The utility of laser irradiation has been demonstrated in basic and clinical studies, albeit with an associated risk of tissue damage. We previously tested a combination of high reactive level laser therapy (HLLT) and low reactive level laser therapy (LLLT) using a carbon dioxide laser for enhanced post-extraction wound healing and observed irreversible changes in the pulps of the teeth adjacent to the extracted tooth. The aim of this study was to elucidate the histopathological changes in the pulps of teeth adjacent to the site of carbon dioxide laser irradiation performed to achieve enhanced wound healing after tooth extraction; here we report the significance of care for the adjacent tissues in laser irradiation therapy. A total of 20 male Wistar rats (5 weeks old) were divided into an irradiation group that received HLLT combined with LLLT and a non-irradiation (control) group that did not. A tooth socket model was prepared by extracting the maxillary left first molar. HLLT and LLLT were respectively performed immediately and 1 day after tooth extraction. Laser-stimulated tissues surrounding the extracted tooth, namely, the socket and adjacent teeth, were collected from each rat both 7 and 10 days after tooth extraction. The obtained specimens were fixed in 4% paraformaldehyde, decalcified in 10% ethylenediaminetetraacetic solution, and then embedded in paraffin. Serial sagittal sections were stained with hematoxylin and eosin for histopathological examination. Laser-induced injuries, such as enamel ablation and dentin carbonization, were absent 7 days after tooth extraction in both groups. Formation of reparative dentin was observed along the rim of the laser-irradiated area in the dental pulps in the irradiation group but not the control group. Both groups showed no signs of inflammation in pulp tissues. Enamel and dentin injuries were not observed in either group at 10 days after tooth extraction, similar to the findings at 7 days after tooth extraction. Formation of reparative dentin was much more prominent at 10 days after tooth extraction than at 7 days in the irradiation group. In contrast, no formation of reparative dentin was observed at either time point in the control group. These results show that carbon dioxide laser irradiation induces the formation of reparative dentin in the pulps of teeth adjacent to the extracted tooth socket. In sum, carbon dioxide laser irradiation at the low reactive level appears to induce irreversible changes in the tissues surrounding the laser treatment site.

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In recent years, laser technology has been widely used in dental and oral treatment and maxillofacial surgery, and many researchers and clinicians have reported its utility. Because carbon dioxide (CO₂) lasers achieve excellent hemostasis and cause relatively low heat aggression to the surrounding tissue by laser irradiation, there is little postoperative scar formation with these lasers, and the wound healing is good. Therefore, CO₂ lasers are actively used for the excision and evaporation of soft tissue lesions. In this study, we examined the outcomes of cases treated with CO₂ lasers for adhesion abnormalities of the frenulum.
We evaluated 30 cases that received a checkup at Kobe University Hospital for adhesion abnormalities of the frenulum from March 2010 to March 2015 and were operated on using CO₂ lasers. We collected and evaluated the following clinical data: sex, age, site of the frenulum adhesion abnormality, reason for consultation, severity classification, and postoperative course. Regarding the breakdown of the 30 cases, 14 were males and 16 were females, and their ages ranged from 8 months to 69 years. Regarding the breakdown of the site of the frenulum adhesion abnormality, 20 were at the lingual frenulum, 8 were at the upper labial frenulum, and 2 were at the buccal frenulum. Regarding the reasons for consultation, 10 cases (33.3%) were discovered during periodic health checks at school or during a dental clinic consultation, and 9 cases (30.0%) were referred by an orthodontic clinic. Based on the severity classification, many operations for lingual and upper labial frenulum sites were carried out in patients ＜10 years of age, and their disease severity tended to be below the intermediate level. Regarding the postoperative course, there were no cases of serious bleeding or swelling, and the pain was controlled in all cases using internal pain-killers. Furthermore, there were no cases of wound infection or healing delay after surgery, although re-adhesion ultimately occurred in one case after the excision of the lingual frenulum. In conclusion, CO₂ laser excision is suggested to be a useful therapy for both frenulum excision and excision of other oral soft tissue lesions, since the procedure is simple and causes few intraoperative and postoperative complications.

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DIAGNO dent^® is a caries detector using semiconductor laser. The newly-developed DIAGNO dent^® pen - Perio Probe is capable of examining the accumulation of materials such as dental plaque or calculus in the periodontal pocket. However, it is possible that the dye within the plaque tester may affect the measurement value of caries. In this study, we examined how the measurements were affected by the plaque tester. As a result, the plaque tester containing Coomassie Brilliant Blue showed a higher measurement value. This result suggests that when using a plaque tester containing Coomassie Brilliant Blue, the DIAGNO dent^® pen - Perio Probe may not be able to accurately evaluate the accumulation within the periodontal pocket.

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Although Er:YAG laser treatment has been reported to enhance wound healing, the mechanism of action is unclear. Activation of periodontal ligament cells has the potential to accelerate wound healing in periodontal treatment. The purpose of this study was to evaluate the effects of low-level Er:YAG laser irradiation (LLLT: Low reactive Level Laser Therapy) for transforming growth factor-β (TGF-β) in cultured human periodontal ligament (hPDL) cells.
Materials and Methods: After irradiation of hPDL cells with Er:YAG laser (50mJ, 10pps, 10sec), alkaline phosphatase (ALP) activity was determined following the addition of dentin phosphoprotein (DPP), dentin sialoprotein (DSP), tyrosine-rich amelogenin polypeptide (TRAP), and 20kDa amelogenin. Furthermore, the activity of TGF-β by Er:YAG laser irradiation was evaluated by determining ALP activity in hPDL cells with or without the addition of SB431542 (SB), which is a specific inhibitor of TGF-β. Cell proliferation was determined by MTS assay, and the hPDL cells were observed and photographed using a phase-contrast microscope. Thereafter, the activation of TGF-β was investigated by determining ALP activity in hPDL cells due to the latent TGF-β after Er:YAG laser irradiation.
Results: When compared with the non-irradiation group, the Er:YAG laser radiation group showed a tendency to give higher values of ALP activity, and no difference was found between the added physiologically active substances. Moreover, the ALP activity was dramatically increased under the condition without the addition of SB. MTS assay showed that cell numbers of the laser irradiation group were higher than those of the non-irradiation group at day 3. A phase-contrast micrograph of cultured hPDL cells, taken 2 days after Er:YAG laser irradiation, showed irregularly shaped cells in comparison to those of the non-irradiation group. Addition of Er:YAG laser irradiated latent TGF-β to hPDL cells did not result in increased ALP activity.
Discussion: The present study showed a tendency for ALP activity to increase in hPDL cells by irradiating with Er:YAG laser. Therefore, it was suggested that Er:YAG laser irradiation might promote hard tissue formation. Furthermore, this enhancement of ALP activity was considered to be correlated with TGF-β, because the ALP activity was remarkably reduced by the addition of SB, which is a specific inhibitor of TGF-β. However, latent TGF-β was not directly activated by Er:YAG laser irradiation, because an increase of ALP activity in hPDL cells was not found by the addition of laser irradiated-latent TGF-β.

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フェムト秒レーザーを用いたセラミックブロックの切削について検討した。実験材料には，完全焼結ジルコニア，半焼結ジルコニア，アルミナおよびハイドロキシアパタイトを用いた。設定条件は波長，照射光強度，焦点外し距離，オートステージの移動速度および切削粉除去のためのエアーの有無とし，設定条件を変化させてレーザー照射して形成した切削痕の深さと断面積を比較した。
その結果，材料内部に水が浸透すると切削力が増した。ジルコニアは黒化が見られたが，再加熱で消失した。切削力は照射光強度に依存性があった。照射光強度が増加すると切削痕の深さと断面積は増加したが，20mWを超えると増加量は低下した。同じ照射光強度では，波長は短い方，パルス幅は短い方が切削量は大きかった。切削粉の除去が切削に有効であった。窩洞形成した窩底の表面粗さは，臨床応用可能な範囲であった。
以上から，フェムト秒チタンサファイアレーザーは歯科用セラミックの高精度な加工に応用できることが示唆された。

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We investigated the effects of CO₂ laser irradiation combined with immersion in a solution containing fluoride ions on the remineralization of etched dentin surface. Human premolars were divided randomly into four groups (1, control: NL; 2, immersion in fluoride-ion-containing solution: NLF; 3, laser irradiation: L; 4, laser irradiation plus immersion in fluoride-ion-containing solution: LF). Embedded human dentin blocks were etched with phosphoric acid, fixed on a specimen stage, and then a CO₂ laser (10.6-µm wavelength) was applied (15 W/cm²), followed by immersion in fluoride-ion-containing solution. Nanoindentation testing was carried out before and after CO₂ laser irradiation and during the immersion period, and then the dentin surfaces were observed by scanning electron microscopy. Phosphoric acid etching markedly decreased the mechanical properties (hardness and elastic modulus) of dentin surfaces. The mechanical properties of the etched dentin specimens subjected to laser irradiation plus immersion in fluoride-ion-containing solution recovered significantly during the immersion period compared to those of the other specimens. After immersion for 1 month in the fluoride-ion-containing solutions (NLF, LF), the wide-open dentinal tubules caused by acid etching were partly filled by a remineralized layer. In conclusion, CO₂ laser irradiation with low output plus immersion in fluoride-ion-containing solution may enhance the remineralizing ability of etched dentin surface.

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We have examined the mechanism of laser cutting for enamel and dentin, the effect of the ratio of water to air in the water spray on the efficiency of laser cutting, SEM analysis of laser-cut tooth surface and its alteration after applying various adhesive systems, the effect of various adhesive systems on the bond strength of composite resin to laser-cut enamel or dentin, the adaptation of composite resin to laser-prepared cavities, and the effect of laser preparation and adhesive system on pulp reaction using an erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser. From these studies, the following results were obtained. High-speed camera observation clarified that micro-phreatic explosion occurred on the tooth surface during laser irradiation. The ratio of water to air in the spray influenced the efficiency of the laser cutting for dentin. A thin heat denaturation layer was observed on the surface of the dentin prepared with the laser, but this layer disappeared after application of both 40% phosphoric acid and 10% sodium hypochlorite. Pre-conditioning using phosphoric acid or both phosphoric acid and sodium hypochlorite was effective in improving the bond strength of two-step self-etch adhesive system to both enamel and dentin prepared with the laser. Pretreatment of the cavity prepared with the laser using phosphoric acid or sodium hypochlorite did not affect the dental pulp healing of rat tooth.

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Presently, various lasers are used in many dental fields, including operative dentistry, endodontic care, periodontal care, oral surgery, prosthetics, implants, esthetic dentistry, and preventive dentistry. Removal of caries and dental scaling associated with periodontal surgical procedures began to be covered by national health insurance and have become more widespread in Japan. Laser ablasion of teeth is more time-consuming than rotary cutting but has many advantages: pain control and less gingival bleeding, and it is more convenient for the treatment of subgingival caries. In the future, it will also be important to develop materials and procedures that lead to more effective laser use. For example, selective removal of the infected layer of carious dentin by a laser using a caries-detector dye that specifically absorbs laser energy is expected to be effective, along with the above advantages, for the treatment of root caries, which is difficult to treat by conventional procedures. In addition, the coating of enamel with a hydroxyapatite film using a laser is considered to be a promising technique for the management of tooth wear such as abrasion, especially in the future aging society. In this paper, prospects for the application of lasers to various hard tissue disorders of the tooth are discussed.

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Lasers may provide various unique and high-quality cure and care in the treatment of dental hard tissue that cannot be achieved through ordinary treatments. The present paper describes therapeutic innovations in the treatment of dental caries by fully utilizing the characteristics of lasers.
Preventive cure by modifying the characteristics of enamel or dentin surface and surgical intervention for removing dentin caries and subsequent adhesive restorative procedures were reviewed based on a series of studies by the authors.

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