Effects of various chemical sterilization methods on the crosslinking and enzymatic degradation characteristics of an epoxy-fixed biological tissue

Due to the nature of bioprostheses, which are mainly biological tissues that cannot be sterilized with heat or irradiation, the sterilization method by choice is generally liquid chemicals. It is known that a number of liquid chemicals can have rapid germicidal effect and can be used to sterilize bioprostheses. The study was to evaluate the effects of various chemical sterilization methods on the crosslinking and enzymatic degradation characteristics of an epoxy-fixed biological tissue. The chemical sterilants employed were: a 70% ethanol solution (EtOH), a 2% epoxy compound + 20% ethanol solution (EX-810), a 2% propylene oxide + 20% ethanol solution (PO), and a 0.625% glutaraldehyde + 20% ethanol + 0.2% polysorbate solution (GA). Both masking and crosslinking of the free amino groups within the epoxy-fixed tissue were observed subsequent to sterilization with GA or EX-810. This improved the resistance of the GA or EX-810 sterilized tissues against collagenase degradation as compared to its nonsterilized counterpart. However, subsequent to sterilization with PO, only masking of the free amino groups within the epoxy-fixed tissue was noted. The inhibition of the collagenase degradation by masking of the free amino groups was traded off by the more random molecular packing of the PO sterilized sample due to the introduction of the side branches. Sterilization of the epoxy-fixed tissue with EtOH may increase its denaturation temperature and tensile strength, while neither masking nor crosslinking of free amino groups within the tissue took place. The resistance to degradation of the EtOH sterilized tissue, however, did not improve as compared to its nonsterilized counterpart.

[The shear bond strength of porcelain and base metal alloys for metal-ceramic crown (VII)]

The popularity of the base metal alloys has increased in the past decade because of their lower price, high tensile strength and high elastic modulus. Several factors are critical in ensuring successful bonding: the matching of the thermal coefficients of expansion and constraction of the porcelain and metal, the metallurgic composition of the alloy and the pretreatment procedures used in preparation of the metal substructure. Two ceramic base alloys (one alloy contains beryllium, another without) were studied. The surface textures were created by 50 microns, 100 microns aluminum oxide sandblasting, carbide bur, carborundum point and disk upon two base alloys, Rexillium III and Wiron 88. The purposes of this investigation were to determine how these variations in surface texture affect the bond strength of the two ceramo-metal alloy systems. The following results were obtained: 1. Statistics revealed that bond strength was not significantly increased with surface roughness (p > 0.05). 2. The shear bond strength for variable pretreatment methods were in the following sequence: 100 microns Al2O3 sandblasting, carbide bur, 50 microns Al2O3 sandblasting, carborundum point, disk. 3. The Rexillium III alloy had a significantly higher bond strength than Wiron 88 alloy (p < 0.05). 4. The Noritake porcelain showed a significantly higher bond strength than Biobond porcelain (p < 0.05). 5. The fracture site was cohesive and adhesive mode treated with 50 microns Al2O3, 100 microns Al2O3, carbide bur. But carborundum point and disk was adhesive mode.

[The shear bond strength of porcelain and base metal alloys for metal-ceramic crown (VI)]

The popularity of base metal alloy for porcelain fused to a metal crown and bridges has increased recently because of lower price, superior yield strength and modulus of elasticity (rigidity). The use of these alloys give them the potential advantage of thinner coping with less material and the required rigidity for long-span fixed partial dentures. The addition of beryllium to base metal alloys increases fluidity and improves casting fit. Beryllium also controls surface oxidation and bonding strength. Oxidation heat treatment of the metal is used to remove entrapped air, eliminate organic material and form the metal oxidized layer. The bonding agent and gold bonding agent also affect the bonding strength between porcelain and metal alloys. Four commercially available ceramic base alloys (two alloys contain beryllium element, another two do not) are studied. The purposes of this investigation are to test the shear bond strength between porcelain and metal alloy under different conditions (oxidized layer removed or not, gold bonding agent and uniseal bonding agent used in combination, separately or not at all). The following results were obtained: 1. Whether the oxidized layer was removed or not did not have a significant effect on the bond strength of porcelain (p > 0.05). 2. When different metal alloys was used, Wiron 88 alloy showed significantly the best bond strength of all alloys tested (p < 0.05). 3. When different bonding agent were used, the combination of bonding agent and gold bonding agent showed the best bond strength of all bonding agents tested. It showed a significantly higher bonding strength than opaque layer and gold bonding agent. 4. Vita porcelain powder showed a significantly higher bond strength than did Unibond porcelain (p < 0.05). 5. When opaque layer was used and when no bonding agent was used, the porcelain powder significantly affected the bond strength (p < 0.0001). The Vita porcelain showed a significantly higher bond strength than did Unibond porcelain. Wiron 88 alloy showed significantly the high bond strength than Rexillium III alloy (p < 0.05). 6. When bonding agent was used, the porcelain powder and alloy significantly affected bond strength. The Vita porcelian showed a significantly higher bond strength than did Unibond porcelain. Wiron 88 alloy showed significantly the best bond strength than other alloys Wiron (p < 0.05). 7. When bonding agent and gold bonding agent were used, the porcelain powder significantly affected the bond strength (p < 0.05). The Vita porcelain showed a significantly higher bond strength than did Unibond porcelain (p < 0.05). 8. When gold bonding agent was used, there was not any bond strength between metal and powder.

Dibutyryl cAMP prevents increased vascular permeability caused by air embolism in isolated rat lungs

BACKGROUND AND HYPOTHESIS

Venous gas bubbles are routinely detected in astronauts undergoing extravehicular activities at lower suit pressure. Venous air embolism increases the pulmonary arterial pressure and the vascular permeability leading to acute lung injury. In the present study we evaluated the protective effect of dibutyryl cAMP, aminophylline, and pentoxifylline on the pulmonary vasculatures after air embolism.

METHOD

In isolated and perfused rat lungs, we induced air embolism by introducing air bubbles into the pulmonary artery. We measured the pulmonary arterial pressures and capillary pressure. Vascular permeability was determined by measuring the filtration coefficient (Kf) and the protein concentration in the lung lavage fluid.

RESULTS

Air infusion caused pulmonary hypertension and increased vascular permeability, resulting in pulmonary edema. The Kf (in g.min-1.cm H2O-1.100 g-1) increased from 0.44 +/- 0.05 at baseline to 2.98 +/- 0.47 after air infusion. Pretreatment with DBcAMP prevented the increase in Kf (0.63 +/- 0.09) caused by air embolism without altering the hemodynamics. Aminophylline and pentoxifylline did not prevent lung injury induced by air embolism. Although aminophylline did not alter the response of pulmonary arterial pressure to air infusion, it elevated the capillary pressure to 5.1 +/- 0.4 mmHg, which was significantly greater than that in the lung receiving air infusion alone.

CONCLUSION

Our results suggest that DBcAMP prevents the increase in vascular permeability caused air embolism. The ineffectiveness of aminophylline and pentoxifylline on the prevention of air embolism-induced lung injury remains for further investigation.

Degradation potential of biological tissues fixed with various fixatives: an in vitro study

The purpose of this study was to investigate the in vitro degradation potential of porcine pericardia fixed with various aldehyde or epoxy compound (EC) fixatives, using bacterial collagenase and pronase. The fixatives investigated were formaldehyde (FA), glutaraldehyde (GA), monofunctional EC (EX-131), and multifunctional ECs (EX-810, EX-313, and EX-512). Fresh porcine pericardium was used as a control. The test samples were well immersed in a 20-U/mL collagenase solution or a 10-U/mL pronase solution and incubated at 37 degrees C at pH 7.5 for 24 h. The extent of degradation of each test sample was determined by measuring its increment in free amino group content and changes in collagen structure, denaturation temperature, and tensile stress after degradation. In general, the extent of tissue degradation with pronase was more notable than with collagenase. As observed with fresh tissue, the EX-131 EC fixed tissue radically disintegrated after either collagenase or pronase degradation, whereas the other test samples remained intact. The reason for this may reside in the more random molecular packing of the EX-131 EC-fixed tissue, which led to some loss in its helical integrity. This made penetration of enzymes into biological tissue easier. Of the multifunctional EC test groups, tissues fixed with tetrafunctional EC (EX-521) or trifunctional EC (EX-313) had relatively better resistance to degradation than those fixed with bifunctional EC (EX-810). The extent of degradation for the EX-313 or EX-512 EC fixed tissues was similar to that observed for the FA- or GA-fixed tissues. The results of this study indicated that the biological tissue fixed with monofunctional EC (EX-131) cannot resist bacterial collagenase or pronase degradation. However, resistance to degradation of the multifunctional EC (EX-313 or EX-152)-fixed tissues was comparable to that of the aldehyde (FA or GA)-fixed tissues. Therefore, of various EC fixatives, the EC with a greater number of functional groups should be chosen for tissue fixation to increase its resistance to enzymatic degradation.

Fixation of various porcine arteries with an epoxy compound

The clinical results of biological vascular grafts have been unsatisfactory. The poor results of these vascular grafts may be attributed to the fixatives, aldehydes, used in fixing tissues. In an attempt to overcome this problem, a new fixative, epoxy compound, has recently been used to fix biological vascular grafts. The study was undertaken to investigate the crosslinking characteristics, fixation index and denaturation temperature, of various porcine arteries fixed with an epoxy compound. The porcine arteries investigated in the study were the common carotid artery, internal thoracic artery, abdominal aorta, and saphenous artery. In addition, the effects of sonication on the porcine arteries before fixation on their crosslinking characteristics were analyzed. The fresh and glutaraldehyde-fixed arteries were used as controls. It was noted that glycine, proline, and alanine were the most abundant amino acids found in the porcine internal thoracic artery. In the amino acid analysis, it was observed that the amino acids in the porcine arteries reacted with epoxy compound or glutaraldehyde were lysine, hydroxylysine, histidine, and arginine. Of these amino acids, lysine was the most reactive. In general, the fixed arteries were relatively stiffer than their fresh counterparts. The fixation indices and denaturation temperatures of various porcine arteries were comparable throughout the entire fixation process. The amounts of free amino groups of the sonicated arteries were significantly lower than those of their unsonicated counterparts (p < 0.05). It is speculated that the diminishing free amino groups of the sonicated arteries may be attributed to the removal of the destroyed cell debris and adherent proteins of the arteries after sonication. However, it was learned that sonication on the porcine arteries before fixation did not seem to affect their fixation indices and denaturation temperatures. The results obtained in this study may help one in selecting the raw materials for developing a small-diameter biological vascular graft

Physical properties of a porcine internal thoracic artery fixed with an epoxy compound

This study aimed to investigate the physical properties of a porcine internal thoracic artery fixed with an epoxy compound. Fresh and glutaraldehyde-fixed porcine arteries were used as controls. Both the epoxy-fixed and glutaraldehyde-fixed porcine arteries showed significant increases in fixation index and denaturation temperature as compared to the fresh one. Additionally, the resistance of porcine arteries against bacterial collagenase in vitro degradation increased significantly after cross-linking with the epoxy compound of glutaraldehyde. The reduction of the tensile strength of the epoxy-fixed artery after bacterial collagenase degradation was more severe than in its glutaraldehyde-fixed counterpart. Generally, with increasing pH, temperature or fixative concentration, the fixation indices and denaturation temperatures of the epoxy-fixed porcine arteries increased. The results obtained in this study may be used to optimize the fixation process for developing a small-diameter biological vascular graft fixed by an epoxy compound.

[The shear bond strength of porcelain and base metal alloys for metal-ceramic crown the study of metal roughness and microstructure]

The metal-ceramic crown has become a predominant restoration in fixed prosthodontics. The base metal has the quality of lower price, high tensile strength, high elastic modulus. The base metal alloy that contain beryllium element increases fluidity and improved casting performance. Beryllium also controls surface oxidation and affects the metal ceramic bonds. Preparation of surface prior to porcelain bonding has been a subject of controversy among dental ceramists. Two ceramic base metal alloys (one alloy contains beryllium, another is not) were studied. This investigation evaluated the polishing effects of 50 microns, 100 microns aluminum oxide sandblasting, carbide bur, carborundum point and separating disk upon two base metal alloys, Rexillium III and Wiron 88. A scanning electron microscope was used to study the surface texture. The following results were obtained: 1. The most roughest surface was created with 50 microns aluminum oxide sandblasting. The carbide bur produced the least roughed surface. 2. There are specific surface texture patterns after polishing with five different grinding materials. 3. The metal surfaces treated with 50 microns and 100 microns aluminum oxide have same micro-structure pictures, but there are much more undercuts treated with 100 microns aluminum oxide. 4. The usage of carbide bur resulted in less undercuts of metal surface at two metal alloys. 5. The usage of carborundum point and disk resulted in abrasive particles that retained on the grinding metal surface at two metal alloys. 6. The surface of Wiron 88 alloy usually had wrinkle texture but not the Rexillium III alloy.

Anionic gels as vehicles for electrically-modulated drug delivery. I. Solvent and drug transport phenomena

PURPOSE

The purpose of this study was to elucidate the in vitro behavior of anionic gels as formulation matrices for electrically-modulated drug delivery. Agarose and combinations of agarose with other anionic polymers (carbomer 934P; xanthan gum) were selected and tested to evaluate their potential for drug delivery.

METHODS

Electrical current was applied by an automatic crossover power supply to minimize the current fluctuation. Hydrocortisone was selected as the model drug in order to minimize electrostatic interference with drug transport. Syneresis and drug migration were evaluated as a function of current application time and the intensity of electrical current.

RESULTS

The data show that electrical current strength and gellant content can affect both the syneresis and drug migration. A linear correlation was found between hydrocortisone loss and mass loss via the exudate. Moreover, in agarose-carbomer 934P gel systems, cumulative gel mass loss is a linear function of time at low intensities of electrical current (e.g., 0.5 mA and 1 mA). However, hydrocortisone distribution, after electrical application, is relatively asymmetric in those agarose-carbomer 934P gels (and in agarose-xanthan gum gels) in contrast to gel matrices containing only agarose.

CONCLUSIONS

In this study, the use of carbomer 934P in conjunction with agarose enables the formulator to achieve zero-order release with electrical application. Increased anisotropicity of a gel system due to the application of electrical current could alter the effectiveness of a drug delivery system.

Crosslinking characteristics of an epoxy-fixed porcine tendon: effects of pH, temperature, and fixative concentration

Injury to the anterior cruciate ligament (ACL) often results in functional instability within the knee joint and may induce a severe articular deterioration. Clinically, these patients may require an ACL reconstruction. In an attempt to develop an improved ligament prosthesis, a prototype xenograft--an epoxy-fixed porcine Achilles tendon--was developed. The study was intended to investigate the crosslinking characteristics of the epoxy-fixed porcine tendons fixed at different pHs (4.0, 7.4, 9.0, and 10.5), temperatures (4, 25, and 37 degrees C), and fixative concentrations (1, 2, or 4%). Samples of each group were taken out at various elapsed fixation periods. The crosslinking characteristics-fixation index, denaturation temperature, and moisture content-of each sample were determined. Additionally, the stiffness of the epoxy-fixed tendons under various fixation conditions was qualitatively compared. In the study it was noted that the color of porcine Achilles tendons remained natural after epoxy fixation. With increasing pH, temperature, or fixative concentration, the fixation indices and denaturation temperatures of the epoxy-fixed tendons increased. However, the fixed porcine tendons tended to be stiffer at a higher pH, temperature, or fixative concentration. The moisture contents of the epoxy-fixed tendons were relatively lower than the fresh ones, while they were approximately the same at different pHs, temperatures, and fixative concentrations. The implications of these findings for the epoxy-fixed porcine tendons in ACL reconstruction require further investigation.

[The bonding mechanisms of base metals for metal-ceramic crown microstructure analysis of bonding agent and gold bond between porcelain and base metals]

The use of base metal alloys for porcelain fused to a metal crown and bridges has increased recently because of lower price, high hardness, high tensile strength and high elastic modulus. The addition of beryllium to base metal alloys increased fluidity and improved casting fitness. Beryllium also controlled surface oxidation and bonding strength. The bonding agent and gold bonding agent also affected the bonding strength between porcelain and metal alloys. Four commercially available ceramic base alloys were studied (two alloys contained beryllium element, another two did not). The purpose of this investigation was to study the microstructure between porcelain matrix, bonding agent and alloy matrix interfaces. A scanning electron micro-probe analyzer and energy dispersive X-ray spectroscopy (EDXS) were used to study the distribution of elements (Ni, Cr, Mo, Cu, O, Si, Sn, Al) in four base alloys. The following results were obtained: 1. The thickness of the oxidized layer of Rexillium III alloy and Unitbond alloy (contained beryllium) was thinner than Unibond alloy and Wiron 88 alloy (no beryllium). 2. The thickness of the oxidized layer of alloys in air (10 minutes and 30 minutes) was thinner in Unitbond (2.45 microns and 3.80 microns) and thicker in Wiron 88 (4.39 microns and 5.96 microns). 3. The thickness of the oxidized layer occurring for a duration of ten minutes (in vaccum) showed that the Rexillium III alloy was the thinnest (1.93 microns), and Wiron 88 alloy was the thickest (2.30 microns). But in thirty minutes (vacuum), Unitbond alloy was the thinnest (3.37 microns), and Wiron 88 alloy was the thickest (5.51 microns). 4. The intensity of Cr elements was increased obviously near the interface between Unitbond alloy, Wiron 88 alloy (no beryllium) and oxidized layer, but the intensity of Ni and Mo elements was slightly increased. The intensity of Cr element was not increased markedly between Rexillium III alloy, Unitbond alloy (beryllium) and oxidized layer. 5. A white-grayish oxidized layer appeared at the metal-ceramic interfaces but the thickness of oxidized layer was not obviously different. 6. The use of bonding agent at metal-ceramic interface leads to the deposition of many Sn elements at about 40 microns range within the porcelain surface. 7. Second interaction phases at the porcelain layer appeared when gold bonding agent was used, and a 50-100 microns microleakage occurred at the metal-ceramic interface.

Recurrent epistaxis following nasotracheal intubation--a case report

Epistaxis is one of the common complications of nasotracheal intubation. Clinical patterns of all nasal bleeding are mild and may stop spontaneously in most patients. Serious nasal bleeding requiring hospitalization are rare. Nasal bleeding occurs more frequently in children than in adults. Among adults, men have a higher incidence than women. Although numerous publications have reported the cases of initial epistaxis caused by nasotracheal intubation, recurrent epistaxis was reported rarely. We experienced a case of recurrent epistaxis occurring in the 6th, 8th, 15th and 18th day after nasotracheal intubation. Herein, we describe the clinical events and discuss the causes of epistaxis.

Crosslinking characteristics of porcine tendons: effects of fixation with glutaraldehyde or epoxy

Anterior cruciate ligament (ACL) injuries, if left untreated, often produce significant disability in the athletically active population. Currently, autogenous tissue is the most commonly used substitute for ACL reconstruction because its immunogenicity is virtually nonexistent. However, the functional amount of autogenous tissue available for transplantation is limited. Additionally, this transplantation procedure may create a defect at the donor site, which can result in functional disability. To address these concerns, a prototype xenograft ligament prosthesis, epoxy-fixed porcine Achilles tendon, was developed. This study was intended to investigate the crosslinking characteristics of the epoxy-fixed porcine tendon. The fresh and glutaraldehyde-fixed porcine Achilles tendons were used as controls. Fresh porcine Achilles tendons procured from a slaughterhouse were used to fabricate the ligament prostheses. A 4% epoxy (ethylene glycol diglycidyl ether) solution or a 0.625% glutaraldehyde solution was employed to fix the porcine tendons. Samples of each group were taken out at various elapsed fixation periods. The crosslinking characteristics- denaturation temperature, moisture content, and fixation index-of each sample were then determined. In the study, it was learned that the crosslinking rate for the glutaraldehyde fixation was faster than that for the epoxy fixation. While the denaturation temperatures and the fixation indices for both studied groups were higher than for the fresh one, the denaturation temperature of the glutaraldehyde-fixed tendon was relatively higher than its epoxy-fixed counterpart. However, the fixation index and the moisture content for both studied groups were comparable. Also, it was noted that the epoxy-fixed tendon appeared more natural as compared to its glutaraldehyde-fixed counterpart. The implications of these findings for the epoxy-fixed tendon in the clinical ACL reconstruction require further investigation.

[Arytenoid subluxation following endotracheal intubation--a case report]

A previously healthy 39-yr-old man was scheduled for exploratory laparotomy due to acute abdomen. There was no sign of difficult intubation. After induction of anesthesia with thiopental and succinylcholine, the trachea was easily intubated with a 7.0 mm cuffed endotracheal tube. Surgery for a ruptured appendix with 2 drainage tubes lasted for 75 min was uneventful. At the end of surgery, the endotracheal tube was removed without difficulty. On the 1st postoperative day, the patient developed stridor. The symptom persisted even after conservative treatment and removal of NG tube. On the 12th postoperative day, a telescopic videolarygoscopy revealed immobile right vocal cord with anterior and medial displacement to the right. Arytenoid cartilage was moderately edematous. A diagnosis of right arytenoid subluxation was then made. On the 17th postoperative day, a closed reduction of right arytenoid cartilage using direct laryngoscope was performed successively under general anesthesia. Eight weeks after the reduction, his voice and laryngoscopic findings were normal. There has been only 18 reports with 27 cases of this complication found in the literature. However, it is generally believed that it is not so unusual. The post-intubation syndromes, such as sore throat, dysphonia, odynophagia, difficulty in swallowing or breathing which persists beyond 5 days warrant ENT consultation. Abnormal mobility of vocal cord, edema over arytenoid area found by indirect laryngoscopy should suggest the complication. Further confirmation is then needed. Although the result of our case is good, the reduction should ideally be done within 24-48 h after the incidence to avoid unfavorable long-term sequelae.

Serious suppurative group A beta-hemolytic streptococcal infection in previously well children: report of six cases

Recently, among adults and children, an increase in the incidence of invasive disease caused by group A beta hemolytic streptococcus (GABHS) has been noted. From December 6, 1981 to January 19, 1991, we experienced six cases of serious infection caused by GABHS in previously well children. Among them, five cases were found in recent two years. The clinical manifestations were varied. One child had sepsis, one had streptococcal toxic shock-like syndrome, two had pyogenic arthritis, and the other two newborn infants had empyema and cellulitis associated with sepsis. Early diagnosis and treatment with appropriate antibiotic are necessary for a good outcome. In addition, empyema and pyoarthritis of the hip often need surgical drainage.

[The stress distribution of prefabricated screw posts. Part III: Techniques]

Some commonly used endodontic screw posts were analysed for various techniques of post insertion by photoelastic stress distribution. These endodontic dowels were installed in assumed clinical conditions. These conditions included: (1) no backing off during post installation, (2) the channelling of the post without cleaning, (3) a smaller drill was used prepare the post channel, and (4) an axis deviated contrangle was used to prepare the post channel. According to this photoelastic analysis, the techniques of post insertion may affect the stress distribution. Suggestions for post insertion are as follows: 1. The stress can be reduced by counterrotating the dowel one-fourth turn after resistance to installation has been detected. 2. The channel should be cleaned thoroughly before post insertion. 3. Because accurate post fit is important to maximize both retention and support, the screw post should be used with the matched post/reamer system; and accurate contrangle drilling should be maintained.

The cytological diagnosis of nasopharyngeal carcinoma using a silk swab stick

A prospective study was carried out to investigate the efficacy of exfoliative cytology for the diagnosis of nasopharyngeal carcinoma. Exfoliated nasopharyngeal cells were collected from patients with a clinical suspicion of carcinoma by scraping the nasopharyngeal mucosa with a piece of silk wrapped around one end of a wooden stick. Ninety-eight patients were investigated in this manner, and the results of cytological investigation compared with the histological findings. The sensitivity of cytological investigation was 71% and the overall accuracy was 86%. The combined use of cytology and serology as a method of screening for nasopharyngeal carcinomas is discussed.

A strategy for efficient characterization of macromolecular heteroassociations via measurement of sedimentation equilibrium

A method is proposed for the selection of experimental conditions for sedimentation equilibrium experiments that will provide maximal information about the values of equilibrium association constants within a given scheme for heteroassociation of two solute components. A discriminator function is proposed that indicates the sensitivity of the experimentally observed gradient or gradients to alterations in the underlying association constants. The value of this function is plotted or tabulated as a function of the concentrations of the two components, over a broad range of solution compositions. It is suggested that experiments performed with loading compositions corresponding to large absolute values of the discriminator function will yield the most information with respect to determination of the underlying association constants. This method was tested by predicting optimal conditions for three different types of sedimentation equilibrium experiments: (i) measurement of total (natural) solute absorbance; (ii) measurement of individual component gradients via measurement of tracer absorbance; and (iii) global analysis of multiple experiments. Experimental data resulting from sedimentation equilibrium experiments carried out under the specified conditions were simulated by addition of realistic levels of random error to calculated equilibrium gradients. The simulated data were then analyzed exactly as real experimental data, i.e., without prior knowledge of the underlying association constants. It was found that the highest accuracy and precision in determination of heteroassociation constants are obtained by global analysis of multiple experiments performed using significantly different loading compositions, each of which is selected from 'sensitive' regions of the discriminator map.

Effect of isoproterenol on the uptake of [14C]glucose into glial cells

The effect of isoproterenol on the uptake of [14C]glucose into cultured glial cells was investigated in the present study. Isoproterenol markedly stimulated the uptake of [14C]glucose 30 min after incubation. This action was produced in a dose-dependent manner. A positive correlation between the increase of [14C]glucose uptake and the stimulation of adenylate cyclase induced by isoproterenol was obtained (r = 0.99). The effect of isoproterenol was reduced by the beta-adrenergic blockers but not by other blockers, indicating the selective action of isoproterenol. The results obtained suggest that isoproterenol stimulates the uptake of glucose into glial cells through the activation of beta-adrenoceptors which are linked to adenylate cyclase.

[Changes in microstructure of ceramic alloys after heat and electrochemical acid treatment]

The technique of electrochemical etching was developed by Dr. Tegart for application in both research and industry in 1959. There is considerable evidence showing that in conjunction with chemical bonding, surface roughness of etched casting restorations can apparently improve the mechanical adherence between the porcelain and the metal. It is obvious that surface roughness produced by sandblasting or electrochemical etching of the metal substrate not only provides mechanical interlocking but also increases the surface area for porcelain attachment. It was observed in this study that a properly heat-treated surface was significantly rougher than a surface without appropriate treatment after electrochemical acid etching. The roughness of base metals also treated with 0.5N nitric acid appeared greater obvious than those treated with 10% sulfuric acid. The etching pattern can be evaluated by selective removal of the alloy phases present between the dendritic arms in the base metal alloy. The technique of electrochemical acid etching is limited to alloys that solidify with a multiphasic structure- that is, a base metal alloy. And there are no known noble alloys suitable for this technique in this experiment. Electrolytic etching is most conveniently evaluated under a light microscope at about 30-80 magnifications to inspect surface relief and etching patterns. It remains to be determined by further research what is the exact cause of the increased roughness and how it improves the metal for ceramic mechanical bonding.

Shear strength of the composite bond to etched porcelain

The shear bond strength of composite resin to porcelain was investigated to optimize variables for bonding porcelain laminate veneers. Scanning electron microscopy was initially used to examine the surface configuration of porcelain prepared under various conditions. A factorial experiment was undertaken to determine the effects of three different bonding methods on both etched and non-etched porcelain. Composite resin was bonded to the porcelain groups using (a) unfilled resin, (b) silane, and (c) silane with dentin adhesive. The results indicated a significant difference in shear bond strength for the three bonding groups, depending on the porcelain surface condition. For the unetched samples, significant differences in bond strength were obtained for all three bonding conditions. However, for the etched group, there were no differences between the silane and silane-with-dentin-adhesive groups. Porcelain etching significantly increased bond strength across all three bonding methods and was the main contributor to the obtained values.