INTRODUCTION:

The acid etching technique was first introduced by Buonocore [1] in 1951 and this technique was used by Newman [2]in 1965 to bond orthodontic brackets using the then available auto polymerizing materials. This process was colloquially known as ‘bonding. With the increase in the use of straight wire or pre-adjusted appliances in orthodontics, practitioners have switched their focus from wire bending to bracket positioning. In the straight wire and pre adjusted edgewise fixed-appliance treatment, the most important requirementis correct bracket positioning [3].

Bonding orthodontic brackets with visible light-cured adhesives was first reported by Tavas and Watts [4]. Diacrylate resin, commonly referred to as Bowen's reshz or bisglyceral methacrylate (bisphenol A glycidyl dimethacrylate), were designed to improve bond strength and increase dimensional stability by cross linking, Stainless steel orthodontic brackets can be secured to teeth with this resin. The predominantly weak link in this bonding chain is at the resin/bracket base interface.

It was not until 1977 that the first detailed post treatment evaluation of direct bonding in orthodontics during a full treatment time (mean of 17 months) in a large sample of patients was published. These studies concluded that acid etching and bonding with filled composite resins would make a major impact on the orthodontic world for bracket placement: A major drawback of this system is the inability of the practitioner to manipulate the setting time of the composite resin. The clinician must position the brackets correctly on the teeth to assure a functional end result. However, must be done rapidly when the chemically cured resins are used, because polymerization starts immediately on mixing. If left around the bracket, the excess composite resin will lead to plaque accumulation and resultant enamel decalcification. However, the clinician must wait until final setting of the composite resin to remove any excess from around the bracket." The incorporation of air in mixing the composite resin could lead to a weakening of the bond strength of the resins and to increased surface porosity. The fact that light-cured composite resins exhibit markedly less porosity than chemically cured resins has been reported numerour author [3-5].

The polymerization of light-activated resins undermetal brackets by transillumination has been shown to be successful, because the tooth conducts visible lightwell. Have been made that light polymerization (command curing) improves the accuracy of bracket positioning and thus minimizes the need for [5] position in grealigning of teeth after debonding [6] Excess composite material can also be removed before light polymerization because any accidental movement of the bracket will not affect the bonding capacity of the resin.

The advantage of a light-cured adhesive system is that it gives the clinician the ideal working time to position the bracket, reduces the risk of contamination, and helps in easy removal of excess material after bonding[5,7]Adhesive bonding is important for orthodontics, especially in terms of fixation of brackets to teeth. Tremendous advances in the development of orthodontic adhesives have allowed orthodontists to bond brackets (or attachments) to tooth surfaces quite successfully. Many factors affect the retention of the brackets during fixed orthodontic treatment [3] However, studies have shown that clinical bond failure still occurs with 5% to 7% of brackets bonded with light cured or chemical-cured composite resins for different reasons [4,5]. The light cure composite resins exhibit less porosity than the chemically cured resins as reported by numerous authors[6].

The polymerization of light activated resins under metal brackets by transillumination has been shown to be successful, because the tooth conducts visible light well [7,8]. Light polymerization improves the accuracy of bracket positioning and thus minimizes the need for realigning of teeth after debonding [9]. Excess composite material can be removed before light polymerization because any accidental movement of the bracket will not affect the bonding capacity of the resins. Recently, a new LED curing light unit (woodpecker)has become commercially available for orthodontic bonding. This product has 2225 mW per square centimeter of light intensity[ figure :[6]. Because of its high-intensity light waves, it is claimed to cure adhesive materials in 1 or 3 seconds.

Currently, no studies have evaluated the performance of this LED curing unit. Bond failures of brackets can significantly increase chair-side time, treatment time, and efficiency. Therefore, much effort has been put into improving the quality of the adhesive systems for direct bonding. Bond strength can be influenced by various factors such as light-curing devices, type of enamel conditioner, acid concentration, etching time, composition of the adhesive, bracket base design, and bracket material.[2-4]. The most commonly used adhesive systems are light-cured or chemically cured composite resins, usually combined with acid-etching.

Mostly, sufficient bond strength of composite resins was found, but undesirable effects such as loss of enamel during acid-etching [5] and enamel decalcification around the brackets [6-8] have been reported. Recently, the adhesive grengloo(Ormco)was developed; it not only possesses the property of color change with temperature but, according to the manufacturer, also has much greater bond strength when used with the Damon bracket (Ormco).

Transbond XT (3M UNITEK) bonding system is a gold standard for bonding of brackets and buttons in orthodontic practice because of its ideal consistency, light curing ability, superior tooth/bracket adhesion and availability.

Recently, the adhesive grengloo(Ormco)was developed; it not only possesses the property of color change with temperature but, according to the manufacturer, also has much greater bond strength when used with the esthetic Damon 3 bracket (Ormco).

Grengloo adhesive has the properties like color changing in two ways, that revolutionizes metal bracket bonding by combining the strength, flexibility and intelligent features. Provides great working time for better placement under ambient conditions, affording more flexibility to place and position brackets, remove flash and begin light curing. Quick-cure polymerization provides greater shear bond strength at initial force loading. The fillers that present it provides excellent handling characteristics, making cleanup easy and virtually eliminating bracket drift. Color contrast feature aids in fast and accurate cleanup at bonding and debonding. At the body temperature, the color disappears, remaining clear throughout treatment. When debonding, apply a air or water to bring the bonding surface temperature lower, and Grengloo turns green again for easy and thorough cleanup.

The objectives of this study were to determine shear bond strengths and to compare 2 common orthodontic adhesives-Transbond XT and Grengloo.

MATERIALS AND METHODS:

This study was conducted to evaluate the Shear Bond Strength of two different orthodontic adhesives used for orthodontic bonding. Ten premolar teeth, extracted for orthodontic purposes, and free from enamel cracks, caries, and fillings were used in this research. The teeth were cleaned in water to remove any traces of blood and then they were placed in saline. Subsequently, they were stored in distilled water, which was changed at regular intervals to avoid deterioration.

They were divided into two groups: [Figure :1,2]

1. Group I (n= 5) samples were color-coded with white.

[Transbond XT- 3M UNITEK]

2. Group II ( n = 5) samples were color-coded with pink

[Grengloo - ORMCO]

FIGURE:1 FIGURE:2

Then teeth in each group were mounted vertically on two different color-coded acrylic boxes for identification (white-Transbond XT, pink -Grengloo).

Bonding procedure:

Ten metal premolar brackets were used for the study. The base area of each bracket was calculated. Prior to bonding, the buccal surfaces were subjected to prophylaxis, polished with a rubber cup, pumice powder and rinsed with water[figure:3]. Etched with 37% phosphoric acid gel for 30 seconds, and then washed with water. Subsequently, the enamel surfaces were completely dried with compressed air. A thin layer of Transbond XT primer was applied to the tooth and light cured in both groups. Brackets were bonded on buccal surfaces with Transbond XT in group 1 and Grengloo in group 2 according to manufacturer’s instructions.

Figure:3 pumice polishing

Figure:4 Bonding with two different adhesive

In group -1 The Transbond XT was applied to the bracket base and then pressed firmly onto the tooth. First the mesial side was cured for 20 sec and the distal side was cured for 20 sec. Each bracket is cured to a total of 40 sec.

In group -2 The Grengloo was applied to the bracket base and then pressed firmly onto the tooth. First the mesial side was cured for 20 sec and the distal side was cured for 20 sec. Each bracket is cured to a total of 40 sec.

Excess adhesive was removed with a probe from around the base of the bracket and then the adhesive was cured with 6second i. LED light cure unit.[figure :5] , the unit was positioned on each interproximal side for 3 seconds. Intensity of light cure unit is 2250 mW/cm²

Figure:5 i.LED LIGHT CURE UNITS

Figure:6 CURING RADIOMETER

Bond strength test:

Group I (n = 5): 5 samples were color-coded with white.[figure:7]

Group II (n = 5): 5 samples were color-coded with pink[figure:8]

Figure:7 Bonding done with Transbond XT

Figure:8 Bonding done with Grengloo

Each groups having 5 teeth which were used to carry out Shear Bond Strength testing, with the instron testing machine Universal testing at the across head speed of 0.5 mm/min machine[figure:9]

Figure:9 The tooth held in the crossheads of the universal testing machine before the debonding

Statistical Analysis :

The data obtained from the study was tabulated. The level of significance was at (0.08). The mean and standard deviation was calculated for both the groups to get the arithmetic average of the observations. Independent t-test was performed to determine the statistical difference between the shear bond strength of the two groups

RESULT:

Shear bond strength:

All data showed normal distribution and homogeneity of variances. Grengloo, produced particularly for bonding Damon 3 brackets, had the highest shear bond strength values with a mean of 15.01 MPa(Table II), closely followed by the light-cured adhesives Transbond XT (14.81 MPa)(table :2) Light-cured Transbond XT had the lowest shear bond strength, lower than that of grengloo, with the highest bond strength. In tested adhesives, the differences in shear bond strength were smaller . The results of the independent `t’ testare summarized in [Table 3]. However, a statistically no significant difference was found between Tansbond XT and Grengloo composites.

TABLE:1 SHEAR BOND STRENGTH OF TRANSBOND XT – GROUP:1

TRANSBOND XT	SHEAR BOND STRENGTH [Mpa]
GROUP:1	14.57
	9.72
	8.78
	19.28
	21.73

TABLE:2 SHEAR BOND STRENGTH OF GRENGLOO – GROUP:2

GRENGLOO	SHEAR BOND STRENGTH [Mpa]
GROUP: 2	15.44
	14.69
	15.27
	15.43
	14.23

TABLE 3. STATISTICAL SUMMARY OF THE SHEAR BOND STRENGTHS OF THE TESTED ADHESIVES

Groups		N	Mean	Std. Deviation	Std. Error Mean
Bondstrength	1.00	5	14.8160	5.70512	2.55141
Bondstrength	2.00	5	15.0120	.53378	.23871

GRAPH:1 TRANSBOND XT GROUP

GROUP:2 GRENGLOO GROUP

GRAPH: 3 Comparison of group1and group 2

DISCUSSION:

Bonding of orthodontic brackets has become an accepted clinical technique since 1970 (Zachrisson, 1994). Bonding has largely replaced banding and is superior to banding in terms of gingival and dental health and esthetics. The bonding procedure is based on enamel alteration created by acid etching of enamel as developed by Buonocore.

(1)The advantages of direct bonding are easy bracket placement, acceptable clinical success rate, and reduction in chairside time. The bond failure rate is reported to vary between 0.5% and 16% [31-33] which is very minimum. However, this technique imposes the risk of demineralization of enamel adjacent to brackets and requires drying of enamel surface; which is important in increasing the bond strength of brackets [29, 30].

To be employed for bracket bonding a material needs to provide adhesion to the tooth surface sufficient to withstand masticatory and orthodontic forces consistently applied. The use of a bonding agent prior to bonding with composite has the advantage of immediate obliteration of enamel pores caused by acid etching that are not covered by the bracket base, thereby, preventing decalcification. Conventional bonding system has three different agents the conditioner, a primer solution and an adhesive resin for the process of bonding orthodontic brackets to enamel. The use of primer was an essential part of the bonding procedure of composite adhesives to allow good wetting and penetration of the sealant into the etched enamel surface. Light cured composites are filled resin consisting of a single paste that becomes polymerized through the use of a photosensitive initiator system (CQ-Camphorquinone and amine initiator ) and light source activator ( visible blue light).UV light cured composite have been replaced by visible blue light activated system with greatly improved in depth of cure and controlled working time.

Grengloo is the two way color change adhesive that revolutionizes metal bracket bonding, has quick – cure polymerization provides greater shear bond strength at initial force loading. And warms to body temperature, the color disappear, remaining clear throughout treatment, When ready to cure, Grengloo quick – cure initiator cures in as little as 5 seconds with a broad spectrum curing lights (led) to quick deliver strength while reducing chairtime. Grengloo formula includes a unique hybrid filler materials that provides excellent handling characteristics making cleanup easy and virtually eliminating bracket drift. Exposure of light in the blue region produces an excited state of the photosenitizer, which than interacts with the amine to form free radicals that initiate addition polymerization. The free radical initiating system consisting of a photosensitizer and amine initiator is contained in this paste. Camphorquinone is commonly used photosenitizer that absorbs blue light. Only small quantities of camphorquinone rare required (0.2% or less in the paste). A number of amine initiators are suitable for interaction with camphorquinone, such as dimethylaminoethyl metha acrylate, which is also present at low level that is approximately 0.15wt%.

The mean shear bond strength of Transbond XT achieved in our study was 14.81+5.70 MPa. This was lower than achieved in some previous studies [10-21] but was comparable to the studies of Tecco et al[22] (23.23 MPa + 5.23 MPa), D’Atillio et al[23](23.47 MPa, +4.86 MPa), Rock and Abdullah[24](8-23 MPa), Sinha et al[25](18.9 MPa), Tang et al[26], Sunna et al[27] (11-22 MPa) and Rix et al [28] (20.19 MPa). One mentioned advantage of bonding with Transbond XT is greater control of working time by orthodontists, which facilitates the proper placement of brackets on the teeth[.11] We evaluated the shear bond strengths of two common adhesive systems marketed for orthodontic bonding..In the present study, there is slight increase in shear bond strength values of bonded brackets using Grengloo( 15.01MPa) compared with the light-cured composite resin Transbond XT(14.81 MPa).There was a no significant difference in the shear bond strength of the Transbond XT and Grengloo in our study. However, the bond strengths of both the composites tested were greater than the recommended values of Reynolds, it is the recommendation of the authors that the Transbond XT be preferably used for bonding of the orthodontic attachments, because of its higher bond strength. In our study Grengloo has a slight increase in shear bond strength compared to Transbond XT.

CONCLUSIONS:

Both the materials Transbond XT and Grengloo showed a no significant difference in shear bond strength. The overall bond strength and mean value for Greegloo was slightly higher than Transbond XT.

Therefore, grengloo can be used as an ideal orthodontic adhesive in terms of increase shear bond strength, quick cure polymerization, quick cure intiator provides faster cure, two- way color changing properties during bonding and deboing saves chair time, as analyzed in this study. We would also recommend that these composites be tested invivo in a randomized clinical control trial. Grengloo, had the slightly increased shear bond strength than the Transbond XT.

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Received on 17.08.2018 Modified on 07.09.2018

Research J. Pharm. and Tech 2018; 11(12): 5593-5598.

DOI: 10.5958/0974-360X.2018.01017.X