Biomedical subjects

Y Papadogiannis

Publications and source records attributed to Y Papadogiannis.

At least 19 recordsLinked to original sources

PubMed2007

The effect of temperature on viscoelastic properties of glass ionomer cements and compomers.

The objective of this study was to determine the viscoelastic properties of different types of glass ionomer cements (GICs) and compomers under varying temperature conditions found in the mouth. The materials tested were a conventional GIC (Aqua Ionofil U), a resin modified GIC (Fuji II LC), a highly viscous GIC (Voco Ionofil Molar), and two polyacid modified composite resins/compomers (Glasiosite and Dyract Flow). Six groups of four specimens were prepared from each material. One group was stored dry for 24 h and was subsequently tested dry at 21 degrees C. Each of the remaining five groups was stored for 24 h in distilled water at the temperatures 21, 30.5, 37, 43.5, and 50 degrees C, respectively, and was subsequently tested at that temperature. Shear storage modulus and loss tangent were determined by conducting dynamic torsional loading. Static shear moduli were determined by applying a constant torque (below the proportional limit of the materials) for 10 s and recording the angular deformation of the specimens. Data were analyzed by ANOVA and Duncan's test (alpha= 0.05). It was found that the viscoelastic properties varied significantly (p < 0.05) across the different materials. The compomer Glasiosite, with the highest filler content, and the highly viscous GIC Voco Ionofil Molar exhibited the highest elastic moduli and lowest loss tangents. Viscoelastic properties varied also significantly (p < 0.05) with temperature levels, but changes in the tested region were not indicative of a glass transition. Dynamic shear storage moduli were highly correlated to the static ones. Storage in water lowered the values of elastic moduli.

Compomers↗

PubMed2006

Fatigue of packable dental composites.

OBJECTIVE: The purpose of the study was to measure the fatigue properties of four dental resin composites using a dynamic mechanical analysis and to relate the results with viscoelastic properties. METHODS: Dynamic torsional loading was conducted at resonance at 30-50Hz. Specimens were thoroughly cured and tested dry at 21 degrees C. RESULTS: All of the specimens showed a loss of strength following repeated stress, due to material fatigue. The material with the highest shear modulus had the lowest damping and the highest fatigue strength. SIGNIFICANCE: Dental composites exhibit a modest loss of strength due to fatigue. Since mastication involves many cycles of stress during the life of a restoration, fatigue properties should be taken into account in restoration design.

Compliance↗

PubMed2005

Dynamic and static elastic moduli of packable and flowable composite resins and their development after initial photo curing.

OBJECTIVE: The purpose of this study was to evaluate the dynamic (storage) shear modulus and the static shear modulus of elasticity of packable and flowable composite resins and to investigate their development after initial photo-curing. METHODS: Three pairs of a packable versus a flowable composite and a microfill composite resin were tested (Alert/Flow It, Filtek P60/Filtek Flow, Admira/Admira Flow, A 110). Cylindrical specimens (0.85 mm x 18 mm) were made for each material. All specimens were conditioned and tested dry at 21 degrees C. The specimens were tested at 30 min, 24h and 1 week after the end of photo curing. Storage shear modulus and loss tangent were determined by conducting dynamic torsional loading in the frequency range from 1 to 150 Hz. Static shear modulus measurements were made by applying a constant load (below the proportional limit of the materials) for 10s and recording the angular deformation of the specimens. Data were analyzed by ANOVA and Duncan's Post hoc test (alpha=0.05). RESULTS: Storage shear moduli (at 1 week measurement) ranged from 3.39 to 9.67 GPa, and loss tangents from 0.0735 to 0.0235; static shear moduli ranged between 2.66 and 9.80 GPa. High values of elastic moduli and low tandelta values were obtained with packable composites, while low moduli values were obtained with flowable composites. Statistically significant (alpha=0.05) differences were recorded between materials of the same category. Storage time, 24h and 1 week after initial polymerization, resulted in significant increases in both moduli of elasticity. Dynamic shear storage moduli were highly correlated to the static ones (r(2)=0.92; P<0.05). SIGNIFICANCE: The results of the aging studies showed that the rigidity of these materials increases significantly even 1 week after the clinician turns off the curing unit.

Analysis of Variance↗

PubMed2004

Dynamic mechanical analysis of viscoelastic functions in packable composite resins measured by torsional resonance.

The objective of this study was to evaluate the viscoelastic functions of packable composite resins with the use of a resonant dynamic mechanical analysis technique in torsion. The materials tested were: Alert (Jeneric Pentron), Prodigy Condensable (Kerr Corporation), Surefil (Dentsply DeTrey), and Filtek P60 (3M Dental Products). Dynamic torsional loading was conducted in the frequency range from 1 to 150 Hz. Composite specimens were tested after storage in water at 37 degrees C for 24 h. One group was thermal cycled for 3000 cycles with temperatures of 5-37-50 degrees C. Measurements were taken at 21 degrees C dry, and at 37 and 50 degrees C wet. Storage modulus, loss tangent, and other viscoelastic parameters were determined from the amplitude/frequency curves. Data for storage modulus and loss tangent of the materials were analyzed by means of ANOVA and Student-Newman-Keuls test (alpha = 0.05). It was found that there were significant differences (P < 0.001) in storage modulus and loss tangent among the packable composites tested. The highest value of storage modulus, in measurements at 21 degrees C, was for Alert (10.3 GPa), followed by Filtek P60 (9.31 GPa), Surefil (7.29 GPa), and Prodigy Condensable (6.74 GPa). There were significant differences (P < 0.001) in storage modulus and loss tangent among the four different conditions tested. Storage modulus decreased at higher temperatures, whereas the loss tangent increased. Thermal cycling increased storage modulus and decreased loss tangent. The results showed that both monomer and filler composition and filler loading of the materials significantly affect their viscoelastic functions, and the mechanical properties of the products cannot be characterized from the packability alone.

Algorithms↗

PubMed2004

The effect of pulse activation on microleakage of a 'packable' composite resin and two 'ormocers'.

The purpose of the study was to examine the effect of pulse polymerization on microleakage of one packable composite resin and two organically modified ceramics (ormocers), within a high C-factor preparation. Class-V cavity preparations with occlusal margins in enamel and gingival margins in dentin were prepared on 60 freshly extracted premolars or molars. Teeth were randomly assigned to 12 experimental groups (five teeth each) representing the different restorative systems, mode of polymerization and thermal cycling test. Three groups of 20 teeth each were restored with one of the following restorative systems: Scotch bond 1/Filtek P 60, Admira bond/Admira, Etch&Prime 3.0/Definite. 10 restorations of each restorative system (two experimental groups) were conventionally polymerized, whereas the other 10 restorations were polymerized with a pulse program. The specimens were stored in double-distilled water at 37 degrees C for 24 h. Ten restorations from each restorative system (30 restorations, half of the specimens) were thermocycled, the other 30 restorations were kept in double-distilled water at 37 degrees C for 24 h. Then all 60 restorations stained with dye, sectioned and scored for microleakage. Results showed that there were no significant differences (P > 0.05) among the materials with respect to microleakage scores. The experimental groups that were conventionally polymerized revealed significantly more microleakage (P < 0.05) after thermal cycling than all the other groups. The gingival microleakage was significantly more (P < 0.05) than occlusal in conventionally polymerized, thermocycled experimental groups.

Bicuspid↗

PubMed2003

Dynamic viscoelastic behavior of resin cements measured by torsional resonance.

OBJECTIVE: The purpose of the study was to measure the viscoelastic properties of four dental resin composite cements using a dynamic mechanical analysis technique. METHODS: Dynamic torsional loading was conducted in the frequency range from 1 to 80 Hz. Cement specimens were tested after storage in 37 degrees C water for 24 h. One group was thermal cycled prior to testing. Measurements were taken at 21, 37, and 50 degrees C. Storage modulus, loss tangent and other viscoelastic parameters were determined from the amplitude/frequency curves. RESULTS: Storage moduli of the cements ranged from 2.9 to 4.1 GPa at 37 degrees C. Loss tangents ranged from 0.054 to 0.084. Storage moduli decreased in a regular way with increasing temperature, whereas, loss tangents increased. Thermal cycling caused small decreases in storage moduli. SIGNIFICANCE: Resin cements with higher filler loading were found to have higher storage moduli and lower loss tangents. Since these properties have been associated with better clinical performance in the areas of retention and prevention of fracture of porcelain and resin restorations, the more highly filled cements may be recommended. Temperature variations influenced viscoelastic behavior of the cements. However, within the temperature range studied no sharp drop in modulus was seen, so the materials should function satisfactorily in the oral cavity.

Analysis of Variance↗

PubMed2001

In vitro cytotoxicity of six dentin bonding agents.

The cytotoxicity of six dentin bonding agents (Syntac, Solobond, Bond 1, Scotchbond 1, Heliobond and F-2000) was tested against an established cell line, L929. Under aseptic conditions 3, 5 and 10 microL dentin bonding agents were placed in the centre of Petri dishes. Each dish was covered with a 5-mL suspension of fibroblasts at a concentration of 40 000 cells mL(-1). The cultures were incubated at 37 degrees C and cytotoxicity was assessed by a quantitative technique at 24 and 72 h. All the dentin bonding agents were found to be cytotoxic. Scotchbond 1 and F-2000 showed the highest cytotoxicity followed by Solobond and Bond 1. Heliobond and Syntac were the least toxic materials.

Acrylates↗

PubMed2001

Fluoride release from restorative materials and a luting cement.

STATEMENT OF PROBLEM: In addition to conventional glass ionomers, a considerable number of different types of materials have been formulated to release fluoride. Variation in composition results in quantitative differences in the amount of fluoride release by these materials. PURPOSE: This study evaluated and compared fluoride release in distilled water from different types of restorative materials and a luting cement. MATERIAL AND METHODS: Fluoride release from 4 glass ionomer formulation restorative materials (Miracle-Mix, Fuji ionomer type III, Fuji II LC improved, and Ketac-Silver), a luting cement (Ketac Cem), a compomer (Compoglass Flow), 2 sealants (Fissurit F, Helioseal F), and a composite resin (Tetric) was evaluated at time intervals of 4, 8, 12, and 24 hours and 2, 3, 7, 14, 28, 56, and 112 days. Seven disks of each material were made and stored for equilibration in double distilled water at 37 degrees C for the time of each measurement. The equilibrated solution was analyzed for fluoride with a TISAB and an ion-specific combination electrode (ORION 960900) connected to an expandable ion analyzer (Crison micropH 2002). Data were analyzed by means of univariate analysis of variance, the Dunnett C post hoc test, and repeated measures analysis. RESULTS: Fluoride was released from all the evaluated materials, with considerable variation in the rate of release but a similar pattern. Among the materials tested, fluoride release from glass ionomer formulations was greater than that from composite resin formulations; the rank of decreasing order was as follows: Miracle Mix > Fuji III, Ketac Cem > Fuji II LC > Ketac Silver, Compoglass F > Fissurit F, Helioseal F > Tetric (> indicates statistical significance; P< .05). CONCLUSION: Under the conditions of this study, glass ionomer formulations and the compomer released more fluoride than the sealants and the composite resin tested.

Cariostatic Agents↗

PubMed1998

Artificial caries formation around fluoride-releasing restorations in roots.

Secondary caries is one of the most important factors leading to replacement of dental restorations. This investigation assessed the capacity of fluoride-releasing restorative materials to resist caries in vitro when used in roots. Class 5 cavities were prepared in the buccal and lingual surfaces of 30 extracted premolars. The six materials used were: glass-ionomer cement (Fuji), glass-ionomer cement with silver particles added (Ketac-silver), fluoride-containing composite resin (Tetric), composite resin (Silux plus), fluoride-containing amalgam (Fluor-Alloy) and high-copper amalgam (Dispersalloy). After 5 weeks in an acid gel for caries-like lesion formation, the teeth were sectioned longitudinally and examined with polarized light. The results showed that repair with glass-ionomer materials of a carious lesion may be of great importance in the prevention of secondary caries around the restorations in roots.

Bicuspid↗

PubMed1998

Development of a computer-assisted learning software package on dental traumatology.

The development of computer-assisted learning software packages is a relatively new field of computer application. The progress made in personal computer technology toward more user-friendly operating systems has stimulated the academic community to develop computer-assisted learning for pre- and postgraduate students. The ability of computers to combine audio and visual data in an interactive form provides a powerful educational tool. The purpose of this study was to develop and evaluate a computer-assisted learning package on dental traumatology. This program contains background information on the diagnosis, classification, and management of dental injuries in both the permanent and the deciduous dentitions. It is structured into chapters according to the nature of the injury and whether injury has occurred in the primary or permanent dentition. At the end of each chapter there is a self-assessment questionnaire as well as references to relevant literature. Extensive use of pictures and video provides a comprehensive overview of the subject.

Computer-Assisted Instruction↗

PubMed1998

Viscoelasticity and aging of dental composites.

Effects of aging on several dental composites were studied using a torsion creep apparatus. A constant torque was applied from 1 second to 3 hours, and recovery was observed from 10 seconds to 2 days, for specimens aged from 3 hours to 8 weeks following polymerization. Specimens aged for shorter times exhibited more creep and less complete recovery than specimens aged for longer times. Modulus and creep results were qualitatively consistent with a composite model for particulate inclusions.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1996

Degree of microleakage of some pit and fissure sealants: an in vitro study.

The purpose of this study was to evaluate and compare the degree of microleakage exhibited by five resin sealants (Concise, Helioseal, Durafil. Fissurit, Sci-Pharm) and a glass-ionomer sealant (Fuji Glass lonomer Type III). The fissure systems of the occlusal surfaces of freshly extracted teeth were opened using a pear-shaped bur; the preparations were confined to enamel. For each material, 14 teeth were prepared. From each group, seven teeth were thermocycled through 5 degrees, 37 degrees, 60 degrees and 37 degrees for 2000 cycles, and the other seven teeth were not thermocycled. All teeth were immersed in 0.5% solution of basic fuchsin dye for 48 hours. Each tooth was sectioned longitudinally in the buccolingual direction and three 1 mm-thick sections (distal, central and proximal) were obtained from each tooth. Each section was cleaned, examined, and photographed in a stereomicroscope. All the materials presented microleakage in both the thermocycled and non-thermocycled specimens; the degree of microleakage was greater in the thermocycled specimens. The results support the practice of opening up questionably carious fissures and removing caries (if present) before sealing.

Bicuspid↗

PubMed1995

A study of the microstructure of some dental retention pins and prefabricated root canal posts.

Pins and root canal posts are generally considered indispensible aids in clinical restorative dentistry. To secure the long-term efficiency of pins and posts, such devices should be of sufficient strength to carry the relevant loads. It is, however, essential that their properties do not decline as a consequence of corrosion, or that corrosion of metallic pins and posts does not cause unfavourable effect in contacting biological tissues. The microstructure of certain commercially available dental retention pins and prefabricated root canal posts has been investigated using optical microscopy and standard metallographic techniques. The specimens were then examined by scanning electron microscope and energy dispersive X-ray analysis (EDAX). The results indicate differences in microstructure and condition between the types examined. The results also showed the presence of included particles in some pins and posts. These differences and the presence of inclusions may have an important bearing on service life and corrosion resistance.

Copper↗

PubMed1993

Temperature dependence of the dynamic viscoelastic behavior of chemical- and light-cured composites.

The relationship of temperature to the viscoelastic properties of six composites, three light-cured and three chemical-cured, was studied, using constant dynamic loading over the narrow range of temperatures (20-60 degrees C) which can be encountered in the mouth. The parameters measured were: storage modulus G(1), loss modulus G(2), tan delta, quality factor Q, coefficient of decay alpha, and dynamic viscosity. It was found that the dynamic viscoelastic properties of the tested materials are temperature-dependent, but probably not to a clinically significant degree. Chemical-and light-cured composites of the same filler loading do not exhibit significantly different viscoelastic dynamic properties.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1991

Creep behavior of glass-ionomer restorative materials.

The creep of microspecimens of five glass-ionomer filling materials and one glass-ionomer-cermet cement was studied by means of a torsional creep apparatus. The glass-ionomer specimens were aged one week and conditioned in 37 degrees C water. Shear stress of 2.47 x 10(-4) N.m was maintained for three h, and recovery was followed for 50 h. Creep curves were obtained at 21, 37, and 50 degrees C. The effect of temperature increase was studied. All the glass ionomers exhibited linear visco-elastic behavior at low deformations. Their shear moduli and resistance to creep were similar to those of some composites measured by the same method. The increase of temperature influenced the creep behavior and moduli of the materials (i.e., increased creep and residual strains and decreased shear modulus). Although the applied torque was very small, there was permanent deformation, the result of viscous flow in all experiments which was more pronounced at 50 degrees C.

Cermet Cements↗

PubMed1991

Resistance of cavity varnishes to solubility: a study in vitro.

Cavity varnishes are resinous materials used under permanent restorations to protect dental tissues from marginal leakage and harmful components of the restorative material. These materials are soluble in the fluids of the oral cavity. The purpose of this study was to investigate, in vitro, the degree of solubility of these materials in different solvents over a period of time, to obtain an idea of their effectiveness.

Dental Cavity Lining↗

PubMed1987

Creep of amalgam at low stresses.

The creep and recovery of dental amalgam were studied with a torsional creep apparatus. The purpose was to investigate viscoelastic behavior in a low stress range that might result from normal chewing forces. The creep of specimens up to six months old was also studied. Four types of alloys for amalgam were used: two single-composition sphericals (SCS), an admixture-lathe-cut eutectic (ALE), and a conventional (CON). Constant torque was applied to dumbbell-shaped specimens for three hr and, after the stress was released, recovery was followed for 50 hr. All measurements were made in water at 37 degrees C after storage of the specimens for one week in 37 degrees C water. Creep was also measured at nine intervals on specimens aged from three hr to six months. The SCS amalgams exhibited the least amount of creep, followed by the ALE amalgam. The CON amalgam had the highest creep. The SCS amalgams approached linear viscoelastic behavior in the shear stress range of 0.78-4.10 MPa at 37 degrees C. They did not exhibit steady-state (viscous) creep at stresses less than 4.10 MPa. Recovery was complete but proceeded more slowly than creep. The ALE and CON amalgams exhibited viscous creep at 1.23 MPa and higher. The steady-state creep rate depended on stress, and the stress exponent ranged from 2.3-3.5. All except the ALE amalgam showed essentially constant creep compliance when aged up to six months, once the amalgamation reaction was completed after 24 to 48 hr. The compliance of the ALE amalgam gradually decreased over the six-month period.

Chemical Phenomena↗

PubMedDate not supplied

Fluoride release from three glass ionomers, a compomer, and a composite resin in water, artificial saliva, and lactic acid.

The amounts and the pattern of fluoride release from one metal-reinforced glass ionomer cement, two resin-modified glass ionomer cements, one compomer, and one composite resin placed in double-distilled water, artificial saliva, and lactic acid were evaluated in this study. Measurements of fluoride ion release were made for a total of 105 cylindrical specimens (10 mm in diameter and 1.5 mm in height). They were taken over a period of 16 weeks at the intervals of 4, 8, 12, and 24 hours, as well as 2, 3, 7, 14, 28, 56, and 112 days. The pattern of fluoride release was similar for all of the examined materials. The greatest amount of fluoride was released from the metal-reinforced glass ionomer Argion. The resin-modified glass ionomers Vitremer, Fuji II LC; the compomer Dyract; and the composite resin Tetric followed in ranking order. The pH of the environment strongly affected the fluoride release from the materials. There was a significant difference (P < 0.001) in the amounts of fluoride released in lactic acid vs water and artificial saliva, whereas, there was no significant difference (P > 0.05) in the amounts of fluoride released in water vs artificial saliva.

Analysis of Variance↗