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In brief This study tested Sta-Guard and Proform mouth protectors that were worn by 280 football players aged 9 to 12 years. Laboratory studies were also conducted to test tensile and tear strength, dynamic modulus and resilience, and hardness. The players received new mouth guards every two weeks for 12 weeks and reported any problems with gagging, taste, speech, feel, and durability. Ninety percent of the boys preferred the Sta-Guard mouth protector, stating that it was softer, more resilient, and more comfortable than the Proform mouth guard.

The isothermal enthalpy changes with time of a dental composite were examined by microcalorimetry to isolate the effects of different filler concentrations and curing times on chemical aging of these composites. Urethane dimethacrylate (UDMA) monomer, zirconia-silica (ZS) powder, and 3-methacryloxypropyltrimethoxysilane (MAPM) were used as organic and inorganic matrices, and a coupling agent, respectively. The composite was mixed in different ratios and cured by visible light. The enthalpy changes with time for 0, 15, 45, 75% ZS-filled UDMA and 75% MAPM-silanated ZS-filled UDMA cured for 13, 30, 90, 150, and 300 s were measured at 37.0°, 57.0°, and 65.5°C until equilibrium. Increased curing time and filler concentration caused the excesss enthalpy changes (dH) and their rate of change (dH/dt) to increase with annealing time and apparent equilibrium was reached faster. In addition, dH showed nonlinear dependence with the increase in filler concentration by showing a maxima for samples containing 25 wt % filler. Further, filler silanation caused dH/dt to increase and required shorter times to reach apparent equilibrium. dH also reached a minimum when samples contained silanated filler, compared to composites containing unsilanated filler. It was concluded that the shorter curing time caused the occurrence of spontaneous densification, which facilitated continual resin curing; and longer curing time caused higher crosslinking of the organic phase. Moderate concentration of inorganic phase restricts the molecular motion of the surface layer of polymer onto filler particles, and the polymer is regarded as highly crosslinked, while a higher filler concentration forms aggregates that are covered by the polymer which causes a decrease in the molecular packing of the resin, and is reflected as low enthalpy values. Finally, silanation of the filler showed a highly endothermic reaction that is probably due to breaking and forming of bonds at the interface between the organic and the inorganic phases in the composites. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 40, 224–232, 1998

The in vitro cytotoxicity of urethane dimethacrylate composites cured at different times by visible light and after different aging times and extraction treatments was evaluated using succinic dehydrogenase activity in the mitochondria of a fibroblastic cell line to reflect cell viability. In addition, extractable chemicals associated with cell response were identified. The composite samples were tested untreated, polished, or extracted with water or 75% ethanol-water. Balb/c 3T3 fibroblasts were used as the cell culture system while MTT-formazan production was used as the toxicity parameter. Cell viability was calculated as a percentage of Teflon controls. Identification of the chemicals was measured by extracting the composites with 75% ethanol-water, separating the extract by HPLC, and identifying the fractions with mass spectroscopy. In general, cell viability increased continuously with curing time for differently treated samples at high aging times (288 h) while it decreased when the composites were not aged (0 h). In addition, for 75% ethanol or water-extracted composites, cell viability increased within the first 24 h of aging and reached a plateau after 72 h. Lowest cytotoxicity occurred when the samples were extracted with the 75% ethanol solution. The highest cytotoxic effects were found when the samples were untreated. Slightly reduced cytotoxic effects were seen with polished composites. The results suggest that curing the light-activated composites for a minimum of 150 s and post-curing for 24 h is required to attain comparable biocompatibility with the Teflon control. Removing the oxygen-inhibited layer from these composites decreased the cytotoxicity by 33% while extracting the composites with 75% ethanol-water decreased it by 77%. Chemicals released from the surface accounted for approximately 40% of cellular response while about 60% of the response was due to chemical components released from the bulk. The primary leachable component from the composites was UDMA monomer. Small quantities of 1,6 hexane diol methacrylate, camphoroquinone, and 2,4,6-tritertiarybutyl phenol also were found.

The preparation and characterization of high-surface-area polymeric substrates suitable for the microcalorimetry of protein adsorption are described. High-surface-area polystyrene, poly(styrene-co-butyl methacrylate) and poly(styrene-co-allyl alcohol) were prepared by adsorbing polymer from solution onto fumed silica. Verification of adsorption of polystyrene by silica was determined by noting peak shifts of the surface silanol group in the infrared. The amount of polymer adsorbed was determined from adsorption isotherms. The minimum thickness of polystyrene required to mask silicon oxide properties was found to be that thickness at which contact angles became constant, about 35 A. Polymer densities were measured. Water contact angles on each polymer surface indicate that poly(styrene-co-allyl alcohol) has the surface most wettable by water. Polymer-water interfacial energies were estimated from pendant drop results and a harmonic mean equation along with contact angles. Two methods were used to estimate the polar and dispersion components of the three polymers. Both methods predicted polystyrene to have the highest interfacial energy against water, and one method predicted poly(styrene-co-allyl alcohol) to have the lowest. A Wilhelmy plate study verified the change in interfacial properties as a function of contact time with water. A study of the heats of adsorption of lysozyme by each substrate using a modified Tien-Calvet microcalorimeter demonstrated the suitability of the substrates for microcalorimetry.

SUMMARY The effect of the method of silanation of zirconia-silica hy 3-methacrylox ypropyItrimethoxysilane (MAPM) and 3-acryloxypropyltrimethoxysilane (APM) on the diametral tensile and transverse strength of composites made from these silanated fillers and a urethane dimethacrylate was determined after 0-lOSh of hoiling in water. The water sorption of these composites was also measur-?d at times up to 108 h. Silanation with either silane significantly increased the tensile and transverse strengths and decreased water sorption relative to comparable unsilanated controls. Silanation with MAPM from ethaaol solution at three times the minimum uniform coverage gave the best overall results, and the tensile strength tests appeared to be most predictive of effectiveness of the silane treatments.

The long-term stability of a soft denture liner depends to a large extent on the sorption and solubility of the liner. Because sorption and solubility are accompanied by a volumetric change, bacterial infestation, hardening, and color change, it is a physical property of importance. The purpose of this investigation was to determine the sorption and solubility of 12 soft denture liners (Verno-Soft, Super Soft, ProTech, Soft-Pak, Flexor, Novus, Molloplast-B, Durosoft, Justi Soft, Velvesoft, VinaSoft and Prolastic). They include nine copolymers, two silicones and one polyphosphazene fluoroelastomer. The sorption and solubility test was performed as outlined in American Dental Association (ADA) specification 12 for denture base polymers. Five specimens of each material were tested and data were collected at 1 week, 1 month, 3 months, 6 months, and 1 year. Sorption data varied from 0.2 to 5.6 mg/cm2 at 1 week; 0.3 to 12.5 mg/cm2 at 1 month; 0.1 to 22.0 mg/cm2 at 3 months; 0.1 to 13.6 mg/cm2 at 6 months; and 0.1 to 35.7 mg/cm2 at 12 months. Solubility data varied from 0.0 to 0.4 mg/cm2 at 1 week; 0.1 to 0.8 mg/cm2 at 1 month; +0.1 to 1.2 mg/cm2 at 3 months; 0.0 to 1.9 mg/cm2 at 6 months; and +0.2 to 2.3 mg/cm2 at 1 year. A statistical analysis of the data by two-way ANOVA and calculated Tukey intervals showed significant differences between materials at all time intervals. The results of this study have clinical implications because the sorption and solubility may affect the long-term life expectancy of the soft denture liner.

This study compares the tensile strength, elongation, Shore-A hardness, and tear resistance of three silicone maxillofacial materials before and after aging to provide comparative data for evaluation of new or experimental elastomers. The materials evaluated were MDX-4-4210, Factor II (A-2186), and Cosmesil. Tests were conducted 24 hours after specimen preparation and were repeated after aging for 900 hours in a Weather-Ometer device. Five samples were made for each material under all test conditions. After testing, mean values were calculated for all materials under all test conditions and were compared by two-way analysis of variance and Tukey intervals at p ≤ 0.05.

The effects of an oligomer, urethane dimethacrylate (UDMA), on two human cell lines were studied using flow cytometry (FCM). Untreated and treated cultures of propidium iodine-stained KB (epidermal oral carcinoma cells) and human foreskin fibroblas (HFF) cells were analyzed for cellular DNA content. Concentrations of 10 and 25 μM of UDMA slightly perturbed the KB cell cycle progression at 24 and 48 h of incubation. However, the effect of 50 μ M was more pronounced at the latter incubation time period. In cell growth experiments, the sublethal concentrations (10 and 25 μM) produced inhibition of KB cell growth rate at a moderate level, which resulted in the prolongation of cell population doubling time. Significant inhibition of cell growth occurred when 50 μM (lethal concentration) was used. Data obtained from the cell cycle perturbation analysis, evidenced by FCM, correlated with the extent of inhibition in KB cell growth rates. The effects of sublethal concentrations were reversible during a 24 h period of oligomer withdrawal from culture medium. In contrast, the effects of 50 μM were not reversible. In HFF cells the depletion of S phase in the cell cycle was the major effect of 50 μM of UDMA. It was concluded that FCM technology is an ideal and practical approach for studying the cytotoxicity of components of dental composites. © 1994 John Wiley & Sons, Inc.

Effects of materials and techniques on the accuracy of models used to make indirect restorations was measured using a 4-unit posterior model containing a MOD and full crown preparation. Improved stone and fast setting epoxy dies backed with either improved stone or a thermoplastic hot melt stone were made from single-viscosity addition silicone impressions. Technique variations included heating or not heating the impression, cooling and pouring dies and placement of the hot melt stone on set or unset epoxy. The dimensions of the MOD (L, W, H) and of the crown (W, H) dies were measured at 1 and 24 h. No clinically significant changes occurred between 1 and 24 h. The stone control reproduced the dimensions of the master die best, and models made by pouring epoxy into the impression followed by immediate pouring of the hot melt stone gave the poorest reproduction. Other variations in technique using epoxy for the anatomical portion gave no practical differences in accuracy. Of the epoxy dies, those prepared from a previously heated impression with hot melt poured after the epoxy set had the best values; however, epoxy dies were smaller than stone dies. The fast set epoxy was noteworthy for rapid processing and sharp detail, however, negative changes for W and H of the crown and H and L of the MOD showed that a die spacer would be essential in the preparation of indirect restorations.

Compliance measurements, used in the past to measure the viscoelastic properties of dental impression materials, were used to assess these properties in vulcanized cis-polyisoprene orthodontic elastics, and the results were compared with traditional force decay measurements. Both methods were also used to evaluate the effect of repeated stretching on these elastics. Compliance measurements successfully characterized the viscoelastic behavior of the elastics, and the results agreed with force decay measurements. Repeated stretching significantly reduced the force and the compliance of the elastics. There was no statistical difference in the force or compliance measurements after the elastics were stretched more than 200 times. Stretching for 1000 cycles of 400% extension reduced elastic force by approximately 12%.

The bond strength of six commercial soft denture liners was evaluated using a modified tensile test. The soft denture liners investigated were Prolastic, VinaSoft, Flexor, Molloplast-B, Novus, and Super-Soft. The samples were processed according to the manufacturers' instructions to cured denture base resin (polymethyl methacrylate; PMMA). The soft denture liners were 10 x 10 x 3 mm and were processed between two PMMA blocks. The samples were placed in tension until failure. The mode of failure, cohesive or adhesive, was also recorded. The results of this study showed that the bond strength is related to the components of the materials. Prolastic, VinaSoft, and Flexor had the lowest bond strength to cured PMMA and ranged from 9.6 to 11.3 kg/cm2. Super-Soft, Novus, and Molloplast-B demonstrated better bond strengths and ranged from 16.7 to 17.6 kg/cm2. The bond strength of Novus could be improved by using the recommended bonding agent and bonded Novus at 26.1 kg/cm2 had the highest bond strength of all materials tested.

The kinetics of the release of elements from six dental casting alloys into cell-culture medium was assessed by means of atomic absorption spectroscopy. Alloys were evaluated in the polished and polished-cleaned conditions so that the effects of cleaning could be determined. Auger scanning microscopy was used for analysis of the surfaces of selected alloys before and after exposure to the cell-culture medium. Release patterns for each element were characterized by the shape of the dissolution us. time curve, concentration of the element at 12 h as a percentage of the 72-hour concentration, and the relative slope of the curve from 48 to 72 h. Three patterns of release were observed for elements in these alloys. Type I patterns had logarithmic shapes with relatively large 12-hour concentrations and low 48-72-hour slopes. Type II patterns had logarithmic shapes but with moderate 12-hour concentrations and 48-72-hour slopes. Type III patterns were polynomial in shape, had relatively low 12-hour concentrations, and had large 48-72-hour slopes. Cleaning did not change the pattern of release but did generally significantly decrease the quantities of elements released (p = 0.05). The type of dissolution vs. time curve appeared to be dependent upon the element and the composition of the alloy. When cleaning reduced dissolution, surface analyses showed that the cleaning process increased the abundance of elements such as Au and Pd and reduced the abundance of Ag and Cu. Elements which were released from the alloys were more abundant on the surface than in the bulk in both polished and polished-cleaned conditions. Auger analyses of alloy surfaces after exposure to medium showed the presence of organic films up to 50 nm thick. This study demonstrated the importance of consideration of the cleaning method and kinetic release pattern when in vitro tests which assess the cytotoxicities of these alloys are planned.

A two-dimensional photoelastic stress analysis method was applied to study the relative magnitude of stress and concentration induced by four commercially available posts for endodontically treated teeth. Three types of threaded posts; VLock, Radix Anchor, and Flexi-Post, and one nonthreaded prefabricated post, the Para-Post Plus post were tested. Stress was recorded at installation, at vertical and inclined load, and the threaded posts were compared with the nonthreaded post. At installation and on loading, stress was induced where posts were in contact with the model. Higher apical stresses were demonstrated for the Para-Post Plus post whereas the threaded posts concentrated stress where they engaged the model through threads or flanges.

The objectives of this study were to determine the cytotoxic concentrations of 11 components of resin composites on monolayers of cultured Balb/c 3T3 fibroblasts, to study the inhibitory effects of these components on DNA synthesis, total protein content, and protein synthesis, and to determine whether effects were reversible when the components were withdrawn from the medium. These data were reported as concentrations which inhibited 10% (ID10) and 50% (ID50) of a particular metabolic process as well as the range of concentrations over which cell metabolism was irreversibly inhibited. For any individual component, the ID50 values for all three metabolic parameters were of the same magnitude. The same was true for the ranges of irreversibility. Ethoxylated Bis-phenol A dimethacrylate (E-BPA) was the most toxic molecule of the group (ID50 being between 1 and 10 μmol/L). The ID50 concentrations for three of the components, including Bis-GMA, UDMA, TEGDMA, and Bis-phenol A, ranged between 10 and 100 μmol/L, while the ID 50 values of three components (N,N dihydroxyethyl-p-toluidine, camphoroquinone, and N,N dimethylaminoethyl methacrylate) were above 100 μmol/L. The concentrations to which the cells and tissues are exposed in uiuo are not known. This study should help to identify the concentrations of organic composite components which pose clinical cytotoxic hazards.

Cell culture techniques were used to determine the source of cytotoxic agents in a commercial BIS-GMA composite. The material was polymerized according to the manufacturer's directions and leachable components were removed by room temperature extraction in ethanol, chloroform, or toluene. The leachable components in the extracts were identified using infrared spectrographic analysis. Thin layer chromatographic analysis was used to determine the number of constituents. These constituents were separated by gas chromatography and then identified by mass spectrographic analysis. Succinic dehydrogenase activity and radioactive labeling with tritiated leucine were used to evaluate cell metabolism and protein synthesis, respectively. The infrared analysis of the extracts showed that the primary component was unreacted BIS-GMA. Trace amounts of 2-hydroxy-4-methoxy-benzophenone, a light stabilizer, as well as a phenyl ester of benzoic acid which was probably degraded from BIS-GMA, were detected by the mass spectrographic method. The removal of leachable components caused a 90% decrease in toxicity compared to the nonextracted BIS-GMA samples. The extracted BIS-GMA samples showed no cellular response compared to the Teflon negative control.

The conformation of blood proteins adsorbed on biomaterial surfaces probably plays a significant role in the biocompatibility of blood-contacting implants. This paper reports heats of adsorption of a globular protein, lysozyme, onto three uncharged polymeric substrates. Variations in heats among substrates reflect differences in the lysozyme/substrate interaction as well as the possibility of substrate-dependent conformations. In each case, a series of plateaus appeared in the adsorption isotherm with increasing concentration. In the cases of two substrates, polystyrene and poly(styrene-co-butyl methacrylate), endothermic discontinuities appeared at rises between plateaus. It is proposed that the step pattern in each isotherm reflects distinct conformational states of lysozyme on the substrate surfaces. Endothermic discontinuities may be latent heats associated with change to a more stable conformation after initial adsorption. The absence of discontinuities in the case of poly(styrene-co-allyl alcohol) suggests structural transitions occur to a smaller extent on this material and results in conformations different from those which occur when lysozyme is adsorbed by polystyrene or by poly(styrene-co-butyl methacrylate).

The properties of a variety of mouth protectors and sheet materials used to fabricate custom mouth protectors were determined in order to recommend limits for a specification. Hardness, water sorption, water solubility, impact absorption, and tear strength were measured, and limits for these properties were suggested.

The polymer-filler interaction of a dental composite was examined by dielectric measurements to determine how a non-compatible inorganic phase modifies the molecular behaviour of the polymer chains and how modification of this phase by silanation can affect these molecular behaviours. Urethane dimethacrylate (UDMA) monomer and zirconia-silica (ZS) powder were used as organic and inorganic phases, respectively. 3-Acryloxypropyltrimethoxysilane (MAPM) and 4-aminobutyltriethoxysilane (ABTE) were used as silanating coupling agents. The components of the composite were mixed in different ratios after treating the filler with from 0 to 30 times the minimum uniform coverage with the silane, then the composite was made into thin films. The dielectric spectra of five replicas for each filler-monomer ratio were measured, and three replicas were measured for each silane and for each amount of silane used to treat the filler. Increasing the filler concentration in the composites decreased the intensity of Tan(delta)epsilon for the alpha- and beta-relaxations, where the beta-relaxations also became broader and the alpha-relaxations were totally obstructed. The alpha-relaxations were shifted to higher temperatures, while the beta-relaxations were shifted to lower temperatures. Filler treatment with small amounts of MAPM shifted the alpha-relaxations to higher temperatures; they were shifted back to lower temperatures when the filler was treated with large amounts of silane. Filler treatment with large amounts of ABTE (30-fold) caused an extra peak to emerge in the high-temperature region. It can be concluded that increasing filler concentration restricts the mobility of the main chains and decreases the thickness of the surface layer, while allowing more movement of the local chains. Filler treatment with MAPM was shown to be a compatible coupling agent with the ZS and the UDMA systems. Such compatibility was observed through the effectiveness of the chemical linkage of the silane to the filler and the polymer without forming a separate inter-phase. Filler treatment with ABTE was shown to be an incompatible coupling agent for the ZS-filled UDMA system. The incompatibility was observed by the occurrence of a new peak that characterizes an inter-phase.

The developments in biomaterials over the past 40 years were listed in a questionnaire. Groups of dentists with and without a Master's degree ranked each development on the basis of the impact they believed it has had on the practice of dentistry. The results of the questionnaires were analysed and the rankings were discussed and used as a guide to the projection of the probable future needs and developments in biomaterials, based on the needs of current and future dental patients.

A filler for a urethanedimethacrylate composite was silanated with mixtures of fluoroalkyl-, aminoalkyl-, phenyl-, vinyl-, bis silyl ethane- and 3-methacryloxypropyltrimethoxysilane (MAOP) in an attempt to increase the hydrophobicity of the coupling agent layer. Diametral tensile strength was used to evaluate composites stored for (1) 24 h in 23 degrees C (RT) air; (2) 24 h in RT air plus 24 h in 100 degrees C air; (3) 24 h in RT air plus 24 h in 100 degrees C water; and (4) 24 h in RT air plus 24 h in 100 degrees C air plus 24 h in 100 degrees C water. Water sorption and solubility of composites was also determined on samples stored for 24 h in RT air. Heating composites for 24 h in 100 degrees C air increased the tensile strength in eight of 13 silane treatments, while heating in 100 degrees C water for 24 h caused decreases for five silane treatments, no change for six and increases in tensile strength for two silane treatments. When composites that had been stored for 24 h at RT plus heated for 24 h in 100 degrees C air were then heated for 24 h in 100 degrees C water, only one silane treatment, the vinyltriethoxysilane at 25% (25% V), showed no significant decrease in tensile strength. Also, the composite silanated with 25% V had the highest value for tensile strength after storing for 24 h at RT air plus 24 h in 100 degrees C air plus 24 h in 100 degrees C water. These data indicate that the use of vinyltriethoxysilane increases the hydrolytic stability of the composite. Water sorption and solubility of the silanated composites were not satisfactory tests for evaluating hydrolytic stability of composites.

SUMMARY Fluorinated Bis-GMA was synthesized and used with other commercially available fluorinated monomers and diluents to prepare hydrophobic composites. The composites were formulated as onepaste systems and were polymerized using blue light. Mechanical properties and water-related qualities were determined. Fluorination generally improved the hydrophobicity of the composites, but there was no clear-cut effect on mechanical properties.

The effect of silanation on the dispersion of quartz and zirconia-silica fillers by monomers used to formulate composites was studied. Sixteen silane coupling agents and three methods were used, and the amounts of the monomers needed to reach wet and flow point values were determined. The silanes were selected to have a variety of organofunctional and hydrolysable groups. Silanation was done from an ethanol-water solution of the silanes and by adding the silanes directly to the filler at room temperature (24 degrees C) and at the boiling temperature of the silanes. The amount of silane used was either that required to produce minimum uniform coverage on the fillers or three times the minimum coverage. All silanes and all methods of treatment decreased the flow values for both fillers compared to the unsilanated controls. Generalizations were that the effectiveness of silanation on the dispersion of the filler particles was greater (i) when silanation from ethanol solution was used compared to direct addition; (ii) when three times the minimum uniform coverage was used; (iii) when the silane contained methoxy rather than ethoxy groups; (iv) when the silanes were trialkoxy rather than dialkoxy compounds; (v) when the length and bulkiness of the organic functional group was smaller; and (vi) when the organic functional group was methacrylate rather than acrylic. The strength of composites prepared from one of the monomer systems and quartz silanated with methacryloxypropyltrimethoxysilane was higher than those silanated with acryloxypropyltrimethoxysilane, which supports the use of the wet and flow point values as screening tests for estimating the dispersability of fillers.

The effects of Ag[sup +1], Au[sup +3], Cd[sup +2], Cu[sup +2]; Ga[sup +3]; In[sup +3], Ni[sup +2], Pd[sup +2], and Zn[sup +2] on DNA synthesis, protein synthesis, succinic dehydrogenase activity, and total cellular protein of mammalian fibroblasts were measured for exposures less than 12 h. The rates at which these cellular functions responded to metal ion exposure were compared and related to the uptake rate of the ions into the cells. These rates of response were significantly different: DNA synthesis decreased the fastest, followed by protein synthesis, succinic dehydrogenase activity, and total protein. This order of response was similar for most metal ions. At 4 h, the rate of uptake of the metal ions correlated most closely with depression of succinic dehydrogenase activity, whereas at 8 h, the uptake correlated most closely with depression of protein synthesis. The similar response of cells to all metal ions may imply that these ions act on cells by similar mechanisms. The rates of uptake of Ag[sup +1], Cu[sup +2], and Zn[sup +2] were sufficiently fast that in vivo exposures of tissues to these metals for periods less than 12 h would be capable of disrupting cellular metabolism.

The effect of cell density (number of cells per unit area of a monolayer culture) on the in vitro cytotoxicity of metal ions which are known to be released from dental materials was investigated. The effects of cell density (1) may explain previous discrepancies in in vitro tests, (2) may be important in wound healing where cell density changes over time, and (3) may help clarify the mechanisms of cytotoxicity of metal ions. Balb/c 3T3 fibroblasts were plated at cell densities ranging from 10,000-80,000 cells/cm2 and were exposed to 8 concentrations of 10 different metal ions. After 24 h, the succinic dehydrogenase activity and DNA synthesis were measured to quantify the cytotoxic effect. Higher cell densities markedly reduced the sensitivity of these fibroblasts to all metal ions except Al+3 and Zn+2, but the magnitude of the reduction was metal dependent. In addition, the DNA synthesis was inhibited more than the succinic dehydrogenase activity for all metal ions except Zn+2. The unique effect of cell density on each metal ion supported the hypothesis that the effect was not simply caused by a dilution of the number of metal ions per cell. Given these results, the effect of cell density should be carefully selected in in vitro cytotoxicity tests.

Atomic absorption spectroscopy was used to assess uptake of Ag+1, Au+4, Cd+2, Cu+2, In+3, Ni+2, Pd+2, and Zn+2 by in vitro cultures of Balb/c 3T3 fibroblasts as a function of concentration of the cations in cell-culture medium. Reversibility of this uptake was also measured. Metal cations exhibited a 400-fold difference in their tendency to accumulate in the cells; In+3 tended to accumulate the most, whereas Pd+2 accumulated the least. Uptake of the cations in the cells increased linearly with the concentration of the cation in the medium for all cations up to their 50% toxicity concentrations. Reversal of this uptake was slower than that of the initial uptake for three cations studied in more detail (Cd+2, In+3, and Ni+2). The duration of the initial exposure affected the proportion of the metal cations that were retained by the cells 5 h after the cations were removed from the medium. The proportion of retained Cd+2 did not change when the initial exposure was increased from 2 h to 6 h, whereas the proportion of retained In+3 decreased and Ni+2 increased over the same period. The tendency of the cells to accumulate these cations correlated with their cytotoxic potency (measured previously). © 1993 John Wiley & Sons, Inc.

Soft denture-lining materials are an important treatment option for patients who have chronic soreness associated with dental prostheses. Three distinctly different types of materials are generally used. These are plasticized polymers or copolymers, silicones, or polyphosphazene fluoroelastomer. The acceptance of these materials by patients and dentists is variable. The objective of this study is to compare the tensile strength, percent elongation, hardness, tear strength, and tear energy of eight plasticized polymers or copolymers, two silicones, and one polyphosphazene fluoroelastomer. Tests were run at 24 hours after specimen preparation and repeated after 900 hours of accelerated aging in a Weather-Ometer device. The data indicated a wide range of physical properties for soft denturelining materials and showed that accelerated aging dramatically affected the physical and mechanical properties of many of the elastomers. No soft denture liner proved to be superior to all others. The data obtained should provide clinicians with useful information for selecting soft denture lining materials for patients.

Effects of duration of exposure of single metal cations (Ag+1, Cd+2, Cu+2, Ga+3, Ni+2, and Zn+2) on 3H-thymidine (3H-Tdr) incorporation and 3-[4,5-dimethyl-thiazol-2yl-]-2,5-diphenyl tetrazolium bromide-formazan (MTT-f) production in cultured murine fibroblasts (Balb/c 3T3) were investigated, and the synergistic and antagonistic effects of two metal cations applied simultaneously to the fibroblasts were assessed. The effects of duration of exposure were quantified using TC50 values (concentration of an element required to cause 50% toxicity compared with controls) measured after 24, 48, or 72 h. Using MTT-f production, Cd+2, Cu+2, Ga+3, and Ni+2 showed significantly lower TC50 values with increasing time of exposure, whereas the TC50 values for Ag+1 and Zn+2 remained constant. The TC50 values using 3H-Tdr incorporation exhibited a similar pattern with time of exposure, but the effects were less pronounced. The TC50 values for 3H-Tdr and MTT-f tended to equalize at 72 h. All combinations of cations tested (Ag-Cu, Ag-Zn, Ag-Ni, Cu-Zn, Cu-Ni, Ga-Ni, and Cu-Cd) exhibited synergistic and antagonistic effects as measured by MTT-f production. Synergistic and antagonistic effects were not necessarily mutually exclusive in the same system.

The viscosity of monophase addition silicone impression materials was measured as a function of shear rate. The setting of mixed catalyst and base was prevented by addition of a small amount of phenyl propiolic acid. All products showed a 6- to 10-fold decrease in viscosity with an increasing shear rate (shear thinning). The addition of phenyl propiolic acid had little or no effect on the viscosity of three materials. However, when added to the catalyst or base only of two products, it increased their viscosity and exaggerated the shear thinning effect.

Soft denture liners are an important treatment option for patients who have chronic soreness associated with their prostheses. The objective of this study is to determine the tensile strength, elongation, hardness, tear strength, and tear energy of eight plasticized polymers or copolymers, two silicones, and one polyphosphazene fluoroelastomer. Tests were made on samples that were stored in a humidor for 24 hours before testing. The range of data is as follows: tensile strength, 8 to 85 kg/cm 2 ; percent elongation, 150% to 542%; hardness, 25 to 95 Shore-A units; tear energy, 1.43 × 10 6 to 40.4 × 10 6 ergs/cm 2 ; tear resistance, 2.6 to 26.3 kg/cm. It can be concluded that (1) the data obtained can be useful in characterizing the performance of soft denture liners, (2) there is considerable variability in the physical/ mechanical properties of soft denture liners, and (3) the required essential properties for soft denture liners are as yet not known.

Previous studies have utilized in vitro alloy cytotoxicity tests to evaluate dental casting alloys. The purposes of this study were to: (1) evaluate the precision of the optical density and visual tests previously used, (2) evaluate a new test measuring absorbance of solubilized formazan dyes, and (3) test the correlation between these tests for cytotoxicity. Balb/c 3T3 cells were plated in 24-well culture trays at 25,000 cells/cm2 around ten types of dental casting alloys (six samples/alloy) and incubated for 72 h. Cells were histochemically stained with MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide)/succinate for 2 h, then fixed, washed, and dried. Toxicity was measured by optical densitometer (OD) scanning, visual assessment, and 560-nm absorbance of DMSO-solubilized dyes. Measurements of rings of inhibition were not used, because they did not provide precise data, and correlated poorly with the other methods. The results were analyzed by ANOVA, Tukey intervals, and coefficients of variation (CV's). MTT required shorter incubation times for adequate staining, allowed for solubilization of the monolayers, and was less expensive than NBT (2,2'-di-p-nitro-phenyl-5,5'-diphenyl-3,3'-dimethoxy-[3,3'-dimethoxy-4,4 '-biphenylene] ditetrazolium chloride). Results showed that all three methods ranked alloy toxicities similarly (p = 0.05). The solubilization method was most discriminating due to lower CV's. Correlation between densitometer and solubilization methods was excellent (R2 = 0.96). Between-experiment CV's were generally less than 20%, and often less than 10%. Between-sample CV's were generally less than 20%.(ABSTRACT TRUNCATED AT 250 WORDS)

The in vitro cytotoxicity of nine metal cations common in dental casting alloys was evaluated using Balb/c 3T3 fibroblasts and four toxicity parameters: total protein production, 3H-leucine incorporation, 3H-thymidine incorporation, and MTT-formazan production. Concentrations causing 50% toxicity compared to controls (TC50's) and reversibility of these effects were determined. The range of potency of the metal cations was 2-3 orders of magnitude, with Cd2+ showing the greatest potency and In3+ showing the least. Potency did not correlate with atomic weight for these metals. For each metal cation, the TC50's of the various toxicity parameters were similar in most cases. However, several cations (Cu2+, Ga3+) showed greater potency with 3H-thymidine incorporation. Reversibility of the toxic effects was observed for all cations; the effects generally became irreversible at concentrations in the range of the TC50 value for each cation. Several stimulatory effects were seen. Small but statistically significant stimulations were observed after 24 h of metal exposure for Ag1+, Au4+, Cu2+, Ga3+, and Ni2+. Residual stimulations 24 h after removal of the metal cations were observed for Au4+, Cd2+, Ni2+, and Zn2+. Stimulations always occurred at concentrations below the TC50 concentrations. This study should be useful in evaluating the potential cytotoxic effects of metal cations released from dental alloys.

Ten dental casting alloys were tested for alloy-element release into cell-culture medium, and this release was related to alloy composition, alloy microstructure, and alloy cytotoxicity (previously determined). Cell-culture medium was analyzed for alloy elements by flame atomic absorption. Concentrations of elements in the medium were normalized by dividing them by their atomic abundance in the alloy, giving element medium-alloy ratios (EMA ratios). Results showed that Au, In, and Pd generally did not dissolve into the medium, but that Ag, Cd, Cu, Ga, Ni, and Zn frequently dissolved. Comparison of EMA ratios for Ag, Cu, and Zn showed that each element retained a behavioral identity in diverse metallurgical environments, but that these environments influenced the release behavior to some degree. Some EMA ratios in multiphase alloys were greater than those in solid solutions, and EMA ratios showed great diversity within all the alloys. Nominal composition seemed to be of little value in the prediction of metal release unless the composition supported multiple-phase formation. In addition, release of alloy elements did not, in itself, completely predict alloy cytotoxicity measured previously. However, cytotoxicity was associated with metal release in each case. The commercial alloys used in this study exhibited more complex and less predictable release behavior than did the simpler ternary alloy systems used by previous investigators. It is believed that the use of commercial preparations is necessary for their in vivo behavior to be modeled.

The cytotoxicity of a series of 29 experimental alloys and six pure metals was determined with cell culture techniques and succinic dehydrogenase histochemistry. The width of any ring of inhibition, optical density of the histochemically stained cells, and a visual ranking of the intensity of the blue color of the stained cells were compared for determination of cytotoxicity. Twenty-four of the 35 metals and alloys (-70%) had the same rankings by the three methods. Of the pure metals, Au, Pd, and Ti were the least cytotoxic, followed by Ag, then Ni, and finally, Cu. Single-phase alloys with moderately high Cu and without high Pd and Au concentrations had high cytotoxicity, as did multiphase alloys, even when they were high in Au and Ag. High Pd was more effective in maintaining the biocompatibility of alloys containing Cu than was Au. Single-phase alloys with compositions typical of those to be used for porcelain-fused-to-metal restorations showed good biocompatibility, as did those base metal alloys that formed adherent oxide surface layers.

The objectives of this study were to introduce a different method for evaluating the accuracy of impression materials using a vertical height gauge, and to determine the vertical (axial) and horizontal (transversal) changes of four impression materials. Comparison of means demonstrated the changes for addition and condensation type silicones, and larger changes for the agar/alginate combination and the visible light cured (polyetherurethanedimethacrylate) impression material. The results were in agreement with an earlier study of the agar/alginate combination, and the values for the condensation and addition silicones were about half those reported in previous studies. These small changes might indicate the use of a mandibular stock tray for the upper jaw when a putty/wash technique is employed. The findings suggest that, when the horizontal changes (delta X) of impressions taken with a mandibular stock tray have a negative sign (contraction), then the vertical changes (delta L) will have a positive value (expansion), and vice versa. Thus the pattern of distortion can be formulated as delta X/delta L less than 0.

The photoinitiated impression material is supplied premixed as a light-bodied material in a light-tight plastic syringe and as a heavy-bodied material in a tube. The impression material has excellent physical, mechanical, and clinical qualities with noteworthy long working times, short setting times, dimensional stability, accuracy, high tear strength, good wettability, biocompatibility, and ease of cold disinfection without loss of quality. The impression material is also compatible with gypsum and silver or copper metallizing baths. Accurate casts can be obtained by means of either a double-impression technique or a double-mix technique.

Dielectric characterization evaluated the influence of sorbed moisture on urethane dimethacrylate (UDMA) polymer matrix and unsilanated and silanated zirconia-silica (ZS)-filled UDMA composites. The moisture content (MC) of samples tested ranged from 0 to 7.32% with maximum values for UDMA, silanated and unsilanated ZS-filled UDMA were 3.72, 6.0 and 7.32%, respectively. Dielectric spectra were measured from 0.053 to 100 kHz and from -180 to 180;C. Small MC stiffened the polymers, which was shown by a shift of beta-peaks to higher temperatures, a decrease in the half width of bands and an increase in the change of activation energies. Higher MC resulted in water plasticizing the polymer by shifting the beta-peaks to lower temperatures. Maximum water sorption restricted the motion of the polymer chains and the b-peaks shifted to higher temperatures. Further, increasing MC shifted the a-relaxation to lower temperatures in both UDMA and composites. However, in composites with unsilanated ZS, a new relaxation occurred at high temperatures and low frequencies which was attributed to Maxwell-Wagner-Sillars (MWS) polarization. Thus, in UDMA, water occurs as fragments that form non-freezing clusters. However, in unsilanated ZS-UDMA composites, bulk water can exist at the polymer-filler interface and form disordered structures of ice at low temperatures which can evaporate at high temperatures. Silanated ZS-UDMA composites function similarly to UDMA at low MC but are more plasticized at high temperatures.

Summary The effects of molecular weight of the base silicone, filler and copolymer concentrations on compression set, strain, creep and dynamic elastic modulus were determined. The molecular weight of the base silicone had the least effect on these properties although low molecular weights showed better properties. Chain extenders were detrimental to physical properties of creep, compression set and dynamic elastic modulus. Increased copolymer concentrations decreased compression set, strain and creep and increased the dynamic elastic modulus. The useful copolymer/base functional group ratio was from 1:1 to 3:1. Filler affected properties to a lesser extent than copolymer ratio. Compression set, strain, and creep decreased and the dynamic elastic modulus increased with increasing filler with the properties being directly proportional to the weight fraction. All properties were interrelated with In strain linearly related to In compression set, creep proportional to set, and the dynamic elastic modulus was inversely correlated with strain and creep.

Fracture toughness, critical strain energy release rate and critical stress intensity factor were determined for lathe-cut, spherical, admixed, and two atomized high-copper dental amalgams. At a loading rate of 0.005cm min−1 for 24-hour samples, the spherical amalgam had the highest resistance to unstable crack propagation. At a loading rate of 0.05cm min−1 for both 24-hour and one-month samples, the lathe-cut amalgam had the highest resistance to unstable crack propagation. One of the atomized high copper amalgams showed the lowest resistance to crack propagation. The values were consistent with data obtained in single-pass wear studies.

An equation was developed from studies of single-pass wear and fracture toughness of filled and unfilled dental restorative resins and dental amalgams relating the sliding frictional force F to the normal load N , fracture toughness, modulus of elasticity, yield strength and slider diameter. This equation was of the same form as that reported for viscoelastic materials ( F = KN n ). Friction was caused primarily by ploughing or deformation of the material under the conditions tested.

Wear of microfilled composites, a visible light-cured composite, and a conventional composite were characterized by two-body abrasion and single-pass sliding. There were differences in abrasion rates among the materials. Tangential forces, wear track widths, and surface failure modes were different among materials. Wear characteristics are combinations of these properties.

The free energies of immersion for three hydroxyapatite samples of different origin and method of preparation were determined from water adsorption isotherms at 20 and 25 C. The free energies varied with the temperature of the isotherm, changing linearly with the outgassing temperature in the range of 20 and 300 C. The samples outgassed at 300 C yielded free energy of immersion values of 365, 432, and 476 ergs/ cm2 for the VIC-, NBS-, and TVA-HAP, respectively. Work of adhesion and work of spreading were calculated for water on these samples.

A two-dimensional finite element model of a mandibular quadrant was used to examine the stresses and displacements resulting from a 100 N load placed as follows: (i) distributed on the second molar, (ii) concentrated at 30 degrees to the vertical on the second molar, and (iii) distributed on the second premolar and second molar. Each tooth was supported by periodontal ligaments, cortical and cancellous bone. The modulus and Poisson's ratios for each material were selected from accepted values. The principal stresses were determined throughout the model, with special emphasis being placed for elements in the immediate vicinity of the teeth mentioned above. It was found that for the case where the load was uniformly distributed on the second molar the stresses sigma min were mostly compressive (-) in nature while sigma max were mostly tensile (+). In the case where the load was concentrated and at 30 degrees to the vertical, the magnitude of the stresses were three to five times greater and the pattern less uniform than those resulting from the distributed load. The concentrated load at 30 degrees to the vertical resulted in higher bending stresses than the distributed load and hence higher sigma max stresses.

The rates of abrasion of six composite restorative resins, an unfilled resin, a dental amalgam, two experimental formulations of commercially available composites, and two coating materials were determined with use of a two-body abrasion test. The wear of composite restorative resins, coating materials, and a dental amalgam was evaluated by a two-body abrasion test. Commercial composite resins were ranked. The rate of abrasion of the dental amalgam was similar to that of the composites but less than that of a commercial unfilled resin. The coating materials were abraded more rapidly than the composites. An experimental composite resin containing quartz was abraded less rapidly than one containing lithium aluminum silicate and barium aluminum silicate. This study evaluates the wear of composite restorative resins by an abrasion test. Composite restorative resins, an unfilled resin, and a dental amalgam are ranked. Two experimental formulations, one the resin matrix of a composite material and the other the resin matrix and inorganic filler without a silane coupling agent, are compared for each of two commercial composite restorative materials. Finally, the abrasion resistance of two commercial coating (glazing) materials is evaluated.

In recent years, the topic of land prices has received considerable attention in the literature. Part of the interest stems from the importance of land as a factor of production in agriculture. Land prices have a direct influence on the ability of young farmers to operate and expand their operations. Thus, the interest in land prices by farmers, bankers and input suppliers is easily understood.

The effect of sterilization and irrigants on the cutting ability of stainless steel files was determined. Dry heat or salt sterilization had no effect, but autoclave sterilization caused a reduction in their cutting ability. Sodium hypochlorite, hydrogen peroxide, and EDTA-urea peroxide (UP) irrigants caused a decrease in the cutting ability of the files, but the saline irrigant had no effect.

The sensitivities of Fourier transform infrared spectroscopy, Knoop hardness, water sorption, and resin leaching were compared for their ability to distinguish differences between composite samples cured through different thicknesses of overlying resin. The method developed allowed samples of light-cured composite to be made with controlled conversion for parameter testing, and eliminated effects of resin lost to slurry during polishing or an increase in conversion as a result of heat generated during grinding. Sensitivity to differences was greatest and equal for FTIR spectroscopy and Knoop hardness, while resin leaching proved to have moderate sensitivity, and water sorption none. The ability of these parameters to predict monomer conversion as measured by FTIR spectroscopy was also determined. Knoop hardness proved the best conversion predictor, resin leaching the next best, and water sorption the worst. Water sorption values did not vary with changes in specimen conversion.