It is very important to prevent decalcification and loss of dental substance on tooth surfaces, as occurs in dental cavities. Various treatment procedures have been proposed for this purpose. One of the most prominsing methods is an improvement of the tooth surface using laser, irradiation to render it resistant to acid. Tuning a laser wavelength to the stretching vibration of specific bio-molecules has some advantages in ablating hart tissue and surface modification induced by the photo-thermal or photo-mechanical interaction. The radiation can be realized by Er: YAG laser, CO2 laser and free Electron Laser in the infrared region. This procedure has been used widely for multiple purposes and its clinical outcome has been assessed. In this paper, I summarize the basis of laser tissue interaction to the surface phenomena of dentine.
Various kinds of lasers have been developed and applied to a variety of lesions in medical and dental fields. However, few papers have reported in detail how to use contact lasers in oral and maxillofacial surgery. Here we describe how to use Nd: YAG and KTP contact lasers in surgery for head and neck tumors, and specify the advantages and disadvantages of scalpels, electric knives, and contact lasers. The 169 subjects had head and neck tumors (28 benign, 141 malignant) treated with Nd: YAG or/and KTP contact lasers during the period 1998-2002. A KTP/YAG laser (Model SL 20/50, Laserscope) was most commonly used, although an SLT contact laser (DCL-50, SLT Japan) and an Nd: YAG laser Hercules 5100 (Laser Sonics) were also used occasionally. The above lasers were mainly used for hemostatic cutting. In the KTP/YAG system, the Nd: YAG laser was basically applied at 12-13 W with quarz fiber (0.6mm diameter) held using a microstat handpiece. Power was increased to 17-18 W, when cutting was difficult. For larger tumors, the KTP laser was used at more than 10 W. Both lasers were used in continuous mode. In all cases, cutting was performed satisfactorily with the Nd: YAG or/and KTP contact lasers according to the above conditions. Based on our experience, we specified the advantages and disadvantages of scalpels, electric knives, and contact lasers, as follows. Scalpels cut the fastest, but offered no hemostasis. Electric knives (cutting mode) were second in cutting speed, but less effective in hemostasis than lasers. Where hemostasis was important, electric knives were used in coagulation mode. However, the cutting speed decreased in this mode. The KTP contact laser was slower to cut than electric knives, but more effective than the latter in hemostasis. The Nd: YAG laser was slowest in cutting among the four instruments. However, this laser was next to the KTP laser in hemostatic cutting. In addition, the glass filter for the Nd: YAG laser was not as dark as that for the KTP laser, which latter caused surgeons to have difficulty discerning anatomical structures during surgery. As a result, we used the Nd: YAG laser primarily, and the KTP laser for larger tumors requiring more hemostatic cutting. The present study demonstrated the advantages of Nd: YAG and KTP contact lasers used appropriately in oral and maxillofacial surgery.
The purpose of this study was to evaluate acid-resistance using HA granules. HA granules samples were divided into the following four groups. 1) HA granules were reacted with APF. 2) HA granules were irradiated with Nd: YAG laser. 3) HA granules were reacted with APF and irradiated with Nd: YAG laser. 4) Control: HA granules were no treated. Reacted specimens were immersed in sodium-acetate buffer solution. Each aliquot was centrifuged. The calcium content of the supernatant was then measured using the ortho-cresolphthalein complexone method. Fluoride content was measured using an ion meter. The calcium flow rates of groups 1) and 3) were both significantly lower than groups 2) and 4) (ANOVA p<0.01). The fluoride flow rate of APF group 3) was significantly lower than group 1). (Mann-Whitney's U-test p<0.05) was suggested that APF treatment and combined use of APF and laser irradiation treatment are effective for acid resistance. This study model indicated usefulness of evaluating acid resistance treatments.
Biostimulatory effects of near-infrared irradiation, such as anti-inflammation and relieving pain have been reported. However, the molecular based mechanisms are not elucidated yet. Human synovial tissues were obtained from the patient with a condylar process fracture of the TMJ undergoing extraction of the mandibular head and arthroplasty. The cells were isolated from TMJ synovial tissues and primary cultured using outgrowth method. The confluent-stage cells were treated with IL-1β, as the same time, near-infrared irradiation was treated to the cells. Three levels of band pass filtering were set at the 700-800nm, 800-900nm, and 900-1000nm wavelengths and irradiation was conducted. The amounts of chemokines in conditioned medium were measured by ELISA kit. After synovial cells were exposed to IL-Iβ, the production of IL-8 and MCP-1 was elevated, though the amounts of increase were reduced at early time after irradiation as compared to without irradiation. The production of IL-8 were significantly reduced at the 900-1000nm wavelength, and the production of MCP-1 were significantly reduced at the 700-800nm, 800-900 nm, and 900-1000nm wavelengths. These findings suggest that near-infrared irradiation may have anti-inflammatory effect on TMJ disorder through the reduction of chemokines production. And the results at each filter waveband were different, which suggested that a difference in potency may be likely.
The laser beam ordinarily comes out from the tip of the fiber, and moves straight to targeted tissues. This is the usual way to use the beam for surgical treatment. However, when the beam is applied for the incision of soft tissue, or the removal of melanin pigment in gingival tissue, a periodontal pocket, an infected root canal etc., a diffused and circumferential beam from the tip of the fiber, is more effective than an ordinary straight beam. An ordinary straight beam has difficulty making incisions in oral soft tissues and removing some outer layers of the gingiva. To obtain a diffused and circumferential beam, the tip of the optical fiber must be processed. Some black colored substance such as carbon paste is applied on the tip portion of an optical fiber before passing through the laser beam. In this experiment, we obtained a diffused beam in circumferential direction by doping with TiO2 within a several millimeter portion of the tip of the fiber. Further, this experiment compared characteristics of the fiber before and after processing with TiO2, using a laser power meter and a thermotracer. As a result, a decreased beam of straight direction, and an increased beam for circumferential direction with a stable thermal distribution were observed at the tip of the optical fiber that was doped with TiO2. These results strongly suggest that processed fiber for a high-peak pulse Nd-YAG laser is useful in clinical applications.
The reactions of cells and tissues following CO2 laser irradiation are classified into two types: photobiodestructive reaction and photobioactive reaction. It has been suggested that photobioactive reaction can simulate mechanical force, which is used to treat bone disease because bone remodeling is very sensitive to mechanical force. This study histologically evaluated the responses of bone following low-level laser treatment (LLLT) by CO2 laser in rattibiae. The left tibia and right tibia of each rat received injury by CO2 laser irradiation and dental bur, respectively. CO2 laser irradiation was applied for 1.0 second (calculated energy density, 139.8J/cm2). The injury induced by dental bur was approximately 1.0mm in diameter and 0.5mm in depth. On days 3, 5, 10, 15, and 20 after injury, tibiae were removed and serial sections were prepared for osteoid staining (Yoshiki's method) and in situ hybridization to detect mRNA expression of type I collagen, osteopontin (OPN), and osteocalcin (BGP). The sections from tibiae on day 5 after injury were prepared for immunohistochemistry of type II collagen. The specimens on day 20 after injury were examined for bone mineral density (BMD) using dual energy X-ray absorptiometry. None of the sections from tibiae treated by dental bur throughout the experimental period exhibited histological features of newly-formed bone within the marrow cavity. However, sections from tibiae on day 5 after laser irradiation exhibited osteoid deposition within the marrow cavity subjacent to the laser treatment site, and woven bones were formed within the marrow cavity subjacent to the site on day 10 after laser irradiation. The woven bones transformed into lamellar bone in the marrow cavity on day 15 after laser irradiation and finally made contact with the original cortical bone surface subjacent to the laser treatment site. In situ hybridization of the sections from the specimens treated with laser demonstrated that type I collagen, OPN, and BGP mRNA were expressed in the osteoblasts of the newly-formed bone matrix. Type I collagen mRNA expression was recognized in all specimens after laser irradiation throughout the experimental period. However, OPN mRNA expression was recognized in the specimens on days 3, 5, and 10 after laser irradiation, whereas BGP mRNA expression was recognized in the specimens on days 10, 15, and 20 after laser irradiation. BMD of tibiae treated with CO2 laser was higher than that of tibiae treated with dental bur on day 20 after the treatments. No evidence of type II collagen expression was found in the newly-formed bone matrix by laser irradiation. These results indicate that LLLT by CO2 laser accelerates new bone formation within the marrow cavity subjacent to the laser treatment site, and that this bone formation occurs by membranous ossification. The present study suggests that LLLT by CO2 laser can be used in the treatment of bone.
The dual quality of light, “that it is both particle and wavelike”, brought a revolution to modern scientific thinking. Lasers, which are a a kind of light and an outgrowth of quantum mechanics, have essential roles in many phases of everyday life in the recent years. Also in the clinical routine of dentistry, lasers are beginning to see more use. Industry has been successful in making the delivery apparatus much smaller and advancing the fibre optic technology and more importantly, achieving better cost performance. There have been numerous studies to date on laser ever since the invention by Dr Mainman in 1960. As is well known, it was begun with ablation of a tooth by laser, which lead to discovery of its improved acid resistant quality. Ruby lasers were used in the early stage, but due to their effect on dental pulp, interest was shifted to the studies with other kinds of laser. Clinical applications require lasers to be used in extremely confined spaces such as pits, fissures and root canals, for which light guide systems and tips were developed. In today's clinical dentistry, dental applications by a wide variety are being studied. The lasers used for clinical applications are mainly CO2, Nd: YAG, Er: YAG, Ar, and Diode. Among the latest models of laser device recently adopted for clinical applications, there are those using such mediums as Er, Cr: YSGG and Nd: YAP. Studies are beginning to be made for understanding reactions of various lasers with different materials using a free electron laser apparatus. Significance of the studies is based on the fact that, depending on each different wavelength, absorption and reflection of laser light on the surface of materials vary. And absorption level of energy varies under the surface according to composition, colour, water content etc. of the materials. Irradiation by laser on different parts of human body will obtain various reactions depending on wavelength, output cacpcity tissue, laser medium, etc. Applications of laser are made in the extensive fields of prevention, prosthesis, oral surgery, orthodontics etc. (Table 3). Nevertheless, there is a significant variety of problems that need to be resolved before lasers become really safe and effective to use in dentistry. In this sense, now is the time when the following questions require answers with proper explanations and detailed demonstrations by both researchers and clinicians: “Are lasers really effective?”;“What are the conditions in order to achieve real effectiveness?”
1968, Gordon et al. of the USA conducted the first experiments on dental alloy welding using an Nd: Glass laser. In 1971, the author started experimenting with laser welding using an Nd: YAG laser, and has extended the experiments through various basic studies and clinical applications. In 1978, Van Benthem et al. of Germany conducted many studies using an Nd: YAG laser. Although studies on laser welding in dentistry started early and experiments were done, it did not draw much attention for about 25 years. Why is it laser welding popular now? In the development of dental laser welders, we have been seeking to overcome allergies to metals with soldering.First, laser welding is essential to increase the use of titanium, which is gentle to the human body. Laser welding efficiently eliminates the problems of investment soldering. Secondly, laser welding enables even beginners to perform complicated techniques compared to investment soldering which requires experience and skill, and also reduces the stress on technicians and saves time and energy for technical works. Furthermore, laser welding can lead to new technology development (the NANRI technique). Unfortunately, laser welding is now mostly used for repairing dentures and bad castings. Laser welding should be used for not only repair or temporary joints but also for casting machines and porcelain furnaces. This paper describes the optimum conditions for laser welding, and suggests better methods for oral treatment by laser.