| Abstract|| |
Background: Newer available composite resin adhesives have chromatic agents that change their color during setting from pink to colorless. It has an advantage of easy flash removal thus reducing the amount of plaque accumulation and helping patients to maintain better hygiene.
Aim: The aim of the present study was to compare shear bond strengths of light-cure orthodontic bonding agents, namely glass ionomer (FujiOrthoLC, GC Orthodontics), conventional composite resin (Transbond XT, 3M Unitek), and color-changing composite resin (Transbond Plus, 3M Unitek) with conventional etch and self-etch primer (Transbond PlusSEP, 3M Unitek).
Materials and Methods: Maxillary premolars (n=300) were bonded on the facial surface in five groups. The INSTRON machine was used for shear bond strength testing.
Statistical Analysis: Comparison of the mean rank among the groups was done by Kruskal-Wallis one-way analysis of variance (ANOVA). To determine the mean difference among groups, the Mann-Whitney test with Bon Ferroni adjustment was applied.
Observations: It was observed that light-cure conventional composite resin with the conventional etchant group had the highest and glass ionomer resin adhesive had the lowest shear bond strength. There was no statistically significant difference between conventional composite used with conventional etchant and color-changing composite resin used with conventional etchant or with self-etch primer.
Conclusion: Considering the advantages of a color-changing composite and self-etch primer especially in patients having high DMFT scores or physically and mentally compromised patients unable to maintain their hygiene properly, it was concluded in the present study that it would be the most suitable material for direct bonding.
Keywords: Color-changing composite resin, composite resin, glass ionomer cement, in vitro, self-etch primer, shear bond strength
|How to cite this article:|
Maurya R, Tripathi T, Rai P. New generation of color bonding: A comparative in vitro study. Indian J Dent Res 2011;22:733-4
The acid etch technique, first suggested by Buonocore, markedly improved bonding to enamel.  It was suggested for orthodontic use by Newman and is now widely accepted. 
|How to cite this URL:|
Maurya R, Tripathi T, Rai P. New generation of color bonding: A comparative in vitro study. Indian J Dent Res [serial online] 2011 [cited 2020 Sep 23];22:733-4. Available from: http://www.ijdr.in/text.asp?2011/22/5/733/93472
Bisphenol A glycidyl dimethacrylate, more commonly known as Bowen's resin or BIS-GMA, was patented in 1962. It is an acrylic-modified epoxy resin, combining the setting versatility of acrylic and the strength, and dimensional stability of epoxy. 
Tavas and Watts first described the use of visible light to cure composites used in orthodontic bonding in 1979. 
Wilson and Kent introduced glass polyalkenoate, or glass ionomer cement, to dentistry in 1972.  In response to the demand for improvement of the original product, Antonucci introduced resin-modified glass ionomer cements (RMGICs) in 1988. Light-activated resin-modified glass ionomer cements (RMGICs) were formulated to overcome the problems of moisture sensitivity of composites and low mechanical strength in initial stages of glass ionomers, while maintaining the clinical advantages of conventional glass ionomers.  Light activation also helped in obtaining flexible working time for the material.
Traditionally, the use of acid etchants followed by a primer was an essential part of the bonding procedure of composite adhesives to allow good wetting and penetration of the primer into the enamel surface. However the contemporary self-etch primers simplify the clinical handling of the adhesive systems by combining the etchant and the primer in one application.
Nowadays further additions of certain chromatic agents into composite resin adhesive are being done which change color during setting. This has an advantage of easy flash removal thus reducing the amount of plaque accumulation and decalcification and also helping patients to maintain better oral hygiene. A number of studies have been conducted comparing in vitro shear bond strength of composite resin adhesive with either glass ionomer cement or its resin-modified hybrid.
However considering the advantages of a color-changing adhesive it was imperative to know its shear bond strength compared to the other bonding agents.
| Materials and Methods|| |
The study was conducted in the Department of Orthodontics and Dentofacial Orthopaedics, Maulana Azad Institute of Dental Sciences, New Delhi.
The sample size comprised 300-extracted human premolars. The collection of the teeth was done over a period of 6 months. All teeth were stored in distilled water containing 0.1% (weight/volume) thymol to inhibit the bacterial growth. Selection of the teeth was done based on the following criteria:
- Tooth with intact buccal enamel with no cracks due to pressure of extraction forceps.
- There should be absence of any carious lesion.
- The tooth should not have been subjected to any chemical treatment during storage.
Preadjusted stainless steel brackets with Roth prescription (Leonne, Italy) were bonded to all the extracted human premolars according to manufacturer's instructions.
The following five groups of light-cure bonding agents were used during the study.
- Group I: Glass ionomer resin adhesive (Fuji Ortho LC, GC America).
- Group II: Composite resin with conventional etchant (Transbond XT, 3M Unitek).
- Group III: Composite resin with self-etch primer (Transbond XT, Transbond Plus SEP, 3M Unitek).
- Group IV: Color-changing composite resin with conventional etchant (Transbond PLUS, 3M Unitek).
- Group V: Color-changing composite resin with self-etch primer (Transbond PLUS, Transbond Plus SEP, 3M Unitek).
Shear bond strength measurement
Instron Universal testing Machine (Instron Corp., Canton, Mass) was used for shear bond strength analysis [Figure 1].
The sample comprising 300 extracted human teeth was randomly divided into five equal groups. The buccal crown surface of each tooth was rinsed and dried after a 15-second polish with fluoride-free pumice slurry. Stainless steel metal preadjusted premolar brackets were positioned parallel to the long axis of the tooth in the middle third of the buccal surface and pressed onto the enamel surface until fully seated. Bonding was done with different adhesives in each group as per the manufacturer's instructions.
After bonding all teeth were stored in distilled water containing 0.1% (weight/volume) thymol at room temperature in a closed plastic jar for 24 hours. The debonding procedure was carried out in the same time interval for every tooth after bonding. Occluso-gingival load was applied to the bracket at the wing, producing a shear force at the bracket-tooth interface using an attachment to the cross-head of Instron Universal testing Machine, Instron Corp., Canton, Mass [Figure 2].
A cross-head speed of 1.0 mm/min was used. A computer connected with the Instron machine recorded the result of each test. The load applied at failure was recorded as Newton (N) and calculated into Mega Pascals (MPa) by dividing it with the bracket base area of 12 mm 2 .
| Results|| |
The mean shear bond strength, standard deviation, median, minimum, and maximum of bond strength for each group are shown in [Table 1]. It was observed that the mean shear bond strength was maximum in group II, i.e., 8.33 ± 2.19 and minimum in group I, i.e., 5.63 ± 1.98. The mean shear bond strength of group III-V is found to be 6.97 ±2.08, 7.30 ± 1.71, and 7.47 ± 1.80, respectively. The bar diagram comparing mean and standard deviation of shear bond strength among all five groups is depicted in [Figure 3].
|Table 1: Descriptive statistics (mean, median, standard deviation, minimum, and maximum value) of the shear bond strength in MPa of study subjects (N=60)|
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Since too much of variation between standard deviation of different groups was found, comparison of the mean rank among the five groups was done by Kruskal-Wallis one-way analysis of variance (ANOVA) as shown in [Table 2]. The mean ranks of all five groups are being depicted in bar diagram format in [Figure 4]. Further with Kruskal-Wallis test statistics it was found that the mean shear bond strength among the groups had a significant difference as shown in [Table 3].
|Figure 4: Diagramatic representation of the mean rank according to the Kruskal-Wallis test|
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|Table 2: Mean rank of the shear bond strength for five groups as done by the Kruskal-Wallis test|
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Multiple comparisons of all five groups by using the Mann-Whitney test with Bon Ferroni adjustment to determine the mean difference among groups are tabulated in [Table 4]. P<0.05 was considered as a significant level of difference between different groups.
|Table 4: Mann-Whitney test for multiple comparison of the mean shear bond strength|
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| Discussion|| |
The direct bonding of orthodontic brackets has revolutionized and improved the clinical practice of orthodontics. However, there is a need to improve the bonding procedure by saving time and also a need to minimize enamel loss without jeopardizing the ability to maintain clinically useful bond strength. Self-etch primers had been used in studies conducted by Bishara et al.; their study showed its clinical usefulness in reducing chair time during bonding.  The present study utilized a self-etch primer with both conventional and color-changing composite resin adhesive to re-evaluate its usefulness without compromising the strength of the material. Studies by Fricker, McLachlan, Fajen et al. and White have been conducted comparing in vitro shear bond strength of composite resin adhesive with either glass ionomer cement or its resin-modified hybrid. ,, Color-changing composite resin adhesives have chromatic agents that change their color during setting from pink to colorless. Hence they have an advantage of easy flash removal thus reducing the amount of plaque accumulation and helping patients to maintain better hygiene. Considering the advantage of a color-changing orthodontic bonding adhesive it was imperative to know its shear bond strength compared to the other conventional bonding agents.
Previous in vitro studies conducted by Mehmet have used incisors for measuring shear bond strength whereas canine, premolar, or molars have been used for measurement of shear bond strength by Corel and McInnes. , Use of premolars in the present investigation was followed by extensive review of literatures mentioning its use as in the study conducted by Fajen et al. and also by McCourt, Cooley, and Barnwell and further supported by Compton et al.,, The added advantage was ease of availability of these teeth in our institution as the sample size was very high in number and premolars are the most commonly extracted healthy teeth in field of orthodontics for treatment purpose. Thus a bigger sample size was used in the present study.
Stainless steel preadjusted premolar brackets without hook were preferred to reduce any biased values while measuring the shear bond strength with the Instron machine since during testing hooks may interfere with the force delivering machine attachment. Meehan, Foley, and Mamandras, Schaneveldt and Foley, Douglas, Foley, and Mamandras and Swanson have also favored its use. ,,,
Distilled water with 0.1% (weight/volume) thymol was used for storage of teeth during collection and after bonding in the present investigation. This storage medium does not alter the properties of the tooth surface and at the same time maintains the hydration level of teeth. Further addition of 0.1% (weight/volume) thymol is reported to inhibit the bacterial growth. Similar storage media was used by studies conducted by Cacciafesta et al., Manar and Khier. , Use of autoclave and other chemicals like peroxides, gluteraldehyde, or normal saline were avoided as they can alter the properties of enamel and can give bias results as reported by Eliades and Brantley in their study. 
A study conducted by Fox, McCabe, and Buckely have also reported softening of enamel when teeth are stored in normal saline. 
After bonding, teeth were stored for 24 hours at room temperature in closed jars containing distilled water to allow the complete curing of the adhesives to take place before debonding. Graenlaw, Way, and Khadry also confirm this procedure in their study. 
The brackets were debonded with a shear load by means of Instron testing machine having a cross-head speed of 1 mm/min. The bracket was positioned parallel to the plunger of the testing machine. The loading of the bracket was done on the wings rather than close to the base. This was attributed to the fact that application of load on the wings may be more representative of the in vivo loading and may ensure a more consistent application of the debonding force. This debonding procedure was in accordance with the study conducted by Katona for the measurement of shear bond strength of various orthodontic adhesives. 
In the present investigation the mean shear bond strength varied between 5.6 and 8.3 MPa. The minimum shear bond strength that is required to withstand normal orthodontic force was 6-8 MPa (58.8-78.4 kg/cm 2 ) as reported by Reynolds. 
In the present investigation no significant difference in shear bond strength was found between the conventional and color-changing composite resin materials. However, there was a significant difference between the composites and the glass ionomer resin adhesive. It was observed in the present study that composite resin adhesive is approximately 30% stronger than light-cure glass ionomer adhesives. These findings are in agreement with Bishara et al., Meehan, Foley, and Mamandras who have reported a lower shear bond strength of glass ionomer resin adhesives compared to composites. ,
The study showed that the use of self-etch primer along with conventional composite resin adhesive demonstrates statistically significant lower shear bond strength in comparison to conventional etchant when used with the same adhesive. Bishara in his studies on self-etch primer along with composite resin also showed a inferior shear bond strength compared to conventional etchant.  The shear bond strength of color-changing composite resin adhesive when used with self-etch primer was comparable to shear bond strength of color-changing composite resin when used with the conventional etchant.
Color-changing composite resin adhesive used with self-etch primer showed comparable shear bond strength as was obtained with conventional composite used with conventional etchant.
From the above observations of the present study it can be stated that use of self-etch primer along with color-changing composite resin adhesive can be time saving and more convenient in handling as lesser steps will be required in bonding. Further, the color-changing property of the composite resin, from pink to colorless, as it is cured, will be of an advantage for easy excess flash removal.
Thus due to the advantages of the color-changing composite resin along with self-etch primer, this combination is recommended as the most suitable bonding adhesive especially in patients having high DMFT scores or physically and mentally compromised patients who are unable to maintain their hygiene properly.
| Conclusions|| |
The following conclusions were made:
- Light-cure conventional composite resin with the conventional etchant group showed the highest shear bond strength (8.33 MPa) and hence was found to be the strongest orthodontic bonding adhesive. The glass ionomer resin adhesive has the lowest shear bond strength value (5.63 MPa) among all the materials tested in this study and hence was found to be the weakest bonding adhesive among all the study groups.
- There was no statistically significant difference between conventional composite used with conventional etchant and color-changing composite resin when used with conventional etchant or with self-etch primer.
- Considering the advantage of color-changing composite and self-etch primer without compromising the shear bond strength, color-changing composite used with self-etch primer was the most suitable material for direct bonding as found in the present investigation.
This study was an in vitro study; it had limitations in terms of factors that are affecting shear bond strength of adhesive saliva, intraoral temperature, occlusal forces, and others in comparison to in vivo studies. Hence it is proposed that studies need to be conducted for further in vivo assessment of shear bond strength of bonding agents.
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Department of Orthodontics and Dentofacial Orthopaedics, Maulana Azad Institute of Dental Sciences, New Delhi
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4]