An assessment of the perceived benefits and challenges of participating in a practice-based research network

BACKGROUND

A survey was conducted to describe the benefits of and challenges to practitioner participation in the Practitioners Engaged in Applied Research and Learning (PEARL) Network, a dental practice-based research network (PBRN). The results were compared with results from medical PBRNs across different tiers of participation (based on practitioner-investigators previous involvement with PEARL research protocols).

METHODS

A 39-item web-based survey addressed the benefits of PBRN participation on three levels: individual/practitioner, practice (office), and community/professional. Participants were also asked to rate challenges to participation.

RESULTS

A total of 153 of 216 PEARL practitioner-investigators participated, a response rate of 71%. The majority (70%) was male, with a median of 23 years in private practice. 'Means to stay informed of new developments in my profession' was considered a 'very important' benefit for nearly three-quarters of the sample (71%). 'Opportunity to improve clinical procedures' was considered as 'very important' by 73% of respondents. In terms of benefits related to the community and profession, 65% of respondents reported 'means to directly contribute to the evidence base of dental practice' as being 'very important'. 'Disruption in practice routine/clinical practice' was considered the most important challenge to participation.

CONCLUSIONS

The benefits of and challenges to participation identified did not differ across tiers of participation and were similar to benefits identified by participants in medical PBRNs. The results of this study will help facilitate the design of future PBRN protocols to encourage greater participation by the profession. Results suggest that practitioners with similar interests could be recruited to collaborative studies between medicine and dentistry.

Periodontal pathogens and gestational diabetes mellitus

In previous cross-sectional or case-control studies, clinical periodontal disease has been associated with gestational diabetes mellitus. To test the hypothesis that, in comparison with women who do not develop gestational diabetes mellitus, those who do develop it will have had a greater exposure to clinical and other periodontal parameters, we measured clinical, bacteriological (in plaque and cervico-vaginal samples), immunological, and inflammatory mediator parameters 7 weeks before the diagnosis of gestational diabetes mellitus in 265 predominantly Hispanic (83%) women in New York. Twenty-two cases of gestational diabetes mellitus emerged from the cohort (8.3%). When the cases were compared with healthy control individuals, higher pre-pregnancy body mass index (p=0.004), vaginal levels of Tannerella forsythia (p=0.01), serum C-reactive protein (p=0.01), and prior gestational diabetes mellitus (p=0.006) emerged as risk factors, even though the clinical periodontal disease failed to reach statistical significance (50% in those with gestational diabetes mellitus vs. 37.3% in the healthy group; p=0.38).

Interactions between chronic renal disease and periodontal disease

The incidence of end-stage renal disease (ESRD) is increasing and patients receiving renal replacement therapy including hemodialysis, peritoneal dialysis or renal transplantation will comprise an enlarging segment of the dental patient population. Renal replacement therapy can affect periodontal tissues including gingival hyperplasia in immune suppressed renal transplantation patients and increased levels of plaque, calculus and gingival inflammation and possible increased prevalence and severity of destructive periodontal diseases in ESRD patients on dialysis maintenance therapy. Also, the presence of undiagnosed periodontitis may have significant effects on the medical management of the ESRD patient. Periodontitis has been found to contribute to systemic inflammatory burden including the elevation of C-reactive protein (CRP) in the general population. Atherosclerotic complications including myocardial infarction and stroke are the primary causes of mortality in the ESRD population and, in contrast to that of the general population, the best predictor of all cause and cardiac death in this population is CRP. Consequently, periodontitis may be a covert but treatable source of systemic inflammation in the ESRD population. The objective of this review was to explore the interaction between chronic renal disease, renal replacement therapy and periodontal diseases based upon the results of studies published within the last decade.

Effect of enamel matrix proteins on the periodontal connective tissue-material interface after wound healing

The periodontal ligament has the potential to regenerate a complete periodontal connective tissue attachment, starting with the deposition of cementum, on pathologically exposed root surfaces as well as several materials including titanium oxide. However, most commonly used dental materials result in a fibrous encapsulation or a chronic inflammatory response after periodontal wound healing rather than the formation of a periodontal connective tissue attachment. Recently, an extract of porcine enamel matrix (Emdogain(R), EMD) has been reported inductive of cementum formation in both in vivo and in vitro studies. The aim of this study was to determine the effect of EMD, when applied to materials previously reported not supportive of periodontal connective tissue formation, on the periodontal connective tissue-material interface obtained with these materials in vivo. Bilateral osteotomies were performed on the mandible of a Yucatan minipig exposing the buccal root surface of four premolars. A series of four preparations were placed in each root surface that were subsequently filled with calcium hydroxide, gutta percha, mineral trioxide aggregate (MTA), or left unfilled. One side, in addition, received an application of EMD prior to surgical closure. A bioabsorbable surgical barrier membrane was placed over the osteotomy sites to exclude gingival connective tissue from the wound-healing environment. The mucoperiosteal flaps were then readapted and sutured in position. The animal was euthanized 10 weeks after the procedure, block sections obtained and prepared for light microscopy. Results demonstrated complete regeneration of alveolar bone and periodontal ligament in all four teeth from the EMD-treated side. Fibers from the periodontal ligament were observed to insert into a mineralized matrix consistent with cementum on all four root preparations. In contrast, massive root resorption without regeneration of alveolar bone was found on all teeth from the side not treated with EMD. The results of this pilot study suggest that the application of EMD to material surfaces that normally do not support periodontal connective tissue attachment formation can alter the type of periodontal connective tissue interface obtained with these materials.

Effect of enamel matrix proteins on the phenotype expression of periodontal ligament cells cultured on dental materials

Cells within the periodontal ligament have the potential to regenerate a periodontal connective tissue attachment on pathologically exposed root surfaces as well as on several material surfaces including titanium. However, rather than a periodontal connective tissue attachment, a fibrous encapsulation or chronic inflammatory response has been reported at the material connective tissue interface for most dental materials. Cementum is the first tissue of the periodontal connective tissue attachment to develop and the secretion of enamel matrix related proteins on the newly mineralized dentin surface precedes and is thought to induce cementum formation. Enamel matrix-related proteins may also function in the adult because the application of an acid extract of porcine enamel protein matrix (Emdogain(R), EMD) on pathologically exposed root surfaces has been shown to result in cementum regeneration. Therefore, the objective of the present study was to determine whether the application of EMD to materials that do not normally support cementogenesis in vivo would alter the in vitro phenotype of periodontal ligament (PDL) cells including the synthesis of cementum-associated extracellular matrix proteins. Primary PDL cells were established from 21-day-old Sprague-Dawley rats, and were cultured on four materials commonly encountered in dental practice (gutta percha, calcium hydroxide, amalgam, and super EBA cement) with and without the application of EMD. After 7 or 14 days of culture, total-DNA content, collagen synthesis, alkaline phosphatase activity, and the synthesis of a 42-kDa cementum-associated extracellular matrix protein were determined. PDL cells cultured on all materials had decreased total DNA content. The application of EMD further decreased total DNA content. PDL cells cultured on gutta percha and calcium hydroxide with the application of EMD had similar levels of collagen synthesis and alkaline phosphatase activity but also expressed a 42-kDa cementum extracellular matrix-associated protein when compared to the other groups. These results suggest that EMD can alter the phenotype of PDL cells when cultured on these dental materials.

Properties of athletic mouth protectors and materials

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.

Prevalence and risk indicators for destructive periodontal diseases in 3 urban American minority populations

BACKGROUND, AIMS

Destructive periodontal diseases have been reported disproportionately more prevalent and severe in African-Americans relative to other American populations. Differences in subgingival microbiota and host immune response have also been reported for African-Americans, implying that risk factors for disease progression may also differ for these populations. Since it is not clear whether these differences are truly genetic or due to confounding variables such as social economic status, we examined a series of clinical, environmental, demographic, and microbiologic features associated with periodontal disease status in a group of 185 urban minority subjects resident within the greater New York metropolitan area.

METHODS

The study population consisted of 56 Asian-American, 71 African-American and 58 Hispanic subjects. Clinical data recorded included pocket depth, attachment level, gingival erythema, bleeding upon probing, suppuration, and the presence of supragingival plaque. Environmental and demographic data recorded included smoking history, years resident in the United States, whether the subject reported a private dentist and occupational status. Subgingival plaque was sampled from the mesial aspect of all teeth exclusive of third molars and the levels of 40 subgingival species enumerated using checkerboard DNA-DNA hybridization.

RESULTS

The African-American group had more missing teeth, deeper periodontal pocket depth and more attachment loss than the Asian-American or Hispanic groups. However, the African-American group were less likely to report having a private dentist, had a greater proportion of smokers and a greater proportion of unskilled individuals. The profile of subgingival species differed among the three ethnic/racial groups with A. actinomycetemcomitans, N. mucosa, S. noxia and T. socranskii significantly elevated in the Asian-American group and P. micros significantly elevated in the African-American group. When subset by occupational status, numbers of missing teeth, pocket depth, attachment level and prior disease activity were all found increased in the unskilled relative to the professional group. Local factors including the mean % of sites with plaque, marginal gingival erythema, bleeding upon probing and suppuration were also elevated in the unskilled group. The microbial profile differed among the 3 occupational groups with the unskilled group having elevated numbers of species associated with destructive periodontal diseases.

CONCLUSIONS

Although greater destructive periodontal disease prevalence and severity were found in the African-American group, these results suggest that environmental and demographic variables, such as occupational status, may have a greater influence on risk indicators associated with disease prevalence and progression in these populations.

The effects of moisture on the dielectric relaxation of urethane dimethacrylate polymer and composites

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.

The effects of different additives on the dielectric relaxation and the dynamic mechanical properties of urethane dimethacrylate

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.

Early events associated with periodontal connective tissue attachment formation on titanium and hydroxyapatite surfaces

Endosseous dental implants can support at least three types of biomaterial/connective tissue interfaces: osseointegration, fibro-osseous integration, and periodontal connective tissue attachment. Although a periodontal connective tissue attachment offers distinct advantages, only osseointegration and fibro-osseous integration are at present clinically achievable. Recent studies indicate a periodontal regeneration-competent cell population and an appropriate biomaterial substrate both are required for periodontal connective attachment formation on biomaterial surfaces. We therefore have developed an in vitro model to characterize the effects of various biomaterial substrates on the early events of periodontal connective tissue attachment formation. Primary cultures of periodontal ligament and gingival connective tissue cells were cultured on uncoated (control) and coated (titanium- and hydroxyapatite-coated) tissue culture plastic, and the level of cell proliferation, collagen, and noncollagen protein synthesis, alkaline phosphatase activity, and expression of a 42 kD cementum extracellular matrix protein were measured over 5, 7, and 9 days in culture. While all three substrates supported cell attachment, proliferation, and protein synthesis, only uncoated and titanium-coated tissue culture plastic supported expression of the cementum extracellular matrix protein after 9 days of culture. In addition, the levels of cell proliferation and collagen and noncollagen protein synthesis for cells grown on hydroxyapatite-coated surfaces lagged behind cells cultured on the control or titanium-coated surfaces at each of the three time points. These data suggest that biomaterial substrates markedly can influence the temporal sequence of extracellular matrix proteins associated with periodontal connective tissue attachment formation. In addition to surface composition (titanium versus hydroxyapatite), surface properties (e.g., topography) also may have an effect on periodontal connective tissue attachment formation. This model may be of use in designing biomaterials to support the formation of periodontal connective tissue attachment in vivo.

Advances in biomaterials from 1957 to 1997

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.

Effects of curing time and filler concentration on curing and postcuring of urethane dimethacrylate composites: a microcalorimetric study

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 degrees, 57.0 degrees, and 65.5 degrees C until equilibrium. Increased curing time and filler concentration caused the excess 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.

A chemically modified tetracycline inhibits streptozotocin-induced diabetic depression of skin collagen synthesis and steady-state type I procollagen mRNA

Wasting of connective tissues including skin, bone, and cartilage have been closely associated with elevated matrix metalloproteinase (MMP) activity and depressed collagen content in the streptozotocin (STZ)-induced diabetic rat, while tetracyclines have been reported to normalize total body weight, skin hydroxyproline and collagen content in this model, in part through inhibition of MMPs. In the present study, we report the effect of CMT-1, a chemically modified tetracycline that lacks antimicrobial properties but retains divalent cation binding and MMP inhibitory activity, on diabetic skin collagen synthesis and steady-state levels of procollagen alpha 1(I) mRNA. Male, 4-month old Sprague-Dawley rats received a single injection of 75 mg/kg STZ or citrate vehicle alone and diabetic status was confirmed by positive glucosuria. Some diabetic animals received 10 mg/day of CMT-1 by oral gavage and, 28 days after STZ treatment, body weight, blood glucose values and the in vivo rates of skin collagen production were measured using the pool-expansion technique. Steady-state levels of procollagen alpha 1(I) mRNA were analyzed 21 days after STZ treatment by hybridization of total RNA with a 32P labelled cDNA to rat type I procollagen alpha 1(I) mRNA in a dot-blot assay. STZ treatment was found to significantly depress body weight, skin collagen hydroxyproline content, the in vivo rate of collagen production, and hybridizable levels of type I procollagen alpha 1(I) mRNA. CMT-1 administered daily to STZ-treated rats inhibited the diabetic depression of these parameters but had little or no effect on non-diabetic controls or on STZ-induced hyperglycemia. Thus, in addition to the inhibition of MMP mediated extracellular collagen degradation, these results suggest CMT-1 also acts to inhibit diabetic connective tissue breakdown in STZ-induced diabetes by increasing both steady-state levels of type I procollagen mRNA and collagen synthesis through mechanism(s) that are independent of the antibacterial properties of tetracyclines.

Cytotoxicity of urethane dimethacrylate composites before and after aging and leaching

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 effect of endodontic materials on periodontal ligament cell proliferation, alkaline phosphatase activity, and extracellular matrix protein synthesis in vitro

Recent studies have demonstrated that periodontal ligament-derived (PDL) cells have the potential to regenerate a complete periodontal connective tissue attachment apparatus on both root and artificial substrates. To study the characteristics of endodontic materials conducive to periodontal regeneration, we have established an experimental model using PDL cell cultures that express a 42 kDa protein (CP42) associated with cementum extracellular matrix. In this report, the effect of gutta percha, dental amalgam, composite and calcium hydroxide on PDL cell proliferation, collagen and noncollagen protein synthesis, alkaline phosphatase activity, and CP42 expression are presented. While all substrates supported PDL cell attachment and proliferation, highest levels of alkaline phosphatase activity, collagen and noncollagen protein synthesis were observed in control cultures. Lowest levels of the above parameters were observed with gutta percha while amalgam, composite and calcium hydroxide had intermediate levels. Only control PDL cultures demonstrated CP42 expression. These data suggest that culture substrate can markedly influence periodontal extracellular matrix gene expression in vitro and provide an experimental model to select and develop endodontic materials compatible with periodontal regeneration in vivo.

Bond strength of six soft denture liners processed against polymerized and unpolymerized poly(methyl methacrylate)

The bond strength of six commercial soft denture liners was evaluated by a two-phase tensile test. The soft denture liners investigated were VinaSoft, Prolastic, Flexor, Molloplast-B, Novus, and SuperSoft. The samples were fabricated by processing them (1) against polymerized poly(methyl methacrylate), and (2) against unpolymerized poly(methyl methacrylate). The soft denture liners were processed according to the manufacturers recommendations. The samples were tested using an Instron Universal Testing Machine. The mode of failure, adhesive or cohesive, was also recorded. The bond strength when processed against unpolymerized poly(methyl methacrylate) ranged from 0.48 to 2.60 MPa, and when processed against polymerized poly(methyl methacrylate) the bond strength ranged from 0.94 to 2.56 MPa. A two-way analysis of variance (P = .05) revealed a significant increase in bond strength when the liners were processed against polymerized poly(methyl methacrylate), except for Novus, which had no change, and VinaSoft, which decreased. The Tukey interval between materials was .22 and between methods of polymerization was .08. Four of the six liners investigated demonstrated increased bond strength when processed against polymerized poly(methyl methacrylate). It was concluded that bonding can be influenced by the processing method.

Effect of mixed silanes on the hydrolytic stability of composites

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.

Preparation and characterization of high-surface-area polymer substrates for microcalorimetry

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.

Synthesis of fluorinated Bis-GMA and its use with other fluorinated monomers to formulate hydrophobic composites

Fluorinated Bis-GMA was synthesized and used with other commercially available fluorinated monomers and diluents to prepare hydrophobic composites. The composites were formulated as one-paste 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.

Element release and cytotoxicity of Pd-Cu binary alloys

The release of elements from a series of palladium-copper alloys into cell-culture medium was measured using atomic absorption spectroscopy. The effect of the alloys on the succinyl dehydrogenase activity of Balb/c 3T3 fibroblasts was also measured. Palladium inhibited the release of Cu in alloys up to 70 atomic weight percent Cu. Below 70 at. % Cu, Cu release was < 0.8 micrograms/cm2 at 72 hours. Palladium release was lower from pure Pd (0.08 micrograms/cm2) at 72 hours than from Pd-Cu alloys containing > 70 at. % Cu, where it increased to 1.2 micrograms/cm2. The cytotoxicity of the alloys correlated closely with the release of Cu, becoming markedly cytotoxic above 70 at. % Cu, when Cu release was greater than 2.2 micrograms/cm2.

Hydrolytic stability of silanated zirconia-silica-urethane dimethacrylate composites

The effect of the method of silanation of zirconia-silica by 3-methacryloxypropyltrimethoxysilane (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 0-108 h of boiling in water. The water sorption of these composites was also measured 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 ethanol 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.

Effect of silanation of fillers on their dispersability by monomer systems

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.

Sorption and solubility of 12 soft denture liners

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.

Trends in elastomeric impression materials

In the past three years more addition silicones have been supplied as hydrophilic materials and heavier viscosities have been provided in automatic mixing cartridges. Also, a polyether is now supplied in an automatic mixing system. There has been an increase in the number of products available as monophase or single viscosity systems. Both addition silicones and polyethers are available as bite registration materials.

In vitro effects of metal ions on cellular metabolism and the correlation between these effects and the uptake of the ions

The effects of Ag+1, Au+3, Cd+2, Cu+2, Ga+3, In+3, Ni+2, Pd+2, and Zn+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+1, Cu+2, and Zn+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.

Physical properties of three maxillofacial materials as a function of accelerated aging

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 < or = 0.05.

Application of flow cytometry to determine the cytotoxicity of urethane dimethacrylate in human cells

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 fibroblast (HFF) cells were analyzed for cellular DNA content. Concentrations of 10 and 25 microM of UDMA slightly perturbed the KB cell cycle progression at 24 and 48 h of incubation. However, the effect of 50 microM was more pronounced at the latter incubation time period. In cell growth experiments, the sublethal concentrations (10 and 25 microM) 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 microM (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 microM were not reversible. In HFF cells the depletion of S phase in the cell cycle was the major effect of 50 microM of UDMA. It was concluded that FCM technology is an ideal and practical approach for studying the cytotoxicity of components of dental composites.

Strategies to affect bone remodeling: osteointegration

Osteointegration was defined as a "direct structural and functional connection between ordered living bone and the surface of a load-carrying implant." Although osteointegration was meant originally to describe a biologic fixation of the titanium dental implants, it is now used to describe the attachment of other materials used for dental and orthopedic applications as well. Analyses of material-bone interface showed that osteointegrated implants can have an intervening fibrous layer or direct bone apposition characterized by bone-bonding depending on the composition and surface properties of the biomaterial. This article reviews biologic (host tissue properties and response), biomechanical, and biomaterial factors affecting osteointegration. Biologic factors include the quality of bone. Biomaterial factors include the effect of material composition on the bone-material interface. Suggested areas for future research include determining the correlation between oral bone status and osteoporosis, the effect of gender, age, and endocrine status (e.g., osteoporosis) on implant success or failure, the effect of calcium phosphate coating composition and crystallinity on in vivo performance of implants, the factors contributing to accelerated osteointegration, and development of osteoinductive implants.

Photoelastic stress analysis of self-threading pins

In this laboratory study six self-threading retention pins were evaluated using the two-dimensional photoelastic technique. The experimental samples consisted of 60 blocks of PSM-1 photoelastic material measuring 1" by 1" by 1/4". The samples were divided into six groups of 10 blocks each, with each group representing one of the pins used in the study. Pins were inserted and cores of amalgam and composite were fabricated over the pins. The samples were observed in the polariscope and photographed after pin insertion and after loading the cores with a constant, compressive force of 20 pounds. Using magnification, fringe orders were counted and rounded to the highest 0.5 fringe order. Each sample was evaluated for apical and shoulder stress. All statistical analyses were done using ANOVA at the P = 0.05 significance level. It was concluded from this study that the insertion of self-threading retention pins results in stress at the apical and shoulder areas of the pin. Pin design features, such as shoulder stops, significantly affect the magnitude and location of stress. There were no significant differences in either the apical or shoulder stresses induced when cores were made of either amalgam or composite resin.

Accuracy of models for indirect posterior restorations

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.

The effect of cell monolayer density on the cytotoxicity of metal ions which are released from dental alloys

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.

Uptake of metal cations by fibroblasts in vitro

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).

Physical property comparison of 11 soft denture lining materials as a function of accelerated aging

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 denture-lining 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.

The effect of repeated stretching on the force decay and compliance of vulcanized cis-polyisoprene orthodontic elastics

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%.

Two-input programmable optical processing units

Descriptions of several two-input programmable Boolean optical processing units are presented. These units were designed specifically for use within the optical cellular logic image processor architecture. Results from an experimental implementation of one of these processors are given. Expansion upon one of these units to produce a serial full-adder and subtractor circuit is also shown to be possible.

In vitro synergistic, antagonistic, and duration of exposure effects of metal cations on eukaryotic cells

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.

Comparison of bond strength of six soft denture liners to denture base resin

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 effects of cleaning on the kinetics of in vitro metal release from dental casting alloys

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 vs. 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.(ABSTRACT TRUNCATED AT 250 WORDS)

Viscosity of monophase addition silicones as a function of shear rate

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.

Comparison of the physical properties of 11 soft denture liners

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/cm2; percent elongation, 150% to 542%; hardness, 25 to 95 Shore-A units; tear energy, 1.43 x 10(6) to 40.4 x 10(6) ergs/cm2; 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.

Stress analyses of four prefabricated posts

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.

Precision of and new methods for testing in vitro alloy cytotoxicity

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)

Cytotoxic effects of resin components on cultured mammalian fibroblasts

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 mumol/L). The ID50 concentrations for three of the components, including Bis-GMA, UDMA, TEGDMA, and Bis-phenol A, ranged between 10 and 100 mumol/L, while the ID50 values of three components (N,N dihydroxyethyl-p-toluidine, camphoroquinone, and N,N dimethylaminoethyl methacrylate) were above 100 mumol/L. The concentrations to which the cells and tissues are exposed in vivo are not known. This study should help to identify the concentrations of organic composite components which pose clinical cytotoxic hazards.

The in vitro effects of metal cations on eukaryotic cell metabolism

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.