Biomedical subjects

C J Andres

Publications and source records attributed to C J Andres.

At least 19 recordsLinked to original sources

PubMed2005

Effects of coupling methods on galvanic corrosion behavior of commercially pure titanium with dental precious alloys.

BACKGROUND: When a dissimilar couple is exposed to corrosive environment, it will normally exhibit a galvanic corrosion. The galvanic corrosion might be influenced by various factors, including type and concentration of electrolyte, surface area ratio between anode and cathode, type of coupling material, and coupling manner. PURPOSE: The purpose of this study was to investigate and compare the galvanic corrosion behavior of commercially pure titanium when coupled with type IV Au alloy, Au-Ag-Pt alloy, and Ag-Au-Pd alloy by different coupling methods. MATERIALS AND METHODS: Couples were prepared by a laser welding or a mechanical adhering method. Electrochemical corrosion studies were conducted in a Ringer's solution at a scanning rate of 0.1 mV/sec in a range from -250 mV to +250 mV with respect to E(OCP). Corrosion parameters (E(OCP), I(CORR), E(CORR)) were obtained. RESULTS: It was found that (i) there was a significant difference between LWC and AJC for three couples (p<0.05), (ii) the crevice line caused all three couples more corrosive than weld joint line, (iii) for both joint, it was found that type (IV) Au alloy exhibited discoloration to some extent. CONCLUSIONS: It is concluded that among the three couples with two different coupling methods, Ti/Ag-Au-Pd couple exhibited best corrosion resistance in a room temperature Ringer's solution.

Corrosion↗

PubMed2004

Mechanical properties of four methylmethacrylate-based resins for provisional fixed restorations.

The use of a provisional restoration is an important phase in the treatment of the dental prosthetic patient. A good provisional restoration should satisfy the following requirements: pulpal protection, positional stability, ease in cleaning, accurate margins, wear resistance, dimensional stability, and serve as a diagnostic aid in treatment assessment and esthetics. There is a tendency for discoloration, occlusal wear, and fracture that eventually leads to unnecessary repair. Heat-processed and reinforced methacrylate-based resins have been used to improve the mechanical and physical properties of provisional restorations. Among various improvements, the interpenetrating network crosslinked PMMA (IPN) has been shown to have superior mechanical properties if manufactured through a dough compression molding process at 130 degrees C. However, there have been no published data that relate with the use of this material for fixed provisional restorations. The objective of this study was to compare four methyl methacrylate-based resins for provisional crowns and bridges with varying processing cycles, including JET [self-cure], ACRALON [heat-cured], titanium dioxide filled PMMA [heat-cured], and IPN [heat-cured denture tooth resin]. Properties studied included transverse strength, toughness, rigidity, and hardness. From the results of this study the following conclusions can be made: the IPN group may have had a lower degree of conversion as demonstrated by decreased strength, toughness, and hardness data as compared with Acralon. Increasing the polymerization cycle of unmodified Acralon resin causes a significant increase in strength.

Biocompatible Materials↗

PubMed2002

Reinforcement of acrylic resins for provisional fixed restorations. Part III: effects of addition of titania and zirconia mixtures on some mechanical and physical properties.

Acrylic resins have been used in many different applications in dentistry, especially in the fabrication of provisional fixed partial dentures. Ideally, a provisional crown and bridge material should be easy to handle and should protect teeth against physical, chemical, and thermal injuries. Some of the problems associated with this use are related to the material's poor mechanical properties. It has been demonstrated that acrylic resin can be strengthened through the addition of structural component of different size distributed in the acrylic matrix, thus forming a composite structure. The purpose of this study was to investigate the addition effects of mixtures of titania (titanium dioxide, TiO(2)) powder and zirconia (zirconium dioxide, ZrO(2)) powder being incorporated with pre-polymerized beads mixed in monomer liquid, on some mechanical and physical properties of PMMA resin. The pre-polymerized powder poly(methyl methacrylate) resin was admixed with titania and zirconia powder. A mixing ratio was controlled by volume % of 0, 1.0, 2.0, and 3.0 (samples with 0 v/o served as control groups). For using mixture of titania and zirconia, total amount of the mixture was controlled by volume % of 1.0, 2.0, and 3.0, in which titania and zirconia were mixed at the ratio 1 :1, 1 :2 and 2 :1. Prior to mechanical tests, all rectangular-shaped samples (25 mm x 2 mm x 5 mm) were stored in 37 degrees C distilled water for 7 days after polishing all six sides of samples. Samples were then subjected to the three-point bending flexion test to evaluate the bending strength as well as the modulus of elasticity. Weight gain and exothermic reaction survey were investigated as well. All data were collected and analyzed with one-way analysis of variance (ANOVA) and Sidak method (p=0.05). It was found that the addition of particles generally decreased the water absorbed by the composite system. Only 1 percent by volume concentration of 1 :1 ratio and 2 percent by volume concentration of 1 :2 and 2 :1 ratios had significantly higher strength than control group. There was significantly higher toughness (in terms of energy-to-break) for 1 percent by volume concentration of 1 :1 ratio and 2 percent by volume concentration of 2 :1 ratio than control group. There was no significant difference between control group and all percent by volume combinations in modulus of elasticity. In addition, there was no significant variations of exothermic reaction.

Absorption↗

PubMed2001

Electrochemical corrosion of titanium and titanium-based alloys.

STATEMENT OF PROBLEM: Two varieties of unalloyed titanium, Ti-6Al-4V and NiTi, commonly are used in medical and dental fields. Several other types of alloys for potential use in these fields have been developed, including Ti-4.5Al-3V-2Mo-2Fe and vanadium-free alloys (Ti-5Al-2.5Fe and Ti-5Al-3Mo-4Zr). The corrosion of these alloys under simulated physiologic conditions is not known. Purpose. This study compared the corrosion behaviors of 6 titanium materials through electrochemical polarization tests in 37 degrees C Ringer's solution. MATERIAL AND METHODS: The applied voltage was potentiostatically scanned from -0.6 to 1.0 V. From polarization curves, the corrosion rate (averaged over 3 samples) for each alloy was calculated and compared with that of other alloys. Analysis of variance (ANOVA) and the Student-Newman-Keuls multiple range test were performed at a 95% overall confidence level to identify statistically significance differences in corrosion rates. Surface oxide films were identified by electron diffraction, and the electrolyte medium was analyzed by atomic absorption spectrophotometry after each alloy was tested. RESULTS: Commercially pure titanium and Ti-5Al-2.5Fe were the most resistant to corrosion; Ti-5Al-3Mo-4Zr, Ti-6Al-4V, and NiTi were the least resistant to corrosion. NiTi exhibited pitting corrosion along with transpassivation. CONCLUSION: Electron diffraction patterns indicated that all titanium alloys were covered mainly with rutile-type oxide (TiO(2)) after corrosion tests. The oxides that formed on Ti-5Al-2.5Fe were identified as a mixture of TiO(2) and Ti(9)O(17), and those that formed on NiTi were identified as a mixture of TiO(2) and Ni(2)Ti(4)O.

Alloys↗

PubMed2001

Titanium-porcelain system. Part III: effects of surface modification on bond strengths.

During its development, titanium was found to be incompatible with conventional dental porcelains due to weak bond strength brought about by titanium's high yet oxidative nature. In spite of the development of new low-fusing porcelains designed for titanium application, previous studies have shown that sandblasting pre-treatment prior to porcelain application led to weakening of the metal-ceramic bonding. The aim of this study is to search for an effective alternative to sandblasting for the surface treatment of the titanium substrate in the titanium-porcelain system. The research evaluated the bond strength of 165 samples of titanium-porcelain systems divided into 11 groups. A three-point flexural bend test was conducted to measure the force required to fracture the porcelain on the titanium substrate. A correlation between the type of surface treatment and the bond strengths of each group was evaluated if it resulted to significant differences. The study found significantly differences in the energy-to-break of titanium-porcelain systems treated with hydrochloric acid and sandblasting compared with the control group. The bonds strength achieved by the titanium-porcelain system when treated with hydrochloric acid is comparable to that of conventional metal-ceramic alloy system. Hydrochloric acid treatment of the titanium substrate is a promising alternative to sandblasting for the surface treatment of the titanium substrate in the titanium-porcelain system.

Aluminum Oxide↗

PubMed2000

4-Thiazolidinones: novel inhibitors of the bacterial enzyme MurB.

4-Thiazolidinones were synthesized and evaluated for their ability to inhibit the bacterial enzyme MurB. Selected 4-thiazolidinones displayed activity against the enzyme in vitro. This activity, coupled with the design principles of the thiazolidinones, supports the postulate that 4-thiazolidinones may be recognized as diphosphate mimics by a biological selector.

Bacteria↗

PubMed2000

Study of the physical properties of type IV gypsum, resin-containing, and epoxy die materials.

STATEMENT OF PROBLEM: Little published information is available comparing the properties of recently developed resin-modified gypsum and epoxy resin die materials, which are claimed to be superior to conventional type IV gypsum die materials. PURPOSE: This study compared the properties of 3 new die materials and 2 conventional type IV gypsum products. METHODS AND MATERIAL: The linear dimensional change, detail reproduction, surface hardness, abrasion resistance, and transverse strength of 2 recently introduced, resin-modified gypsum die materials (Resinrock and Milestone), a new epoxy resin die material (Epoxy-Die), and 2 conventional type IV gypsum die materials (Silky-Rock and Die-Stone) were studied. RESULTS: All gypsum products expanded, whereas the epoxy resin material contracted during setting. The epoxy resin exhibited much better detail reproduction, abrasion resistance, and transverse strength than the gypsum materials, which were similar in these properties. A conventional type IV gypsum exhibited the highest surface hardness, whereas the epoxy resin had the lowest value. CONCLUSION: The resin-modified gypsum products were not significantly superior to the conventional type IV gypsum die materials. In general, the epoxy resin exhibited the best properties of the materials studied; however, its setting shrinkage may necessitate alterations in technique to achieve well-adapted castings.

Analysis of Variance↗

PubMed2000

Laboratory-fabricated, acrylic resin cylinders for fixed, provisional implant restorations.

Commercially produced provisional cylinders are commonly used during fabrication of fixed, provisional implant restorations. A procedure is presented for the fabrication of fixed, provisional implant restorations using laboratory-fabricated, autopolymerizing acrylic resin cylinders. These cylinders offer a number of advantages over commercially produced cylinders and may reduce the treatment cost of implant prosthodontics.

Acrylic Resins↗

PubMed1999

Hemifacial microsomia and treatment options for auricular replacement: A review of the literature.

STATEMENT OF PROBLEM: Although surgical reconstruction is the treatment of choice for auricular deformities that result from hemifacial microsomia, the implant-retained auricular prosthesis must be considered when surgical reconstruction is not possible. The competent and successful practitioner should be knowledgeable of the nature of this congenital disease. PURPOSE: This article reviewed the first and second branchial syndrome, treatment approaches, and potential advances in surgical and prosthetic rehabilitation for patients with hemifacial microsomia. CONCLUSION: Advantages and disadvantages of autogenous and alloplastic ear reconstructions are discussed. New research initiatives, such as tissue engineering and fabrication of auricular prosthesis by CAD/CAM, offer the potential for improved treatment for the future treatment of hemifacial microsomia.

Branchial Region↗

PubMed1999

Color stability and colorant effect on maxillofacial elastomers. Part I: colorant effect on physical properties.

STATEMENT OF PROBLEM: The average clinical life span of a maxillofacial prosthesis is approximately 6 months, at which point it needs to be refabricated, mainly because of degradation of the color and physical properties of the prosthesis. PURPOSE: This first part of a 3-part study evaluated the effect of coloring agents on the physical properties of maxillofacial elastomers. METHODS AND MATERIAL: Five dumbbell-shaped and 5 trouser-shaped specimens were fabricated for each of the combinations of the 3 elastomers (Silastic medical adhesive type A, Silastic 4-4210, and Silicone A-2186) and 6 colorants (dry earth pigments, rayon fiber flocking, artist's oil paints, kaolin, liquid cosmetics, and no-colorants), for a total of 180 specimens. Evaluations of hardness and tear strength were made with the trouser-shaped specimens. Evaluations of the ultimate tensile strength and the percentage elongation were made with the dumbbell-shaped specimens. A within elastomer analysis compared the 6 colorants using a 1-way analysis of variance for each of the 4 physical properties. When significant differences were observed, the Student-Newman-Keuls multiple range test was used to identify differences between groups at a significance level of.05. RESULTS: Physical properties of maxillofacial elastomers were changed by the incorporation of coloring agents. Dry earth pigments, kaolin, and rayon flocking acted as a solid filler without bonding to the Silicone, and artists' oils and liquid cosmetics acted as a liquid phase without bonding to the silicone matrix. CONCLUSION: No clearly superior colorant-elastomer combination was demonstrated in all the tests in this study.

Analysis of Variance↗

PubMed1999

Color stability and colorant effect on maxillofacial elastomers. Part II: weathering effect on physical properties.

STATEMENT OF PROBLEM: The clinical life of a maxillofacial prosthesis averages about 6 months, before it needs to be refabricated. Degradation of the color and physical properties of the prosthesis are the principle reasons for replacement. PURPOSE: This second part of a 3-part in vitro investigation evaluated the change in physical properties of popular colorant-elastomer combinations as a result of weather exposure. MATERIAL AND METHODS: Fifteen dumbbell-shaped and 15 trouser-shaped specimens were fabricated for each of the 3 elastomers (Silastic medical adhesive type A, Silastic 4-4210, and Silicone A-2186) and 6 colorant combinations (dry earth pigments, rayon fiber flocking, artist's oil paints, kaolin, liquid cosmetics, and no-colorants) for a total of 540 specimens. The 15 dumbbell-shaped and trouser-shaped specimens of each elastomer colorant combination were separated into 5 of each shape among 3 test condition groups (control, time passage, and natural weathering). Control specimens were evaluated within 1 month of fabrication. The time passage group was sealed in glass containers and kept in the dark for 6 months before testing. The natural-weathering groups were placed on the roof of the dental school for 6 months and exposed to sunlight and weathering. Evaluations of hardness and tear strength were made on trouser-shaped specimens, and evaluations of the ultimate tensile strength and percentage elongation on dumbbell-shaped specimens. Physical property data for each elastomer-colorant combination were subjected to a 1-way analysis of variance to examine effects among the test conditions. When significant differences were observed, the Student-Newman-Keuls multiple range test was performed to identify differences in elastomer-colorant combinations among each test condition at a significance level of .05. RESULTS: Exposure to weathering and time changes of the physical properties of many colorant-elastomer combinations indicated that properties of a clinical prosthesis can change with time. CONCLUSION: The addition of colorants to the silicones altered the effects of weathering. In addition, the silicones were not as stable as previously assumed.

Analysis of Variance↗

PubMed1999

Color stability and colorant effect on maxillofacial elastomers. Part III: weathering effect on color.

STATEMENT OF PROBLEM: Maxillofacial prostheses are serviceable for approximately 6 months, after which they need to be refabricated because of the deterioration of color and physical properties. PURPOSE: This third article in a 3-part series evaluated the color stability of commonly used colorant-elastomer combinations as a result of exposure to weathering. METHODS AND MATERIAL: Fifteen specimens were fabricated for each of the 3 elastomers (Silastic medical adhesive type A, Silastic 4-4210, and Silicone A-2186) and 6 colorants (dry earth pigments, rayon fiber flocking, artist's oil paints, kaolin, liquid cosmetics, and no colorant) for a total of 270 specimens (18 groups of 15 specimens). The 15 specimens of each elastomer-colorant combination were separated into 3 test condition groups (control, time passage, and natural weathering) of 5 specimens per test condition group. Control specimens were evaluated within 1 month of fabrication. The time passage group was sealed in glass containers and kept in the dark for 6 months before testing. The natural weathering groups were placed on the roof of the dental school for 6 months and exposed to sunlight and weathering. Color and optical density data for each elastomer-colorant combination were subjected to a 1-way analysis of variance to examine effects among test conditions (control, time passage, and weathering). When significant differences were observed, the Student-Newman-Keuls multiple range test was performed to identify differences in elastomer-colorant combinations among each test condition at a significance level of .05. RESULTS: Changes in color, as a result of weathering, were noted in many of the colorant-elastomer combinations. Also, color change occurred not only to the colored, but also to uncolored materials over time without exposure to weathering. CONCLUSION: Clinically, the addition of colorants could have a stabilizing effect on the elastomer color when it is exposed to weathering.

Analysis of Variance↗

PubMed1999

A novel cleavage protocol for use with Rf-encoded split pool synthesis technology: product cleavage and collection in standard 96 well format.

A novel protocol which employs commercially available, standard tools and hardware has been developed. This protocol allows for cleavage and collection of IRORI Microkan products in 96 well plate format. Typically, 640 compounds can be cleaved in a 4 hour time period using approximately 3 square feet of space. This protocol has been used successfully for the liberation of thousands of individual compounds, in single compound per well format from the solid phase. Additionally, this protocol is the first example of making IRORI Microkan technology directly compatible with standard 96 position deep well blocks.

Equipment and Supplies↗

PubMed1999

Recent advances in the solid phase synthesis of drug-like heterocyclic small molecules.

Phage display is a biological system which facilitates the cloning and rapid selection of peptides from large combinatorial libraries. In compa-rison to the chemical combinatorial approach, the advantages of phage display lie in its simplicity and replicability. While phage display has many diverse applications, this review will focus on the use of phage peptide libraries to discover epitopes recognised by monoclonal antibodies. As monoclonal antibodies are useful tools for the detection of proteins and for the investigation of molecular interactions, the identification of their epitopes will serve to elucidate the structure and function of proteins, as well as aid in the discovery of new drugs and the development of vaccines.

Drug Design↗

PubMed1998

Transition-metal-mediated reactions in combinatorial synthesis.

Transition-metal-mediated reactions have played an important role in expanding the scope of combinatorial chemistry from synthesis of peptidic libraries to synthesis of nonoligomeric, small-molecule libraries. Versatile reactions such as heteroannulations, olefin metathesis and dipolar cycloadditions are used for preparation of libraries of historical, as well as novel, pharmacophores. Transition-metal-mediated reactions have also been used strategically to provide traceless linkers' in solid-phase synthesis.

Alkenes↗

PubMed1998

Using a colorimeter to develop an intrinsic silicone shade guide for facial prostheses.

PURPOSE: To determine if using CIE L*a*b* color measurements of white facial skin could be correlated to those of silicone shade samples that visually matched the skin. Secondly, to see if a correlation in color measurements could be achieved between the silicone shade samples and duplicated silicone samples made using a shade-guide color formula. MATERIALS AND METHODS: A color booth was designed according to ASTM specifications, and painted using a Munsell Value 8 gray. A Minolta colorimeter was used to make facial skin measurements on 15 white adults. The skin color was duplicated using custom-shaded silicone samples. A 7-step wedge silicone shade guide was then fabricated, representing the commonly encountered thicknesses when fabricating facial prostheses. The silicone samples were then measured with the Minolta colorimeter. The readings were compared with the previous L*a*b* readings from the corresponding patient's skin measurements, and the relative color difference was then calculated. Silicone samples were fabricated and analyzed for three of the patients to determine if duplication of the visually matched silicone specimen was possible using the silicone color formula, and if the duplicates were visually and colorimetrically equivalent to each other. The color difference Delta E and chromaticity was calculated, and the data were analyzed using a coefficient-of-variation formula expressed by percent. A Pearson Product Moment Correlation Coefficient was performed to determine if a correlation existed between the skin and the silicone samples at the p < or = .05 level. RESULTS: The highest correlation was found in the b* dimension for silicone thicknesses of 1 to 4 mm. For silicone thicknesses of 6 to 10 mm, the highest correlation was found in the L* dimension. All three dimensions had positive correlations (R2 > 0), but only the 1-mm and 4-mm b* readings were very strong. Patient and silicone L*a*b* measurement results showed very little change in the a* axis, while the L* and b* measurements showed more change in their numbers, with changes in depth for all patient silicone samples. Delta E numbers indicated the lowest Delta E at the 1-mm depth and the highest Delta E at the 10-mm depth. All duplicated samples matched their original silicone samples to a degree that visual evaluation could not distinguish any color differences. Using volumetric measurements, a shade guide was developed for all 15 patients. CONCLUSIONS: There was good correlation between the patient's colorimeter measurements and the silicone samples, with the b* color dimension the most reproducible, followed by the L* and the a*. Silicone samples at 6, 8, and 10 mm matched the patient the best, and this study showed that silicone samples can be duplicated successfully if a good patient-silicone match is obtained. Rayon flocking fibers and liquid makeup are effective at matching facial prostheses and can be used to develop a simple shade guide for patient application.

Color↗

PubMed1996

Serum concentrations of melatonin in prepubertal gilts exposed to either constant or stepwise biweekly alteration in scotophase.

Melatonin (MEL), a hormone known to mediate photoperiodic cues, is secreted from the pineal gland in a circadian fashion in numerous species. The transduction of photoperiodic information into the secretion of MEL, however, remains controversial in the pig. To determine whether domestic pigs have a nocturnal increase in serum melatonin when exposed to equatorial photoperiods only, 24 prepubertal gilts (38.7 +/- 0.7 kg; 104.5 +/- 0.8 d) and 12 mature ewes, serving as positive controls, were randomly assigned to one of two environmentally regulated rooms. The light (L):dark (D) schedule in one room remained constant (10 L:14 D), while the other room scotophase (darkness duration) was decreased by 1 hr every 2 wk (Experiment 1). After a 2-wk acclimation to each new schedule, 6 ewes and 6 gilts in each room were bled by venipuncture at 2-hr intervals for 22 hr. Experiment 2 was conducted as described for Experiment 1, except that the LD schedule in one room remained constant (15L:9D) while length of scotophase in the other room was increased by 1 hr every 2 wk. In gilts that were exposed to constant 10L:14D, scotophase MEL in serum averaged 103 +/- 13 pg/ml as compared with 57 +/- 13 pg/ml in the photophase. Using each gilt's initial photophase value as a statistical covariate, scotophase MEL in the constant 10L:14D schedule was higher (P < 0.001) than photophase MEL. A similar analysis of MEL in gilts exposed to stepwise biweekly decreases in scotophase revealed a scotophase elevation (P < 0.05) in only certain LD schedules (i.e., 12L:12D and 13L:11D), but the same trend was present throughout all LD schedules. Subjective examination of individual gilt profiles revealed that 56% of gilts had a nocturnal increase in serum MEL in Experiment 1. However, only 10% of the MEL profiles were closely coupled to the environmental LD periods. Overall, mean serum MEL in gilts was of lesser magnitude and more variable than in ewes. Data from these two experiments suggests that the domestic pig has an inherently weak nocturnal elevation in serum MEL, and the ability to detect these rises is dampened by considerable pig-to-pig variability.

Animals↗

PubMed1996

A color-enhanced aid for location of the transverse horizontal opening and closing axis of the mandible.

This article describes the use of a device for assisting in identification of the direction of the arc of rotation while locating the transverse horizontal opening and closing axis of the mandible. Translucent disks are mounted on the point of the styli of a kinematic face-bow and centering magnets are aligned with them, with no overlapping of the colors. The direction of the arcing movement is enlarged by the overlapping of the translucent disk over the centering magnet. The different color value generated by the overlapping identifies the arcing direction. After correction on the microadjustable arm, the centering magnet is realigned on the translucent disk. This sequence is repeated until the disk no longer overlaps with the centering magnet during the opening and closing movements of the mandible. This device uses the different color generated by mixing the color of the disk against a template of darker color. The disk enlarges the point of the stylus, thus magnifies the direction of the arc of rotation, and potentially reduces the clinical time necessary to locate the points of pure rotation.

Biomechanical Phenomena↗