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.

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.

Effect of partial hepatectomy on tumor incidence and metabolism of mice fed thioacetamide.

Six-week-old male Swiss mice were given 0.03% thioacetamide (TAA) in the diet 24, 72, and 168 hours after partial hepatectomy. TAA-treated mice from all three groups were killed when they were 4, 9, and 13 months old. Intact and partially hepatectomized animals on normal diets served as controls. None of the controls evidenced neoplasms at any age. All three experimental groups developed liver tumors earlier than did intact mice treated with the TAA diet. Progressive metabolic studies on the livers or tumor tissues of treated mice showed that the levels of glucose-6-phosphatase, fructose-1,6-diphosphatase, and glycogen decreased significantly in the 4-month-old treated group when there was no significant alteration in liver histology. These parameters were lowest in the tumor tissues of treated mice.

Induction of oral mucosal tumors in hamsters and rats treated with methyl(acetoxymethyl)nitrosamine.

An oral tumor model has been developed in inbred Syrian golden hamsters by continuous applications every 2 weeks of methyl(acetoxymethyl)nitrosamine [(DMN-OAC) CAS: 56856-83-8; methylnitrosaminomethyl ester acetic acid] at 2 mg/kg body weight alone or by a single application of DMN-OAC followed by continuous twice weekly applications of 12-O-tetradecanoylphorbol 13-acetate (TPA) (1 microgram/animal). Similar studies were done in the W rat buccal mucosa. In the hamsters treated continuously with DMN-OAC, 100% of the tumors were observed in the cheek pouch; none were observed at other sites. In contrast, in the rats treated similarly, only a 67% tumor incidence was observed, of which only 42% were oral tumors. A promoter effect of TPA was observed in hamster cheek pouch tumors induced by DMN-OAC, whereas rat oral mucosa did not respond to TPA treatment.

Independence of sialic acid levels in normal and malignant growth.

Sialic acid content in breast or tumor tissue and serum of mouse strains that are either susceptible or resistant to breast cancer was measured at various age periods. Sialic acid content was also studied in normal lung tissue and in lung adenoma and hepatoma. Sialic acid levels during nonmalignant growth of a tissue were measured in breast tissue during pregnancy and lactation, and in regenerating liver, as well as in newborn and postnatal liver. The sialic acid content, when expressed per mg of protein, increased in mammary tumor, lung adenoma, and hepatoma. It also increased in nonmalignant growth of breast tissue during pregnancy and lactation and of regenerating liver and postnatal liver. Increase in sialic acid per mg DNA was observed only in lung tumors, regenerating liver, and postnatal liver. It appears that the changes in sialic acid level are independent of the normal or malignant growth of a tissue and that these changes might be the function of the parameter used to express the sialic acid values, i.e., either the DNA content or protein content of a given tissue.

Carcinogenicity studies of tobacco extract in vitamin A-deficient Sprague-Dawley rats.

Long-term carcinogenicity studies were carried out in male Sprague-Dawley rats maintained on vitamin A-sufficient (SLO+) and vitamin A-deficient (SLO-) diets and treated with tobacco extract (TE). Three-week-old rats received by gavage a total dose of 860 mg of TE at a daily dose of 3 mg/rat over a period of 21 months. Besides tumorigenicity, drug-metabolizing phase I and phase II enzymes in lung and liver as well as vitamin A and C levels in plasma and liver were measured at 12 and 21 months of age. The cumulative tumor incidence in TE-treated SLO- rats was significantly higher (77-100%) than that observed in TE-treated SLO+ rats (20-22%). Furthermore, SLO+ rats treated with TE showed lung and forestomach tumors, whereas TE-treated SLO- rats showed a preponderance of pituitary adenomas (87%). It was observed that TE treatment increased the activity of the hepatic and pulmonary phase I enzymes and decreased the glutathione/glutathione S-transferase detoxification system at both time points in SLO- rats. On TE treatment the vitamin A levels in the liver and plasma were significantly decreased with a concurrent increase in vitamin C levels. The data show that a vitamin A-deficient diet renders male Sprague-Dawley rats more susceptible to TE treatment than the vitamin A-sufficient diet, an effect which was associated with the augmented induction of P-450 content and activities and depletion of the glutathione/glutathione S-transferase pathway by TE.

Ligand-induced structural changes in amylose partially complexed with iodine.

The influence of complexing agents such as methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, cyclohexanol and 2-octanol on the formation of a blue coloured amylose - iodine complex (pH 4.8), under suboptimum concentrations of iodine and in the absence of potassium iodide, is studied by recording the absorbance at 640 nm. A drop in absorbance at 640 nm accompanied by a blue shift in the spectrum (640-580 nm) was observed at higher concentrations of the complexing agents. This behaviour of amylose partially complexed with iodine appears to be due to ligand-induced structural changes in the amylose chain. The fall in absorbance at 640 nm observed when the temperature of amylose - iodine complex in the presence of complexing agents is raised, and the subsequent regeneration of the absorbance on cooling, indicates the possible helix to random coil transition of the amylose chain in an aqueous system.

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 antioxidants and antitoxicants of isoniazid on the formation of lung tumours in mice by isoniazid and hydrazine sulphate.

The present study reports the effects of antioxidants and antitoxicants on the formation of lung tumours in Swiss mice induced by isoniazid (INH) and hydrazine sulphate (HS). Dietary administration of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) or simultaneous oral administration of antitoxicants (L-arginine, L-sodium glutamate and pyridoxine hydrochloride) failed to prevent HS-induced lung tumours. On the other hand BHA and BHT inhibited the formation of lung tumours in groups of mice receiving INH. Folic acid supplementation had marginal effect on the formation of lung tumours in groups receiving HS (P less than 0.1). Higher lung tumour incidence was observed in groups maintained only on BHT diet as compared to animals maintained on standard diet.

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 gingerol and shogaol and antimutagenicity of zingerone in Salmonella/microsome assay.

Ginger extract and its constituents gingerol, shogaol and zingerone were tested in Salmonella typhimurium strains TA 100, TA 98, TA 1535 and TA 1538 in the presence and in absence of S9 mix. It was observed that ginger extract, gingerol and shogaol were mutagenic on metabolic activation in strains TA 100 and TA 1535, but zingerone was non-mutagenic in all the four strains with or without S9 mix. When mutagenicity of gingerol and shogaol was tested in presence of different concentrations of zingerone it was observed that zingerone suppressed mutagenic activity in both the compounds in a dose dependent manner.

Polycyclic aromatic hydrocarbon profiles of pyrolysed tobacco products commonly used in India.

The polycyclic aromatic hydrocarbon (PAH) profile of bidi (an indigenous substitute for cigarettes in India), masheri (a charred tobacco product used for cleaning teeth) and Indian snuff was determined. The effect of the extracts of these tobacco products on the liver microsomal mixed function oxygenase system was studied. Cytochrome P-450 and benzo[a]pyrene (B[a]P) hydroxylase levels were significantly increased.

Mutagenic and cytogenetic studies of N'-nitrosonornicotine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone.

The tobacco specific nitrosamines (TSNA) N'-nitrosonornicotine (NNN) and 4-(Methylnitrosoamino)-1-(3-pyridyl)-1-butanone (NNK) were tested for mutagenic and clastogenic effects using a battery of short-term test systems. These test systems include the Ames test, micronucleus test (MNT), induction of chromosomal aberrations and sister chromatid exchange (SCEs). NNN and NNK were tested for their potency in inducing mutations in the Ames Salmonella/microsome assay and their clastogenic action were tested by the micronucleus inducing ability in vivo using Swiss mice. Studies on the induction of chromosomal aberrations and SCE exchange were carried out using human peripheral blood lymphocyte cultures. In the Ames test and MNT, NNN was positive but in comparisons with NNK, NNK was a more potent mutagen. Present studies clearly proves the genotoxic potential of both NNN and NNK and between the two NNK is more potent.

Effect of tobacco extract and N'-nitrosonornicotine on the carcinogen metabolising enzymes under different dietary vitamin B status.

Studies were carried out to evaluate the changes in the phase I and II enzymes of xenobiotic metabolism, on treatment with tobacco extract (TE) and a tobacco specific carcinogen, N'-nitrosonornicotine (NNN) in Sprague-Dawley rats maintained on vitamin B complex sufficient and deficient semi-synthetic diets. Both TE and NNN significantly increased the hepatic and pulmonary phase I enzymes in the vitamin B sufficient (SB+) and deficient (SB-) animals. However, the percent increase in enzyme activities was drastically higher in the SB- treated group as compared to those in the SB(+)-treated group. On the other hand, TE and NNN significantly depressed the liver and lung glutathione (GSH) level and glutathione S-transferase (GST) activity in the SB- animals, while the opposite effect was observed in the SB(+)-treated animals. Furthermore, both the treatments depleted the hepatic pool of vitamin A, with a concurrent increase in that of vitamin C in SB+ and SB- groups.

Mutagenicity and carcinogenicity of mono- and diacetyl hydrazine.

Two hydrazine derivatives, monoacetyl hydrazine (MAH) and diacetyl hydrazine (DAH), have been tested for mutagenic response in the Salmonella/mammalian microsome assay and micronucleus test. MAH but not DAH, increased the revertant mutants in TA100 and TA1535 and also increased the frequency of micronuclei in polychromatic erythrocytes. Gavage administration of MAH but not of DAH, resulted in increased incidence of lung tumors. These observations record for the first time the mutagenicity/carcinogenicity of MAH which is one of the metabolites of isoniazid in animals and humans.

Anticarcinogenic effect of betel leaf extract against tobacco carcinogens.

Epidemiological studies have implicated that betel quid offers some protection to tobacco induced carcinogenesis. Earlier studies in our laboratory have shown betel leaf extract (BLE) to be antimutagenic against standard mutagens and tobacco-specific N'-nitrosamines (TSNA), N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). In the present study, we have tested the anticarcinogenic effect of BLE using Swiss male mice. Two protocols of study were used to test this effect. In the first protocol, the effect of BLE was tested against the standard carcinogen benzo[a]pyrene (BP) using Wattenberg's stomach tumor model, Cancer Res., 41 (1981) 2820-2823. In this protocol, BLE inhibited the tumorigenicity of BP to a significant extent. In the second protocol, the effect of BLE against the two tobacco-specific nitrosamines, NNN and NNK was studied using long-term studies on Swiss male mice. The nitrosamines were administered on the tongues of the mice, while the BLE was supplied in drinking water. Two doses of NNN (22 mg and 72 mg) and one dose of NNK (22 mg) were used. In this study, it was observed that the number of tumor bearing animals decreased, but the difference was significant only in the group treated with the low dose of NNN in combination with BLE. However, in all the BLE treated animals, irrespective of the dose of nitrosamine, the hepatic vitamin A and C levels were elevated significantly as compared to the corresponding nitrosamine-treated controls. These results indicate that BLE has a promising anticarcinogenic role to play in tobacco induced cancer.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

Transplacental passage of isoniazid (INH) and its interaction with fetal tissues of mice.

When INH was administered orally or intraperitoneally to pregnant female mice, the concentrations of acetyl INH and acetyl hydrazines did not vary significantly in circulating blood and in amniotic fluid. However, the concentration of INH in the amniotic fluid was significantly higher than that observed in the serum. Autoradiographic studies using 14C-labelled INH revealed that INH crosses the placental barrier and grains can be observed in lung and liver tissues of the fetus. Studies on interaction of 14C-labelled INH with nucleic acids clearly demonstrated that significant amounts of radioactivity were present in all the macromolecules of the whole embryo as well as in those isolated from fetal lung and liver tissues.