Biomedical subjects

Bum Soon Lim

Publications and source records attributed to Bum Soon Lim.

2 recordsLinked to original sources

PubMed2002

Effect of filler fraction and filler surface treatment on wear of microfilled composites.

OBJECTIVES: The aim of this study was to determine the effect of filler content and surface treatment on the wear of microfilled composites. METHODS: Four microfilled composites with different filler contents (A=20, B=25, C=30, and D=35 vol.%) were made with a light-cured resin (Bis-GMA/UDMA/TEGDMA). The surface treatment of the colloidal silica in each varied: F=functional silane, NF=non-functional silane, U=untreated. Silux Plus served as a control. Specimens were made in steel molds and cured in a light curing unit Triad II (40s/side). Abrasion and attrition wear were evaluated in vitro in a wear tester (OHSU oral wear simulator) with an abrasive slurry (poppy seeds + PMMA) and a human enamel antagonist. The average of five specimens was computed and compared using a ANOVA/Tukey's test at P < or = 0.05. The surface of the wear patterns and the distribution of filler particles were examined using a scanning electron microscope and digital imaging. RESULTS: As filler volume increased, wear was reduced regardless of filler treatment. Amounts of wear for specimens C and D were significantly lower than specimens A and B. Composites with functional silane treated microfiller (Group F) produced significantly less wear than those with non-functional microfiller (Group NF) at 30 and 35 vol.%, and less than the untreated microfiller (Group U) at 30 vol.%. Scanning electron microscopy of specimens of group NF showed large filler agglomerates (size > 1 microm) in the resin matrix, while specimens of group F and U showed fewer agglomerates. Digital imaging analysis revealed small filler clusters (size < or = 1 microm) in the resin matrix of all specimens. SIGNIFICANCE: Wear resistance of microfilled composites is enhanced by higher filler volumes irrespective of surface treatment, but good filler/matrix adhesion is needed to minimize wear.

Analog-Digital Conversion↗

PubMed2002

Dynamic mechanical analysis of storage modulus development in light-activated polymer matrix composites.

OBJECTIVES: The goal of this study was to evaluate the potential for using dynamic mechanical analysis of tubular geometry in a three-point flexure fixture for monitoring the storage modulus development of a light-activated polymer matrix composite. METHODS: Composite samples were inserted into PTFE tubes and tested in a three-point bend fixture in a dynamic mechanical analyzer (DMA) at 200 Hz with 20 microm amplitude. Samples were light activated for 60s (385 mW/cm(2) at the composite surface) and storage modulus (E') was measured continuously for the seven light-activated composites studied (one microfill, four hybrids and two unfilled resins). Cores of composite were removed from the PTFE sheath after 13.5 min and evaluated with the same parameters in the DMA. A finite element model of the test configuration was created and used to estimate operating parameters for the DMA. Degree of conversion (DC) was measured using micro-Fourier Transform Infrared (FTIR) spectroscopy for the microfilled composite samples and one hybrid 13.5 and 60 min after light activation. RESULTS: The E' for a generic hybrid and microfilled composite was 13,400+/-1100 and 5900+/-200 MPa, respectively, when cured within the tube and then removed and tested in the DMA. DC was 54.6% for the hybrid and 60.6% for the microfill. A linear regression of E' for the sheath and core vs core alone (r(2)=0.986) indicated a linear scaling of the sheath and core values for E' enabling a correction for estimated E' values of the composite core. SIGNIFICANCE: This method estimates the storage modulus growth during light-activated polymerization of highly filled dimethacrylates. Although the approach is phenomenological in that quantitative measurements of E' are not made directly from the DMA, estimates of early polymerization kinetics appear to be validated by three different approaches.

Barium Compounds↗