Many researches have been performed on the application of lasers to dentistry in the last two decades, and many types of laser devices are now clinically used. On the other hand, photodynamic diagnosis (PDD) and photodynamic therapy (PDT) have other possibilities for applying lasers to dentistry. Firstly, the basic concept and present state in medicine of PDD and PDT are summarized in this article. PDD and PDT have been used for the diagnosis and treatment of cancer including oral cancer, and other nonmalignant diseases such as aged-related macular degeneration. Attempts to use PDT started in the 1960s. Nowadays, some diseases are already being treated by PDT and some of those treatments are covered by national health insurance. PDD and PDT are based on the phenomenon that a photosensitizing agent as photosensitizer (PS) can be preferentially localized in certain cells and tissues and activated by light of the appropriate wavelength. In PDD, the fluores cence induced by the light is detected and used for diagnosis. In PDT, PS activated by the light generates singlet oxygen and free radicals that are cytotoxic to the target cells and tissues. Secondly, the basic researches of PDD and PDT in the dental field are reviewed. Attempts have been made to apply PDD to diagnosis of oral cancer in vivo. Moreover, the possibility of applying autofluorescence for detection of oral cancer was discussed, and detection of autofluorescence for pulpal tissue and root canal components was outlined. In PDT, when a diode laser was irradiated in the root canal with ophthagreen, melted root canal surface was observed, and when a Nd: YAG laser was irradiated in the root canal with TiO2, the root canal was slightly enlarged. In conclusion, PDD and PDT have the potential to be used in general dentistry including endodontics in the future.
Photodynamic therapy (PDT) enables selective treatment of tumor tissue, by combining the use of a photosensitizer, which is specifically taken up by tumor tissue and newly formed blood vessels, and induces cytocidal effects by highly active oxygen created by laser excitation, without damaging surrounding normal tissue. PDT holds hope for elderly patients and patients at high risk, because PDT preserves organ function and is less invasive than surgery. The first generation of tumor photosensitizers was a porfimer sodium (Photofrin®), and the second generation includes talaporfin sodium (Laserphyrin®) and verteporfin (Visudyne®). These procedures are all recognized and reimbursed by the health insurance system of Japan. We performed preclinical experiments on PDT and photodynamic diagnosis (PDD) using Laserphyrin. Microscopically, scat tered fluorescence from Laserphyrin in tumor tissue was observed in a fresh malignant tumor specimen obtained 2 hours af ter injection, and the treatment effect of PDT using Laserphyrin was recognized in mouse tumors which had received trans planted human squamous cell carcinoma cells. We subsequently applied Laserphyrin in clinical cases and report the results in a case of tongue cancer. Good results were obtained with both PDD and PDT.
Photodynamic therapy (PDT) is a treatment modality that utilizes photosensitizer activated by laser light, having the advantage of selective destruction of malignant tumor cells. However, the conventional dye laser used for PDT, such as the excimer dye laser system, is too large and costly. We developed a diode laser device, which is small, lightweight and easy to use, for PDT in combination with porfimer sodium and estimated its efficacy in tumor models. As a result, necrosis to a depth of about 10mm was obtained. This novel laser device may help expand the clinical applications of PDT.
The main etiologic factor of periodontitis is bacteria inhabiting the oral cavity, especially gram negative anaerobes. These bacteria contain proteases and endotoxin that can destroy periodontal tissue. Most of them in periodontal pockets form a biofilm and attach to subgingival calculus or the inner surface of pockets, or even invade into periodontal tissue. In addition, bacterial entotoxin invade into diseased cementum. Therefore, during periodontal treatment not only calculus but also diseased cementum infected by bacteria must be removed. Nd: YAG, Er: YAG, CO2, Er, Cr: YSGG, and diode laser devices with various conditions have been used in periodontal treatment until now. The advantages of laser irradiation in periodontal treatment are that it is possible to evaporate most of the bacteria because of momentary heat, and laser irradiation, unlike a hand scaler, does not injure the healthy surface of the pocket to avoid bacteria infection. However, laser light only travels in a straight line and so does not reach the bottom of spiral pockets caused by occlusal trauma. In the past several years, fundamental studies of photodynamic therapy (PDT) using laser devices and photosensitizers for periodontal treatment have been reported. The advantage of PDT is that it only affects the target tissue by a combination of laser light with a specific wavelength to activate a photosensitizer and this photosensitizer does not have any toxicity. There fore, the heat effect from the laser device on other tissues is reduced. Additionally, it may be possible to destroy bacteria in the pocket where the laser fiber can not reach and to avoid side effects such as those caused by antibiotics. In this paper, various basic studies of photodynamic therapy (PDT) which have been reported until now and our studies are introduced. The possibility of applying PDT to periodontal treatment is also discussed.
The purpose of this study was to evaluate the application of Nd: YAG laser irradiation with dentin coating to dentin hypersensitivity. The Nd: YAG laser irradiation protocol was evaluated and approved by the Tsurumi Dental University Human Study Review Committee before the initiation of any treatment to patients. Ten adult male patient volunteers participated in this study. The cervical exposed dentin areas were coated with 1) primer (ALL-BOND2), surface sealant (FORTIFY BISCO) and 2) primer and bonding agent bonding system (Clearfil SE Bond, Kuraray, Japan). Nd: YAG laser (INCISIVE, USA) was irradiated to the cervical area (30sec×2 times: level of 100mJ pulses at 15 pulses/sec). All pulp responses were measured by pulp vitality/sensitivity with an electric pulp tester (Analytic Technology, Redmond, WA) before and after dentin coating treatment and laser irradiation treatment. The threshold values of the electric pulp test showed 1) 33.5±5.25 (control), 43.0±5.25 (dentin coating treatment) and 45.1±7.92 (laser irradiation treatment), and 2) 31.04±6.08 (control) 42.50±4.56 (dentin coating treatment) and 45.50±2.40 (laser irradiation treatment). The threshold values of the electric pulp test after dentin coating treatment and laser irradiation treatment were significantly higher (p<0.01) than the control. This study suggested that application of Nd: YAG laser irradiation with dentin coating may be useful for relieving the pain of dentin hypersensitivity.
According to current reports, DIAGNOdent® has become established as one method of dental caries detection and diagnosis. We have reported that this value is influenced by bacteria, and speculate that DIAGNOdent® is a useful tool for root canal treatment. The aim of this study was to evaluate of DIAGNOdent® value when using root canal disinfectant, filling drugs and cement for endodontic therapy of primary and premature permanent teeth. The results were as follows. Formalin cresol, camphorated phenol, iodine glycerin, sodium hypochlorite, hydrogen peroxide solution and their mixture were not affected by the DIAG NOdent® value. The value of Calcipex® II VITAPEX® was about 10. Liquid of CALVITAL®, Palpac V, NEODYNE®-α, BASE CEMENT and PALPACK V powder were not affected. The values of other powders were between 8 to 13. The paste of PALPACK V and BASE CEMENT did not increase in value after mixing. On the other hand, CALVITAL® and NEODYNE®-α showed a significant increase of value after mixing. This report suggests that drugs and cement related root canal treatment have a wide variety of DIAGNOdent® values.
In dental treatment with Nd: YAG laser beam, a quartz optical fiber is generally used to transmit the laser beam, which is irradiated to the hard and soft tissues for caries treatment and periodontal tissue excision. Recently, a diffused and circumferential laser beam, which is produced by using a processed optical fiber at the tip, is widely used for these treatments. The advantage of using a processed fiber is that an ordinary beam has difficulty in making incisions in oral soft tissue and removing some outer layers of the gingiva. In the previous study, a method of processing an optical fiber tip with TiO2 powder was proposed, and the performance of the processed optical fiber (TP fiber) for processing hard and soft tissues was investi gated. The laser beam radiated from the tip of the TP fiber is partitioned into a straight beam, a sideways beam and heat generat ed by the absorption of the laser beam. In this paper, an experimental instrument to measure the energy partition radiated from the TP fiber is developed, and the relation between processing conditions and energy partition of the laser beam emitted from the tip of the TP fiber is investigated in detail. As a result, an effective tip of the TP fiber is obtained under suitable processing conditions and the laser beam radiated from the fiber tip is controllable. The laser beam radiated as a straight beam and a sideways beam at the TP fiber tip was measured respectively, and an appropriate TP fiber tip for each type of dental treatment was obtained.
A fine flexible glass fiber made of quartz has been developed to transmit laser beams more effectively to a specific area. This may increase the potential usefulness of the Nd: YAG laser for root canal treatment. Recent investigations revealed that colloidal TiO2 irradiated by lasers generated laser photolysis and electron paramagnetic resonance (EPR). The aim of this study was to evaluate root canal preparation using Nd: YAG laser with TiO2 solution. Twenty-seven roots removed at 11mm from the apex were used. Root canal patency was confirmed using a No.10 K-file. Then, each sample was fixed to a movable stage, and the fiber tip was inserted near to the apex. The root canal walls were irradiated for 10 sec by Nd: YAG laser. The fiber tip was moved from the apical portion of the root canal towards the canal orifice at a speed of 1mm/sec. The root canal was filled with 5% TiO2 solution during lasing. As to laser irradiating parameters, the output energy was 120mJ, pulse frequency was 15, 30 and 60pps, and the repetition of lasing was 2, 4 and 8 times. Before lasing, the fiber was processed by Nd: YAG laser irradiation through itself in TiO2 solution for 30 sec. This procedure changed the laser irradiating pattern from straight to spherical. The lased samples were evaluated by contact microradiography, digital microscopy and scanning electron microscopy. The mean rates of increase of longitudinal cross sectional root canal space were 100.13±5.51% (15pps, 2 times), 94.42±14.37% (15pps, 4 times), 97.91±8.02% (15pps, 8 times), 100.16±20.88% (30pps, 2 times), 120.52±16.40% (30pps, 4 times), 103.55±10.66% (30pps, 8 times), 102.41±8.46% (60pps, 2 times), 101.01±24.54% (60pps, 4 times), and 96.13%±1625% (60pps, 8 times), respectively. No carbonization of the lased dentin surfaces was observed by digital microscopy and scanning electron microscopy when pulse repetition rate was less than 20pps. In conclusion, the lasing parameters of pulse energy 120mJ and repetition rate 30pps may be appropriate for Nd: YAG laser irradiation of root canals filled with TiO2 solution.