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PubMed2002

Influence of polymerization conditions on monomer elution and microhardness of autopolymerized polymethyl methacrylate resin.

Residual monomer contents and surface hardness are important factors in determining the serviceability of provisional restorations. The intent of this study was to systemically evaluate the effects of curing conditions on provisional polymethyl methacrylate (PMMA) resins which utilize a free-radical polymerization reaction. Combinations of the three curing factors of temperature, pressure, curing environment (water/air) were adjusted during the fabrication of autopolymerized specimen disks. The initial hardness of tested materials was measured with a microhardness tester 1 h after disc fabrication, and the amounts of residual methyl methacrylate (MMA) released into water were analyzed by reverse-phase HPLC after 7 d of water immersion. Results from multiple regressions showed that curing temperature was the dominant factor in improving resin surface hardness, whereas curing in water was the key factor for reducing the quantity of residual monomer. The pressure factor, which was thought to be critical for managing autopolymerized resins, showed no significant influences on the properties tested. ANOVA results showed that provisional PMMA resins cured in hot water, with or without pressure, significantly reduced the amount of residual MMA elution (up to 80%) and increased the microhardness values (up to 50%).

Acrylic Resins↗

PubMed2000

Evaluation of calcium phosphates and experimental calcium phosphate bone cements using osteogenic cultures.

In this study, rat bone marrow cells (RBM) were used to evaluate two biodegradable calcium phosphate bone cements and bioactive calcium phosphate ceramics. The substances investigated were: two novel calcium phosphate cements, Biocement F and Biocement H, tricalcium phosphate (TCP), surface-modified alpha-tricalcium phosphate [TCP (s)] and a rapid resorbable calcium phosphate ceramic consisting of CaKPO(4) (sample code R5). RBM cells were cultured on disc-shaped test substrates for 14 days. The culture medium was changed daily and also examined for calcium, phosphate, and potassium concentrations. Specimens were evaluated using light microscopy, and morphometry of the cell-covered substrate surface, scanning electron microscopy, and energy dispersive X-ray analysis and morphometry of the cell-covered substrate surface. Areas of mineralization were identified by tetracyline labeling. Except for R 5, rat bone-marrow cells attached and grew on all substrate surfaces. Of the different calcium phosphate materials tested, TCP and TCP (s) facilitated osteoblast growth and extracellular matrix elaboration to the highest degree, followed by Biocements H and F. The inhibition of cell growth encountered with R 5 seems to be related to its high phosphate and potassium ion release.

Absorbable Implants↗

PubMed2002

Holding power of bioabsorbable ciprofloxacin-containing self-reinforced poly-L/DL-lactide 70/30 bioactive glass 13 miniscrews in human cadaver bone.

Antibiotics-plus bioactive glass-containing bioabsorbable self-reinforced (SR) polylactide screws have been developed for antibacterial osteoconductive bone fixation. The aim of the present study was to test the pullout properties of these recently developed miniscrews. Ciprofloxacin-plus bioactive glass-containing SR-polylactide miniscrews (BC) were compared with miniscrews made of neat SR-polylactide (A), SR-polylactide with bioactive glass (B), and ciprofloxacin-containing SR-polylactide (C). BC miniscrews and their controls (A, B, C) (all of length 6.0 mm, core diameter 1.45 mm, thread diameter 2.0 mm) were applied to one pair of cadaveric fibulae. Pullout force was measured using a materials testing machine. We carried out 49-50 pullout tests for each implant type. The Mann-Whitney test and Student's t-test were used for statistical evaluation. The pullout force for BC miniscrews was 114.9 +/- 34.0 (SD) N. Pullout forces for control miniscrews were 162.7 +/- 37.8 N (A), 99.1 +/- 16.2 N (B), and 142.9 +/- 26.9 N (C). Differences between the four groups were statistically significant (p < 0.001). Ciprofloxacin-plus bioactive glass-containing polylactide miniscrews have good holding power to human cadaver fibulae. However, adding bioactive glass and ciprofloxacin components to neat SR-polylactide results in lower pullout values.

Absorbable Implants↗

PubMed2001

Surface and biological evaluation of hydroxyapatite-based coatings on titanium deposited by different techniques.

Hydroxyapatite coatings have been deposited on titanium cp by plasma spray, sol-gel, and sputtering techniques for dental implant applications. The latter two techniques are of current interest, as they allow coatings of micrometer dimensions to be deposited. Coating morphology, composition, and structure have been investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). All coatings were homogeneous and exhibited a rough morphology suitable for implant applications. The sputtered (after annealing), plasma spray, and sol-gel coatings all showed diffraction peaks corresponding to hydroxyapatite. The surface contaminants were observed to be different for the different coating types. The sputtered coatings were found to have a composition most similar to hydroxyapatite; the sol-gel deposits also showed a high concentration of hydroxyl ions. A discrepancy in the Ca/P ratio was observed for the plasma spray coatings, and a small concentration of carbonate ions was found in the sputter-deposited coatings. The in vitro cell-culture studies using MG63 osteoblast-like cells demonstrated the ability of cells to proliferate on the materials tested. The sol-gel coating promotes higher cell growth, greater alkaline phosphatase activity, and greater osteocalcin production compared to the sputtered and plasma-sprayed coatings.

Alkaline Phosphatase↗

PubMed1995

Color changes in dry-pigmented maxillofacial elastomer resulting from ultraviolet light exposure.

Five dry pigments and one maxillofacial elastomer were evaluated for color changes (delta E) resulting from prolonged exposure to two types of ultraviolet light. The elastomer, pigments, and pigmented elastomers were subjected to each ultraviolet light source for 400, 600, and 1800 hours, and delta E color shifts were determined. The unpigmented elastomer underwent minimally perceptible color change after 600 hours of exposure to both types of ultraviolet light. Two pigments underwent substantial color change after 400 hours, whereas the remaining three pigments remained color stable after 1800 hours. It was concluded that for the materials tested, early color changes in a prosthesis may be the result of degradation of certain ultraviolet light-susceptible pigments, whereas longer term color shifts may be caused by color changes within the elastomer.

Analysis of Variance↗

PubMed1991

Microleakage in composite resin restorations.

The aim of the present study was to evaluate the marginal microleakage of the newest generation of composite resin restorative materials. Class V restorations were prepared in human extracted teeth. Different combinations of restorative materials were used. All the materials tested showed marginal microleakage along the dentinal walls, suggesting that the adhesion value is not sufficient to counteract the composite shrinkage and to reduce the marginal space.

Adult↗

PubMedDate not supplied

Biological induced corrosion of materials II: new test methods and experiences from MIR station.

During previous long-term manned missions, more than 100 species of microorganisms have been identified on surfaces of materials (bacteria and fungi). Among them were potentially pathogenic ones (saprophytes) which are capable of active growth on artificial substrates, as well as technophilic bacteria and fungi causing damages (destruction and degradation) to various materials (metals and polymers), resulting in failures and disruptions in the functioning of equipment and hardware. Aboard a space vehicle some microclimatic parameters are optimal for microorganism growth: the atmospheric fluid condensate with its specific composition, chemical and/or anthropogenic contaminants (human metabolic products, etc.) all are stimulating factors for the development of bacteria and mould fungi on materials of the interior and equipment of an orbital station during its operational phase(s). Especially Russian long-term missions (SALYUT, MIR) [correction of SALJUT] have demonstrated that uncontrolled interactions of microorganisms with materials will ultimately lead to the appearance of technological and medical risks, significantly influencing safety and reliability characteristics of individual as well as whole systems and/or subsystems. For a first conclusion, it could be summarized, that countermeasures and anti-strategies focusing on Microbial Contamination Management (MCM) for the International Space Station (ISS, next long-term manned mission) at least require a new materials test approach. Our respective concept includes a combined aging/biocorrosion test sequence. It is represented here, as well as current status of MCM program, e.g. continuous monitoring (microbiological analyses), long-term disinfection, frequent cleaning methods, mathematical modeling of ISS, etc.

Aerospace Medicine↗

PubMed1987

Activation of complement in human serum by some synthetic polymers used for intraocular lenses.

Determination of the potential to activate complement can be used as one criterion in testing the biocompatibility of various synthetic polymers that are utilized in the medical field. Intraocular lenses (IOLs) made of poly(methyl methacrylate) (PMMA) with PMMA loops, poly(hydroxyethyl methacrylate) (PHEMA) lenses, silicone lenses, and PMMA lenses with polypropylene loops were examined in this study. The concentrations of the activation peptides C3a, C4a and C5a were measured by radioimmunoassay (r.i.a.) in human serum after incubation with and without IOLs for up to 12 h. The presence of silicone lenses caused an increase in C3a levels. In the presence of polypropylene loops, the concentrations of both C3a and C5a were significantly higher than in serum incubated alone. There was no statistically significant increase in the concentration of C4a caused by any of the materials tested. The results suggest that IOLs made from silicone or lenses with polypropylene loops activate the complement system via the alternative pathway.

Biocompatible Materials↗

PubMed2004

An ex vivo method for evaluating the biocompatibility of neural electrodes in rat brain slice cultures.

Failure of neural recording electrodes implanted in the brain is often attributed to the formation of glial scars around the implant. A leading cause of scar formation is the electrode material. Described below is an approach to evaluate the biocompatibility of novel electrode materials in a representative three-dimensional model. The model, brain slice culture, accounts for the response of the neural tissue in the absence of the systemic response. While limitations of any in vitro model exist, brain slice culture provides an indication of the response of neurons and glia in an environment more indicative of the in vivo environment than two-dimensional cell culture of glia or neurons alone. Polybenzylcyclobutene (BCB) electrodes were developed as test materials for flexible electrodes due to ease of processing, low water uptake, and inherent flexibility when formed in thin sheets. Biocompatibilty of the BCB neural electrodes was evaluated using living brain slices derived from the hippocampal regions of 100 g CD rats. Importantly, fewer animals can be used in brain slice culture to evaluate the neural tissue response than when using live animals, since several slices can be obtained per animal. Cellular response to the electrodes was evaluated at 0, 7, and 14 days. At all time points living cells, both neurons and glia, were observed in the vicinity of the electrode. In addition, cells were observed migrating out from the brain slices onto the shank of the BCB electrode. Brain slice culture is shown to be a viable alternative to in vivo evaluation, in that the response of both neurons and glia can be evaluated in a native three-dimensional state, while sacrificing fewer animals. Future in vivo evaluation with BCB will provide definitive answers on the degree of glial scarring in response to this new and biocompatible electrode material.

Animals↗

PubMed1995

An in vitro comparison between a bonded retainer system and a directly bonded flexible spiral wire retainer.

Bonded lingual retainers are becoming more popular to stabilize the results of orthodontic treatment. The in vitro shear strength of a flexible spiral wire (FSW) retainer (Zachrisson, 1977, 1983) bonded with Prisma Fil was compared to the 'A'-Company bonded lingual retainer system, bonded with either Concise or Right-On, to human enamel. Statistical analysis of the results showed no significant differences between the 'A'-Company system when bonded with Concise or Right On, Concise having a greater mean bond strength, but also a greater range of bond strength values. All the materials tested gave bond strengths that were adequate for clinical practice and it is concluded that the choice of bonded retainer system can be made upon grounds of clinical convenience or cost.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1992

Biocompatibility studies on plasma polymerized interface materials encompassing both hydrophobic and hydrophilic surfaces.

The biocompatibility of radiofrequency plasma polymerized films (less than 100 nm thick) deposited on biomedical polymer supports has been characterized by in vitro and in vivo methods. The polymer interface materials covered a wide range of elemental composition and surface properties, and were prepared from N-vinyl-2-pyrrolidone, gamma-butyrolactone, n-hexane, and hexamethyldisilazane (PPHMDSZ). The biocompatibility studies showed that the interface materials were noncytotoxic to mouse and human fibroblasts, as shown by morphologic evaluation, and by determination of extracellular LDH; and they did not stimulate interleukin-1-like production from human monocytes, as indicated by a thymocyte proliferation assay. The human fibroblast proliferation assay showed that three of the polymers supported cell growth at levels comparable to, or greater than, polymer controls, while the hydrophobic PPHMDSZ inhibited both cell attachment and proliferation. The response to subcutaneous implantation for all test materials was indicative of biocompatibility, with rapid resolution of the acute phase response and normal wound healing. The wide range of composition and surface properties for the plasma polymerized films evaluated in this study suggest that this general class of materials is likely to exhibit excellent biocompatibility.

Animals↗

PubMedDate not supplied

Roughness of denture materials: a comparative study.

PURPOSE: Surface properties of denture materials are of clinical importance since they may affect plaque accumulation and staining. This in vitro study investigated the roughness of 20 commercially available denture materials. MATERIALS AND METHODS: Four denture base resins, nine hard lining materials, and seven soft denture lining materials were evaluated for roughness. Roughness measurements were made using a Mitutoyo Surftest SV-400, and the mean arithmetic roughness values (Ra) obtained were used for the comparisons. RESULTS: The overall Ra values ranged from 0.7 to 7.6 microns. The denture base materials group exhibited Ra values from 3.4 to 7.6 microns, whereas the hard liners were from 0.7 to 4.4 microns. The autopolymerized and visible light-cured soft liners presented Ra values from 0.7 to 3.5 microns, while the heat-cured soft liners ranged from 3.5 to 4.0 microns. CONCLUSION: The roughness exhibited by all of the materials tested (Ra values greater than 0.7 micron) indicates that there is a possibility for plaque accumulation, since 0.2 micron is considered the threshold below which no further bacterial adherence can be expected.

Acrylic Resins↗

PubMed2001

The influence of water storage and C-factor on the dentin-resin composite microtensile bond strength and debond pathway utilizing a filled and unfilled adhesive resin.

OBJECTIVE: To test the elastic wall concept utilizing adhesive resins of varying stiffness in a low- and high-C-factor cavity design after short- and long-term water storage. METHODS: A flat and box-shaped cavity was restored on occlusal dentin with a resin composite using a filled and unfilled adhesive resin from which microtensile specimens with a 0.5mm(2) cross-sectional area were formed. After storage for 30- and 150-days the microtensile bond strength (muTBS) was determined in a Zwick materials testing machine and the subsequent debond pathway was examined under scanning electron microscopy. Fisher's exact test was used to determine differences in joint and substrate failure modes and a Weibull regression model with gamma frailties was used to test for differences between failure distributions. Tests for three-way and two-way interactions were also completed for storage time, C-factor and adhesive. All tests were at 95% confidence levels. RESULTS: The characteristic strength (TBS degrees ) for the Optibond FL adhesive applied on a flat cavity was 47.57 and 20.90MPa and a box-shaped cavity was 49.26 and 17.49MPa for short- and long-term storage, respectively, while the corresponding TBS degrees for the unfilled Optibond adhesive on the flat cavity design was 36.93 and 32.68MPa and in a box-shaped cavity was 32.84 and 15.46MPa. Combining all groups according to storage time revealed a three-fold increase in the debond pathway including the bottom of the hybrid layer. SIGNIFICANCE: Evidence suggests that the durability of the bonded joint is threatened by hydrolysis and the most susceptible region is the bottom half of the hybrid layer and in low C-factor cavity designs a more flexible adhesive resin liner was more durable.

Adhesiveness↗

PubMed2002

The effect of augmentation with resorbable or conventional bone cement on the holding strength for femoral neck fracture devices.

OBJECTIVES: To compare maximum extraction torque and pull-out load for femoral neck fracture implants inserted with standard technique or after augmentation with polymethylmethacrylate (PMMA) or calcium phosphate cement (Norian SRS). DESIGN: Biomechanical study using synthetic bone. INTERVENTION: Implants were inserted in foam blocks with three different densities for simulation of normal bone or slight or severe osteoporosis. Tested implants included three screws (AO, Olmed, Hansson), one screw with both threads and a barb (Hybrid), and one pin with a hook (LIH hook-pin). Implants were inserted by standard technique and after augmentation with PMMA or Norian SRS. MAIN OUTCOME MEASUREMENT: The effect of (a) density of the synthetic bone (low, medium, high), (b) augmentation (none, PMMA, SRS), and (c) type of implant (AO, Olmed, Hansson, Hybrid, LIH) on the maximum extraction torque and pull-out load was determined using a material testing machine. Analysis of variance with Fisher's PLSD post hoc test was used to determine statistical differences. RESULTS: PMMA significantly increased maximum torque and pull-out load for all implants and block densities when compared without cement (p < 0.0001), whereas enhancement with SRS was far less pronounced and most obvious in low density blocks. For screws normally inserted without predrilling (Olmed and Hansson) the use of SRS in high density blocks caused a significant reduction in maximum torque (p < 0.0001) and pull-out load (p < 0.0001). SRS-augmented specimens failed through the cement at the periphery of the threads, whereas PMMA-augmented specimens failed between the cement and the synthetic bone. CONCLUSION: This study suggests that augmentation with PMMA around femoral neck fracture implants will increase the holding power significantly when compared with standard insertion technique as well as augmentation with calcium phosphate cement. Augmentation with calcium phosphate cement like SRS will increase the holding characteristics mainly in low density bone, whereas in high density bone it might even reduce the maximum torque because of the need for predrilling when using the cement for augmentation.

Biomechanical Phenomena↗

PubMed2005

Selective influence of dentin thickness upon cytotoxicity of dentin contacting materials.

The effect of three dentin contacting materials on three-dimensional cultures of pulp-derived cells was evaluated in a dentin barrier test device. The test materials (Syntac Classic, Prompt L-Pop, Vitrebond) were applied on dentin disks of different thicknesses ranging from 100 to 500 microm. After 24 h of exposure with and without perfusion of the test chamber, cell survival was evaluated using the MTT assay and related to a nontoxic control material. Syntac Classic decreased cell activity significantly (p </= 0.0003), independently of the dentin thickness. For Prompt L-Pop and Vitrebond a significant influence of dentin thickness was found on the cell reaction. After exposure of the control material, photometric readings showed no dependency of the cellular reaction on dentin thickness (p > 0.05). It could be demonstrated that dentin acts as a barrier, decreasing the elicited cytotoxicity with increasing thickness. This effect is material related, showing little influence for the nontoxic or the glutaraldehyde containing material.

Animals↗

PubMed1990

Characterization of short-fibre reinforced thermoplastics for fracture fixation devices.

This study focuses on determining the effects of clinically relevant procedures on the flexural and fracture toughness properties of three short-fibre thermoplastic composites for potential application as fracture fixation devices. The procedures included sterilization, heat contouring and saline soaking. The three materials tested were polysulphone, polybutylene terephthalate and polyetheretherketone, all reinforced with 30% short carbon fibres. The polysulphone composite showed significant degradation in mechanical properties due to saline soaking. The polybutylene terephthalate exhibited significant degradation of mechanical properties following both contouring and saline soaking. The polyetheretherketone composite, however, exhibited no degradation in mechanical properties. The results demonstrated that flexion and fracture toughness testing were effective for determining the response of the composites to different applied conditions and demonstrated the stability of polyetheretherketone subjected to these treatments. Scanning electron microscopy demonstrated the most effective fibre-matrix bonding to be in the polyetheretherketone.

Benzophenones↗

PubMed1996

A comparison of microwave and dry-heat curing methods on the bond strength of silicone facial materials applied to acrylic resin.

PURPOSE: This study compared two curing methods (microwave irradiation and dry heat) on the tensile bond strength of silicone facial materials to cured acrylic resin. The facial materials studied were Mollomed, Silskin II, MDX4-4210, and A-2186. MATERIALS AND METHODS: The samples were processed with microwaves for 13 minutes at 90 W plus 2 minutes at 500 W and dry heat for 3 hours at 100 degrees C to cured acrylic resin. Facial materials 3-mm thick were processed between two half-dumbbells of acrylic resin. The bonding surfaces were treated with a primer. The samples were placed in tension until failure. RESULTS: The results showed that the bond strength was affected by the type of silicone material and not by the curing methods used. CONCLUSIONS: Mollomed had the highest bond strength of all materials tested. MDX4-4210 and A-2186 showed the lowest, and Silskin II had intermediate bond strength. Microwave irradiation has the potential of saving time, energy, and resources during the fabrication of facial prostheses, but further laboratory studies and clinical trials are indicated.

Acrylic Resins↗

PubMed2002

A new device for measuring the viscoelastic properties of hydrated matrix gels.

Determinations of the viscoelastic properties of extracellular matrices (ECMs) are becoming increasingly important for accurate predictive modeling of biological systems. Since the interactions of the cells with the ECM and surrounding fluid (e.g., blood, media) each affect cell behavior; it is advantageous to evaluate the ECM's material properties in the presence of the hydrating fluid. Conventional rheometry methods evaluate the bulk material properties of gel materials while displacing the hydrating liquid film. Such systems are therefore nonideal for testing materials such as ECMs, whose properties change with dehydration. The new patent pending, piezoelectrically actuated linear rheometer is designed to eliminate this problem. It uses a single cantilever to apply an oscillating load to the gel and to sense the gel's deflection. Composed of two thin film piezopolymer layers, the cantilever uses one layer as the actuator, and the second piezopolymer layer to measure the lateral movement of its attached probe. The viscoelastic nature of the ECM adds stiffness and damping to the system, resulting in the attenuation and phase shift of the sensor's output voltage. From these parameters, the ECM's shear storage and loss moduli are then determined. Initial tests on the BioMatrix I and type I collagen ECMs reveal that the first prototype of the piezoelectrically actuated linear rheometer is capable of accurately determining the trend and order of magnitude of an ECM's viscoelastic properties. In this paper, details of the rheometer's design and operating principles are described.

Animals↗