Biomedical subjects

Chang-Gok Chang

Publications and source records attributed to Chang-Gok Chang.

3 recordsLinked to original sources

PubMed2005

Effect of the hydrophilic nanofiller loading on the mechanical properties and the microtensile bond strength of an ethanol-based one-bottle dentin adhesive.

This study evaluated the hypothesis that if hydrophilic nanofillers were dispersed evenly within the adhesive layer under moist conditions, adding them to a one-bottle dentin adhesive might improve the mechanical properties of the adhesive layer, and accordingly increase the bond strength. The flexural strength (FS), the degree of conversion (DC), and the microtensile bond strength (MTBS) to the dentin of four experimental ethanol-based one-bottle dentin adhesives containing 0, 0.5, 1.0, and 3.0 wt % of 12-nm hydrophilic fumed silica were evaluated, and the distribution of the nanofillers were compared using transmission electron microscopy (TEM). Although the nanofiller content did not affect the DC, the FS tended to increase with increasing nanofiller content. The MTBS appeared to increase when up to 1.0 wt % of the nanofillers were added, but they were statistically not significant. However, when 3.0 wt % of the nanofillers were added, the MTBS decreased significantly comparing to the adhesive containing 0.5 wt % nanofillers (p < 0.05). The TEM image suggested that if the nanofillers within the adhesive were 3.0 wt % and applied to a wet dentin surface, they aggregated easily into large clusters and would decrease the MTBS.

Cementation↗

PubMed2002

Decrease in genu of the corpus callosum in medication-naïve, early-onset dysthymia and depressive personality disorder.

BACKGROUND: The purpose of this study was to detect differences in regional areas of the corpus callosum (CC) in subjects with early-onset minor depression (dysthymia or depressive personality disorder) and healthy comparison subjects. Based on previous reports that have suggested reduced frontal lobe volume and reduced hemispheric lateralization in the frontal regions of the brain in depression, we hypothesized that the area of the CC that interconnects the frontal regions of the brain, i.e., the genu, will be smaller compared to that of healthy comparison subjects. METHODS: Forty female subjects with early-onset dysthymia or depressive personality disorder, as defined by the Structured Clinical Interview for DSM-III-R and the Diagnostic Interview for Depressive Personality, respectively, and age- and gender-matched healthy comparison subjects (n = 42) were recruited (age: 21.4 +/- 2.1 and 20.9 +/- 2.8 years, respectively). All subjects were psychotropic medications-naïve and right-handed. A 1.5T GE Sigma scanner was used to acquire 124 1.5-mm-thick contiguous coronal images. Midsagittal slice images were carefully selected from reconstructed magnetic resonance images both from native and stereotaxic space to measure seven regional areas of the CC. RESULTS: There were significant diagnosis by CC region interactions [F(6,480) = 4.06, p <.001; F(6,480) = 3.30, p =.003, native and stereotaxic space, respectively]. Early-onset minor depression subjects had a 9.9% (native space) and 6.9% (stereotaxic space) smaller genu of the CC compared to the healthy comparison subjects (the Newman-Keuls post hoc test, p =.005 and.019, native and stereotaxic space, respectively). Early-onset minor depression subjects also had a 7.8% smaller posterior midbody relative to the comparison subjects (the Newman-Keuls post hoc test, p =.033) only in the native space. Severity of current depressive symptoms or duration of illness did not correlate with the size of the genu or the posterior midbody parts of the CC. CONCLUSIONS: These results suggest frontal lobe structural, and possibly functional, abnormalities in the brain in young female adults with a milder spectrum of depression, i.e., DSM-IV early-onset dysthymia or depressive personality disorder. The present findings point out the possible role of frontal lobe abnormality in pathophysiology of early-onset minor depression.

Adolescent↗

PubMedDate not supplied

Effect of interfacial bond quality on the direction of polymerization shrinkage flow in resin composite restorations.

Shrinkage in light curing resin composites is assumed to be directed toward the light source. However, the strong bond at the dentin-resin interface achieved by newer generation dentin bonding systems may affect the direction of polymerization shrinkage. In this study, various curing modes of adhesive resin simulating different bond qualities were applied to determine the extent of interfacial gap formation with a scanning electron microscope. We also measured the free surface depression with a profilometer. The direction of polymerization shrinkage was inferred from the ratio of the interfacial gap measurement at the floor to the free surface depression. Various curing modes used in this study include Group 1: light curing of resin composite without the bonding agent as the negative control; Group 2: simultaneous light curing of the bonding agent and resin composite; Group 3: start of the chemical cure of the dual-cured bonding agent before light curing the resin composite; Group 4: curing the light-initiated bonding agent before insertion and light curing of the resin composite. When the bonding agent was light cured prior to inserting the resin composite (Group 4), the free surface depression was the greatest and the interfacial gap smallest among those in all groups. Therefore, if a good bond between dentin and resin composite can be established, the shrinkage flow will be directed toward a center located near the bonded interface rather than toward the incident light, thus reducing detrimental shrinkage stress.

Acid Etching, Dental↗