Mesoscopic modelling of enamel interaction with mid-infrared sub-ablative laser pulses

Using a finite element approach the authors model the influence of enamel's microstructure and water distribution on the temperature and stress at the centre of the laser spot, for a CO2 laser working at 10.6 μm, with 0.35 μs pulse duration and sub-ablative intensity. The authors found that the distribution of water in enamel significantly influences the stress generated at the end of one laser pulse: much lower (two orders of magnitude) stress values occur in models with homogeneously distributed water than in models with 0.27 vol.% water located in pores or 4 vol.% in layers. The amount of water in enamel has a strong influence on the stress distribution, but not on the maximum stress values reached. However, different water contents do not influence the temperature distribution in enamel. These results suggest that adequate modelling of the ablation mechanisms in enamel, as in other highly inhomogeneous materials, must include their structure at the mesoscopic scale

Laser-tissue interactions: fundamentals and applications

Laser-Tissue Interactions by Prof. Dr. Markolf H. Niemz (Heidelberg University) has become the standard reference book in this fast growing field. It addresses basic concepts such as optical and thermal tissue properties, hard and soft tissue ablation, and photobiomodulation. Clinical applications are reviewed according to the latest references. The last chapter covers today's standards of laser safety with a careful selection of essential guidelines published by the Laser Institute of America. This fourth edition has been completely revised and updated. Color illustrations, summaries, and questionnaires with solutions transform this book into a useful guide for graduate students, scientists, and medical practitioners. OPHTHALMOLOGY DENTISTRY GYNECOLOGY UROLOGY NEUROSURGERY ANGIOPLASTY AND CARDIOLOGY ORTHOPEDICS DERMATOLOGY AND COSMETICS GASTROENTEROLOGY OTORHINOLARYNGOLOGY “An extremely useful reference companion.” LASERS IN SURGERY AND MEDICINE

Cosmology based on non-expanding 4D space, no true dimension of time, and no dark energy

We present a theory of relativity based on four dimensions of space. In terms of impact, 4D space compares to 4D spacetime as the heliocentric compares to the geocentric model! We claim that 4D space is neither expanding nor curved by energy or mass. We also claim that time, although a useful concept in everyday life, is not a dimension of the universe. Time is just a misinterpretation of a suppressed dimension of space. The suppression is due to length contraction when moving at the speed of light. We derive this effect from 4D space geometry and prove that time dilation is equivalent to length contraction in one dimension of 4D space. We claim that the universe is a 3D projection of an expanding 4D hypersurface. Our situation is similar to that of an ant: Since it doesn't observe a third dimension, it can't understand 3D effects. Since we don't observe a fourth dimension, we can't understand 4D effects unless we discuss them in 4D space! We solve ten mysteries at one single blow: (1) the mystery of time, (2) of time's arrow, (3) of E_0=mc^2, (4) of why the background radiation is isotropic, (5) of Hubble's law, (6) of why the universe is flat, (7) of discrepancies in the Hubble constant, (8) of expanding space, (9) of dark energy, and (10) of spontaneity in particle physics. The secret to 4D space is its full symmetry in all dimensions. It thus shines with simplicity and beauty

Laser-induced generation of pure tensile stresses

While short compressive stresses can readily be produced by laser ablation, the generation of pure tensile stresses is more difficult. We demonstrate that a 90° prism made of polyethylene can serve to produce short and pure tensile stresses. A compressive wave is generated by ablating a thin layer of strongly absorbing ink on one surface of the prism with a Q-switched frequency-doubled Nd:YAG laser. The compressive wave driven into the prism is reflected as a tensile wave by the polyethylene-air interface at its long surface. The low acoustic impedance of polyethylene makes it ideal for coupling tensile stresses into liquids. In water, tensile stresses up to −200 bars with a rise time of the order of 20 ns and a duration of 100 ns are achieved. The tensile strength of water is determined for pure tensile stresses lasting for 100 ns only. The technique has potential application in studying the initiation of cavitation in liquids and in comparing the effect of compressive and tensile stress transients on biological medi

Laser in Pediatric Dentistry

Laser technology has different applications in dentistry, and, particularly, in Paediatric Dentistry. Depending on laser wavelengths and the physical properties of the tissue which is to be targeted; it is possible obtain different results in three main dental fields: Diagnosis, Prevention and Operative Therapy. Conventional treatments can sometimes be replaced by laser treatments and better results may be achieved. Laser treatments offer new treatment opportunities in the dental field that were unknown in the past. This chapter aims to outline the clinical protocols and possible applications of different laser systems in Paediatric Dentistry