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Table of Contents   
ORIGINAL RESEARCH  
Year : 2015  |  Volume : 26  |  Issue : 4  |  Page : 411-415
Bond efficacy of recycled orthodontic brackets: A comparative in vitro evaluation of two methods


1 Department of Orthodontics, YMT Dental College and Hospital, Navi Mumbai, Maharashtra, India
2 Private Practitioner, Mumbai, Maharashtra, India

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Date of Submission26-Jun-2015
Date of Decision02-Jul-2015
Date of Acceptance09-Jul-2015
Date of Web Publication20-Oct-2015
 

   Abstract 

Context: Recycling of orthodontic brackets in developing orthodontic economies is an extremely common procedure. Bonding protocols and reliability of these brackets is, however, questionable, and still the subject of research. Aims: The aim was to evaluate and compare the shear bond strength of brackets recycled with sandblasting and silicoating. Materials and Methods: Ninety extracted human premolars were bonded with 0.022” SS brackets (American Orthodontics, Sheboygan USA) and then debonded. The debonded brackets were divided into three groups of 30 each. Group I: Sandblasting with 50-μm aluminum oxide (control group) Group II: Sandblasting with 50-μm aluminum oxide followed by metal primer application Group III: Silicoating with 30-μm Cojet sand followed by silane application and rebonded with Transbond XT. The sandblasted brackets and silicoated brackets were viewed under the scanning electron microscope, immediately after surface conditioning before rebonding. The shear bond strength with each group was tested. Statistical Analysis Used: One-way analysis of variance, post-hoc Scheffe multiple comparison tests. Results: The results showed that sandblasting created more irregularities and deeper erosions while silica coating created superficial irregularities and shallow erosions.

Keywords: Bonding, etching, orthodontic brackets, recycling, silane

How to cite this article:
Shetty V, Shekatkar Y, Kumbhat N, Gautam G, Karbelkar S, Vandekar M. Bond efficacy of recycled orthodontic brackets: A comparative in vitro evaluation of two methods. Indian J Dent Res 2015;26:411-5

How to cite this URL:
Shetty V, Shekatkar Y, Kumbhat N, Gautam G, Karbelkar S, Vandekar M. Bond efficacy of recycled orthodontic brackets: A comparative in vitro evaluation of two methods. Indian J Dent Res [serial online] 2015 [cited 2019 Jul 19];26:411-5. Available from: http://www.ijdr.in/text.asp?2015/26/4/411/167635


Debonding of orthodontic brackets can occasionally occur, making it necessary to either rebond the dislodged bracket, bond a new bracket, or use a bracket welded to an orthodontic band in case of persistent bond failure.

The recycling process basically consists of removal of remnants of bonding agents, thus allowing the brackets to be reused without causing damage to the retention mesh and preserving its retentive characteristics.[1] Various methods are used for bracket recycling such as use of heat,[2] chemicals,[3],[4],[5] abrasives.[6] The shortcomings of recycled brackets are in terms of biosafety and increased friction with the archwire, due to distortion of the bracket slot.

The present study evaluates the efficacy of two surface treatments on debonded stainless steel brackets, in terms of shear bond strength after rebonding. As well as, to examine the surface characteristics of bracket bases using scanning electron microscope.


   Subjects and Methods Top


An in vitro study was carried out to evaluate and compare the shear bond strength of brackets recycled with sandblasting and silicoating. Ninety extracted human premolars were selected, cleaned of soft tissue and stored in distilled water at room temperature prior to bonding. The criteria for selection included:

  • Good morphology with intact enamel surface, devoid of any developmental defects
  • No pretreatment with any chemical agents
  • No cracks on extraction surfaces
  • The absence of carious lesions.


Selected premolars were bonded with ninety standard stainless steel brackets (0.022 with 80 gauge mesh, American Orthodontics, Sheboygan, USA). The bracket base area was 10.258 mm 2 as specified by the manufacturer. Transbond™ XT Light Cure Orthodontic Adhesive System (3M Unitek, Monvrovia, USA) was used as the bonding material. Bonded brackets were separated from the tooth. All the debonded brackets were divided into three groups of 30 each.

Preparation of samples

Enamel surface of all the debonded teeth was polished with pumice slurry using rubber prophylactic cups. Samples were then rinsed thoroughly with water and dried with oil and moisture free air spray. Enamel was then etched with 37% phosphoric acid.

Group I

The 30 bracket samples in this group were subjected to sandblasting procedures. Sandblasting with 50 mm aluminum oxide was done vertically from a distance of 10 mm standardized with the help of a jig with 2.5 bar pressure using a sandblaster until bonding resin was totally removed from the bracket brace. Approximately, 15–20 s were required. A sandblasted bracket was then viewed under scanning electron microscope (Jeol JSM-6380 LA Japan) for ×30, ×150, ×300, ×1000.

Group II

The 30 bracket samples in this group were subjected to sandblasting procedures with 50 mm aluminum oxide was done vertically from a distance of 10 mm standardized with the help of a jig with 2.5 bar pressure using a sandblaster until bonding resin was totally removed from the bracket brace. Approximately, 15–20 s were required. The metal primer (Vivadent) was then applied to the conditioned bracket base and allowed to dry for 3 min.

Group III

The 30 bracket samples in this group were subjected to the silicoating procedure. Silica coating with 30 mm silicon dioxide (Cojet sand – 3M ESPE) was done vertically from a distance of 10 mm standardized with the help of a jig with 2.5 bar pressure using a sandblaster until bonding resin was totally removed from the bracket base. Approximately, 15–20 s were required. A silicoated bracket was then viewed under scanning electron microscope for ×30, ×150, ×300, ×1000. Silane (ESPE Sil, 3M ESPE) was then applied to the conditioned bracket base and allowed to dry for 5 min.

After etching and drying, a single layer of Transbond XT primer was applied on the enamel surface. Immediately after the priming procedure, the surface conditioned brackets were rebonded with a light cure adhesive system, Transbond XT. After bonding all specimens were immersed in water, and testing for the shear bond strength was done after 24 h.

Testing of samples

The shear bond strength of the samples was evaluated using the universal testing machine, 5567 model Instron. Each tooth was oriented so that its labial surface was parallel to the shear force during the test. The tooth was mounted on the machine such that the root of the tooth was held firmly between the lower jaws of the machine. A screwdriver rod with a knife-edged clamped to the self-centering upper jaw of the testing machine. The edge of the rod was placed in such a manner that it sliced/sheared the bracket off the tooth surface. Shear force was applied to the enamel adhesive interface.

Each specimen was stressed in an occlusogingival direction to the failure with a cross head of 1 mm/min. A computer electronically connected to the testing machine recorded, the results of each test as the force needed to debond the brackets in Kg, these values were later converted to megapascals (MPa) by using the formula:



where,

9.81 = Gravitational acceleration constant,

10.258 mm 2 = Bracket base area as provided by the manufacturer.

The MPa values were then tabulated for Group I, II, and III, respectively.


   Results Top


The sandblasted and silicoated brackets were viewed under scanning electron microscope (Jeol JSM-6380 LA, Japan). Sandblasting and silicoating procedures changed the bracket base surfaces significantly. Sandblasting created more irregularities and deeper erosions while silicoating created superficial irregularities and shallow erosions silicoating process resulted in charring of the bracket base surface due to the tribochemical reaction as silica was coated on the bracket base.

Statistical analysis

The values obtained from the bond strength testing were subjected to statistical analysis using SPSS Version 15 (SPSS INC., Chicago IL). The descriptive statistics for the three groups [Table 1] showed it to be suitable for analysis by using parametric methods, and hence were evaluated with one-way analysis of variance (ANOVA) and post-hoc Scheffe multiple comparison tests. The level of significance was set at P < 0.05.
Table 1: Descriptive statistics of all the three groups (values in MPa) and SEM

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   Discussion Top


Successful orthodontic treatment depends on the adequate bond strength of brackets to enamel. It is extremely difficult to obtain adequate bond strength with recycled metal brackets adding to the fear of debonding. Metal primers have claimed to promote adhesion to metallic surfaces, as also Cojet sand (3M ESPE) has claimed to be effective in increasing the bond strength due to the tribochemical reaction.

In the present study, the brackets were recycled and bonded to the tooth surface. Later, the shear bond strength tests were carried out with standard methods by the same operator to minimize technique inconsistencies. The samples were kept in distilled water at 37°C for 24 h because orthodontic adhesives are routinely subjected to thermal changes in the oral cavity.[7]

According to Tavares et al.,[8] aluminum oxide air-abrasion has been proved to be a good option for bracket recycling by offering a simple and easy technique, which can be performed in the dental office, thus reducing the cost and working time. It also creates a micro-roughened surface on the bracket base, which increases the area available for composite bonding.[9]

In the present study, for Group 1 (Sandblasting with 50-μm aluminum oxide), a bond strength value of (9.11 SD 4 MPa) [Table 1] was achieved, which was the lowest among the three groups but clinically acceptable. Mizrahi and Smith [10] and others [11],[12] have suggested bond strengths ranging from 2.8 MPa to 10 MPa as being adequate for clinical applications.

The chemically recycled brackets achieved a bond strength of 9.94 MPa, which is very similar to the present study group I value.[13] Metal/Zironia Primer (Vivadent) contains a phosphonic acid compound as the active ingredient, which establishes a chemical bond between metal alloys or oxide ceramics (zirconium oxide, aluminum oxide) and methacrylate-based luting composites thus resulting in high bonding values.[14]

The values of the present study [Table 1] revealed that the mean shear bond strengths of Group 1 (Sandblasting) and Group 3 (Silicoating followed by silane application) were significantly different from each other at 0.05 level of significance as analyzed by the one-way ANOVA and Post-hoc Scheffe test [Table 2] and [Table 3]. The mean shear bond strengths of Group 1 (Sandblasting) and Group 2 (Sandblasting + metal primer) did not differ significantly (P > 0.05). Furthermore, there was no statistically significant difference (P > 0.05) between mean shear bond strengths of Group 2 (Sandblasting + metal primer) and Group 3 (Silicoating followed by silane application) [Table 3].
Table 2: One-way ANOVA summary table for load_MPa

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Table 3: Scheffe multiple comparison tests: Dependent variable: Load_MPa

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[Table 1] shows the descriptive statistics of all the three groups, a summary of the means and standard error of the mean for three groups. The total mean shear bond strength for Group 1 that is, sandblasting with 50-μm aluminum oxide was 9.11413 MPa, for Group 2 that is, sandblasting with 50-μm aluminum oxide followed by metal primer application was 11.98477 MPa and for silicoating with 30-μm silicon dioxide followed by silane application was 12.52670 MPa. This showed that there seemed to be a type of technique effect on mean load in MPa.

[Table 2] shows the table for one-way ANOVA summary. It shows that there is a significant difference in the groups, which was proved by the results for the F-value being 4.779 found to be significant at 0.05 level of significance.

[Table 3] shows the pairwise comparison of the three groups using the Scheffe multiple comparison tests. It showed that there was a significant difference in Group 1 (Sandblasting) and Group 3 (Silicoating followed by silane application). The values of this test revealed that the mean shear bond strengths of Group 1 (Sandblasting) and Group 3 (Silicoating followed by silane application) were significantly different from each other at 0.05 level of significance. This was also found by Toroglu and Yaylali [11] showing similar results. Furthermore, it was showed that Group 2 would achieve comparable bond strengths with Group 3, which was also proved statistically by having no significant difference between the bond strengths of the two groups. There was no significant difference found in the shear bond strengths of Group 2 (Sandblasting + metal primer) and Group 3 (Silicoating followed by silica application). There was no significant difference found in the shear bond strengths of Group 1 (Sandblasting) and Group 2 (Sandblasting + metal primer).

In the present study, for Group III (Silica coating with 30-μm silicon dioxide followed by silane application) highest bond strength value (12.53 sd5.06 MPa) [Table 1] was achieved. When compared with the other groups, the bond strength of this group was higher than the other two groups.

In the present study, scanning electron microscope photographs of the sandblasting [Figure 1]a and silicoating [Figure 1]b brackets were evaluated, sandblasting created slightly more prominent irregularities and deeper erosions while silica coating created superficial irregularities and shallow erosions on the bracket base surface. In this technique, abrasion with aluminum trioxide particles modified with silicic acid followed by silanization increased the silica content on the metal surface due to the tribochemical reaction and enhanced the bond between the metal and the composite resin. Since, the silica layer is embedded in the metal surface this provides a basis for silanes to enhance the resin bond.[15]
Figure 1: (a) scanning electron microscope image of sandblasted and silicoated brackets X30 , X150 (b) scanning electron microscope image of sandblasted and silicoated brackets X300 , X1000

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It is usually believed to be cost-effective to rebond an undamaged metallic or ceramic bracket. On the other hand, clinicians should also considered the chair-side time required for cleaning and preparing the bracket bases for rebonding, and the costs of additional materials or equipment for these techniques.

Future prospects for further research are a comparison of the bond strengths achieved with these techniques in vivo. Studies can also be done to evaluate the number of recycles sustained by a bracket while achieving clinically acceptable bond strength. New recycling methods can be discovered so as to improve bond strength while reducing the chair-side cleaning and preparing time for the bracket.


   Conclusion Top


Silica coating followed by silanization produced highest bond strength values for rebonded metallic brackets. Standard error of mean photographs showed that silica coating created superficial irregularities and showed erosion on the bracket surface.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
   References Top

1.
Koo BC, Chung CH, Vanarsdall RL. Comparison of the accuracy of bracket placement between direct and indirect bonding techniques. Am J Orthod Dentofacial Orthop 1999;116:346-51.  Back to cited text no. 1
    
2.
Maccoll GA, Rossouw PE, Titley KC, Yamin C. The relationship between bond strength and base surface area using conventional and micro-etched foil-mesh bases. Am J Orthod Dentofacial Orthop 1996;109:338-9.  Back to cited text no. 2
    
3.
Mascia VE, Chen SR. Shearing strengths of recycled direct-bonding brackets. Am J Orthod 1982;82:211-6.  Back to cited text no. 3
    
4.
Buchman DJ. Effects of recycling on metallic direct-bond orthodontics brackets. Am J Orthod 1980;77:654-68.  Back to cited text no. 4
    
5.
Buchwald A. A three-cycle in vivo evaluation of reconditioned direct-bonding brackets. Am J Orthod 1989;95:352-4.  Back to cited text no. 5
    
6.
Creugers NH, Welle PR, Vrijhoef MM. Four bonding systems for resin-retained cast metal prostheses. Dent Mater 1988;4:85-8.  Back to cited text no. 6
    
7.
Sonis AL. Air abrasion of 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.  Back to cited text no. 7
    
8.
Mizrahi E, Smith DC. Direct cementation of orthodontic brackets to dental enamel. An investigation using a zinc polycarboxylate cement. Br Dent J 1969;127:371-5.  Back to cited text no. 8
    
9.
Retief DH. Effect of conditioning the enamel surface with phosphoric acid. J Dent Res 1973;52:333-41.  Back to cited text no. 9
    
10.
Pus MD, Way DC. Enamel loss due to orthodontic bonding with filled and unfilled resins using various clean-up techniques. Am J Orthod Dentofac Orthop 1980;77:269-76.  Back to cited text no. 10
    
11.
Toroglu MS, Yaylali S. Effects of sandblasting and silica coating on the bond strength of rebonded mechanically retentive ceramic brackets. Am J Orthod Dentofacial Ortho 2008;134:181.e1-181.e7.  Back to cited text no. 11
    
12.
Heravi F, Naseh R. A comparative study between bond strength of rebonded and recycled orthodontic brackets. Dent Res J 2006;2:1-6.  Back to cited text no. 12
    
13.
Antoniadou M, Kern M, Strub JR. Effect of a new metal primer on the bond strength between a resin cement and two high-noble alloys. J Prosthet Dent 2000;84:554-60.  Back to cited text no. 13
    
14.
de Freitas AP, Francisconi PA. Effect of a metal primer on the bond strength of the resin-metal interface. J Appl Oral Sci 2004;12:113-6.  Back to cited text no. 14
    
15.
Vandekar M, Kulkarni P. Bond reliability: Difficult areas, easy solutions. APOS Trends Orthod 2012;2:5.  Back to cited text no. 15
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Correspondence Address:
Vikram Shetty
Department of Orthodontics, YMT Dental College and Hospital, Navi Mumbai, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0970-9290.167635

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