Biomedical subjects

E P Lautenschlager

Publications and source records attributed to E P Lautenschlager.

At least 19 recordsLinked to original sources

PubMed2005

Hot compaction of poly(methyl methacrylate) composites based on fiber shrinkage results.

Uniaxial self-reinforced composite poly(methyl methacrylate) (SRC-PMMA) is being investigated as a pre-coat material for the femoral component of total hip replacements. Hot compaction of self-reinforced composites is largely an empirical process which varies the processing parameters of time, temperature and pressure until the desired properties are obtained. Previous work has shown that PMMA fibers have unique thermal relaxation properties dependent upon the retained molecular orientation in them. This work processed composites at times and temperatures that span the relaxation process for a single fiber. It was found that molecular orientation, as measured by birefringence, was lost in composites processed at times greater than relaxation times for single fibers. Flexural properties were also found to vary with processing conditions, with the highest values of 165 +/- 15 MPa and 168 +/- 3 MPa found at high and low processing times, respectively. These are significantly stronger than unreinforced PMMA which has a flexural strength of 127 +/- 14 MPa. It is hypothesized that diffusion between fibers occurs much more quickly than the loss of molecular orientation and it was seen that SRC-PMMA processing conditions can be predicted from the relaxation times and temperatures from single fibers.

Biocompatible Materials↗

PubMed2001

A system to impose prescribed homogenous strains on cultured cells.

There is presently significant interest in cellular responses to physical forces, and numerous devices have been developed to apply stretch to cultured cells. Many of the early devices were limited by the heterogeneity of deformation of cells in different locations and by the high degree of anisotropy at a particular location. We have therefore developed a system to impose cyclic, large-strain, homogeneous stretch on a multiwell surface-treated silicone elastomer substrate plated with pulmonary epithelial cells. The pneumatically driven mechanism consists of four plates each with a clamp to fix one edge of the cruciform elastomer substrate. Four linear bearings set at predetermined angles between the plates ensure a constant ratio of principal strains throughout the stretch cycle. We present the design of the device and membrane shape, the surface modifications of the membrane to promote cell adhesion, predicted and experimental measurements of the strain field, and new data using cultured airway epithelial cells. We present for the first time the relationship between the magnitude of cyclic mechanical strain and the extent of wound closure and cell spreading.

Algorithms↗

PubMed2000

Surface modification of poly(ethylene terephthalate) angioplasty balloons with a hydrophilic poly(acrylamide-co-ethylene glycol) interpenetrating polymer network coating.

An interpenetrating polymer network (IPN) of poly(acrylamide-co-ethylene glycol) (p(AAm-co-EG)) hydrogel was covalently grafted to polyethylene terephthalate (PET) angioplasty balloons to increase surface hydrophilicity and improve lubricity. A 2-step graft polymerization protocol was followed to first polymerize and cross-link acrylamide onto the substrate with a photosensitizer and/or oxygen plasma pretreatment. The effects of varying photo-initiation and plasma exposure times were investigated separately and conjunctively using water contact angles to obtain optimal coating deposition parameters. A poly(ethylene glycol) network was then grafted by swelling the preexisting polyacrylamide network to allow inter-diffusion of the monomer and cross-linker, which were then polymerized by photo-initiation. When the photo-initiation time was long enough to reach near gelation, pretreatment of PET with oxygen plasma did not offer significant benefit. X-ray photoelectron spectroscopy confirmed the presence of both polymer layers, and composition depth profiles supported the assessment that an interpenetrating network was formed. Tensile testing and application of Weibull statistics on unmodified and modified films indicated that the surface modification approach did not significantly alter the mechanical integrity of the material. These findings indicate that a p(AAm-co-EG) coating can be effectively deposited on PET surfaces without compromising the structural integrity of the substrate.

Acrylic Resins↗

PubMed2000

A theoretical and experimental analysis of polymerization shrinkage of bone cement: A potential major source of porosity.

A theoretical basis for understanding polymerization shrinkage of bone cement is presented based on density changes in converting monomer to polymer. Also, an experimental method, based on dilatometry and the Archimedes' principle is presented for highly precise and accurate measurement of unconstrained volumetric shrinkage of bone cement. Furthermore, a theoretical and experimental analysis of polymerization shrinkage in a constrained deformational state is presented to demonstrate that porosity can develop due to shrinkage. Six bone-cement conditions (Simplex-Ptrade mark vacuum and hand mixed, Endurancetrade mark vacuum mixed, and three two-solution experimental bone cements with higher initial monomer levels) were tested for volumetric shrinkage. It was found that shrinkage varied statistically (p< or = 0.05) from 5.1% (hand-mixed Simplex-Ptrade mark) to 6.7% (vacuum-mixed Simplex-Ptrade mark) to 10.5% for a 0.6:1 (polymer g/monomer mL) two-solution bone cement. Shrinkage was highly correlated with initial monomer content (R(2) = 0.912) but with a lower than theoretically expected rate. This discrepancy was due to the presence of residual monomer after polymerization. Using previously determined residual monomer levels, the theoretic shrinkage analysis was shown to be predictive of the shrinkage results with some residual monomer left after polymerization. Polymerization of a two-solution bone cement in a constrained state resulted in pores developing with volumes predicted by the theory that they are the result of shrinkage. The results of this study show that shrinkage of bone cement under certain constrained conditions may result in the development of porosity at the implant-bone cement interface and elsewhere in the polymerizing cement mantle.

Animals↗

PubMed2000

Mechanical properties of small fragment screws.

For many years, stainless steel small fragment screws have been produced by one manufacturer. Recently, other implant makers have begun offering similar stainless steel screws. In addition, screw geometry and material composition have been modified in an attempt to produce screws for a wide range of clinical situations. This study compared the mechanical properties of several commonly used small fragment screws. Seven sets of screws were tested mechanically, including three brands of geometrically identical standard stainless steel cortical screws and one brand each of cannulated stainless steel cortical screws, titanium cortical screws, stainless steel cancellous screws, and bioabsorbable polylactic acid screws. Screws from each group were tested for pullout strength, torque to failure, and three-point bending to failure. There were no differences in the mechanical properties of the identical 3.5-mm standard stainless steel cortical screws. No difference in pullout strength was found between the five sets of cortical screws. However, the cancellous screws had 4% to 24% less pullout strength. Torsion tests showed that cannulated stainless steel cortical, titanium cortical screws, stainless steel cancellous screws, and polylactic acid screws failed at significantly less torque than did standard stainless steel cortical screws. Standard stainless steel cortical screws had the highest mean yield point and maximal load at failure of all screws in three-point bending. Other metal screws had lower yield strength and maximal load at failure than did the standard stainless steel cortical screws, and polylactic acid screws had the least bending strength.

Biomechanical Phenomena↗

PubMed2000

Effect of rotational speed on the breakage of nickel-titanium rotary files.

Nickel-titanium 0.04-tapered rotary files were evaluated for breakage at different rotational speeds in semicircular bovine bone simulated root canals of identical size and radius for each file size group tested. The bovine bone canals had a radius of curvature of 5 mm and a canal width equivalent to the D1 diameter of the file plus 0.04 mm. Profile instrument #3, #4, and #5 were tested at 150, 250, and 350 rpm. A contra-angle electric handpiece was mounted on an Instron machine that was set to deliver a constant downward speed of 5 mm/min. The electric handpiece and Instron machine were activated until the files broke. The amount of file tip penetration into the semicircular bovine bone canal was measured in degrees with a protractor from a radiographic image taken of the file inside the bone model. Greater degrees of tip penetration indicated greater resistance to breakage. Statistical analysis was done and the results indicated that there was a significant difference for all file sizes in the extent of file tip penetration before breakage. In the rotation range between 150 and 350 rpm the greatest extent of penetration occurred at 150 rpm. This study concluded that 0.04 taper nickel-titanium rotary file breakage is less likely to occur if the files are rotated at lower speeds.

Animals↗

PubMed1999

A novel high-viscosity, two-solution acrylic bone cement: effect of chemical composition on properties.

Solutions of poly(methyl methacrylate) (PMMA) powder predissolved in methyl methacrylate (MMA) have been developed as an alternative to current powder/liquid bone cements. They utilize the same addition polymerization chemistry as commercial cements, but in mixing and delivering via a closed system, porosity is eliminated and the dependence of material properties on the surgical technique is decreased. Twelve different sets of compositions were prepared, with two solutions of constant polymer-to-monomer ratio (80 g of PMMA/100 mL of MMA) and all combinations of four benzoyl peroxide (BPO) initiator levels added to the first solution and three N, N-dimethyl-p-toluidine (DMPT) activator levels added to the second. These compositions were tested, along with Simplex-P bone cement, for effects of BPO and DMPT concentrations on polymerization exotherm, setting time, flexural strength, modulus, and maximum strain. The results show that each of these dependent variables was affected significantly by the individual concentrations of BPO and DMPT and their interactions. The flexural strength, modulus, and polymerization exotherm reached their maximums at about a 1:1 molar ratio of BPO to DMPT. Most compositions had exotherms, setting times, and maximum strains within the range of commercial cements and flexural strengths and moduli up to 54 and 43% higher than Simplex-P, respectively.

Benzoyl Peroxide↗

PubMed1999

Super-EBA as an endodontic apical plug.

Forty extracted human single-rooted teeth were sequentially instrumented with nickel-titanium rotary files to a size 0.36 mm at the working length. Ten teeth were randomly assigned to the two control groups. The other 30 teeth were randomly divided into three groups and were obturated by a 5-mm apical plug of either Super-EBA, IRM, or laterally condensed gutta-percha and Roth's sealer. After 2 days, and at 1 month, the samples were tested for microleakage by the fluid filtration system under 15 psi. The negative controls were used to consider the time that it took the fluid filtration system to stabilize. A one-way analysis of variance showed that, at 1 month post obturation, there was no statistical difference in the ability of the three materials to seal the apex from coronal microleakage. However, at 2 days, Super-EBA gave a significantly better seal than IRM or laterally condensed gutta-percha and sealer.

Analysis of Variance↗

PubMed1999

Corrosion in stainless-steel and nickel-titanium files.

This study evaluated and compared the corrosion susceptibility of stainless-steel and nickel-titanium (NiTi) endodontic files immersed in sodium hypochlorite. For each of the stainless-steel files (Kerr K-Flex, Caulk Flex-O, and Union Broach Flex-R) plus the NiTi files (Union Broach NiTi and Tulsa NiTi), the cutting flutes of 24 ISO size 20 files were immersed into 5.25% sodium hypochlorite. Their open circuit potential (OCP) was recorded for 1 h on a strip chart with high impedance. The strip chart recording for each file was classified into a stability score: (i) stable, (ii) unstable, or (iii) erratic. The OCP was measured by a potentiostat and a standard calomel electrode reference. The OCP classification of unstable and erratic for the files evaluated were as follows: K-Flex (16%), Flex-R (12%), Flex-O (75%), Union Broach NiTi (62%), and Tulsa NiTi (0%). After OCP testing, each of the 120 files was inspected by light microscopy at x 25. The frequencies of visually observed corrosion were detected as follows: K-Flex (2/24), Flex-R (1/24), Flex-O (6/24), Union Broach NiTi (2/24), and Tulsa NiTi (0/24). There was a significant difference in corrosion frequency between brands when evaluated by OCP and light microscopy; however, there was no significant difference between stainless steel and NiTi.

Analysis of Variance↗

PubMed1999

Evaluation of key parameters in a potentiostatic corrosion test for dental amalgam.

OBJECTIVES: Participation in a Round Robin study of potentiostatic corrosion test guidelines for dental amalgam was undertaken for the purpose of developing an accurate set of draft guidelines. METHODS: Dispersalloy, sybraloy, aristalloy, phasealloy, and tytin were used as the amalgam specimens. They were prepared following the guidelines, then coupled to a copper wire, cemented into glass tubes, and polished to a 600-grit finish. A corrosion cell was prepared using a carbon counter-electrode, a standard calomel electrode (SCE) as the reference electrode, and amalgam as the working electrode. A 37 degrees C solution of 10 g/l NaCl with a minimum volume of 300 ml was used. Within 5 min of polishing, the open circuit potential (OCP) was recorded for 10 min. Next, the specimen was polarized to 0 mV versus SCE, and the currents were recorded for a 24-h time period. Corrosion results were analyzed statistically with one-way ANOVA (p < 0.05) and the multiple comparisons Student-Newman-Keuls post-hoc test. RESULTS: Problems that occurred with evaporation, beaker size, carbon electrode length, SCE cap removal, glass tube fracture, polishing technique, and fresh electrolyte are easily avoidable with further explanation or reminder notes. Observations made concerning starting time, initial OCP recording, millivoltage, and solution temperature were determined to be necessary for the accuracy of test results. Analysis of results should include clarification of units, and graph interpretations. Finally, the number of specimens per amalgam should be increased from one to three so that statistical analysis can be performed. Using three specimens per amalgam, the method revealed corrosion susceptibility as measured by the improved test: aristalloy > sybraloy > (dispersalloy, phasealloy, tytin). SIGNIFICANCE: Having run the initially proposed guidelines, a number of clarifying changes were made so that the corrosion susceptibilities of five dental amalgams could be clearly differentiated.

American Dental Association↗

PubMed1999

The effect of processing temperature and time on the structure and fracture characteristics of self-reinforced composite poly(methyl methacrylate).

A novel material, self-reinforced composite poly(methyl methacrylate) (SRC-PMMA) has been previously developed in this laboratory. It consists of high-strength PMMA fibers embedded in a matrix of PMMA derived from the fibers. As a composite material, uniaxial SRC-PMMA has been shown to have greatly improved flexural, tensile, fracture toughness and fatigue properties when compared to unreinforced PMMA. Previous work examined one empirically defined processing condition. This work systematically examines the effect of processing time and temperature on the thermal properties, fracture toughness and fracture morphology of SRC-PMMA produced by a hot compaction method. Differential scanning calorimetry (DSC) shows that composites containing high amounts of retained molecular orientation exhibit both endothermic and exothermic peaks which depend on processing times and temperatures. An exothermic release of energy just above Tg is related to the release of retained molecular orientation in the composites. This release of energy decreases linearly with increasing processing temperature or time for the range investigated. Fracture toughness results show a maximum fracture toughness of 3.18 MPa m1/2 for samples processed for 65 min at 128 degrees C. Optimal structure and fracture toughness are obtained in composites which have maximum interfiber bonding and minimal loss of molecular orientation. Composite fracture mechanisms are highly dependent on processing. Low processing times and temperatures result in more interfiber/matrix fracture, while higher processing times and temperatures result in higher ductility and more transfiber fracture. Excessive processing times result in brittle failure.

Journal Article↗

PubMed1998

Interfacial properties of self-reinforced composite poly(methyl methacrylate).

Total joint prostheses are often fixed in the bone using bone cement. The cement mantle, however, is prone to fatigue fracture that can lead to failure of the mantle, evolution of bone cement particles, and eventual loosening and failure of the prosthesis. A new material, self-reinforced composite poly(methyl methacrylate) (SRC-PMMA) was developed previously by the authors. This material has a similar chemical composition to bone cement, with the matrix and reinforcing fibers both fabricated from PMMA. One potential use for this material is as a precoat for hip prostheses or other stemmed prostheses. This study sought to examine the strength of the bonds that SRC-PMMA forms with simulated prostheses and bone cement. SRC-PMMA was woven about Co-Cr rods and push out tests were performed. Samples were tested in air as processed or after immersion in saline for 30 days at 37 degrees C. Three different weaves were investigated and compared to bone cement. Bone cement and SRC-PMMA formed interfacial bonds with Co-Cr rods that failed at an average load (stress) of 980 N (2.0 MPa). After saline immersion, the bone cement's interfacial bond strength was 642 N (1.23 MPa) and the tight weave SRC-PMMA was statistically stronger at 973 N (1.86 MPa). The shear strength within bone cement alone as measured by push out tests was an order of magnitude higher at 9210 N (15.2 MPa) in air and 9900 N (15.7 MPa) after saline immersion. The bond between SRC-PMMA and bone cement was 10,900 N (17.9 MPa) in air and 9610 N (15.8 MPa) after immersion in saline. Woven SRC-PMMA performed as well or better than bone cement in these push out tests.

Bone Cements↗

PubMed1998

Comparison of four techniques for monitoring the setting kinetics of gypsum.

STATEMENT OF PROBLEM: Setting time of gypsum depends on the method of measurement. PURPOSE: In this study, four methods for ascertaining the setting time of gypsum were compared. MATERIAL AND METHODS: Gypsum setting was evaluated with Gillmore needles, setting expansion, scanning electron microscopy, and x-ray diffraction. Both die stone (Vel-Mix) and fast-setting dental stone (Snap-Stone) were investigated. By using Gillmore needles, both initial set and final set were recorded. Setting expansion was monitored until equilibrium was achieved. For scanning electron microscopy, samples of mixed stone were immersed into liquid nitrogen to stop the reaction. The water was subsequently removed by freeze-drying. Samples were then examined in a scanning electron microscope. For x-ray diffraction, the percentages of dihydrate and hemihydrate crystals were monitored every 1.5 minutes. RESULTS: Setting times for the fast-setting type III stone and for the regular-setting type IV stone were approximately 3 and 10 minutes, respectively, with the Gillmore needle indentation tests; 10 and 20 minutes with scanning electron microscopy; and 20 and 60 minutes with x-ray diffraction. CONCLUSION: Scanning electron microscopy, setting expansion, and x-ray diffraction indicated changes that occurred at times after a clinically relevant set was obtained in the gypsum setting reaction.

Calcium Sulfate↗

PubMed1998

Risk assessment of the toxicity of solvents of gutta-percha used in endodontic retreatment.

Three randomly assigned groups of single-canaled extracted teeth obturated with gutta-percha were retreated using controlled application of one of three organic solvents: chloroform, xylene, or halothane. Two additional groups of teeth served as positive and negative controls. Residual volume of solvent expressed through the apical foramen during retreatment was determined by the difference of pretreatment and posttreatment weights of hermetically sealed receptacles attached to the root surface of the teeth. Results indicate that the amount of solvent that has been determined to have leached out through the apical foramen is several orders of magnitude below the permissible toxic dose. Thus, it is proposed that the use of any of the aforementioned solvents used in the retreatment of root canals would pose negligible risk to the patient.

Chloroform↗

PubMed1998

Intraorifice sealing of gutta-percha obturated root canals to prevent coronal microleakage.

A study was conducted to evaluate Cavit, Intermediate Restorative Material, and Super-EBA as intraorifice filling materials to prevent coronal microleakage. Root canal instrumentation and obturation was done on 74 extracted single-rooted teeth. Three and one-half millimeters of the gutta-percha was removed from the coronal aspect of the root canal and replaced with one of the three filling materials. The teeth were suspended in scintillation vials containing trypticase soy broth, and human saliva was added to the pulp chambers. Microbial penetration was detected as an increase in turbidity of the broth corresponding to bacterial growth. At the end of 90 days, the results showed that 15% of the Cavit-filled orifices leaked, whereas 35% of the Intermediate Restorative Material and Super-EBA-filled orifices leaked. The gutta-percha obturated root canals that received an intraorifice filling material leaked significantly less than the obturated, unsealed control group--all of which leaked in < 49 days.

Calcium Sulfate↗

PubMed1998

Microleakage of endodontically treated teeth restored with posts.

A fluid filtration system using 15 psi of pressure on the penetrating fluid was used to quantify the amount of microleakage of a stainless-steel post and a carbon-fiber post system, each placed with various cements. Statistical analysis showed that there was a significant difference in microleakage between the cements (p < 0.001). Zinc phosphate cement showed the most microleakage, whereas C & B Metabond cement showed the least. There was no significant difference in microleakage between the stainless-steel and carbon-fiber posts. The results of this study showed that both posts, when cemented with dentin-bonding resin cements (C & B Metabond and Panavia-21), exhibited less microleakage than when cemented with non-dentin-bonding cements (glass ionomer and zinc phosphate).

Analysis of Variance↗

PubMed1997

Bending and fracture toughness of woven self-reinforced composite poly(methyl methacrylate).

Loosening remains an impediment to the long-term success of total hip replacements despite numerous improvements in the materials used. In cemented prostheses, fatigue and fracture of bone cement have been implicated in the failure of these devices. A new material, self-reinforced composite poly(methyl methacrylate). (SRC-PMMA), has been developed. SRC-PMMA is formed by a novel processing method that will be described. The composite consists of high strength, highly oriented PMMA fibers embedded in a matrix of PMMA. Using a woven form of SRC-PMMA, an in vitro physical and mechanical evaluation was performed to assess the feasibility of its use in an orthopedic prosthesis. Three different weaves of SRC-PMMA were evaluated in bending and fracture toughness in air, after immersion for 30 days in 37 degrees C saline, and after gamma irradiation followed by immersion. Bending modulus and strength were decreased by gamma irradiation followed by saline immersion. The effect of saline immersion alone on bending strength and modulus was negligible. Saline immersion and gamma irradiation followed by saline immersion was shown to have little or no effect on the fracture toughness of woven SRC-PMMA. Differences in the fracture processes of the different weaves were found and can be related to the differing orientation of fibers to the fracture toughness pre-crack. Optimally incorporated SRC-PMMA absorbs the same amount of water as bone cement. Comparison to previous and current work with bone cement controls shows that SRC-PMMA is a material equal to or better than bone cement in all tests performed. It deserves further consideration as a candidate biomaterial.

Adsorption↗

PubMed1997

Comparison of chemical analysis of residual monomer in a chemical-cured dental acrylic material to an FTIR method.

OBJECTIVE: The purpose of this work was to perform quantitative analysis of residual monomer in chemical-cured acrylic using an infrared spectroscopic method and to compare it to an accepted form of quantitative chemical analysis. Identical samples of acrylic were analyzed and compared using Fourier transform infrared (FTIR) spectroscopy with multiple standard additions vs. "wet" chemical analysis of bromination followed by titration. METHODS: Two 6 g disks from a single mix of cold-cured acrylic (Lang Dental Mfg. Co., Inc.) were prepared and cured in room air for 1 hr using a ratio of 12 g of powder to 8 mL of liquid. One of the cold-cured acrylic disks was dissolved in glacial acetic acid and analyzed according to the "wet" technique described by Smith and Bains (Smith and Bains, 1956). The other disk was dissolved in methyl isobutyrate (MIBT). Five aliquots, zero plus four incremental additions of pure methyl methacrylate (MMA), were prepared from the MIBT solution. Absorption spectra were collected for all five aliquots. The data were plotted with the ratio of the mass of methyl methacrylate added to the mass of aliquot of MIBT solution as the independent variable, and the absorption, corrected for dilution, as the dependent variable. Least squares fit of the data yielded the slope and intercept. The ratio of intercept to slope divided by the weight fraction of the acrylic disk dissolved in MIBT yielded the concentration of methyl methacrylate in the disk. RESULTS: The plot of absorbance as a function of mass ratio of MMA added to MIBT solution was linear over the concentration range covered (r = 0.999). Analysis of the spectroscopic data revealed a concentration of residual C = C double bonds of 0.32 +/- 0.01 mol/kg. "Wet" chemical analysis of the acrylic yielded a concentration of residual C = C double bonds of 0.288 +/- 0.003 mol/kg. There was significant difference (students t-test, 99% confidence level) between the two techniques with respect to the amount of residual monomer calculated. SIGNIFICANCE: The multiple standard additions technique works well for the quantitative analysis of small amounts of residual double bonds in the poly(methyl methacrylate) chemical-cured acrylic polymer system, eliminating the need for an internal standard or external calibration.

Absorption↗