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Biomedical subjects

R M Carvalho

Publications and source records attributed to R M Carvalho.

48 records · Page 3Linked to original sources
PubMed1995

Bond strength versus dentine structure: a modelling approach.

Bond strengths of a hypothetical hydrophilic dentine-bonding agent were calculated as a function of dentine depth and resin strength to evaluate the importance of several variables in a simple model. The tested hypothesis was that the total bond strength was the sum of the strengths of resin tags, hybrid layer and surface adhesion. Each of these three variables has a range of values that can influence its relative contribution. The resulting calculations indicate the potential for higher bond strengths to deep dentine than to superficial dentine in non-vital dentine and the importance of resin strength in the development of strong bonds. Comparison of the calculated bonds with published values indicated that they were within the same order of magnitude. Such theoretical modelling of dentine bonding can identify the relative importance of variables involved in the substrate, resins and surface adhesion.

Acid Etching, Dental↗
PubMed1995

Adhesion testing of dentin bonding agents: a review.

Adhesion testing of dentin bonding agents was reviewed starting with the adhesion substrate, dentin, the variables involved in etching, priming and bonding, storage variables and testing variables. Several recent reports attempting to standardize many of these variables were discussed. Recent advances in the development of new bonding systems have resulted in bond strengths on the order of 20-30 MPa. At these high bond strengths, most of the bond failure modes have been cohesive in dentin. As this precludes measurement of interfacial bond strength, new testing methods must be developed. One such new method, a microtensile method, was described along with preliminary results that have been obtained. The last decade has produced major advances in dentin bonding. The next decade should prove to be even more exciting.

Adhesiveness↗
PubMed1995

Strength of base materials.

PURPOSE: To compare the punch resistance of VariGlass and Vitrebond. MATERIALS AND METHODS: Discs measuring 1.4 cm in diameter and 1.5 mm thick of VariGlass (VG) and Vitrebond (VT) light-activated lining materials, were prepared and submitted to punch testing in a universal testing machine at 7 minutes, 30 minutes and 24 hours after mixing. RESULTS: VG showed higher resistance to punch testing than the VT in the three periods evaluated (P< 0.01). The results were further compared to previous data obtained from three calcium hydroxide lining cements which gave much lower values than VG and VT (P< 0.01).

Acrylic Resins↗
PubMed1995

Bonding mechanism of VariGlass to dentin.

PURPOSE: This study investigated the hypothesis that the new resin-reinforced, light-cured ionomer cement (GIC) can develop mechanical retention by forming a hybrid layer in acid-etched dentin. MATERIALS AND METHODS: Dentin discs were obtained from extracted human third molars and sanded with 320 SiC abrasive paper. One third of the surface was acid etched with 10% maleic acid for 15 seconds, washed and gently air-dried for 5 seconds. ProBond primer from the VariGlass (VG) GIC kit was applied onto the acid-etched surface (A) and another third of the unetched surface (B) for 30 seconds. One third of the surface was not treated (C). VG GIC was then applied onto the ++entire surface of the disc. After 24 hours the discs were fractured along their diameters. One half of the fractured disc was highly polished at the interface and treated with 6N HCl for 30 seconds while the other half of the fractured specimen was left untreated. Both halves were viewed by SEM. In another part of the study, a micro-tensile bond strength (MTBS) test was carried out to compare the acid-etched group vs. the nonetched group. RESULTS: SEM pictures revealed a well defined demineralized, resin-infiltrated zone approximately 3 micrometers in thickness for group (A) for both fractured and polished surface. Dentin surfaces that only received primer (B) showed an irregular zone 0.5 micrometers thick. Such a resin-infiltrated layer was resistant to HCl treatment. A gap was observed between the GIC and dentin in group (C). Polished interfaces appeared to be highly infiltrated. However, fractured interfaces revealed considerable porosity within the demineralized-infiltrated zone. MTBS results were (X +/- SD, MPa): 28.9 +/- 5.8 for the etched group and 24.5 +/- 4.9 for the nonetched group. This difference was statistically significant.

Acid Etching, Dental↗
PubMed1994

Glass ionomer cement surface protection.

PURPOSE: To evaluate the effectiveness of various surface treatments for glass ionomer cement (GIC) by determining quantity of dye uptake spectrophotometrically. MATERIALS AND METHODS: Sixty specimens, 4.5 mm diameter and 2 mm thick, were made from Shofu GIC and divided into 10 groups. Positive control (A) and negative control (B) specimens were not protected while experimental specimens were protected with ARM chemically-cured bonding resin (C), Durafill Bond light-cured bonding resin (D), Bondlite light-cured bonding resin (E), Colorama nail varnish (F), Shofu varnish (G), Copalite varnish (H), Vaseline (I) or Vaseline followed by Copalite (J). The discs were immersed in 0.05% methylene blue solution 10 minutes after mixing except group B specimens which were immersed in deionized water. After 24 hours the discs were removed, washed, and individually placed in 1 ml 65% nitric acid for 36 hours. The solutions were filtered, centrifuged and the absorbance determined spectrophotometrically at 590 nm. Dye uptake was expressed in microgram dye/restoration and the data analyzed by ANOVA and Tukey Kramer test. RESULTS: The mean (SD) of dye uptake were: A:95.12 (11.28); B:0 (0); C:40.90 (5.06); D:33.89 (3.63); E:35.73 (3.36); F:3.29 (0.79); G:14.87 (2.86); H:21.99 (3.25); I:47.21 (7.06); J:29.74 (3.49). All the surface agents were effective in protecting setting restorative glass ionomer cement, but nail varnish provided the best results.

Analysis of Variance↗
PubMed1991

[Multiple sclerosis: objective criteria of diagnosis].

The frequency of multiple sclerosis in Brasil is assumed to be lower than in some geographically comparable regions, but internationally available objective diagnostic criteria are not generally used. We have reviewed a number of such criteria and applied those of Poser and colleagues to all patients who could be examined specifically for this study; who had been under our care between 1982-87; with clinically satisfactory history, physical exam, ancillary investigations and follow-up; with enough information to warrant immunosuppressive therapy with azathioprine, methyl-prednisolone or cyclophosphamide. There were 35 (88%) females and 5 (12%) males, with clinically definite (85%), probable (10%) disease according to Poser and cols, as well as 2 patients with chronic progressive disease. Age at time of study was 39 +/- 11 years, age at onset had been 32 +/- 10 years, and length of history was 6 +/- 7 years (mean +/- sd). Mode of onset was a disturbance of gait in 50%, of vision in 25% and dizziness in 10%. Physical exam at time of study showed motor deficits in 92.5%, sensory in 67.5%, ocular visual in 65%, spastic bladder in 35%, and vestibulo-cerebellar disturbances in 32%. Visual evoked responses were abnormal in 65% of 31 cases, auditory in 23% of 22 cases, and somatosensory in 80% of 20 cases. This study shows that international diagnostic criteria, specifically those of Poser and colleagues are applicable in Brasil, providing clear guidelines for diagnosis of multiple sclerosis. We suggest objective diagnostic criteria form the backbone of teaching about the disease, at various levels of medical education. Their wide utilization will in due time provide conditions for epidemiological, clinical and therapeutic studies which have not as yet been carried out in this country.

Adult↗
PubMed1981

Isolation of the intracellular stage of Trypanosoma cruzi and its interaction with mouse macrophages in vitro.

Interaction between Trypanosoma cruzi spheromastigotes (amastigotes) and mouse macrophages was studied. The spheromastigotes, isolated from the spleens of infected mice, were incorporated and digested by the macrophages. By use of horseradish peroxidase labeling of the macrophage lysosomes we showed that fusion of lysosomes with phagocytic vacuoles containing T. cruzi occurred. Parasites showing alterations indicative of digestion were seen inside the phagocytic vacuoles. Our results suggest that intracellular sphermastigotes of T. cruzi, isolated from the spleens of infected mice, and not able to induce a protective infection in mouse macrophages maintained in vitro.

Animals↗
PubMedDate not supplied

A joint TEM-HLEM geophysical approach to borehole sitting in deeply weathered granitic terrains.

The accurate location of aquiferous fracture zones in granite beneath a > 50 m thick weathered mantle in semi-arid regions is a major hydrogeological problem. It is expected that the zone of intensive fracturing will be more susceptible to weathering and thus be characterized by the thickest development of saprolite, a good electrically conductive target for deep-probing electromagnetic systems. The single-loop transient electromagnetic (TEM) technique is well known to have the capability for detecting concealed steep mineralized targets in mining environments and can be adapted to this hydrogeological problem. We propose that combining the conventional frequency-domain horizontal-loop electromagnetic (HLEM) and single-loop TEM is an effective practical approach to locating concealed aquiferous fracture zones. In the supporting case studies presented here, we deployed multifrequency HLEM profiling (with 50 m transmitter-receiver separation) and TEM soundings with contiguous 10 or 20 m sided loops along the survey lines in a granitic terrain affected by deep (> 50 m) weathering in northeast Brazil. A somewhat layered structure consisting of resistive hardpan/leached zone, conductive saprolite, and resistive basement is identifiable in the typical TEM depth sounding data. We obtained coincident HLEM and TEM anomalies at all the sites, enabling a relatively straightforward selection of potential drilling positions. Simple resistivity-depth transformation of the TEM data was done for each site, yielding an approximate section from which drilling depths were estimated. All of the boreholes located were successful. Although our results appear to indicate that the single-loop TEM method could be used independently for borehole sitting in deeply weathered granitic terrains and that the weathering profile over granite can be mapped using TEM depth soundings of appropriate observational bandwidth, we recommend a joint electromagnetic approach for optimal well sitting.

Electric Conductivity↗
PubMedDate not supplied

Aggressiveness of self-etch adhesives on unground enamel.

Manufacturers of mild self-etch adhesives advocate the adjunctive use of phosphoric acid etching when bonding to unground enamel. This study tested the null hypothesis that there is no difference between the recently introduced, more aggressive self-etch adhesives and a total-etch adhesive in bonding to unground enamel. The ultrastructure and microtensile bond strengths (microTBS) of Xeno III (Dentsply) and Simplicity (Apex Dental Materials), bonded to unground enamel, were examined after thermocycling. Clearfil SE Bond (Kuraray), a mild self-etch adhesive, was used as the negative control, and One-Step (BISCO), a total-etch adhesive bonded to phosphoric acid-etched unground enamel, was used as the positive control. Differences in the thickness of enamel hybrid layers were observed and the aggressiveness of apatite dissolution in the four adhesives.

Analysis of Variance↗
PubMedDate not supplied

A review of polymerization contraction: the influence of stress development versus stress relief.

The insertion of bonded resin composites into cavity preparations leads to a competition between polymerization contraction forces and the strength of bonds to tooth structure. The degree of stress development can be controlled, to some extent, by the cavity design (C-factor), the use of bases, the size, shape, and position of increments of composite resins placed in the cavity, and whether the resin is light- or chemically cured. Stress relief can be accomplished by maintaining the C-factor as low as possible, using chemical-curing resins, low modulus liners, and, over time, by water sorption. A thorough understanding of these principles permits clinicians to exercise more control over these variables, thereby improving the quality of their bonded restorations.

Absorption↗