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Biomedical subjects

E H Greener

Publications and source records attributed to E H Greener.

At least 19 recordsLinked to original sources
PubMed1998

The effect of noble metals on the mechanical properties of dispersed phase dental amalgam.

The effects of noble metals added as part of a Ag-Cu dispersant on the compressive strength and creep of dental amalgams was determined. The Ag-Cu eutectic used in high copper dispersant alloy L(0), was altered by adding 15 per cent by weight (wt%) of noble metal in place of Ag. In L(1) the noble metal was Pd. In L(2), Au and Pd were combined in equal proportions. In L(3), the noble metal content was Pd and Pt in equal proportions. A low copper lathe-cut amalgam, Aristalloy was used as the matrix. Amalgams S(0) and S(1) had the same composition as L(0) and L(1) except that the the low copper alloy matrix was Spheralloy, a low copper spherical amalgam. The compressive strength and creep were measured according to American Dental Association specification No. 1 and the results analysed by ANOVA. The addition of noble metals to the dispersant significantly lowered the 1-h compressive strength of amalgams. Compared to the control amalgam L(0), the 24-h compressive strength was increased for L(1) and L(2) but lowered for L(3). The ADA creep values were significantly lowered by addition of all combinations of noble metals. Reported microstructural changes such as an increase in unreacted particles, and a slowed setting reaction may account for the findings.

Compressive Strength↗
PubMed1996

Laser acoustic emission thermal technique (LAETT): a technique for generating acoustic emission in dental composites.

OBJECTIVES: This study was designed to investigate a new method for generating interfacial debonding between the resin matrix and filler particles of dental composites. METHODS: A pilot study was conducted to evaluate laser-induced acoustic emission in dental resins filled with varying quantities of particles. Model systems of 50/50 BisGMA/TEGDMA resin reinforced with 0, 25, and 75 wt% 5-10 micrometers silanated BaSiO(6) were analyzed. The sample size was 3.5 mm diameter x 0.25-0.28 mm thick. A continuous wave CO2 laser (Synrad Infrared Gas Laser Model 48-1) was used to heat the composite samples. Acoustic events were detected, recorded and processed by a model 4610 Smart Acoustic Monitor (SAM) with a 1220A preamp (Physical Acoustic Corp.) as a function of laser power. RESULTS: Initially, the acoustic signal from the model composites produced a burst pattern characteristic of fracturing, about 3.7 watts laser power. Acoustic emission increased with laser power up to about 6 watts. At laser powers above 6 watts, the acoustic emission remained constant. The amount of acoustic emission followed the trend: unfilled resin > composite with 25 wt% BaSiO(6) > composite with 75 wt% BaSiO(6). SIGNIFICANCE: Acoustic emission generated by laser thermal heating is dependent on the weight percent of filler particles in the composite and the amount of laser power. For this reason, laser thermal acoustic emission might be useful as a nondestructive form of analysis of dental composites.

Analysis of Variance↗
PubMed1996

Effects of food/oral simulating fluids on microstructure and strength of dentine bonding agents.

This study evaluated the effect a food simulating solution, 75% v/v ethanol/water, and an artificial saliva, Moi-Stir, have on the microstructure and on the diametral tensile strength (DTS) of three dentine bonding agents (Tenure, Scotchbond Multi-Purpose and Optibond). The microstructure was examined by using a scanning electron microscope (SEM). The DTS data were analysed using ANOVA and the Tukey LSD test. The microstructural observations were compared with changes in DTS. The SEM observation revealed deterioration of all bonding agents due to conditioning in the solutions for 30 days. The different solutions appeared to cause different reactions in the bonding agents. However, these effects may be exaggerated due to the presence of an air-inhibited surface layer. Those conditioned in Moi-Stir showed swelling. The presence of filler particles in the Optibond bonding agent appears to decrease the deterioration resulting from soaking. Materials conditioned in ethanol exhibited both dissolution and thinning. Diametral samples of each bonding material were tested after being conditioned in the above-mentioned solutions for 1, 7, 14 and 30 days. Conditioning significantly decreased the DTS of all bonding agents, except Optibond in Moi-Stir. Filled Optibond maintained its DTS longer than did the two unfilled bonding agents. The decrease in DTS of all the ethanol-conditioned groups is a function of the square root of time (P < 0.001) and conforms to Fick's laws of diffusion. The filled Optibond showed a lower ethanol diffusivity (0.5 x 10(-5) cm2 s-1) than the other two unfilled bonding agent systems (average 1.2 x 10(-5) cm2 s-1) (P < 0.05). The high ethanol diffusivities were thought to be due to the presence of HEMA, a hydrophilic resin, in the bonding agent. These results also suggest that solution uptake occurred through the resin matrix. Filler particles may therefore play an important role in weathering resistance of these materials to oral environment solutions. The physical appearance and strength of dentine bonding agents are significantly altered by exposure to oral environment solutions.

Absorption↗
PubMed1996

An accurate and simple method for the measurement of dental composite wear.

This study describes a relatively simple mechanical technique for measuring occlusal wear at the margin of dental restorations. The device was essentially a custom profilometer which consisted of a linear variable differential transformer with its core supported by double cantilever springs, a specially shaped stylus, a motor driven microscopic stage, custom computer software utilizing a colour coding to separate differences in slope, and a cross-hair-shaped mouse cursor to differentiate the boundary of wear. Two sets of visual standard stone casts were evaluated. The first set consisted of 17 stone replicas of machined steel dies and the second set consisted of five clinical casts, which have been used to measure the wear of composite restorations by direct vision. The reproducibility found when measuring the stone replicas of the machined steel dies was 2 microns, while, for the clinical standards, it was 16 microns.

Calcium Sulfate↗
PubMed1996

Visual versus mechanical wear measurement of dental composite resin.

This study compares a visual method for measuring composite wear with a relatively inexpensive mechanical technique. The visual measurements used a set of 17 graduated stone standards as the reference. Two sets of 10 unknown casts were evaluated. The first was a set of 10 stone replicas selected from the reference set in the range of 25-250 microns. The second set was composed of 10 casts of clinical restorations. The mechanical test employed a computer-controlled custom profilometer. Depth was recorded at 50 equidistant positions around the margin. A significant correlation was found (r > 0.98) between the visual and mechanical means for both measurement techniques. Mean values were equivalent for the standard casts. However, visual estimation of the clinical casts were significantly lower (61% of mechanical values) and thus not accurate for clinical use.

Analysis of Variance↗
PubMed1995

Detection of leached moieties from dental composites in fluids simulating food and saliva.

OBJECTIVES: The purpose of this study was to analyze the IR spectra of a liquid simulating food and an artificial saliva following exposure to resin composites. METHODS: Fourier transform infrared (FTIR) spectroscopy was used to analyze two solutions in which three commercially available dental composites (Marathon One, Den-Mat Co.; Z100, 3M Co.; Herculite XRV, Kerr Co.) were stored. The solutions used were: a food simulating fluid, 75 vol% ethanol/water, and an artificial saliva, Moi-Stir (Kingwood Labs., Inc.). Specimens (4.3 mm diam. X 2 mm thick) of the three resin composites were stored at 37 degrees C in 60 mL of either Moi-Stir or the 75% ethanol solution for 7, 14, and 30 d. The FTIR spectra were obtained using a liquid sample ATR (attenuated total reflection) cell. RESULTS: No obvious leachable materials were seen from any of the composite specimens stored in artificial saliva up to 30 d of immersion. For the composites stored in ethanol, the observed spectra revealed increases in the principal absorption bands for the components of the three composite systems. Methacrylate skeletal vibrations (1015-815 cm(-1)) and -CH3 alkane, C-H asymmetrical deformation vibrations (1520-1460 cm(-1)) appeared after 14 d of storage. A very strong peak characteristic of the aliphatic C=C moiety (1640 cm(-1)) and carbonyl C=O (1730 cm(-1)) occurred after 14 d. The peak heights of these two functional bands increased as a function of time and after 30 d of storage were approximately 5-7 times those produced after 7 d. Irregular O-H bands (3500-3300 cm(-1)) were also observed after 30 d in ethanol. SIGNIFICANCE: Irreversible processes such as the leaching of components occurs in the presence of ethanol. This phenomenon may contribute to irreversible material degradation.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1995

Effect of food and oral simulating fluids on structure of adhesive composite systems.

This work evaluates the degradation of three adhesive/composite systems (Tenure/Marathon One. Scotchbond Multi-Purpose/Z100 and Optibond/Herculite XRV) upon immersion in 75% ethanol solution and in an artificial saliva (Moi-Stir). Shear bond strength (SBS) and diametral tensile strength (DTS) specimens were employed for this study. For the SBS specimens, the bonded interface and composite were exposed to food and oral simulating fluids at 37 degrees C for up to 30 days. A similar control series was stored in air. DTS specimens were stored in 75% ethanol at 37 degrees C for up to 30 days. The SBS specimens were sheared to failure. Small quantities of bonding resin were removed from the tooth side of the fractured surface and from the non-fractured fractured end of the composite for Fourier transform infrared microscopic evaluation. Similar scrapings were taken from DTS specimen surfaces. The infrared absorbance intensity (AI) of the major peaks was measured as a function of storage time and ratioed against the aromatic C = C (1609.4 cm-1) peak. The data were analysed using ANOVA and the Tukey LSD test. The AI of major peaks was similar for the materials stored either in air or in Moi-Stir for all testing periods. Storage in ethanol caused the AI of aliphatic C = C (1638 cm-1) and of O-H (approximately 3500 cm-1) bonds to significantly decrease (30-50%) for specimens of bonding resin while the AI of C = O bonds (1730 cm-1) increased (60-120%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adhesives↗
PubMed1995

A study of the apical microleakage of a gallium alloy as a retrograde filling material.

The feasibility of utilizing mercury-free Gallium alloy GF for retrograde filling was investigated by comparing apical microleakage in 184 extracted human teeth. The teeth were divided into four experimental and two control groups. Three experimental groups were apical cavity retrofillings with the Gallium alloy GF, a mercury-containing amalgam, and a glass ionomer. The fourth experimental group was filled with gutta-percha and heat-burnished after apicoectomy. After 24 h, 1 wk, 4 wk, and 12 wk immersion in dye solution, the roots were vertically sectioned, and the deepest point of dye penetration was recorded. The glass ionomer showed the least leakage, followed by the amalgam group and the gallium group (no significant difference). The gutta-percha heat-burnished group displayed the greatest leakage. Gallium alloy GF was shown to have an equivalent sealing potential to dental amalgam for a retrograde filling material.

Analysis of Variance↗
PubMed1995

The effect of matrix phase morphology on the structure of Ag-Cu-Pd dispersed phase dental amalgam.

The effect of an Ag-Cu-Pd dispersant alloy on the structure of amalgams fabricated with two different particle types of low-copper amalgam matrices was investigated. In amalgams L and L (0), a low-copper lathe-cut amalgam Aristalloy was used as the matrix. In amalgams S and S(0), the matrix used was Spheralloy, a low-copper spherical amalgam. X-ray diffraction was used to analyse the relative content of the phases in the amalgams. The presence of Pd in the dispersant of amalgams L and S resulted in a decrease in the amount of eta' (Cu6Sn5) and an increase in the amount of unreacted particles when compared to the controls L(0) and S(0). Amalgams fabricated with a spherical alloy matrix (S and S(0)) showed a greater effect than amalgams fabricated with a lathe-cut matrix alloy (L and L(0)).

Chemical Phenomena↗
PubMed1994

Effect of photoinitiator on degree of conversion of unfilled light-cured resin.

In general, the concentrations of photosensitizer and reducing agent in light-cured dental polymers are fixed by manufacturers for a specific product. These concentrations vary from product to product and the effect of photoinitiator concentration on the final network structures is not clear. Accordingly, the influence of varying concentrations of camphorquinone (CQ) and amine reducing agent, 2-(N, N-dimethylamino)ethyl methacrylate (DMAEMA), on the degree of conversion (DC) of an unfilled light-cured resin was investigated. The resin consisted of 50 wt% triethyleneglycol dimethacrylate (TEGDMA) and 50 wt% 1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4-trimeth ylhexane (UDMA) activated with varying concentrations of CQ (0.25-5 mol.%) and DMAEMA (0.125-5 mol.%). At low CQ concentrations, the DC measured by a Fourier Transform Infrared (FTIR) spectrometer increased rapidly with increasing concentration of DMAEMA and reached a plateau. At CQ concentrations of 0.5 mol.% and above, the plateau DC values were approximately 75-77%. On the basis of the systematic variations of CQ and DMAEMA, a contour representing the optimal combination of photoinitiator concentration from the standpoint of DC was established.

Analysis of Variance↗
PubMed1994

Effect of food and oral simulating fluids on dentine bond and composite strength.

The effect of up to 30 days' immersion in 75% ethanol solution and in an artificial saliva (Moi-Stir) on the dentine shear bond strength (SBS) of three adhesive/composite systems (Tenure/Marathon One, Scotchbond Multi-Purpose/Z100 and Optibond/Herculite XRV) was evaluated. Two control series were stored either in 100% humidity or in air. Diametral tensile specimens (DTS) of the composites studied were stored in 75% ethanol for up to 30 days. The fracture mode and morphology of the failure interface were examined by scanning electron microscopy (SEM). Data were analysed using ANOVA and the Tukey LSD test. The SBS for all systems stored in Moi-Stir (24.8 +/- 3.0 MPa) and air (28.3 +/- 3.0 MPa) was not influenced by length of storage. Microscopic (SEM) examination of the debonded air, and Moi-Stir stored specimens showed that failure had primarily occurred through the dentine. Significant decreases (30-50%) in the SBS of all systems occurred after immersion in 75% ethanol. There was no significant difference among brands. The DTS of the composites showed significant decreases as a function of ethanol exposure. Marathon One and Herculite XRV showed significantly lower DTS after 14 days' storage while Z100 showed no reduction in DTS until after 30 days. The decrease in both SBS and DTS after storage in ethanol was a function of the square root of time (P < 0.001) and followed Fick's laws of diffusion. Ethanol diffusivity was approximated as 1.8 x 10(-6) cm2 s-1 for both SBS and DTS specimens, suggesting that alcohol attack in SBS specimens occurred primarily in the composite system.(ABSTRACT TRUNCATED AT 250 WORDS)

Composite Resins↗
PubMed1994

Effects of coupling agents on mechanical properties of metal oxide-polymethacrylate composites.

The effects of several coupling agents on the mechanical properties of metal oxide-polymethacrylate composites reinforced with titanium dioxide (TiO2), aluminium oxide (Al2O3), silica (SiO2) and zirconium dioxide (ZrO2), as fillers for opaque resins were assessed. The prepared composites consist of 24.75 wt% triethyleneglycol dimethacrylate (TEGDMA), 24.75 wt% 1,6-bis(methacryloxy-2- ethoxycarbonylamino)-2,4,4-trimethylhexane (UDMA), 0.5 wt% benzoyl peroxide (BPO) and 50 wt% metal oxide filler. Three methacrylate coupling agents--methoxydiethyleneglycol trimethacryloyl titanate, 3-trimethoxysilylpropyl methacrylate and 2,2-di(allyloxymethyl)butyl trimethacryloyl zirconate--were used for surface treatment of TiO2, SiO2 and ZrO2, respectively, while Al2O3 was treated with 4-methacryloxyethyl trimellitate anhydride (4-META). 4-META was also adopted as a coupler for TiO2, SiO2 and ZrO2 powders. Compressive and transverse strength specimens were prepared with the use of coupled or untreated filler and heat cured at 110 degrees C and 0.5 MPa for 30 min. All coupled metal oxide composites had significantly higher compressive and transverse strengths than did untreated composites after 1 month's immersion in 37 degrees C water. Scanning electron microscopy (SEM) of fractured TiO2 composite surfaces after storage in water for 1 month showed an interface failure between TiO2 filler and matrix resin for untreated TiO2 composite and cohesive failures within the resin for treated specimen. Similar results were observed with silanated SiO2 composite. However, cohesive and interface failures were seen in zirconated ZrO2- and 4-META-coupled Al2O3 composites. Thus, titanated TiO2-polymethacrylate composite may be useful as a composite pigment for opaque resin materials.

Analysis of Variance↗
PubMed1994

Effect of excitation energy on dentine bond strength and composite properties.

A number of available dentine adhesives and dental composites require light activation for polymerization. There are many variables which affect the light absorbing properties (e.g. bond strength) of these materials. The purpose of this study was to determine the influence of excitation energy (EE) on the dentine shear bond strength (SBS) of two lengths (2.1 mm and 3.25 mm) of light-cured (or dual-cured) dentine adhesives/dental composites. Diametral tensile (DTS) and compressive (CS) strengths of the same composites were also studied as a function of EE. Three resin composites with their respective adhesives (Marathon One/Tenure, Z100/Scotchbond Multi-Purpose and Herculite XRV/Optibond) were used. Five commercial curing lights were used to produce spectra of 100-650 mW cm-2. The data were analysed using ANOVA and the Tukey LSD test. No significant correlation was observed at the P > 0.05 level between EE and SBS in the shorter specimens. The SBS of Optibond is independent of EE and composite length. The SBS data were also analysed with Weibull statistics. The characteristic strengths calculated varied between 14 and 27 MPa. For the composites tested, mean values of DTS varied between 33 and 54 MPa and CS varied between 167 and 414 MPa. The DTS and CS of Z100 were significantly greater than those of the other materials. Intensities > or = 250 mW cm-2 produced equivalent mechanical properties within all composite materials and equivalent bond strengths in systems which included dentine, adhesive and composite resin.

Absorption↗
PubMed1993

Effects of two amine reducing agents on the degree of conversion and physical properties of an unfilled light-cured resin.

The influence of varying concentrations of two amine reducing agents commonly used in commercial light-cured composites, N,N-dimethyl-p-toluidine (DMPT) and 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA), on the degree of conversion (DC), Knoop hardness, and compressive and transverse strengths of an unfilled light-cured resin was investigated. The DC obtained from employing two different internal standard peaks, carbonyl (C=O) at 1730 cm-1 and urethane (N-H) at 3350 cm-1, was compared. The resin consisted of 50 wt% triethyleneglycol dimethacrylate (TEGDMA) and 50 wt% 1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4-trimeth ylhexane (UDMA) activated with 0.5 mol% camphorquinone (CQ) and varying concentrations of either DMPT or DMAEMA. The DC calculated by use of either C=O or N-H absorption peak as an internal reference showed similar values. For both amines, the physical properties were directly related to DC and appeared to reach maximal values at an amine/CQ molar ratio of 4.0. The DC, however, appeared to reach a maximum at an amine/CQ molar ratio of 3.0. Generally, for the same amine/CQ molar ratios, the polymers formulated with DMAEMA, had greater DCs and better physical properties than those formulated with DMPT.

Amines↗
PubMed1993

Radiometric and spectroradiometric comparison of power outputs of five visible light-curing units.

The spectral distributions of the radiation emitted by five visible range curing lights were measured spectroradiometrically. The light intensities in specific wavelength bands were evaluated by graphical integration. The results were then compared with the instantaneous readings of power density of all of the units as measured with a commercial curing radiometer. The data obtained by both techniques correlated well at narrower specific wavelengths (450-500 nm), which are assumed to be more effective for photopolymerization. This finding indicates that curing radiometer is sensitive to the desired wavelengths and may be an effective tool to quickly characterize the curing efficiency of dental photocuring sources in a clinical setting.

Absorption↗
PubMed1993

Shear bond strengths of two luting cements to laboratory-cured prosthetic resin composite.

This study evaluated the effect of four types of surface preparations for laboratory-cured prosthetic resin composite on the shear bond strengths of glass ionomer and resin luting cements. Two sizes of light-cured resin composite disks were treated and cemented with two types of luting cements. The specimens were stored in 37 degrees C water for up to 16 weeks before shear mode testing at a crosshead speed of 0.5mm/min in an Instron. The application of dichloromethane and an unfilled bonding resin was an effective surface treatment which improved the shear bond strength of glass ionomer cement to resin composite compared with no-treatment. However, the resin composite, treated with dichloromethane and then coated with bonding resin containing a silane coupler, followed by cementation with resin cement, consistently yielded the strongest shear bond strength with cohesive failures occurring within the resin composite for all specimens.

Analysis of Variance↗