An In vitro Shear Bond Strength Study to Evaluate the Efficacy of Moisture-Insensitive Primer.

Aims: We aimed to evaluate and compare the efficacy of moisture-insensitive primer (MIP) Transbond MIP while bonding to wet enamel surface. Materials and
Methods: This study was done on 100 freshly extracted human premolar teeth, collected from the Department of Oral Surgery, Government Dental College, Calicut. They were stored in distilled water at room temperature. All teeth were healthy and without caries lesion, no evidence of surface defects, or any developmental morphological aberrations. Teeth were divided into 5 groups of twenty each for the testing and Brackets were bonded onto the tooth surface in 5 different bonding sequences using Transbond XT and Transbond MIP..
Results: All the three groups of MIP have gained statistically significant higher SBS compared to Group I (Transbond XT primer in wet). Marked decrease in SBS of Transbond XT resin in wet environment was deduced. MIP in repriming sequence (Group IV) is found to have higher bond strength than other MIP groups. Conclusions: Clinical acceptability of Transbond MIP in wet environment could be recommended. MIP repriming should be done in cases where there is a doubt of contamination with saliva after initial primer application. Copyright:

INTRODUCTION

During the early years of orthodontics, banding of attachments to teeth of the entire arch was the routine. This was indeed time-consuming and attaining precision was a difficult task.

Introduction of acid etching by Buonocore[1] in 1955 with 85% phosphoric acid opened a whole new world to bonding to tooth material. With the advent of epoxy resin, Newman[2] in 1965 introduced the principles of direct bonding to orthodontics. Indirect bonding was routinely used by 8% and occasionally by 17% of the US specialists.[3]

Moisture contamination and decreased strength of the bonded attachment leading to bond failure are noted in many of the cases (Hormati et al.[4] and Silverstone et al.[5]).

With the introduction of moisture-insensitive primer (Transbond MIP), manufacturers claim that it is now possible to overcome this difficulty and obtain high shear bond strength (SBS) even in the presence of saliva.

Being a relatively new material, there is a dearth of available studies on their efficacy. Hence, the study is performed to evaluate scientifically and objectively the SBS of brackets bonded using MIP (Transbond MIP) and compare its efficacy with conventional bonding system.

MATERIALS AND METHODS

This study was done on 100 freshly extracted human premolar teeth, collected from the Department of Oral Surgery, Government Dental College, Calicut. They were stored in distilled water at room temperature. All teeth were healthy and without caries lesion, no evidence of surface defects, or any developmental morphological aberrations.

Teeth were divided into five groups of twenty each for the testing, twenty being the least recommended by Fox et al.[6] for an in vitro study of SBS.

The study employed 100 stainless steel Begg Brackets (series 256-500) of the TP Orthodontics company. Base of bracket is approximately 3.42 mm × 3.31 mm.

MIP chemically is dentin bonding agents dissolved in ethanol.

Transbond MIP (3M Unitek) was used for the study.

Methodology

Each tooth was mounted on an acrylic block in such a manner that teeth were exposed till a short distance apical to cementoenamel junction.

Initial tooth preparation was similar for all groups. Teeth were rinsed in water. Nonfluoridated oil-free pumice was applied for 30 s and then rinsed to produce a clear surface. Surface was then dried thoroughly with air.

Group I (cream)

After cleaning surface with pumice and drying, etchant 3M-Scotchbond (3M-ESPE Dental Products) was applied to the surface with an applicator brush and kept for 20 s (Kinch et al.,[7] 1989, and Wang et al.,[8] 1991). Etchant was rinsed off with water and dried thoroughly. Appearance of a frosty white area was noted. Saliva contamination was done by applying two coats of saliva onto the tooth surface with an applicator brush provided by the Transbond MIP kit. Thin coat of XT-primer was applied to the enamel surface. Stainless steel bracket was also coated with a very thin layer of XT primer. Transbond XT resin was coated on the bracket surface and placed onto the tooth. Curing was done for 40 s with Hilux curing light.

Group II (brown)

The surface was cleaned with the etchant 3M-Scotchbond and left for 20 seconds, much like Group 1. Etchant was washed away with water and well dried. Saliva contamination was achieved by applying two coatings of saliva to the tooth surface using the Transbond MIP Kit's application brush. Then, on the tooth surface, a thin layer of MIP Primer was applied. The bracketbase was also given a thin layer, and the bracket was bonded using Transbond XT Resin.

Group III (purple)

After etching of the teeth and frosty appearance, primer (MIP) was applied to the tooth surface. Saliva contamination was done after primer application. Brackets were bonded onto the tooth surface after this and curing was done.

Group IV (red)

After etching and primer (MIP) application, saliva contamination was done. After this, a secondary primer application of a single coat of MIP was done. Brackets were then bonded in the similar ways to other groups.

Group V (pink)

After the etching process, tooth surface was thoroughly cleaned and a thin coat of Transbond XT primer was applied to the tooth surface as well as bracket base. Brackets were bonded using Transbond XT resin, as has been done in the earlier tests.

Treatment sequences

Transbond XT primer in dry/wet environment:

Group I (cream): Etch, dry, saliva contamination, primer, and composite curing

Group V (pink): Etch, dry, primer, and composite curing.

Transbond MIP in wet environment:

Group II (brown): Etch, dry, saliva contamination, primer, and composite curing

Group III (purple): Etch, dry, primer, saliva contamination, and composite curing

Group IV (red): Etch, dry, primer, saliva contamination, primer, and composite curing

All the bonded teeth were stored in distilled water for 24 h before debonding.

Tensile strength

Bond strength of the teeth was tested using Universal Testing Machine (Shimadzu Corporation, Japan), National Institute of Technology, Calicut. Maximum load, maximum displacement, maximum stress, break load, break displacement, and break stress were recorded.

Statistical analysis

Statistical analysis was done using ANOVA test and Scheffe test.

RESULTS

Maximum stress of (Group I) Transbond XT in wet was highly significant compared to other groups. Maximum stress of Group I is a significantly lower value compared to other groups. The difference of the SBS of each group of MIP sample (Groups II, III, and IV), when compared with moisture without MIP (Group I/Transbond XT primer in wet), was found to be higher, and the difference was statistically significant. MIP with repriming (Group IV) is found to produce the highest bond strength in the MIP sequence even though it is not statistically significant. All the three groups of MIP have gained statistically significant higher SBS compared to Group I (Transbond XT primer in wet), showing that the efficacy of MIP is validated. Marked decrease in SBS of Transbond XT resin in wet environment is noted. MIP in repriming sequence (Group IV) is found to have higher bond strength than other MIP groups [Tables 1 and 2]. Maximum stress of Group I (cream) is highly significant from the maximum stress of all other groups [Table 3].

Table 1

Findings regarding maximum load, maximum displacement, and maximum stress of the various groups

Name of the group	Mean maximum load in Newton	Mean maximum displacement in mm	Mean maximum stress (MPa)
Group I (cream)	120.08	0.200	10.0500
Group II (brown)	182.653	0.50747	16.3083
Group III (purple)	181.734	0.35538	16.2263
Group IV (red)	195.001	0.36830	17.4108
Group V (pink)	216.392	0.49445	19.3207

Table 2

Summary of all effects obtained through ANOVA test

	Df effect	MS effect	Df error	MS error	F	P
Group	4	242.104767	96	23.3781452	10.35603	5.15E-07<<0.01

Group factor is highly significant. MS: Maximum stress

Table 3

Variable maximum stress data for multiple comparison of groups got through Scheffe test

	Cream (1)	Brown (2)	Purple (3)	Red (4)	Pink (5)
Average	10.05506	16.30835	16.22631	17.41088	19.32076
Red (1)	0.0003246	0.97112942	0.96090114		0.81529391
Pink (2)	2.525E-06	0.42745322	0.38619712	0.815293908
Purple (3)	0.0036969	0.99999887		0.960901141	0.38619712
Brown (4)	0.0036429		0.99999887	0.971129417	0.42745322
Cream (5)		0.00364286	0.0036969	0.000324556	2.525E-06

Bolded P values are <0.001

DISCUSSION

Studies by Hormati et al.[4] on effect of saliva contamination of acid-etched enamel and its effect on SBS showed that SBS decreased by 50% in the presence of moisture and simply drying was not enough. Scanning electron microscopic studies revealed that etched porosities get plugged by the moisture contamination.

In the study Silverstone et al.[5] it was found that the etched enamel was covered with a tenacious organic surface coating even when the etched enamel was contaminated for a second or more which is in line with our findings.

General values were higher compared to studies by Grandhi et al.[3] It was found that MIP in wet had comparable values to the XT in dry (a little lower however) in both the studies. Effectiveness of MIP with varying degrees of moisture contamination needs to be tested as this study has produced a significantly low value for XT primer in wet environment.

As with Webster et al.[9] study, even though a lower value was obtained, the proportion of bond strength decrease of XT primer in wet as compared to dry environment was similar. MIP repriming produced greater strength than the other two MIP treatment sequences. Treatment sequences adopted in this study were taken from the Webster et al.[9] study.

Reynolds[10] proposes 6–8 MPa as adequate strength for orthodontic bracket attachment to enamel under the tensile load.

Similarities between the values of SBS of MIP in wet and conventional primer in dry were also found to be comparable as in the case of a study by Rajagopal et al.[11]

Studies by Zeppieri et al.[12] showed that moisture contamination before or after primer application did not make any significant difference in SBS. Repriming helped to increase the bond strength.

Transbond XT in dry environment and Transbond MIP in wet environment in (repriming) produced higher SBS values compared to other groups. This could also be seen in a study by Schanveldt and Foley.[13]

Hobson et al.[14] compared the effectiveness of MIP in dry/moist/blood-contaminated environment and found that MIP has the most strength in dry environment followed by MIP in moist environment. Even in blood contamination, strength was found at 11MPa in contrast to the study by Cacciafesta et al.[15] showing very low bond strength below 5MPa in blood-contaminated field.

Littlewood et al.[16] in the study of clinical failure rates of brackets bonded with hydrophilic primer (3M Unitek) and conventional primer using APC brackets put the bracket failure of hydrophilic primer at twice that of the conventional in 6-month period.

Comparing MIP with XT, Littlewood et al.[17] (2000) study was done in dry environment because of difficulty in standardizing not only the amount of moisture but also the type. The study suggests that the SBS of the brackets bonded with the hydrophilic primer is inferior to the conventional primer.

Two in vivo studies were done in the environment, in which it has to perform using the split-mouth technique arrived at contrasting conclusions.

Littlewood et al.[16] in their studies concluded that hydrophilic primer could not be recommended for routine use

Mavropoulos et al.[18] have suggested that MIP can be used as an alternative to conventional primers.

A study was done by Girish Kumar et al.[19] showed that under dry condition, the SBS of conventional primer (Transbond XT) was significantly increased when compared to MIP. Under wet conditions, MIP (Transbond MIP) showed the highest SBS and hence can be considered a material of choice in wet conditions. Different types of contaminants such as blood, saliva, and gingival fluid would have varying effects on the SBS in an oral environment in accordance with a study done by Prasad et al.[20]

CONCLUSION

Clinical acceptability of Transbond MIP in wet environment could be recommended

MIP repriming should be done in cases where there is a doubt of contamination with saliva after initial primer application

Further studies could be done to evaluate the effects of the degree of moisture contamination and the composition and viscosity of the contaminant on the bond strength of the attachment.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.