Tae Yub Kwon

Degree of conversion of dual-cured resin cement light-cured through three fibre posts within human root canals: an ex vivo study

AIM To evaluate the degree of conversion of one dual-cured resin cement light-cured through three fibre posts within extracted human teeth. METHODOLOGY Fifteen mandibular premolars were root filled and then divided into three groups. Variolink II was light-cured through the posts (LP, D.T. Light-Post; PP, FRC Postec Plus; SP, Snowpost) within the root canal. The degree of conversion was obtained at 1 mm intervals in 9 mm-deep longitudinally sectioned root canals using an optical microscope connected to an FTIR spectrophotometer (n = 10). The light transmission of each post tested was also examined using UV-Vis spectroscopy. Data were analysed using ANOVA and Tukeys test (alpha = 0.05). RESULTS The LP and PP posts revealed a light transmission of 10.2% and 7.7%, respectively, whereas the SP post exhibited a significantly lower value of 0.5%. The degree of conversion mean value ranged from 32.78% to 69.73% depending on the depth and type of post. For all the groups, there were significant decreases in the degree of conversion values for the middle region when compared with those for the cervical region (P < 0.05). Except at a depth of 1 mm, the SP group consistently exhibited significantly lower degree of conversion values than the other groups (P < 0.05). The linear regression analysis revealed a strong correlation between the light transmission of the posts and the overall degree of conversion value for each group (R(2) = 0.9888). CONCLUSIONS The decrease in the degree of conversion for Variolink II relative to the depth was dependent on the light transmission capacity of the posts tested.

Preparation and characterization of anodized titanium surfaces and their effect on osteoblast responses.

In this study, titanium (Ti) surface was modified by anodizing with a mixture of beta-glycerophosphate sodium and calcium (Ca) acetate, and the anodized surfaces were characterized by scanning electron microscopy, X-ray diffraction, and electron probe microanalysis. In vitro osteoblast response to anodized oxide was also evaluated. The anodic oxide produced was observed to have interconnected pores (0.5-2 microm in diameter) and intermediate roughness (0.60-1.00 microm). In addition, anodic oxide was observed to have amorphous and anatase oxide. Calcium and phosphorus ions were deposited on the Ti oxide during anodization. Osteoblast differentiation, as indicated by alkaline phosphatase production, was enhanced on anodized surfaces. It was thus concluded from this study that Ca phosphate can be deposited on Ti surfaces by anodization. It was also concluded that the phenotypic expression of osteoblast was enhanced by the presence of Ca phosphate and higher roughness on anodized Ti surfaces.

Different Morphology of Hydroxyapatite Coatings on Titanium by Electrophoretic Deposition

Commercial hydroxyapatite powders were electrophoretically deposited on titanium substrates. In this study, the effect of deposition durations and applied voltages on deposition yield was investigated. Green and sintered coatings were studied by SEM and XRD. It was observed that by applying low voltages and presedimentation, uniform and smooth hydroxyapatite coating can be prepared. In order to obtain roughened hydroxyapatite coatings, high voltages have to be applied. It was concluded that experimental conditions of powder concentration, applied potential, and presedimentation have a significant effect on the deposited coating morphology.

Combustion Synthesis of Hydroxyapatite and Hydroxyapatite (Silver) Powders

Hydroxyapatite powder is produced using combustion synthesis method. The powder was produced using a low-temperature processing method involving time as short as 15 minutes. As silver is known to have anti-bacterial properties, silver-doped hydroxyapatite was also produced by the same method. Both the powders were fully crystalline. XRD indicated the presence of an additional phase of CaO in both the samples. FT-IR indicated the presence of hydroxide, phosphate and carbonate groups. Silver addition tends to control the reactions of powder with a test Tris buffer environment and maintain a stable pH for a longer period of 500-hour duration.

Development of Hydroxyapatite Thin Film on Titanium Substrate by Electrophoretic Deposition

Electrophoretic deposition was used for HA coating on dental implants with different coating thickness. The HA coating thickness was examined in terms of applied voltage and time, and powder concentration in suspension. Nano-size HA and SiO2-CaO-P2O5-B2O3 bioglass powders were synthesized by sol-gel method. Polyvinyl alcohol (3 wt%) as a binder was resolved in ethyl alcohol, then, nano HA powder was dispersed ultrasonically in the mixture for 15 min and pH was adjusted with HNO3 for positive charging on particle. Titanium substrate was held on cathode and counter electrode was platinum. HA with 0.5 % and 0.03 % of powder concentration was deposited electrophoretically at 10~20 V for 1~20 minutes. The thickness of as-deposited HA layer decreased from nearly 80 µm (0.5 %, 20 V, 10 min) to 4~5 µm (0.03%, 10V, 1 min) as powder concentration, applied voltage and time decreased, respectively. The surface of HA coating layer deposited in lower powder concentration showed much more homogeneous and relatively dense morphology, in contrast, the surface in thick suspension became rough or porous and was easily spalled. In a co-deposition of HA and bioglass, co-deposited glass played an important role in increasing bonding strength between coating layer and substrate. It is believed that electrophoretic deposition method can be one of alternatives for relatively thin and easy HA coating.