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PubMedDate not supplied

Alternative treatments for resin-based composite and amalgam restorations with marginal defects: a 12-month clinical trial.

This clinical trial sought to evaluate the effectiveness of alternative treatment for replacing amalgam and resin-based composite restorations with marginal defects. The study recruited 66 patients with 271 restorations. Each restoration was assigned randomly to one of five groups: Sealant, Refurbishing, Repair, Replacement, and Untreated. Two clinicians evaluated the restorations according to USPHS/Ryge criteria at baseline (Kappa 0.74) and one year after the treatment (Kappa 0.81). The scoring of the margins improved (from bravo to alfa) after the experimental treatments. None of the treatments showed significant degradation of the margins during the 12-month observation period.

Adolescent↗
PubMed2001

Cavity preparation devices: effect on microleakage of Class V resin-based composite restorations.

PURPOSE: To evaluate the effect of cavity preparation device (i.e. carbide bur, diamond bur, air abrasive, Sonicsys, and Er:YAG laser) on microleakage of Class V resin-based composite (RBC) restorations, the tooth restoration interface and dentin ultrastructure. MATERIALS AND METHODS: Eight groups (n=18) of 9 human molars each were prepared on the buccal and lingual surfaces for Class V RBC restorations using five preparation devices: Group 1: carbide bur #8 round; Group 2: diamond bur #801; Group 3: KCP 1000 air abrasion unit; Group 4: Sonicsys Approx.; Group 5: Er:YAG laser; Group 6: carbide bur plus air abrasive; Group 7: carbide bur plus laser, and Group 8: laser without etching. Circular cavity preparations, 3 mm diameter and 1.5 mm deep, were cut at the CEJ on the buccal and lingual surfaces of each tooth. A bevel was placed on the enamel margin. All cavities were restored using Single Bond adhesive system and Silux Plus according to manufacturer's directions, with the exception that no etchant was used with Group 8. After thermocycling, specimens were tested for microleakage using silver nitrate methodology. Dye penetration data was collected and subjected to non-parametric statistical analysis. SEM analysis of the dentin-RBC interface, as well as the effect of each cavity preparation device on the surface of dentin was performed. RESULTS: Microleakage did not occur in enamel for any method of cavity preparation when the enamel was etched prior to adhesive application. Kruskal-Wallis One-way ANOVA revealed differences in dentin microleakage among the tested groups at alpha=0.05. Mann-Whitney Test for Paired Comparisons at alpha=0.01 demonstrated significantly greater dentin microleakage in Groups 5 and 7 compared to all groups except Group 3 (air abrasive). Although Group 8 had the least microleakage in dentin, this was not significantly different from Groups 1, 2, 4 and 6. SEM observation revealed hybridization at the dentin-resin interface for all groups except for Group 8 (laser prepared, non-etched). Surface analysis showed differences related to the operating mode of each preparation device. CLINICAL SIGNIFICANCE: The method of cavity preparation did not affect microleakage in etched enamel. When using a laser for cavity preparation, enamel should be etched although not etching dentin may help to improve marginal seal.

Acid Etching, Dental↗
PubMed2000

A unique pattern of intrastrand anomalies in base composition of the DNA in hypotrichs.

The 50 non-coding bases immediately internal to the telomeric repeats in the two 5' ends of macronuclear DNA molecules of a group of hypotrichous ciliates are anomalous in composition, consisting of 61% purines and 39% pyrimidines, A>T (ratio of 44:32), and G>C (ratio of 17:7). These ratio imbalances violate parity rule 2, according to which A should equal T and G should equal C within a DNA strand and therefore pyrimidines should equal purines. The purine-rich and base ratio imbalances are in marked contrast to the rest of the non-coding parts of the molecules, which have the theoretically expected purine content of 50%, with A = T and G = C. The ORFs contain an average of 52% purines as a result of bias in codon usage. The 50 bases that flank the 5' ends of macronuclear sequences in micronuclear DNA (12 cases) consist of approximately 50% purines. Thus, the 50 bases in the 5' ends of macronuclear sequences in micronuclear DNA are islands of purine richness in which A>T and G>C. These islands may serve as signals for the excision of macronuclear molecules during macronuclear development. We have found no published reports of coding or non-coding native DNA with such anomalous base composition.

Animals↗
PubMedDate not supplied

Two-year clinical comparison of a microfilled and a hybrid resin-based composite in non-carious Class V lesions.

The purpose of this double-blind clinical trial was to compare the retention rate in noncarious Class V lesions of two resin-based composite restorative materials with contrasting stiffness. Isolation with retraction cord, pressed paper triangles, and cotton rolls was used to closely mimic the procedures generally used in a practice setting. Thirty pairs of restorations were placed, one using Silux Plus and one using Z100. The assignment of material was randomized, and the subjects were unaware of the material used. All restorations were placed with a fourth-generation adhesive liner, Scotchbond Multi-Purpose. Evaluations were performed at baseline, 6, 12, 18, and 24 months by two independent examiners using criteria developed by Cvar and Ryge in a forced consensus model. Examiners were unaware of the restoration's group identity. No difference between the retention rates for the two groups was found after 24 months, bringing into question the role that a material's stiffness plays in determining retention in a noncarious Class V lesion.

Adult↗
PubMed2000

Effect of light source position and bevel placement on facial margin adaptation of resin-based composite restorations.

PURPOSE: To evaluate the effect of direction of first cure and the presence or absence of a facial margin bevel on the adaptation of facial margins of Class III resin-based composite (RBC) restorations. MATERIALS AND METHODS: Custom polyvinyl siloxane (PVS) light shields were fabricated for both the mesial and distal surfaces of 20 extracted incisors. Class III cavities were prepared in the mesial and distal surfaces of the incisors. On the facial, lingual, and gingival margins of 20 of the preparations a 0.5 mm wide enamel bevel was placed. The lingual and gingival, but not the facial, margins were beveled on the other 20 preparations. The PVS light shield was adapted to the tooth and trimmed to allow 1-2 mm of the facial margin to be exposed on 10 of the beveled and 10 of the non-beveled preparations. For the remaining 20 preparations the PVS light shield was trimmed to allow access of the curing light only from the lingual. Teeth were restored with Prisma TPH RBC. Using the appropriate shield, restorations in the facial first cure group were cured first from the facial and then from the lingual. Restorations in the lingual first cure group were cured only from the lingual. Restorations were finished flush with enamel margins and thermocycled following storage. Samples were exposed to a 50% solution of silver nitrate followed by light exposure. Teeth were sectioned and microleakage was evaluated at three levels (incisal, middle, and cervical). Four evaluators (blinded to direction of cure) independently scored microleakage using a categorical evaluation scale. Statistical analysis included non-parametric descriptive statistics, Cohen's kappa, chi-square analysis, and Kruskal-Wallis ANOVA. RESULTS: Samples prepared without a facial bevel revealed significantly more (P = 0.01) microleakage than preparations with a facial bevel. At the most incisal level, restorations cured first from the facial revealed significantly more (P < 0.001) microleakage than restorations cured first from the lingual. At the middle and cervical levels, restorations cured first from the facial revealed significantly less (P < 0.001) microleakage than restorations cured first from the lingual. When a facial bevel was present, samples cured first from the facial showed significantly less (P < 0.001) microleakage than those cured only from the lingual.

Analysis of Variance↗
PubMed2002

Effect of multiple application of a dentin adhesive on contraction gap width of a resin-based composite.

PURPOSE: To test the efficacy of the multiple application of a total-etch dentin adhesive was investigated by measuring (1) the contraction gap width of a light-activated resin-based composite in a cylindrical dentin cavity and (2) the early tensile bond strength to a flat dentin surface with the Single Bond Dental Adhesive System. MATERIALS AND METHODS: Contraction gap width was measured in a cylindrical dentin cavity (3 mm x 1.5 mm) treated with a single coat or double coats of the Single Bond adhesive and restored with Silux Plus or Z-100. As control, the cavity was treated with an experimental dentin bonding system consisting of EDTA, 35% GM and Clearfil Photo Bond. Early tensile bond strengths of Silux Plus or Z-100 were measured on the flat dentin surface treated with the three bonding procedures as in the contraction gap study within 10 min. after final cure. RESULTS: The contraction gap of Silux Plus and Z-100 was prevented with the double coats of the Single Bond adhesive, whereas the contraction gap of Z-100 was not prevented with the single coat of the Single Bond and the experimental system. When the film thickness of the Single Bond system was less than 2 microm, the gap could not be prevented. The tensile bond strengths of Silux Plus and Z-100 to flat dentin mediated with the three bonding procedures were not significantly different (P>0.05).

Acid Etching, Dental↗
PubMedDate not supplied

Clinical evaluation of a polyacid-modified resin composite-based fissure sealant: two-year results.

A 24-month clinical study was carried out to evaluate and compare the retention rate, marginal integrity and caries preventing effects of a polyacid-modified resin composite based fissure sealant, Dyract Seal, to that of a resin based fluoride fissure sealant, Delton FS+. Fifty-three patients (27 female and 26 male), 7 to 10 years old, were included in the study. At baseline, a total of 192 permanent first molars were sealed with either fissure sealant (n=96, each), using invasive technique. The sealed teeth were evaluated at post-operative 3, 6, 12 and 24 months with respect to evaluation parameters. The data were analyzed with the Chi-Square tests where alpha=0.05. There were no statistically significant differences between fissure sealants as regards to retention and prevention of caries for all periods of the evaluation (p>0.05). However, regarding marginal integrity of the sealants, Delton FS+ gave significantly better results than Dyract Seal for the 3-, 6- and 12-month evaluations, respectively (p<0.05). In conclusion, the use of Dyract Seal on permanent molars with invasive technique was found to be clinically comparable to Delton FS+ for the 24-month evaluation period.

Bisphenol A-Glycidyl Methacrylate↗
PubMed2006

Graphene-based composite materials.

Graphene sheets--one-atom-thick two-dimensional layers of sp2-bonded carbon--are predicted to have a range of unusual properties. Their thermal conductivity and mechanical stiffness may rival the remarkable in-plane values for graphite (approximately 3,000 W m(-1) K(-1) and 1,060 GPa, respectively); their fracture strength should be comparable to that of carbon nanotubes for similar types of defects; and recent studies have shown that individual graphene sheets have extraordinary electronic transport properties. One possible route to harnessing these properties for applications would be to incorporate graphene sheets in a composite material. The manufacturing of such composites requires not only that graphene sheets be produced on a sufficient scale but that they also be incorporated, and homogeneously distributed, into various matrices. Graphite, inexpensive and available in large quantity, unfortunately does not readily exfoliate to yield individual graphene sheets. Here we present a general approach for the preparation of graphene-polymer composites via complete exfoliation of graphite and molecular-level dispersion of individual, chemically modified graphene sheets within polymer hosts. A polystyrene-graphene composite formed by this route exhibits a percolation threshold of approximately 0.1 volume per cent for room-temperature electrical conductivity, the lowest reported value for any carbon-based composite except for those involving carbon nanotubes; at only 1 volume per cent, this composite has a conductivity of approximately 0.1 S m(-1), sufficient for many electrical applications. Our bottom-up chemical approach of tuning the graphene sheet properties provides a path to a broad new class of graphene-based materials and their use in a variety of applications.

Journal Article↗
PubMed2003

Biological response to wear debris generated in carbon based composites as potential bearing surfaces for artificial hip joints.

UHMWPE wear particles have been implicated in osteolysis, implant loosening, and long-term failure of total hip arthroplasties in vivo. This study examined four carbon-based composite materials as alternatives for UHMWPE in joint bearings. These materials were HMU-CVD, SMS-CVD, P25-CVD, and CFR-PEEK. New bearing materials should satisfy certain criteria: they should have good wear properties that at least match UHMWPE, and produce wear particles with low levels of biological activity. Of the four materials tested in multidirectional pin-on-plate tribological tests, SMS-CVD, P25-CVD, and CFR-PEEK showed lower volumetric wear factors than UHMWPE. P25-CVD had the lowest wear factor of 0.54 +/- 0.34 x 10(-7) mm(3)/Nm. Analysis of P25-CVD wear particles by transmission electron microscopy showed that the debris was very small, with the vast majority of particles being under 100 nm in size, which was similar in size to metal wear particles. The P25-CVD particles were isolated and cultured with L929 fibroblasts and U937 monocytic cells to assess their effect on cell viability. P25-CVD particles were significantly less cytotoxic (p < 0.01, ANOVA) to both cell types than CoCr metal wear particles. This work suggests that carbon-carbon composite materials may have potential for use in total hip replacement bearings. Of the materials tested P25-CVD had the lowest wear factor, and produced very small wear debris that had minimal cytotoxic effect on L929 and U937 cells in vitro. Therefore carbon-carbon composites, such as P25-CVD, may be important in the development of next-generation implants with lower wear rates and reduced cytotoxic potential.

Animals↗
PubMed1982

The longitudinal differentiation produced by photo-oxidation and acridine-orange staining in eukaryote chromosomes: role and involvement of DNA base composition.

Photo-oxidation and staining with acridine-orange result in a longitudinal green/orange-red/brown-red color differentiation in fixed chromosomes of Drosophila melanogaster, D. virilis, Culiseta longiareolata, and Mus musculus. Such a result has been correlated with specific DNA base sequences situated in specific chromosomal areas. In fact, given the known base composition of satellite DNA's in three of the species we studied, a correspondence seems to exist between molecular hybridization in situ of AT-rich satellite DNA's and the location of specific stain reactions in specific chromosome regions. Moreover, our results support previous findings suggesting preferential guanine destruction as a consequence of photo-oxidation.

Acridine Orange↗
PubMed2006

Investigation of polymerisation shrinkage strain, associated cuspal movement and microleakage of MOD cavities restored incrementally with resin-based composite using an LED light curing unit.

OBJECTIVES: To investigate the polymerisation shrinkage strain, associated cuspal movement, degree of conversion (DC) and cervical gingival microleakage of mesio-occlusal-distal (MOD) cavities restored with four resin-based composite (RBC) filling materials placed incrementally using a light emitting diode (LED) light curing unit (LCU). METHODS: Standardised extensive MOD cavity preparations on extracted teeth were performed on 40 sound upper premolar teeth. Restoration of the teeth involved the placement of RBCs in eight increments with the appropriate bonding system before irradiation using an LED LCU. Buccal and palatal cusp deflections at each stage of polymerisation were recorded using a twin channel deflection measuring gauge. Following restoration, the teeth were thermocycled, immersed in a 0.2% basic fuchsin dye for 24 h, sagittally sectioned and examined for cervical microleakage. The DC was determined using a Fourier transform infra-red (FT-IR) spectrometer. RESULTS: No significantly difference (P=0.677) in cuspal movement was recorded for Z100 (13.1+/-3.2 microm) compared with Filtek Z250 (8.4+/-3.5 microm), P60 (7.3+/-3.8 microm) and Admira (6.7+/-2.7 microm). The LED LCU deflections were compared with a halogen LCU used in a conventional (Fleming GJP, Hall D, Shorthall ACC, Burke FJT. Cuspal movement and microleakage in premolar teeth restored with posterior filling materials of varying reported volumetric shrinkage values. Journal of Dentistry, 2005;33:139-146) and soft-start mode (Fleming GJP, Cara RR, Palin WM, Burke FJT. Cuspal movement and microleakage in premolar teeth restored with posterior filling materials cured using 'soft-start' polymerization. Dental Materials, 2006, , in press) and a significant reduction in cuspal movement was identified for curing type and material type (P<0.001 and P=0.002, respectively). No significant differences were noted between the four RBC materials investigated when the DC or microleakage scores were examined for the LED LCU. SIGNIFICANCE: It would appear that irradiation of RBCs using the LED LCU offered a significant reduction in associated cuspal movement in large MOD cavities. However, the microleakage scores following polymerisation were significantly increased with dye penetration into the pulp chamber from the axial wall evident in teeth restored with the LED LCU.

Bicuspid↗
PubMed2001

[Base composition of DNA from fluoride resistant strains of streptococcus mutans and streptococcus sobrinus].

OBJECTIVES: To evaluate the genotype change of fluoride-resistant strains of S.mutans and S.sobrinus. METHODS: High potential liquid chromatography was used to measure the base composition of DNA from F-resistant strains of S.mutans and S.sobrinus and their parent strains. RESULTS: The data showed that the DNA G+C mol% of F-resistant and F-sensitive S.mutans were quite different, the difference was over 5%. The four F-resistant strains were 54.45, 44.86, 54.41, 55, 390, whereas the corresponding four parent strains were 35.38, 37.4, 43.35, 46.62, respectively. CONCLUSION: The genotypes of F-resistant strains of S.mutans and S.sobrinus have been changed and may comprise several gene mutations.

English Abstract↗
PubMed1974

Base composition and hybridization studies of the three double-stranded RNA segments of bacteriophage phi 6.

The three double-stranded ribonucleic acid (dsRNA) segments of the bacteriophage phi6 were isolated and shown to have similar melting temperatures and base compositions. RNA:RNA hybridization experiments with the isolated segments eliminate the possibility that the two smaller dsRNA segments arise from a cleavage of the large dsRNA segment. The two smaller RNA segments reanneal rapidly even at low temperatures; in contrast, the large dsRNA reannealed only at higher temperatures. Evidence is also presented which suggests that the dsRNAs may contain a short single-stranded RNA tail.

Bacteriophages↗
PubMed1980

[On the taxonomy of Actinobacillus, Haemophilus, and Pasteurella: DNA base composition, respiratory quinones, and biochemical reactions of representative collection cultures (author's transl)].

In a comparative study, 63 collection cultures representing 38 nomenspecies of, or assigned to, the genera Actinobacillus, Haemophilus, or Pasteurella were characterized by phenotypical features and deoxyribonucleic acid base composition. The latter was calculated from the thermal denaturation point. Biochemical reactions were tested in differential media commonly used for Enterobacteriaceae, and two test procedures were compared: (i) pure cultures with haematin and nicotine adenine dinucleotide added, where necessary, and (ii) xenocultures with an asaccharolytic Acinetobacter strain (ST 661/60). Furthermore, the respiratory quinones, and the effect of fumarate on oxygen-limited growth were considered. On the basis of these and some additional physiological and morphological criteria, a definition of the Actinobacillus-Haemophilus-Pasteurella group as a whole was established which appears to rank as a family. Several misclassified species, i.e. the so-called Actinobacillus actinoides, Haemophilus piscium, Haemophilus vaginalis, Pasteurella anatipestifer, and the organisms of the Bovine Lymphangitis group were eliminated, and the position of so-called Pasteurella piscicida was questioned. Some principles of subdivision of the group, and some of the practical identification procedures were discussed.

Actinobacillus↗
PubMed2002

Nuclear DNA content, base composition, heterochromatin and rDNA in Picea omorika and Picea abies.

Two closely related spruces, Picea abies and Picea omorika, a Balkan paleoendemic species, often share habitats, yet never hybridize in nature. The present study adresses their characteristics such as nuclear DNA content, base composition, heterochromatin and rDNA pattern. The genome size of P. abies was 10% larger than that of P. omorika when assessed by flow cytometry, respectively 2C=37.2 pg and 33.8 pg; although when estimated as total chromosome length it was virtually the same. The heterochromatin Chromomycin-A (CMA)/ DAPI fluorochrome banding patterns of both P. abies and P. omorikaare given here for the first time. Simultaneous FISH (fluorescent in situ hybridization) using 18S-26S and 5S rDNA probes revealed 16 18S rDNA sites in P. omorika, 12 18S rDNA sites in P. abies, and a single 5S rDNA locus in both species. The genomes have about 41% GC. The number and position of CMA/DAPI bands and rDNA loci provide good chromosome markers to clarify the karyotypes of the two species.

Journal Article↗