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Year : 2015  |  Volume : 9  |  Issue : 2  |  Page : 89-93

Evaluation of the effectiveness of low power diode laser with different wavelengths in dental caries prevention

1 Faculty of Dentistry, University of Medical Science and Technology, Khartoum, Sudan
2 Institute of Laser, University of Sciences and Technology, Khartoum, Sudan

Date of Web Publication26-Nov-2015

Correspondence Address:
E M Awooda
Faculty of Dentistry, University of Medical Science and Technology, Khartoum
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0976-2868.170568

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Objectives: To investigate the effectiveness of low power diode lasers, with different wavelengths and different irradiation times in caries prevention an ex vivo study. Materials and Methods: True experimental posttest design on 130 extracted human premolar teeth by measuring caries-like lesions examined by polarized light electron microscope after irradiation by four low power diode lasers 532 nm (4 mW), 671 nm (100 mW), 675 nm (30 mW), and 810 nm (20 mW). A fifth group was added as a control (without irradiation). The specimens were prepared by coating the teeth with acid resistance nail varnish leaving uncovered 2 mm × 2 mm of the enamel surface mesially or distally below the contact area. For each wavelength, samples were divided into three groups for three irradiation time as 4, 8, and 12 min; each group consisted of 10 teeth. Irradiated samples and the control were immersed in lactic acid (4.8 pH) and incubated for 21 days under controlled temperature of 37°C and controlled PH of 4.8. After the incubation period, the teeth were sectioned longitudinally by dissecting the 2 × 2 enamel window and the depth of the lesion was measured microscopically. ANOVA test was used to compare between different wavelengths and different irradiation times with level of significant set at P ≤ 0.05. Results: The depth of the caries-like lesions in 810 nm and 675 nm was more than that in control group (180 μm), while statistical significant difference was found (P = 0.002); when the 671 nm and 532 nm lasers wavelengths revealed depth of 70 μm and 112 μm, respectively. Increasing irradiation time decreases the depth of caries-like lesions. Conclusion: Diode laser of wavelengths 532nm and 671 nm showed less depth than control group, indicating caries prevention effect. Increasing irradiation time to a certain value increases resistance to acid dissolution.

Keywords: Diode lasers, laser caries prevention, low power laser

How to cite this article:
Awooda E M, Almuslet N A. Evaluation of the effectiveness of low power diode laser with different wavelengths in dental caries prevention. J Dent Lasers 2015;9:89-93

How to cite this URL:
Awooda E M, Almuslet N A. Evaluation of the effectiveness of low power diode laser with different wavelengths in dental caries prevention. J Dent Lasers [serial online] 2015 [cited 2022 Oct 7];9:89-93. Available from:

  Introduction Top

Dental caries is chronic and destructive disease to the teeth; many efforts have been exerted in its prevention. Using fluoride strengthening the teeth and increases resistance to acid dissolution, especially in smooth surfaces, but it is apparently less effective for pits and fissures areas. Fissure sealant is used to fill in anatomical pit and fissure that are normally too narrow for the removal of bacterial plaque by the bristles of a tooth brush. However, complete or partial loss of sealant and secondary caries is common.[1] Caries prevention representing a challenging global problem as a current review by Bagramianet al., of the available epidemiological data from many countries clearly indicates that there is a global marked increase in the prevalence of dental caries among children and adults.[2] Use of laser technology in caries prevention is gaining attention and currently under investigation and to some extends in use. The mechanism of caries prevention suggested for fluoride or laser is to make enamel more resistance to acid dissolution by changing the structure of the enamel. There is no absolute prevention, but it decreases the lesion depth and enhances remineralization. The laser tissue interaction is controlled by irradiation parameters: Wavelength, continuous or pulse emission, repetition rate, pulse duration, pulse energy, beam size and delivery method, and optical properties of the tissues. When laser light is incident on tissue surface, it can be reflected, scattered, absorbed or transmitted.[3] Theories regarding the mechanism by which laser irradiation enhances enamel resistance to artificial caries range from a physical seal achieved by melting the surface through partial fusion and recrystallization of enamel prisms to change in enamel composition only.[4] Most of the lasers used are of high powers and interact with enamel thermally justifying recrystallization and changing enamel structures to be more resistance to acid dissolution. Diode lasers are absorbed weakly in the enamel, so studies for their uses in caries prevention are few and mainly postulated on chemical interaction and changing in the chemical enamel structures. The methods used in caries prevention are costly and time consuming and need sustainability. Use of laser, especially cold lasers (soft or low level lasers), as characterized by low cost, portable and not heavy weight, easy application and handling, can be an alternative. Very few studies used diode laser with low power for caries prevention.

The aim of the study was to evaluate and to compare the effectiveness of low power diode laser with different wavelengths and different irradiation times in caries prevention.

  Materials and Methods Top

Study design and area

An Ex vivo true experimental posttest design among extracted premolar irradiates by four different wavelengths of low power diode lasers. The study was carried at the Institute of Laser, Sudan University of Sciences and Technology, Khartoum, Sudan.

Study population and sample

The studied populations were extracted human premolar teeth. The reason for extraction was orthodontic treatment. The included teeth were single rooted, sound, caries free (if any doubt were checked by X-ray). Teeth with congenital anomalies or abnormalities, sign of wear or dental caries were excluded. 130 teeth were studies, 10 teeth allocated for each group with power of the study set at 80%.

Materials, equipment, and devices

Lactic acid (extra-pure C3H6O3) supplied from Loba, Chemie, India. Nail varnish from golden Rose Paris Lacquer, France. Sterile collecting glass tubes with different sizes (10 and 20 ml). Diode laser with wavelength 532 nm and output power of 4 mW supplied from Roithner Lasertechnik GmbH, Austria; diode laser with wavelength 671 nm and output power of 100 mW (VA-11 DPSS Laser Driver) supplied from Roithner Lasertechnik GmbH, Austria; Diode laser with wavelength 675 nm and output power of 30 mW from Omega Laser, UK; diode laser of wavelength 810 nm and maximum output power 20 W (Ora Laser Jet 20) supplied from Oralia Company, Germany. Polarized light microscope with Digital camera from Zeiss, Germany. PH meter (H1 255, combined meter, pH/mv, and Ec/TDS/Nacl) from Hanna Instruments, UK. Incubator (Merret, Germany). Cutting motor with slow speed diamond disk (Isomet, Buehler, lake Bluff, IL, USA).

Preparation of teeth

The included teeth were cleaned from blood, debris, and remnant of periodontal ligament under running water and then washed and autoclaved for 15 min under pressure of 15 psi and temperature of 121°C. The sterilized teeth were stored in closed bottle filled with deionized water until the time of irradiation.

Before lasing, the teeth were placed on a clean towel to be dried in air for few minutes. A window of 2 mm × 2 mm was marked using pencil and metric ruler on the smooth surfaces of mesial or distal surfaces of the tooth in the area below the contact point (in this area usually smooth caries lesions initiated). Remaining surfaces of the crown and root were coated by acid resistance nail varnish leaving only the window marked before. The coating was done carefully using the varnish brush, and left to dry for few minutes.

Preparation for lasing and grouping

Diode lasers with different wavelengths were calibrated according to their powers. Four groups were studied according to the four wavelengths used: 532 nm (4 mW), 671 nm (100 mW), 675 nm (30 mW), and 810 nm (50 mW). According to irradiation time, each group was subdivided into three subgroups, each with 10 teeth, the first subgroup was irradiated for 4 min and the second was irradiated for 8 min while the third subgroup was irradiated for 12 min. A fifth group with 10 teeth was kept as control (without irradiation).

The laser beam was directed perpendicular to the window area after fixing the tooth in a piece of hard wax. The distance between the tooth specimen and the tip of laser probe was kept at 2 cm. After irradiation, specimens in each group were stored in 10 ml of lactic acid pH (4.8) in a glass container with a closed cap. The specimens were labeled and marked for identification according to group and irradiation times. All samples including control group (without irradiation) were incubated for 21 days in an incubator under controlled temperature of 37.5°C. After each 7 days, the pH of each of the tube was measured and sustainability of (4.8) pH were insured.

Preparation of the specimens for microscopic examination

After 21 days, specimens were washed with deionized water and each group stored in a new glass tube filled with this water until microscopic examination. Teeth were prepared for examination using a cutting disc with water cooling by sectioning each tooth longitudinally from the center of the 2 mm × 2 mm. Slides were prepared; a calibrated microscopic ruler was used to measure the depth of caries like lesion in the 10th µm and photomicrographs were taken, by attached digital camera.

Statistical analysis

The measured depths for all groups were calculated and presented in the form of a table with mean (standard deviation). The comparison between wavelength groups and within groups according to different irradiation times by ANOVA test with a level of statistical significant different set at P ≤ 0.05.

Ethical consideration

The study was approved by Ethical Committee of the University of Medical Science and Technology. Patients were requested to leave their extracted teeth voluntary for the purpose of the study with signed informed written consent. Data were kept confidentially and were used only for writing this manuscript.

  Results Top

The mean depth of caries-like lesions for each group with different irradiation time was calculated and displayed in [Table 1]. Increasing time led to increase the resistance to demineralization as in group two irradiation by diode laser 671 nm (12 min showed the lowest depth of 70 µm) followed by group one 532 nm (12 min 112 µm depth). Both groups showed less depth compared to control group when irradiated by 8 and 12 min. The other two groups (three and four) with wavelengths (675 nm and 810 nm) showed variation in relation to time, compared with control group. Irradiation by 675 nm for 4 min resulted in a depth of 196 µm while 12 min resulted in 256 µm lesion depth. The irradiation with 810 nm led to caries-like lesion of depth equal to 260 µm for three different times. The results from microscopic examination for the depth of caries-like lesions showed that the effective wavelengths were the shorter, as in case of 532 nm and 671 nm, while the other two wavelengths (675 nm and 810 nm) revealed discrepancy in the depth when increasing time and when compared to the control group (P = 0.002).
Table 1: Mean±SD of caries depth after irradiation by diode lasers with different wavelengths; compared with the control (no irradiation)

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  Discussion Top

Saliva plays an important role in caries prevention by washing, buffering and antimicrobial agents, so the study of using laser for caries prevention in vivo will be reliable and justified. Factors, that play a crucial role in caries progress, are diet, fluoride, and oral hygiene measures can adversely affect its prevention.In vivo study of dental caries prevention by laser for the time being, still facing some difficulties, because it needs double blinded experimental design, subjectivity and many confounding factors, so our study was conducted as an ex vivo. It was justified in an ex vivo, as we can simulate the oral environment. Demineralization of the enamel leads to loss of minerals primary calcium from biological hydroxyapatite. The phosphate group of hydroxylapatite can be protonated in an acid environment causing them to dissolve. The loss of calcium is often dependent on the pH of the acid solution used, temperature, humidity, and length of application. In this study lactic acid (pH 4.8) was used to demineralize enamel, which is thought to be conditions under which dental caries formed in the oral cavity. The temperature and humidity were kept similar to that of the mouth. Therefore, this technique could provide a similar environment for measuring caries-like lesion as in real life. The studies of using low power lasers for caries prevention are very few. The use of high power lasers still not commonly used, but were proved by some studies to be of good effects.[5],[6],[7] Other types of laser have shown excellent results in caries prevention.[8],[9] In these studies, most of the used lasers were high power (hard lasers). They inherited high cost, large sized devices with limitation of movement, handling, and application, so they are not widely employed in routine practice. Interest in diode lasers has grown steadily since its invention due to its inherent advantages and its range of applications with a wide range of wavelengths; however, there are few studies on dental tissue interactions using diode lasers.[10],[11]

The mechanism by which laser is thought to produce acid resistance is still under controversy results. The most accepted explanation, by how hard laser causes an effective reduction in acid dissolution, is based on thermal changes of dental enamel by changing its structures due to high temperature offered by laser reaching between 300°C and 400°C.[12] Heating will lower water permeability of the dental enamel. More hydroxide and pyrophosphate but less carbonate is also generally found in comparison with unheated enamel.[13]

This study showed that there was a significant laser-induced reduction in caries depth like lesion. Our postulation is that low level laser induces chemical and structural changes in dental enamel with modification of the organic matrix content. The results of this study are in agreement with the theoretical explanation of the change in organic substances, this may be based on the assumption that the demineralization of dental enamel depends, among other factors, on organic components. The organic matrix is located in the interprazmtaic and intraprasmatic spaces and thus exactly in the diffusion path of the demineralization process. Laser irradiation destroys the organic components and the decomposition product block the diffusion path of the irons.[14] Acid resistance is also attributed to development of micropores, the cause of which is slight contraction of the x-axis in the apatite crystal as a result of reduction in the water and carbonate content.[15] It also assumed that dissolved ions are caught in micropores and thus prevent demineralization. Further investigation is needed to explain the exact mechanism of how low power laser can reduce caries lesion depth.

Near infrared wavelength (810 nm) of diode laser used in this study seem to be not effective; Similar result was obtained by Kato et al.,[10] but disagree with the study used low power [16] or others used high power [7],[11],[17] as their result concluded significance reduction in caries like lesion. The objectives of their studies mainly concentrated on the effect of diode laser on increasing fluoride uptake, thus increase caries prevention. This contradiction of our result with these studies may be due to addition of fluoride compound that may enhance laser absorption. Diode laser with 675 nm wavelength showed similar pattern like 810 nm, in contrast to 671 nm. There are no previous data using 675 nm up to our knowledge.

When the present results of decreased caries-like lesion depth are compared with other studies conducted by different types of lasers (Ar + 129 µm,[6] Ar + 133 µm,[18] Ar + 117 µm [19]), it revealed excellent findings. The results obtained in this study reject the null hypothesis and proved that there is a significant difference between low power diode laser application for caries prevention in vitro and when compared to control group.

It is promising to use diode laser with these two wavelengths (532 nm and 671 nm) that can give a new approach in caries prevention due to their advantages compared with other types of lasers. From spectroscopy and absorption coefficient of enamel to the laser light, diode laser with wavelength of 532 nm should give more acid resistance than 671 nm wavelength, as it located near the high absorption of laser light in the enamel tissue.

Increasing irradiation time to certain value may increase the effect as more energy is deposited when increasing time, consequently the chemical composition of the exposed enamel will be affected, especially when the energy absorbed is high enough to drive organic and carbonate out of the enamel crystals and this resulted in more acid resistance.

The artificial caries-like lesion created in this study subjected enamel to a continuous challenge without period of remineralisation and this system created lesions in enamel that were identical histologically to enamel caries formation in a tooth of a real patient.

  Conclusions Top

Diode lasers with wavelengths 675 nm and 810 nm have less effect on caries inhibition when compared with control group.

The caries depth measured by microscope showed a depth of 70 µm at 671 nm and 112 µm for 532 nm when compared with 181 µm depths in the control group.Increasing irradiation time from 4 min to 12 min decrease the depth of the lesion.

Financial support and sponsorship

Sudan University Science and Technology, Sudan.

Conflicts of interest

There are no conflicts of interest.

  References Top

Bravo M, Montero J, Bravo JJ, Baca P, Llodra JC. Sealant and fluoride varnish in caries: A randomized trial. J Dent Res 2005;84:1138-43.  Back to cited text no. 1
Bagramian RA, Garcia-Godoy F, Volpe AR. The global increase in dental caries. A pending public health crisis. Am J Dent 2009;22:3-8.  Back to cited text no. 2
Dederich DN. Laser/tissue interaction: What happens to laser light when it strikes tissue? J Am Dent Assoc 1993;124:57-61.  Back to cited text no. 3
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Zezell DM, Boari HG, Ana PA, Eduardo Cde P, Powell GL. Nd:YAG laser in caries prevention: A clinical trial. Lasers Surg Med 2009;41:31-5.  Back to cited text no. 5
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Yu DG, Kimura Y, Fujita A, Hossain M, Kinoshita JI, Suzuki N, et al. Study on acid resistance of human dental enamel and dentin irradiated by semiconductor laser with Ag (NH3) 2F solution. J Clin Laser Med Surg 2001;19:141-6.  Back to cited text no. 7
Flaitz CM, Hicks MJ, Westerman GH, Berg JH, Blankenau RJ, Powell GL. Argon laser irradiation and acidulated phosphate fluoride treatment in caries-like lesion formation in enamel: An in vitro study. Pediatr Dent 1995;17:31-5.  Back to cited text no. 8
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Kato IT, Kohara EK, Sarkis JE, Wetter NU. Effects of 960-nm diode laser irradiation on calcium solubility of dental enamel: An in vitro study. Photomed Laser Surg 2006;24:689-93.  Back to cited text no. 10
González-Rodríguez A, de Dios López-González J, del Castillo Jde D, Villalba-Moreno J. Comparison of effects of diode laser and CO2 laser on human teeth and their usefulness in topical fluoridation. Lasers Med Sci 2011;26:317-24.  Back to cited text no. 11
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Hsu CY, Jordan TH, Dederich DN, Wefel JS. Effects of low-energy CO2 laser irradiation and the organic matrix on inhibition of enamel demineralization. J Dent Res 2000;79:1725-30.  Back to cited text no. 14
Oho T, Morioka T. A possible mechanism of acquired acid resistance of human dental enamel by laser irradiation. Caries Res 1990;24:86-92.  Back to cited text no. 15
de Sant'anna GR, dos Santos EA, Soares LE, do Espírito Santo AM, Martin AA, Duarte DA, et al. Dental enamel irradiated with infrared diode laser and photoabsorbing cream: Part 1 – FT-Raman study. Photomed Laser Surg 2009;27:499-507.  Back to cited text no. 16
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Hicks MJ, Flaitz CM, Westerman GH, Blankenau RJ, Powell GL, Berg JH. Enamel caries initiation and progression following low fluence (energy) argon laser and fluoride treatment. J Clin Pediatr Dent 1995;20:9-13.  Back to cited text no. 18
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