Optimal power settings of aluminum gallium arsenide lasers in caries inhibition - An in vitro study.

CONTEXT: Incipient carious lesions are characterized by subsurface dissolution due to more fluoride ions in the 50-100 microns of the tooth's outer surface. AIMS: To determine an optimal power setting for 810 nm aluminum gallium arsenide laser for caries inhibition.
MATERIALS AND METHODS: Fifty-four caries-free extracted teeth were sectioned mesiodistally. The samples were divided into 18 groups for each power setting being evaluated. Each group had six samples. The laser used is 810 nm aluminum gallium arsenide laser with power setting from 0.1 watts to 5 watts. Laser fluorescence based device was used to evaluate the effect of irradiation. STATISTICAL ANALYSIS USED: Paired "t" test, one-way analysis of variance (ANOVA), Tukey's post hoc test, and the Pearson's correlation test.
RESULTS: The paired t-test showed that there is minimum divergence from the control for 3.5 watts. Tukey's post hoc test also showed statistically significantly results for 3.5 watts. The Pearson's correlation test showed that there was negative correlation between the watts and irradiation.
CONCLUSIONS: The power setting that gave statistically significant results was 3.5 watts.

INTRODUCTION

Dental caries is a dynamic progressive disease with varying phases of demineralization and remineralization.[12] Enamel is not homogenous throughout its thickness. Hydroxyapatite crystals in outer 50-100 micron surface contain more fluoride, but below which there are more carbonate ions. So, whenever the oral conditions are conducive for demineralization, there is subsurface mineral loss and outer layer remains intact. Preventive management strategies are directed toward making the enamel more resistant toward acid dissolution. One such option is to explore the possibility of lasers in caries inhibition.

The first laser was developed by Maiman and since then initial lasers, such as CO2 laser, have been experimented to improve acid resistance, followed by neodymium-doped yttrium aluminum garnet (Nd:YAG), erbium-doped yttrium aluminum garnet (Er:YAG), erbium, chromium-doped:yttrium, scandium, gallium, and garnet (Er,Cr:YSGG) lasers.[34] Currently, aluminum gallium arsenide laser has been shown to be an affordable and effective method for caries inhibition but the optimal power to bring about desired changes have not been explored.[4567]

Thus, this in vitro study was undertaken to determine the optimal power of aluminum gallium arsenide laser that brings upon the changes in enamel as evaluated by laser fluorescence method.

Aim

To evaluate the caries inhibitory potentiality of aluminum gallium arsenide laser at different power settings.

Objectives

To ascertain the power settings that bring about optimum caries inhibitory potentiality of aluminum gallium arsenide laser.

MATERIALS AND METHODS

Material

Laser fluorescence device (DIAGNOdent pen 2190 KaVo, Biberach, Germany).

Aluminum gallium arsenide laser (Whitestar™, Creation, Verona, Italy).

Thirty-seven percent phosphoric acid gel (Total Etch™-Ivoclar Vivadent AG, Schaan/Liechtenstein).

Procedure

The laser included in the study was 810 nm aluminum gallium arsenide laser (Whitestar™, Creation, Verona, Italy) with power setting of 0.1-5 watts. Fifty-four freshly extracted teeth that were caries free and without any structural defect were selected. They were sectioned mesiodistally, in order to obtain 108 samples and the tooth section was coated with nail varnish to obtain windows of 3 mm × 3 mm on facial surface, which aided in standardizing the sample's dimensions. The samples were divided into 18 groups for each power setting being evaluated. Each group had six samples. The power settings range of 0.1-5 watts was selected. For each sample, the preoperative value of the exposed tooth section was evaluated by laser fluorescence method (DIAGNOdent pen 2190 KaVo, Biberach, Germany) and this served as control. The tooth section was surface treated with 37% acid etchant gel (Total Etch™– Ivoclar Vivadent AG, Schaan/Liechtenstein) for 20 s. The laser fluorescence device's values were noted. Then, they were irradiated in a noncontact mode with biostimulation handpiece aluminum gallium arsenide laser of 810 nm wavelength for 30 s, and each group was individually evaluated for different power settings for example Group 1 was evaluated for 0.1 watts, and six samples were evaluated in that group. The power setting that were evaluated were 0.1 watts, 0.2 watts, 0.3 watts, 0.4 watts, 0.5 watts, 0.6 watts, 0.7 watts, 0.8 watts, 0.9 watts, 1 watts, 1.5 watts, 2 watts, 2.5 watts, 3 watts, 3.5 watts, 4 watts, 4.5 watts, and 5 watts. The biostimulation handpiece was held stationary in a noncontact mode at an angle of 90° to occlusal surface of the tooth, 2 mm away from occlusal surface, so that laser irradiation field covers the entire occlusal surface. After irradiation for 30 s, the laser fluorescence method reading was again noted. The results were tabulated and computed. The statistical analysis was done using one-way analysis of variance (ANOVA) testing, paired “t” test was used to compare the control and test groups, Tukey's post hoc test and Pearson's correlation test were used to compare the correlation between watts and irradiation.

RESULTS

Paired t-test was applied to compare whether divergence from control is significant or not. The inference drawn is if there is less divergence from the control those values of watts should be considered for the treatment. Thus, the best results seen are with 3.5 watts.

Tukey's post hoc test compares the means of every treatment to the means of every other treatment; that is, it applies simultaneously to the set of all pairwise comparisons. The inference drawn from the test are that values that are statistically significant and are computed, out of which 3.5 watts is the optimal watts followed by 2 watts, 2.5 watts, 5 watts, 3 watts, and 4.5 watts.

Graph 1: Comparison of the mean values of the three groups that is control, demineralization, and treatment by laser irradiation was done. The laser fluorescence method was used to evaluate and compare among the control group, demineralized group, and treated group. There is an increase in values from baseline that is control when the samples are demineralized. But on being treated by laser irradiation, the values decrease and are comparable to that of the corresponding control.

Graph 1

The mean values of the control group, demineralized group, and the group treated by laser irradiation are compared. The demineralized groups have increase in laser fluorescence method values as compared to the control group. Control and irradiated samples have comparable values. Thus, it can be inferred that the treatment by laser irradiation leads to comparable values between the control and treatment groups

Graph 2: The graph shows a correlation between watts and laser fluorescence values of irradiated surface. The statistical test of correlation that is Pearson's parametric test was applied and inference drawn was that there is negative correlation between the watts and irradiation. If the watts was increased, the value of laser fluorescence method reading was closer to that of the control. The power settings that gave statistically significant results were at setting of 3.5 watts.

Graph 2

There is an inverse correlation between increase in power and laser fluorescence i.e. laser fluorescence method values of irradiated surface. Indicating that the increase in watts alters the tooth and makes it more closer in its configuration in tooth structure to that of control, thus the values of control and treated groups i.e. laser irradiated by laser D = demineralized, T = treated

DISCUSSION

Moriyama et al. in an in vitro study evaluated the effectiveness of fluorescence-based methods and concluded that the laser fluorescence method was a more effective diagnostic tool to detect in situ demineralization and remineralization.[8] Bahrololoomi inferred that laser fluorescence is an effective method for detection of demineralization in an in vitro condition, but it was not so efficient in the detection of remineralization.[9] Based on the studies by Fung,[10] Patil,[11] and Vashisht,[12] who used laser fluorescence to assess remineralization, it was decided upon to use it too as an evaluator for watts selection in this study. The laser fluorescence method picks up fluorescence based on the porosity of the enamel surface. Laser irradiation changes the lattice arrangement and thus laser fluorescence method value decreases with laser irradiation.

The CO2 laser was the first laser that showed reduced dissolution of enamel in acid. The hypothesized mechanisms of actions have ranged from reduced permeability of enamel to chemicals agents caused by melting of hydroxyapatite crystals to changed enamel crystal lattice orientation.[4567] Carounanidy has hypothesized that laser-activated fluoride method can enhance the remineralization potential by reducing the critical pH.[13] Boran TL, Powell compared different lasers, such as Er:YAG, Er:YSGG, Nd:YAG, diode, CO2, argon, and found that all lasers cause caries inhibition but the mechanism of action of each may differ.[1415] Currently, aluminum gallium arsenide laser is being investigated as an alternative to high-powered lasers. The hypothesized mechanism of action is that these wavelengths selectively target and remove carbonate ions from hydroxyapatite crystals that result in increasing acid resistance of enamel.[4567]

De Sant’anna and Vitale[1617] in their respective studies found the diode laser an effective caries inhibition device. All studies agreed upon the caries inhibitory role of lasers but none ascertained the parameters such as optimal watts to bring about the desired result.[341617]

In the current study, we correlated the effect of different watts on demineralized enamel. Graph 1 illustrates that there is a significant increase in the laser fluorescence method values in demineralized group from control when the means of all groups of samples are compared. The result indicates a statistically significant decrease of laser fluorescence method values in the treatment group that is irradiated by different watts. It can be inferred that when evaluated by laser fluorescence method there is an appreciable change for all the watts under study. Thus, our study is in agreement with the works of de Sant’anna et al[16] and Vitale et al[17] proving that diode lasers bring about a structural change that is corroborated by fall in values of laser fluorescence method that are closer to the values of the control.

We also found a negative correlation between the watts and the irradiation values as assessed by laser fluorescence method. The value that brings about the best results is 3.5 watts [Graph 2]. It can be deduced that between 2 watts and 3.5 watts, the changes in enamel are appreciable. None of the studies in past have established the optimal watts that leads to making the tooth more resistant to decay.

The least amount of deviation that is there from the control i.e. the closest the laser fluorescence value to that of the control, the more successful is the treatment. This has shown that 3.5 watts is the most optimal value as it has shown laser fluorescence values closest to the corresponding control. The results are statistically significant.

CONCLUSION

Thus, it can be concluded that irradiation by 3.5 watts brings about the optimal desired changes in enamel that renders the tooth more acid resistant.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.