Journal of Dental Lasers

: 2015  |  Volume : 9  |  Issue : 1  |  Page : 11--15

Effect of laser and fluoride application for prevention of dental caries: A polarized microscope analysis

Akanksha Malik1, Girish Parmar2, Parul Bansal3, Amit Bhattacharya4, Niyanta Joshi5,  
1 Department of Conservative and Endodontics, AMC Dental College, Ahemdabad, Gujarat, India
2 Department of Conservative and Endodontics, GDC, Ahemdabad, Gujarat, India
3 Department of Conservative and Endodontics, Subharti Dental College, Meerut, Utter Pradesh, India
4 Department of Orthodontia, GDC, AMC Dental College, Ahmedabad, Gujarat, India
5 Department of Pedodontia, AMC Dental College, Ahmedabad, Gujarat, India

Correspondence Address:
Dr. Parul Bansal
58/6, Jagriti Vihar, Meerut, Utter Pradesh


Aim: Aim of the study was to evaluate the effect of CO 2 pulse laser on acid resistance when irradiated alone or prior to fluoride treatment. Materials and Methods: Totally, 80 extracted premolars were prepared and randomly assigned to four groups (n = 20 for each group): (i) Untreated (control), (ii) fluoride treated, (iii) CO 2 laser treated, (iv) CO 2 laser + fluoride treated. Specimens were exposed to pH cycling, and acid resistance was evaluated by determining the initial surface demineralization of enamel assessed under polarized light microscope. Results: Significant differences were found between the control group and fluoride, laser or laser + fluoride groups (P < 0.05). There was significant difference between laser group and control (P = 0.01) or fluoride group (P = 0.05). There was no significant difference between laser and laser + fluoride group. Conclusion: All applied treatments were capable of reducing caries like lesion progression in dental enamel when compared with the control group. From the parameters measured, the rank order of anti-cariogenic potential of the treatment was, CO 2 laser combined with fluoride varnish, CO 2 laser alone and fluoride varnish alone.

How to cite this article:
Malik A, Parmar G, Bansal P, Bhattacharya A, Joshi N. Effect of laser and fluoride application for prevention of dental caries: A polarized microscope analysis.J Dent Lasers 2015;9:11-15

How to cite this URL:
Malik A, Parmar G, Bansal P, Bhattacharya A, Joshi N. Effect of laser and fluoride application for prevention of dental caries: A polarized microscope analysis. J Dent Lasers [serial online] 2015 [cited 2021 Jan 15 ];9:11-15
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In spite of the decline observed in dental caries, it still represents the most prevalent chronic childhood oral disease. Caries is a dynamic process, fluctuating between demineralization and remineralization process, beginning with the microscopic loss of crystal structure progressing to complete destruction and cavitation.

In the past, fluoride and fissure sealants were the primary caries preventive agents. Fluoride has been proven to be an effective treatment for the prevention of dental caries by inhibiting demineralization and enhancing remineralization. [1] Of all the new avenues open to caries prevention through increased acid resistance, the use of laser in the prevention of demineralization is one of the most fascinating and promising of all. The use of laser irradiation as a means of inhibiting dental caries was first suggested by Stern and Sognnaes. [2]

Laser treatment is effective in elevating the resistance of enamel to cariogenic challenge by changing the surface structure and physical properties, including melting and recrystallization of the enamel hydroxyapatite crystals. [3] Several investigators have demonstrated that treatment with various lasers such as the CO 2 , Nd: YAG and Argon lasers can reduce the subsurface demineralization rate in enamel. [4] CO 2 laser appears to be the most efficient in this regard due to the enamel absorption coefficient which closely corresponds to the CO 2 laser emission wavelength. [5]

The efficacy of CO 2 laser irradiation combined with fluoride in inhibiting enamel demineralization has been demonstrated in several laboratory investigations. [6],[7] The aim of the present study was to compare the effect of CO 2 laser; fluoride varnish; and CO 2 laser and fluoride varnish on initial surface demineralization of permanent dentition enamel. Thereby, to assess the caries preventive potential of CO 2 laser treatment of enamel compared to topical fluoride application.

 Materials and Methods

Teeth selection and grouping

Totally, 80 mandibular and maxillary premolars extracted for orthodontic treatment were collected and carefully assessed by stereomicroscope to ensure the absence of any caries or defect. Teeth were cleaned of tissue tags and washed with deionized water. Samples were stored in 0.1% thymol solution. Teeth were coated with an acid-resistant varnish leaving a window of 2 mm × 2 mm area of exposed enamel surface for the creation of artificial caries-like lesions.

Teeth were divided into four groups consisting of 20 teeth.

Group I (control): No fluoride varnish application or laser irradiation was done prior to pH cyclingGroup II (fluoride test group): Enamel was treated with 0.1 mg of fluoride varnish over a period of 6 hGroup III (laser test group): Enamel was irradiated with a pulsed CO 2 laserGroup IV (laser and fluoride test group): Laser irradiation was, followed by fluoride varnish application over a period of 6 h.Laser treatment

The laser and fluoride and laser groups were subjected to laser irradiation with a CO 2 laser (Denta K, ESC/Sharplan, UK) at a wavelength of with 1.6 W power, 10 ms pulse duration, 10 ms of time off, 50 Hz repetition rate, 0.3 mm beam diameter and 10 J/cm 2 per pulse fluence. Irradiation was carried out by scanning the exposed enamel of each tooth for approximately 30 s from an X-Y positioning platform while maintaining a 10 mm distance from the tip of the hand piece to the tooth in order to provide uniform coverage of each window. The scanning speed was approximately 1 mm/s.

Fluoride treatment

The fluoride and laser, and fluoride groups were treated with topical fluoride varnish (Bifluorid, Voco), containing 6.0% NaF and CaF 2 w/w for 6 h, immediately after the FL group received laser treatment.

pH-cycling process

A 9 days and night pH-cycling scheme was performed, with 6 h of demineralization, followed by 17.5 h of remineralization at 37°C. The demineralization solution contained 2.0 mmol/L calcium, 2.0 mmol/L phosphate, and 0.075 mol/L acetate at pH 4.3. The remineralization solution was supersaturated with calcium phosphate (calcium = 1.5 mmol/L, phosphate = 0.9 mmol/L), with potassium chloride at 150 mmol/L and cacodylate buffer to pH 7.0 (20 mmol/L). A 10 min wash in deionized and distilled water was performed between the demineralization and remineralization phases and at the end of the process. Both demineralization and remineralization solutions were changed daily.

Polarized light microscopy analysis

Samples were sectioned with a carborundum disc mounted on a micromotor hand piece, of approximately 0.5 mm thickness in a buccolingual direction. Samples were then observed under polarized light microscope at ×100 using water as imbibition media. Observations are presented in the [Table 1] and [Figure 1] [Figure 2] [Figure 3] [Figure 4].{Figure 1}{Figure 2}{Figure 3}{Figure 4}{Table 1}

Statistical analysis

To compare the proportion between the different groups Tukey test for significance was done. For the purpose of comparison, P < 0.05 is considered for statistical significance [Table 2].{Table 2}


The results of the present study showed that all applied treatments were capable of reducing caries like lesion progression in dental enamel (P < 0.05) when compared with the control group. The present data revealed that the laser-treated samples presented significantly less caries formation than the other group specimens. In addition, the combination of CO 2 laser irradiation with fluoride varnish provided significantly more protection against demineralization than did the fluoride varnish use alone. There was no significant difference between laser and laser and fluoride groups. From the parameters measured, the rank order of anti-cariogenic potential of the treatment was, CO 2 laser combined with fluoride varnish, CO 2 laser alone and fluoride varnish alone.


In various approaches to preventive dentistry relating to dental caries, efforts have been made by chemical means to reduce the solubility of the enamel surface and to create conditions that would promote the penetration of caries-preventive agents to subsurface enamel, fluorides being one among them. The fluoride concentration and pH of topical fluoride solution have an influence on fluoride uptake into enamel. [8] As an alternative to fluoride application, laser pretreatment of enamel inhibit subsequent, acid-induced dissolution of enamel. The implications of laser irradiation as a means of inhibiting dental caries were first suggested by Stern and Sognnaes, [2] Since then, several studies using several types of laser apparatus have demonstrated that laser pretreatment of enamel can inhibit subsequent artificial caries-like lesions. [6],[9]

Continuous wave or pulsed CO 2 lasers, Nd: YAG, and Excimer lasers have been used to enhance caries resistance and support remineralization. [4] However, the wavelengths (k) of argon lasers (k ¼ 488-514 nm) and Nd: YAG lasers (k ¼ 1064 nm) seemed to fail to be effectively absorbed by an enamel. [10] Furthermore, cavity preparation performed by Er: YAG (k ¼ 2940 nm) and Er, Cr: YSGG (k ¼¼ 2780 nm) was also not found to be capable of reducing the susceptibility of the prepared enamel to in vitro demineralization.

Studies carried out to evaluate the effect of a CO 2 laser on enamel and dentin structures showed its absorption by dental tissues to be high. This is a result of the fact that the CO 2 laser produces radiation in the infrared region, which coincides closely with some of the apatite absorption bands, mainly phosphate and carbonate group absorption bands and also due to the enamel absorption coefficient, which closely corresponds to the CO 2 laser emission wavelength. [8] Therefore, it seems that the CO 2 laser may exhibit promising results in increasing the resistance of enamel to acid dissolution. [3],[11] Hence, CO 2 laser radiation at safe energy levels can be used to thermally modify enamel that is more resistant to acid dissolution. Some investigators have found that the most efficient wavelengths for prevention of dental caries was 9.3 mm and 9.6 mm, due to the high absorption coefficient in dental enamel at these wavelengths. [5]

In the present study, only laser group was found to be significantly superior to only fluoride group (P < 0.05). Similar results have been reported in various studies [3],[4],[12] suggesting less caries inhibition in the fluoride group as compared to the laser treated group thereby, corroborating with the results of the present fluoride study group.

Similar to our study, various pH cycling studies using fluoride, have reported inhibition of caries progression by 70-80%, [13],[14] while studies [6] on laser inhibition of caries reported an inhibition in the range of 70-85% various other studies, [15],[16] in contrast to the present study, have reported a higher percentage of caries inhibition in the only fluoride treated group as compared to the laser treated samples. The possible explanation to this, as suggested by Dawes and Weatherell, could be that laser treatment does not enhance remineralization in the absence of fluoride, but only inhibits demineralization, and since fluoride interferes physicochemically with caries development by reducing demineralization and enhancing remineralization, it has shown to have improved caries prevention. [17]

In the present study lesion inhibition in laser only group was less (85%), as compared to that of the combined group, wherein the lesion inhibition accounted to about 90%. However, no statistically significant difference was found between laser alone and combined group. These results are in accordance with the studies [18],[19] which showed similar results. On the contrary, several other studies have shown that lasers and fluoride combined treatment was significantly superior to laser alone treatment. [16] This effect can be attributed not only to enamel changes promoted by the CO 2 laser, but also to a possible increase in fluoride uptake in irradiated enamel. [5]

Similar to our study, several studies with fluoride and laser irradiation have demonstrated an increased inhibition of demineralization. [13],[14],[19] Combined applications of laser irradiation and fluoride have been reported to have synergistic effects, [20] enhancing the fluoride uptake of the irradiated enamel.

Based on the literature various mechanisms are involved in the cariostatic effect of low-energy laser-fluoride treatment on enamel demineralization.

Purification of enamel hydroxyapatite

One of the main mechanisms may be the laser-induced compositional changes in enamel by formation of a less-soluble enamel structure resulting from decreased carbonate and crystalline water, increased structural OH and the potential formation of pyrophosphate. [11]

Reduction of enamel diffusion

The photothermal effect of a low-energy laser treatment may also cause a reduction in enamel permeability. [12]

Increased fluoride deposition on enamel surfaces

After CO 2 laser irradiation, [13] fluoride uptake on the enamel surface increased by 37% more and may be released from the surface during acid attack to reduce the demineralization and enhance remineralization. [14]

Formation of fluoridated hydroxyapatite

CO 2 laser treatment may transform synthetic hydroxyapatite into "fluorapatite" in the presence of fluoride. [12] Fluoride uptake was shown to be greater when laser treatment was done before the fluoride treatment rather than after fluoride application. [8]

Various possible mechanisms have been suggested for the laser-induced increase of fluoride uptake. One theory proposes that during laser irradiation, many partially coalescent globular granules are also produced by the process of melting and the subsequent resolidification of enamel crystals. [8] In this situation, fluoride can easily penetrate into the spaces between the granules. The microspaces formed by laser irradiation may trap the demineralized ions and provide space to allow them to combine with fluoride. [21] One possible explanation to this could be that there may have been a presence of some surface induced changes, such as an increase in cracks and roughness which might play an important role in increasing calcium-fluoride-like material formation. [16] Another mechanism emphasizes the role of lasers in enhancing fluoride uptake into the tooth crystalline structure in the form of firmly bound fluoride. [15] These facts help explain the remarkable synergism achieved by laser combined with fluoride over either respective treatment modality. Since fluoride was not present at the time of irradiation, heat does not seem to be responsible for fluoride uptake.


The emergence of a new philosophy of prevention, rather than repair and replacement has been one of the most visionary approaches in preventive dentistry, so that the present study has been carried out in an attempt to explore the possibilities of the effects and applications of lasers in preventive dentistry. Like various other studies, the present study also supports the use of laser and fluoride for the prevention of dental caries.


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