Physical properties of materials derived from diamondoid molecules.

Diamondoids are small hydrocarbon molecules which have the same rigid cage structure as bulk diamond. They can be considered the smallest nanoparticles of diamond. They exhibit a mixture of properties inherited from bulk cubic diamond as well as a number of unique properties related to their size and structure. Diamondoids with different sizes and shapes can be separated and purified, enabling detailed studies of the effects of size and structure on the diamondoids' properties and also allowing the creation of chemically functionalized diamondoids which can be used to create new materials. Most notable among these new materials are self-assembled monolayers of diamondoid-thiols, which exhibit a number of unique electron emission properties.

Effect of different surface treatments and adhesives on repair bond strength of resin composites after one and 12 months of storage using an improved microtensile test method.

OBJECTIVES: To evaluate the effect of surface treatments and bonding systems on the repair bond strength between composite materials after one and 12 months of storage, using an improved microtensile test method. METHODS: A total of 72 composite cylinders (Tetric Evo Ceram, Ivoclar) were fabricated, stored in distilled water for two weeks followed by thermal cycling (5000 times between 5°C and 55°C), and served as substrate. The cylinders were mechanically roughened using 320-grit silicon carbide sandpaper, etched with 37% phosphoric acid gel, rinsed with water, and divided equally into three experimental groups: group 1, unchanged surface; group 2, sandblasting of the surface (CoJet tribochemical silica sand, 3M ESPE; Microetcher II, Danville Engineering Inc); and group 3, surface silane coating (Bis-Silane, BISCO Inc). Eight control cylinders were prepared and underwent similar aging as the substrate. Each experimental group was divided into subgroups that received the following bonding systems: one-step self-etching adhesive (AdheSE One, Ivoclar Vivadent), two-step self-etching adhesive (Clearfil SE, Kuraray America), and three-step etch-and-rinse adhesive (Adper Scotchbond Multi-Purpose, 3M ESPE). Fresh composite (Tetric Evo Ceram, Ivoclar) was placed and cured on top of the prepared substrate cylinders. The specimens were placed in distilled water for a week and thermocycled the same way as before. Eight composite control cylinders were also stored and thermocycled for the same period of time. Half of the cylinders in each test group were tested at one month and the second half at 12 months. The cylinders were serially sectioned in an automatic cutting machine, producing 10 to 20 1.1 × 1.1-mm test specimen beam from each cylinder. Specimens were prepared for microtensile testing and the tensile strength calculated based on the force at fracture and specimen dimension. The fracture surfaces were examined under a stereomicroscope and the type of fracture noted. RESULTS: The mean tensile strength of composite control was 54.5 ± 6.0 MPa at one month and 49.6 ± 5.1 MPa at 12 months. The mean tensile strength for the repaired groups ranged from 26.4 ± 6.8 MPa to 49.9 ± 10.4 MPa at one month and 21.2 ± 9.9 to 41.3 ± 7.5 at 12 months. There was a statistical difference between all groups (p<0.05) at one month. This difference was less pronounced at 12 months. The highest repair strength was obtained in the group having a silane-coated surface and Clearfil, the two-step self-etching adhesive. Clearfil also had the highest repair strength within each surface treatment group. There was a tendency for lower tensile strength at 12 months compared with one month. Most fractures were of the adhesive type; the highest number of cohesive fractures, 16% at one month and 12% at 12 months, were in groups with the highest tensile strength. CONCLUSION: The best repair bond strength was achieved by using freshly mixed silane solution on the substrate in addition to an adhesive, rendering a thin bonding layer.

Side effects of external tooth bleaching: a multi-centre practice-based prospective study.

OBJECTIVE: The study was performed to assess the risk of at-home and in-office bleaching procedures, and to recognise potential predictors for side effects. DESIGN: Multi-centre, questionnaire-based prospective study with follow-ups at around 14 days and around one year post-treatment. SETTING: General practices and university clinics during the years 2007-2009 in Scandinavia. SUBJECTS: Patients with tooth bleaching as part of the treatment plan. RESULTS: The prevalence of experienced tooth sensitivity at first follow-up was independent of bleaching procedure (at-home = 50.3% [n = 143]; in-office = 39.3% [n = 28]; p >0.05; 95% CI [OR]: 0.198-1.102) whereas prevalence of gingival irritation was higher after in-office treatment (at-home = 14.0%; in-office = 35.7%; p <0.05) (mean age: 37.3 years; 73.7% women; n = 171). At the second follow-up, two and three patients reported side effects attributed to the bleaching treatment in the at-home and in-office groups, respectively. Predictors for side effects were tooth sensitivity, surface loss and gingivitis when observed at inclusion. Treatment-related predictors were bleaching concentration and contact between tray and gingiva. CONCLUSIONS: Bleaching treatment, irrespective of method, caused a high prevalence of side effects. Patients associated with the predictors at inclusion mentioned above should be notified of the risk for side effects and treated only if bleaching is indicated based on a proper diagnosis.

Biotransformation enzymes and lung cell response to 2-hydroxyethyl-methacrylate.

The aim of this in vitro study was to investigate possible involvement of cytochrome P450 (CYP) enzymes in modifying the toxic potential of 2-hydroxyethyl-methacrylate (HEMA). Primary cultures of CYP expressing rat alveolar type 2 cells were exposed to varying concentrations of HEMA. Nuclear translocation of aryl hydrocarbon receptor (AhR) after HEMA exposure (100 µM) was demonstrated by immunocytochemical staining. Using reverse transcriptase PCR, increased mRNA level of AhR-regulated genes encoding enzymes associated with detoxification of xenobiotics were found. Exposure to 1 mM HEMA rapidly (6 h) resulted in cells with an apoptotic like morphology as suggested by marked nuclear condensation. Cotreatment of the HEMA exposed cells with a CYP inhibitor (disulfiram) or an antioxidant (vitamin C) effectively rescued the cells from this fate. Despite this effect of vitamin C, no increased level of reactive oxygen species was observed in the HEMA exposed cells. Our results suggest that HEMA activates AhR regulated gene transcription and that CYP is involved in the formation of a highly reactive HEMA metabolite.

The development of T cell-dominated inflammatory responses induced by sodium lauryl sulphate in mouse oral mucosa.

The effect of a single time exposure of SLS to the buccal mucosa of mice was compared to one application of the hapten OXA (oxazolone), evaluated by routine histology, immunohistochemistry and ELISA quantifications of cytokines. The SLS concentrations (2%, 4% and 8%) resulted in epithelial surface necrosis at 1-6 h, after 2-6 h accumulation of intra-epithelial neutrophils and at 24 h the main inflammatory cells were mononuclear. Increased concentrations of SLS gave more severe damage. CD4(+) T cells were found at 6 h and increased slightly up to 24 h and were most frequently seen at the lowest SLS dose. The CD8(+) T cells were kept at a low number during the whole 24 h observation period, but increased proportionally to the CD4(+) T cells. One application of 1% OXA did not raise the number of cells of either phenotype (2-24 h). Neither IL-2 nor IFN-γ demonstrated increased levels during the week of observation at any concentration of SLS, contrary to one application of OXA which caused increased IL-2 levels both at the local application site and in the regional and distant lymph nodes. Regardless of SLS concentration, a minor increase in regional lymph node weight was observed 8-12 h after substance application, quickly to subside whilst one OXA application gave a maximal weight increase at 48-72 h. We conclude that oral mucosa irritant SLS reactions gave early surface necrosis and neutrophil infiltrations and later mononuclear cell infiltrations dominated by CD4(+) T cells. The cytokines IL-2 and IFN-γ and lymphocyte proliferation in the regional lymph nodes was not observed after SLS application, contrary to hapten application.

DNA-damage, cell-cycle arrest and apoptosis induced in BEAS-2B cells by 2-hydroxyethyl methacrylate (HEMA).

The methacrylate monomer 2-hydroxyethyl methacrylate (HEMA) is commonly used in resin-based dental restorative materials. These materials are cured in situ and HEMA and other monomers have been identified in ambient air during dental surgery. In vitro studies have demonstrated a toxic potential of methacrylates, and concerns have been raised regarding possible health effects due to inhalation. In this study we have investigated the mechanisms of HEMA-induced toxicity in the human lung epithelial cell line BEAS-2B. Depletion of cellular glutathione (GSH) and an increased level of reactive oxygen species (ROS) were seen after 2h of exposure, but the levels were restored to control levels after 12h. After 24h, inhibited cell proliferation and apoptotic cell death were found. The results of the Comet assay and the observed phosphorylation of DNA-damage-associated signalling proteins including Chk2, H2AX, and p53 suggest that the toxicity of HEMA is mediated by DNA damage. Further, the antioxidant trolox did not counteract the HEMA-induced cell-cycle arrest, which indicates that the DNA damage is of non-oxidative origin.

Role of thiol-complex formation in 2-hydroxyethyl- methacrylate-induced toxicity in vitro.

Methacrylate monomers that are found to leach from cured resin-based dental materials induce biological effects in vitro. The underlying mechanisms have not been fully elucidated although involvement of increased cellular reactive oxygen species (ROS) and DNA-damage has been suggested. In this in vitro study we have elucidated the impact of a commonly used methacrylate monomer, HEMA, on the level and oxidation state of cellular glutathione, intracellular ROS level, as well as the formation of complex between HEMA and glutathione. HEMA exposure rapidly led to increased level of ROS and reduced level of GSH (reduced form of glutathione). Antioxidants effectively counteracted the ROS increase, but had no effect on the GSH depletion. No change in glutathione-disulphide (GSSG; oxidized form of glutathione) concentration was detected in the HEMA treated cells, showing that oxidation of glutathione was not responsible for the reduced GSH concentration. Further we demonstrated spontaneous formation of a complex between HEMA and GSH. In conclusion, we showed that exposure to HEMA led to drop in cellular glutathione level probably caused by complex formation with HEMA. A similar covalent binding of HEMA to macromolecules combined with increased level of cellular ROS due to lower levels of GSH is suggested to be important factors triggering the toxic response.

HEMA reduces cell proliferation and induces apoptosis in vitro.

OBJECTIVES: Methacrylate monomers have been identified in aqueous extracts of freshly cured compomers. Both cells in the pulpal cavity and various cells of the oral mucosa can potentially be exposed to these leachables. Short-term exposure to dental monomers at relatively high concentrations induces adverse biological effects in vitro. The mechanisms involved have not been fully elucidated although involvement of various signaling pathways including ROS formation, activation of MAP-kinases and caspases has been suggested. The aim of this study was to investigate potential cellular responses following long-term exposure to relatively low and potentially more clinical relevant HEMA concentrations. METHODS: A submandibular gland cell line was exposed to HEMA (20-600 microM) for up to 72h. The impact on cell proliferation, apoptosis, and possible underlying mechanisms was assessed by flow cytometry, microscopy and western blotting. RESULTS: Exposure to HEMA (600 microM) resulted in reduced cell proliferation after 24h and increased apoptosis after 60h. Further, we observed ATM dependent phosphorylation of p53, advocating an initial DNA damage in the HEMA exposed cells. SIGNIFICANCE: In conclusion, we show that exposure to relatively low concentration of HEMA for a prolonged time result in cell death, possibly as a consequence of DNA damage.

Experimental determination of the ionization potentials of the first five members of the nanodiamond series.

The ionization potentials of size- and isomer-selected diamondoids (nanodiamond containing one to five crystal cages) have been measured by means of total-ion-yield spectroscopy. We find a monotonic decrease of the ionization potential with increasing diamondoid size. This experimental result is compared to recent theoretical predictions and comparable investigations on related carbon clusters, the fullerenes, which show isomer effects to be stronger than size dependence.

Monochromatic electron photoemission from diamondoid monolayers.

We found monochromatic electron photoemission from large-area self-assembled monolayers of a functionalized diamondoid, [121]tetramantane-6-thiol. Photoelectron spectra of the diamondoid monolayers exhibited a peak at the low-kinetic energy threshold; up to 68% of all emitted electrons were emitted within this single energy peak. The intensity of the emission peak is indicative of diamondoids being negative electron affinity materials. With an energy distribution width of less than 0.5 electron volts, this source of monochromatic electrons may find application in technologies such as electron microscopy, electron beam lithography, and field-emission flat-panel displays.

Cytotoxicity of new resin-, calcium hydroxide- and silicone-based root canal sealers on fibroblasts derived from human gingiva and L929 cell lines.

AIM: To assess ex vivo the cytotoxic effects of five new root canal sealers (RC Sealer, Epiphany, EndoREZ, GuttaFlow and Acroseal) and three existing products (AH Plus, RoekoSeal and Apexit) using primary human gingival fibroblasts (HGF) and a mouse fibroblast cell line, L929. METHODOLOGY: Eight samples of each sealer were fabricated in sterile cylindrical Teflon blocks, 4.4 mm diameter and 2 mm height and then divided into two groups, fresh and aged specimens. Extraction of fresh specimens was carried out after setting whilst aged specimens were placed in Petri dishes and kept in a humid chamber at 37 degrees C for 7 days before extraction in cell culture medium using the ratio 1.25 cm(2) mL(-1). Undiluted eluates were used for the dimethylthiazol diphenyltetrazolium bromide (MTT) assay with HGF and L-929. Morphology of HGF cells was also examined by an inverted microscope using undiluted eluates of the sealers. The results were analysed using a two-tailed t-test (alpha = 0.05) between groups. RESULTS: Resin-based (Epiphany and EndoREZ) and calcium hydroxide-based (Apexit and Acroseal) sealers were significantly more cytotoxic than other sealers (P<0.05). However, L929 cells were more sensitive to Apexit and EndoREZ than HGF cells. RC Sealer showed mild cytotoxicity to HGF at both setting times. AH Plus did not exert any cytotoxic effect to HGF and aged specimens appeared to induce cellular proliferation. RoekoSeal and GuttaFlow also demonstrated mild cytotoxicity. GuttaFlow was slightly more cytotoxic to both cultures, especially when tested fresh. CONCLUSIONS: Toxicity varied but RC Sealer and GuttaFlow were the least toxic new sealers.

Molecular limits to the quantum confinement model in diamond clusters.

The electronic structure of monodispersed, hydrogen-passivated diamond clusters (diamondoids) in the gas phase has been studied with x-ray absorption spectroscopy. The data show that the bulk-related unoccupied states do not exhibit any quantum confinement. Additionally, density of states below the bulk absorption edge appears, consisting of features correlated to CH and CH2 hydrogen surface termination, resulting in an effective redshift of the lowest unoccupied states. The results contradict the commonly used and very successful quantum confinement model for semiconductors, which predicts increasing band edge blueshifts with decreasing particle size. Our findings indicate that in the ultimate size limit for nanocrystals a more molecular description is necessary.

Tooth bleaching--a critical review of the biological aspects.

Present tooth-bleaching techniques are based upon hydrogen peroxide as the active agent. It is applied directly, or produced in a chemical reaction from sodium perborate or carbamide peroxide. More than 90% immediate success has been reported for intracoronal bleaching of non-vital teeth, and in the period of 1-8 years' observation time, from 10 to 40% of the initially successfully treated teeth needed re-treatment. Cervical root resorption is a possible consequence of internal bleaching and is more frequently observed in teeth treated with the thermo-catalytic procedure. When the external tooth-bleaching technique is used, the first subjective change in tooth color may be observed after 2-4 nights of tooth bleaching, and more than 90% satisfactory results have been reported. Tooth sensitivity is a common side-effect of external tooth bleaching observed in 15%-78% of the patients, but clinical studies addressing the risk of other adverse effects are lacking. Direct contact with hydrogen peroxide induced genotoxic effects in bacteria and cultured cells, whereas the effect was reduced or abolished in the presence of metabolizing enzymes. Several tumor-promoting studies, including the hamster cheek pouch model, indicated that hydrogen peroxide might act as a promoter. Multiple exposures of hydrogen peroxide have resulted in localized effects on the gastric mucosa, decreased food consumption, reduced weight gain, and blood chemistry changes in mice and rats. Our risk assessment revealed that a sufficient safety level was not reached in certain clinical situations of external tooth bleaching, such as bleaching one tooth arch with 35% carbamide peroxide, using several applications per day of 22% carbamide peroxide, and bleaching both arches simultaneously with 22% carbamide peroxide. The recommendation is to avoid using concentrations higher than 10% carbamide peroxide when one performs external bleaching. We advocate a selective use of external tooth bleaching based on high ethical standards and professional judgment.

Isolation and structure of higher diamondoids, nanometer-sized diamond molecules.

We exploited the exceptional thermal stability and diverse molecular shapes of higher diamondoids (C22 and higher polymantanes) to isolate them from petroleum. Molecules containing 4 to 11 diamond-crystal cages were isolated and crystallized, and we obtained single-crystal x-ray structures for representatives from three families. Rigidity, strength, remarkable assortments of three- dimensional shapes, including resolvable chiral forms, and multiple, readily derivatizable attachment sites make them valuable nanometer-size molecular building blocks.

Rat lung inflammatory responses after in vivo and in vitro exposure to various stone particles.

Rat lung alveolar macrophages and type 2 cells were exposed for 20 h in vitro to various stone particles with differing contents of metals and minerals (a type of mylonite, gabbro, feldspar, and quartz). The capability to induce the release of the inflammatory cytokines interleukin-6 (IL-6), tumour necrosis factor-alpha (TNF-alpha), and macrophage inflammatory protein-2 (MIP-2) was investigated. We found marked differences in potency between the various particles, with mylonite being most potent overall, followed by gabbro, and with feldspar and quartz having an approximately similar order of lower potency. The results also demonstrated differences in cytokine release pattern between the two cell types. For all particle types including quartz, type 2 cells showed the most marked increase in MIP-2 and IL-6 secretion, whereas the largest increase in TNF-alpha release was observed in macrophages. To investigate possible correlations between in vitro and in vivo inflammatory responses, rats were instilled with the same types of particles and bronchoalveolar lavage (BAL) fluid was collected after 20 h. The results demonstrated a correlation between the in vitro cytokine responses and the number of neutrophilic cells in the BAL fluid. The BAL fluid also showed a strong MIP-2 response to mylonite. However, this was the only particle type to give a significant cytokine response in the BAL fluid. We further examined whether a similar graded inflammatory response would be continued in type 2 cells and alveolar macrophages isolated from the exposed animals. Again a differential cytokine release pattern was observed between type 2 cells and macrophages, although the order of potency between particle types was altered. In conclusion, various stone particles caused differential inflammatory responses after both in vitro and in vivo exposure, with mylonite being the most potent stone particle. The results suggest the alveolar type 2 cell to be an important participant in the inflammatory response following exposure to particles.

Cytotoxicity of dental glass ionomers evaluated using dimethylthiazol diphenyltetrazolium and neutral red tests.

The purpose of this study was to assess the cytotoxicity of some commonly used glass ionomers. Three chemically cured glass ionomers (Fuji II, Lining cement, and Ketac Silver) and one light-cured (Fuji II LC) were tested. Extracts of mixed non-polymerized materials and polymerized specimens were prepared in accordance with ISO standard 10993-12. The polymerized specimens were cured and placed either directly in the medium (freshly cured), left for 24 h (aged), or aged plus ground before being placed in the medium. The cytotoxicity of extracts was evaluated on mouse fibroblasts (L, 929), using dimethylthiazol diphenyltetrazolium (MTT) and neutral red (NR) assays. Further, the concentrations of aluminum, arsenic and lead were analyzed in aqueous extracts from freshly cured and aged samples, and the fluoride levels analyzed in aqueous extracts from freshly cured samples. All extracts except that of non-polymerized Ketac Silver were rated as severely cytotoxic in both assays. Extracts of polymerized material were significantly more cytotoxic than extracts of non-polymerized material. All freshly cured glass ionomers released aluminum and fluoride concentrations far above what is considered cytotoxic (aluminum >0.2 ppm and fluoride >20 ppm). Extracts from freshly cured Lining Cement contained the highest concentrations of aluminum and fluoride (215 ppm and 112 ppm). Extracts from freshly cured Ketac Silver had the lowest concentrations of aluminum and fluoride but the highest of lead (100 ppm). It can be concluded that all extracts from non-cured, freshly cured, and aged glass ionomers contained cytotoxic levels of substances. Curing did not reduce the toxicity significantly.

Corrosion and biocompatibility testing of palladium alloy castings.

OBJECTIVE: The biocompatibility of palladium-copper alloys has been questioned in the literature. The intention of the present work was to study: (a) the release of ions in an immersion test from a copper-containing alloy, Option((R)) (79% Pd, 10% Cu, 9% Ga, 2% Au), compared with an alloy without Cu, IS85 (82% Pd, 6% Ga, 3.5% Sn, 3.5% In, 2.5% Ag, 2.5% Au); (b) the effect of oxide films produced by preoxidation on corrosion resistance; and (c) the possibility of biologically synergetic effects of ions released. METHODS: Specimens of both alloys were cast, rubbed and ultrasonically cleaned. Metallographic specimens were prepared after (a) casting and (b) preoxidizing treatment at approximately 1000 degrees C and studied by SEM and EDS. Immersion tests were carried out in a solution of 0.1mol/l of NaCl and 0.1mol/l of lactic acid at 37 degrees C for 7 days. The alloy specimens were tested in the following three steps: (1) as preoxidized; (2) after subsequent removal of a 0.1mm thick layer by grinding; and (3) after an additional removal of approximately 0.1mm by grinding. The test solutions were analyzed by means of ICP to record the amounts of ions that had leached out from the alloy specimens. The biocompatibility was studied by cell culture tests and the HET-CAM method. Test solutions were prepared by dissolving PdCl(2) and CuCl(2) to appropriate concentrations. RESULTS: The metallographic investigations revealed moderate segregations in interdendritic regions and grain boundaries. After preoxidation in air a zone of oxidation from 25 up to 200 microm thickness for Option and from 5 to 10 microm for IS85 was found. Oxidation was observed along a rim for both alloys and for Option also along interdendritic positions. The oxides were seen as small, dark spots <1 microm in a metallic matrix. These results indicate that: (1) the oxidation of the copper-containing palladium alloy is far more severe than that of the alloy with no copper; and (2) the elemental release from these oxides is substantially larger than that from the corrosion of the metallic structure. The results of the cell culture testing showed that Cu was most toxic, followed by Cu(2+)+Pd(2+) (1:2), based on the determination of the concentration that caused 50% cytotoxicity. The HET-CAM testing showed Cu(2+)+Pd(2+) (1:2) to have the highest irritation score. SIGNIFICANCE: The copper-containing Pd alloy developed a 0.1mm thick rim with small oxide particles in a metallic matrix during preoxidation. If this rim is not completely removed, significantly more Cu, Ga and Pd ions have been shown to leach into the test solution than from the alloy structure. No synergetic effect of Cu and Pd ions was observed in cultured cells, while the mixture Pd(2+)+Cu(2+) (1:2) was most irritating to mucous membrane as evaluated by the HET-CAM method.

Irritation test of tissue adhesives for facial prostheses.

STATEMENT OF PROBLEM: Adhesives are commonly used to improve the retention of a facial prosthesis to the skin. Although no requirement exists for facial prosthetic adhesives, an adhesive should be nonirritating and nontoxic. PURPOSE: This study assessed the irritative potential of facial prosthetic adhesives by using an in vitro technique for detection of eye-irritating chemicals. MATERIAL AND METHODS: Ten adhesives were evaluated by the hens egg test chorioallantoic membrane method. Adhesives were applied to the chorioallantoic membrane in fertilized hen eggs, and the membrane examined by a photomacroscope for injury to the blood vessels. The average irritation score was calculated from the recorded times for the debut of hemorrhage, lysis, and coagulation, and the products were classified as being non, slight, moderate, or strong irritants, based on the irritation score. RESULTS: The predominant injury to the membrane was coagulation of blood vessels, and the exposure time needed to initiate the reaction was dependent on the composition of the product. Four products were classified as strong irritants, 1 as moderate, and the remaining 5 as slight or nonirritant. CONCLUSION: On the basis of a test for eye irritation, the irritant potential of tissue adhesives varied from non to severe. The most severe reactions were mainly seen in products containing the solvent ethyl acetate.

Cytotoxicity of dental alloys, metals, and ceramics assessed by millipore filter, agar overlay, and MTT tests.

STATEMENT OF PROBLEM: Biocompatibility of dental materials is dependent on the release of elements from the materials. In addition, the composition, pretreatment, and handling of the materials influence the element release. PURPOSE: This study evaluated the cytotoxicity of dental alloys, metals, and ceramics, with specific emphasis on the effects of altering the composition and the pretreatment. MATERIAL AND METHODS: By using cells from a mouse fibroblast cell line and the agar overlay test, Millipore filter test, and MTT test, cytotoxicity of various metals, metal alloys, and ceramics for dental restoration were studied. Effects of altering the composition of a high noble gold alloy and of pretreatment of a ceramic-bonding alloy were also studied. In addition, the release of elements into the cell culture medium by the materials studied was measured using an inductively coupled plasma optical emission spectrophotometer. The results of the MTT test were analyzed statistically using ANOVA and Scheffé test at a significance level of P <.05. RESULTS: Specimens manufactured from materials intended for dental restorations and handled in accordance with the manufacturers' instructions were ranked from "noncytotoxic" to "mildly cytotoxic" according to the agar overlay and Millipore filter tests. For the MTT test, no significant differences were observed between these materials and controls, with the exception of JS C-gold and unalloyed titanium. The modified materials were ranked from "mildly cytotoxic" to "moderately cytotoxic" in the agar overlay and Millipore filter tests and from "noncytotoxic" to "moderately cytotoxic" in the MTT test. Thus, cytotoxicity was related to the alloy composition and treatment. The release of Cu and Zn seemed to be important for the cytotoxic effect. CONCLUSION: Alterations in the composition and the pretreatment can greatly influence the cytotoxicity, and the results stress the importance of carefully following the manufacturers' instructions when handling dental materials.

Age of restorations at replacement in permanent teeth in general dental practice.

The ages of 6,761 restorations replaced in permanent teeth, 6,088 in adults > or =19 years of age and 673 in adolescents < or =18 years, were available for analyses. The results showed that the median age of amalgam restorations in adults was 11 years and that of resin-based composite restorations 8 years. This difference in longevity was significant (P = 0.000 l). The median age of failed conventional glass ionomer restorations in adults was 4 years and for resin-modified glass ionomer 2 years. In adolescents, the median longevity of failed amalgam restorations was 5 years and that of composite restorations 3 years, while both types of glass ionomers had a median longevity of 2 years. The data were subdivided based on clinician gender and practice setting. The results showed that the median age of amalgam and composite restorations replaced Its male clinicians was higher than that for female clinicians irrespective of clinical setting. The median age of amalgam and composite restorations replaced by salaried dentists was significantly lower than that by private practitioners. Minor differences were noted in longevity of restorations between male and female patients. The age of replaced restorations was shortest for the group of clinicians with the least clinical experience and highest for those that graduated > or = 30 years ago.