The use of holmium-yttrium aluminum garnet laser as pit and fissure cleaner

Background: The prevention and management of pit and fissure caries has become relatively more important in recent times. There is a need for an effective preventive measure against pit and fissure caries. Purpose: The purpose of this study was to investigate the effect of laser beam as a cleaning method of pits and fissures. Methods: Ho-YAG laser which has a wavelength of 2.1 μm was used in this experiment. The specimens were extracted human teeth. The effect of three cleaning methods was examined comparatively by scoring the cleaned area of fissure, namely laser irradiation with Ho-YAG laser, chemico-mechanical with combination of 10% NaOCl and ultrasonic scaler and mechanical with ultrasonic scaler. Vertico-bucco-lingual serial ground sections of each tooth were observed under light microscopy. Scoring the depth of cleaned area was performed by comparing the depth of fissure. result: Progressive result was obtained on the cleaning effect of three methods laser irradiation methods which was the most effective compared to other methods but statistically was not significant. Cleaned area of laser irradiation method was 48.91%, chemico-mechanical method was 41.77% and mechanical method was 36.78%. Conclusion: Holmium -yttrium aluminum garner laser is a relatively new method for pit and fissure cleaning even though the effectivity is not yet maximal. More research is needed to maximize the use of this laser.


introduction
The factor concerned in the initial destruction of tooth is a biomechanical process resulting from the activity of microbiological agents existing in the environment concerned.Pit and fissure caries is therefore primarily of environmental origin, although its initial progression may be governed by the enamel structure.
Relative caries incidence is low on smooth, self cleaning surfaces but increase significantly on interproximal and occlusal surface.Several investigations have shown that the oral surfaces are especially susceptible to dental decay accounting for nearly 50% of all dental caries.
The prevention and management of pit and fissure caries has become relatively more important in recent times.There is a need for an effective preventive measure against pit and fissure caries, which now account for more than 90% of the total caries experience in some child populations. 1 The immature permanent teeth, especially the first molar shows a high caries rate prior to the start of their functioning as teeth.
Many previous studies have reported in prevention of pit and fissure caries such as drilled pit and fissure to have a better shape of pit and fissure.However, this method damaged to the tooth structures.Some investigators used fluoride application, but penetration was difficult to the area of pit and fissure.More recently various adhesive materials that act as agents to seal the fissures from oral environment have been investigated.
Pit and fissure sealant is known to prevent occlusal surface caries. 2 While a sealant is generally applied as part of the system for the prevention of caries, the cleaning of tooth surface, pit and fissure is very important.For obtaining the better retention of sealant, necessity of cleaning of pit and fissure is widely recognized.Aoki 3 have used the solution of 1N HCl, 50% H 3 PO 4 , 1N NaOH and 10% NaOCl, ultrasonic and combination of ultrasonic and NaOCl to clean pit and fissure.
The use of CO 2 laser in dental caries prevention and the effects of CO 2 laser in combination with fluoride have been investigated. 4CO 2 laser irradiation can decrease enamel demineralization, it has still not been clarified which laser wavelength and which irradiation conditions represent the optimum parameters for application as preventive treatment.Scanning electron microscopy examination did not reveal any obvious damage caused by the laser irradiation. 5rior to the sealant therapy, it is also possible to clean up a pit and fissure with the yttrium aluminum garnet (YAG) laser to remove organic and inorganic debris.Myers & Myers used a pulsed YAG laser beam on the technique effectively vaporized the organic and debris. 6In reaching the depth of pit and fissure using laser irradiation is needed in order to remove fissure of the contents and to facilitate direct penetration without any alterations of size and shape of the fissure.There is no detailed study has been reported yet concerned about the effectiveness of laser irradiation through pits and fissures.Holmium-yttrium aluminum garnet (Ho-YAG) laser was saved used in the human teeth.Laboratory findings by Roy 7 suggested that when used with collateral water spray, the Ho-YAG laser can ablate human dentine in a controlled manner without adverse thermal effects.Ho-YAG laser at a wavelength of 2.12 microns can be safely and effectively used for photoconditioning of the dental surfaces of teeth in clinical conditions. 8In this study, the effect of Ho-YAG laser on cleaning of pit and fissure was compared to other methods.

materials and methods
Fifty extracted human teeth, particularly molars and premolars were used in this study.Samples without any lesions in the area of pit and fissure were carefully selected.Since we measure the percentage of cleaned area of fissure content, the depth and shape of fissures were exclusive criteria.
The tooth specimens were fixed with formalin and CaCO 3 , washed in distilled water for 15 minutes, cleaned with brush cone and placed in ultrasonic bath for 15 minutes.
Samples were divided into 4 groups.Each 10 teeth treated with laser irradiation, chemico-mechanical with 10% NaOCl and ultrasonic scaler for 2 minutes, mechanical with ultrasonic scaler for 2 minutes and no treatment after cleaned with brush cone for control group.200 µm diameter of tip of scaler was used for chemico-mechanical and mechanical methods.
The longitudinal ground sections were prepared buccolingual from the fissure area of each group.The specimens were fixed into slide glass and processed for examinations under light microscope.Scoring the depth of cleaned area was performed by comparing to the depth of fissure.
Ho-YAG laser with a wavelength of 2.1 mm was used in this study.Cleaning of pit and fissure with Ho-YAG laser irradiation which has a repetition rates of 10 pps with an energy of 40 Joule/cm 2 .The 200 mm diameter of fiber was used.
The direction of laser beam for irradiation was vertical to the occlusal surface, pit and fissure of enamel.Black ink was applied into the fissure before laser irradiation to have better absorption of laser beam.
The cleaning effect of pit and fissure was evaluated by determining the distance between the entrance of the pits and fissures and the top of residues.Percentage of cleaned area was calculated by comparison between length of cleaned area and depth of fissure × 100%.ANOVA test was used to reveal any significant differences in the cleaning effect of the pits and fissures among the four groups.
result Cleaning effects of pit and fissure with laser irradiation, chemico-mechanical and mechanical are presented in table 1 shows a cleaned area of control group.The comparison of cleaning effect of laser irradiation, chemicomechanical method, mechanical method and cleaning with brush cone only as a control is shown in table 2.
There are no significant different of cleaning effect of pit and fissure content between laser application and chemico-mechanical method (p = 1.00), laser application and mechanical method (p = 0.85), but significant different of cleaning effect of pit and fissure content between laser application and cleaning with brush cone only as control group (p = 0.002).There are no significant different of cleaning effect of pit and fissure content between chemicomechanical method and mechanical method (p = 1.00), but significant different of cleaning effect of pit and fissure  content between chemico-mechanical method and cleaning with brush cone only as control group (p = 0.025).There is no significant different of cleaning effect of pit and fissure content between mechanical and cleaning with brush cone only as control group (p = 0.12).The findings showed that the cleaning effect of laser irradiation resulted was seemingly most effective than other methods.The findings showed that the cleaning effect of laser irradiation resulted 48.91% of cleaned area.Chemicomechanical method was 41.77% and mechanical method was 36.78% compared to control was 17.11%.
Condition of fissure's content after exposure to laser irradiation, cleaning with chemico-mechanical, mechanical and control were demonstrated in Figure 2, 3, 4, and 5 Cleaning effect of laser irradiation was seemingly more effective than other methods, however, laser irradiation and other methods was not statistically different.discussion Since Stern and Sognnaes 9 showed in their pioneering work that laser irradiation of enamel with a ruby laser increased its acid resistance, many attempts have been made to apply lasers in preventive dentistry.Stern and Sognnaes 10 also demonstrated in vivo that enamel subjected to 10 to 15 J/cm2 showed a greater resistant to dental caries than the controls.
Pit and fissure sealant is known to prevent occlusal surface caries.While a sealant is generally applied as part of the system for the prevention of caries, the cleaning of tooth surface, pit and fissure is very important.For obtaining the better retention of sealant, necessity of cleaning of pit and fissure is widely recognized.Prior to the sealant therapy, it is also possible to clean up a pit and fissure with the YAG laser to remove organic and inorganic debris. 6ost of researcher investigated the effect of laser irradiation in the smooth surface of enamel.The prevention of pits and fissures caries has become relatively important to be investigated.Lenz et al. 11 has been suggested the CO 2 laser irradiation for sealing of enamel defects.Walsh and Perkins 12 demonstrated the technique for enamel fusion using CO 2 laser has potential application for sealing pits and fissures and producing physico chemical alterations in enamel which may have preventive benefits.Preliminary findings by Myers 6 showed that the YAG laser has the potential to remove organic and inorganic debris from pits and fissures without causing pulpal or enamel injury due to minimal laser energy.
Ho-YAG laser were used in this study for cleaning of pits and fissures and tried to compare with chemicomechanical and mechanical methods.The progressive results were obtained that the cleaning effects of three approaches, laser irradiation was seemingly most effective compared to other methods and control (Table 2).Scoring the depth of cleaned area was performed by comparing to the depth of fissure.The differences of cleaned area of chemico-mechanical and mechanical method was not significant compared to laser irradiation method.However, cleaning method with chemico-mechanical and mechanical had consequence in the alteration of the shape of fissure and damage the enamel surfaces of fissures.The cleaned area supposed to be higher in percentage if the black ink as a removable absorptive coating which was used in this study could penetrates deeply into the fissure to have better absorption of laser beam.The study by Tagomori and Morioka 13 has shows that the use of black ink on enamel greatly enhances Nd-YAG laser absorption in it.Because of the shape of fissures, application of black paint into the enamel surface of fissure in this study may be was not penetrate deeply into the fissures.
On the other hand, effect of laser irradiation also has the potential to increase acid resistance of the enamel.Many previous studies have reported that the lased enamel surface was more resistant to demineralization of the enamel. 9,10,14,15Consequently besides effect of cleansing, laser irradiation has also increasing acid resistance on the area of pit and fissure.
Two hundred µm diameter of fiber of laser beam was used in this study, whereas generally width of fissure's entrance is less than 200 µm.The result should be better if its possible to use fiber with diameter smaller than 200 µm, because there will be better adaptation to the entrance of fissure.
Cleaning effects of laser irradiation was seemingly more effective compared to chemico-mechanical method.
Cleaned area of chemico-mechanical and mechanical method was not statistically significant different compared to laser irradiation method.However, cleaning method with chemico-mechanical and mechanical had consequence in the alteration of the shape of fissure and damage the enamel surfaces of fissures.Laser irradiation has also increasing acid resistance on the area of pit and fissure.The cleaned area supposed to be higher in percentage of the black ink as removable absorptive coating could penetrates deeply into the fissure to have better absorption of laser beam.For better adaptation to the entrance of fissure, using fiber with a diameter smaller than 200 mm is recommended.In conclusion, holmium -yttrium aluminum garner laser is a relatively new method for pit and fissure cleaning even though the effectivity is not yet maximal.More research is needed to maximize the use of this laser.acknowledgement This work was partially supported by Faculty of Dentistry, Niigata University, Japan.

figure 2 .figure 3 .figure 4 .figure 5 .
figure 2. C l e a n i n g o f fissure content.

table 1 .
Cleaning effect of pit and fissure with laser irradiation, chemico-mechanical method, mechanical method compared to control

table 2 .
The comparison of cleaning effect of laser irradiation, chemico-mechanical method, mechanical method and control group (cleaning with brush cone only)