Joerg Meister

Screening of CO2 Laser (10.6 μm) Parameters for Prevention of Enamel Erosion

OBJECTIVE The aim of this study was to screen CO(2) laser (10.6 μm) parameters to increase enamel resistance to a continuous-flow erosive challenge. BACKGROUND DATA A new clinical CO(2) laser providing pulses of hundreds of microseconds, a range known to increase tooth acid-resistance, has been introduced in the market. METHODS Different laser parameters were tested in 12 groups (n=20) with varying fluences from 0.1 to 0.9 J/cm(2), pulse durations from 80 to 400 μs and repetition rates from 180 to 700 Hz. Non-lased samples (n=30) served as controls. All samples were eroded by exposure to hydrochloric acid (pH 2.6) under continuous acid flow (60 μL/min). Calcium and phosphate release into acid was monitored colorimetrically at 30 sec intervals up to 5 min and at 1 min intervals up to a total erosion time of 15 min. Scanning electron microscopic (SEM) analysis was performed in lased samples (n=3). Data were statistically analysed by one-way ANOVA (p<0.05) and Dunnetts post-hoc tests. RESULTS Calcium and phosphate release were significantly reduced by a maximum of 20% over time in samples irradiated with 0.4 J/cm(2) (200μs) at 450 Hz. Short-time reduction of calcium loss (≤1.5 min) could be also achieved by irradiation with 0.7 J/cm(2) (300μs) at 200 and 300 Hz. Both parameters revealed surface modification. CONCLUSIONS A set of CO(2) laser parameters was found that could significantly reduce enamel mineral loss (20%) under in vitro erosive conditions. However, as all parameters also caused surface cracking, they are not recommended for clinical use.

Use of a genetic algorithm technique in solid-state laser pump cavity development

We apply a genetic algorithm to optimize the pump cavity of a complex miniaturized diode-pumped laser to find a balance between the efficient energy transfer of the pump light and the homogeneous illumination of the laser crystal. These two points are in contradiction to each other, whereby a complex optimization situation is given. The genome determines the geometry of the internal optical elements of the pump cavity in which a laser rod is placed. After optimization of the internal optical elements, a homogeneous illumination over the crystal length and a coupling efficiency of 59% were achieved. The results showed that genetic algorithms can find solutions and blueprints for laser pump cavities of consistent quality.