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Biomedical subjects

M W Beatty

Publications and source records attributed to M W Beatty.

18 recordsLinked to original sources
PubMed2006

Static and dynamic loading effects on temporomandibular joint disc tractional forces.

UNLABELLED: Mechanical fatigue-related degeneration of the temporomandibular joint (TMJ) disc may be promoted by tractional forces. This study tested the hypotheses that tractional forces following static loading of the TMJ disc: (1) increase with compressive strain at the start of movement, and (2) are velocity-dependent during movement. Sixty-four porcine discs received a 10-N static load via an acrylic indenter for 1 or 30 sec before cyclic movement. Physical data were recorded and analyzed by ANOVA. The results showed that compressive strain and tractional forces were largest for the start of movement following 30 sec of static loading (p <or= 0.0001) and were correlated (R(2) = 0.84). Peak tractional forces were linearly and positively related to velocity of movement (R(2) = 0.85), and were highest during Cycle 1 after 30 sec of loading (p <or= 0.0067). The results demonstrated that tractional forces were strain-related at the start of movement and velocity-dependent during movement. ABBREVIATIONS: ANOVA = analysis of variance, PBS = phosphate-buffered physiological saline solution, TMJ = temporomandibular joint, mu(T) =tractional coefficient, mu(s) = static coefficient of friction.

Analysis of Variance↗
PubMed2004

Laboratory stresses and tractional forces on the TMJ disc surface.

The etiology of degenerative disease of the TMJ may involve fatigue produced by surface tractional forces and compressive stresses. This study tested the time-dependent effects of compressive loading and stress-field translation on TMJ disc-surface tractional forces and stresses. In laboratory experiments with 50 porcine discs, an acrylic indenter imposed 10 N static loads for 10 and 60 sec, followed by translation of the loaded indenter along the mediolateral axis of the disc. Maximum tractional forces were found to occur following 60 sec of static loading (p < 0.001), and increased with translation velocity (R(2) = 0.73); whereas maximum compressive stresses occurred after 10 sec of static loading (p < 0.001). Overall, the results were consistent with current mechanical theories of the time-dependent effects of compressive loading of cartilage.

Animals↗
PubMed2001

Strain rate dependent orthotropic properties of pristine and impulsively loaded porcine temporomandibular joint disk.

The purpose of this study was to characterize the tensile stress-strain behavior of the porcine temporomandibular joint (TMJ) disk with respect to collagen orientation and strain rate dependency. The apparent elastic modulus, ultimate tensile strength, and strain at maximum stress were measured at three elongation rates (0.5, 50, and 500 mm/min) for dumbbell-shaped samples oriented along either anteroposterior or mediolateral axes of the disks. In order to study the effects of impact-induced fissuring on the mechanical behavior, the same properties were measured along each orientation at an elongation rate of 500 mm/min for disks subjected to impulsive loads of 0.5 N. s. The results suggested a strongly orthotropic nature to the healthy pristine disk. The values for the apparent modulus and ultimate strength were 10-fold higher along the anteroposterior axis (p < or = 0.01), which represented the primary orientation of the collagen fibers. Strain rate dependency was evident for loading along the anteroposterior axis but not along the mediolateral axis. No significant differences in any property were noted between pristine and impulsively loaded disks for either orientation (p > 0.05). The results demonstrated the importance of choosing an orthotropic model for the TMJ disk to conduct finite element modeling, to develop failure criteria, and to construct tissue-engineered replacements. Impact-induced fissuring requires further study to determine if the TMJ disk is orthotropic with respect to fatigue.

Animals↗
PubMed2001

The effect of disc thickness and trauma on disc surface friction in the porcine temporomandibular joint.

The pathomechanics of osteoarthritis in the human temporomandibular joint (TMJ) are unknown. Compromised lubrication is a potential factor, but, lubrication within even the normal TMJ is not understood completely. Weeping lubrication is a concept that may be applicable to the TMJ. A characteristic of weeping lubrication is a slow increase in friction during static loading. The rate of increase in friction is related to the rate of lateral movement of synovial fluid away from the loading area. The TMJ disc is expected to be the main source of TMJ lubrication. This study tested two variables, disc thickness and magnitude of trauma to the disc, as factors that can affect the rate of flow of synovial fluid and thus alter lubrication of the disc surfaces. To test these variables, TMJ disc surface friction was measured before and after an impulse load. Before the impulse load, all discs demonstrated a gradual increase in friction during light static loading. The rate of increase in friction was inversely related to the disc thickness (R(2)=0.75). After an impulse load of known magnitude and peak force, disc surface friction was higher. The magnitude of this surface friction was correlated with the magnitude of the impulsive blow (R(2)=0.89) and the area of surface damage (R(2)=0.85). Disc thickness was a significant factor in determining the minimal impulse needed to produce higher surface friction (R(2)=0.99). These results confirm that disc thickness and trauma to the disc affect surface friction in the TMJ, and therefore may be important factors in compromised lubrication and the development of osteoarthritis.

Animals↗
PubMed1999

Nickel release from orthodontic arch wires and cellular immune response to various nickel concentrations.

AIMS: Results from two previous clinical studies suggested that exposure to high nickel-containing orthodontic arch wires may induce hypersensitivity in certain individuals. The purpose of this study was to measure the amount of nickel released from three types of nickel-containing arch wires into a synthetic saliva in vitro, and determine if the concentrations were sufficient to elicit either cytotoxic (trypan blue exclusion test) or stimulatory (MTT test) responses in human peripheral blood mononuclear cells (PBMCs) derived from nickel-sensitive and nickel-nonsensitive individuals. PBMCs were exposed to five concentrations of nickel sulfate solutions ranging from 0-29 ppm, and results were compared, particularly at concentrations obtained from nickel release experiments. FINDINGS: The amount of nickel released into synthetic saliva ranged from 0.4-4.1 ppb. Wires subjected to a combination of soaking and cyclic straining released significantly more nickel than those that were soaked only (p </= 0.05), and NiTi wires released significantly more nickel than did stainless steel or nitrogen-implanted NiTi wires (p </= 0.05). For PBMCs, significant increased cell proliferation was not observed for any nickel concentration. PBMC cell death rates were highest at nickel concentrations of 29 ppm when the cells were cultured without a cell growth promoter (p </= 0.05), and MTT test values were significantly reduced at both 2.9 and 29 ppm when a growth promoter was included (p </= 0.05). CONCLUSION: The maximum amount of nickel released from all tested arch wires was 700 times lower than the concentrations necessary to elicit cytotoxic reactions in human PBMCs.

Adult↗
PubMed1999

Ultraviolet radiation-induced color shifts occurring in oil-pigmented maxillofacial elastomers.

STATEMENT OF PROBLEM: Oil-based pigments are added to a maxillofacial prosthesis either as base colorants present within the elastomer or as surface tints that are painted on with an adhesive. Color stability of the pigments and pigmented prosthetic materials on exposure to ultraviolet radiation are unknown. PURPOSE: This study measured DeltaE* color changes caused by ultraviolet radiation for materials colored with 5 oil pigments, applied either as base colorants (intrinsic) or surface tints (extrinsic) to a silicone elastomer. MATERIAL AND METHODS: One of 5 oil pigments was added to polydimethyl siloxane disks to serve as a base colorant (0.2 weight percent present throughout a 2 mm thick disk) or as a concentrated surface tint (2.0 weight percent concentrated in upper 0.3 mm thickness). Pigmented disks, along with pigment-only and elastomer-only control disks, were exposed to ultraviolet radiation for 400, 600 and 1800 hours. DeltaE* color changes were measured at baseline and for each time interval. RESULTS: Control samples underwent minimum color changes after 1800 hours (DeltaE* </= 2.0), whereas samples containing oil pigments as base colorants demonstrated a wide range of susceptibility to ultraviolet radiation, with the greatest changes occurring for pigments cadmium red, cadmium yellow, and yellow ochre (7.1 </= DeltaE* </= 9.4). Elastomers coated with the same oil pigments as concentrated surface tints demonstrated significantly lower color shifting after 1800 hours of radiation exposure (maximum DeltaE* = 4.2, P </= .05). CONCLUSION: Customizing a prosthesis with an oil-pigmented surface tint may reduce the incidence of color change, provided a sufficient amount of pigment is present.

Coloring Agents↗
PubMed1998

Effect of microfiller fraction and silane treatment on resin composite properties.

A series of microfilled resin composites were formulated by incrementally mixing either agglomerated 20 nm or unagglomerated 50 nm silica microfillers into monomers composed of diphenyloxymethacrylate and TEGDMA. The microfiller particles were prepared with and without a gamma-methacryloxypropyl-trimethoxy silane coupling agent. Following polymerization, five material properties were tested: uniaxial tensile strength, Young's modulus in slow compression, Knoop hardness, water sorption, and toothbrush abrasion resistance. Results from these tests indicated that microfiller content clearly was the most influential parameter affecting material property performance. Composites containing 20 nm particles demonstrated greater water sorption, higher Knoop hardness, and better resistance to toothbrush wear. Surprisingly, the application of silane to microfiller surfaces did not greatly improve composite performance for most of the material properties tested in this study. However, water sorption behavior over a 3-year period was observed to be more stable for materials possessing silane-treated particles. Future evaluation of coupling agents should include long-term water storage prior to conducting mechanical tests.

Biocompatible Materials↗
PubMed1996

Factors influencing retention of a CeraOne gold cylinder.

Missing single teeth may be replaced using an endosseous dental implant. The CeraOne system uses a gold alloy cylinder that is cemented to a titanium abutment. This study evaluated the effect of three variables on cement failure loads required to unseat a gold alloy cylinder from its abutment. Two chimney heights (commercially available 3.7 mm and custom fabricated 5.0mm), three luting agents (zinc phosphate, Tempbond NE, and Tempbond), and two luting volumes (0.01 mL and 0.02 mL) were tested. A mechanical testing instrument was used to exert a uniaxial tensile force on the gold cylinders 2 hours after cementation. An analysis of variance and Tukey post hoc test demonstrated that both the choice of luting agent and chimney height affected cement failure loads (P <0.0001). An interactive effect between luting agent and chimney height was observed, with the combination of zinc phosphate and a 5.0 mm abutment-gold alloy cylinder complex resulting in significantly greater retention (P<0.0001). The use of 0.01 mL or 0.02 mL of luting agent resulted in comparable retention values. The results indicate that both chimney height and choice of luting agent may affect retention of a CeraOne gold alloy cylinder. The use of 0.01 mL of luting agent is recommended to minimize expression of excess cement at the restoration-abutment interface.

Analysis of Variance↗
PubMed1995

Fracture toughness determination of dental materials by laboratory testing and finite element models.

This study assessed the effectiveness of finite element analysis in predicting the stress intensity factor (KIC) for three types of dental materials: a glass ionomer, a dental amalgam, and a composite resin. Laboratory tests were conducted on small single-edge notch specimens loaded in three-point bending to determine values for fracture toughness (KQ). Using the dimensions measured for each laboratory specimen, a J integral approach was employed to calculate KIC using finite element analysis. Both two-dimensional plane strain and three-dimensional models were used in determining KIC for each specimen, and these values were compared to the KQ values obtained from laboratory tests. The results indicated that no significant differences existed between laboratory results and those obtained from both two- and three-dimensional finite element models (P > .85). For the three-dimensional model, values for KIC were found to vary across the specimen thickness, with the values at the center of the specimen closely paralleling those obtained from the two-dimensional plane strain model. It was concluded that the two-dimensional plane strain J integral technique was as effective as the three-dimensional technique in calculating values for KIC.

Dental Materials↗
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↗
PubMed1995

The effect of cementing agent and technique on the retention of a CeraOne gold cylinder: a pilot study.

Endosseous dental implants are routinely used for the replacement of missing teeth. The CeraOne system uses a gold cylinder that is luted to a metal abutment. This study evaluated two luting agents and two luting techniques on the retention of a CeraOne gold cylinder to a CeraOne titanium abutment. A mechanical testing instrument was used to provide an uniaxial tensile force on the gold cylinder, which was cemented with zinc phosphate or Tempbond NE. The access opening to the gold abutment screw was filled or unfilled. Filling the access opening resulted in significantly higher retentive values (P < 0.01) compared to leaving the access opening unfilled. The gold cylinder was significantly more retentive when cemented with zinc phosphate as compared with Tempbond NE (P < 0.01). A Tukey post hoc test demonstrated that all means were significantly different at the P = 0.01 level. The results suggest that the choice of luting agent and luting technique may affect retention of a CeraOne gold cylinder.

Analysis of Variance↗
PubMed1995

Determination of blood mercury concentrations in Alzheimer's patients.

Trace element neurotoxicity can be an etiologic factor for Alzheimer's disease. This cross sectional clinical study determined blood mercury in patients with diagnosed Alzheimer's disease as compared to control subjects without known central nervous system and renal disorders. Unique within the confines of a nursing home, all subjects were exposed to the same environment and consumed a diet without fish and seafood for a period of three months prior to the study. The results of this study show that blood mercury concentrations detected in subjects with Alzheimer's disease were not statistically different than that of control subjects. Ratios of blood mercury to blood selenium were also determined and no statistical difference was found between these two groups.

Aged↗
PubMed1993

Effect of crosslinking agent content, monomer functionality, and repeat unit chemistry on properties of unfilled resins.

Seven mechanical/physical properties were used to evaluate 10 unfilled resins: eight aromatic dimethacrylates and two urethane dimethacrylates. Physical property tests included compressive strength, Young's modulus in compression, uniaxial tensile strength, intrinsic yield point, toothbrush abrasion, Knoop hardness, and water sorption. Controlled changes were made in the following four material parameters: amount of crosslinking diluent present in the uncured monomer, functionality of the monomer, repeat unit chemistry of the monomer (urethane vs. aromatic structure) and mode of activation (chemical vs. visible light). Polymers containing a high concentration of crosslinking agent (50 wt%) were found to be tougher and to possess lower hardness than materials containing lesser amounts of crosslinking agent. This was attributed to the flexible nature of the triethylene glycol dimethacrylate crosslinking molecule. Exposure to water plasticized the highly crosslinked materials to the degree that the yield point and elastic modulus were effectively lowered. Most of the tested properties were unaffected by differences in functionality except resistance to toothbrush abrasion, which was enhanced for polymers derived from high functionality monomers. The urethane-based polymers sorbed substantially more water than the aromatic-based materials, which presumably resulted in lower values for surface hardness. However, the urethane resins were very tough, and excellent resistance to toothbrush abrasion was observed. Property differences caused by differences in activation mode were small, although the visible light materials did sorb more water.

Absorption↗
PubMed1993

Elastic and fracture properties of dental direct filling materials.

Five dental direct filling materials were tested in tension and compression in order to define their stress-strain behaviour for both types of applied stress. In addition, fracture toughness was determined from three-point bending tests. Linear and non-linear stress-strain behaviour was observed, and the response was specific for each material and also to the type of applied stress. Fracture resistance was also found to be material specific, which was related to differences in composition.

Ceramics↗
PubMed1992

Materials and techniques in fixed prosthodontics.

If we have learned anything from our experiences with all-ceramic systems such as Cerestore, Cerapearl, and even Dicor, it is that it takes years to uncover the strengths, weaknesses, and limitations of new materials and technologies. Manufacturers' initial claims for fit, strength, esthetics, biocompatibility, wear characteristics, and clinical performance should be viewed as preliminary until supported by independent laboratory and clinical studies. Laboratory testing alone may not provide sufficient insight into the relative strengths and weaknesses of products or assure comparable performance in the commercial dental laboratory or the ultimate testing arena, the oral environment. Moreover, the diversity of the new materials and techniques discussed demonstrates the breadth and depth of the technologic changes in dental biomaterials. The rate at which these dental products enter the marketplace and their sheer number alone are indeed staggering. Furthermore, these advances are not emerging from any single nation but from manufacturers all around the world (Japan, Germany, as well as the United States), indicating our international reliance on one another. Clearly, the decade of the 1990s is emerging as an exciting period in the development of biomaterials in comprehensive fixed prosthodontics and dentistry in general.

Calcium Sulfate↗
PubMedDate not supplied

Mercury determination in nursing home patients with Alzheimer's disease.

Trace-element neurotoxicity contributing to the development of Alzheimer's disease (AD) may be an important etiologic factor for this disorder. This clinical study was conducted to determine the urine concentrations of mercury (Hg) from patients with AD disorders. Within the confines of a nursing home, all subjects were exposed to the same environment and a diet that excluded seafood. The results of this study do not indicate that subjects with AD have a greater body burden of Hg, according to urinary excretion. This can be further evidence that Hg from amalgam restorations or diet is not related to etiology and pathogenesis of AD.

Aged↗
PubMedDate not supplied

The effect of dentin surface moisture on bond strength to dentin bonding agents.

This in vitro study compares the mean shear bond strengths of two dentin bonding agents to dry and to moist human dentin. The occlusal surfaces of 60 extracted human molars were ground to produce flat dentin surfaces. The teeth were divided into four groups of 15 specimens each. For Scotchbond Multi-Purpose dentin bonding agent, the teeth were etched, rinsed, and then either blotted with gauze, which left the dentin moist, or dried with compressed air. The primer and adhesive were then applied, and composite cylinders were bonded to the teeth. For Optibond, the teeth were again either blotted with gauze or dried with air. The primer and dual-activated adhesive were applied, and composite cylinders were bonded to the teeth. After storage in room-temperature distilled water for 48 hours, the specimens were thermocycled. Shear bond strength testing was performed at 1 week. Analysis using two-sample t-tests found no significant difference for either product in bond strengths to moist and to dry dentin (P > 0.05). This study indicated that for some current-generation dentin bonding agents, the presence of moisture on dentin surfaces does not compromise short-term bond strength.

Bisphenol A-Glycidyl Methacrylate↗