No abstract

Transverse Brillouin spectra of orthoterphenyl are measured in the (250-305 K; 0.1-100 MPa) temperature-pressure range, which corresponds to the supercooled phase of this organic glass former. We show that the analysis of these spectra combined with an extrapolation of the reorientation times under pressure leads to an estimate of the static shear viscosity in a pressure range whose validity extends beyond the range of the Brillouin measurements. The relative contributions of temperature and of density to the change of this reorientation time measured along an isobar are extracted from our results in a large temperature range extending from the liquid to the low temperature supercooled state. They appear to be always of the same order of magnitude. It is also shown that in the range of the experiment, the orientational time is depending on a unique parameter built on temperature and density.

The aims of this paper are to briefly describe laser physics, the types of lasers currently available for use on soft tissues focusing primarily on CO2 and Nd:YAG laser energies, the histological effects of lasers on oral tissues, laser safety, the clinical applications of lasers on oral soft tissues, and future directions. Of the two types of lasers currently available for dental applications, both the CO2 and Nd:YAG lasers can be used for frenectomies, ablation of lesions, incisional and excisional biopsies, gingivectomies, gingivoplasties, soft tissue tuberosity reductions, operculum removal, coagulation of graft donor sites, and certain crown lengthening procedures. The advantages of lasers include a relatively bloodless surgical and post-surgical course, minimal swelling and scarring, coagulation, vaporization, and cutting, minimal or no suturing, reduction in surgical time, and, in a majority of cases, much less or no post-surgical pain. CO2 lasers, compared to Nd:YAG are faster for most procedures, with less depth of tissue penetration and a well-documented history. There have been recent reports on the use of the Nd:YAG laser for periodontal scaling, gingival curettage, and root desensitization, but further research needs to be conducted. Both the CO2 and the Nd:YAG laser have limited use in conventional flap therapy.

RksumB.-Certains complexes hexacoordonnes de l'ion Fez+ presentent une transition thermique du premier ordre entre deux &tats : low spin et high spin. Lorsque leurs parametres (rayon ionique, energie du fondamental, champ cristallin) different peu, une interaction d'Ising entre Fez+ explique ce comportement.

A new technique for the removal of phenytoin hyperplasia using the carbon dioxide (CO2) surgical laser is presented as well as a review of laser physics and the current uses of the CO2 laser in dentistry. Twelve cases of phenytoin hyperplasia removed surgically by the CO2 laser are presented; hence a laser gingivectomy. Advantages of the procedure include lack of hemorrhage yielding a dry field, noncontact surgery, sterilization of the surgical area, prompt healing, minimal post operative discomfort, and minimal time spent to perform the procedure. At the present time the use of the laser in dentistry is new and limited. In the future the laser may offer an alternative or an advancement to current procedures now used in dentistry.