Ultrastructural Properties of Laser-irradiated and Heat-treated Dentin

Abstract

Previous studies using scanning electron microscopy and infrared absorption spectroscopy reported that laser irradiation causes compositional changes in enamel. The purpose of this study was to evaluate the ultrastructural and compositional changes in dentin caused by irradiation with a short-pulse laser (Q-switched Nd:YAG). The irradiated and non-irradiated areas of the lased dentin samples were investigated by scanning (SEM) and transmission electron microscopy (TEM), micro-micro electron diffraction, and electron microprobe analysis of dispersive energy (EDX). Heat-treated dentin was similarly investigated. This study demonstrated that laser irradiation resulted in the recrystallization of dentin apatite and in the formation of additional calcium phosphate phases consisting of magnesium-substituted beta-tricalcium phosphate, beta-TCMP, beta-(Ca,Mg)3(PO4)2, and tetracalcium phosphate, TetCP, Ca4(PO4)O. TEM analyses of the modified and unmodified zones of the irradiated areas showed two types of crystal populations: much larger crystals from the modified zone and crystals with size and morphology similar to those of dentin apatite in the unmodified zone. The morphology of crystals in the modified zones in the irradiated dentin resembled those of dentin sintered at 800 or 950 degrees C. In the irradiated areas (modified and unmodified zones), the Ca/P ratio was lower compared with that in the non-irradiated dentin. The Mg/Ca ratio in the modified zones was higher than that in the unmodified zones and in the non-irradiated dentin. In sintered dentin, the Mg/Ca ratio increased as a function of sintering temperature. The ultrastructural and compositional changes observed in laser-irradiated dentin may be attributed to high temperature and high pressure induced by microplasma during laser irradiation. These changes may alter the solubility of the irradiated dentin, making it less susceptible to acid dissolution or to the caries process.

Effect of Different Laser Devices on the Composition and Microhardness of Dentin

“…11,[26][27] During SEM-EDS atomic analysis, the interaction of the primary beam with atoms in the sample causes shell transitions that result in the emission of an x-ray. The emitted x-ray has an energy characteristic of the parent element.…”

“…In addition, compositional changes created by laser irradiation were considered to decrease or increase the solubility of irradiated enamel or dentin. 11 Different types of laser systems were introduced to the dental market in order to reduce thermal sideeffects during the irradiation of dental hard tissue and increase the cut efficiency of the laser beam. The Er:YAG laser, operating at a wavelength close to the absorption peak of water (2.94 µm), has been thoroughly investigated for the ablation of dental hard tissues.…”

“…Nelson and others 10 claimed that dentin apatite crystals melted and recrystallized into the larger apatite crystals containing less carbonate during laser irradiation without water cooling. Rohanizadeh and others 11 reported that, after the Nd:YAG laser ablation of dentin, recrystallization and phase transformation occurred and the Ca/P ratio decreased in irradiated areas. Dentin apatite, like all biological apatites, is best described as carbonate hydroxyapatite (CHA) associated with minor elements, such as magnesium, sodium and HPO 4 .…”

“…29 During laser irradiation without cooling, heat changes are rapid, and the temperatures experienced by the tissue could reach 10,000°C in a short amount of time. 11 In fact, the dentin apatite crystals melt during the laser pulse and recrystallize during the time between two successive pulses. Rapid recrystallization could induce the incorporation of various ions, cause the formation of nonapatitic calcium phosphate phases and/or introduce crystal defects into the apatitic structure due to the temperature increase.…”

Impact of welding the dental enamel walls of the fissure system using semiconductor laser: In-Vitro study

“…The real phenomenon that causes the impact is related to the chemical-physical changes induced on enamel by laser. The irradiated enamel surface is subjected to water loss between 80 and 1200C, to decomposition of the small quantity of organic substance at 3500 C, to initial loss of carbonate hydroxyapatite between 400-6000C, and to enamel melting at more than 800-10000 C.The high temperatures reached in the superficial layers of the irradiated areas of the tooth cause melting of the enamel, which at that point recrystalizes forming hydroxapatite crystals larger than the initial ones [8].…”