Although root canal irrigation is an important process for successful root canal treatment, there is a high risk of irrigant extrusion into the periapical region. However, periapical pressure generated by laser-activated irrigation (LAI) using an Er:YAG laser has not been studied yet. The aim of this study was to investigate the root canal irrigation pressure generated outside the apical foramen during LAI using an Er:YAG laser in comparison with passive ultrasonic irrigation (PUI) and conventional irrigation (CI).
A plastic root canal model shaped to a working length of 20 mm with an apical diameter of 0.40 mm was used. They were assigned into the following three groups:
1) LAI group: Distilled water was activated by Er:YAG laser (Erwin AdvErL, Morita, Japan, 70 mJ 10 pps) with a cone-shaped tip (R200T, Morita, φ = 200 μm) positioned 2 mm short of the working length for 20 seconds.
2) PUI group: PUI was performed for 20 seconds with an ultrasonic file, which was positioned 2 mm short of the canal end and driven by an ultrasonic device (Piezon Master 400, EMS, Switzerland, highest power setting).
3) CI group: Hand irrigation with 1 ml of distilled water was performed using a 27 gauge conventional flat needle (Nipro needle and syringe, Nipro, Japan) positioned 2 mm short of the working length for 20 seconds.
Each irrigation was performed ten times repeatedly. The mean maximum pressure caused by the irrigation was measured using a pressure sensor (AP-12S, Keyence, Japan) connected via a plastic tube to the model. Data were analyzed by one-way ANOVA and Tukey-Kramer test at a significance level of p = 0.05.
The mean maximum pressure caused by LAI and PUI was significantly lower than that caused by CI (p < 0.05), and that caused by PUI was significantly lower compared to LAI (p < 0.05). Under the conditions of this preliminary study, the pulsed Er:YAG laser did create irrigation pressure outside the simulated apical foramen. Although it was smaller than that caused by CI, possible irrigant extrusion through the apical foramen should be considered also in LAI.

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The usefulness of high reactive-level laser therapy (HLLT) and low reactive- level laser therapy (LLLT) using a carbon dioxide laser for socket preservation in clinical cases has recently been reported. However, the mechanism of the healing-promoting effects of carbon dioxide laser irradiation remains unclear. Therefore, the emergence of osteoclasts and change of new bone formation of rats' extraction sockets by the carbon dioxide-enhanced healing process were investigated.
Ninety-nine 5-week-old male Wistar rats were divided into an HLLT irradiation group (group L1), a combination of HLLT+LLLT irradiation group (group L2) and a non-irradiation group (control group) and compared. The upper-left first molar was extracted to prepare an extraction socket model. The laser irradiation groups (groups L1 and L2) underwent HLLT immediately after tooth extraction and then LLLT 1 day post-extraction (group L2). The irradiated tissues including the extraction socket were excised 6 hours and 3, 5, 7, 10 and 21 days after extraction. Then, they were fixed in 4% paraformaldehyde, decalcified in 10% EDTA solution, and paraffin-embedded employing the standard method. Next, serial sagittal sections were prepared, and granulation tissue of the extraction socket was histologically investigated using hematoxylin-eosin staining.
On day 3, many osteoclasts appeared and active bone resorption at the socket was noted in the irradiation groups (groups L1 and L2) compared to the control group. On day 7, new bone formation started from the superficial layer to the middle layer of the socket in the irradiation groups. However, new bone formation was observed around the socket in the control group. On day 21, a concavity existed in the alveolar crest region in the control group, whereas the region was flat without concavity in the irradiation groups (groups L1 and L2). On osteomorphometry, the alveolar crest height in group L2 (0.7660 ± 0.039) was significantly higher than that in the control group (0.6516 ± 0.079).
Carbon dioxide laser irradiation may enhance the rapid bone resorption and new bone formation on the superficial layer over the middle layer. It is suggested that carbon dioxide laser irradiation promotes the healing of tooth extraction sockets.

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The Er:YAG laser is useful for not only removing dental caries, but also for oral surgery, endodontics, and periodontal therapies, and has many advantages compared with traditional treatments. The irradiation conditions of wavelength, output power, and pulse repetition are important for treatment efficacy. Moreover, morphological changes to the irradiated tip are a major factor affecting the adjustment of laser power to specific tissues. However, there is insufficient data regarding tip alterations during treatment. The aim of this study was to conduct a morphological analysis of tips using micro focus X-ray computed tomography (micro-CT). Quartz contact tips for cavity preparation or for soft tissue surgery were analyzed. Micro-CT was performed on five unused tips each. Micro-CT images were obtained under the following conditions: tube voltage 90 or 100kV; current 100 or 200μA; and slice width 0.16 or 0.08mm, respectively. The obtained 3D reconstructions were analyzed using software. The 3D data was correctly obtained from the shape of the contact tips by micro-CT. These results revealed that micro-CT is useful for 3D morphological analysis of irradiated tips.

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