Assessment of external root temperature during root canal irradiation by Nd:YAG and Er:YAG lasers

Different types of laser have been widely studied for applicability in the oral health area. In the endodontic area, investigations with some types of laser have been conducted to establish safe parameters for clinical application in root canals. However, it has not been duly explained whether the temperature increase caused by laser irradiation could cause alteration in the temperature on the external surface of the root and, consequently, alterations in the cells of the periodontal ligament, causing resorption and even loss of the dental element. The proposal in this paper was to gauge the external root temperature in the apical and cervical regions of the roots of human teeth during root canal irradiation with Nd:yttrium aluminum garnet (YAG) and Er:YAG lasers using different parameters. The novel approach of this paper is the use of the technique of laser applications along the total length of the root canal with series of repetitive irradiation, however, using time of 1 s of irradiation associated with 1 s off to avoid cumulative thermal effects. Experimental results confirm the accuracy of the parameters and exposure regimen obtained. All the parameters used in this paper are acceptable from a clinical as well as a biological point of view. (C) 2009 Laser Institute of America.

Evaluation of subsurface dentin microhardness after Er : yttrium-aluminum-garnet and Nd : yttrium-aluminum-garnet laser irradiation

Background and objectives: To assess the microhardness of dentin subsurface after Er:yttrium-aluminum-garnet (YAG) and Nd:YAG laser irradiation. Study design/materials and methods: Twenty-four bovine incisors, without pulp, were used. The vestibular surface was worn out until the dentin was reached and divided in mesial and distal regions. The samples were divided into two groups: GI-distal, irradiated by Er: YAG laser, and GII-distal, irradiated by Nd: YAG laser. The mesial area was protected so as to not receive the laser irradiation. The measurements were made on Vickers digital microhardmeter. Results: For GI-there was no significant statistical difference, Cl(-4.59 to 0.78), between the values of irradiated (55.61 +/- 4.38) and unirradiated (57.51 +/- 4.00) areas. For GII-the values were higher for the irradiated (62.21 +/- 6.48) compared to the unirradiated (57.82 +/- 5.42) area, CI(1.65 +/- to 7.13). Conclusions: There was an increase of dentin microhardness when the Nd: YAG was used, but the Er: YAG did not cause significant alterations in dentin microhardness. (c) 2007 Laser Institute of America.

Use of carbon dioxide (CO2) laser radiation in exposure of implants (stage II): A metallography evaluation in dogs

In this study we analyzed possible damages that vaporization from laser radiation could cause to implant material. Fifteen standard titanium implants, measuring 3.75 mm in diameter by 7 mm in length, were placed into the upper and lower jaws of three dogs according to Branemark's system. After osseointegration, all implants were exposed. In group I (control) conventional exposure with a punch was used; in group II, a CO2 laser with 2 W (power density: 256 W/cm(2); fluency: 0.077 J/cm(2), and a pulse mode of 0.30 ms) was used, and in group III 4 W (power density: 512 W/cm(2), fluency: 0.154 J/cm(2), and a pulse mode of 0.30 ms) was used. After vaporization, the cover screws were removed and sent for metallographic examination. The results showed that cover screws irradiated with 2 and 4 W power caused no superficial or microstructural alteration. The results also showed that the prescribed power densities, fluencies, and the use of the pulse mode were suitable for exposing implants without damage to tissue or implant material. (C) 2002 Laser Institute of America.

Design of the main racetrack microtron accelerator end magnets of the Institute of Physics of University of São Paulo

This work deals with the design of the Institute of Physics of the University of São Paulo (IFUSP) main racetrack microtron accelerator end magnets. This is the last stage of acceleration, comprised of an accelerating section (1.04 m) and two end magnets (0.1585 T), in which a 5.10 MeV beam, produced by a racetrack microtron booster has its energy raised up to 31.15 MeV after 28 accelerations. POISSON code was used to give the final configuration that includes auxiliary pole pieces (clamps) and auxiliary homogenizing gaps. The clamps create a reverse fringe field region and avoid the vertical defocusing and the horizontal displacement of the beam produced by extended fringe fields; PTRACE code was used to perform the trajectory calculations in the fringe field region. The auxiliary homogenizing gaps improve the field uniformity as they create a magnetic shower that provides uniformity of ±0.3%, before the introduction of the correcting coils that will be attached to the pole faces. This method of correction, used in the IFUSP racetrack microtron booster magnets, enabled uniformity of ±0.001% in an average field of 0.1 T and will also be employed for these end magnets. © 1999 The American Physical Society.

Informe sobre las actividades del Instituto Latinoamericano de Planificación Económica y Social = Report on the activities of the Latin American Institute of Economic and Social Planning

Incluye Bibliografía

Public administration problems in Latin America and solutions from the United Nations of America

Includes bibliography

Estudio económico de los Estados Unidos 1987 = Economic survey of the United States of America 1987

Incluye Bibliografía

Estudio económico de los Estados Unidos, 1988 = Economic survey of the United States of America, 1988

Incluye Bibliografía

Book Review of Twilight of the Mammoths: Ice Age Extinctions and the Rewilding of America by Paul S. Martin

Applying ecological studies to the adaptations of prehistoric human hunter-gatherer groups has greatly increased our abilities to interpret effects of an ever-changing environment and our access to critical resources on these populations. The Pleistocene/Holocene transition, its climate and human genesis in the new world, draws intensive interest from a number of scientific communities. In Twilight of the Mammoths, Paul Martin adds his views, which are of no surprise, on the megafaunal extirpations during a cultural period referred to in North America as Clovis.