Accuracy of ringless casting and accelerated wax-elimination technique: a comparative in vitro study.

PURPOSE: The purpose of this study was to determine whether the ringless casting and accelerated wax-elimination techniques can be combined to offer a cost-effective, clinically acceptable, and time-saving alternative for fabricating single unit castings in fixed prosthodontics. MATERIALS AND METHODS: Sixty standardized wax copings were fabricated on a type IV stone replica of a stainless steel die. The wax patterns were divided into four groups. The first group was cast using the ringless investment technique and conventional wax-elimination method; the second group was cast using the ringless investment technique and accelerated wax-elimination method; the third group was cast using the conventional metal ring investment technique and conventional wax-elimination method; the fourth group was cast using the metal ring investment technique and accelerated wax-elimination method. The vertical marginal gap was measured at four sites per specimen, using a digital optical microscope at 100× magnification. The results were analyzed using two-way ANOVA to determine statistical significance. RESULTS: The vertical marginal gaps of castings fabricated using the ringless technique (76.98 ± 7.59 µm) were significantly less (p < 0.05) than those castings fabricated using the conventional metal ring technique (138.44 ± 28.59 µm); however, the vertical marginal gaps of the conventional (102.63 ± 36.12 µm) and accelerated wax-elimination (112.79 ± 38.34 µm) castings were not statistically significant (p > 0.05). CONCLUSIONS: The ringless investment technique can produce castings with higher accuracy and can be favorably combined with the accelerated wax-elimination method as a vital alternative to the time-consuming conventional technique of casting restorations in fixed prosthodontics.

Assessment of the impact strength of the denture base resin polymerized by various processing techniques.

AIM: To measure the impact strength of denture base resins polymerized using short and long curing cycles by water bath, pressure cooker and microwave techniques. MATERIALS AND METHODS: For impact strength testing, 60 samples were made. The sample dimensions were 60 mm × 12 mm × 3 mm, as standardized by the American Standards for Testing and Materials (ASTM). A digital caliper was used to locate the midpoint of sample. The impact strength was measured in IZOD type of impact tester using CEAST Impact tester. The pendulum struck the sample and it broke. The energy required to break the sample was measured in Joules. Data were analyzed using Student's " t" test. RESULTS: There was statistically significant difference in the impact strength of denture base resins polymerized by long curing cycle and short curing cycle in each technique, with the long curing processing being the best. CONCLUSION: The polymerization technique plays an important role in the influence of impact strength in the denture base resin. This research demonstrates that the denture base resin polymerized by microwave processing technique possessed the highest impact strength.

Marginal discrepancy as affected by selective placement of die-spacer: an in vitro study.

An increase in the marginal discrepancy is seen after cementation with a luting agent and provision of cement space with a die-spacer is the most preferred method to avoid it. Recommended thickness of die-spacer is 25-40 µm. Smaller die-spacer thickness was consistently found at the axio-occlusal line angles as compared to the other surfaces which has been postulated to that the spacer paint tends to flow away from the sharp line angles and cusp tips as a result of increased surface tension. The absence of adequate relief spaces in these areas impedes the flow of cement beyond the occlusal portion of the casting, which would result in incomplete seating because of hydraulic pressure. Fifty stone dies were duplicated from a steel die and were divided into five groups of sample size 10, where the die-spacer was selectively placed. Measurements were taken at four points, 90° apart from each other with the help of optical microscope. Later all the castings were cemented using Glass Inomer cement as a luting agent, under a 10 kg static load and measurements were recorded. Statistical analysis showed samples with no spacer had the maximum pre and post cementation gap while the least discrepancy was seen in group with additional layer of die-spacer painted over the axio-occlusal line angle. The results were highly significant which clearly indicated the superiority of this group over others. Within limitations of the study, it can be said that application of additional layer of die-spacer at the axio-occlusal line angle will help in decreasing the post cementation marginal discrepancy in full cast metal crowns.

Influence of the processing technique on the flexural fatigue strength of denture base resins: an in vitro investigation.

BACKGROUND: Though acrylic resins possess many desirable properties, denture fracture due to flexural fatigue or impact failure is a common problem. One major factor influencing the flexural fatigue strength of denture base resins is the processing technique used. AIM: To measure the flexural fatigue strength of denture base resins polymerized using short and long curing cycles using water bath, pressure cooker, and microwave polymerization techniques. MATERIALS AND METHODS: Flexural fatigue strength of 60 samples (n=10) were measured using a cyclic 3-point loading method on a dynamic universal testing machine. Data were analyzed using a Student 't' test. RESULTS: Comparative evaluation using Student's 't' test of mean flexural fatigue strength of samples processed by water bath processing (660.6) and the microwave technique (893.6) showed statistically significant (P < 0.01) result with microwave processing being higher. Comparison of water bath (660.6) and pressure cooker (740.6) processing and microwave (893.6) and pressure cooker (740.6) processing using Student's 't' test was not statistically significant (P > 0.05). In the intra-group analysis, it was found that there was statistically significant difference in samples processed using the short and long curing cycle, the latter being better in all groups, P-values being < 0.05, < 0.001, and < 0.001 for water bath, microwave, and pressure cooker polymerization techniques, respectively. CONCLUSION: The polymerization procedure plays an important role in influencing the flexural fatigue strength of denture base resins, and the microwave long curing processing technique produced denture bases with highest flexural fatigue strength.

Efficacy of different disinfectant systems on alginate and addition silicone impression materials of Indian and international origin: a comparative evaluation.

Study was planned to evaluate the efficacy of commonly used disinfectants and to study qualitatively and quantitatively the persistence of microflora on the untreated (control group) and the disinfected impression surface after 24 h. Disinfectant systems used were immersion systems like glutaraldehyde, sodium hypochlorite and the ultraviolet chamber. The effect of disinfectant on most commonly used Indian impression materials was carried out in this study and results compared with the most commonly used foreign brands for irreversible hydrocolloid and addition silicone. Impressions were made of 25 healthy volunteers. These were disinfected and incubated in an incubator for 24 h at 37°C for aerobic organisms. The inoculation in nutrient media was done to test the viability of microorganisms that can persist after rinsing and disinfection of the impression surface. The colony forming units were counted and compared with that of control group. Control group of all the impression material samples showed growth of Streptococcus viridans, Diphtheroids, Streptococcus pneumoniae to a greater extent. The growth of Candida albicans, Pseudomonas aerugenosa and Staphyloccus albus was present in all the groups but to a lesser extent. The persistence of the microflora on the impression surface of both the studied brands was similar but the concentration of organisms in the alginate control group was two folds as compared to addition silicone group. Use of ultraviolet chamber gave better results compared to the studied immersion systems. All the disinfection systems were effective in reducing the microbial load with ultraviolet chamber as the most effective.

An isolectin complex from Trichosanthes anguina seeds.

Sepharose 4B affinity chromatography of Trichosanthes anguina seed extract and subsequent elution with galactose resulted in the isolation of an apparently single lectin with molecular weight of 45,000 +/- 700. However, major amount of the hemagglutinating activity was recovered as unadsorbed protein fraction. High affinity matrix Lactamyl Seralose could retain most of the galactose specific lectin activity from fraction 'A' which was eluted with lactose. It is evident from PAGE and SDS-PAGE analysis of the purified protein that T. anguina seeds contains a mixture of isolectins ranging in molecular weight from 30,000 to 50,000 +/- 1300. Periodic Acid Schiff's staining of the gels revealed this lectin complex to be a combination of glycosylated and non-glycosylated lectins. Two Isolectins SLc and IEL from within this complex have been isolated by affinity and ion exchange chromatography respectively. Apparent homology of these two lectins is indicated by their identical molecular weight (45 kDa), sub unit composition, non glycoprotein nature and immunological identity. However, these two lectins show minor differences in their biological and physicochemical properties. The peptide maps of the two lectins obtained after digestion with Trypsin and Pronase E also indicate minor changes in the primary structure.

Protective effect of turmeric (Curcuma longa L.) extract on carbon tetrachloride-induced liver damage in rats.

The protective effect of tumeric extract (TE) in diet on CCl4-treated rats was studied. Rats were divided into 5 groups: (1) untreated, (2) CCl4 treated, (3) pre-TE for 2 weeks followed by CCl4, (4) TE + CCl4 given concurrently and (5) 5% TE as positive control. The serum levels of bilirubin, cholesterol, aspartate aminotransferase, (AST), alanine amino transferase (AST), (ALT) and alkaline phosphatase were estimated after 1, 2 and 3 months. CCl4 caused a maximum increase (2-3-fold in all the above parameters. As compared to CCl4 group, a short pre-treatment of TE showed reduction in cholesterol, bilirubin, AST, ALT and alkaline phosphatase activity whereas concurrent treatment of TE + CCl4 reduced to a greater extent the levels of all parameters except ALT. To conclude, concurrent treatment of TE gave significant protection against CCl4 though the values did not reach the normal levels.

O6-methylguanine-DNA methyltransferase activity in human buccal mucosal tissue and cell cultures. Complex mixtures related to habitual use of tobacco and betel quid inhibit the activity in vitro.

Extracts prepared from tissue specimens of normal, non-tumourous human buccal mucosa, and cultured buccal epithelial cells and fibroblasts, exhibited O6-methylguanine-DNA methyltransferase (MGMT) activity by catalysing the repair of the premutagenic O6-methylguanine lesion in isolated DNA with rates of 0.2 to 0.3 pmol/mg protein. An SV40 T antigen-immortalized buccal epithelial cell line termed SVpgC2a and a buccal squamous carcinoma line termed SqCC/Y1, both of which lack normal tumour suppressor gene p53 function, exhibited about 50 and 10% of the MGMT activity of normal cells, respectively. The normal, experimentally transformed and tumourous buccal cell types showed MGMT mRNA levels which correlated with their respective levels of MGMT activity. Exposure of buccal cell cultures to various organic or water-based extracts of products related to the use of tobacco and betel quid, decreased both cell survival (measured by reduction of tetrazolium dye) and MGMT activity (measured subsequently to the exposures in cellular extracts). Organic extracts of bidi smoke condensate and betel leaf showed higher potency than those of tobacco and snuff. An aqueous snuff extract also decreased both parameters, whereas an aqueous areca nut extract was without effect. The well-established sulph-hydryl-reactive agent Hg2+, a corrosion product of dental amalgam, served as a positive control and decreased MGMT activity following treatment of cells within a range of 1-10 microM. Taken together, significant MGMT activities were demonstrated in buccal tissue specimens and in the major buccal mucosal cell types in vitro. Lower than normal MGMT activity in two transformed buccal epithelial cell lines correlated with decreased MGMT mRNA and lack of functional p53. Finally, in vitro experiments suggested the potential inhibition of buccal mucosal MGMT activity by complex mixtures present in the saliva of tobacco and betel nut chewers.

Effect of turmeric oil and turmeric oleoresin on cytogenetic damage in patients suffering from oral submucous fibrosis.

In vitro studies on the effect of alcoholic extracts of turmeric (TE), turmeric oil (TO) and turmeric oleoresin (TOR), on the incidence of micronuclei (Mn) in lymphocytes from normal healthy subjects showed that the test compounds did not cause any increase in the number of Mn as compared with those found in untreated controls. Further it was observed that all three compounds offered protection against benzo[a]pyrene induced increase in Mn in circulating lymphocytes. In subsequent studies, patients suffering from submucous fibrosis were given a total oral dose of TO (600 mg TO mixed with 3 g TE/day). TOR (600 mg + 3 g TE/day) and 3 g TE/day as a control for 3 months. It was observed that all three treatment modalities decreased the number of micronucleated cells both in exfoliated oral mucosal cells and in circulating lymphocytes. TOR was found to be more effective in reducing the number of Mn in oral mucosal cells (P < 0.001), but in circulating lymphocytes the decrease in Mn was comparable in all three groups.

Protective effect of food additives on aflatoxin-induced mutagenicity and hepatocarcinogenicity.

Food additives such as turmeric (Curcuma longa), and active ingredient curcumin (diferuloyl methane), asafoetida (flavouring agent), butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and ellagic acid were found to inhibit the mutagenesis induced by aflatoxin B1 (AFB1) (0.5 microg/plate) in Salmonella tester strains TA 98 and TA 100. Turmeric and curcumin, which were the most active, inhibited mutation frequency by more than 80% at concentrations of 2 microg/plate. Other food additives were also significantly effective. Dietary administration of turmeric (0.05%), garlic (0.25%), curcumin and ellagic acid (0.005% each) to rats significantly reduced the number of gammaglutamyl transpeptidase-positive foci induced by AFB1 which is considered as the precursor of hepatocellular neoplasm. These results indicate the usefulness of antioxidant food additives in ameliorating aflatoxin-induced mutagenicity and carcinogenicity.

Cytogenetic damage in exfoliated oral mucosal cells and circulating lymphocytes of patients suffering from precancerous oral lesions.

One hundred patients suffering from oral submucous fibrosis (OSF), oral leukoplakia (OL) and oral lichen planus (OLP) were studied for the cytogenetic damage in oral mucosal cells and in circulating lymphocytes along with their habit patterns. It was observed that OSF was largely associated with betel nut containing masticants while OL was associated with chewing or smoking habit. It was further observed that their exfoliated oral mucosal cells had significantly higher numbers of micronucleated (Mn) cells as compared to these of healthy normal subjects without any chewing or smoking habit. Similar cytogenetic damage in the form of increased sister chromatid exchanges (SCE) was observed in circulating lymphocytes indicating that the carcinogenic agents produce damage not only in target tissue but also in other host cells such as circulating lymphocytes.

Metabolism of N'-nitrosonornicotine by adult and fetal human oesophagal cultures.

The metabolism of [3H]labelled N-Nitrosonornicotine a major constituent of the class of Tobacco Specific Nitrosamines was studied in adult and fetal human oesophageal cultures. The metabolites were separated by HPLC and were identified when compared to the standards as OH-acid from 5'hydroxylation, NNN-1-N-oxide formed via the pyridine N-oxidation pathway and Keto acid from 2'hydroxylation in both the adult and fetal cultures. These results indicate that hydroxylation which leads to electrophilic diazohyroxides is the major pathway of NNN metabolism in cultured human oesophagus. In the adult cultures levels of metabolites formed were 20.32 pmoles/micrograms DNA of OH acid 11.08pmoles/micrograms DNA of NNN-1-N-oxide and 7.67pmoles/micrograms DNA of Keto acid. In the fetal cultures levels were 10.85pmoles/micrograms DNA of OH acid, 9.40pmoles/micrograms DNA of NNN-1-N-oxide and 7.91pmoles/micrograms DNA of Keto acid. These results indicate that alpha-hydroxylation is the key step in the metabolic activation of NNN in human oesophagus.

Adjuvant chemoprevention of experimental cancer: catechin and dietary turmeric in forestomach and oral cancer models.

Catechin and dietary turmeric (Curcuma longa) were used as chemopreventive agents in benzo[a]pyrene induced forestomach tumors in Swiss mice and methyl-(acetoxymethyl)-nitrosamine induced oral mucosal tumors in Syrian golden hamsters. Catechin in drinking water and dietary turmeric significantly inhibited the tumor burden and tumor incidence in both tumor models. The induction of oral tumors in golden hamsters was delayed by catechin and dietary turmeric. Adjuvant chemoprevention utilising both catechin and dietary turmeric inhibited both the gross tumor yield and burden more effectively than when compared to individual components in both tumor models. A single i.p. injection of catechin to male Swiss mice induced increased forestomach and hepatic glutathione S-transferase (GST) activity when compared to controls. These findings suggest that catechin and turmeric which are regularly consumed natural products, are effective in mice or golden hamsters as chemopreventive agents.

Endogenous formation of N-nitrosoproline and other N-nitrosamino acids in tobacco users.

The endogenous formation of N-nitroso compounds in tobacco users, namely chewers of tobacco + lime, betel quid with tobacco, and without tobacco, was determined by N-nitrosoproline test. Twenty-four- or six-hour urine samples were collected from volunteers for 3 days: day 1 without proline, day 2 after ingesting 100 mg proline three times a day and day 3 after ingesting 100 mg proline together with 100 mg ascorbic acid three times a day. The urine samples were analysed for the following N-nitrosamino acids: N-nitrosoproline, N-nitrososarcosine, N-nitrosopropionic acid, N-nitrosobutyric acid, N-nitrosothiozolidine-4-carboxylic acid, and N-methyl nitrosothiozolidine-4-carboxylic acid using gas chromatography-thermal energy analyser. It was observed that chewers of tobacco + lime excreted high basal levels of N-nitrosoproline on day 1 as compared with betel quid chewers with tobacco and without tobacco and those in the 'no habit' group. Levels of N-nitrosoproline on day 2 were 15.14 +/- 4.51 microns/mole creatinine in the tobacco + lime group, 3.55 +/- 1.22 microns/mole creatinine in the betel quid tobacco group, 4.72 +/- 1.35 microns/mole creatinine in the betel quid group while levels were 3.34 +/- 0.83 microns/mole creatinine in the 'no habit' group. A decrease in the N-nitrosoproline levels was observed in all the four groups on ingestion of ascorbic acid. This preliminary study suggests that there is a statistically significant increase in endogenous nitrosation in tobacco + lime chewers as compared with those with no habit, and ascorbic acid has an anti-nitrosating action in vivo.

Mutagenicity of some Indian commercial alcoholic liquors.

Different commercial brands of country liquors from three states of India (Maharashtra, Andhra Pradesh and Bihar) were tested in the Ames test using bacterial strains S. typhimurium TA 98 and TA 100 with and without metabolic activation. The commercial brands tested from Andhra Pradesh were nonmutagenic while those from Maharashtra and Bihar were mutagenic both with and without metabolic activation. Two brands of Maharashtra country liquors were further tested in a mammalian test system and were found to induce significantly higher numbers of micronuclei in Swiss mouse bone marrow cells in a dose-dependent manner.

Chemoprevention of mammary tumor virus-induced and chemical carcinogen-induced rodent mammary tumors by natural plant products.

The natural plant products turmeric, beta-carotene, catechin, and betel leaf extract were evaluated for their antitumor effects on mammary tumorigenesis in murine mammary tumor expressing C3H (Jax) mice and in Wistar rats treated with the chemical carcinogen 7-12-dimethylbenz(a)anthracene (DMBA). Administration of turmeric through the diet and of beta-carotene, catechin, and betel leaf extract through the drinking water to virgin female C3H mice resulted in decreased tumor incidence and tumor burden. Administering 5% turmeric in the diet from 2 months of age showed suppression of mammary tumor virus-related reverse transcriptase activity and of preneoplastic changes in the mammary glands. Furthermore, feeding turmeric from 6 months of age resulted in a 100% inhibition of mammary tumors. In the DMBA model of rat mammary tumorigenesis, administration of turmeric, catechin, and betel leaf extract resulted in decreased tumor burden and tumor incidence, and a delay in the onset of mammary tumors.

In vitro studies on chemoprotective effect of Purnark against benzo(a)pyrene-induced chromosomal damage in human lymphocytes.

Human lymphocytes were used as an assay system to test chemopreventive activity of natural products. Purnark, a mixture of extracts of turmeric, betel leaf and catechu, was tested for its chemoprotective activity against BP induced DNA damage. Sister chromatid exchange and micronuclei were used as markers to assess the protective activity of Purnark. Purnark gave 50-60% protection against BP induced SCEs and micronuclei. Purnark at 100 micrograms dose did not show any genotoxicity.

Effect of four plant phenols, beta-carotene and alpha-tocopherol on 3(H)benzopyrene-DNA interaction in vitro in the presence of rat and mouse liver postmitochondrial fraction.

The modulatory effect of beta-carotene, alpha-tocopherol and the four plant phenols eugenol, hydroxychavicol, curcumin and catechin on mouse and rat liver postmitochondrial fraction (S9 mix)-mediated 3(H)benzopyrene (B(a)P)-DNA interaction in vitro was studied. All the plant phenolics significantly inhibited 3(H)B(a)P-DNA interaction in the presence of both mouse and rat liver S9 fractions. In contrast, alpha-tocopherol proved to be ineffective in the presence of both types of S9 mix, whereas beta-carotene inhibited only mouse S9 mix-mediated 3(H)B(a)P-DNA interaction.

Effect of benzo(a)pyrene and methyl(acetoxymethyl) nitrosamine on thymidine uptake and induction of aryl hydrocarbon hydroxylase activity in human fetal oesophageal cells in culture.

Primary cultures of human fetal oesophageal cells were set up and maintained for 45 days. Epithelial cells were the dominant cell type in the culture for the first four weeks. Thereafter, both epithelial cells and fibroblasts were seen with the fibroblasts becoming the dominant cell type by the 6th week and until the cultures degenerated. The tritiated thymidine uptake showed an upward trend from day 10 up to day 30, with peak uptake at day 30 in the untreated, B(a)P treated and OAc treated cultures and decreased thereafter. The thymidine uptake levels were significantLy higher in the B(a)P treated cultures when compared with levels in the untreated cultures. A concurrent increase/decrease was also seen in the cell number in all the three groups of cultures. Cultures with B(a)P and DMN-OAc showed significantly higher AHH levels as compared with untreated cultures. These results indicate that the human fetal oesophageal cells could be viably maintained under in vitro conditions for long periods of time and also showed capacity to metabolise the carcinogens through aryl hydrocarbon hydroxylase activity.