Low level laser therapy (LLLT) has been used widely in the treatment of various chronic painsyndromes in dentistry, pain clinics, and orthopedics. In particular, in dentistry the application of LLLT isincreasing in many cases, such as dentin hyperesthesia, aphtha, and temporomandibular joint dysfunction.There is general agreement that LLLT is effective for improving blood circulation, for pain attenuation, andfor wound healing. Although a large number of studies have been done on laser effects, most of them areclinical reports, and only a few studies have so far focused on cell biological research. As such, themechanism of laser-induced analgesic effects remains unknown. In this report, we describe the effects of lowlevel laser irradiation on nerve cells in vitro, and demonstrate the mechanism of the analgesic effect in LLLT. A Ga-Al-As diode laser (trinpl D, YOSHIDA, Japan) was used as the laser apparatus. The experimentalcells were from the neurosecretory PC12 cell line, established from rat adrenal pheochromocytoma by Greeneand Tischler in 1976. After short-term laser irradiations (0.3-0.5J/cm2) to PC12 cells differentiated bytreatment with nerve growth factor, terminals of neurites underwent swelling within a few minutes. At thesesites, the density of the cytoplasmic matrix was reduced, and the number of synaptic vesicles was decreased.After long-term laser irradiations (15.0J/cm2), synaptic vesicles completely disappeared from terminals thatwere extremely swollen, and the density of the cytoplasmic matrix was greatly reduced, whereas cell bodieswere still well preserved. Some of the cells appeared to be in degeneration and had retracted their neurites, accompanied by alterations of F-Actin structures. The laser irradiation induced a temporary increase in intracellular free calcium ion concentrations ([Ca2+] i), making them 1.7-fold higher in terminals and 2.7-fold higher in cell bodies, and enhanced the amplitude ofcalcium oscillation. In terminals, the peak level of [Ca2+] i. was 1400nM, and the interval time of each peak wasabout 200 ms, but in cell bodies, calcium oscillation was not clear. Thus, the mechanism of the laser-induced analgesic effect is clearly demonstrated to be that the laserstimulates calcium ion influx and neurotransmitter release, and then degenerates terminals and processes ofneurites, according to alterations of actin organization. These findings suggest that LLLT attenuates thesensibility of nerve cells to painful stimuli and produces analgesic effects.
Recently, many studies have been performed on the Er: YAG laser to expand its clinical use.This investigation aimed at evaluating the effects of Er: YAG laser irradiation using newly designed contactprobes on human dentin surfaces. Dentin disks were prepared from tooth crowns of human molars. An Er: YAG laser (MEY-1, J. Morita, Kyoto, Japan) was irradiated at 30mJ through two kinds of newly designedcontact probes, and a conventional flat end-type contact probe. The newly designed probes, which had a sharpend, were used for experimental groups (Group C, n=10, Group J, n=10), and a flat end contact probe (GroupA, n=10) was used as a control. Touching the end of the contact probes with the surfaces of dentin disks, onelaser pulse was delivered under water spray cooling. After the laser irradiation, samples were stained withrhodamine 123, and observed by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM), to evaluate the laser-irradiated surfaces three-dimensionally. Results obtained were as follows. 1. In every dentin disk, a cavity was created by the laser shot. The cavities were significantly deeper inGroups C and J than in Group A (P<0.0001, ANOVA). On the other hand, cavities of Group A had asignificantly larger diameter compared with those of Groups C and J (P<0.0001, ANOVA). 2. SEM observation showed no debris on the cavity surfaces in any group. However, melted dentin surfaceswere observed only in the experimental groups.
Recently, application of low-power laser rays to wound healing of oral soft tissue has becomeroutine. To elucidate the effects of a low-power laser on wound healing at the oral mucosa, we examined thechange of cytoskeletal formation of normal human gingival fibroblasts after irradiation of low-power laserrays in vitro, by confocal laser scanning microscopy. Cells were cultured for 4, 7, and 24 hours after laser irradiation once, for 30 sec, with a diode laser (905nm, GaAlAs diode, pulse wave, 1.2kHz, 10W (peek), 2.4mW (average), 1.25J/cm2 (150sec)), and cells cultured forthe same times without laser irradiation were used as control groups. After 4 and 7 hours, developed actin filaments were observed, associated with increasing and accumulatingfibronectin in extracellular component on the basal surface of fibroblasts, in the laser irradiation groups.However, actin filament and fibronectin were not significantly different compared with the control groups after24 hours. These results suggest that low-power laser irradiation activates cell adhesion ability and promotes thedevelopment of actin filament and early accumulation of fibronectin of human gingival fibroblasts.
Various biostimulatory effects of low-energy laser irradiation (LLLI) have been reported thatinvolve the acceleration of bone regeneration. We reported that LLLI stimulated cellular proliferation, bonenodule formation, alkaline phosphatase activity, and osteocalcin expression. However, the molecular basis ofthe mechanisms leading to these findings has not been elucidated. To accomplish this, we constructed thecDNA library of MC3T3-El, a clonal osteoblastic cell line, which enhanced gene expressions by LLLI using asubtracted gene cloning procedure. In the present study, we further characterized gene library by DNAnucleotide sequence and homology-search with a DNA database. Among 88 subtractive genes, several clonesexhibited high homology with mitochondrial protein genes, signal transduction-related genes, and EST genes.These findings may help to elucidate the molecular-based mechanisms for the biostimulatory effect of LLLI onosteoblasts.
This case report presents the application of a high pulse rate Er: YAG laser to remove gingivalmelanin hyperpigmentation. A 19-year-old female complained of an esthetic problem caused by gingivalmelanin pigmentation. The patient desired improvement of gingival color by laser treatment. Themelanin-pigmented gingiva of the maxilla was divided into three sections, and each section was treated at onevisit. In total, three Er: YAG laser treatments were given. The Er: YAG laser irradiation was performed at theoutput energy of 27-47mJ/pulse (panel setting 42-72mJ/pulse) and 20-30Hz, with water spray in a contactmode using an 80-degree curved contact tip. At the first and second treatments, the irradiation was performedwith only topical anesthesia. At the third treatment, the irradiation was performed under local anesthesia byinjection, with microscopic observation. The wound healing was basically evaluated immediately, and at 1, 2, and 4 weeks, and at 3 and 6 months, after the irradiation. The visual analog scale (VAS) was used to evaluatethe pain level experienced by the patient. Ablation of the hyperpigmented epithelial tissue of gingiva waseasily achieved, without prominent bleeding complications. The use of water spray provided a clear operationfield. The microscopic monitoring during laser irradiation was of great advantage for complete removal ofslightly remaining melanin pigmentation. The irradiated site showed no major thermal damage, such aswhitish coagulation or carbonization. The patient perceived slight to moderate pain, such as irritation orcontact pain, until 3 days after treatment. At one week, the gingiva had recovered an almost normalappearance, with a healthy pink appearance, although the gingiva was immature and thin and at two weeks, the gingiva showed complete healing, with normal thickness. Healing delay, complications, or side effectswere not observed during this observation period. Slight recurrence of the melanin pigmentation was observed after six months. The results of the present clinical study suggest that the removal of gingival melanin pigmentation can be performed safely and effectively by high pulse rate Er: YAG laser irradiation.
The objective of this study was to clarify the effect of CO2 laser irradiation on oral tissue problemsin children, especially to treat mucocele. This study was carried out in the pedodontic clinic of Tokyo Medicaland Dental Hospital for 7 years between 1995 and 2001. A CO2 laser was used on 29 subjects, of ages between0 to 15, having a mucocele on lip, lingual, or buccal mucosa. In each case, after administration of localanesthesia, the border of the mucocele was first incised around by a CO2 laser in 3 or 4 watt continuous mode.Thereafter, the mass of the mucocele was completely removed away from the adjoining normal tissue, withoutbreaking its wall. No cases required suturing. The results were as follows: 1. A mucocele of lip or lingualmucosa, with a rich blood supply, was efficiently removed, without bleeding, giving a clear operative fieldduring the operation; 2. The surgery itself was simple and less time-consuming; 3. After two or three weeksthe wound was completely healed without almost any discomfort in all patients; 4. Wound contraction andscarring were decreased or eliminated; 5. Reoccurrence of a mucocele was not seen, except for one case of alingual mucocele. In conclusion the use of a CO2 laser proved to be a very safe and effective mode for theremoval of mucocele, especially in small children.