|Year : 2012 | Volume
| Issue : 3 | Page : 131-135
Ultra morphological changes of root canal dentin induced by 940 nm diode laser: An in-vitro study
Muliya Vidya Saraswathi1, Nidambur Vasudev Ballal1, Indhya Padinjaral1, Subraya Bhat2
1 Department of Conservative Dentistry and Endodontics, Manipal College of Dental Sciences, Manipal University, Manipal, Karnataka, India
2 Department of Periodontics, Manipal College of Dental Sciences, Manipal University, Manipal, Karnataka, India
|Date of Web Publication||30-May-2013|
Muliya Vidya Saraswathi
Department of Conservative Dentistry and Endodontics, Manipal College of Dental Sciences, Manipal University, Manipal - 576 104, Karnataka
Source of Support: None, Conflict of Interest: None
Aim: The aim of this in-vitro study was to investigate the ultra-morphological changes of the root canal dentin after irradiation with 940 nm diode laser along with 2.5% sodium hypochlorite (NaOCl) and 17% ethylenediaminetetraacetic acid (EDTA) irrigation. Materials and Methods: Ten freshly extracted human permanent mandibular premolar teeth were selected. Teeth were decoronated and the working length was established. Cleaning and shaping was performed using protaper rotary system and the canals were enlarged up to F3 size. Canals were irrigated with 2.5% NaOCl between each instrument change and later with a final flush of 5 ml of 17% EDTA for 1 min. All the prepared teeth were then longitudinally grooved and split into two halves. One-half of each tooth (Group A) (n = 10) was analyzed without laser irradiation and other half (Group B) (n = 10) was analyzed after irradiation with 1.5 W continuous wave of 940 nm diode laser. Samples from both groups A and B were then subjected to scanning electron microscope analysis. Photomicrographs were taken at 2 mm, 7 mm, and 12 mm from the apex representing the apical, middle, and coronal regions at 2000Χ. Energy dispersive X-ray spectroscopy (EDX) analysis of the same samples was done under EDX analyzer to assess the calcium (Ca), phosphorus (P) and magnesium content and to determine the Ca P ratio. Results: Examination of the surface of the root canals revealed that, at middle and apical thirds smear layer removal was better with laser irradiated group. However, in the coronal third there was no statistically significant difference between both the groups. There was a mild variation in values when both group A and group B were compared to Ca, P, magnesium content, and the Ca phosphorous ratio but the difference was not statistically significant. Conclusion: 940 nm diode laser irradiation of root dentin along with NaOCl and EDTA irrigation, resulted in better removal of smear layer without significant additional loss of mineral content.
Keywords: Diode laser, scanning electron microscope, smear layer
|How to cite this article:|
Saraswathi MV, Ballal NV, Padinjaral I, Bhat S. Ultra morphological changes of root canal dentin induced by 940 nm diode laser: An in-vitro study. Saudi Endod J 2012;2:131-5
|How to cite this URL:|
Saraswathi MV, Ballal NV, Padinjaral I, Bhat S. Ultra morphological changes of root canal dentin induced by 940 nm diode laser: An in-vitro study. Saudi Endod J [serial online] 2012 [cited 2019 Dec 8];2:131-5. Available from: http://www.saudiendodj.com/text.asp?2012/2/3/131/112704
| Introduction|| |
Three-dimensional cleaning and shaping of the root canal system is one of the main goals of the root canal treatment.  Microcomputed tomography scans before and after mechanical instrumentation shows that, regardless of the instrumentation technique used, 35% or more of the root canal surfaces remained uninstrumented.  This is in addition to lateral canals, accessory canals, anastomoses, fins, and other irregularities create a three-dimensional network  providing an environment for microbes to colonize and cause disease. 
Irrigation of the root canal system is important in endodontic therapy for its antimicrobial effect, lubrication and smear layer removal ability, which causes dissolution of both organic and inorganic components. , Alternate use of ethylenediaminetetraacetic acid (EDTA) and sodium hypochlorite (NaOCl) solution has gained wide acceptance and has been advocated as an effective irrigation regimen to remove organic and inorganic remnants of smear layer. ,,, Studies have shown that, conventional needle irrigation with NaOCl and EDTA is less effective in cleaning apical areas compared to coronal areas of root canal systems. ,
Calcium (Ca) and phosphorus (P) in hydroxyapatite crystals are the major inorganic components of dental hard-tissue. It has been reported that, use of EDTA alone or in combination with NaOCl is capable of decreasing the Ca/P ratio of the root canal dentin significantly. , Any change in the Ca/P ratio may change the original proportion of organic and inorganic components, which in turn changes the permeability, microhardness and solubility of root canal dentin and may also adversely affect the sealing ability and adhesion of resin based cements and root canal sealers. ,
Lasers have the potential applications in the field of endodontics mainly for their effectiveness in antibacterial action and smear layer removal. ,,,, Diode lasers have got good depth of penetration inside the dentinal tubules (500 μm) compared to chemical solutions (100 μm). ,, To date, the potential application of 940-nm diode laser energy in endodontics has seldom been addressed except for its application in the disinfection of the root canals after endodontic instrumentation. Hence, the aim of this in-vitro study was to investigate the ultra morphological changes of the root canal dentin after irradiation with 940 nm diode laser along with 2.5% NaOCl and 17% EDTA irrigation, using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX).
| Materials and Methods|| |
Ethical clearance was obtained from the institutional review board, Manipal University, India. Ten freshly extracted human mature permanent mandibular premolar teeth were selected from the age group of 16-25 years. All the teeth were radiographed to verify the presence of single canal, mature apex and absence of any resorption or endodontic obturation. The teeth with caries, cracks and dilacerations were excluded. The soft-tissues were removed from the root surface by a soft brush and teeth were stored in 0.2% sodium azide (Sigma Chemical Co, St. Louis, MO) at 4°C until the experiment. Teeth were then decoronated using a low-speed diamond disc (Diatec, Swiss Dental, Switzerland) to obtain a uniform root length of 14 mm. The pulp tissue was extirpated using barbed broach and the working length was established by inserting a No. 10 K file (Mani Inc-Tochigi Ken, Japan) into each root canal until it was just visible at the apical foramen (observed under magnifying loupes) and by subtracting 1 mm from this point. Root apices were then closed with sticky wax to simulate the closed end model. Cleaning and shaping was performed using protaper rotary system (Dentsply-Maillefer, Ballaigues, Switzerland) and the canal was enlarged up to F3 size.
Irrigation was performed using a 27 gauge side vented needle (Appli Vac, Vista Dental Products, USA). The needle was placed within 1-2 mm of the working length in each canal. Canals were irrigated with 2 ml of 2.5% NaOCl (KMC Pharmacy, Manipal, India) for 1 min between each instrument change. After instrumentation, canals received a final flush of 5 ml of 17% EDTA (Merck, Darmstadt, Germany) for 1 min. This was followed by a flush of 5 ml of distilled water for 1 min to remove any remnants of irrigating solutions and the canals were dried with sterile paper points (Dentsply-Maillefer, Ballaigues, Switzerland). All the prepared teeth were then longitudinally grooved using a diamond disk (Diatec Swiss Dental, Switzerland) to obtain a total of 20 halves. One-half of each tooth (Group A) (n = 10) was analyzed without laser irradiation and other half (Group B) (n = 10) was analyzed after irradiation with 1.5 W continuous wave of 940 nm diode laser (Ezlase Biolase, San Clemente, CA). Tooth preparation and irrigation was performed by a single operator.
The 940-nm diode (gallium aluminium arsenide) (Biolase, San Clemente, CA) laser was used for irradiation in group B. A 200 μm fiber optic tip was activated and moved from coronal to apical direction (2 mm/s) for a total of 7 s. The fiber optic tip was held in an oblique direction to the root canal dentin to mimic the clinical situation. 
Scanning electron microscopy and EDX analysis
Samples from both groups A and B were irrigated with 5 ml of distilled water for 1 min and subsequently dehydrated at 120°C in a hot air oven for 30 min. Specimens were then mounted on aluminium stubs, sputter-coated with gold and introduced into the vacuum chamber of a SEM (LEO 440i, Tokyo, Japan). Photomicrographs of the root canal walls were taken at 2 mm, 7 mm, and 12 mm from the apex representing the apical, middle, and coronal regions at 2000× [Figure 1]. The photomicrographs were evaluated by two independent evaluators who were unaware of the experimental groups to which the samples belonged. To guide examiners during morphological and ultra-structural analyses, scores were established based on images obtained under the SEM. The amount of smear layer was graded between 1 and 4. EDX analysis of the same samples was done under EDX analyzer (Oxford Inc, Concord, MA, USA) to assess the Ca, P and magnesium content and to determine the Ca P ratio.
|Figure 1: Photomicrographs of root canal walls of group A and B at the coronal, middle and apical third|
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Scoring criteria for the presence or absence of smear layer done with modified criteria of Rome et al.
Score 1: Clean root canal wall with complete absence of smear layer; all dentinal tubules open and clean.
Score 2: Minimal amount of smear layer; more than 50% of the dentinal tubules open.
Score 3: Moderate amount of smear layer; less than 50% of dentinal tubules open.
Score 4: Heavy smear layer with complete obliteration of dentinal tubules.
Wilcoxon signed rank test was used to evaluate the smear layer score and paired t-test was used to evaluate the mineral content. P < 0.05 was considered statistically significant.
| Results|| |
The frequency distribution of the scores for smear layer, the difference in mean rank scores between group A and B are presented in [Table 1]. Examination of the surface of the root canals revealed that, at middle (P = 0.015) and apical thirds (P = 0.005) smear layer removal was better with laser irradiated group [Table 1]. However, in the coronal third there was no statistically significant difference in removal of smear layer between both the groups (P = 0.414).
|Table 1: Frequency distribution of smear layer scores and the difference in the mean rank scores in both the groups at coronal, middle and apical third|
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The mean Ca, P, magnesium content and the Ca phosphorous ratio are presented in [Table 2]. There was a mild variation in values when both group A and group B were compared but the difference was not statistically significant.
|Table 2: The mineral content (weight) values and the calcium phosphate ratio of the test groups|
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| Discussion|| |
Recent advances in dental research have incorporated laser technology as a potential adjunct in root canal treatment, aimed at reducing the number of microorganisms within the root canal system.  The GaAlAs diode laser of 940 nm wavelength was used in the present study since its clinical application in endodontics has been scarcely studied and also because of its low cost, greater versatility and portability due to its compact size. The thin flexible fiber of 200μm tip provides better access to the apex. The penetration of diode laser energy into the dentinal tubules is better compared to Er, Cr: YSGG due to less absorption of the laser beam by both hydroxyapatite and water. , It also works efficiently at lower power with less heat production with power output ranging from 0.5 W to 7 W. ,
In a previous study by by de Souza et al.,  it was demonstrated that 830 nm diode laser irradiation provided increased disinfection of deep radicular dentin along with 0.5% NaOCl and 17% EDTA compared to use of these irrigants alone. It has also been reported that 980 nm diode laser irradiation of root canal dentin increased the bond strength of AH plus sealer after irrigation with 1% NaOCl and 17% EDTA. This result was attributed to the alterations caused by the laser on dentin surface, such as fissures and topographic changes. 
Smear layer acts as a barrier between the filling material and sound dentin, which inhibits the penetration of irrigants, medicaments and sealer into dentinal tubules. This in turn increases microleakage and decreases bond strength of sealers and other resin based dental materials.  In the present study, the use of the 940 nm diode laser irradiation of root canal dentin along with NaOCl and EDTA irrigation, resulted in better removal of smear layer. The results are similar to another study, where the use of 980-nm diode laser irradiation at 5 W caused vaporisation of smear layer and the opening of orifices of dentinal tubules in all portions of root canal walls. However, localized melting, fusion and re-crystallization of dentin walls were observed in the apical third of the root canal system in the previous study.  These ultramorphological changes could be attributed to the photothermal, photochemical, photodisruption, photodissociation, photoplasmolysis and photoaccoustic effect of the diode laser. 
The result of the present study is in accordance with a previous study by Marchesan et al.,  in which 980-nm diode laser irradiation of root canal dentin showed ultra-morphological changes ranging from smear layer removal to dentin fusion. However, in their study, lava melting was seen on the dentinal surface unlike in this study, which could be attributed to use of higher power of 3 W (pulsed mode) and laser tip was also held perpendicular to the entire root canal surface at a distance of 1 mm.
NaOCl and EDTA have shown to decrease the Ca/P ratio of the root canal dentin by altering its organic and inorganic components. This alteration might change the microhardness, permeability and solubility characteristics of the root canal dentin, thereby affecting the sealing ability and adhesion of the resin based sealers and decreases the bond strength. , The results of the present study have proven that, 940 nm diode laser when used along with NaOCl and EDTA did not have any effect on the Ca/P ratio of root dentin.
Thus, within the limitation of this study, it can be concluded that, a 940 nm diode laser irradiation of root canal dentin along with NaOCl and EDTA irrigation, resulted in better removal of smear layer without significant additional loss of mineral content compared to the use of NaOCl and EDTA alone.
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[Table 1], [Table 2]