Yasuaki Takase

Influence of output energy and pulse repetition rate of the Er:YAG laser on dentin ablation.

OBJECTIVE We sought to improve the efficiency of dentin ablation with the Er:YAG laser by investigating the effects of output energy and pulse repetition rate on ablation. BACKGROUND DATA The Er:YAG laser is superior to other lasers in ablating dental hard tissues. However, the factors affecting the efficiency of ablation with an Er:YAG laser remain unclear. METHODS Fifty bovine root dentin plates were irradiated with an Er:YAG laser at an output power of 1.0 W, 1.5 W, or 2.0 W under a water spray while moving the plate at 1 mm/sec. After irradiation, the depth and volume of each ablated site were measured by laser microscopy and the ablated surfaces were examined by scanning electron microscopy. RESULTS The output power showed a strong positive correlation with the depth and volume of ablation. The output energy had much more pronounced effects on the depth and volume of ablation compared to the pulse repetition rate. The shape of the ablated site varied with the output power, and no cracking or vitrification was observed under the irradiated dentin. The most effective parameters for dentin ablation were an output power of 2.0 W, with an output energy of 80 mJ/pulse at 25 pulses per second (pps) or 100 mJ/pulse at 20 pps. CONCLUSION These findings suggest that the output energy is the main factor affecting the efficiency of dentin ablation with an Er:YAG laser. We propose that the efficiency of dentin ablation can be improved by choosing an optimal combination of output energy and repetition rate.

Light-curing of dental resins with GaN violet laser diode: The effect of photoinitiator on mechanical strength

The purpose of this study was to evaluate whether a Gallium Nitride (GaN) -based violet laser diode (VLM500) could be used as a light source for light-cured dental resins. Three experimental unfilled resins containing different photoinitiators (camphorquinone, CQ; phenyl propanedione, PPD; or mono acylphosphineoxide, MAPO) were evaluated. These resins were light-cured with a VLM500 laser diode, and their ultimate micro-tensile strengths (μTS) were compared to those cured with three different LED light sources (Curenos, G-Light Prima-normal mode and G-Light Prima-PL mode). The VLM500 produced high μTS values in all three resins, and we concluded that this violet laser diode can be used as a light source for light-cured dental resin materials.

Light-curing efficiency of dental adhesives by gallium nitride violet-laser diode determined in terms of ultimate micro-tensile strength

The purpose of this study was to evaluate whether violet-laser diode (VLD) can be used as light-curing source. The ultimate (micro-)tensile strength (μTS) of three adhesives was determined when cured by VLD in comparison with curing by two different types of commercial LED light-curing units. One VLD (VLM 500) and two LED units (Curenos and G-Light Prima) were used to cure the adhesive resin of the two-step self-etch adhesives Clearfil SE Bond, Tokuso Mac Bond II, and FL-Bond II. A 0.6-mm thick acrylic mould was filled with adhesive resin and cured for 60 s. After 24-h water storage, specimens were trimmed into an hourglass shape with a width of 1.2 mm at the narrowest part, after which the μTS was determined (n=10). In addition, the light transmittance of each adhesive was characterized using a UV-vis-NIR spectrometer. No significant difference in curing efficiency between VLD and LED were observed for both Tokuso Mac Bond II and FL-Bond II (p>0.05). For Clearfil SE Bond, the μTS of VLD-cured specimens was higher than that of the specimens cured by the LED Curenos unit (p<0.05). Spectrometry revealed that this marked difference must be attributed to a different light transmittance of Clearfil SE Bond for visible blue light versus for the lower area of UV and visible violet light. In conclusion, A GaN-based violet laser diode can be used as light-curing source to initiate polymerization of dental resins.

Influence of handpiece maintenance sprays on resin bonding to dentin

Objective To investigate the influence of maintenance spray on resin bonding to dentin. Materials and methods The crown of extracted, caries-free human molars was transversally sectioned with a model trimmer to prepare the dentin surfaces from mid-coronal sound dentin, and then uniformly abraded with #600 silicon carbide paper. The dentin surfaces were randomly divided into three groups: oil-free spray group where maintenance cleaner for air bearing handpieces was sprayed onto the dentin surface for 1 s and rinsed with water spray for 30 s; oil-containing spray group where maintenance cleaner for micro motor handpieces was sprayed onto the dentin surface for 1 s and rinsed with water spray for 30 s; and control group where the surface was rinsed with water spray for 30 s and then air-dried. These surfaces were then bonded with Clearfil SE Bond (Kuraray Medical), and resin composite (Clearfil AP-X, Kuraray Medical) build-up crowns were incrementally constructed on the bonded surfaces. After storage for 24 h in 37°C water, the bonded teeth were sectioned into hour-glass shaped slices (0.7-mm thick) perpendicular to the bonded surfaces. The specimens were then subjected to microtensile bond strength (μTBS) testing at a crosshead speed of 1.0 mm/min. Data were analyzed with one-way ANOVA and the Tukey-Kramer test. Results Maintenance spray-contaminated specimens (oil-free and oil-containing spray groups) showed significantly lower μTBS than control specimens (P < 0.05). However, there was no significant difference between the spray-contaminated groups (P > 0.05). Conclusion Maintenance spray significantly reduces the bond strength of Clearfil SE Bond to dentin.

Experimental oral soft tissue surgery with a high-repetition-rate Er:YAG laser

Abstract The purpose of this study was to evaluate performance in oral soft tissue surgery and the periodontal tissue interactions resulting from increasing the repetition rate of a pulsed-mode Er:YAG laser system from 10 to 30 pulses per second (pps). Five beagle dogs aged 2 or 3 years old were used in this study. The specific maneuvers were performed for a gingivectomy and the removal of melanin pigmentation. A trial Er:YAG laser, which is adjustable up to 30 pps of repeated rate, was used. As for gingivectomy, the output power was made under eight conditions (35 mJ–30 pps, 35 mJ–20 pps, 70 mJ–10 pps, 70 mJ–20 pps, with or without water). The irradiation condition for the removal of melanin pigment was set at 35 mJ–30 pps with or without water. The observation periods were immediately, 7 and 28 days. Specimens were made and observed under a light microscope. Procedures of the gingivectomy and removal of melanin pigmentation resulted in favorable healing, regardless of the irradiation conditions. Increasing the repetition rate up to the 30 pps with low power significantly improved the smoothness and morphology. The high-repetition-rate Er:YAG laser technology described is advantageous, compared with low-repetition-rate Er:YAG lasers, and is applicable in a variety of oral soft tissue surgical procedures.

Pulpal reaction of Er:YAG laser irradiation by different power/pulse conditions

Abstract In this study, using a prototype Er:YAG laser of which pulse repetition rate can be adjusted up to 30 pps, we histopathologically investigated the damage to pulpal response at the time of cavity preparation in relation to the pulse repetition rate. After the Beagle dogs received systemic anesthesia, a contact tip of 600 μm in fiber diameter was placed in the Er:YAG laser and a Blacks V cavity was prepared under the following radiation conditions with watering. After cavity preparation was completed, the interior of the cavity was cleansed and filled with a hydraulic sealing material. Observation periods lasted both 7 and 28 days. Paraffin sections were obtained via a conventional method, stained with a double-staining of hematoxylin and eosin, and histopathologically investigated for changes in the pulp under a microscope. In both the 7th and 28th day follow-up observation cases, circular disorders such as vasodilation and hemorrhage were found at a high rate in both groups, although inflammatory changes such as infiltration of round cells were few. Under the radiation conditions set in this experiment, it was confirmed that cutting of the dental hard tissue could be made without severe changes to the pulp. Because the pulse repetition rate can be changed, we will be able to study in detail the cutting efficiency with changes in the width of the radiation conditions at various cutting sites, such as the dental enamel, dentine and soft dentine.