Biomedical subjects

G Eliades

Publications and source records attributed to G Eliades.

At least 37 records · Page 2Linked to original sources

PubMed1998

Long-term behaviour of the Charnley offset-bore acetabular cup.

We report the long-term radiological results of 58 total hip arthroplasties (THA) using the Charnley offset-bore acetabular socket. Wear was measured at four sites and radiolucent lines and possible migration were recorded. Four cups were retrieved at revision and were examined using light microscopy, SEM and X-ray microanalysis. At a mean follow-up of seven years the mean wear in the DeLee and Charnley zone I was 0.4 mm and in zone II 0.26 mm. The wear rate was 0.06 and 0.04 mm/year, respectively. Progression of radiolucent lines was seen in five cases (8.6%). Three sockets (5.2%) were revised because of aseptic migration at a mean follow-up of 9.8 years and one socket for infection at two years. The offset-bore acetabular cup had excellent wear behaviour and a low migration and revision rate. We recommend that it should be considered in THA since the use of small cups is increasing, particularly in revision cases.

Acetabulum↗

PubMed1997

Effect of topical fluoride agents on the morphologic characteristics and composition of resin composite restorative materials.

STATEMENT OF PROBLEM: The high reactivity of fluoride agents used in topical fluoride treatments have raised important questions on their potential adverse effects on restorative materials. PURPOSE: The purpose of this study was to evaluate the effect of topical fluoride agents used for office or home treatments on the surface morphologic characteristics and composition of composite restoratives. MATERIAL AND METHODS: The fluorides used were Act, Phosflur, Gel II, Prevident, Stop, Butler APE, Nupro, and Omni Gel & Rinse. The composites tested were Brilliant DI, Heliomolar Ro, Herculite XRV, and P-50. The pH of the fluorides was measured as received and after dilution with water at a 1:3 volume ratio. The composites were subjected to the fluoride treatments until the total number of applications simulated the equivalent of 4 years under treatment. The changes induced on the surface morphologic features and composition of the restoratives were assessed by multiple internal reflectance Fourier transform infrared spectroscopy, scanning electron microscopy, and x-ray microanalysis. RESULTS: All fluorides showed an acidic pH that was not significantly changed after dilution, except Stop, which exhibited a significant pH reduction. All fluorides increased the amount of loosely bound water in the composite matrix. Butler APF gel was the most aggressive for Brilliant DI and Herculite XRV, leading to excessive surface degradation, porosity, destruction of the filler-matrix interface, filler dissolution, and debonding. A reduction in the extent of remaining C = C bonds was observed in Herculite XRV after Butler APF treatment; Phosflur, Gel II, and Prevident had a milder effect. Treatment of Brilliant Dl and Herculite XRV with Omni Gel & Rinse resulted in the formation of a stable precipitation layer rich in barium, phosphorus, tin, oxygen, and fluoride. P-50 was severely affected at the resin-matrix interface after Stop treatment, whereas Omni Gel & Rinse induced fewer surface changes. Heliomolar Ro was the least affected restorative regardless of the type of fluoride used.

Acidulated Phosphate Fluoride↗

PubMed1997

Interaction of calcium hydroxide with zinc oxide-eugenol type sealers: a potential clinical problem.

When a ZnOE type sealer was placed in root canals treated previously with calcium hydroxide dressing, an accelerated sealer setting rate occasionally occurred. This clinical observation led to the present experimental design aiming to investigate the effect of calcium hydroxide on a ZnOE cement and ZnOE type sealers and to preliminarily assess the removal efficiency of a calcium hydroxide preparation from root canal systems. Micro-MIR FTIR spectroscopy was used to quantify the effect of calcium hydroxide on the setting reactions of a ZnOE cement and two ZnOE type sealers. The removal efficiency of calcium hydroxide from root canal systems was evaluated after treatment with NaOCl; NaOCl and filing; and NaOCl plus EDTA and filing. Calcium hydroxide preferentially interacted with eugenol inhibiting the ZnO-eugenol chelate formation. The Ca(OH)2-eugenol interaction was rapid, and kinetically dependent, leading to residual eugenol in the set product. The set ZnOE cement and the ZnOE type sealers in contact with calcium hydroxide were brittle in consistency and granular in structure. Although none of the treatments tested completely removed calcium hydroxide from root canals, treatment with EDTA significantly reduced the extent of residual calcium hydroxide.

Analysis of Variance↗

PubMed1997

Effect of acidic conditioners on dentin morphology, molecular composition and collagen conformation in situ.

OBJECTIVE: The aim of the study was to evaluate the effect of some acidic conditioners on dentin morphology, molecular composition and collagen conformation in situ. METHODS: Smear layer-covered dentin specimens prepared from third molars immediately after extraction were imaged by tapping made AFM and analyzed by MIR-FTIR spectroscopy. The same specimens were subjected to conditioning treatments with CA Agent (Kuraray), Scotchbond Etchant (3M Dental Products) and Scotchbond MP Etchant (3M Dental Products) gels and then imaged and analyzed again. The extent of dentin decalcification at the uppermost 2 microns region was calculated from the percentage reduction in the-PO4/amide I peak area ratio of conditioned specimens relative to their individual smear layer-covered references. These results were compared by ANOVA and Scheffé statistical analyses. The conformational changes of dentin type I collagen at the region were studied qualitatively by deconvoluting the amide I bands of MIR-FTIR spectra and assigning the band components to carbonyl hydrogen bonding states related to the alpha-helix structure. RESULTS: All the conditioners removed the smear layer, funneled the tubules, increased the intertubular roughness and contaminated the dentin surfaces with residues from irreversibly adsorbed thickening agents. Conditioned dentin surfaces showed a reduction in orthophosphates and carbonates and an increase in amide I, II and III groups. CA Agent manifested a significantly lower extent of dentin decalcification than Scotchbond etchants (p < 0.05). Collagen conformational changes involved a decrease in intermolecular hydrogen bonded amide I carbonyls associated with the alpha-helix structure and enhancement of imide carbonyls hydrogen bonded to water, which suggest collagen denaturation. SIGNIFICANCE: Apart from dentin decalcification, the acidic conditioners induced considerable changes on dentin collagen conformation mostly associated with denaturation processes. In addition, irreversibly adsorbed residual thickeners substantially modified the morphology and composition of dentin surfaces. These findings show the complex interaction pathways between conditioners and dentin surfaces and the great potential of modern in situ imaging and analysis techniques in probing these interactions.

Acid Etching, Dental↗

PubMed1996

Chloroform uptake by gutta-percha and assessment of its concentration in air during the chloroform-dip technique.

The use of chloroform as an adjunct to the practice of endodontics has been a matter of debate. In the present study the chloroform uptake of gutta-percha cones was determined by a gravimetric assay for different times of chloroform dip. In conjunction with an assessment of the amount of gutta-percha dissolved during dip, this provided an estimate of the amount of chloroform that patients are exposed to in clinical conditions. An assay was also performed of the chloroform concentration in the air in a dental office. Chloroform uptake was shown to increase with an increasing dipping time. There also seems to be a difference in this uptake between pure chloroform and a chloroform preparation with colophonium. The concentration levels of chloroform evaporated during the practice of chloroform dip within a dental office do not exceed the safety limits.

Air Pollution, Indoor↗

PubMed1996

An FTIR study on the setting mechanism of resin-modified glass ionomer restoratives.

OBJECTIVES: An experimental method was used to assess the glass ionomer and resinous character in three "dual-cure" (Fuji II LC, Photac-Fil, Variglass) and a "triple-cure" (Vitremer) resin-modified glass ionomer restoratives to evaluate their acid-base and free-radical setting mechanisms. METHODS: Four groups (A-D) of three specimens (5 x 4 x 1 mm) were prepared from each material and subjected to the following treatments: A: mixing; B,C: mixing, 60 s irradiation, 20 min dark/dry storage; and D: mixing, 20 min dark/dry storage and then 60 s irradiation. Micro-multiple internal reflectance FTIR spectroscopy was used to determine: 1) the curing efficiency of the products immediately after irradiation; 2) the effect of irradiation 20 min after dark/dry storage on the curing efficiency; and 3) the extent of the acid-base reaction on irradiated and non-irradiated specimens after 20 min dark/dry storage. RESULTS: The curing efficiency immediately after irradiation was determined from the percentage of residual double bonds which ranged from 33-50% for these materials. Irradiation after 20 min dark/dry storage significantly reduced curing efficiency in all the products, except Variglass. The latter showed no acid-base reaction under the conditions of this study. Non-irradiated specimens after the dark storage period demonstrated higher carboxylate yields compared to their irradiated analogues. Non-irradiated specimens from Vitremer had the highest carboxylate yield and a curing efficiency of approximately 50% residual double bonds. SIGNIFICANCE: Photopolymerization seemed to greatly reduce the acid-base reaction during the early setting stages of resin-modified glass ionomer restoratives. The free-radical formation rates are slower than those achieved by chemically initiated polymerization, but they produce adequate conversion and high carboxylate salt yields. This study demonstrated an experimental model for identification and characterization of the acid-base reaction in water-containing resinmodified glass ionomer restoratives.

Acid-Base Equilibrium↗

PubMed1995

Polymerization efficiency of chemically cured and visible light-cured orthodontic adhesives: degree of cure.

The use of light-cured orthodontic adhesives in combination with the new generation of ceramic brackets has become popular from an esthetic standpoint. The purpose of this article was to evaluate the degree of cure (DC) of selected light-cured and chemically cured adhesives bonded to ceramic and stainless steel brackets. The optical properties of eight types of brackets (single-crystal alumina, polycrystalline alumina, polycrystalline allumina with polycarbonate base, and stainless steel) were evaluated by diffuse visible light transmittance spectroscopic analysis. The degree of cure (DC) of a visible light-cured orthodontic adhesive bonded to these brackets under direct (20 seconds through the bracket) and indirect (2 x 10 seconds from the incisal and cervical edges of the bracket) irradiation was measured by micro-MIR FTIR spectroscopy. Brackets bonded to a chemically cured, two-paste orthodontic adhesive were used as a control group. According to the results the single-crystal alumina brackets showed the highest diffuse transmittance values at 468 nm followed by polycrystalline alumina and polycarbonate-base alumina types. Direct irradiation resulted in low DC values that were strongly correlated to the diffuse transmittance measurements at 468 nm (r = 0.73, p < 0.05). Indirect irradiation manifested significantly higher DC values than direct irradiation in the stainless steel bracket group, which yielded values comparable to those found in some indirectly irradiated polycrystalline bracket groups.

Acrylic Resins↗

PubMed1995

Residual monomer leaching from chemically cured and visible light-cured orthodontic adhesives.

The objective of this study was to quantify the amount of residual monomer leached from chemically cured and visible light-cured orthodontic adhesives based on Bis-GMA/TEGDMA monomers, when bonded to ceramic and stainless steel brackets. The residual TEGDMA and Bis-GMA monomer concentrations were determined by high performance liquid chromatographic (HPLC) analysis of the extracts after specimen immersion in ethanol/water solution for 15 days at 37 +/- 1 degree C. According to the results the highest monomer concentrations eluted were obtained from the chemically cured adhesive. Direct (through the bracket) irradiation of stainless steel brackets bonded to the visible light-cured adhesive showed high monomer elution as well. A polycarbonate base ceramic bracket manifested significantly greater amount of monomer release compared with ceramic brackets when combined with the visible light-cured adhesive. Indirect (from the incisal and cervical edges of the bracket) irradiation of the visible light-cured adhesive bonded to the stainless steel brackets resulted in lower residual monomer elution compared to that of directly (through the bracket) irradiated metallic brackets. No statistical difference was found between direct or indirect irradiation of the ceramic brackets tested, with respect to monomer elution from the light-cured adhesive.

Adhesives↗

PubMed1995

Microbial attachment on orthodontic appliances: I. Wettability and early pellicle formation on bracket materials.

The objectives of this study were to investigate the wettability of orthodontic bracket material surfaces and the composition of salivary films adsorbed onto them after 30 and 60 minutes in vivo exposure. Specimens from stainless steel, fiber-reinforced polycarbonate, and polycrystalline alumina bracket manufacturing raw materials were subjected to (a) contact angle measurements with a homologous series of liquids, (b) micro multiple internal reflection Fourier transform infrared spectroscopy (microMIR FTIR) for the characterization of the molecular composition of the in vivo adsorbed groups, and (c) incident light optical microscopy of the acquired films. The highest critical surface tension was obtained from stainless steel (40.8 +/- 0.4 dynes/cm) followed by polycarbonate (32.8 +/- 1.3 dynes/cm) and alumina (29.0 +/- 0.9 dynes/cm), suggesting a higher potential for increased plaque-retaining capacity for the stainless steel brackets. Accordingly, the total work of adhesion and its polar and nonpolar components were consistent with the surface tension ranking. The nonpolar component of the work of adhesion was higher than its polar counterpart for all materials tested, implying a possible higher attachment prevalence for those microorganisms using dispersive forces, such as van der Waals forces, as the predominant attachment mechanism to surfaces. Qualitative and quantitative variations were observed in the adsorbed films after 30 and 60 minutes intraoral exposure that may reflect the influence of the surface properties of these substrates on the structure of the pellicle formed in vivo.

Adhesiveness↗

PubMed1995

Direct light transmittance through ceramic brackets.

The objective of this study was to investigate the degree of direct light transmittance (%T) of various types of esthetic brackets and to correlate these values with their structure, morphologic factors, and composition. Eight types of brackets were used in the study; six brackets of each type were tested. An ultraviolet-visible spectroscopic direct transmission analysis was performed at 320 to 700 nm wavelength range. From each spectrum, the %T corresponded to the peak absorbance wavelength of the photoinitiator of the polymerization was recorded (468 nm). Recorded data were analyzed with one-way analysis of variance and Scheffe's test at alpha = 0.05 significance level. In addition, scanning electron microscope (SEM) images were used to reveal the structure and morphologic factors of the brackets tested. Highest %T values (Mean +/- 1 SD) were obtained from a monocrystal type of bracket (Starfire ["A" Company, San Diego, Calif.] 35.02 +/- 1.59%), followed by a polycrystalline (Fascination [Dentaurum, Pforzhein, Germany] 5.70 +/- 1.41%) and a ceramic/polycarbonate base one (Ceramaflex [TP Orthodontics, Inc., La Porte, Ind.] 4.02 +/- 0.96%). Also other brands presented the following data: Allure (GAC, Central Islip, N.Y.) 3.62 +/- 0.5%; Transcend 2000 (Unitek/3M, Monrovia, Calif.) 2.62 +/- 0.5%; Fascination (edgewise) (Dentaurum, Pforzhein, Germany) 1.97 +/- 0.69%; Lumina (Ormco, Glendora, Calif.) 1.57 +/- 0.5%; Signature (RMO, Denver, Colo.) 1.22 +/- 0.5%. The results showed that the structure, morphologic factors, and composition of the brackets tested were found to affect direct light transmission significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum Oxide↗

PubMed1994

Clinical relevance of the formulation and testing of dentine bonding systems.

The formulation of a dentine bonding system requires several properties which control the performance of the adhesive film. Numerous tests have been introduced for material screening purposes. Understanding the clinical relevance of the formulation principles and laboratory testing pertinence to in vivo conditions are of great importance in order to establish meaningful criteria for product development and evaluation.

Adhesiveness↗

PubMed1994

Surface characterization of ceramic brackets: a multitechnique approach.

The purpose of this study was to investigate the microstructure and bonding mechanisms for four types of ceramic brackets by using information from several methods. Two of the bracket types provided exclusively micromechanical retention as a bonding mechanism, with the use of microspheres or microcrystals to achieve a rough structure for the bracket base. A silane layer that provided chemical adhesion was found to cover the bases of the two other types of brackets; one type also used central regions of increased roughness to provide additional micromechanical retention. Polarized-light optical microscopy showed that the silane layer was not continuous. Small area x-ray photoelectron spectroscopy analysis (SAXPS) of the silane layer was consistent with the presence of gamma-methacryloxypropyl trimethoxysilane. The study of the ceramic bracket bases revealed a wide variety in composition, structure, morphologic condition, and coating treatment that implies different bonding mechanisms to orthodontic adhesives.

Aluminum Oxide↗

PubMed1993

Composition, reactivity and surface interactions of three dental silane primers.

Three commercially available dental silane primers, two single-phase prehydrolyzed and one two-component system were investigated for their composition, extent of hydrolysis, surface interactions, bond strength and interfacial topography when used on three representative porcelain alloys (Au-Pd, high-Pd, Ni-Cr). Five tests, 1H FT-NMR, FTIR, GPC, ESCA and EPMA, were used to determine the composition and the surface interaction profiles. Shear tests were performed to assess the bond strength values. According to the results, all the primers contain gamma-methacryloxypropyltrimethoxysilane (gamma-MPTS) at concentrations of 1.15-18.86 g/100 mL, two in ethanol and one in isopropanol. Traces of acetic acid were found in the prehydrolyzed primers. All the primers demonstrated partial hydrolysis of the methoxy groups. Prehydrolyzed primers exhibited a higher rate of hydrolysis and better orientation of hydrolyzed methoxy groups towards the Ni-Cr alloy surface. Due to the extent of surface oxidation, the Ni-Cr alloy provided more bonding sites for silanols than the other two types of alloys. The Ni-Cr alloy demonstrated the highest shear bond strength values on smooth surfaces regardless of the type of primer used. The results of the present study suggest that active prepolymerized primers may provide significant advantages over two-component systems in the repair of Ni-Cr porcelain fractures involving removal of the metal oxide layer.

Analysis of Variance↗

PubMed1993

In vitro characterization of visible light-cured glass ionomer liners.

The purpose of this study was to characterize the in vitro performance of three visible light-cured glass ionomer liners. The liners containing 2-HEMA showed significantly higher compressive strength, diametral tensile strength and Vickers hardness than the liner without 2-HEMA. Statistically significant differences were found in the optical properties of the materials tested. The liners containing 2-HEMA manifested higher shear strength at liner/composite than at dentin/liner interfaces. The acid-base reaction was significantly delayed after light exposure in all the liners tested. The liner without 2-HEMA presented the greatest maximum gap at the liner/dentin interface. Significant correlations were detected between the optical properties of the liners and the top-bottom differences in the extent of conversion, as well as between the maximum marginal gap at the dentin/liner interface and the bond strength with dentin and composite. These correlations suggest the following areas for further developments: incorporation of low molecular weight polyalkenoic acids or accelerating agents to increase the initial carboxylate yield, increase in total transmittance and reduction in diffuse reflectance to improve the in-depth conversion, and reinforcement of the dentin liner interface to prevent gap formation.

Analysis of Variance↗

PubMed1992

In vivo corrosion behavior of gold-plated versus titanium dental retention pins.

Two types of titanium dental retention pins and a gold-plated stainless steel pin were tested for their in vivo corrosion behavior. Six paired samples of titanium and gold-plated pins were placed in box preparations of 12 periodontally involved premolars. Half of the samples were restored with a high copper admixed type amalgam while the rest were restored with a BisGMA-POCl2 bonding resin and a hybrid visible light-cured composite resin. After 3 months in vivo, the teeth were extracted, and the pins were removed and examined with an electron microprobe. The surface of the titanium pins was found to be smooth and without defects. Only traces of Ca and P could be identified from dentin. The gold-plated pins demonstrated cracks and pores, especially at the outer part of the serrations, resulting in disruption of the electroplated film. Traces of Hg, Sn, Cu, S, Zn, Ca, K, Cl, P, and S were detected at the gold-plated pin/amalgam interface, while Cl and P were found at the gold-plated pin/composite resin interface. The in vivo corrosion resistance of the titanium pins was found to be superior to that of the gold-plated stainless steel pins.

Calcium↗

PubMed1992

Enamel fluoride uptake from an experimental fluoride-releasing orthodontic adhesive.

The purpose of this study was to evaluate quantitatively the fluoride uptake by enamel from an experimental visible light-cured orthodontic adhesive (VP-862) based on YbF3 filler. Sixteen contralateral premolars were extracted from 10 orthodontic patients and were classified in four groups (A, B, C, D) of four buccal surfaces each. Standardized enamel areas located on these surfaces were acid etched and were subjected to the following adhesive treatments: (A) VP-862; (B) Heliosit Orthodontic; (C) Heliobond + VP 862; and (D) Heliobond + Heliosit Orthodontic. Groups B and D were used as a reference. After 9 months in vivo, the teeth were extracted and cross-sectioned, and the enamel-adhesive interfaces were studied by combined wavelength-energy dispersive electron probe microanalysis. According to the results, the cumulative fluoride uptake by enamel from the experimental adhesive was not statistically different from the fluoride detected in the reference groups. No effect of the liquid resin, Heliobond, on the fluoride uptake gradients of enamel could be differentiated.

Acrylates↗

PubMed1991

Bonding of ceramic brackets to enamel: morphologic and structural considerations.

The purpose of this study was to evaluate the form and microstructure of three types of ceramic bracket and to assess their interfacial surface shapes and bond strengths with visible light-cured and chemically cured adhesives after thermocycling. One monocrystalline and two polycrystalline structures were identified. The form of the bonding bases implied three types of bonding with the adhesive: a chemical bonding, a combination of mechanical retention and adhesion, and a combination of micromechanical retention and adhesion. All the ceramic bases were covered with a layer of gamma-methacryloxypropyltrimethoxysilane coupling agent. The thickness of the adhesive layer was affected by the design of the bracket bases. The highest bond strength was obtained from the brackets by a combination of micromechanical retention and adhesion, with the site of failure located at the resin/bracket interface. The other types of ceramic brackets had a greater amount of resin left on the enamel and some cases of cohesive bracket fractures.

Adhesives↗

PubMed1991

Corrosion pattern of silver points in vivo.

The purpose of this study was to examine the electrochemical behavior of silver points in vivo. The apices of silver points removed from teeth with successful or failed endodontic treatments were subjected to complete surface characterization by small-area ESCA, scanning electron microscopy, and electron probe microanalyzer. Cross-sections of the points near the apex were examined with scanning electron microscopy and electron probe microanalyzer to identify the depth of corrosion involvement. According to the results, all silver points manifested evidence of corrosion attack. Electron probe microanalyzer showed no difference in the elemental distribution found on the points. ESCA analysis of the uppermost 5-nm point layer revealed the presence of N on silver points removed from failed treatments. The examination of cross-sections manifested deep S penetration in the bulk of the points removed from failed treatments. Considering the results of this study, no direct association seems to exist between the extent of the corrosion involvement and the prognosis of the treatment. Handling factors and the presence of bacteria are probably the parameters determining the outcome of a treatment.

Corrosion↗