Laser irradiation activates a range of cellular processes in a variety of cell types, including stem cells, and can promote tissue repair.
The purpose of this study was to examine the effects of diode laser irradiation on the proliferation and osteogenic differentiation of human dental pulp cells (hDPCs). hDPCs were cultured and exposed to an 810-nm diode laser at a dose of 0 or 1 J/cm2. Cell proliferation was evaluated by cell proliferation ELISA BrdU kit and MTS assay. For osteogenic differentiation, hDPCs at confluence were cultured in osteoblastic differentiation medium (ODM), and were irradiated daily with a diode laser. mRNA and protein levels of bone markers were examined by real-time PCR analysis and Western blot analysis, respectively, Alkaline phosphatase (ALP) activity and calcium concentration were determined. Mineralization was evaluated by Alizarin Red staining. Cell proliferation was enhanced significantly (P < 0.01) by treatment with laser irradiation. mRNA levels of ALP, type I collagen and dentin sialoprotein (DSP) in hDPCs treated with laser irradiation became significantly (P < 0.01) higher compared with non-treated controls. Treatment of hDPCs with laser irradiation also enhanced significantly (P < 0.01) ALP activity and calcium concentration, resulting in enhanced mineralization, as evidenced by the high intensity of Alizarin Red staining.
In conclusion, the present study showed that 810-nm diode laser irradiation may contribute to the regeneration of dental pulp by enhancing hDPC proliferation and differentiation.

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Ideal restoration of tooth substances requires hydroxyapatite (HAp), of which the tooth is composed. However, restoration treatment with HAp is not yet possible, as adherence to ceramics is very difficult. In the present study, we examined a tooth restoration technique using the intraoral laser ablation method. A thin layer of α-tricalcium phosphate (α-TCP) was deposited on the dentin surface by the ablation phenomenon using an Er:YAG laser, which has already been introduced into dental treatment, to irradiate the target α-TCP. The deposited layer was then hydrolyzed by dripping pure water on its surface in order to create a hydroxyapatite (HAp) coating. In this study, we developed a compact pulsed laser deposition (PLD) system using the Er:YAG laser. The interface structure between the HAp coating and the dentin surface was observed by scanning electron microscope (SEM). Electron micrographs showed that the HAp layer was formed on the dentin surface. Moreover, dentinal tubules were sealed with HAp particles. We evaluated the blockade effect of dentinal tubules using Pashle's method. The measured average value for the sealing rate of the dentinal tubules was 85.6±8.6%, which was greater than the value with resin coating treatment. The adhesive strength of HAp films deposited on dentin was evaluated by quasi-static tensile tests. On mechanical evaluation, the adhesive strength was greater than 3.8 MPa. The present results suggest that this technique will be useful for the repair of dentin and the treatment of hyperaesthesia.

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Various studies have revealed that the Er:YAG laser is effective in endodontic, periodontal and surgical treatments, and it is used in actual clinical practice. In particular, the Er:YAG laser shows excellent clinical effects when cutting hard tooth tissue, and there have been many studies on adhesive restoration involving teeth irradiated with Er:YAG laser. In this study, focusing on the one-bottle one-step bonding system, we performed tensile bond and marginal leakage tests to evaluate its adhesive properties to enamel and dentin irradiated with Er:YAG laser.
Experiment 1
Flat bovine enamel or dentin surfaces were prepared using a model trimmer and water-resistant polishing paper (#600), and were irradiated with Er:YAG laser (100mJ, 10pps). Non-irradiated specimens were used as a control. After bonding procedures were performed on these adherent surfaces of 3mm in diameter, the specimens were stored in 37°C distilled water for 24 hours, and were divided into two experimental groups: the 24-hour storage group and the thermal stress group. In the thermal stress group, the specimens were subjected to 2,000 or 5,000 thermocycling in water from 5°C to 55°C with a dwell time of 30s at each temperature. Thereafter, a tensile bond test was performed in each group (n = 10).
Experiment 2
Saucer cavities (3mm in length, 2mm in width, and 1.5mm in depth) in extracted human molars were prepared setting the anatomical cervical line as the center, using a high-speed cutting diamond point. The marginal line was placed in the enamel on the coronal side and in the dentin on the gingival side. After cavity preparation, the internal cavity walls were uniformly irradiated with Er:YAG laser (100mJ, 10pps). Non-irradiated specimens were used as a control (n = 10). After bonding and filling procedures, these specimens were stored in 37°C distilled water for 24 hours, and thermo-stressed after finishing and polishing. Then, the dye-penetration test was performed according to the following procedures. The root apex was sealed using glass-ionomer cement, and the tooth surface was fully coated with nail varnish except for the area approximately 1mm off the cavity margin. After immersion in 0.5% basic fuchsin at 37°C for 24 hours, each specimen was cut longitudinally at the center of the cavity using a low-speed diamond saw. The degree of dye penetration into the coronal (enamel) or cervical (dentin) wall was evaluated by optical microscopy.
From these experiments, the following conclusions were obtained:
1. In the tensile bond test, the lased dentin exhibited lower bond strength than the non-irradiated dentin, while enamel showed almost the same bond strength regardless of the laser irradiation.
2. In the dye penetration test, marginal microleakage was observed in the dentin cavity wall, whereas good marginal integrity was demonstrated at the enamel margin.

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