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At least 307 records · Page 17Linked to original sources
PubMedDate not supplied

Resin-based composite reinforced sealant.

PURPOSE: To describe and picture a technique for using a resin-bonded sealant reinforced by inclusion of resin-based composite, before polymerization. METHOD: Using an extracted mandibular molar, embedded in plaster and isolated with a rubber dam, a step-by-step depiction of the technique is shown. RESULTS: A picture of a six-year-old sealant in a first permanent molar, still in perfect condition, is shown. CONCLUSION: This technique offers a reliable method for treating pits and fissures.

Composite Resins↗
PubMed2003

Prevention of oxidative injury in PC12 cells by a traditional Chinese medicine, Shengmai San, as a model of an antioxidant-based composite formula.

The protective effect of Shengmai San (SMS) on oxidative damage in cultured PC12 cells was studied as a model of an antioxidant-based composite formula usable for the treatment of oxidative stress-related complex disorders. SMS, a traditional Chinese herbal medicine, has previously been shown to prevent cerebral oxidative injury in rats. Neuronal model PC12 cells were incubated with SMS for defined periods, chased with H(2)O(2) for 30 min at 37 degrees C, and subjected to an ELISA-based assay for determining the protein carbonyl content, and a Comet assay for DNA single strand breaks (SSBs). The results showed that both protein carbonyl content and DNA SSBs increased in PC12 cells after the H(2)O(2) chase in a concentration-dependent manner. Both H(2)O(2)-dependent carbonyl formation and DNA damage were markedly prevented in the cells pretreated with SMS, and the SMS effects were dependent on both the SMS concentration and the period of pre-incubation with SMS before the H(2)O(2) abuse. At the same time, cell viability was enhanced in the SMS-pretreated cells after the H(2)O(2) abuse compared to the control cells as determined by an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. It is concluded that SMS functions not only as a simple antioxidant but also as a modulator of cellular antioxidant defense.

Animals↗
PubMed1999

A heterogeneously structured composite based on poly(lactic-co-glycolic acid) microspheres and poly(vinyl alcohol) hydrogel nanoparticles for long-term protein drug delivery.

PURPOSE: To prepare a heterogeneously structured composite based on poly (lactic-co-glycolic acid) (PLGA) microspheres and poly(vinyl alcohol) (PVA) hydrogel nanoparticles for long-term protein drug delivery. METHODS: A heterogeneously structured composite in the form of PLGA microspheres containing PVA nanoparticles was prepared and named as PLGA-PVA composite microspheres. A model protein drug, bovine serum albumin (BSA), was encapsulated in the PVA nanoparticles first. The BSA-containing PVA nanoparticles was then loaded in the PLGA microspheres by using a phase separation method. The protein-containing PLGA-PVA composite microspheres were characterized with regard to morphology, size and size distribution, BSA loading efficiency, in vitro BSA release, and BSA stability. RESULTS: The protein-containing PLGA-PVA composite microspheres possessed spherical shape and nonporous surface. The PLGA-PVA composite microspheres had normal or Gaussian size distribution. The particle size ranged from 71.5 microm to 282.7 microm. The average diameter of the composite microspheres was 180 microm. The PLGA-PVA composite microspheres could release the protein (BSA) for two months. The protein stability study showed that BSA was protected during the composite microsphere preparation and stabilized inside the PLGA-PVA composite microspheres. CONCLUSIONS: The protein-containing PLGA-PVA composite may be suitable for long-term protein drug delivery.

Biocompatible Materials↗
PubMed2003

Effects of lining materials on microleakage and internal voids of Class II resin-based composite restorations.

PURPOSE: To evaluate the ability of various lining materials to reduce cervical marginal microleakage and internal voids within Class II resin-based composite restorations. MATERIALS AND METHODS: 168 extracted molars were prepared with both moderate and deep Class II cavities. The teeth were then randomly divided into 14 groups and restored with direct composite or sandwich techniques using various lining materials [flowable composites, compomers and resin-modified glass-ionomer cements (RMGI)]. Following restoration, the teeth were stored for 24 hours, thermocycled, and placed in fuchsin dye for 24 hours. Subsequently, the teeth were sectioned in halves and observed through a stereomicroscope. Cervical microleakage and internal voids were assessed separately as the length ratio of dye penetration to the cervical wall and the area ratio of voids to sectioned restorations. The data were analyzed with one-way ANOVA. RESULTS: Flowable composite lining groups demonstrated either similar or more cervical microleakage than did their respective direct restoration groups. Groups lined with RMGIs showed similar or better marginal sealing than did their resin restoration groups. In deep cavities, Vivaglass Liner group showed the best marginal sealing. RMGI-lined groups exhibited more internal voids in deep restorations.

Compomers↗
PubMed1979

Base composition heterogeneity of Euglena gracilis chloroplast DNA.

Euglena gracilis chloroplast DNA has an average buoyant density of 1.685 gm/cm3, corresponding to 25 mol% G . C base pairs. To test for base compositional heterogeneity within this 130 kilobase pairs (kbp) genome, previously mapped restriction endonuclease fragments were isolated, and characterized by equilibrium buoyant density centrifugation. The chloroplast DNA can be characterized as containing two major buoyant density components. A segment of 17 kbp, representing 13% of the genome and containing the rRNA genes is 43--44 mol% G . C. The remaining 113 kbp, accounting for 87% of the genome, has an average 20--21 mol% G . C content.

Animals↗
PubMed1999

Microstructural characteristics of calcium hydroxyapatite/poly-L-lactide based composites.

Besides its high osteoinductive properties, hydroxyapatite (HAp) exhibits a relatively low mechanical strength. In order to improve the mechanical properties and reliability of HAp based composites, the addition of selected polymers is highly recommended. The main objective of this work is to study the microstructural characteristics of HAp/poly-L-lactide (PLLA) composites obtained by cold or hot processing. The composites were prepared from a mixture of a chloroform solution of poly-L-lactide with granulated HAp. After elimination of chloroform by vacuum evaporation, dense compacts were obtained by cold or hot pressing. The pressing pressure ranged from 98.10 to 294.3 MPa for both cold and hot pressing. The hot pressing was performed in the temperature region 293-457 K for a time period of 15-60 min. Depending on the PLLA amount and the pressing procedure it is possible to obtain highly porous or nearly fully dense composites. The scanning electron microscopy examination of fracture as well as of free surfaces revealed that the final porosity and wetting are affected to a great extent by the synthesis conditions and amount of polymer added. An increase in temperature to 457 K for a longer period of time results in fully dense compacts. The formation of a nearly continuous polymer network that leads to the hardening of HAp has also been observed. However, it should be pointed out that some layers of HAp may be free of polymer film since PLLA penetrates more deeply into the porous HAp.

Biocompatible Materials↗
PubMed2004

The effect of surface finishing and storage solutions on the color stability of resin-based composites.

BACKGROUND: The authors tested the hypothesis that surface-finishing treatments and the type of storage solutions significantly affected the staining of resin-based composites, or RBCs, and unfilled resins, or URs. METHODS: Fifty-four RBC and 54 UR disks were polymerized through a polyester film strip (Mylar, DuPont, Wilmington, Del.) and polished in one of three groups: 1-micrometer aluminum oxide, 15-microm diamond plate and no treatment (polyester film). All specimens were immersed in water for two days and then in coffee, cola or red wine for seven more days at 37 C. The authors recorded tristimulus color measurements before the immersions; after one and two days in water; and after one, two, three and seven days in the storage solutions. RESULTS: Most of the color changes occurred between day 2 in water and day 7 in the staining solution. Analysis of variance showed that the finishing treatment and storage solution significantly influenced the overall color change (deltaE), and interactions occurred between the finishing treatment and the storage solution (P < .0001) for both materials. RBC specimens generally exhibited greater color changes than did UR specimens. The polyester film finishing exhibited the greatest amount of color change, while the diamond finishing exhibited the least amount of color change. Immersion in wine caused the greatest color change for both materials; cola and coffee resulted in the smallest color change for RBC and UR specimens, respectively. CONCLUSIONS: Finishing treatments and storage solutions significantly affect the surface staining of RBC materials. Polyester film finishing and red wine produced the greatest color change after seven days for RBC specimens. CLINICAL IMPLICATIONS: Clinicians should remove the polyester film-finished surface and advise patients that drinking wine could intensify surface staining on RBC restorations.

Aluminum Oxide↗
PubMed1997

[Estimation of body composition based on total body water determination using phenazone for assessment of body fat gain in cattle. 1. Relationship between body fat content and live weight].

Body composition based on total body water analysis using phenazone were estimated in 251 beef heifers, aged 3 to 17 months, 27 beef bulls aged 15 months and 200 Holstein dairy cows of different age and stage of lactation. Correlation coefficients between body fat content and live weight were estimated to be between 0.59 and 0.97 for groups of animals. In beef heifers there was a fat gain of 294 g per live weight gain of 1 kg, in beef bulls 247g, in cows until third lactation 418 g and 731 g respectively 791 g in entirely full-grown cows. Cows of first lactation showed loss in body fat content with simultaneous gain in live weight. Hence, using body weight for assessment of change in body fat content is dependent on special prerequisites, which will be discussed.

Adipose Tissue↗
PubMed1993

Five-year study of Class II restorations in permanent teeth using amalgam, glass polyalkenoate (ionomer) cerment and resin-based composite materials.

The aim of this study was to compare the clinical performance of an amalgam, a glass polyalkenoate (ionomer) cerment material and a resin-based composite material used in small Class II cavities in permanent teeth. All restorations were inserted under rubber dam. They were examined yearly for 3 years. One clinician continued the study up to 5 years. The clinical examination focused on two criteria: clinically acceptable and failure. In addition, impressions were taken of the prepared cavities immediately before restoration and at each clinical examination using an elastomeric material. The study comprised 274 Class II restorations (88 amalgams, 95 cerments and 91 resin composites) placed in 142 adolescent patients. One hundred and sixty-seven restorations were in molar and 107 in premolar teeth. Patient dropout after 5 years resulted in the loss of 161 restorations, evenly distributed for restorative material and type of tooth involved. Four amalgam restorations, 22 glass ionomer cerment and nine resin composite restorations failed. The glass ionomer cerment and amalgam restorations failed primarily due to bulk fractures, while the resin composite restorations failed due to secondary caries and bulk fractures.

Analysis of Variance↗
PubMedDate not supplied

Marginal gap repair with flowable resin-based composites.

This study was designed to test the hypothesis that the flowable/dentin interface has the weakest bond and highest frequency of failure when a resin-based composite is repaired using a flowable composite. Comparing three specific groups--dentin, flowable composite, and hybrid composite-under the Kruskal-Wallis test showed that the mean bond strength values at the flowable/dentin interface and within the dentin were significantly lower than those at the hybrid/flowable interface and within the flowable resin. Dentin near the pulp chamber yielded consistently lower bond strength values than dentin located at the dentino-enamel junction. Bonding at the flowable resin/dentin interface showed the weakest bond and highest frequency of failure.

Analysis of Variance↗
PubMed1997

Mutans streptococci and incipient caries adjacent to glass ionomer cement or resin-based composite in orthodontics.

Levels of mutans streptococci in plaque adjacent to orthodontic brackets retained with a glass ionomer cement (GIC) (Ketac-Cem) and a resin-based composite (CR) (Concise) were investigated, using the split mouth technique in 11 patients who, before treatment, had more than 10(5) CFU of these microorganisms. After full-term orthodontic treatment (mean 9.5 months), the percentage of mutans streptococci of total CFU count in plaque was lower adjacent to GIC-retained brackets (mean 3.9) than adjacent to CR-retained brackets (6.7), but the difference was not statistically significant. Two subjects harbored S. sobrinus. These subjects were the only ones who developed incipient caries during the orthodontic treatment. Incipient lesion formation occurred only adjacent to CR-retained brackets. This suggests that in patients who have relatively high salivary levels of mutans streptococci before treatment and especially in those who harbor S. sobrinus, the use of GIC for bonding may prevent incipient caries formation during orthodontic treatment.

Adolescent↗
PubMed2003

Production of natural and synthesized aluminum-based composite materials with the aid of ultrasonic (cavitation) treatment of the melt.

The application of ultrasonic melt treatment to the production of natural and synthesized aluminum-based composite materials is considered in terms of underlying basic ideas and commercial implementations. It is shown that the ultrasonic cavitation treatment combined with microalloying of hypereutectic Al-Si natural composites (alloys) promotes the formation of structures suitable for further deformation. The use of highly impure starting materials becomes also possible. The combination of ultrasonic cavitation treatment with electromagnetic stirring allows one to considerably improve the size and spatial distribution of ceramic particles in metal-matrix composites.

Journal Article↗
PubMed2001

Color and optical properties of resin-based composites for bleached teeth after polymerization and accelerated aging.

PURPOSE: To determine changes in color and optical properties after polymerization and accelerated aging of white resin-based composites (RBCs) used to restore bleached teeth and compare them with those of conventional shades. MATERIALS AND METHODS: Four white shades and two conventional shades (A2, A3) of two different brands of RBCs (Vitalescence, Synergy) were measured before and after polymerization and after accelerated aging for 150 kJ/m2. Color was measured according to CIE L*a*b* color scale on a reflection spectrophotometer, and scattering coefficient, absorption coefficient, contrast ratio and translucency parameter were calculated. RESULTS: After curing, the color change ( E*) of white RBC was not significantly higher than that of conventional shade (P= 0.05). Color change after curing was positively influenced by the change of K (beta = 0.55), and negatively influenced by the changes of L*, b* and S (beta = -0.34, -0.95 and -0.70, respectively). After aging for 150 kJ/m2, the color changes of white RBCs were 2.4 and 5.8, and those of conventional shade were 1.7 and 2.9, respectively. Higher a* and b* values had a negative influence on the color change for both polymerization and aging.

Color↗
PubMedDate not supplied

Effect of surface finishing and storage media on bi-axial flexure strength and microhardness of resin-based composite.

This in vitro study tested the following null hypotheses: (1) surface finishing treatments do not significantly affect the biaxial flexure strength and microhardness of resin-based composites (RBC) and (2) storage media do not significantly affect these physical properties. Discs (81 RBC and 81 UR; 3M/ESPE) were prepared using a circular polyethylene mold (2.4-mm thick x 16.7 mm in diameter) that was polymerized through a Mylar strip and divided into three surface finishing treatment groups: 1 microm aluminum oxide slurry; 15 microm diamond and a Mylar strip. Randomly selected controls for each finishing group were stored at room temperature in individual vials. Test specimens were immersed in water, stored at 37 degrees C for two days and transferred for an additional seven days to one of three aqueous storage media at 37 degrees C: coffee (pH 5.1), cola (pH 2.4) or red wine (pH 3.7). Post immersion (nine days total), the specimens were tested for biaxial flexure strength (BFS) and Vicker's microhardness (VHN). ANOVA and Tukey's HSD test were used for statistical analysis. ANOVA results indicated that surface finishing treatments had a significant effect on the biaxial flexure strength and microhardness of the RBC and the UR specimens. BFS results for RBC specimens were AL>DD>ML (p<0.0001) and VHN results were AL, DD>ML (p<0.0001). Storage in wine medium reduced the VHN of UR specimens significantly. Both alternative hypotheses were accepted. In addition, the Mylar finishing group, because of the resin-rich surface layer, yielded the lowest mean values of BFS and VHN.

Aluminum Oxide↗
PubMed1999

Genetic relatedness among species in Aspergillus section Clavati as measured by electrophoretic comparison of enzymes, DNA base composition, and DNA-DNA hybridization.

Aspergillus subgenus Clavati has four recognized species: A. clavatus (the type species), A. clavatonanicus, A. giganteus, and A. longivesica. These species are strictly anamorphic (mitotic) and defined by the morphological species concept. However, their genealogical relationships remain uncertain. In this study, we examined the genetic relatedness among the four species in this section, using electrophoretic comparison of enzymes, DNA base composition, and DNA-DNA hybridization. In a dendrogram based on the calculated similarity values of four enzymes, 10 strains in section Clavati, 3 strains in the xerophilic species, a strain in section Ornati, and a strain in section Cremei were separated into nine major clusters at a 60% similarity level. A. longivesica JCM 10186(T) had Q-10 in our analysis, but Kuraishi et al. (1990) reported A. longivesica JCM 1720(T) had Q-9 (49%) and Q-10 (46%). The G+C contents of the four species of section Clavati ranged from 48 to 50 mol%. The degree of the intraspecific reassociation among the DNAs from the strains of these species ranged from 77 to 99%, whereas the degrees of interspecific relative binding among strains of the four species ranged from 30 to 59%. Our data from enzyme patterns and DNA relatedness support the validity of the three species in section Clavati, except for A. longivesica.

Journal Article↗
PubMed2005

The reliability of standardized flexure strength testing procedures for a light-activated resin-based composite.

OBJECTIVES: To investigate the differences in the reliability of three-point flexure strength (TFS) and bi-axial flexure strength (BFS) data of a dental resin-based composite (RBC) irradiated by a hand-held or an oven light-curing unit (LCU). METHODS: Three-point bar-shaped (25 x 2 x 2 mm3) and bi-axial disc-shaped (12 mm diameter, 2 mm thick) specimens of Filtek Z250 were polymerized utilizing either a hand-held (n = 20) or an oven-LCU (n = 20). The mean TFS and BFS, associated Weibull moduli and degree of conversion (DC) for each curing regime were obtained following 24 h immersion in a light-proof water bath maintained at 37 +/-1 degrees C. RESULTS: A significant decrease in TFS (129 +/- 15 and 127 +/- 13 MPa) compared with BFS (140 +/- 12 and 148 +/- 13 MPa) was identified for specimens irradiated with both LCU types (P < 0.001). The Weibull moduli of TFS data associated with the hand-held--was significantly decreased compared with the oven-LCU since confidence intervals did not overlap (7.5-9.4 and 9.5-10.6, respectively). In contrast, the Weibull moduli of the BFS data associated with either LCU were not significant (11.3-12.4 and 11.3-13.5). A significant decrease in the DC of three-point and bi-axial flexure specimens irradiated with the hand-held compared with the oven-LCU was reported (P = 0.031). CONCLUSIONS: The improved experimental reliability combined with the increased clinical relevance in specimen geometry of disc-compared with bar-shaped specimens may advocate bi-axial flexure testing methodology as the standard to assess the strength of light-activated dental RBCs. The differences in extent of polymerization of RBC specimens cured with either LCU were not consistent with an equivalent dose of light energy density. This phenomenon may be attributed to differences in polymerization efficiency associated with the quantity of useful light energy emitted from the hand-held--compared with the oven-LCU.

Composite Resins↗
PubMed2003

Teaching students the repair of resin-based composite restorations: a survey of North American dental schools.

BACKGROUND: The purpose of this study was to evaluate whether North American dental schools teach students to repair resin-based composite, or RBC, restorations and to compare the findings with those from similar European surveys. MATERIALS AND METHODS: The authors mailed a 15-item questionnaire to 64 dental schools in the United States, Canada and Puerto Rico. The survey asked whether the school taught repair of RBC restorations and inquired about the respondent's experience with such procedures. Questions also elicited reasons why schools taught or did not teach repair, information in regard to relevant decision-making processes, criteria for deciding whether to perform repairs and the nature of the instruction (theoretical, practical, preclinical or clinical). RESULTS: Fifty-two (81 percent) of 64 schools participated in the survey. Thirty-seven (71 percent) of the respondents reported that they taught undergraduate students repair techniques as an alternative to replacing failing RBC restorations. Twenty-seven (73 percent) of these 37 schools reported that such teaching was at the clinical level, while only three schools (8 percent) reported that it was included in formal lectures as part of preclinical courses. The major reasons given for teaching students how to repair RBC restorations were tooth structure preservation and reduction of potentially harmful effects on the pulp. Indications included the correction of marginal defect and marginal discoloration. CONCLUSIONS: More than one-half of the respondents reported that they taught repair of RBC restorations and that patients were willing to accept such treatment. Most schools considered the repair of RBC restorations to be a definitive measure and reported that, on average, expected a repaired RBC restoration to have a longevity of four years.

Canada↗