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Biomedical subjects

X Y Yu

Publications and source records attributed to X Y Yu.

At least 37 records · Page 2Linked to original sources
PubMed1991

Scanning electron microscopic and energy dispersive x-ray evaluation of two smear layer-mediated dentinal bonding agents.

Teeth treated with smear layer-mediated dentinal bonding agents and restored with composite resin were examined at the dentin-restoration interface by means of scanning electron microscopy used in conjunction with energy dispersive x-ray analysis. Results indicated that these dentinal bonding agents actually bonded to the smear layer, and samples demonstrated delamination of the smear layer from underlying dentin following thermocycling. This finding suggests that the stresses developed within the composite resin exceeded the adhesive strength of the smear layer to dentin. Thus, the bond strength for dentinal bonding agents that require the presence of the smear layer cannot exceed the adhesion of the smear layer to dentin.

Acrylic Resins↗
PubMed1991

Bond strength evaluation of a Class V composite resin restoration.

A three-dimensional cavity design was used to test the bond strength between restorative materials and tooth structure. Results indicated that bonding agents that rely on mechanical retention to the dentinal smear layer produced relatively low bond strengths. Bonding agents that require smear layer modification yielded mixed results, possibly because of differences in chemical formulation. The three-dimensional cavity design employed in this study is a replicable one, allowing the creation of standardized, clinically relevant preparations.

Acrylic Resins↗
PubMed1990

Scanning electron microscopic study of dentinal surfaces treated with various dentinal bonding agents.

A three-dimensional cavity design was used to study the morphology of dentin in vitro both after dentinal pretreatment and after restoration failure (debonding). Dentinal bonding agents that require removal of the smear layer (third generation), as well as those that depend on attachment to the smear layer (second generation), were included. Results indicated cohesive failures within both the dentinal bonding agents and the smear layer in second-generation systems. Dentinal conditioners for the third-generation dentinal bonding agents and for an as-yet unclassified agent were effective in removing smear layer debris from the dentinal surface, but they varied in the degree to which they opened the dentinal tubules. Differences in morphology of the dentinal surface following debonding of the restoration were attributed to differences in chemical composition among the agents examined.

Composite Resins↗
PubMedDate not supplied

Influence of finishing technique on microleakage.

Four different finishing techniques were used in a dentin bonding agent/composite resin restoration to evaluate the possible influence of finishing technique on microleakage. Results indicated that finishing technique affects the ability of the restorative system to resist microleakage. Under the conditions of this study, best results were achieved with a 30-fluted bur followed by a short wet polish. Samples finished dry with polishing disks demonstrated considerable microleakage. This study also suggests that homogeneous nonagglomerated microfilled composite resin does not require disk finishing.

Chi-Square Distribution↗
PubMedDate not supplied

Evaluation of microleakage in tenure-based restorations.

This study evaluates the effects of six composite resins, which use three different curing systems, on the ability of Tenure to resist microleakage. The curing systems were a photoinitiated dual-cure system, a dual-cure system, and light-cure systems. A total of 39 human molars were used. Following 2,000 cycles on a thermocycler, specimens were exposed to 0.2 percent basic fuchsin dye for 24 hours and then examined for microleakage. Results indicated that the composite resin plays an important role in the ability of a restorative system to resist microleakage. The photoinitiated dual-cure system produced significantly less microleakage than light-activated systems. No difference in microleakage was found between light-activated systems and the dual-cure system.

Composite Resins↗
PubMedDate not supplied

Microleakage evaluation in amalgam restorations used with bases.

Marginal leakage in amalgam restorations often precedes the development of secondary caries. One potential way to improve the marginal seal of such restorations, and thus minimize the risk of caries development, is to apply a glass-ionomer base prior to amalgam placement. This study compared microleakage resistance among amalgam restorations placed with and without light-cured glass-ionomer base materials. Preparations were made in extracted human molar teeth. Four groups were studied, including copal varnish, which was used as a control. All specimens were restored with amalgam. Results indicated significantly greater leakage at the cavity wall/base interface for restorations with a copal varnish cavity liner than for those with a glass-ionomer base. Leakage differences among bases were also found at the amalgam/base interface. Best results were obtained with a dual-cure resin-based system. These samples showed minimal leakage at both the cavity wall/base and the base/amalgam interfaces. These findings suggest that light-cured glass-ionomer bases can be effective in the prevention of microleakage in amalgam restorations.

Analysis of Variance↗
PubMedDate not supplied

Positional candidate gene approach and functional genomics strategy in atopy gene discovery.

As part of our effort in searching for genetic factors contributing to the susceptibility to atopy and asthma, we have focused on a 'positional candidate' approach in identifying CC chemokine gene polymorphisms and their functional correlates. To date, a single-nucleotide polymorphism was found in the RANTES proximal promoter region, and a high degree of sequence variation was identified in the 3'-untranslated region -of the eotaxin gene. Also, we are pursuing a series of functional genomics' studies designed to identify differentially expressed genes in a panel of allergen-specific human Th2 cells and in antigen-induced hyperreactive murine airways. This is performed using a combination of protocols including suppression-subtractive hybridization and cDNA array hybridizations with 18,363 nonredundant sequences. A data base is being generated from a list of subtracted cDNA sequences and array-positive clones to categorize differentially expressed genes. Sequences are being placed in biologically relevant categories on the basis of function (i.e., receptor, signal transduction pathways, transcription, and translation). With the increasing amount of sequence information compiled by the Human Genome Project, it will be particularly challenging to integrate functional gene-mapping efforts to define and compare aberrant genotypes/phenotypes in atopic diseases.

Chemokine CCL5↗
PubMedDate not supplied

Leakage patterns associated with glass-ionomer-based resin restorations.

This study compared microleakage patterns for glass-ionomer-cement-based resin systems with and without a separating agent placed between the glass ionomer and resin. Results indicated significant leakage (100%) at the dentin glass-ionomer interface for specimens without a separating agent. Those with a separating agent showed almost no leakage between the dentin and glass ionomer (10%) and some leakage at the resin/glass ionomer interface (40%). These results suggest that the forces of polymerization shrinkage are stronger than the chemical bond between glass-ionomer cement and dentin. This bond fails during resin polymerization, eliminating any supplementary retention gained through chemical adhesion to dentin and opening a pathway for microleakage.

Chi-Square Distribution↗