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| Author(s): |
Rosane de Fátima Zanirato Lizarelli
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Carlos. |
| Institution: | Universidade de São Paulo (USP). Instituto de Física de São Carlos (IFSC/BT) |
| Defense date: | 2002-11-14 |
| Examining board members: |
Vanderlei Salvador Bagnato;
Carlos Alberto dos Santos Cruz;
Marcelo Henrique Gehlen;
Renato Amaro Zângaro;
Denise Maria Zezell
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| Advisor: | Vanderlei Salvador Bagnato |
| Abstract | |
Laser is now established as a suitable tool for the selective and precise removal of carious dental tissue. If correctly used, lasers minimize the losses of healthy tissue besides the comfort that it ean promote to patients. The knowledge of basic aspects of laser ablation of dental tissues and materials can lead to the development of a set of parameters that may allow selective removable of deeayed tissues and dissatisfaetory resin preserving healthy dental tissue. Nd:YAG lasers in picosecond regime are not available to dentistry clinical uses yet. Because of that, studies able to allow much information related with this laser system and dental organ are welcome. It could establish safe parameters and rules to its utilization in a brief future in a clinical practice. Three experiments employing Nd: YAG picosecond pulsed laser were executed: thermal map out, micromorphological analysis and ablation rate calculation, all of them considering enamel and dentin, as target-tissues, and, from primary teeth. Thermal map out study resulted in safety operative regions where there are not detrimental heating to dental pulp of primary teeth. Considering micromorphological aspeets as result of laser-tissue interaction in primary teeth, we could observe that collateral damage at the level of enamel more evident than in dentin. While the rate of penetration depth in dentin seems to scale up as the time progress, for enamel the behavior is the opposite. The overall ablated volume is higher in dentin when compared to enamel, which results in a higher ablated rate as well. With relation to decayed tissues, Er: YAG laser has been well established as an efficient and safety tool, however it is not an unique common clinical procedure everyday in offices, total or partial removal or modification of composite resins restorations have became one clinical practice priority. In this manner, to employ this laser system to this proposal seems adequate and starts a necessary research to understand the basic features of laser ablation of composite resin. The last two experiments, presented here, have purposed to investigate ablation rate and micromorphological aspects when dental hard tissues, enamel and dentin, from primary and permanent teeth, are irradiated by Er: YAG laser, besides, photo curable restorative composite resins of three kind of type were irradiated toa: microfiller, hybrid and condensable. Different conditions of work were used to evaluate the real influence of composite resins ablation with Er:YAG laser under different energies per pulse (100, 200, 300 and 400mJ) and immersion time in distilled water (zero, 4 and 7 days). The results allowed concluding that the unique variable factor able to influence statistically the ablation rate of composite was the energy per pulse. The immersion time in water did not influence statistically the ablation rate of resins and the resulted micromorphological aspects showed a dependence considering structure type and chemical composition; they are different to each kind of choose composite studied here, it seems occur even with dental hard tissues. To conclude, combining obtained data from the two cited above experiments with Er:YAG laser, it was possible found parameters to result in a differential and selective ablation, removing exclusively composite resins. The proposed technique seems to be much adequate, however while this idea seems to apply well for enamel of primary and pennanent teeth at the present stage it does not apply well for primary or pennanent dentin. For dentin, the composition and content of water makes the Er: YAG laser ablation equal as superior in rate compared in the three used resins. After understanding the resulted interactions between lasers and substrates, there is an interesting suggestion to search for a more convenient laser system to ablate composite resin. Also, the overall shape of ablation rate indicates that the water flux may well be an important variable to be investigating on the ablation rates. Maybe, like this, this finding could contribute to refine the selective parameters to prevent the useless ablation of enamel and dentin from primary and permanent teeth. (AU) | |