Applications of Laser Welding in Dentistry: A State-of-the-Art Review

The dental industry without lasers is inconceivable right now. This captivating technology has outlasted other possible alternative technologies applied in dentistry in the past due to its precision, accuracy, minimal invasive effect as well as faster operating time. Other alternatives such as soldering, resistance (spot) welding, plasma (torch) welding, and single pulse tungsten inert gas welding have their pros and cons; nevertheless, laser welding remains the most suitable option so far for dental application. This paper attempts to give an insight into the laser principle and types of lasers used for dental purposes, types of dental alloys used by the dentist, and effect of laser parameters on prosthesis/implants. It is apparent from the literature review that laser assisted dental welding will continue to grow and will become an unparalleled technology for dental arena

Multiplexing techniques and applications in fiber-optic spatially resolved sensing networks

International audienceDistributed sensing, based on Rayleigh scattering or arrays of reflectors, can be extended as a multi-fiber, multi-sensor technique by using multiplexing features. Current research has overcome the time-and wavelength-division multiplexing, that has represented the golden standard for fiber Bragg gratings. In this work, we introduce novel domain that allow "parallel" multiplexing applied to distributed sensors, and are routed in the use of specialty fibers. The use of fibers doped with MgO-doped nanoparticles, as well as polymethyl methacrylate fibers, enables new domains for multiplexing, that are discussed in this work. Scattering-level, polarization, and sensitivity based multiplexing are discussed and applied to strain, temperature, and refractive index measurements

Distributed fiber optics 3D shape sensing by means of high scattering NP-doped fibers simultaneous spatial multiplexing

International audienceA novel approach for fiber optics 3D shape sensing, applicable to mini-invasive bio-medical devices, is presented. The approach exploits the optical backscatter reflectometry (OBR) and an innovative setup that permits the simultaneous spatial multiplexing of an optical fibers parallel. The result is achieved by means of a custom-made enhanced backscattering fiber whose core is doped with MgO-based nanoparticles (NP). This special NP-doped fiber presents a backscattering-level more than 40 dB higher with respect to a standard SMF-28. The fibers parallel is built to avoid overlap between NP-doped fibers belonging to different branches of the parallel, so that the OBR can distinguish the more intense backscattered signal coming from the NP-doped fiber. The system is tested by fixing, with epoxy glue, 4 NP-doped fibers along the length of an epidural needle. Each couple of opposite fibers senses the strain on a perpendicular direction. The needle is inserted in a custom-made phantom that simulates the spine anatomy. The 3D shape sensing is obtained by converting the measured strain in bending and shape deformation

Modeling of Material Removal Rate and Surface Roughness Generated during Electro-Discharge Machining

This study reports on the numerical model development for the prediction of the material removal rate and surface roughness generated during electrical discharge machining (EDM). A simplified 2D numerical heat conduction equation along with additional assumptions, such as heat effect from previously generated crater on a subsequent crater and instantaneous evaporation of the workpiece, are considered. For the material removal rate, an axisymmetric rectangular domain was utilized, while for the surface roughness, a rectangular domain where every discharge resides at the end of previous crater was considered. Simulated results obtained by solving the heat equation based on a finite element scheme suggested that results are more realistic by considering instantaneous evaporation of the material from the workpiece and the effect of residual heat generated from each spark. Good agreement between our model and previously published data validated the newly proposed models and demonstrate that instantaneous evaporation, as well as residual heat, provide more realistic predictions of the EDM process

Simultaneous Distributed Sensing on Multiple MgO-Doped High Scattering Fibers by Means of Scattering-Level Multiplexing

International audienceWe introduce a novel multiplexing technique applied to optical fiber distributed sensors, based on optical backscatter re-flectometry (OBR) and high-scattering MgO-doped fibers. In this paper, we demonstrate the possibility of simultaneously detecting multiple fiber with a single scan using an OBR distributed sensor, and successfully discriminating each sensing region (with ∼1 mm spatial resolution). The sensing element is a high-scattering fiber with MgO-based nanoparticles doping in the core, that emits a scattering signal more than 40 dB larger than a standard fiber, while having similar temperature and strain sensitivity. Multiplex-ing occurs as the scattered light from a sensing fiber overshadows the amount of scattering occurring in all the other channels. The setup has been validated for temperature sensing and implemented in an epidural catheter with multiple fibers fixed to the outer walls for strain sensing. The proposed solution goes beyond the multi-plexing methods which exploit 1 × N switches, as the multiplexing is simultaneous and not rearranged in different time slots

Fiber Bragg Grating (FBG) Sensors in a High-Scattering Optical Fiber Doped with MgO Nanoparticles for Polarization-Dependent Temperature Sensing

International audienceFeatured Application: Inscription and interrogation of fiber Bragg gratings into MgO nanoparticle-doped fiber for optical fiber distributed and multiplexed sensing. Abstract: The characterization of Fiber Bragg Grating (FBG) sensors on a high-scattering fiber, having the core doped with MgO nanoparticles for polarization-dependent temperature sensing is reported. The fiber has a scattering level 37.2 dB higher than a single-mode fiber. FBGs have been inscribed by mean of a near-infrared femtosecond laser and a phase mask, with Bragg wavelength around 1552 nm. The characterization shows a thermal sensitivity of 11.45 pm/ • C. A polarization-selective thermal behavior has been obtained, with sensitivity of 11.53 pm/ • C for the perpendicular polarization (S) and 11.08 pm/ • C for the parallel polarization (P), thus having 4.0% different sensitivity between the two polarizations. The results show the inscription of high-reflectivity FBGs onto a fiber core doped with nanoparticles, with the possibility of having reflectors into a fiber with tailored Rayleigh scattering properties

Refractive Index Sensor by Interrogation of Etched MgO Nanoparticle-Doped Optical Fiber Signature

International audienc

Distributed fiber optics strain sensors: from long to short distance

Developed for more than forty years, optical fibers have features that make them particularly attractive for making sensors. One of the strengths of these sensors is that they can measure different physical parameters in a distributed manner over a wide range of lengths (from a few cm up to tens of kilometers) with a spatial resolution ranging from millimeters to meters. In this article, we are particularly interested in distributed fiber sensors, mainly based on light scattering processes, for measuring strain variations. This review concerns both applications requiring long lengths of fiber in a geological context, as well as those using length less than one meter for the medical sector. While distributed fiber optics sensors have already shown their great potential for long-range applications, short-range applications are a niche sector emerging in the last few years

Distributed X-ray dosimetry with optical fibers by Optical Frequency Domain Interferometry

This article reports on the first demonstration of in situ, real-time dosimetry realized with an enhanced backscatttering optical fiber, and a high resolution optical backscattering reflectometry measurement. This work is devised to overcome the current problems in monitoring radiotherapy treatments, in particular, the difficult evaluation of not only the actual X-ray dose that is accumulated on the target volume but also the distribution profile of the ionizing radiation beam. Overall, the research aims at developing a dose sensor with the most demanding features of small form factor, spatial profiling, and remote interrogation. The experiments have been conducted by evaluating the spatial profile of radiation-induced spectral shift of the Rayleigh backscattering along an optical fiber exposed to X-rays. The sensing element is a section of specialty optical fiber whose Rayleigh backscattering signature changes under ionizing radiation. The specialty fiber is designed to exhibit an enhanced backscattering, in order to overcome the poor sensitivity to radiation of standard optical fibers that are normally, used in telecommunications. The enhanced sensitivity is achieved by doping the core with either aluminum or magnesium nanoparticles, and two different fibers have been fabricated and tested. The experimental results show the capability of real time detection of the radiation profile from high-dose rates (700 Gy/min) to low-dose rates (2 Gy/min). Moreover, different sensing mechanisms and responses to high- and low-dose rates are evidenced. A comparison with a quasi-distributed sensing system based on an array of fiber Bragg gratings (FBGs) is discussed, highlighting the superior performance of the backscattering approach in terms of sensitivity and spatial resolution, whereas the array of FBGs exhibits an advantage in terms of sampling speed