الفهرس 
Cover EnglishOnly 14 pages are availabe for public view
 |  | from | 245 |  |  |
| | | from | 245 | | |
Abstract
Enamel demineralization during orthodontic therapy is a problem of clinical importance. Recently a clinical study showed that 50% of the subjects experienced an increase in the number of white spot lesions during treatment with fixed orthodontic appliances when no preventive fluoride programs were used Decalci fication and white spot lesions can occur in a many as 25 to 30 percent or orthodontic patients, even with the use or fluoride, and as early as one month after beginning treatment Alter orthodontic treatment with fixed appliances (braces), brackets that have been bonded to the teeth by composite resin must be removed. There are se-veral techniques for bracket removal, and these leave varying amounts or resin residue on the enamel surface. Subsequent removal of this orthodontic resin alter debonding IS essential to ensure patient comfort and to prevent plaque accumulation and staining The more efficient techniques (e.g. high-speed diamond rotarv cutting) are more likely to induce iatrogenic damage to the enamel surface in the form of surface scratches, enamel loss, and enamel tea-routs. If bonding resin residues could be degraded selectively with laser radiation, these problems might be overcome. VOI1 Fraunhofer and his Colleagues, (/993) declared that there has been growing interest in the application or lasers for treating medical and dental maladies. The first application of lasers In the dental field was reported in 1964. Since then, attention has been focused on the treatment of soft and hard tissue lesions and desensitization of teeth Orthodontic applications of laser treatment were a natural outcome of the earlier studies of laser effects on enamel. Laser treatment of dental hard tissues involves conversion or light energy to thermal energy to resect tissues. In particular, laser irradiation of dental enamel causes thermally-induced changes within the enamel to a depth and the energy applied to the enamel surface. Laser irradiation of dental enamel results in significant reduction of the effective solubility of enamel mineral and that there is a significant synergism between laser irradiation and solution Iluoride with regard to this effect. Several infrared lasers such as CO2 Nd:YAG and Er:YAG lasers have been introduced in the dental clinic to remove carious dental hard tissues in anticipation or replacing the high-speed drill. The dental enamel has specific absorption spectra between 9.0 µm and 11.0 µm which should make the carbon-dioxide laser a more suitable medium. A carbon dioxide laser is one or the most popular and useful sources of coherent electromagnetic waves in the infrared spectrum. This is due to the several ways in which the laser operates (high voltage power supply in continuous wave (C.W.)) or pulsed operation: emission of laser lines in regular, hot or sequential vibrational bands of co2 laser molecules and the several orders of magnitude range of possible laser powers (from milli-watts to giga-watts) that permit laser application In SCience, medicine and technology Zezelle, et al., (1997), stated that there are changes in physical properties of dental enamel were observed by measuring microhardness, analyzing the relative concentration of calcium and phosphorus atoms after acid demineralization of enamel. It was observed increase in enamel micro hardness, increase in enamel tluoride uptake, and a lower lost of calcium when samples were acid exposed, indicating that laser can be useful for prevention of caries. The laser-induced breakdown spectroscopy (LIBS) technique has become, in recent years, a reliable tool for very fast multi-elemental pollutant analysis in atmosphere, and solid matrix. L1BS measurements consist or spectral and time resolved analysis of the atomic and ionic emission lines generated at the surface or the sample after focusing of an intense laser pulse, these atomic and ionic emission lines, once assigned to specific transitions. allow for the qualitative identification of the species present in plasma, while their relative intensities can be used for the quantitative determination of the corresponding elements.