Journal of clinical laser medicine & surgery最新文献

Objective: Until now, there has been no study that demonstrates the effectiveness of Er:YAG laser microprobes to clean and shape the root canal without using any mechanical instrumentation.

Materials and methods: The study was conducted on 28 single-rooted extracted central incisors teeth with straight roots. Fourteen were mechanically prepared and served as the control group, and 14 were treated by Er:YAG laser only. From every group, half of the teeth were examined histiolgically and half by SEM. The instrument tested was an Er:YAG laser with microprobes 200-400 micro in diameter and 20 mm in length, coupled onto special handpieces, attached to the delivery fiber of an OPUS 20 Er:YAG laser. The Er:YAG laser was applied with the following parameters: wavelength 2.94 microm; pulse duration 400 msec; repetition rate 10 Hz; energy per pulse 140 mJ for the 400 micro microprobe and 90 mJ for the 200-micro microprobe.

Results: For the control group, histologically, large amounts of residual pulp tissue were found in the root canal cavity, and open tubules were seen in all the specimens; SEM examination showed very uniform root canal, from apical to cervical portion, high number of open tubules, and different levels of canal debridment. For the study group, histologically, no residual pulp tissue was found in the root canal cavity and open tubules were seen in all the specimens; SEM examination showed the root canal free of debris, removed smear layer, open dentinal tubules, and different levels of enlargement.

Conclusion: Our results show that the Er:YAG laser special microprobes are effective in shaping, cleaning, and enlarging straight root canals faster and more efficiently then traditional methods.

Objective: In this study, we examined the surface morphology of dentin after being ablated by the third, fourth, and fifth harmonics of the Nd:YAG laser. The influences of the repetition rate with respect to the wavelength were also investigated.

Background data: Typically, excimer lasers have been used as the primary sources of ultraviolet (UV) laser wavelengths to investigate laser ablation of dentin. In the past decade, developments in nonlinear optical technology have given rise to higher conversion efficiencies of the fourth and fifth harmonics of the Nd:YAG laser. To this end, sufficient energy densities of the fourth and fifth harmonics of the Nd:YAG laser have been generated to ablate dentin.

Materials and methods: Thin dentin samples (typically 1 mm) were irradiated by the third, fourth, and fifth harmonics of the Nd:YAG laser. Ablation occurred at repetition rates of 1, 5, 10, and 20 Hz, using similar energy densities for each laser wavelength. An environmental scanning electron microscope was used to assess the resultant surface morphology.

Results: Dentine surfaces after 355-nm ablation exhibited plugging at each repetition rate. Similar surfaces were exhibited after 266-nm ablation. "Plugging" over dentine tubules was less obvious after 213-nm laser ablation. The results may highlight the impact of different absorption characteristics of each wavelength.

Conclusion: Solid-state UV laser ablation of dentin exhibits similar properties to excimer laser ablation. At similar energy densities, the deeper UV laser wavelengths exhibit less "plugging" of dentin tubules, suggesting a lower thermal impact.

Objective: The purpose of the present study was to investigate the effect of light on nanobacteria.

Background data: Since their first description in literature, it is not clear whether the nanoparticles called "nanobacteria" are alive or not. The 80-1,000-nm-sized spherical particles are protected by a crystalline carbonate apatite shell and are culturable in cell culture media. Present in mammalians, including humans, nanobacteria seem to cause diseases related to biomineralization processes. Mesoscopic structures found on Martian meteorites and terrestrial rocks indicated that nanobacteria-like biological objects forming apatite, a material fairly transparent to visible light, could have been present on the primitive Earth during an era with the sun as the principal terrestrial energy source.

Materials and methods: To evaluate possible biomedical effects of therapeutically relevant irradiation sources on nanobacteria, we irradiated nanobacteria cultures with polarized light and laser-light at low, nonthermal energy density levels.

Results: Our observations indicated that nanobacteria are alive. Polarized white light was found to clearly accelerate their replication in vitro, resulting in significant dose-dependent increases in the turbidity of the cultures, compared to nonirradiated controls. Laser irradiation did not affect their replication.

Conclusion: The possibility that primordial and present nanobacteria could have been not only exposed to, but actively harvested, solar irradiation for their own development suggests itself. Considering that there exists no published material on the action of light on nanobacteria, the reported effects are expected to have an impact on modeling biomineralization processes, associated photoreceptor mechanisms, and astrobiological and evolutionary theories-on Earth and in space.

Objective: The purpose of this study was to investigate the morphological changes of bovine mandibular bone following Er,Cr:YSGG laser irradiation in different methods in vitro.

Background data: Recently, an erbium, chromium/yttrium, scandium, garmet (Er,Cr:YSGG) laser device that emits a laser beam at the wavelength of 2.78 micro m was introduced. This type of infrared laser proved to ablate dental hard tissues effectively. However, the different effects of bone ablation by this laser in different irradiation methods were still unknown.

Materials and methods: Adult bovine mandibular bones were cut into 24 small pieces, 3-4 cm in length. The parameters of Er,Cr:YSGG laser irradiation were as follows: wavelength was 2.78 micro m, pulse duration was 140-200 micro sec, repetition rate was 20 pulse/sec, power was 4 W, spot size was 1.26 x 10(-3) mm(2), and energy density was 160 J/cm(2). Irradiation methods were different in four groups (six specimens in each group): group A, fixed position and contact mode; group B, fixed position and noncontact mode; group C, nonfixed position and contact mode; and group D, nonfixed position and noncontact mode.

Results: Ablation depth in group A was significantly greater than in group B (p < 0.01). In group A, thermal damage was apparent. In group B, C, and D, thermal damage was minimal.

Conclusion: Er,Cr:YSGG laser allows for precise surgical bone cutting and ablation with minimal thermal damage to adjacent tissue. Irradiation in different methods may achieve different ablation rates and thermal damage.

Objective: The purpose of this in vitro laboratory study was to determine the effect of low-fluence argon laser (AL) irradiation delivered from two different argon laser systems on enamel caries-like lesion initiation and progression.

Background data: Previous in vitro investigations and a recent in vivo pilot study have shown that AL irradiation of enamel provided a protective effect against in vitro and in vivo cariogenic challenges.

Materials and methods: Twenty extracted human molars were selected, and 10 teeth were assigned to the HGM argon laser group and 10 were assigned to the LaserMed argon laser group. The exposed buccal windows of sound enamel were exposed to low-fluence irradiation, while the lingual windows of enamel were not exposed to laser irradiation and served as the no-treatment (control) group. Enamel caries-like lesions were created using an acidified gel. Two longitudinal sections were taken per sample (n = 20 lesions per group) and evaluated by polarized light microscopy for body of the lesion depths after lesion initiation (8 weeks) and progression (12 weeks) periods.

Results: After lesion initiation and progression, the body of lesion depths were similar for both argon-irradiated groups (p > 0.05). With the no-treatment (control) group, there were significant increases in lesion depth with a 61-78% increase for the lesion initiation period and a 50-69% increase for the lesion progression period when compared with the argon laser-treated groups.

Conclusion: Argon laser irradiation provides a certain degree of protection against in vitro enamel caries initiation and progression. Resistance to a continuous caries challenge was similar with either argon laser delivery systems (HGM and LaserMed). Argon laser irradiation may prove to be beneficial in reducing the caries susceptibility of sound enamel and white spot lesions in the clinical environment.

Objective: The objective of this study was to determine of the efficiency of holmium:YAG laser for bone ablation, compared to cartilage and soft tissue of the intervertebral foramen of the lumbosacral spine.

Background data: The holmium:YAG (Ho:YAG) laser has been used for ablation of bulging or prolapsed discs and also has the potential for decompression of the nerve root when there is narrowing of the foraminae (foraminoplasty). It is proposed that laser ablation of bone and ligament of the intervertebral foramen for nerve root decompression using the Ho:YAG laser is able to produce sufficient bone ablation without inducing significant thermal necrosis in surrounding tissues due to its short absorption length, which could result in significant clinical advantages.

Materials and methods: Experiments were performed on samples of laminar bone, facet joint capsule, and cartilage for quantitative and qualitative determination of the effect of Ho:YAG ablation on tissue mass loss using a range of pulse energies from 0.5 to 1.5 J/P at 15 pulses/sec.

Results: The results showed a significant linear correlation between the mass loss and pulse energy, and between the mass loss and radiant exposure. Electron microscopy and histology showed that the Ho:YAG ablation resulted in a very sharp and clear border with little charring. Applying 0.01 k.J of total energy at two different settings (1.5 J/p, high power, and 0.5 J/p, low power) at 15 pulses/sec, the cross-sectional area/mm(2) of the ablated bone was measured, using light microscopy and the Scion Image analysis program. The ablated areas were 2.28 +/- 0.87 and 1.16 +/- 0.43 mm(2) at high and low power, respectively (p = 0.008).