Influência dos níveis de energia do laser Er:YAG na capacidade de ablação, microdureza e morfologia da dentina superficial e profunda / Influence of Er:YAG laser energy levels on ablation rate, microhardness and morphology of superficial and deep dentin

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

This study evaluated the ablation rate and the subsurface microhardness of superficial and deep dentin irradiated with different Er:YAG laser energy levels, and observed the micromorphological aspects of the lased substrates by means of Scanning Electron Microscopy (SEM). Seventy-two molar crowns were bisected, providing 144 specimens, which were randomly assigned into two groups (superficial or deep dentin) and later into six subgroups (160, 200, 260, 300, or 360mJ, or control- not irradiated). Initial masses of the specimens were obtained before irradiation. After laser irradiation, final masses were obtained and cavities were longitudinally bisected in half, being one hemi-section destined to SEM analysis and the other to the Knoop microhardness test. Microhardness measurements were performed at six points (20, 40, 60, 80, 100, and 200 µm) under the middle of the cavity floor. Data were submitted to ANOVA and Fishers LSD Multiple-Comparison Tests (α=0.05). There was no difference between ablation rate of superficial and deep dentin; a significant and gradual increase in the mass-loss values was reached when energies were raised, regardless the dentin depth; the energy level of 360 mJ showed the highest ablation rate and was statistically different to the other energies. SEM images showed that deep dentin was more selectively ablated, especially intertubular dentin, promoting tubule protrusion; at 360 mJ, the micromorphological aspect was similar for both dentin depths. Superficial dentin presented higher microhardness than deep dentin; 160 mJ resulted in the highest microhardness values and 360 mJ the lowest ones; 200 mJ was lower than 160 mJ and the control, but it was higher than 260 and 300 mJ, which presented similar means. Values at all points were different, exhibiting increasing microhardness throughout; superficial dentin microhardness was the highest at 20 µm with 160 mJ, while the other energies demonstrated lower values than the control at all points; on deep dentin, 160 and 200 mJ were similar to the control, and other energies promoted significantly lower values. It may be concluded that the ablation rate did not depend on the depth of the dentin; an energy level lower than 360 mJ is recommended to ablate either superficial or deep dentin effectively without causing tissue damage. The lowest energy level increased superficial dentin microhardness at the closest extension under the cavity preparation; deep dentin subsurface microhardness was not altered by 160 and 200 mJ, while higher energy levels reduced subsurface microhardness of both superficial and deep dentin.

ASSUNTO(S)

microdureza dentinária cavity preparation dentin microhardness dentin ablação ablation morfologia dentinária dentina preparo cavitário laser er:yag dentin morphology er:yag laser

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