The Flexi-Flange post system and its clinical use.
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Dental Prosthesis Design↗
Biomedical subjects
B I Cohen
Publications and source records attributed to B I Cohen.
Open labeled, single arm trial of denture shield for the treatment of dentures.
A new denture product, Denture Shield is described. This product was designed to aid denture wearers. It results in sealing the external surfaces of denture which provides comfort, cleansability and reduces odour while the denture is under function in the mouth. A trial was conducted in which 133 persons were recruited for a four week study. Each participant was well-informed about the product benefits. A total of 71 participants completed the study. The majority of the responses were positive (62 positive responds, representing 87.3% positive). Positive responses included: improved cleansability, food not sticking to the denture, reduced odour, better fitting dentures and more denture comfort. This product is intended as an additional treatment to current denture regimen and seems to provide improved characteristics for denture wearers.
Adult↗
Post removal using a thick-walled hollow tube post design.
PURPOSE: The retention of a post into the root is critical for the successful restoration of an endodontically treated tooth. A total of 80 Access Posts (Nos. 0, 1, 2, and 3) comprising eight groups were cemented in root canals with two different luting agents, Flexi-Flow cem with titanium and zinc phosphate cement. MATERIALS AND METHODS: Removal of these Access Posts was then performed with the corresponding retreatment drills. RESULTS: None of the samples for the No. 0 Access Posts were removed by extraction with the retreatment drills. None of the samples for the No. 1 Access Posts cemented with zinc phosphate were removed by extraction with the retreatment drills. All these posts were removed by hand with a hemostat, after breakage of the cement seal. 60% (group 3) and 40% (group 7) of the samples for the No. 2 Access Posts were removed by extraction with the corresponding retreatment drills. 80% (group 4) and 70% (group 8) of samples for the No. 3 Access Posts were removed by extraction with the corresponding retreatment drills. On an average removal of each Access Post Nos. 0 and 1 took between 1 and 2 minutes. On an average removal of each Access Post (Nos. 2 and 3) took between 2 and 3 minutes. CONCLUSION: No root fractures were observed for any sample with either technique. This was confirmed by visual and radiographic analysis.
Composite Resins↗
Origins of structural diversity within sequentially identical hexapeptides.
Efforts to predict protein secondary structure have been hampered by the apparent structural plasticity of local amino acid sequences. Kabsch and Sander (1984, Proc. Natl. Acad. Sci. USA 81, 1075-1078) articulated this problem by demonstrating that identical pentapeptide sequences can adopt distinct structures in different proteins. With the increased size of the protein structure database and the availability of new methods to characterize structural environments, we revisit this observation of structural plasticity. Within a set of proteins with less than 50% sequence identity, 59 pairs of identical hexapeptide sequences were identified. These local structures were compared and their surrounding structural environments examined. Within a protein structural class (alpha/alpha, beta/beta, alpha/beta, alpha + beta), the structural similarity of sequentially identical hexapeptides usually is preserved. This study finds eight pairs of identical hexapeptide sequences that adopt beta-strand structure in one protein and alpha-helical structure in the other. In none of the eight cases do the members of these sequences pairs come from proteins within the same folding class. These results have implications for class dependent secondary structure prediction algorithms.
Algorithms↗
Age, sex and source of hamster affect experimental cholesterol cholelithiasis.
In the present study, we examined the effect of the following factors on a hamster model of cholesterol cholelithiasis: (i) the source of the golden Syrian hamsters (Sasco, Omaha, NE or Charles River, Wilmington, MA), (ii) the sex of the experimental animals and (iii) their age (4 wk vs. 8 wk of age). All hamsters were fed a semipurified diet which contained cholesterol (0.3%) and palmitic acid (1.2%). No cholesterol gallstones formed in any of the female hamsters regardless of age or source. The 4-week-old male hamsters from Sasco had the greatest incidence of gallstones (93%). The 8-week-old male hamsters tended to have a lower incidence of cholesterol gallstones than the younger ones, regardless of the commercial supplier (67 vs. 93% for Sasco and 27 vs. 40% for Charles River). Female hamsters had higher liver and serum cholesterol levels than the male hamsters; Charles River hamsters had lower serum cholesterol concentrations than the Sasco animals. Total biliary lipid concentrations were highest in Sasco male hamsters, but biliary cholesterol (mol%) was lower in the males than in the females (4.2-4.5% vs. 6.1-7.1%) regardless of age. The cholesterol saturation indices were higher in the Sasco females than the corresponding males; these values were lower in the Sasco hamsters than the Charles River animals, regardless of age or sex. The male Sasco hamsters had a higher total biliary bile acid concentration (98.9 mg/mL) than the Sasco females (58.9 mg/mL) and the Charles River animals (24.6 mg/mL for males and 38.2 mg/mL for females). The percentage of chenodeoxycholic acid in bile was significantly lower, and the percentage of cholic acid was higher in all females as compared to males.(ABSTRACT TRUNCATED AT 250 WORDS)
Age Factors↗
Comparison of the retentive properties of two hollow-tube post systems to those of a solid post design.
The retention of a post in a root is critical for the successful restoration of an endodontically treated tooth. This study compared the retention of two hollow-tube post designs (Access post and World post) cemented with zinc phosphate cement or a titanium-reinforced composite resin cement (Flexi-Flow cement with titanium) with that of the control Para-Post system, a solid post design cemented with zinc phosphate cement. The experiment was divided into 11 groups of 10 samples. Retentive values were measured with a universal testing machine and the data were recorded in pounds. A one-way analysis of variance was computed and included Duncan's multiple comparisons test, Tukey's Student range test, and Dunnett's test. Duncan's multiple comparison test and Tukey's test were inconclusive. Only Dunnett's test revealed a significant difference between group 5, Access post, grooved dentin with Flexi-Flow cement with titanium (mean of 89.7 lb), and the control, group 11, Para-Post dowel cemented with zinc phosphate cement (mean of 61.3 lb). All other groups exhibited similar results with retentive values that ranged from 62 to 76 lb.
Acid Etching, Dental↗
Retentive properties of a threaded split post with attachment sleeves cemented with various luting agents.
This study determined the retention, in pounds, of Nos. 1 through 3 stainless steel attachment sleeves for the threaded split post system cemented with various cements. Post heads and matching sleeves were also sandblasted and compared with attachments not sandblasted. Four luting agents were selected, zinc oxyphosphate cement (ZOP), and three brands of composite resin cement (CRC). The experiment was divided into two parts; in part 1, samples were not treated, and in part 2, samples were sandblasted. Retentive values were recorded with a universal testing machine. A 2 x 3 x 4 factorial three-way analysis of variance was used to compute the effects sandblasting, sleeve and post type, and the luting agent. No statistical differences were recorded for sleeves not sandblasted, Nos. 1 and 2, regardless of the luting agent. The nonsandblasted No. 3 sleeve cemented with Panavia CRC had significantly greater retention than All-Bond CRC or ZOP. There were no statistical differences in retention of sandblasted sleeves for the No. 1 sleeve despite the type of luting agent. For sandblasted sleeves Nos. 2 and 3, ZOP and Panavia CRC recorded significantly greater retention than All-Bond CRC. However, there was no difference between sandblasting and not sandblasting for the No. 1 sleeve. Mean loads for Nos. 2 and 3 sleeves were substantially greater for sandblasted compared with attachments not sandblasted.
Adhesives↗
The retentive and stress distributing properties of split threaded endodontic dowels.
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Cementation↗
MacMatch: a tool for pattern-based protein secondary structure prediction.
A program is described for predicting the secondary structure of globular proteins on an Apple Macintosh computer. MacMatch produces turn predictions using augmented regular expression pattern matching. Helix and strand predictions are based on a neural network. Protein structural class (alpha/alpha), beta/beta, alpha/beta can be exploited to improve secondary structure prediction. The program is simple to use, and the package includes sets of tested patterns and trained neural networks.
Microcomputers↗
Cyclic fatigue testing of six endodontic post systems.
PURPOSE: This study tested the comparative cyclic fatigue of six prefabricated post systems (Flexi-Post (Essential Dental Systems, South Hackensack, NJ), Flexi-Anterior (Essential Dental Systems), Vlock (Brasseler USA, Inc, Savannah, GA), Parapost (Whaledent/Coltenen, New York, NY), Cytco (L.D. Caulk, Milford, DE), and Access post (Essential Dental Systems). MATERIALS AND METHODS: Cyclic fatigue testing was obtained with an in vitro fatigue machine that simulated clinical fatigue conditions. An instantaneous applied force of 5.0 pounds was applied to each post specimen and data was recorded when post breakages occurred. If no breakages occurred, then the test was stopped after 2,000,000 repetitions. RESULTS: Failures only occurred with the Cytco and Vlock post designs. The Flexi-Post, Flexi-Anterior, Parapost and the Access post all had greater resistance to cyclic fatigue with no failures. CONCLUSIONS: This experimental design may simulate biting forces and stresses seen for posts in a clinical situation.
Bite Force↗
Metabolism of beta-muricholic acid in the hamster and prairie dog.
The metabolism of beta-muricholic acid was investigated in the prairie dog and the hamster. Intravenous infusion into bile fistula hamsters showed that beta-muricholic acid was extracted by the liver and secreted into the bile (> 85% in 1 h). Hepatic extraction of this compound and cholic acid in the prairie dog was not as rapid as in the hamster. In the bile of the prairie dog, most (93%) of the administered beta-muricholic acid was present as the taurine conjugate. In the hamster, 28% of infused beta-muricholic acid was secreted in unconjugated form, 43% as the taurine conjugate, and 22% as the glycine conjugate. In both species, the administered compound underwent little biotransformation. After intraduodenal injection of [6 alpha-3H]-labeled beta-muricholic acid into bile fistula hamsters, the bile acid was rapidly secreted into the bile; more than 80% of the administered radioactivity was recovered in 3 h. In the prairie dog, biliary recovery after intraduodenal administration of either beta-muricholic acid (43% in 3 h) or cholic acid (22% in 3 h) was slower than in the hamster. After intragastric administration, more than 80% of beta-muricholic acid was recovered unchanged in feces of both animal species.
Animals↗
Metabolism and choleretic activity of homochenodeoxycholic acid in the hamster.
The hepatic metabolism and the choleretic effect of homochenodeoxycholic acid, the C25 homologue of chenodeoxycholic acid, were investigated in the hamster. After intravenous administration of 3H-labeled homochenodeoxycholic acid into biliary fistula hamsters, more than 80% of the radioactivity was recovered in bile in 4 h. A relatively small proportion of homochenodeoxycholic acid was present in bile as the taurine (22%) or glycine (4%) conjugate. However, more than 70% of the administered compound was biotransformed into C23 bile acids. The major C23 metabolites in bile were norchenodeoxycholic acid (17%), tauronorchenodeoxycholic acid (33%), and a trihydroxy norbile acid (identified as 3 alpha, 5 beta, 7 alpha-trihydroxy-24-nor-5 beta-cholan-23-oic acid, 19%). Small amounts (< 5%) of sulfate(s) and glucuronide(s) were also detected. Homochenodeoxycholic acid, when infused intravenously into the hamster, produced a striking choleresis. The increase in bile flow after infusion of this compound was 6- to 7-times that induced by chenodeoxycholic acid. The apparent choleretic activity of homochenodeoxycholic acid, 181 microliters/mumol, was much greater than that of chenodeoxycholic acid, 11 microliters/mumol. In conclusion, homochenodeoxycholic acid induced a hypercholeresis of the same order of magnitude as norchenodeoxycholic acid, presumably because considerable proportions of this compound were degraded to the hypercholeretic norchenodeoxycholic acid via beta-oxidation in the liver.
Animals↗
Bile acid sulfonates alter cholesterol gallstone incidence in hamsters.
The prevention of cholesterol gallstone formation by three bile acid analogs, sodium 3 alpha,7 alpha-dihydroxy-5 beta-cholane-24- sulfonate, sodium 3 alpha,7 beta-dihydroxy-5 beta-cholane-24-sulfonate and sodium 3 alpha,6 alpha-dihydroxy-5 beta-cholane-24-sulfonate, was examined in a hamster model of cholesterol cholelithiasis. Sodium taurochenodeoxycholate, sodium tauroursodeoxycholate and sodium taurohyodeoxycholate were studied simultaneously for comparison. Gallstones and cholesterol crystals were induced in 14 of 15 hamsters fed a bile acid-free, semipurified lithogenic diet containing 0.3% cholesterol and 4% butterfat for 6 wk. The addition of 0.1% sodium taurochenodeoxycholate and sodium tauroursodeoxycholate to the lithogenic diet had little effect on the formation of gallstones or biliary cholesterol crystals. In contrast, sodium 3 alpha,7 alpha-hydroxy-5 beta-cholane-24- sulfonate and sodium 3 alpha,7 beta-dihydroxy-5 beta-cholane-24-sulfonate, when fed at the same dose, prevented cholesterol gallstone formation significantly. Sodium taurohyodeoxycholate and sodium 3 alpha,6 alpha-dihydroxy-5 beta-cholane- 24-sulfonate inhibited cholesterol gallstone formation effectively. The cholesterol saturation index of bile was greater than 1.00 in all groups, with the exception of the group fed sodium 3 alpha,7 alpha-dihydroxy-5 beta-cholane-24-sulfonate. Liver and serum cholesterol levels tended to be lower in most of the groups that were fed bile acids. This effect was most pronounced in the animals receiving sodium taurohyodeoxycholate. At the end of the experiment, the administered sulfonate analogs were detected in gallbladder bile.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
A segment-based approach to protein secondary structure prediction.
Amino acid sequence patterns have been used to identify the location of turns in globular proteins [Cohen et al. (1986) Biochemistry 25, 266-275]. We have developed sequence patterns that facilitate the prediction of helices in all helical proteins. Regular expression patterns recognize the component parts of a helix: the amino terminus (N-cap), the core of the helix (core), and the carboxy terminus (C-cap). These patterns recognize the core features of helices with a 95% success rate and the N- and C-capping features with success rates of 56% and 48%, respectively. A metapattern language, ALPPS, coordinates the recognition of turns and helical components in a scheme that predicts the location and extent of alpha-helices. On the basis of raw residue scoring, a 71% success rate is observed. By focusing on the recognition of core helical features, we achieve a 78% success rate. Amended scoring procedures are presented and discussed, and comparisons are made to other predictive schemes.
Algorithms↗
Palmitic acid enhances cholesterol gallstone incidence in Sasco hamsters fed cholesterol enriched diets.
In an established hamster model of cholesterol cholelithiasis, a semipurified lithogenic diet containing 4% butterfat and 0.3% cholesterol leads to the production of cholesterol gallstones in only 50-60% of animals after a 6-wk feeding period. The purpose of this study was to investigate whether gallstone incidence could be increased while feeding a nutritionally adequate diet of moderate cholesterol content. The semipurified lithogenic diet was modified as follows: (i) substitution of 1.2% palmitic acid for 4% butterfat, and (ii) varying the amount of dietary cholesterol from 0.0 to 0.3% with either butterfat or palmitic acid as the lipid component of the diet. Substitution of palmitic acid for butterfat produced a significantly higher incidence of cholesterol gallstones (94% vs. 53%). Palmitic acid also raised the incidence of gallstones when added to the 0.1% and 0.2% cholesterol diets as compared to butterfat: 0% vs. 44% and 50% vs. 81%, respectively. Gallstone incidence increased from 0% to nearly 100% when the cholesterol content of the palmitic acid diets was raised from 0.0% to 0.3%, indicating a dose response effect with respect to dietary cholesterol. Hamsters fed cholesterol-free diets did not form gallstones. Increased dietary cholesterol led to increased liver weight associated with a significant increase in liver cholesterol concentration. However, the palmitic acid groups had significantly lower liver cholesterol values than the corresponding butterfat groups. Serum and biliary cholesterol concentrations increased with increasing dietary cholesterol intake, but there were no differences between the butterfat and palmitic acid groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Dietary fat and fatty acids modulate cholesterol cholelithiasis in the hamster.
We tested two hypotheses, i) whether the type and the amount of fat in the diet will affect the formation of cholesterol gallstones in the hamsters, and ii) whether palmitic acid, a major fatty acid component of butterfat, can act as a potentiator of cholesterol cholelithiasis in the hamster. Young, male golden Syrian hamsters (Sasco) were fed a semipurified diet containing casein, corn starch, cellulose and cholesterol (0.3%) to which various types and amounts of fat (butterfat, olive oil, menhaden oil, corn oil) were added. All diets contained 2% corn oil to supply essential fatty acids to the growing hamsters. No deaths or illness occurred during the experiment. Animals fed the semipurified diet plus 4% butterfat (group 1) had a gallstone incidence of 63%. Replacement of butterfat with either olive oil, corn oil or menhaden oil prevented the formation of cholesterol gallstones entirely (groups 2-4). When total butterfat was increased from 4% to 8% (group 8), the incidence of cholesterol gallstones increased to 80%. Substitution of 4% olive oil (group 5), corn oil (group 6), or menhaden oil (group 7) for the additional 4% butterfat significantly reduced gallstones to 35%, 45% and 30%, respectively. The replacement of 4% butterfat with 1.2% palmitic acid gave the highest incidence of cholesterol gallstones (95%). These results suggest that butterfat (and one of its components, palmitic acid) intensifies gallstone formation in this model whereas mono- and polyunsaturated fats act as inhibitors of cholesterol cholelithiasis. A fatty acid, possibly palmitic acid, appears to act as lithogen in our model.
Animals↗
Retentive properties of attachment sleeves for a new cast-post system.
This study determined the retentive values of various size sleeves and their corresponding post heads when these were cemented with zinc phosphate cement. The experiment was divided into four groups of 10 samples each, except for group 3, which had eight samples. In each instance, the retentive values (measured in pounds) were obtained using a universal testing machine. In all samples studied, the retention of the sleeve was greater than 110 pounds. As the post number increased from 0 to 3, there was a corresponding increase in the retentive force needed to dislodge each sleeve. A maximum of 170.5 pounds was found for the No.3 cast-post sample. Comparison shows that the retention of the sleeve (for this cast-post system) onto the post head is in the same range as crown-to-tooth retention values shown by other investigators.
Cementation↗