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Biomedical subjects

G C Eliades

Publications and source records attributed to G C Eliades.

13 recordsLinked to original sources
PubMed1996

Laboratory evaluation of three visible light-cured resinous liners.

OBJECTIVES: The aim of the present study was to evaluate the composition and the laboratory performance of three visible light-cured resinous liners (Cavalite, Ionoseal and Timeline). METHODS: Monomers were separated from fillers and were analysed by HPLC. Set pastes were analysed by FTIR spectroscopy and diametral strengths and water solubility were measured. RESULTS: The monomers identified in the liners were BisEMA/2-HEMA (Cavalite), BisDMA/BisGMA (Ionoseal) and UEDMA (Timeline). Significant variations were found in the filler content but the mechanical response as assessed by the diametral tensile strength showed no statistical differences. The curing efficiency ranged from 24.2 to 31.0% (top surfaces) to 26.0-54.0% (bottom surfaces) of remaining C = C bonds. No positive correlations were found between curing efficiency and optical properties. The bond strength of the liners to dentine was negligible compared with that to composite. All the liners demonstrated extensive gap formation and debonding at the liner-dentine interfaces in marginal adaptation testing. Statistical differences were noticed in the water absorption and water solubility values of the products. Ionoseal showed extensive hydrolytic degradation compared with the other liners. No evidence of acid-base reaction was found in the set products.

Acrylic Resins↗
PubMed1991

Surface alterations on dental restorative materials subjected to an air-powder abrasive instrument.

This study assessed the effect of an air-powder abrasive instrument (Prophy Jet) on the surface integrity of a series of restorative materials. Four types of amalgam alloys (Amalcap, Dispersalloy, Tytin, Ana 2000), three types of composite resins (Silux, Brilliant Lux, Adaptic II), a heat-cured resin (SR Vivadent), and porcelain (Vita VMK) fused to a Gr-Ni alloy at 1 mm and 2.5 mm thickness were subjected from 5 mm distance to the abrasive stream at 100 psi for 5 seconds. The resulting surface topography was studied under an electron probe microanalyzer. All of the amalgams presented increased surface roughness and alterations in the surface composition assigned to the destruction of the soluble gamma-2 and n phases. Composite resins showed excessive matrix disruption, exposure of the filler particles and pitting on the prepolymer surfaces. The crown and fixed partial denture resin was the most affected material. Porcelain at 2.5 mm thickness exhibited moderate stain pitting, whereas in 1 mm thickness severe glaze cracking was identified.

Acrylic Resins↗
PubMed1991

Functional stress modification after high condylectomy surgery.

Surgical removal of the head of the condyles inevitably leads to radical redistribution of loads applied to the mandible. The nature of this redistribution can have important implications on the surgical approach and subsequent reconstructive procedures. The purpose of this investigation was to visualize photoelastically the functionally delivered stresses after high condylectomy surgery. Three identical models of a dentate human mandible were constructed from a photoelastic material. One mandible simulated a unilateral and the other simulated a bilateral high condylectomy. The third mandible had both condyles intact and served as basis for comparisons. Silicone implants were placed on the sectioned condylar heads. The condyles, with the silicone implants, were fitted into simulated fossae and the mandibles were loaded unilaterally and bilaterally. The resulting stresses were observed and photographed in the field of a circular polariscope. Substantial differences in load-generated stresses were observed as a result of both unilateral and bilateral condylectomies, compared to the normal case. The most severe stress conditions occurred with the unilateral condylectomy, where stresses associated with torsion were most evident.

Humans↗
PubMed1989

The strength of layering technique in visible light-cured composites.

Despite the extensive use of the layering technique in light-cured restorations there is limited information for the interfacial strength when curing is accomplished in air and an inhibited zone is formed on the first layer. This study analyzed the nature of the inhibited zone to determine the interfacial topography, evaluated the shear interlayer bond strength in the presence of the inhibited layer, and assessed the effect of various interfacial treatments on bonding. Two microfilled, one hybrid, and three small-particle composite resins were included in the study. According to the results, the inhibited zone is primarily composed of catalyst-free monomer. The presence of this zone reduces bond strength, creating interfacial discontinuities. Removal of the inhibited layer by an organic solvent of low boiling point results in the highest strength and better interfacial topography from the tested treatments.

Chemical Phenomena↗
PubMed1989

31P-NMR study of P-based dental adhesives and electron probe microanalysis of simulated interfaces with dentin.

The structure and function of P in P-based dental adhesives have not been defined properly. The purpose of this study was to evaluate these parameters in some currently available materials. Five dental adhesives were selected: Bondlite, Clearfil New Bond, J&J Dental Adhesive, Prisma Universal Bond, and Scotchbond. High-resolution 31P-NMR spectroscopy was used to identify the phases of the incorporated P and the kinetics of monomer-bonded P in an aqueous environment. Areas of 5 mm diameter located on polished sound dentin were subjected to the corresponding adhesive treatments and covered with translucent molds of the same diameter, which were filled up to 1 mm length with a visible-light-cured hybrid composite. Following 60 sec of light exposure from lateral directions, the specimens were embedded in fast-setting resin, cross-sectioned, and analyzed in an electron probe microanalyzer. The elemental profiles of Ca, P, and Cl were determined from area and line scans. Great differences in the 31P resonance shifts were obtained from the tested adhesives, indicating the presence of monomer-bonded and free P. A rapid hydrolysis of the resin-bonded P in the presence of water was identified. The x-ray images revealed dentin demineralization, with distinct differences in the P distribution pattern and the P/Cl ratio.

Dental Bonding↗
PubMed1989

A comparative in vitro study of visible light-cured sealants.

The introduction of visible light polymerization in dentistry led to the development of a new generation of pit and fissure sealants. The purpose of this study was an overall evaluation of some in vitro characteristics of four new sealants (Delton LC, Helioseal, Pentra-Seal and Visioseal) in comparison with a chemically cured control (Delton). The results indicate that the monomer systems utilized in the new materials have already been used in dental polymer technology. The relatively new monomers TCDDMA/TCDMA were identified in one product. Camphoroquinone is used as a photoinitiator in all the light-cured systems which, after 40 s exposure, present better conversion than the control. The extent of oxygen inhibition was considerably reduced in the new sealants and the surface hardness was enhanced. Great differences were obtained in the penetration coefficient values; these, however, did not affect the enamel retention capacity of the materials tested. Consequently, light-cured sealants should be considered to be strongly compatible with the conventional chemically cured sealants from a laboratory aspect until more clinical evidence is available for their effectiveness in the prevention of pit and fissure decay.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1989

[A comparative analysis of the characteristics of META-DENT denture resin system].

A newly developed denture resin based on a 4-META containing monomer became recently commercially available. It has been claimed that this resin system has the unique ability of creating bond to Cr-Co alloys without any mechanical retention. The objective of this study was to determine the chemical composition of the new resin, to study the bonding mechanism with a Cr-Co alloy and to compare its physical and mechanical properties to a commonly used acrylic denture resin. The analysis revealed that the new system contains 5% by weight 4-META in MMA liquid and 28% poly (ethyl methacrylate) in PMMA. No practical differences were noted in the stress-strain characteristics and hardness values between the resin systems. The META-DENT resin was more abrasion resistant. The bond of META-DENT to the Cr-Co alloy was greatly superior than that of the conventional resin. The bonding mechanism may be related to enhanced physical wetting due to reduced META-DENT viscosity and probably complexation of the anhydride groups with either Cr or Co.

Acrylic Resins↗
PubMedDate not supplied

Curing efficiency of visible light- and dual-cured denture reliners.

PURPOSE: The purpose of this study was to evaluate the curing efficiency of 8 light- and dual-cured denture reliners. MATERIALS AND METHODS: The curing efficiency was measured with Fourier infrared micromultiple internal reflectance spectroscopy, calculating the percentage of remaining carbon double bonds on the top and bottom surfaces of each specimen immediately after exposure to the extraoral light-curing unit according to the manufacturer's instructions and after 1 week of storage in dark and dry conditions. Another group of specimens was photopolymerized initially through a denture base resin prior to the extraoral light-curing polymerization. Five specimens of each reliner were tested. RESULTS: The dual-cured reliners showed no statistically significant differences (P > 0.05) between top and bottom surfaces after immediate exposure to the light-curing unit. On the contrary, light-cured reliners revealed significant differences. The majority of the reliners showed reduction of the percentage of remaining carbon double bonds at both surfaces after 1 week of storage in dark and dry conditions. Photopolymerization of light-cured reliners through a denture base resin induced an increased amount of remaining carbon double bonds, whereas no effect was observed in dual-cured materials. CONCLUSION: Dual-cured denture liners exhibited distinct advantages over light-cured ones concerning the curing efficiency.

Acrylic Resins↗