Comparison of different focusing fiber tips for improved oral diode laser surgery.

BACKGROUND AND OBJECTIVES: State of the art for use of the fiber guided diode laser in dental therapy is the application of bare fibers. A novel concept with delivery fiber and exchangeable fiber tips enables the use of tips with special and optimized geometries for various applications. The aim of this study is the comparison of different focusing fiber tips for enhanced cutting efficacy in oral surgery. MATERIAL AND METHODS: For this purpose various designs of tip geometry were investigated and optimized by ray tracing simulations. Two applicators, one with a sphere, and another one with a taper, were realized and tested on porcine gingiva (diode laser, 940 nm, 5 W/cw; 7 W/modulated). The cutting depth and quality were determined by light microscope. Histological sections of the cuts were prepared by a cryo-microtome and microscopically analyzed to determine the cut depths and thermal damage zones. RESULTS: The simulations show that, using a sphere as fiber tip, an intensity increase of up to a factor of 16.2 in air, and 13.2 in water compared to a bare 200 µm fiber can be achieved. Although offering high focusing factor in water, the cutting quality of the sphere was rather poor. This is probably caused by a derogation of the focusing quality due to contamination during cutting and light scattering. Much better results were achieved with conically shaped fiber tips. Compared to bare fibers they exhibit improved handling properties with no hooking, more regular and deeper cuts (5 W/cw: 2,393 ± 468 µm, compared to the cleaved bare fiber 5 W/cw: 711 ± 268 µm). The thermal damage zones of the cuts are comparable for the various tips and fibers. CONCLUSIONS: In conclusion the results of our study show that cutting quality and efficiency of diode laser on soft tissue can be significantly improved using conically shaped fiber tips.

Development and verification of a snapshot dental intraoral three-dimensional scanner based on chromatic confocal imaging.

We describe the development and verification of an optical, powder-free, intraoral scanner based on a chromatic confocal imaging system, which has been realized in a single-shot multifocal approach. The system is based on a combination of micro-optical and dispersion optical elements. The methodology of recording and analyzing the acquired data are discussed in detail. A proof of concept with the application in intraoral scanning is provided. According to the current findings, the measurement uncertainty, scan speed, and overall performance of the device can well compete with the state-of-the-art of commercially available intraoral scanners.

Mechanism of high-power NIR laser bacteria inactivation.

Lasers are used in dentistry for a variety of indications. One of these is the disinfection of root canals or the sterilization of residual caries. Many studies have demonstrated the capacity to kill bacteria for lasers but the fundamental mechanism of the laser effect remains quite unclear. With our experiments we wanted to determine whether high-power NIR laser bacterial killing is caused by the light itself (photochemical effect) or by a photothermal process. In order to differentiate between mechanisms we heated bacteria suspensions of a nonpathogenic strain of E. coli by a water bath and by a diode laser (940 nm) with the same temporal temperature course. Furthermore, bacteria suspensions were irradiated while the temperature was fixed by ice water. Killing of bacteria was measured via fluorescence labelling. Comparison of killing rates between laser and water-based heating shows no significant differences. The most important parameter is the maximum temperature. Laser irradiation of bacteria at low temperatures does not result in killing. Our experiments show that at least for E. coli bacteria inactivation by high-power laser irradiation is solely based on a thermal process.