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Biomedical subjects

James L Drummond

Publications and source records attributed to James L Drummond.

At least 19 recordsLinked to original sources
PubMed2007

Effect of cyclic loading and environmental aging on the fracture toughness of dental resin composite.

OBJECTIVE: The main purpose of this study was (1) to investigate the effects of cyclic loading and environmental aging on three dental resin composites with different filler compositions: a fiber filler, a hybrid filler, and a microfill; and (2) to predict fracture in dental resin composite under mixed-mode loading conditions. METHODS: Diametral disk specimens 25 mm in diameter and 2 mm in thickness were used in this study. Two methods were used for generating initial cracks in the specimen. The first method involved machining a 3-mm notch in the center of the disk specimens, and then the notch tips were sharpened with a 0.2-mm-diameter jeweler's saw blade. In the second method for obtaining sharper crack tips, a three-way wedge was forced into a 3.175-mm hole drilled in the center of the specimen, resulting in sharp cracks emanating from the notch tips. CYCLIC TESTS: The specimens were aged for 4 months in air, water, artificial saliva, and a 50/50 (by volume) mixture of ethanol and water at room temperature in sealed polyethylene containers. Both unaged and aged specimens (5 specimens for each variable) were subjected to cyclic loading at a frequency of 5 Hz with sinusoidal loads cycling for 1, 1000, and 100,000 cycles at a load level approximately 60% of the fracture load for noncycled specimens. Following load cycling, the specimens were tested in compression in a displacement-controlled loading mode at a loading rate of 1.27 mm/min. RESULTS: Test results show that aging in a 50/50 alcohol-water mixture lowered the fracture toughness of dental resin composite, which was further reduced by cyclic loading. MIXED-MODE TESTS: The maximum tensile stress (MTS) criterion was used to predict fracture in dental resin composite under mixed-mode loading conditions. The loads at failure were used as input into a finite element model. After obtaining the stress field in the specimens by the finite element method, the mixed-mode stress intensity factors were calculated using an interaction energy integral method. RESULTS: Good agreement was obtained between the fracture envelope predicted by the MTS criterion and the experimental fracture toughness data. Hence, it can be concluded that it is only necessary to characterize the mode I fracture toughness to fully characterize the mixed-mode behavior of the dental resin composites that were considered in the present study.

Composite Resins↗
PubMed2007

Application of crosslinkers to dentin collagen enhances the ultimate tensile strength.

The stabilization of dentin collagen with biocompatible crosslinking agents may be of clinical importance to improve dentin bond strength. The present study aimed to evaluate the effect of three collagen crosslinking agents on the ultimate tensile strength (UTS) of undemineralized and demineralized dentin. Ten freshly extracted sound molars were sectioned into 0.5 x 0.5 mm2 thick beams. The beams were either demineralized or kept undemineralized. Then, specimens were subdivided into four groups according to treatments--PBS solution (control), 5% glutaraldehyde (GD), 0.5% proanthocyanidin PBS solution (PA), and 0.625% genipin PBS solution (GE). Specimens were kept in their respective solutions for either 4 or 40 h. To assess UTS, specimens were subjected to tensile forces at a crosshead speed of 1 mm/min. Statistical analysis was performed using two-way ANOVA and Fisher's PLSD test (p < 0.05). Statistically significant increases in UTS were observed for demineralized dentin after PA and GE dentin treatment, when compared with those of the control group. Dentin treated with GD showed no statistically significant differences in UTS when compared with that the control. Undemineralized dentin revealed no significant differences as compared to that of the control, regardless of the collagen crosslinkers. The application of two naturally occurring crosslinkers, i.e., PA and GE, to dentin collagen significantly improves UTS, indicating its potential value in restorative dentistry.

Collagen↗
PubMed2006

Contact versus flexure fatigue of a fiber-filled composite.

OBJECTIVE: The intent of this project was to examine the effect of two different modes of fatigue loading, contact and flexure, on the flexure strength of a dental composite. METHODS: The composite was Restolux (a fiber-filled composite) formed as bars 3 mm x 3 mm x 25 mm in size. The cyclic loading ranges were 30-50, 60-80, and 90-110 N for contact loading and 20-40 and 40-60 N for the flexure loading. Number of cycles completed was 1, 1000 or 100,000 in four different media: air, water, artificial saliva, and a 50/50 mixture of water and ethanol. Specimens were aged in sealed polyethylene containers in their respective media for 4 months at 37 degrees C. RESULTS: Statistical analysis indicated a significantly lower flexure strength for the specimens flexure loaded versus contact loaded. For the flexure loaded specimens, the number of cycles had no significant effect, but the aging, load, and the media were all significant. For the contact loaded specimens, a significant effect was observed for the media, aging, and cycles completed, but no effect for the different cycling loads. SIGNIFICANCE: In summary, the decrease in flexure strength from flexure loading was mainly affected by the aging media, whereas, the decrease from contact loading was attributed mainly to the number of cycles.

Air↗
PubMed2006

Organic overlayer model of a dental composite analyzed by laser desorption postionization mass spectrometry and photoemission.

Some dental composites consist of a polymerizable resin matrix bound to glass filler particles by silane coupling agents. The resin in these composites includes bisphenol A diglycidyl methacrylate (Bis-GMA) as well as other organic components. Silane coupling agents such as 3-(trimethoxysilyl) propyl methacrylate (MPS) have been used to improve the mechanical properties of the dental composites by forming a covalent bond between the glass filler particles and the resin. These resin-glass composites undergo material property changes during exposure to the oral environment, but degradation studies of the commercial composites are severely limited by their chemical complexity. A simplified model of the dental composite has been developed, which captures the essential chemical characteristics of the filler particle-silane-resin interface. This model system consists of the resin matrix compound Bis-GMA covalently bound via a methacryloyl overlayer to amorphous silicon oxide (SiO2) surface via a siloxane bond. Scanning electron microscopy shows the porous characteristic and elemental composition of the SiO2 film, which approximately mimics that of the glass filler particles used in dental composites. LDPI MS and XPS verify the chemistry and morphology of the Bis-GMA-methacryloyl overlayer. Preliminary results demonstrate that LDPI MS will be able to follow the chemical processes resulting from aging Bis-GMA-methacryloyl overlayers aged in water, artificial saliva, or other aging solutions.

Biocompatible Materials↗
PubMed2006

Nanoindentation of dental composites.

The intent of this project was to evaluate the elastic modulus and hardness of four composites with different fillers, a microfill, a hybrid, a dental resin cement, and a fiber filler, using nanoindentation. An indentation load of 0.001 N was used and 100 indents per specimen were taken. The elastic modulus measured for the Choice composite was 30.2-30.3 GPa, 15.9-16.0 GPa for Micronew, 24.6-27.1 GPa for Renew, and 36.4-47.1 GPa for Restolux. The statistical analysis indicated a significant difference in the elastic modulus for all four composites. Micronew had the lowest hardness (1.2-1.3 GPa) followed by Renew (1.6-1.8 GPa), Choice (2.6-2.8 GPa), and Restolux (2.7-4.0 GPa). The statistical analysis indicated a significant difference between Choice and Restolux from Micronew and Renew, with Renew and Micronew not being significantly different from each other. Nanoindentation of dental composites, using a 10 x 10 matrix of indentations, resulted in a wide range of measured values for the elastic modulus and hardness because of the size of the filler particle, the location of the indenter within the filler particle, the composition of the filler particles, and the location of the indenter within the filler/resin matrix.

Biocompatible Materials↗
PubMed2006

Bond strength evaluation of ceramic and stainless steel bracket bases subjected to cyclic tensile loading.

INTRODUCTION: The aim of this study was to evaluate the effects of loading, static and cyclic, on 1 stainless steel and 3 ceramic bracket bonding bases. METHODS: The brackets were chosen because of the different characteristics of their bonding bases. The brackets in each group were bonded to bovine teeth by using the same adhesive and subjected to both static and cyclic tensile loading; the results were analyzed (ANOVA and Scheffé) for statistical differences among the groups. RESULTS: The analysis showed that ceramic brackets have unique characteristics compared with stainless steel; the most significant is higher bond strengths. The effects of cyclic loading were shown to be significant, in that fatigue testing caused a decrease in mean tensile bond strength for most groups. An additional factor on the bond strength might be the composition and design of the bracket base. CONCLUSIONS: Simulations of occlusal forces (a combination of tensile, shear, and compressive forces) to orthodontic materials during in-vitro studies in accordance with clinical use might adequately describe actual clinical performance.

Analysis of Variance↗
PubMed2006

Antimicrobial properties of an orthodontic adhesive combined with cetylpyridinium chloride.

INTRODUCTION: Patients undergoing fixed appliance treatment are at greater risk for increases in salivary and plaque levels of Streptococcus mutans and an elevated risk of dental caries. Cetylpyridinium chloride (CPC) is known to be an effective antiplaque agent. The purpose of this study was to investigate whether incorporating CPC into a commercially available orthodontic adhesive would impart antimicrobial properties without altering the diametral tensile strength of the material. METHODS: CPC was added to a commercially available, filled, photo-activated bracket adhesive (Transbond XT, Unitek 3M, Monrovia, Calif) in varying amounts, to obtain specimens with CPC concentrations of 0% (control), 2.5%, 5.0%, and 10.0% by weight. Adhesive discs 2 mm thick and 4 mm in diameter were incubated with Streptococcus mutans for 48 hours. The diameters of the zones of bacterial inhibition were measured in an agar disc diffusion assay; specimens of each concentration were tested every other week for 196 days. Other discs were soaked in distilled water for 180 days. The amount of CPC released into the water from the modified discs was measured and recorded on days 7, 15, 30, 60, and 180 by using a spectrophotometer at 254 nm. Diametral tensile strength of the modified adhesive discs was measured with a universal testing machine, and the effect of water aging was also evaluated. RESULTS: The measured zone of bacterial inhibition increased as CPC content increased. All CPC-adhesive specimens maintained antimicrobial activity up to 196 days. No zone of bacterial inhibition was measured around the control specimens. CPC release was observed through the end of 180-day period, but the greatest release was recorded in the first week. There was no significant difference (P < .05) in diametral tensile strength between the 2.5% CPC-adhesive group and the control; there were significant differences among the 5.0% and 10.0% CPC-adhesive groups and the control. Water aging had no significant effect on diametral tensile strength other than decreasing it for the test group containing 10.0% CPC. CONCLUSIONS: The incorporation of 2.5% CPC in adhesive material imparted antimicrobial activity without altering diametral tensile strength.

Adhesives↗
PubMed2006

Magnetic strength and corrosion of rare earth magnets.

INTRODUCTION: Rare earth magnets have been used in orthodontics, but their corrosion tendency in the oral cavity limits long-term clinical application. The aim of this project was to evaluate several; magnet coatings and their effects on magnetic flux density. METHODS: A total of 60 neodymium-iron-boron magnets divided into 6 equal groups--polytetrafluoroethylene-coated (PTFE), parylene-coated, and noncoated--were subjected to 4 weeks of aging in saline solution, ball milling, and corrosion testing. RESULTS: A significant decrease in magnet flux density was recorded after applying a protective layer of parylene, whereas a slight decrease was found after applying a protective layer of PTFE. After 4 weeks of aging, the coated magnets were superior to the noncoated magnets in retaining magnetism. The corrosion-behavior test showed no significant difference between the 2 types of coated magnets, and considerable amounts of iron-leached ions were seen in all groups. CONCLUSIONS: Throughout the processes of coating, soaking, ball milling, and corrosion testing, PTFE was a better coating material than parylene for preserving magnet flux density. However, corrosion testing showed significant metal leaching in all groups.

Boron↗
PubMed2005

Three-dimensional tomography of composite fracture surfaces.

The goal of this project was to image the three-dimensional fracture interface of a dental composite with the use of X-ray tomography. With the use of the Advanced Photon Source (APS) at Argonne National Laboratory, three-dimensional images were obtained of the crack interface of a dental composite material that had been subjected to three different treatments: a control, cycled in air, and cycled in a 50/50 mixture by volume of ethanol and distilled water. The cycle-loaded treatments were for 100,000 cycles at a load between 80 and 100 N at 5 Hz. The crack interface extended over 28 slices for the control, 96 for the air-cycled specimen, and 83 slices for the 50/50 solution cycle specimen. It would appear that the fatiguing of the specimens allowed for an increase in the crack interface as demonstrated by the 3D tomographical analysis. This volume increase in the crack interface is attributed to a separation of the filler fiber from the resin matrix. Three-dimensional tomography provides an excellent method to observe crack interfaces of dental composites subjected to different types of mechanical and environmental conditions.

Acrylic Resins↗
PubMed2005

Barium and strontium leaching from aged glass particle/resin matrix dental composites.

OBJECTIVES: This study characterizes the loss of Ba and Sr from glass particle/resin-matrix dental composites during simulated aging. METHODS: X-ray wavelength dispersive spectrometry and secondary ion mass spectrometry were used to analyze the Ba and Sr content from the surfaces of three commercial dental composites after aging for 4 and 8 months in humid air, artificial saliva, water, and 50% ethanol. RESULTS: Aging in artificial saliva caused the greatest leaching of Ba or Sr for all the specimens, compared with either lesser or no leaching for aging in ethanol and water. Differences in leaching were observed between the different composites. Composites aged in artificial saliva also picked up elements in the saliva solution and displayed crystallite formation on the surface. Samples aged in ethanol displayed cracking which was not observed for water or artificial saliva. SIGNIFICANCE: Dental composites display ion leaching from their surfaces over periods of four to eight months. Three mechanisms are proposed to explain differences in leaching for the various composites and aging solutions. Surface mineralization is also proposed to occur as a self-repair mechanism in artificial saliva.

Air↗
PubMed2005

Fracture surface examination of dental ceramics using fractal analysis.

OBJECTIVE: The purpose of this study was to measure the fractal dimensional increment of the fracture surface of six dental ceramics, and to measure the correlation of the fractal dimensional increment with fracture toughness. The six dental ceramics investigated were: a traditional porcelain (Finesse[F], Ceramco, Burlington, NJ, USA), four leucite reinforced pressable ceramics (Finesse Pressable [FP], Ceramco; Empress [E], Ivoclar; New Albany, NY, USA and two shades of OPC [OA2 and OI40], Jeneric-Pentron, MA, USA), and a lithium disilicate containing pressable ceramic ([LD] Ceramco). METHODS: The fracture surfaces examined and the measured fracture toughness (K(IC)) values are from a previous study . An impression was taken of the fracture surface, poured up in epoxy, coated with gold, a second layer of epoxy added, and then the surface polished at an angle to the fracture surface. This fracture interface (slit island) was observed in an optical microscope with an imaging system from which an image of the fracture line was digitized. The slit island perimeter was then measured using five different length rulers. The fractal dimensional increment (D*) was determined using a Richardson technique. A second experiment on three ceramics investigated whether there was a correlation between fracture toughness and the values of D* measured by an alternative technique using a confocal microscope. RESULTS AND SIGNIFICANCE: Fracture toughness was well correlated with D* using either technique.

Aluminum Compounds↗
PubMed2004

Leaching and mechanical properties characterization of dental composites.

The objective of this study was to determine the leaching of Ba, Si, and Sr from four dental composites: Restolux (RX), Micronew (M), Renew (RW), and Choice (C) and to correlate the effects of such leaching with flexure strength and modulus of elasticity. The specimens were 3 x 3 x 25-mm bars, polished with 120- and 240-grit SiC paper, and were aged for 4, 6, and 8 months in artificial saliva, distilled water, and a 50/50 mixture of ethanol and distilled water. Inductively coupled plasma with mass spectroscopy (ICP/MS) was used to determine the ion concentrations after aging. The greatest release of Ba and Sr occurred after aging in 50/50 volume fraction mixture of ethanol/water and for Si in artificial saliva. The 50/50 solution caused a breakdown of the resin and glass matrix, resulting in an increase of Ba and Sr, whereas aging in artificial saliva resulted in an ion charge balance, which allowed an elevated and continuous release of Si. The flexure strength and the elastic modulus showed a gradual decrease over time, with the greatest decreases occurring following aging in the 50/50 water/ethanol solution, but little correlation with the leaching of the filler ions.

Biocompatible Materials↗
PubMed2004

Evaluation of fracture toughness of a fiber containing dental composite after flexural fatigue.

OBJECTIVE: The purpose of this study was to examine the effect of cyclic loading in four different environments on the fracture toughness of a fiber reinforced resin composite. METHODS: The specimens were 3 x 3 x 25 mm3 bars polished with 320 grit SiC paper. A 60 degrees v-notch was machined 1 mm deep at the midspan of each bar. The specimens were loaded in air, artificial saliva, water, and a 50/50 by volume mixture of ethanol and water at a frequency of 5 Hz with sinusoidal loads cycling between 10 and 20 N for 1, 1000, 10,000 and 100,000 cycles. Specimens were also aged for 4 months in each respective media. Following cyclic loading, the specimens were tested in three-point loading. Statistical analysis consisted of four 2-way ANOVAs followed by Tukey's HSD inference, and two 3-way ANOVAs followed by two-sample t-tests. RESULTS: The ANOVAs indicated no difference in the means of fracture toughness for the set numbers of cycles, but a significant difference for the aging solutions and the aging times. SIGNIFICANCE: Statistical analysis showed a significant decrease of fracture toughness from unaged to aged specimens when aged in air, saliva, and 50/50 ethanol/water. The latter showed the most pronounced decrease. The effect of the 50/50 by volume mixture of ethanol and water would appear to attack the resin matrix and/or the bond between the resin matrix and the filler, which resulted in the observed decrease in fracture toughness. In addition, the significant decrease in fracture toughness following aging is attributed to residual matrix stress around the large fiber filler particles resulting in separation of the fiber filler from the resin matrix.

Air↗
PubMed2004

Micro-cracking of tooth structure.

PURPOSE: To determine if the cutting procedure utilized in producing a cavity preparation, i.e., a high speed dental handpiece or an Er:YAG laser may be a factor in initiating the formation of micro-cracks during or after preparation of the cavity and before and after placing and curing the dental composite. METHODS: Class I occlusal and Class II MOD preparations were prepared in extracted third molars using a high speed dental handpiece equipped with a coarse diamond bur or with an Er:YAG laser at 260mJ and 25Hz. Composite was placed into the cavity level with the occlusal surface and bulk cured. The extreme factors of a coarse diamond bur and bulk curing of the composite were utilized to maximize the stresses at the tooth-composite interface. The teeth were vertically sectioned, facio-lingually, and examined, along with resin replicas, under a scanning electron microscope (SEM) to look for the presence of microcracks at the composite/enamel interface and composite/dentin interface. RESULTS: SEM examination indicated that micro-cracking of the tooth structure was not significant or consistent in any of the specimens examined. This study was unable to confirm that micro-cracks form at the composite/tooth interface.

Cracked Tooth Syndrome↗
PubMed2003

Static and cyclic loading of fiber-reinforced dental resin.

OBJECTIVE: The aim of this study was to evaluate the flexure strength of unidirectional fiber-reinforced resins under static and cyclic loading with and without thermal cycling. METHODS: The fiber-reinforced resin materials chosen for this project were commercially available endodontic posts and commercially procured bar samples. For all materials, controls for flexure strength were tested in air and in water using three-point loading. Specimens were thermal cycled between 7 and 63 degrees C for 6000 cycles. A staircase approach was used to determine the flexure fatigue limit and scanning microscopy was used to examine the microstructure. RESULTS: The carbon/graphite fiber-reinforced resin posts and the glass FiberKor posts were significantly stronger than the ceramic (zirconia) and the other glass-reinforced resin materials. Thermal cycling caused a significant lowering (11-24%) of the flexure strength for each resin based post system. The ceramic post system decreased only by 2%. Further, for standard size glass fiber-reinforced resin bars, no significant differences between testing in air and water was observed, but a significant difference between static and cyclic loading was noted. SIGNIFICANCE: The decreases in the strength property due to thermal cycling and the cyclic loading of these materials indicates that their utilization in the oral environment enhances their degradation, and potentially shortens their clinical life.

Air↗
PubMed2003

Particle versus mercury removal efficiency of amalgam separators.

OBJECTIVE: The intent of this project was to evaluate the efficiency of three commercial amalgam separators based on mercury and particle removal. METHODS: Dental wastewater samples were collected from a 54-chair dental clinic and a one chair private dental office. Atomic absorption spectrometry was used to measure mercury, and a laser diffractometer method to determine the particle size distributions. RESULTS: The mercury removal efficiency of the three units ranged from 26.5 to 61.8% for the 54-chair clinic and from 80.8 to 94.7% for the one chair office. Following treatment, the particle size range of the effluent was 8.3-19.2 microm for the 54-chair office and 27.5-41.4 microm for the one-chair clinic. For particle samples based on the silver-copper and copper standards, the three amalgam separators had a particle removal efficiency ranging from 92.3 to 99.9%. The initial particle size distributions for these samples were all under 100 microm. CONCLUSIONS: The efficiency of the amalgam separators is influenced by the initial concentration of the dental wastewater, the physical setup of the discharge system before the dental wastewater reaches the separators, and the addition of chemicals to the dental wastewater. In addition, it is likely that assessment of efficiency based on particle removal by weight may not be as effective as removal based on concentration.

Copper↗
PubMed2003

Mercury generation potential from dental waste amalgam.

OBJECTIVE: The main objective of this study was to quantify the total amount of amalgam used in dental offices in the state of Illinois and to estimate the fractions of amalgam waste material generated during dental procedures. A second objective was to estimate the fractions of non-contact, contact, and tooth retained amalgam through an in vitro study. METHODS: The collection system consisted of containers placed in six dental offices and clinics to collect the material from the in-line trap (contact amalgam) and the excess dental amalgam not placed into the oral cavity (non-contact amalgam). In order to have comparable results, the data was adjusted by the number of dental chairs being used and the number of working days. RESULTS: The range for the non-contact amalgam was from 0 to 102 g, and for the contact amalgam, from 2 to 16 g. The median estimate of non-contact amalgam generated from the 6 dental offices was 421 mg/day/chair, whereas the median estimate of contact amalgam was 64 mg/day/chair. For the in vitro study, 40 one and two surface amalgams (bicuspids and molars), was distributed as follows, 46+/-20% in the tooth, 43+/-19% as non-contact amalgam, and 11+/-4% as contact amalgam. CONCLUSIONS: Based on survey data from the ADA concerning the number of working days per year, the number of practicing dentists, a 50%, by weight, mercury content in amalgam, and the generation estimates from this project, it was estimated that the practicing dentists in the State of Illinois (6455) have the potential to generate 947 kg of non-contact mercury per year, which is recyclable, and 144 kg of contact mercury which has the potential to be discarded in the environment, or be partially recycled. If this approach is applied to the total population of practicing dentist in the United States (123,641), then 18,159 kg of recyclable, non-contact mercury may be generated per year, whereas 2763 kg of contact mercury may be discarded in the environment, or be partially recycled.

Dental Amalgam↗