Biomedical subjects

N Vassilakos

Publications and source records attributed to N Vassilakos.

17 recordsLinked to original sources

PubMed2001

Tobravirus 2b protein acts in trans to facilitate transmission by nematodes.

Analysis of RNA2 of TRV PaY4 showed it to be recombinant, carrying 3'-terminal sequences derived from RNA1. Virus produced using an infectious cDNA clone of PaY4 RNA2 was nematode transmissible, demonstrating that natural TRV recombinant isolates are not necessarily defective. Mutations introduced into PaY4 RNA2 showed that the 2b gene, but not the 2c gene, is required for transmission by both Paratrichodorus pachydermus and P. anemones nematodes. Experiments examined whether infection of plants with two different virus clones would impact upon nematode transmission of either virus. Simultaneous inoculation with TRV clones expressing green or red fluorescent proteins revealed that mixing of the two virus populations did not occur, although, in roots, adjacent cells were found containing green- or red-tagged viruses. Subsequently, in similar experiments it was found that a TRV PaY4 2b mutant was transmitted when combined with wild-type TRV PaY4. Also, transmission of a 2b mutant of an in vitro TRV/PEBV recombinant virus (TRV-C1) occurred after coinfection with wild-type virus. Thus, the tobravirus 2b transmission protein is trans-acting. Although TRV PaY4 and TRV PpK20 are both transmitted by P. pachydermus, a 2b mutant of TRV PaY4 was not transmitted when coinoculated to plants with TRV PpK20.

Amino Acid Sequence↗

PubMed1999

Similarities in the genome organization of tobacco rattle virus and pea early-browning virus isolates that are transmitted by the same vector nematode.

Although sequence data have been obtained for several tobravirus isolates, only two of these isolates are nematode-transmissible. Tobacco rattle virus (TRV) PpK20 is transmitted by Paratrichodorus pachydermus, whereas pea early-browning virus (PEBV) TpA56 is transmitted by Trichodorus primitivus. To clarify whether differences in the genome structure of these isolates are relevant to the specificity of interactions with particular vector nematodes, or merely reflect a taxonomic difference between TRV and PEBV, we have sequenced RNA2 of a new isolate of TRV (TpO1) that is transmitted by the same vector nematode as PEBV TpA56 but is not transmitted by the nematode vector of TRV PpK20. TRV TpO1 RNA2 encodes, in 5' to 3' order, a coat protein (CP), a 9K protein, a 2b (29K) protein and a 2c (18K) protein. Amino acid sequence comparison shows that both the CP and 2b proteins of TRV TpO1 resemble more closely the analogous proteins from PEBV TpA56 than those from TRV PpK20. Also, the TRV TpO1 9K protein has similarities with the PEBV 9K protein whereas this protein is lacking in TRV PpK20.

Amino Acid Sequence↗

PubMed1993

Effect of plasma treatment on the wettability of elastomeric impression materials.

This study investigated the effect of "plasma treatment" on the wettability of impression materials and void formation in die stone casts. Four addition reaction silicones, one condensation reaction silicone, and one polyether impression material were used. Wettability was determined before and after plasma treatment by contact angle registration of a saturated aqueous solution of calcium sulfate (CaSO4) on flat surfaces made from the tested impression materials. Two groups of surfaces were used for each material. The surfaces in one of the groups were exposed to saliva for 5 minutes. The same impression materials were used to produce four groups of die stone casts from a master die. Two groups were produced from impressions that had been exposed to milk. One group from the exposed and one from the bare surfaces were plasma-treated before pouring. Voids in the stone casts were counted under a stereoscopic microscope. The results indicated that after plasma treatment, the drop of CaSO4 solution completely spread over the addition type silicone surfaces. The corresponding die stone casts were found to be void free. It was concluded that plasma treatment produced high-energy impression surfaces that result in void-free die stone casts from the addition type silicone materials.

Adult↗

PubMed1993

Accuracy, detail reproduction, and hardness of gypsum casts produced from silicone impressions treated with glow discharge.

Plasma treatment has been reported to improve the wettability of silicone impression materials. This study investigated whether plasma treatment of silicone impressions influenced the linear dimensional accuracy, detail reproducibility, and surface hardness of models produced from a type IV dental die stone. Five silicone impressions materials were used in this study. Linear dimensional accuracy and detail reproduction were tested according to ISO standards. Surface hardness was evaluated with a Vickers hardness test. The results indicated that plasma-treated impressions from Xantopren and Provil silicone impression materials had significantly smaller dimensional change than their respective controls, and the other materials were not influenced. The detail reproduction was superior in casts produced from plasma-treated impressions from President silicone. Surface hardness was not influenced by the treatment. Plasma treatment of silicone impressions has no negative influence on the tested physical properties of die stone models.

Analysis of Variance↗

PubMed1993

Surface properties of elastomeric impression materials.

This study investigated the wettability of commonly used elastomeric impression materials and their gypsum castability. The wettability was evaluated by determining the contact angles of drops of a CaSO4 aqueous solution on flat impression surfaces. Gypsum castability was determined by counting the number of voids formed in die stone casts made from impressions of a critical die. All specimens used in this study were exposed to saliva to simulate clinical conditions, where materials spontaneously acquire salivary origin biofilms. The results indicate that the condensation silicones and conventional addition silicones exhibited the largest contact angles and the highest number of voids. The new generation of 'hydrophilic' addition silicones had higher wettability than the conventional silicones and an improved gypsum castability, comparable to that of the polyether materials.

Adult↗

PubMed1993

Reflectometry: a new method for quantitative determinations of intraoral film formation.

A simple optical method--reflectometry--is described to determine the thickness and mass of salivary films formed on solid surfaces at oral exposure. Reflectometry is based on the fact that p-polarized light is reflected with minimum intensity at an interface when the angle of incidence equals the so-called pseudo-Brewster angle. Hydrophilic and hydrophobized silica surfaces were used as substrates and the reflectometer was calibrated against a null ellipsometer. A linear relation was found between the square of the ellipsometrically measured thickness of silicon oxides on silicon substrates and the reflectometrically registered intensity of the reflected light at these surfaces. Thirty volunteers participated in the study of the thickness of films formed on the test substrates at oral exposure. The test silica surfaces were positioned in the vestibular sulcus of each test subject for periods of 1, 5, 15, 30, 60, and 120 min. The results show that films formed on hydrophobic surfaces leveled-off to a thickness value of 140 A after 60 min. Films formed on hydrophilic surfaces, however, reached a plateau value of approximately 100 A after only 300 min. Reflectometry seems to be an accurate and valid, yet inexpensive and quick method for quantitative investigations and thickness measurements of early salivary pellicles in large subject groups.

Adsorption↗

PubMed1993

An in vitro study of salivary film formation at solid/liquid interfaces.

The aim of this study was to use the technique of in situ null ellipsometry to study some aspects of salivary film formation at solid/liquid interfaces. Experiments were performed in a fused quartz cell, and hydrophilic plasma cleaned silica and methylated hydrophobic silica surfaces were used as substrates. Samples of unstimulated whole saliva were allowed to adsorb on the test surfaces for 30 min. After the adsorption period, rinsing was performed for 5 min. Recordings were continued for another 30 min, and then new saliva samples were added in the cell. The results showed that statistically significant higher amounts were adsorbed on the hydrophobic than on the hydrophilic surfaces. The adsorbed films on both types of tested substrates consisted of loosely associated parts which were removed after rinsing and of more tightly adsorbed fractions. A significantly larger fraction was desorbed from the films adsorbed on the hydrophobic than on the hydrophilic surfaces. When saliva was introduced again in the cell, it was shown that the amounts adsorbed attained the values obtained before the rinsings. Increase in the concentration of saliva in the cell without previous rinsing did not cause any further increase in the mass of the adsorbed film.

Adsorption↗

PubMed1993

Interactions of chlorhexidine with salivary films adsorbed at solid/liquid and air/liquid interfaces.

Chlorhexidine is a cationic compound which has been shown to bind to salivary proteins and enamel through electrostatic interactions. The aims of this study were to investigate the interaction of chlorhexidine molecules with salivary films adsorbed on solid surfaces with varying physico-chemical characteristics and to investigate the effect of different concentrations of chlorhexidine on the surface tension of saliva. The interactions between 0.2% chlorhexidine digluconate with films adsorbed from whole saliva were monitored by a Rudolph Thin-film ellipsometer equipped with a He-Ne laser (632.8 nm). The films were adsorbed on hydrophilic silica surfaces which were plasma cleaned or on methylated hydrophobic surfaces. Experiments of chlorhexidine adsorption on bare surfaces were also performed. The surface tension of mixtures of whole saliva with various concentrations of (0.1%, 0.2%, 1%) chlorhexidine was monitored with a tensiometer. The results show that chlorhexidine adsorbs on both types of studied substrates. Addition of the substance followed by rinsing caused a partial desorption of the adsorbed pellicles. Furthermore, at all studied concentrations chlorhexidine reduced the interfacial tension. There are indications that the amphiphilic characteristics of the molecule play an important role in the retention of the substance in the oral cavity.

Adsorption↗

PubMed1993

In vitro interactions of delmopinol hydrochloride with salivary films adsorbed at solid/liquid interfaces.

Delmopinol hydrochloride is a highly surface active substance which has been shown to reduce the amount of plaque in vitro and in vivo and the level of gingivitis in vivo. Ellipsometry was used to evaluate the effect of delmopinol on films formed from whole, parotid and sublingual/submandibular saliva on solid surfaces. Hydrophilic plasma cleaned silica and methylated hydrophobic substrates were used. The adsorption processes of the salivary proteins and their interactions with delmopinol were monitored in situ with a Rudolph thin-film ellipsometer. The adsorption of delmopinol on bare substrates with out previous salivary adsorption was also investigated and the results indicate that delmopinol molecules were adsorbed on both hydrophilic and hydrophobic surfaces. When delmopinol interacted with the films formed from the different types of saliva an initial increase in the adsorbed amounts was observed in the majority of the cases indicating binding to the salivary pellicles and/or substrate surface. The noted increases were largest for the films adsorbed from whole and sublingual/submandibular saliva. After rinsing in the system, partial desorption of the salivary films took place. It is thus indicated that delmopinol binds to salivary proteins within the pellicles and alters the cohesive and adhesive properties of these films.

Dental Deposits↗

PubMed1993

Masticatory efficiency of patients treated with implant retained fixed bridges in the upper jaw over a 2-year period.

The aim of this study was to investigate the effect of the rehabilitation of the upper jaw with a fixed bridge supported by Brånemark implants upon patient's masticatory efficiency. Five patients wearing complete dentures in the upper jaw were selected for the study. Chewing tests using Optosil tablets were performed before fixture installation, immediately after bridge connection and 2 years after bridge delivery. The results indicated that treatment with fixed bridges retained by osseointegrated implants did not give immediate improvements in masticatory efficiency. Only after the subjects had enough time to adapt to the reconstruction was an improvement in the masticatory efficiency index observed.

Adaptation, Physiological↗

PubMed1993

Effect of salivary films on the surface properties of elastomeric impression materials.

Impression materials exposed to the oral cavity are subjected to spontaneous adsorption of salivary films. The aim of this study was to evaluate the effect of adsorbed salivary films on some surface properties of one condensation, four addition silicone and one polyether impression materials. The results showed that adsorbed salivary films caused an increase in the critical surface tension and in the polarity ratios for all materials tested. A reduction in the number of voids in die stone casts was also noticed, along with an improvement in the gypsum compatibility with the impression materials tested. It can be concluded that the presence and effect of salivary films should be taken into consideration when studying the surface properties of elastomeric impression materials.

Calcium Sulfate↗

PubMed1992

Adsorption from salivary fractions at solid/liquid and air/liquid interfaces.

Ellipsometry and the drop-volume technique were used to study the interfacial behaviour of fractions obtained from unstimulated whole saliva. Fractionation was by gel filtration on a Superdex 200 Hiload column equilibrated with 10 mM potassium phosphate buffer, pH 6.8, containing 0.15 M NaCl. The fractions were reconstituted to have the same absorbance at 215 nm (estimated molecular-weight range, F1 greater than 760-460 K, F2 205-39 K, F3 14-4.5 K, F4 4.5-2.5 K, F5 1.5-0.85 K, F6 0.85 less than or equal to 0.5 K). The fractions were analysed for amino acid composition and studied by hydrophobic interaction chromatography on a Phenyl-Superose column. Fraction 3 contained the largest amounts of proline, followed by fractions 4 and 2. Fraction 3 showed the highest relative hydrophobicity. Ellipsometric measurements on negatively charged silica surfaces and methylated hydrophobic surfaces revealed that larger amounts of material adsorbed on hydrophobic than on hydrophilic surfaces. On hydrophilic surfaces the largest amounts were adsorbed from the high molecular-weight fraction 1. Fractions 4 and 6 did not give any adsorption at all on these surfaces. Fraction 3 gave the largest amounts adsorbed on the hydrophobic surfaces. Drop-volume measurements showed distinct differences in the ability of the salivary fractions to lower the surface tension. Fractions 2 and 3 showed the greatest reduction in surface tension. It was concluded that the adsorption behaviour of salivary proteins showed a wide variation among the different fractions and that it is influenced by the physicochemical characteristics of the interfaces present in the mouth.

Adsorption↗

PubMed1992

Surface properties and castability of elastomeric impression materials after plasma cleaning.

The wettability of impression materials is an important requirement for accurate reproduction of intraoral structures. The aims of this study were to evaluate the effect of plasma cleaning on critical surface tension and die stone castability of five silicone impression materials. Critical surface tension was calculated using a contact angle analysis according to Zisman (1964), before and after plasma cleaning. Die stone casts were produced from impressions of a master die and the area extension of the reproduction was measured planimetrically. The results showed a general increase in the critical surface tension and in the polar force component of the composite free energy for materials treated with plasma cleaning. An improvement in castability of all materials was also noted.

Analysis of Variance↗

PubMed1992

Adsorption of whole saliva onto hydrophilic and hydrophobic solid surfaces: influence of concentration, ionic strength and pH.

The influence of the concentration of salivary proteinaceous material from solutions of whole saliva on the kinetics of in vitro pellicle formation were studied together with the effects of ionic strength, pH and certain substrate characteristics. The pellicle formation was monitored by an automated Rudolph ellipsometer, equipped with a He-Ne laser (wavelength 632.8 nm). The substrates compared in the study were hydrophilic negatively charged silica surfaces and hydrophobic methylated silica surfaces. The results show that the adsorption of salivary proteins is a very rapid process on both types of surfaces. Part of the formed biofilm, however, desorbed upon rinsing, indicating that the proteinaceous material was adsorbed with varying binding strengths. Larger adsorbed amounts were recorded on hydrophobic than on hydrophilic surfaces. Increase of ionic strength caused larger amounts to be adsorbed on both types of surfaces but change of pH did not affect the adsorption on either of the studied surfaces. Ellipsometry was found to be a suitable technique to monitor the adsorption of salivary proteins at solid/liquid interfaces.

Adsorption↗

PubMed1992

In vitro interactions of anionic and cationic surfactants with salivary fractions on well-defined solid surfaces.

Ellipsometry was used to study the interaction of one anionic (SDS) and one cationic (CTAB) surfactant with films adsorbed from six different salivary fractions obtained after fractionation of whole unstimulated saliva on a Superdex 200 Hiload gel filtration column. Experiments were performed on both hydrophilic silica and hydrophobic methylated silica surfaces. The results of this study indicate that the adhesive and cohesive properties of the films adsorbed from the individual fractions were strongly dependent on the surface characteristics of the substrates and that the outcome of protein/surfactant interactions was dependent on factors such as protein composition, surfactant charge, and substrate characteristics. These interactions probably involve replacement of the adsorbed proteins by surfactants or protein/surfactant complex formation. The anionic surfactant seemed to be more efficient in removing adsorbed salivary proteins than the cationic one.

Adhesiveness↗

PubMed1991

Effect of a buffering sugar-free lozenge on intraoral pH and electrochemical action.

Two double-blind crossover studies were performed to test a sugar-free lozenge containing bicarbonate and phosphate buffers (Profylin). The studies were performed in groups of 20 and 13 individuals. In Study I active buffering or placebo lozenge (not buffered) was given, and the pH of plaque and saliva was measured after 2, 5, 10, 20, and 30 min. In study II the lozenges were given 10 min after a sucrose rinse, and both the pH and the potential and polarization of amalgam restorations that made contact in the oral cavity were measured. In study I both lozenges increased the pH of plaque and saliva, but the values after sucking on the active lozenge were significantly higher than after placebo. In study II a pH recovery of plaque and saliva after the sucrose rinse was recorded for both types of lozenge, but it was most pronounced for the active, buffering lozenge. A statistically significant difference was, however, found only 5 min after sucking on the lozenge. No influence on the current magnitude was observed. The results thus indicate that the buffering sugar-free lozenge raises the pH of plaque and saliva and accelerates the pH recovery after a sucrose rinse but seems to have no influence on the galvanic current magnitude of amalgam restorations in contact.

Buffers↗

PubMed1990

Oral electrochemical action after soft drink rinsing and consumption of sweets.

The aim of this study was to investigate the influence of pH changes in dental plaque and saliva on the magnitude of the galvanic current created when amalgam restorations make contact in the oral cavity. Ten persons with 46 contacts between amalgam fillings in all participated in the experiments. Potential, polarization, and pH measurements were performed before and after Coca-Cola and orange juice rinsing and intake of sweets, which were used as test products. Distilled water was used as a control. The measurements were performed 2, 5, 10, 20, and 30 min after the rinsing or intake. There was no statistically significant difference in the current magnitude after any test product or between the time intervals after the different products. The results indicated that changes of the plaque and saliva pH for a short time after food and soft drink intake do not influence the magnitude of the galvanic current flowing between amalgam restorations in contact.

Adult↗