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.

Abstract Background and objective: Endoscopic laser lithotripsy is the preferred technique for minimally invasive destruction of ureteral and kidney stones, and is mostly performed by pulsed holmium:yttrium-aluminum-garnet (Ho:YAG) laser irradiation. The absorbed laser energy heats the water creating a vapor bubble which collapses after the laser pulse, thus producing a shock wave. Part of the laser energy strikes the stone through the vapor bubble and induces thermomechanical material removal. Aim of the present study was to visualize the behavior and the dynamics of the cavitation bubble using a specially developed ultra-short-time illumination system and then to determine important characteristics related to clinically used laser and application parameters for a more detailed investigation in the future. Materials and methods: In accordance with Toepler’s Schlieren technique, in the ultra-short-time-illumination set-up the cavitation bubble which had been induced by Ho:YAG laser irradiation at the fiber end, was illuminated by two Q-switched lasers and the process was imaged in high contrast on a video camera. Cavitation bubbles were induced using different pulse energies (500 mJ/pulse and 2000 mJ/pulse) and fiber core diameters (230 μm and 600 μm) and the bubble dynamics were recorded at different times relative to the Ho:YAG laser pulse. The time-dependent development of the bubble formation was determined from the recordings by measuring the bubble diameter in horizontal and vertical directions, together with the volume and localization of the center of the bubble collapse. Results: The results show that the bubble dynamics can be visualized and studied with both high contrast and high temporal resolution. The bubble volume increases with pulse energy and with fiber diameter. The bubble shape is almost round when a larger fiber core diameter is used, and elliptical when using a fiber of smaller core diameter. Moreover, the center of the resulting bubble is slightly further away from the fiber end and the center of the bubble collapse for a smaller fiber core diameter. Conclusion: The experimental set-up developed gives a better understanding of the bubble dynamics. The experiments indicate that the distance between fiber tip and target surface, as well as the laser parameters used have considerable impact on the cavitation bubble dynamics. Both the bubble dynamics and their influence on the stone fragmentation process require further investigation.

The presented work describes the development and verification of a novel optical, powder-free intra-oral scanner based on chromatic confocal technology combined with a multifocal approach. The proof of concept for a chromatic confocal area scanner for intra-oral scanning is given. Several prototype scanners passed a verification process showing an average accuracy (distance deviation on flat surfaces) of less than 31μm ± 21μm and a reproducibility of less than 4μm ± 3μm. Compared to a tactile measurement on a full jaw model fitted with 4mm ceramic spheres the measured average distance deviation between the spheres was 49μm ± 12μm for scans of up to 8 teeth (3- unit bridge, single Quadrant) and 104μm ± 82μm for larger scans and full jaws. The average deviation of the measured sphere diameter compared to the tactile measurement was 27μm ± 14μm. Compared to μCT scans of plaster models equipped with human teeth the average standard deviation on up to 3 units was less than 55μm ± 49μm whereas the reproducibility of the scans was better than 22μm ± 10μm.

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?mu m 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?mu m, compared to the cleaved bare fiber 5?W/cw: 711?+/-?268?mu m). 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. Lasers Surg. Med. 44: 815823, 2012. (c) 2012 Wiley Periodicals, Inc.

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 mm 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 mm, compared to the cleaved bare fiber 5 W/cw: 711 268 mm). 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. Lasers Surg. Med. 2012 Wiley Periodicals, Inc.

Diode lasers are used in dentistry mainly for oral surgery and disinfection of root canals in endodontic treatment. The purpose of this study was to investigate and to improve the laser induced bacteria inactivation in endodontic treatment. An essential prerequisite of the optimization of the irradiation process and device is the knowledge about the determinative factors of bacteria killing: light intensity? light dosis? temperature? In order to find out whether high power NIR laser bacterial killing is caused by a photochemical or a photothermal process we heated bacteria suspensions of E. coli K12 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 labeling. In order to optimize the irradiation of the root canal, we designed special fiber tips with radial light emission characteristic by optical ray tracing simulations. Also, we calculated the resulting light distribution in dentin by voxelbased Monte Carlo simulations. Furthermore, we irradiated root canals of extracted human teeth using different fiber tip geometries and measured the resulting light and heat distribution by CCD-camera and thermography. Comparison of killing rates between laser and water based heating shows no significant differences, and irradiation of ice cooled suspensions has no substantial killing effect. Thus, the most important parameter for bacterial killing is the maximum temperature. Irradiation of root canals using fiber tips with radial light emission results in a more defined irradiated area with minor irradiation of the apex and higher intensity and therefore higher temperature increase on root canal surface. In conclusion, our experiments show that at least for E. coli bacteria inactivation by NIR laser irradiation is solely based on a thermal process and that heat distribution in root canal can be significantly improved by specially designed fiber tips.

Summary Background and objective Diode lasers are used in dentistry for oral surgery or disinfection of root canals in endodontic treatment. The aim of the study was to elucidate the basic mechanism of action in laser-induced root canal disinfection, which could be a photothermal and/or photochemical effect. Materials and methods To find out whether high-power NIR laser bacterial killing is caused by the light itself (photochemical effect or direct bacterial heating by selective absorption) or by a general thermal process, bacterial suspensions of a non-pathogenic strain of Escherichia coli were heated in a water bath and by diode laser (940 nm) each with the same temporal temperature course. Furthermore, bacterial suspensions were irradiated during which the temperature was fixed by iced water. Efficacy of bacterial inactivation was determined using double fluorescence labeling to distinguish vital from dead bacteria. Results Comparison of bacteria-killing efficacy between laser and water bath-induced heating showed no significant differences. The most important parameter was the maximum temperature achieved during heating. Laser irradiation of bacteria at low temperatures (elimination of temperature effect) did not show any bactericidal effect. Conclusion The experiments show that the inactivation of bacteria, at least for E. coli , using high-power 940 nm laser irradiation is solely based on a thermal mechanism. This should be taken into consideration during laser-assisted endodontic disinfection, where efficient bacterial inactivation must be achieved whilst preserving temperature-sensitive neighboring tissue.

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. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)