonding agent; Group 5 : Repeated recycled orthodontic bracket with bracket base bonding agent; Group 6 : Repeated recycled orthodontic bracket without bracket base bonding agent. The teeth were embedded horizontally in die stone in a plastic ring. The buccal surface of the teeth were be cleaned with a non-fluoridated prophylaxis powder (pumice stone) with a rubber cup at low speed hand piece for 15 s, then were rinsed with water for 10 s, and were dried with a light/brief stream of oil-free compressed air. The teeth were etched with 35% phosphoric acid gel for 15 s (UnitekTM Etching Gel Syringe Delivery System 35%, 3M Unitek orthodontic products, Monorovia, CA, USA), were thoroughly rinsed with water for 15 s 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, was thinned with gentle stream of air and was cured for 10 s according to the manufacturer’s recommendations and cured for 10 s. Primer was added to half of total number of brackets, cured for 10 s. Composite resin was placed to all bracket bases. The brackets were then firmly pressed to teeth surfaces with a plastic instrument and the excess adhesive were removed with an explorer before curing. Polymerization was carried out using LED light, and both mesial and distal sides were cured for 10 s each. After photo polymerization, Groups 1–6 were subjected to a shear force within half hour to simulate as done clinically with a universal testing machine (Shimadzu Trapezium X, Shimadzu Corporation, Kyoto, Japan) until the bracket debond as in Fig. 2A. The block with the tooth was placed vertically and the slot of the bracket was parallel to the jig blade (Fig. 2B). The sample were loaded till debond with a crosshead speed of 1 mm/min. The force in Newton (N) was recorded. The stress were calculated by dividing the force in Newton/surface area and calculated in MPa. F s ¼ ¼ N=mm2 A where s = stress, F = force in Newton, A = surface area in mm2. The teeth were examined by SEM at magnification 30 using SEM (HITACHI TM3000). Any remaining adhesive were assessed with the Adhesive Remnant Index (ARI) scores according to Artun and Bergland [12] with criteria illustrated in Table 2. Data were subjected to statistical analysis to identify differences in mean SBS between Groups 1 and 6. The analysis was carried out using the SPSS program (SPSS, Chicago, IL, USA). For group comparison, the single factor
20
orthodontic waves 72 (2013) 16–22
[(Fig._1)TD$IG]
Fig. 1 – Scanning electron microscopy (SEM) evaluation (100T, 300T, and 1000T) of the surfaces of new (I), recycled (II) and repeated recycled (III) metal orthodontic bracket bases. I A: SEM evaluation 100T of the surface of new bracket base. II A: SEM evaluation 100T of the surface of recycled bracket base. III A: SEM evaluation 100T of the surface of repeated recycled bracket base. I B: SEM evaluation 300T of the surface of new bracket base. II B: SEM evaluation 300T of the surface of recycled bracket base. III B: SEM evaluation 300T of the surface of repeated recycled bracket base. I C: SEM evaluation 1000T of the surface of new bracket base. II C: SEM evaluation 1000T of the surface of recycled bracket base. III C: SEM evaluation 1000T of the surface of repeated recycled bracket base.
variance analysis (ANOVA) was used. The level of significance was established at p < 0.05.
3.
Results
Mean and standard deviation for all groups were recorded in Table 3. Statistical analysis was performed using one-way ANOVA test, p < 0.05. Thus, at least one pair of means differ
significantly. The test of homogeneity of variances gave a pvalue of 0.858. Hence equality of variance assumption was met. Based on the Tukey’s post hoc test: the mean for the G1 (new with bond) was significantly higher compared to the G6 (repeated recycle without Bond).
Table 3 – One-way ANOVA for groups (1–6). Group
Table 2 – ARI Point Scale. Point 0 1 2 3
Description No adhesive left on the tooth. Less than half of the adhesive left on the tooth. More than half of the adhesive left on the tooth. All adhesive left on the tooth with distinct impression of the bracket mesh.
G1: G2: G3: G4: G5:
New with bond New without bond Recycle with bond Recycle without bond Repeated recycle with bond G6: Repeated recycle without bond
Mean
Std. Deviation
F
9.41 9.15 8.98 8.77 8.29
2.11 2.33 2.36 2.22 1.98
2.74
7.19
1.96
p-Value 0.023
21
orthodontic waves 72 (2013) 16–22
[(Fig._2)TD$IG]
Fig. 2 – (A) Shimadzu Precision Universal Testing Machine (Shimadzu Trapezium X, Shimadzu Corporation, Kyoto, Japan). (B) The Specimen with the Jig: the teeth were embedded horizontally in die stone in a plastic ring. The block with the tooth was placed vertically and the slot of the bracket was parallel to the jig blade (B).
Table 4 – Independent Samples t-test for sub-group 1 and sub-group 2.
Table 6 – Independent Samples t-test for sub-group 5 and sub-group 6.
Group
p-Value
Group
0.714
G5: Repeated recycle with bond G6: Repeated recycle without bond
G1: New with bond G2: New without bond
Mean
Std. Deviation
t
9.41 9.15
2.11 2.33
0.37
Mean
Std. Deviation
t
p-Value
8.29
1.98
1.78
7.19
1.96
0.084
Table 5 – Independent Samples t-test for sub-group 3 and sub-group 4. Group G3: Recycle with bond G4: Recycle without bond
Mean
Std. Deviation
t
8.98 8.77
2.36 2.22
0.28
p-Value
Table 7 – Independent Samples t-test for Group 4 with Groups 2 and 6, respectively.
0.779
Group
The Independent Samples t-test was used to compare between each categories’ groups 1 & 2, 3 & 4 and 5 & 6, there were not significantly different in the mean of the each two groups (Tables 4–6). Based on the Independent Samples t-test, the mean for the G6 (repeated recycled without bond) was significantly different compared to the mean for the G2 (new without bond) and G4 (recycled without bond). The G6 had significantly lower strength than both G2 and G4 (Table 7).
G6: Repeated recycled without bond G2: New without bond G4: Recycled without bond
Mean
Std. Deviation
t
p-Value
7.19
1.96
–
–
9.15 8.77
2.33 2.22
2.88 2.40
0.006 0.022
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 8).
Table 8 – Frequency of percentage distribution of the ARI scores in the study groups. Group G1: G2: G3: G4: G5: G6:
New with bond New without bond Recycle with bond Recycle without bond Repeated recycle with bond Repeated recycle without bond
ARI = 0, No. (%) 2 1 0 0 0 0
(10.0) (5.0) (0.0) (0.0) (0.0) (0.0)
ARI = 1, No. (%) 12 10 8 7 5 4
(60.0) (50.0) (40.0) (35.0) (25.0) (20.0)
ARI = 2, No. (%) 6 9 12 11 13 13
(30.0) (45.0) (60.0) (55.0) (65.0) (65.0)
ARI = 3, No. (%) 0 0 0 2 2 3
(0.0) (0.0) (0.0) (10.0) (10.0) (15.0)
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orthodontic waves 72 (2013) 16–22
references
4.
Discussion
The present study measured the SBS of rebonded brackets that were recycled one and two times by sandblasting. The mean SBS of all groups were more than that recommended by Reynolds in 1975, as he stated that for brackets bonded to teeth to overcome intraoral and orthodontic forces, SBS in the range of 5.9–7.8 MPa was required [15]. Although G6 (repeated recycle without bond) showed lowest mean SBS, but still enough according to Reynolds [15]. The mean SBS of new bracket groups were slightly higher than recycled groups which also were slightly higher than repeated recycled groups. There was no significantly different between G2 and G4, while there was significantly different between G2 & G6 and G4 & G6. The G6 had significantly lower strength than the G2 and G4. The current study showed that using recycled-sandblasted brackets may provide a sufficient SBS rate which was in agreement with other studies [9,10,13,14,16], so sandblasted recycled bracket can be used instead of new one in case of bond failure for cost saving. However, in case of second bracket bond failure to the same bracket, clinician may prefer to use a new one instead of reuse it for second time. According to Lunardi et al. [11] repeated bracket recycling using sandblasting method did not affect the SBS of metallic brackets. While in the current study the SBS of repeated bracket recycling was less than SBS of new and recycled bracket, unless bonding agent was applied which showed enough SBS. The mean SBS of new, recycled and repeated recycled with bonding agent applied to bracket base were slightly higher but not significantly different from the mean SBS of the same groups without bonding agent. From this study, it can be concluded that: Sandblasted recycled orthodontic brackets can be used as an alternative to new brackets which might provide cost reduction. In case of using repeated recycled brackets, better to apply bonding agent on bracket base for more bond strength.
Acknowledgment This work was supported by Faculty of Dentistry, UITM, Malaysia.
[1] Knox J, Hubsch P, Jones ML, Middleton J. The influence of bracket base design on the strength of the bracket–cement interface. Br J Orthod 2000;27:249–54. [2] Sunna S, Rock WP. An ex vivo investigation into the bond strength of orthodontic brackets and adhesive system. Br J Orthod 1999;26:47–50. [3] Owens SE, Miller BH. A comparison of shear bond strengths of three visible light-cured orthodontic adhesives. Angle Orthod 2000;5:352–6. [4] Brantly WA, Eliades T. Orthodontic materials: scientific and clinical aspect. New York, USA: New York Press; 2001. p. 146. [5] Maijer R, Smith DC. Corrosion of orthodontic bracket bases. Am J Orthod Dentofacial Orthop 1982;81:43–8. [6] Wendl B, Muchitsch P, Pichelmayer M, Droschl H, Kern W. Comparative bond strength of new and reconditioned brackets and assessment of residual adhesive by light and electron microscopy. Eur J Orthod 2001;33:288–92. [7] Matasa GC. Pros and cons of the reuse of direct-bonded appliances. Am J Orthod Dentofacial Orthop 1989;96:72–6. [8] Quick AN, Harris AM, Joseph VP. Office reconditioning of stainless steel orthodontic attachments. Eur J Orthod 2005;27:231–6. [9] Khosravanifard B, Nemati-Anaraki S, Nili S, Rakhshan V. Assessing the effects of three resin removal methods and bracket sandblasting on shear bond strength of metallic orthodontic brackets and enamel surface. Orthod Waves 2011;70:27–38. [10] Faltermeiera A, Behrb M. Effect of bracket base conditioning. Am J Orthod Dentofacial Orthop 2009;1 . 12.e1–12.e5. [11] Lunardi N, Gameiro GH, Borges MB, Nouer DF, Vieira VC, Consani S, et al. The effect of repeated bracket recycling on the shear bond strength of different orthodontic adhesives. Braz J Oral Sci 2008;7:1648–52. [12] Artun A, Zachrisson B. Improving the handling properties of a composite resin. Am J Orthod Dentofacial Orthop 1982;81:269–76. [13] Tavares SW, Consani S, Nouer DF, Magnani MB, Nouer PR, Martins LM. Shear bond strength of new and recycled brackets to enamel. Braz Dent J 2006;17:44–8. [14] Basudan AM, Al-Emran SE. The effects of in-office reconditioning on the morphology of slots and bases of stainless steel brackets and on the shear/peel bond strength. J Orthod 2001;28:231–6. [15] Reynolds IR. A review of direct orthodontic bonding. Br J Orthod 1975;2:171–8. [16] 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.