In vitro Study - Comparative Evaluation of Bond Strengths of Stainless Steel Brackets and Ceramic Brackets after Curing with the Argon Laser and the Conventional Visible Light.

Aim: The purpose of this study was to compare the bond strengths of stainless steel brackets and ceramic brackets after treated with conventional visible light and argon laser. Methodology: Extracted 80 human premolar teeth were collected and stored in distilled water. They are classified into four groups. All teeth were placed in acrylic block where long axis of the tooth should be perpendicular to the mold's bottom. Teeth were subjected to ×10 magnification after debonding.
Results: There is no statistically significant difference was found between the shear bond strength of argon laser and conventional visible light for stainless steel and ceramic bracket. Ceramic brackets had significantly increased bond strength than stainless steel brackets.
Conclusion: Argon laser can be used for bonding orthodontic brackets using a visible light-cure orthodontic adhesive system, and ceramic brackets had significantly increased bond strength than stainless steel. Copyright:

INTRODUCTION

The principle of orthodontic treatment is to apply force to the teeth. This can be accomplished with either a movable or a fixed appliance. Brackets were welded to the bands fabricated for each tooth, and this force was transmitted to the teeth. Buonocore's discovery of the acid-etch technique in 1955 revolutionized orthodontics, resulting in modern direct bonding systems that eliminated bands and allowed brackets to be attached directly to the tooth.[1] These systems were originally chemically activated, which had the disadvantage of not allowing the operator to manage the working time for bracket placement and requiring clean-up operations. To combat this, light-curing systems that were originally cured with ultraviolet light were introduced. Individual composite resins that polymerize when exposed to visible light in response to concerns about the impact of UV radiation on human health.[23]

A diketone initiator, such as camphorquinone, is used to induce polymerization in visible light-activated resins. The highest activity of this photoinitiator system is focused around 480 nanometers (nm) wavelength. Outside of the blue band, light has little or no influence on camphorquinone starting the polymerization synthesis.[4] It has been discovered that the properties of commonly used halogen light-curing units are inconsistent. These devices produce light with a 120 nm broadband width, which lies between 400 nm and 520 nm. Due to light divergence from the source, the resulting energy density is typically around 400w/cm2, and with increasing distance, the power density of light reaching the composite decreases dramatically. Reflectors, bulbs, and filters can all decay and reduce curing efficiency.

The capability of argon lasers to photo polymerize composite resins has been the subject of recent research. The word argon is derivative of the Greek word Argo, which means “inactive.” The features are colorless, odorless, tasteless, and is nontoxic. In 1894, Lord Rayleigh and Sir William Ramsay discovered argon in Scotland. It is a type of ion laser in which the active medium is noble gas. In forensic medicine, general and ophthalmic surgery, holography, and dentistry, it has applications. It comes in two different wavelengths. Soft-tissue operations such as gingivoplasty and gingivectomy are performed with the 514.5 nm green beam argon laser. Light-activated composite resins are cured using a 480 nm blue beam.[56]

With an intensity of around 800w/cm2, the argon laser operates at a combined bandwidth of 488 nm in the visible light spectrum. The argon laser's wavelength specificity, combined with its ability to consistently emit visible light with substantial energy density or unusable emissions, has been shown to improve the physical properties of composite resins by achieving a more thorough cure with up to 75% shorter exposure time when compared to conventional light-curing units. These considerations may help explain why laser curing of composite resins is more efficient than visible light curing.[5] During this in vitro investigation, the shear bond strength of stainless steel and ceramic brackets were compared after curing with conventional curing light (40 s), and argon laser (10 s) and adhesive remnant index (ARI) were compared after debonding.

METHODOLOGY

The study was carried out at Annamalai University's Rajah Muthiah Dental College and Hospital, Annamalai Nagar, in collaboration with the Department of Manufacturing Engineering, Annamalai University, Chidambaram, and the Regional Institute of Ophthalmology, Government Ophthalmic Hospital, Chennai. All 80 human premolar teeth were extracted and stored in distilled water immediately. They were classified into four groups.

Group I-Light-cure orthodontic adhesive system (Transbond XT) was used to bond stainless steel brackets, which were then cured with an argon laser for 10 s.

Group II-Light-cure orthodontic adhesive system (Transbond XT) was used to bond stainless steel brackets, which were then cured with conventional visible light for 40 s.

Group III-Light-cure orthodontic adhesive system (Transbond XT) was used to bond the ceramic brackets, which were then cured with an argon laser for 10 s.

Group IV-Light-cure orthodontic adhesive system (Transbond XT) was used to bond the ceramic brackets, which were then cured for 40 s with conventional visible light.

Teeth were placed in acrylic with the teeth's long axis perpendicular to the mold's bottom [Figure 1]. Brackets were made up of stainless steel and ceramic materials were bonded by means of a standard visible light unit. Brackets made of stainless steel and ceramic were bonded using an argon laser model. All brackets were bonded to the teeth using the method described below. To remove any surface material, rubber cup and pumice powder were used to clean the teeth, then subjected to etching for 30 s with 37% phosphoric acid. The teeth were then washed thoroughly with duration of 30 s before being dried in an oil-free air stream for duration of 10 s. The enamel shows frosty-white appearance. Following the manufacturer's guidelines, a brackets (0.022” premolar brackets) were bonded with Transbond XT (3M). The teeth under Group (I, II) were bonded using argon laser for time period of 10 s and conventional visible light for time period of 40 s, respectively [Figure 2]. Teeth in the Group (III, IV) were bonded using argon laser for 10 s and conventional visible light for 40 s, respectively. After that, all samples were debonded and stored in deionized water for 24 h in a light-sealed container. Every tooth's shear bond strength was assessed using the Unitek universal testing machine. The sample was placed in the Instron machine's lower arm with the purpose of applying force parallel to the tooth surface (gingiva-occlusal). An acrylic was threaded using circular stainless steel wire loop. The wire loop was threaded between the bracket's wings. In the upper arm of a Unitek universal testing machine, where acrylic with wire loop was fixed at a crosshead speed of 1 mm/min.

Figure 1

Teeth mounted in acrylic blocks

Figure 2

Argon laser unit

The following formula was used to convert values of the force reported at the point of failure to shear stress.

After debonding, the teeth were examined under ×10 magnification. According to ARI, any adhesive left on the teeth surface after bracket removal was evaluated. The ARI scale goes from 0 to 3.

0-No adhesive on the tooth

1-less than half of the adhesive on the tooth

2-More than half of the adhesive on the tooth

3-All adhesive on the tooth.

RESULTS

This study was implemented on 80 premolars extracted for orthodontic purpose and was free of caries. They were divided into four groups containing 20 teeth each. After etching brackets were bonded onto the teeth. Groups I, III were cured with argon laser with duration of 10 s.

There is no statistically significant difference found between the shear bond strength of argon laser for duration of 10 s and conventional visible light for duration of 40 s for stainless steel and ceramic bracket [Table 1].

Table 1

Mean and standard deviation of shear bond strength for stainless steel and ceramic bracket

	Group	n	Mean	SD	t	P
Argon laser	Stainless steel	20	8.93333	2.397530	1.629	0.121
	Ceramic	20	10.80000	2.717824
Conventional visible light	Stainless steel	20	7.26667	1.790303	1.974	0.064
	Ceramic	20	8.88010	1.864566

SD: Standard deviation

There is no statistically significant difference found between the bond strength of stainless steel brackets and ceramic brackets cured with conventional visible light with duration of 40 s and argon laser with duration of 10 s [Table 2].

Table 2

Mean, standard deviation for bond strength measurements of ceramic brackets

	Group	n	Mean	SD	t	P
Argon laser	Stainless steel	20	8.93333	2.397530	1.629	0.121
	Ceramic	20	10.80000	2.717824
Conventional visible light	Stainless steel	20	7.26667	1.790303	1.974	0.064
	Ceramic	20	8.88010	1.864566

SD: Standard deviation

Ceramic brackets had significantly increased bond strength than stainless steel brackets [Table 3]. The ARI Scores were significantly different between curing procedures, even though there was no significant correlation between mean bond strengths and ARI Scores [Table 4].

Table 3

Mean standard deviation for bond strength measurements for both stainless steel and ceramic brackets

	Group	n	Mean	SD	t	P
Shear bond strength	Stainless steel	40	8.10000	2.229809	2.337	0.025
	Ceramic	40	9.84005	2.472998

SD: Standard deviation

Table 4

Correlation between the mean bond strengths and adhesive remnant index scores for both stainless steel brackets and ceramic brackets

	Groups	Conventional	Argon laser light
Stainless steel brackets	Shear bond strength	1	0.264
	ARI	0.264	1
Ceramic brackets	Shear bond strength	1	0.352
	ARI	0.352	1

ARI: Adhesive remnant index

DISCUSSION

The current study was to compare the shear bond strengths of stainless steel brackets and ceramic brackets after curing with an argon laser with duration of 10 s and the conventional curing light with duration of 40 s in vitro study. The main disadvantage of traditional visible light healing is that it takes a long time to cure. Argon lasers were introduced to solve this time duration, and many research compared the efficacy of argon lasers in curing visible light-cure restorative materials with standard curing light. The minimal clinically acceptable bond strength for directly bonded orthodontic attachments has been proposed (6–8Mpa). According to a statistical analysis of the data from our experiment, all of the groups exceeded the clinically acceptable bond strength. Our results were compared to those of James et al., who evaluated the effect of bond strength using adhesive precoated brackets for the argon laser with specification of (238.1 mW/cm2, 10 s) of 4.2Mpa (SD1.0) versus the conventional visible light with specification of (771.9Mw/cm2, 20 s) of 5.3Mpa (SD1.0); 37% of phosphoric acid and primer (Transbond XT). They stated that shear bond strengths were lesser than the study's mean bond strength. This difference could be due to the fact that James et al. employed a different argon laser system with shorter curing durations, and their conventional visible light showed a higher density.[7] Shanthala and Munshi[8] investigated the effect of bond strength in adult teeth using an argon laser with a 10 s exposure time compared to conventional visible light for 40 s polymerization, and they found no statistical difference in shear bond strength between the two. Lalani et al.,[9] However, the results of this investigation were not comparable to those of the previous study because the shear bond strength in this current study was higher. Our mean shear bond strength was lesser than that stated by Talbot et al.[10] for argon laser with specification of 230 mW/cm2, 10 s, 14.55 Mpa and conventional visible light with specification of 40 s and 15.79 Mpa. Our study's mean shear bond strength was comparable to that reported by Soderquist SA et al.[11] Ceramic brackets feature distinct qualities when compared to stainless steel brackets, the most notable of which being stronger bond strengths. The design and composition of the bracket base may also have an impact on bond strength. Our study's mean shear bond strength was similar to that reported by Joseph and Rossouw.[12] The results showed that the ceramic groups had much-increased bond strengths than the stainless steel groups, and all of these combinations produced shear bond strengths that were higher than clinically acceptable levels. According to Kelsey et al.,[1314] laser power and exposure time parameters appear to be adhesive material, as an orthodontic glue must be removed following treatment. As a result, a superior adhesive should not induce any damage to the enamel while debonding the brackets. The ARI was used to assess this. Von Fraunhofer and Allen.[15] found that a temperature increase of 10 F (about 6 C) can elicit irreversible pulpal reaction, and a temperature increase of 20 F (roughly 11 C) can cause pulp necrosis. They employed a 3W Nd:YAG laser and found that it increased the intra pulpal temperature by more than 6°C. Cobb et al. did a study and determined that argon lasers utilized at 250–300 MW energy levels should not cause a severe thermal risk to the pulp.[16] Powell et al. found pulp chamber temperature fluctuations caused by argon-ion laser at 250–300 MW energy level were substantially lesser than those caused by conventional curing lights; however, histologic pulpal damage occurred at >600J/cm2 in another investigation. For 900J/cm2 energy, the intrapulpal temperature was raised by 6°F. We may conclude from these data that employing an argon-ion laser for resin polymerization will not cause substantial pulpal damage.[17] Hence, using argon laser as a source of curing for light-cure orthodontic adhesive system, the time consumed for bonding could be minimized dramatically.

By viewing the overall performance and advantages of argon laser, it can be used as an alternative for curing of visible light-cure orthodontic adhesive system.

Although all the new advances promise a superior performance than the ones before, it needs controlled clinical studies with a large number of patients, which should be conducted in biological intraoral environment.

CONCLUSION

Argon laser can be used to bond orthodontic brackets using visible light-cure orthodontic adhesive system (Transbond XT)

All of the groups had shear bond strengths that were higher than the clinically acceptable level (6–8 Mpa)

There was no statistically significant difference was found between the bond strength of stainless steel brackets cured with argon laser with duration of 10 s and conventional visible light with duration of 40 s

Ceramic brackets demonstrated much higher bond strengths than stainless steel brackets, but they were not statistically different

The ARI Scores varies among different curing procedures and found that no significant correlation between the mean bond strengths and the ARI score.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.