Bactericidal effects of 2.94 µm and 1.67 µm laser.

The bactericidal effects of lasers with wavelengths of 1.67 and 2.94 µm on cariogenic Streptococcus mutans were investigated. Temperature during irradiation was also measured to determine the mechanism underlying the bactericidal effects of the lasers. An aliquot of 2 µl cell suspension of S. mutans JC-2 strain was placed on anhydrous quartz or dentin plate, covering an area of approximately 5.0 mm in diameter to a depth of approximately 0.1 mm. Cell suspension was then irradiated at a power of 0.8 W (3.1 J/cm²) at a rate of 40 pps for 30 sec. After irradiation, the plate was put into a bottle containing PBS and vigorously voltated. Solution was serially diluted and inoculated on MS agar. After incubation anaerobically for 72 hr, colony forming units on the agar were counted. The experimental group, the number of bacteria decreased significantly compared to the control group under all conditions. No significant differences were observed in effect of wavelength or plate on bactericidal activity. In conclusion, laser irradiation at a wavelength of 1.67 µm for 30 sec showed a bactericidal effect on S. mutans, suggesting that this wavelength is more useful than 2.94 µm due to greater tissue penetration.

Effect of dentin hardness on ablation rate with Er:YAG laser.

OBJECTIVE: This study used artificially demineralized bovine dentin to ascertain the effect of hardness of demineralized dentin on ablation rate with the Er:YAG laser. BACKGROUND DATA: Before restoration of carious teeth, it is necessary to ablate any infected dentin that cannot be remineralized due to softening by the invading caries. A correlation has been suggested between the ablation efficiency of the Er:YAG laser and the progression of caries in dentin. To the best of our knowledge, no studies have investigated the relationship between degree of demineralization by dentinal caries and ablation rate with the Er:YAG laser. MATERIALS AND METHODS: Bovine mandibular anterior tooth roots were used as dentin samples. Each sample was soaked in a demineralizing solution (2 M lactic acid, pH 4.0) for 3 d to obtain demineralized dentin (DD) samples. Another group of samples were prepared without demineralization as a sound dentin (SD) group for comparison. After determining the Knoop hardness number (KHN) of each sample, the dentin surface was ablated with an Er:YAG laser. Tip output and pulse rate were set at 50 mJ and 20 pulses per second (pps), respectively, and the water spray was set at 3.5 mL/min. Ablation width, depth, and volume were measured following irradiation. RESULTS: In the DD group, dentin hardness was 10.4 +/- 1.6 KHN at 100 microm from the surface. In the sound dentin group, Knoop hardness was 51.0 +/- 1.6 KHN cross-sectionally throughout. No differences were observed from the surface to a depth of 2000 microm. In the DD group, dentin ablation volume at the superficial demineralized layer was 2888 +/- 272 x 10(4) microm. In the SD group, dentin ablation volume was 1298 +/- 219 microm(3). The relationship between ablation volume and Knoop hardness was defined as Y = -40.699x + 3350, revealing a marked negative correlation. CONCLUSION: The results demonstrate that the ablation volume for demineralized dentin was greater than that for sound dentin. The results suggest that the Er:YAG laser is capable of ablating infected dentin without damaging sound dentin by adjustment of tip output and pulse rate.

An experimental pathologic study of gingivectomy using dual-wavelength laser equipment with OPO.

BACKGROUND AND OBJECTIVES: This study was conducted to evaluate how soft tissues respond to treatment by a tunable laser with an optical parametric oscillating (OPO) mechanism capable of simultaneously emitting two wavelengths. MATERIALS AND METHODS: Marginal gingiva of dogs was incised by a prototype laser oscillator. The oscillator was set at two wavelengths known to effectively incise tissue and arrest hemorrhage with minimal invasiveness. Four laser irradiation conditions were set based on different combinations of the 1.67 and 2.94 microm wavelengths. The animals were sacrificed immediately after surgery, 7 days after surgery, and 28 days after surgery for histological examination. RESULTS: When irradiation at 1.67 and 2.94 microm wavelengths was simultaneously applied, the former conferred an observable hemostatic effect and the latter incised the tissue. Wound healing was similar to that in conventional methods and no serious inflammation was observed. CONCLUSION: Simultaneous irradiation at wavelengths of 1.67 and 2.94 microm can be an effective method in soft tissue surgery.

Resin bonding to dentin irradiated by high repetition rate Er:YAG laser.

OBJECTIVE: This study evaluated the influence of laser irradiation with a high pulse repetition rate on dentin bonding. BACKGROUND DATA: Although resin bonding to erbium:yttrium-aluminium-garnet (Er:YAG) laserirradiated dentin has frequently been investigated, the effects of a high pulse repetition rate have not yet been sufficiently investigated. METHODS: Four groups treated under different laser conditions were evaluated in this study: 100 mJ/pulse-10 pulses per second [pps], 50 mJ/pulse-20 pps, 33 mJ/pulse-30 pps, and the unlased condition as a control. The total energy used to irradiate each group was adjusted to 1.0 W. After bovine dentin specimens were irradiated by an Er:YAG laser, acid conditioners (10% citric acid/3% ferric chloride) were applied to the lased surface. Thereafter, a PMMA rod was bonded to the lased dentin using 4- META/MMA-TBB resin, and mini-dumbbell-shaped specimens were prepared. These specimens were then tested under tensile mode and fractured surfaces were observed under scanning electron microscopy (SEM). RESULTS: The bond strength of the unlased control was significantly higher than those of the three lased groups. Among the three lased groups, irradiation with higher output energy and lower pulse repetition rate tended to affect the higher bond strength. Upon SEM observation of the fractured surface, the lased groups showed the mixture of failure in the hybrid layer in almost part. There was no significant difference among the three lased groups. CONCLUSION: It can be concluded from the results of this study that a higher pulse repetition rate is not effective for resin bonding to laser-irradiated dentin.

Criteria for a diagnosis of caries through the DIAGNOdent.

OBJECTIVE: The aim of this study was to investigate the correlation between the demineralization depth measured by dental computed tomography (CT) and the measured value from a non-destructive dental caries diagnosis with a laser. METHODS: Optimal cut-off points were obtained for enamel and dentin caries, from the measured levels from a dental caries diagnosis with a laser, to investigate the clinical usefulness of a diagnosis using a laser. Using human teeth, the demineralization depth was measured and the caries were diagnosed by a dental caries diagnosis with a laser. RESULTS: The optimal cut-off point was investigated for accuracy, sensibility, and specificity, which were calculated from the results. These results demonstrated the correlation between the measured values and demineralization depth in both the pit and fissure caries and smooth surface caries. The optimal cut-off points were found to be 16-21 in the fissure caries and 9-11 in the smooth surface caries.

Adhesion of 4-META/MMA-TBB resin to heated dentin: effects of pre-treatments with FeCl3 and/or HEMA.

The purpose of this study was to compare the tensile bond strengths (TBSs) and failure mode of 4-META/MMA-TBB resin to 60 degrees C-heated and unheated bovine dentin, especially to investigate the influence of ferric chloride contained in citric acid pre-conditioning. In addition, the effect of HEMA priming for heated dentin was also evaluated. The TBSs to heated dentin were significantly lower than those to unheated dentin. Adhesive failures were observed in most specimens of the heated and HEMA-non primed group. HEMA application to heated dentin significantly increased the TBSs in each acid conditioning, which were also significantly higher than those of the unheated and ferric chloride-contained citric acid-conditioned group. It was clarified that heating dentin decreased the bond strength without HEMA priming even if the dentin surfaces were acid conditioned with 10-3, while HEMA priming after acid conditioning recovered the bond strength.