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.

X-ray diffraction analyses of commercial and non-commercial ‘hydroxyapatite (HA)’ preparations as well as some biological apatites (enamel, dentin, bone) demonstrated a variability in crystallinity and composition before and after sintering. Coatings obtained by plasma-spraying calcium hydroxyapatite (HA) ceramic showed composition/crystallinity differences between the inner and outer layers of the coating; the coating composition consisting usually of: HA, amorphous calcium phosphate (ACP), α-TCP, β-TCP, tetracalcium phosphate (TTCP) and sometimes calcium oxide (CaO). The comparative extent of dissolution (EOD) in acid buffer of the non-sintered Ca-P materials was: ACP > DCPD > OCP > DCP > ‘AP’. For sintered materials, comparative EOD was: ACP*> TTCP > α-TCP > ß-TCP > HA. (‘AP’, calcium-deficient apatite; ACP, precipitated; ACP*, plasma-sprayed). Results from this study underscored the need for the appropriate characterization of calcium phosphate materials using a combination of analytical techniques: x-ray diffraction, infrared and chemical. Since the dissolution of calcium phosphate materials depend on their composition and crystallinity, these results suggest that these materials used as bone grafts or implant coatings could affect their reactivity and stability in vivo.

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Objective To evaluate the biomechanical effects of different attachments’ position for maxillary molar intrusion with clear aligner treatment by finite element analysis. Methods Cone-beam computed tomography images of a patient with supra-eruption of the maxillary second molars were selected to construct three-dimensional models of the maxilla, periodontal ligaments, dentition, and clear aligner. The models were divided into four groups depending on the attachment location on the first molar: (1) no attachment (NA), (2) buccal attachment (BA), (3) palatal attachment (PA), and (4) bucco-palatal attachment (BPA). After applying an intrusion of 0.2 mm on the second molar, displacements and stress distributions of the teeth, aligner, and periodontal ligament were analyzed with the finite element software. Results All groups displayed equivalent movement patterns of aligners. The NA and BA groups showed buccal tipping of the second molar, while the PA group showed palatal tipping. The BPA group had the highest intruding value and the lowest buccal/palatal tipping value. All groups showed mesial tipping of the second molar. Stress distribution in the periodontal ligament strongly correlated with the attachment position. The BPA group showed the best stress distribution. Conclusion Combined BA and PA could effectively prevent buccal and palatal tipping and showed the best efficiency in intruding the second molar. The second molar showed an unavoidable tendency to tip mesially, regardless of the attachment position.

Laminar burning velocities of premixed ethanol−water−air flames over a range of equivalence ratios from 0.7 to 1.6 at 0.1 MPa and 383 K were determined experimentally at different water contents in a combustion chamber with central ignition. An ethanol oxidation mechanism was selected to simulate one-dimensional planar flames of ethanol−water−air mixtures under the same conditions to observe the effect of the water addition on the planar flame structure, the sensitivity of laminar burning velocity, and the net reaction rates of the elementary reactions. The physical effect of water was separated from its chemical effect by designing a type of fictitious water in the simulation. Results show that unstretched flame speeds and laminar burning velocities of the flames decrease with increasing the water content. When the water content was elevated, the peaks of the mole fractions of the main radical species gradually decrease and the net reaction rates of the elementary reactions with positive sensitivity coefficients decrease more than those of the elementary reactions with negative sensitivity coefficients. Both physical and chemical effects of water suppress laminar burning velocities of hydrous ethanol−air mixtures, and the former dominates. The chemical effect of water promotes production of OH and has a much more remarkable influence on the reaction rates of the elementary reactions with negative sensitivity coefficients than on those of the elementary reactions with positive coefficients. The physical effect of water has an inhibiting effect on both the production of the radicals and the reaction rates of the elementary reactions.