In order to elucidate the mechanism of anti-inflammatory effect of light irradiation, the human rheumatoid synoviocytes, MH7A, were treated with the proinflammatory cytokine interleukin (IL)-1β, and irradiated with linear polarized infrared light by Super Lizer ® (SL) or treated with the glucocorticoid, dexamethasone (DEX), then gene expressions were monitored using Affymetrix Gene Chip. Furthermore, Gene Chip results were analyzed using the signal transduction pathway coreddatabase (Ingenuity Pathway Analysis, IPA). SL and DEX irradiation suppressed IL-1β-induced IL-8 gene expression leveland inflammatory factors. Interestingly, DEX randomly altered many gene expressions, and not only reduced anti-inflammatoryfactors but also increased inflammatory factors, whereas SL only reduced gene expression of anti-inflammatory factors. Thesefindings may support the reason why light therapy has no side effects on the course of therapy.

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Low-reactive level laser therapy has been applied for pain relief and improvement of local circulation, and hasbeen popular in many clinical fields. The cellular mechanism, however, has not been fully clarified. Some basic researches indicated that laser suppresses neural activity by direct action on the nervous tissue, and affects membrane potential and the input membrane resistance of neurons. Using low-reactive level laser irradiation with a near-infrared diode laser (continuouswave; wavelength, 830 nm; power density, 1-5 W/cm²), we achieved inactivation of excitatory synaptic transmission in the central nervous system of rodents. In the study using cultured rat hippocampal neurons, the laser irradiation induced hyperpolarization of the membrane potential and reduction of input membrane resistance, suggesting that the laser suppressed synaptictransmission by opening potassium channels in the cells. The laser irradiation increased the content of adenosine triphosphate (ATP) in the tissue. Furthermore, laser-induced suppression of synaptic transmission was attenuated under application of anATP-sensitive potassium channel opener. These observations indicate that suppression of neural activity by low-reactive levellaser irradiation in a near-infrared wavelength is brought about by opening of ATP-sensitive potassium channels by the increasein intracellular ATP level. Recently, it was demonstrated that laser irradiation suppressed synaptic transmission morepotently in hippocampal slices at a low ATP content. This may contribute to the clinical phenomenon that more potent effectsof low-reactive level laser irradiation are often seen on tissue under pathological states than physiological states.

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Circadian rhythms are oscillations in the behavior and biochemical reactions of organisms, and occur with a periodicity of approximately twenty-four hours. The mammalian cryptochromes (CRY) have been proposed as circadian photoreceptor pigments. Mesenchymal stromal cells (MSCs) are multipotent cells that can differentiate to lineages of mesenchymaltissues. Here we show that laser (wave length: 405nm) irradiation can control the differentiation of mouse MSCs into osteoblasts by altering the intracellular localization of the circadian rhythm protein CRY1. Laser irradiation promoted osteogenesisof MSCs, induced the translocation of CRY1 protein from the cytoplasm to the nucleus and downregulated CRY1 mRNA levels.
Our results indicate that CRY1 is a master regulator of circadian rhythm that regulates the differentiation of MSCs. Laserirradiation could provide a simple and effective means of controlling the fate of MSCs as a therapeutic strategy. Furthermore, this model system may be useful for exploring the crosstalk between circadian rhythm and cell differentiation.

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In dental treatment with Nd: YAG laser beam, a diffused and circumferential laser beam, which is emitted fromthetip of an optical fiber by processing with TiO₂ powder, is widely used for caries treatment and periodontal tissue excision. Thetip of an optical fiber processed with TiO₂ powder (TP fiber) is generally brought into contact with soft and hard tissue, anda laser beam is irradiated to these tissues. In the previous study, it was shown that heat energy was generated at the tip of the TP fiber during laser emission, and the surface at the tip of the TP fiber was melted and resolidified. Too much heatingby laser emission at the TP fiber tip causes necrosis of soft tissue and dental pulp, therefore it is important to control thetemperature at the TP fiber tip in order to prevent accidents during treatment.
In this study, the temperature at the TP fiber tip was measured using a two-color pyrometer with an optical fiber. The influenceof the laser emitted from the TP fiber on the temperature of the tip and the relationship between the laser energy and the TPfiber tip which changes with the emission times were investigated. The characteristics at the TP fiber tip during and afterlaser emission were also examined. As a result, the temperature at the TP fiber tip increased rapidly during the laser emissionand reached the maximum at the time when the laser emission finished. The temperature after finishing the laser emissiondecreased rapidly and the TP fiber cooled to room temperature nearly until the next laser pulse was emitted. The maximumtemperature at the TP fiber tip increased with the increase of the laser energy per pulse, but was not influenced by the pulsewidth and pulse frequency.

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Case 1: A 72yr-old female was referred to our hospital from a general practitioner for root canal treatment on themandibular left and right first molars. Both molars were diagnosed as chronic ulcerative pulpitis and she had a medical historyof endocarditics.
Procedure To prevent infection, 250mg of antibiotic medicine was administered before and after treatment.
Gingivobuccal gingival areas were coated with Indian ink and irradiated with Nd: YAG laser irradiation for 30 sec at an energy level of 100mJ 15pps.
After laser anesthesia was successful, a low-speed round bur was used to penetrate into the chamber, and paraformaldehydewas applied to the exposed pulp.
One week later, endodontic treatment was performed with the conventional procedure.
Case 2: A 72-yr-old female was referred from a prosthodontic department for root canal treatment on the mandibular leftcanine and the left first premolar.
The canine was diagnosed as chronic ulcerative pulpitis and the premolar as dentin caries of intact pulp.
After laser anesthesia, a low-speed round bur was used to penetrate into the canine chamber without pain, however, penetration into the premolar pulp chamber could not be performed due to intolerable pain. Since severe pain was recognized duringthe cavity preparation, infiltration anesthesia was performed for endodontic treatment of pulpotomy.
As a result, Nd: YAG laser was effective as anesthesia for the devitalization of dentin and pulp tissues of chronic ulcerativepulpitis, but was not useful for controlling pain during pulpotomy of sound pulp.
In conclusion, it is suggested that Nd: YAG laser may be applied as anesthesia for dental treatments, which are contraindicationsof dental infiltration anesthesia.

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In the treatment of infected root canals, we must remove both organic and inorganic substances, such as infecteddentin, residual pulp tissue, and bacteria. In the clinic, mechanical cleaning and chemical irrigation of root canals are importantprocesses to ensure healing. However, thorough cleaning of the root canal system is difficult to achieve due to lateral branches, apical ramifications, and strictured root canals such as fins and isthmuses. Today, fine and flexible laser fibers have beendeveloped and applied in the clinic. The aims of this study were to investigate the effects of diode laser irradiation on Staphylococcus aureus, and to evaluate the temperature elevation on the root surfaces during diode laser irradiation in the root canal.
In Experiment 1, extracted human teeth with single roots were used. After removing the crowns, the root canals wereenlarged to #35 1 mm short of the anatomical apex. After root canal irrigation with NaClO and EDTA, the samples were furtherultrasonically irrigated for five minutes. When the laser fiber or the plugger of the heat carrier was irradiated or activatedupon being withdrawn from the apex at a speed of 1 mm/s for ten seconds, the maximum temperature elevation on the rootsurfaces was measured. Laser irradiation parameters chosen were 30mJ 66pps, 45mJ 66pps, 60mJ 66pps, 45mJ 100pps, and 60mJ 100pps, and the tip of the heat carrier was set at 200°. Additionally, the surfaces of the root canal after irradiation wereobserved under a digital microscope and a scanning electron microscope (SEM). In comparison with the heat carrier, a significantly lower temperature elevation was observed for laser irradiation at 30mJ 66pps and 45mJ 66pps. In the digital microscopy and SEM observation, melted dentin was observed without carbonization or defects after lasing at 45mJ 66pps.In Experiment 2, fifteen roots of intact bovine incisors were used. After canal irrigation with NaCIO and EDTA, the sampleswere further ultrasonically irrigated for five minutes. The root surfaces were coated with nail enamel, and the samples weresterilized by an autoclave. Each root canal was filled with 100-E1 of S. aureus (2.0×10⁸ CFU/ml) culture medium and incubatedat 37° for 24 h. Then, the samples were divided into three groups. In group 1, the culture medium in the root canals wasirradiated by diode laser (45mJ 66pps) under an up-and-down motion between the apical and cervical portion with an opticalfiber (diameter=400, μm) for 10 seconds. In group 2, the plugger of the heat carrier was activated as in group 1. In group 3, the laser fiber was moved in the canal without irradiation. After the above procedures, bacterial samples were taken fromeach root canal, and 50μ of each sample was incubated aerobically on Soy Sonic Broth at 37° 24 h. The numbers of colonieson the medium were counted, and colony-forming-units (CFUs) /ml were calculated. CFUs of groups 1, 2 and 3 were 1.2×1011CFUs/ml, 7.6×1011 CFUs/ml, and 5.4×1012 CFUs/ml, respectively. Statistical analysis revealed that CFUs in groups 1 and 2were more reduced than in group 3 and that those in group 1 were more reduced than in group 2 (P< 0.05). These resultssuggest that diode laser irradiation could be used for root canal disinfection safely and effectively.

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CO₂ laser is known to stimulate reparative dentin formation by odontoblasts, but the precise mechanism and molecular basis of this effect remain unclear. This study was designed to elucidate the effect of CO₂ laser on calcified nodule formation in mouse odontoblasts. MDPC-23 (mouse odontoblast-like cells) were serum-starved for 24 hours and irradiated by a CO₂ laser apparatus at 2-5 W, and then incubated with a mineral-inducing medium containing ascorbic acid and β-glycerolphosphate. Laser irradiation at 2 W for 30 sec had little effect on cell proliferation examined by cell counting kit-8. ALP activities in irradiated cells on day 2 and 4 were significantly higher than in the control cells. However, mRNA expressions of bothdentin sialophosphoprotein (DSPP) and type I collagen were not affected by laser irradiation. The total number and areasof calcified nodules in irradiated cells were apparently increased compared with those in control cells. The secretion of collagen into the medium measured by the Sirius red staining method was significantly accelerated by irradiation on day 1 and 2. Interestingly, irradiation stimulated both mRNA and protein expressions of HSP47 (collagen specific chaperone) within 24hours. These results suggest that CO₂ laser irradiation enhanced calcified nodule formation in mouse odontoblast-like cells byinducing the expression of HSP47 which is essential for collagen production.

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Removal of broken instruments from the root canal is often time-consuming and extremely difficult. We reporteda new method of removing intracanal broken instruments using laser welding (9th ISLD, 2004). In short, broken K-files witha tip diameter of more than 0.25mm had been successfully welded to a stainless-steel tube (inner diameter: 0.5 mm). We improved this method to remove K-files (tip diameter: 0.25 mm) from the root canal using a stainless-steel ball with a diameterof 0.5 mm. The objective of this study was to examine the effects of the stainless-steel ball on laser welding between brokenfiles and stainless-steel tubes.
Fifteen K-file tips were used in this experiment. Inserting the stainless-steel ball into the tube mentioned above, the brokenend of each K-file tip was contacted with the ball. Then, Nd: YAG laser was irradiated through the other end of the tube at 900mJ, 10 pps for 1, 2 and 3 sec. Finally the strength of the welding was evaluated using a pair of pliers and a tensile test wasperformed.
The results were as follows: Laser welding was successful in all samples except one in the 1-sec irradiation group. In the 2-sec irradiation group, themeasured tensile welding strength was 25.5N. This may be strong enough to remove broken files from the root canal.
We concluded that fine broken K-files in the root canal could be removed by laser welding using Nd: YAG laser.

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