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ORIGINAL ARTICLE
Year : 2016  |  Volume : 10  |  Issue : 1  |  Page : 10-15

Comparison of microhardness and micromorphology of enamel following a fissurotomy procedure using three different laser systems: An in vitro study


1 Department of Public Health Dentistry, Ragas Dental College and Hospital, Chennai, Tamil Nadu, India
2 Department of Conservative Dentistry and Endodontics, Sri Venkateshwara Dental College and Hospital, Puducherry, India

Date of Web Publication23-Jun-2016

Correspondence Address:
R Pavithra
Department of Public Health Dentistry, Ragas Dental College and Hospital, 2/102, East Coast Road, Uthandi, Chennai, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0976-2868.184601

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  Abstract 

Aim: To compare the microhardness and microstructural changes induced in pits and fissure following a fissurotomy procedure using three different light amplification by stimulated emission of radiation (LASER) systems. Materials and Methods: Thirty caries free premolars, extracted atraumatically for orthodontic treatment were included in the study. Using a diamond low-speed disc, enamel blocks containing the pits and fissure were cut from the tooth and divided into three groups containing 10 samples in each (G1 - diode, G2 - carbon dioxide [CO 2 ], and G3 - erbium). The enamel blocks were mounted using self-cure acrylic resin and irradiated using the three LASER systems at lower energy densities. Post irradiation, the microhardness of enamel in the pit and fissure region was measured using Vickers microhardness test. Scanning electron microscopy analysis was done to check the microstructural changes of the lased enamel. Data obtained were subjected to Kolmogorov-Smirnov test and ANOVA with statistical significance set at P ≤ 0.05. Results: All three groups showed an increase in microhardness when compared to the value taken as control (control - 209.6, diode - 237.56 ± 19.27, CO 2 -294.92 ± 29.38, erbium - 264.39 ± 11.83). ANOVA test revealed a highly significant (P = 0.001) difference between the means of the three groups. Tukey post-hoc analysis showed that CO 2 LASER showed a higher increase in microhardness followed by erbium and diode LASER. Conclusion: This study revealed that the increase in microhardness and microstructural changes obtained with CO 2 LASER was higher than the other two LASER systems. Furthermore, diode LASER can be used as a viable option for fissurotomy procedure as it improves the hardness of enamel, with a homogenous sealing effect of the pits and fissure.

Keywords: Fissurotomy, laser, microhardness, micromorphology, scanning electron microscopy


How to cite this article:
Pavithra R, Sugavanesh P, Lalithambigai G, Arunkulandaivelu T, Madan Kumar P D. Comparison of microhardness and micromorphology of enamel following a fissurotomy procedure using three different laser systems: An in vitro study. J Dent Lasers 2016;10:10-5

How to cite this URL:
Pavithra R, Sugavanesh P, Lalithambigai G, Arunkulandaivelu T, Madan Kumar P D. Comparison of microhardness and micromorphology of enamel following a fissurotomy procedure using three different laser systems: An in vitro study. J Dent Lasers [serial online] 2016 [cited 2020 Jul 4];10:10-5. Available from: http://www.jdentlasers.org/text.asp?2016/10/1/10/184601


  Introduction Top


The incidence of dental caries has been declining substantially worldwide. However, it is still a highly prevalent oral disease that is of great concern in developing countries. [1] Occlusal caries account for 88% of carious lesions and have garnered much attention. There has been a predominant reduction in number, intensity, and spread of caries attack on smooth surface as compared to that of the occlusal surface. Tooth surfaces with deep pits and fissures are particularly vulnerable to caries development. [2] The narrow morphology of pit and fissure sites provides perfect niches for pathogenic caries organisms to proliferate and because these niches are not easily cleansed by traditional methods, they are highly cariogenic sites. These sites are also difficult areas for dentists to effectively prevent or conservatively treat dental caries. [3]

Many years of research resulted in advocation of prophylactic odontotomy and fissure eradication by Bodecker in 1929, which involved mechanical eradication of fissures into cleanable ones. Later, in 1955, Buonocore suggested filling of pit and fissures with bonded resin based sealants. [4] However, studies have demonstrated that complete or partial sealant loss is common, which can result in secondary caries. Therefore, the need for new strategies and preventive measures for caries on occlusal surfaces is observed. [5]

Attention has been directed to light amplification by stimulated emission of radiation (LASER) and its positive effect on fissurotomy procedure. A wide range of LASERS (argon, carbon dioxide [CO 2 ], neodymium: yttrium aluminum garnet [Nd: YAG], and erbium: yttrium aluminum garnet [Er: YAG]) have been used to increase microhardness and resistance of the tooth structure to dental caries. [6] Stern et al. were the first to demonstrate the increase of enamel acid resistance after exposure to LASER irradiation. [7] It has been demonstrated that LASER can alter the permeability and the crystalline structure significantly, promoting enamel's resistance to demineralization. The phenomenon responsible for this effect is related to the chemical and physical changes in the hydroxyapatite crystals induced by LASER. Enamel melting occurs at more than 800-1000°C, which then recrystallizes, forming hydroxyapatite crystals larger than the initial ones. [6]

These changes occurred at higher energy densities (spot size of 1 mm, energy per pulse - 200 mJ, and energy density of 40.3 J/cm 2 ) and resulted in increased hardness of enamel and resistance to acid demineralization. The drawback of this treatment is that it resulted in heating of dentin and pulp causing inflammation and pulpal necrosis. [4],[8]

Cecchini et al. reported that CO 2 and Er: YAG LASER used at higher energy densities are well absorbed by the enamel and results in rapid melting and recrystallization of the hydroxyapatite crystals. However, the recrystallization obtained at higher densities was not homogenous and had adverse effects on the dentin and pulp such as subsurface vaporization, cracking, and necrosis. [9] In order to overcome this, Correa-Afonso et al. used CO 2 and Er: YAG LASER at lower energy densities (spot size of 0.63 mm, energy per pulse - 80 mJ, and energy density of 1.26 J/cm 2 ) and obtained results similar to Cecchini et al. with minimal damaging effects on dentin and pulp. [10]

Saafan et al. reported that diode LASER, a traditional soft tissue LASER, induced enamel fusion in the pits and fissure with no harmful effects on the dentin and pulp. Its low absorption coefficient in enamel causes rapid increase in surface temperature resulting in melting of enamel crystals and recrystallization. [6]

Studies conducted so far have evaluated the effects of individual LASER (CO 2 , Nd: YAG, Er: YAG) system on the pit and fissures, and only few studies have compared the different LASER systems. However, there exists lacuna in literature about the effects of diode LASER on the microhardness and microstructural changes in the pits and fissure of permanent teeth after a fissurotomy procedure. Hence, the aim of our study was to assess and compare the microhardness and micromorphological changes of enamel pits and fissure after fissurotomy using the three different LASER systems, namely diode, CO 2 , and erbium at lower energy densities.


  Materials and Methods Top


Thirty caries free, premolars extracted atraumatically for orthodontic treatment were included in the study. Informed consent was obtained from the patients, and Institutional Review Board, Ragas Dental College and Hospital, gave ethical clearance for this study.

The teeth were divided into three groups, 10 in each group. Teeth in group one were subjected to fissurotomy procedure using diode LASER, group two were treated using CO 2 LASER, and group three using erbium LASER.

Sample preparation

The procedure followed by Correa-Afonso et al. [10] was used in this study. To prevent drying, the extracted premolars were stored in saline until the start of the study. Using a diamond low-speed disc, enamel blocks composed of pits and fissures were prepared from the stored samples. These blocks were mounted using self-cure acrylic resin and polished using pumice powder to remove debris from the pits and fissure.

Laser irradiation

Diode light amplification by stimulated emission of radiation (G1)

The equipment used for diode LASER fissurotomy procedure was manufactured by LITEMEDICS, Italy, emits a wavelength of 980 nm at 2W for 15 s in contact mode, pulsed wave and with an optic fiber transmission system. The fiber tip was positioned perpendicular to the pit and fissure areas, and irradiation was performed in a uniform motion.

Carbon dioxide light amplification by stimulated emission of radiation (G2)

The equipment used for CO 2 laser irradiation was a PCO15-C model manufactured by Mikro Scientific Instrument Pvt., Ltd., India, emitting a wavelength of 10.6 μm. The laser beam was delivered in noncontact mode with an irradiation distance of 2.5 mm from the target site. The parameter settings used were 0.4W and 20 Hz.

Erbium light amplification by stimulated emission of radiation (G3)

The equipment used for erbium laser irradiation was manufactured by Fotona Fidelis, USA, emitting a wavelength of 2.94 μm. The laser beam was delivered at a distance of 4 mm from the target site. The parameter settings used were 80 mJ and 2 Hz. The water flow used was fine water mist at 5 ml/min. Manufacturer instructions were followed, and personal protective equipment were used during LASER irradiation.

Hardness test and scanning electron microscopy analysis

Surface hardness was measured using Vickers microhardness test (Robert L. Smith and George E. Sandland), at Microlabs Pvt., Ltd., Chennai. Each group underwent a load of 100 g to evaluate the variations in surface hardness eventually caused by laser irradiation.

Three samples from each group were analyzed by scanning electron microscopy (SEM), at the Department of Mechanical Engineering, Anna University, Chennai. The samples were gold plated using ion sputter (E-1010, Hitachi, Japan) and analyzed under × 2000 and × 5000 magnification to observe the micromorphological changes.

Statistical analysis

Data obtained from the microhardness test were entered in SPSS 20.0 (Statistical Package for the Social Sciences for Windows; SPSS Inc., Chicago, IL, USA) and subjected to Kolmogorov-Smirnov test to assess the data distribution at a significance level of P ≤ 0.05. The data were normally distributed, and ANOVA test was used to assess whether a statistically significant difference existed between the means of the three groups, followed by a post-hoc analysis.


  Results Top


[Table 1] shows the mean and standard deviation of the Vickers microhardness test for each group. These values were higher than the Vickers hardness value obtained from untreated pit and fissure (209.6). Statistical analysis of the data showed that all three groups had a statistically significant difference in mean.
Table 1: Distribution based on Vickers microhardness values of the different LASER treated pit and fissure enamel

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Tukey post-hoc analysis showed a statistically significant higher microhardness value for CO 2 , followed by erbium and diode LASER.

Images of SEM analysis reveal recrystallization of enamel in all three groups. Group 1 (diode LASER) showed melted homogenous enamel surface with multiple enamel granules. The size and shape of the crystals varied, forming a heterogenous tissue [Figure 1].
Figure 1: Scanning electron microscopy analysis of diode LASER treated enamel showing recrystallized enamel structure of different size and shape

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Group 2 (CO 2 LASER) revealed lava like agglomerates of recrystallized enamel structures [Figure 2]. Group 3 (erbium LASER) showed sharp crystals projecting from the surface [Figure 3].
Figure 2: Scanning electron microscopy analysis of carbon dioxide LASER treated enamel showing lava like recrystallization

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Figure 3: Scanning electron microscopy analysis of erbium LASER treated enamel showing sharp crystals projecting from surface

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  Discussion Top


In this study, three different LASER systems, namely diode, CO 2 , and erbium were tested for their ability to improve microhardness of pits and fissure using low-energy densities, following a fissurotomy procedure. The increase in microhardness and structural alterations were promoted with an aim to reduce the effects on dentin and pulp. Hence, the LASER parameters used in this study remain an important factor.

Fowler and Kuroda [11] reported that the microstructural changes such as melting with a glaze like appearance, surface vaporization, and carbonization of the collagen matrix were obtained at higher densities. However, the new crystals formed were found to be more soluble in acid.

The low-density parameters selected for this study were based on studies conducted by Correa-Afonso et al. [10] and Saafan et al., [6] which reported improved microhardness and reduced solubility in acid after laser treatment.

So far, studies have compared the effect of CO 2 , [12] Er: YAG [10] and Nd: YAG [13] LASER systems in increasing the microhardness of pits and fissure. These studies concluded that the tested lasers have a potential clinical application for caries prevention on pits and fissure, obtaining 30% higher acid resistance. Though these LASER systems offered desirable results, the cost, size, and skill requirement for operating them limited their use in regular practice.

Whereas, the low cost, small size, and ease of use in the oral cavity of the diode LASER system initiated researchers to study the effects of diode LASER on pits and fissure. Hence, this study attempted to compare the effectiveness of diode, CO 2 , and erbium LASER system for fissurotomy procedure.

The use of diode LASER for a hard tissue procedure can be justified from the report given by Romanos and Nentwig. [14] He found that the penetration depth of a diode LASER at 980 nm wavelength was smaller compared to erbium and Nd: YAG LASER. The smaller penetration depth resulted in increased energy deposition at the surface, melting, and recrystallization of the enamel structure. Similar to results obtained by Saafan et al., the diode LASER produced increased microhardness and recrystallization of enamel structure in this study.

The melting and recrystallization effects produced by Er: YAG and CO 2 LASER can be explained based on the absorption peak of the wavelength used on hydroxyapatite crystals. [15]

Correa-Afonso et al. reported a microhardness value of 298 ± 56 and 258 ± 70 for CO 2 and erbium LASER, respectively. [10] The results of the microhardness test obtained in our study for CO 2 and Erbium LASER were similar to that reported by Correa-Afonso et al. However, his study reported that the group irradiated with erbium LASER did not differ significantly from the control group. Whereas in our study, the microhardness value obtained after erbium LASER irradiation (264.39 ± 11.83) was higher than the microhardness of unlased pits and fissure (209.6). The microhardness values obtained after diode LASER irradiation was also higher than the unlased pits and fissure, similar to results obtained by Saafan et al. [6]

The results of SEM analysis of the group irradiated with diode LASER showed crystals of different size and shape due to loss of prismatic structure which correlates with the results obtained by Mercer and Anderson. [16] The release of the inter-rod and intercrystalline substance could be the possible explanation for the granules observed. Zuerlein et al. [17] and Fried et al. [18] reported similar results near the areas directly exposed to diode LASER.

Nagai et al. [19] reported complete melting of the enamel crystals and recrystallization resembling molten lava. Similar results were obtained in our study because of the ability of the CO 2 LASER beam to reach the bottom of the fissures and cause drastic increase in temperature due to the high absorption peak.

SEM analysis images of the group irradiated using erbium LASER demonstrate enamel prisms projecting from the surface due to ablation effect. There was the absence of carbonization and fusion of the enamel structures. This again was due to the high absorption rate of the electromagnetic beam by the water present in the interprismatic space, which was shown by Lima et al. [20]

The following can be seen as few limitations of this study. This study was done in an in vitro setup, and hence, the effect of demineralization and remineralization in an in vivo condition could not be assessed. Further, it has been widely accepted that enamel surfaces show great variation in the microstructure and microhardness depending on the area assessed, which could have biased our study results.


  Conclusion Top


Based on our study results, it could be concluded that microhardness of a lased enamel surface is higher following CO 2 LASER treatment when compared to erbium and diode LASER treatment. However, though diode LASER is traditionally viewed as a soft tissue, it has produced a significant increase in the microhardness compared to the control in our study. Hence, it could also be seen as an alternative for fissurotomy procedure from the traditional hard tissue lasers as it has dual advantage of lesser cost and being safer to the dentin-pulp complex. However, further research is essential towards this end.

Acknowledgment

I would like to thank Mr. Karthik, Microlabs Pvt., Ltd., Chennai, and Mr. Srinivasan, Foreman, Department of Mechanical Engineering, Anna University, Guindy, for providing technical support to carry out this study.

Financial support and sponsorship

There was no financial support for the study. And no scholarship.

Conflicts of interest

There are no conflicts of interest.

 
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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1]


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