Evaluation of shear bond strength of brackets bonded using different hydrophobic and hydrophilic adhesives: An invitro study

Introduction

Bonding is an important orthodontic milestone that replaced the hardest task of banding. The ability to bond orthodontic attachment has reduced patient chair side time and appointment, improved the esthetics and aided in improvement of oral hygiene. Direct bonding became popular after the contributions of the pioneers such as Buonocore (1955) suggested a surface acid treatment of enamel. 1

Newman (1965)2 introduced direct bonding as a viable clinical technique and then orthodontic bonding developed as an excellent over banding.

A review of the long history of orthodontic bonding adhesives shows that many evolutional developments have occurred from the first chemically-cured composite resins to the most recently introduced light-cured color-change adhesives.3

Recently, Color-change light-cured composites were introduced to the orthodontic market to enhance differentiation of adhesive and enamel. Due to their different colors and contrasts, they can be easily detected on the tooth enamel during bonding and debonding procedures. This characteristic enhances their complete removal after bracket debonding. Furthermore, after bracket bonding, excess resin can be easily removed, which is an advantage of Color-change adhesives. Greengloo (ormco), a colour changing adhesive is also develop in the world of orthodontic adhesives, with the purpose of facilitating the discrimination between the adhesive material and enamel. CCAs are becoming popular among clinicians due to promising characteristics reported.4

Over the years a great deal of attention has also been paid to improve the acid-etching technique, primers and adhesives. Traditional bonding materials like Transbond XT present hydrophobic properties and require dry surfaces to obtain clinically acceptable bond strength. Thus, contamination during orthodontic bonding process is undesirable because it interferes on the adhesive and resin properties and causes failure on the adhesive interface because when etched enamel get wet, most of the pores get plugged, and resin penetration get impaired resulting in insufficient resin tags. For this reason, manufacturer introduced hydrophilic primers that promised successful bonding to contaminant enamel surface.5

Buonocore in 1955 demonstrated a simple method to increase adhesion of material to enamel surface by acid pre-treatment with 85% phosphoric acid.

Saliva contamination of etched enamel seems to cause a significant decrease in bond strength between the resin and the enamel surface Klocke et al 20036 stated that contamination during bonding procedure reduces the bond strength. So, hydrophilic resin system like Resin modified GIC (Fuji ortho) are introduced to provide adequate bond strength in presence of moisture.7

They are fluoride-releasing adhesives which inhibit caries lesion development during fixed orthodontic treatment. The use of these cements for direct bonding of orthodontic brackets has been proposed because of their ability to adhere to base metal alloys.8

Recently, new adhesive material like Aqualine L.C(Tomy japan) has been introduced for bonding metal brackets which form strong bond to etched enamel surface without priming. The ability of combining conditioning and priming into single step has reduced patient chairside time, improved the esthetics and aided in the improvement of oral hygiene. 9

An ideal orthodontic adhesive should have adequate bond strength while maintaining unblemished enamel after debonding. Bond strength of 90orthodontic brackets to the enamel should be high enough to maintain the brackets in place during the treatment period. It must be high enough to resist occlusal loads as well. On the other hand, very high bond strength is not favorable since it increases the risk of enamel fracture and subsequent pulp injury during debonding. According to Reynolds, bond strength as high as 5.9–7.8 MPa can resist masticatory forces. It is clinically favorable and minimizes enamel fracture. Bond strength higher than 14 MPa can cause enamel cracks on the tooth surface. Therefore, researchers have been working hard to achieve the best quality and gentlest materials for bonding orthodontic brackets.

Aim

The aim of the invitro study is to evaluate the shear bond strength of brackets bonded using different hydrophobic and hydrophilic adhesives.

Materials and Methods

Bonding materials:

Brackets: Metal Brackets – Stainless steel brackets [Maxillary and mandibular first and second premolar brackets of both side] were selected.Teeth Samples: - 80 extracted human maxillary and mandibular premolar teeth of both side were used.

Exclusion criteria

1. Absence of caries

2. Absence of cracks

3. Absence of any developmental defects or restorations.

4. Absence of Fluorosis and any anamolies.

Storage: The samples were stored in distilled water at room temperature in airtight container to prevent dehydration.

Figure 1

Bonding materials

Figure 2

Premolar brackets

Figure 3

Teeth sample mounted in acrylic block

Figure 4

Light curing procedure

Figure 5

Curing light

Figure 6

Shear bond strengthdone in universal testing machine.

Figure 7

Universal testing machine

Figure 8

Artificial saliva used

Table 1

Descriptive statistics of shear bond strength of brackets bonded using different adhesives (without saliva contamination)

(in Mpa)	Mean	SD	SE	Minimum	Maximum
Group I (Transbond XT)	8.19	0.83	0.26	6.9	9.38
Group II (Greengloo)	4.51	0.6	0.19	3.42	5.42
Group III (RMGIC)	3.0	0.4	0.12	2.38	3.71
Group IV (Aqualine LC)	6.93	0.72	0.22	5.8	8.04

Table 2

Inter group comparison of shear bond strength of brackets bonded using different adhesives (without saliva contamination)

	Mean	SD	One-way Anova F test	P value, Significance
Group I (Transbond XT)	8.19	0.83	F = 125.78	p < 0.001**
Group II (Greengloo)	4.51	0.6
Group III (RMGIC)	3.0	0.4
Group IV (Aqualine LC)	6.93	0.72
Tukey’s post hoc test for pairwise comparison
Group	Comparison Group		Mean Difference	P value, Significance
Group I (Transbond XT) Vs	Group II (Greengloo)		3.68	p<0.001**
	Group III (RMGIC)		5.18	p<0.001**
	Group IV (Aqualine LC)		1.26	p=0.001*
Group II (Greengloo) Vs	Group III (RMGIC)		1.5	p<0.001**
	Group IV (Aqualine LC)		2.42	p<0.001**
Group III (RMGIC) Vs	Group IV (Aqualine LC)		3.92	p<0.001**

[i] p>0.05 – no significant difference*p<0.05 – significant**p<0.001 – highly significant

Table 3

Descriptive statistics of shear bond strength of brackets bonded using different adhesives (with saliva contamination)

(in Mpa)	Mean	SD	SE	Minimum	Maximum
Group I (Transbond XT)	6.78	0.53	0.17	5.82	7.6
Group II (Greengloo)	3.91	0.57	0.18	3.04	4.85
Group III (RMGIC)	2.09	0.39	0.12	1.52	2.57
Group IV (Aqualine LC)	5.48	0.65	0.2	4.61	6.42

Table 4

Inter group comparison of shear bond strength of brackets bonded using different adhesives (with saliva contamination)

	Mean	SD	One-way Anova F test	P value, Significance
Group I (Transbond XT)	6.78	0.53	F = 135.916	p < 0.001**
Group II (Greengloo)	3.91	0.57
Group III (RMGIC)	2.09	0.39
Group IV (Aqualine LC)	5.48	0.65
Tukey’s post hoc test for pairwise comparison
Group	Comparison Group		Mean Difference	P value, Significance
Group I (Transbond XT) Vs	Group II (Greengloo)		2.86	p<0.001**
	Group III (RMGIC)		4.68	p<0.001**
	Group IV (Aqualine LC)		1.29	p<0.001**

[i] p>0.05 – no significant difference*p<0.05 – significant**p<0.001 – highly significant

Results

The study was to evaluate the shear bond strength of brackets bonded with hydrophilic and hydrophobic adhesives in presence and in absence of saliva.

Table 1 Descriptive statistics of shear bond strength of brackets bonded using different adhesives (without saliva contamination).

Table 2 Intergroup comparison of shear bond strength of brackets bonded using different adhesives (without saliva contamination)

Table 3 Descrpitive statistics of shear bond strength of brackets bonded using different adhesives (with saliva contamination).

Table 4 Intergroup comparison of shear bond strength of brackets bonded using different adhesives (with saliva contamination).

Descriptive statistics of shear bond strength values (in MPa) obtained in the study without saliva contamination are shown in Table 1 and with saliva contamination are shown in Table 3.

One way ANOVA test was used to compare the differences in the bond strength among the four different groups and when significant differences were found, Tukey’s post hoc

test for pairwise comparison was used to verify specific group in which such differences had occurred. They are specified in Table 2 and Table 4.

The study data was analysed using SPSS software version 21. The frequency distribution for shear bond strength is expressed in terms of means and standard deviations.

Includes the Mean, Standard Deviation, Standard error, minimum and maximum bond strength values of all the four adhesives in dry condition.

Includes the pairwise intergroup comparison of shear bond strength of brackets bonded using different adhesives in dry condition.

Includes the Mean, Standard Deviation, Standard error, minimum and maximum bond strength values of all the four adhesives in saliva contamination condition.

Includes the pairwise intergroup comparison of shear bond strength of brackets bonded using different adhesives in saliva contamination condition.

The Transbond XT (Group 1) which is a hydrophobic adhesive was used as a control group.

The mean shear bond strength value of Group I and Group IV were significantly higher than those with Group II and Group III.

In dry conditions, statistically highly significant difference was found in mean SBS among Transbond XT, Greengloo(Group II), RMGIC(Group III) given in (Table 1) However there was slight less significant difference in mean SBS of Transbond XT and Aqualine LC (Group IV) (p=0.001).In Wet conditions (saliva contamination condition) the mean SBS was found to have highly significant difference among the Transbond XT, Greengloo, RMGIC and Aqualine LC.

Discussion

Ever since the introduction of direct bonding of orthodontic brackets in fixed appliance mechanotherapy, enormous improvements have occurred in the range of the orthodontic direct bonding adhesives and materials available. Enamel bonding for orthodontic appliances was introduced in 1965 and is considered a significant milestone in orthodontic treatment. As reported by Owens and Miller, 10direct bonding of orthodontic brackets to enamel was made a reality by Buonocore, Bowen, and Tavas and Watts. These researchers were instrumental in developing procedures and materials that have led to present-day standards in orthodontic adhesives. Traditionally, the use of acid etchants followed by primer has been an essential part of the bonding procedure for composite adhesives to allow good wetting and penetration of the sealants into the enamel surface. Acid-etching, self-cure composite resins, glass ionomer cements, and visible light curing adhesives have evolved from these early efforts. New technologies using novel materials are constantly evolving to improve the quality of the bond between the brackets and tooth. Initially, hydrophilic primers were used for dentin bonding in restorative dentistry. However now, hydrophilic enamel primers have also been introduced in orthodontic bonding to displace moisture from enamel surface. Manufacturer has introduced new self-etching primers, which reduce clinical bonding steps and chair time. Self-etching primers, which combine acid etchant and primer, simplify the bonding procedure avoiding the side-effects of acid-etching. Salivary control and maintenance of a dry operating field is a prime requisite of orthodontic bonding, because the most commonly used orthodontic primers and adhesives contain hydrophobic functional monomers (bis-GMA formula). A reduction in bond strength of composite resins to etched enamel after moisture and saliva contamination has been reported by several authors. An area for clinical improvement is the tolerance to moisture contamination during bonding to reduce the incidence of bond failures.

Every orthodontist and orthodontic patient prefer best treatment in shorter duration of time but orthodontic treatment time can be greatly influenced by the frequency of debonding occurring during treatment that can lead to lack of progress in the treatment and in some cases even relapse. Therefore bond strength between the bracket and enamel has become an important issue in research. It has been suggested that bond strength values between 5.9 and 7.8 MPa are sufficient for a clinically effective orthodontic bonding. These bond strength are considered to be able to withstand various tensile loads. However, the clinical acceptable SBS for orthodontic brackets to enamel is still unknown. There is a wide variation in the bond strength values in the literature.

In the present study we did Tukey’s post hoc test for pairwise comparison of different hydrophobic and hydrophilic adhesives. It show highly significant values.

Conclusion

In this In -Vitro Study, we found that the bond failure mode differed among the adhesives.

Ethical Approval

Study is approved by ethical committee of institute and MUHS committee.

Source of Funding

None.

Acknowledgement

I would like to express my sincere gratitude to my mentor and guide Dr.Tushar Patil (HOD and Professor, Department of orthodontics,YCMM & RDF Dental College and Hospital , Ahmednagar ) who provided inspiration and guidance behind the idea of the study.