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Biomedical subjects

P Pera

Publications and source records attributed to P Pera.

At least 37 records · Page 2Linked to original sources
PubMed1998

All-ceramic restorations: an overview.

Advantages and disadvantages of metal-ceramic and all-ceramic restorations are reviewed particularly from the aesthetic point of view. All-ceramic restorations offer the best results because they let the light through optimally. In constructing all-ceramic crowns on teeth which have been endodontically treated, the material used to rebuild the pin-abutments must be taken into consideration if the best aesthetic results are to be achieved. Materials which, because of their translucent characteristics, are the most aesthetic alternatives to metal alloy pin-abutments in rebuilding teeth which have been endodontically treated, are then described.

Aluminum Silicates↗
PubMed1997

Syntheses and structure-activity relationships of taxoids derived from 14 beta-hydroxy-10-deacetylbaccatin III.

A series of new taxoids derived from 14 beta-hydroxy-10-deacetylbaccatin III was synthesized by means of the beta-lactam synthon method. Most of the new taxoids thus synthesized possess excellent cytotoxicity against human ovarian (A121), non-small-cell lung (A549), colon (HT-29), and breast (MCF-7) cancer cell lines, and several of these taxoids show subnanomolar IC50 values which are severalfold to 1 order of magnitude better than those of paclitaxel and docetaxel. Modifications at the 3'- and 3'-N-positions exert marked effects on the activity. For the substituents at C-3', the cytotoxicity decreases in the order 2-furyl approximately 2-methyl-1-propenyl > or = 2-methylpropyl > (E)-1-propenyl > or = n-propyl > phenyl > > 2,2-dimethylpropyl. For the 3'-N substituents, the activity decreases in the order t-BuOCO > Ph > n-hexanoyl. A significant increase in the cytotoxicity against the doxorubicin-resistant human breast cancer cell line MCF7-R that expresses the multidrug resistance (MDR) phenotype is observed by the proper modification of the substituent at C-10. The observed remarkable effects of the substituents at C-10 on the activity against MCF7-R can be ascribed to the effective inhibition of the binding of these new taxoids to P-glycoprotein that is responsible for MDR.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Synthesis and structure-activity relationships of nonaromatic taxoids: effects of alkyl and alkenyl ester groups on cytotoxicity.

Several new nonaromatic taxoids are synthesized by means of the beta-lactam synthon method. These include taxoids modified with 3-methylbut-2-enoate, 3-methylbutanoate, and cyclohexanecarboxylate groups in place of the benzoate at the C-2 position. In addition, taxoids with 2-methylprop-1-enyl, 2-methylpropyl, (E)-prop-1-enyl, and cyclohexyl groups at the C-3' position are also prepared in combination with the modifications at C-2. The alkyl and alkenyl ester groups at C-2 displayed pronounced effects on the in vitro cytotoxicity. Two of the fully aliphatic taxoids possess similar or stronger activity than paclitaxel and docetaxel. It is clear that the 2-benzoate does not play a unique role, and replacement with the appropriate alkyl and alkenyl groups provides taxoids with equivalent or superior activity.

Antineoplastic Agents, Phytogenic↗
PubMed1996

Syntheses and structure-activity relationships of the second-generation antitumor taxoids: exceptional activity against drug-resistant cancer cells.

A series of new 3'-(2-methyl-1-propenyl) and 3'-(2-methylpropyl) taxoids with modifications at C-10 was synthesized by means of the beta-lactam synthon method using 10-modified 7-(triethylsilyl)-10-deacetylbaccatin III derivatives. The new taxoids thus synthesized show excellent cytotoxicity against human ovarian (A121), non-small-cell lung (A549), colon (HT-29), and breast (MCF-7) cancer cell lines. All but one of these new taxoids possess better activity than paclitaxel and docetaxel in the same assay, i.e., the IC50 values of almost all the taxoids are in the subnanomolar level. It is found that a variety of modifications at C-10 is tolerated for the activity against normal cancer cell lines, but the activity against a drug-resistant human breast cancer cell line expressing MDR phenotype (MCF7-R) is highly dependent on the structure of the C-10 modifier. A number of the new taxoids exhibit remarkable activity (IC50 = 2.1-9.1 nM) against MCF7-R. Among these, three new taxoids, SB-T-1213 (4a), SB-T-1214 (4b), and SB-T-1102 (5a), are found to be exceptionally potent, possessing 2 orders of magnitude better activity than paclitaxel and docetaxel. The observed exceptional activity of these taxoids may well be ascribed to an effective inhibition of P-glycoprotein binding by the modified C-10 moieties. The new taxoid SB-T-1213 (4a) shows an excellent activity (T/C = 0% at 12.4 and 7.7 mg/kg/dose, log10 cell kill = 2.3 and 2.0, respectively) against B16 melanoma in B6D2F1 mice via intravenous administration.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

[14-O-hemiesters and 13-hydrazones of anthracyline antibiotics of the daunorubicin series. Synthesis and cytostatic activity with respect to tumor cells sensitive or resistant to doxorubicin].

Doxorubicin and 14-hydroxycarminomycin 14-O-hemiadipates and 14-O-hemipimelates, synthesized from 14-bromo derivatives of daunorubicin and carminomycin and monosodium adipate and pimelate, were converted to the corresponding N-trifluoroacetylated compounds. 13-(4-Methylpiperazine-1-yl)imino derivatives of the anthracycline antibiotics were also obtained. The cytostatic activity of the compounds synthesized was studied using a panel of human and animal tumor cell lines sensitive or resistant to doxorubicin. N-Trifluoroacetylation of the antibiotics resulted in a decrease in the cytostatic activity. The activity of the water-soluble 13-(4-methylpiperazine-l-yl)imino derivatives is close to that of the corresponding parent antibiotics.

Animals↗
PubMed1994

In vitro marginal adaptation of alumina porcelain ceramic crowns.

This study evaluated the dimensional stability during firing of In-Ceram alumina porcelain ceramic and examined the marginal fit for three different configurations of tooth preparation. A stereomicroscope was used to measure the space between the margin of restorations and tooth preparations. The three methods of tooth preparation were statistically compared and revealed suitable dimensional stability during the firing and glazing process. A better marginal fit was recorded for artificial crowns fabricated on a chamfer or 50-degree shoulder tooth preparation.

Aluminum Oxide↗
PubMed1989

[Impression method in patients with maxillo-facial loss with reduction of the degree of oral opening].

The article describes a method for obtaining an impression in patients suffering from a loss of maxillo-facial structure with reduced oral aperture. This involves making an individual resin tray, which is then divided in two, with four plugs on the underside for precise re-alignment later. The method suggested facilitates the insertion and removal of the tray. Thus an accurate impression of the perimeter can be obtained without the risk of trauma.

Dental Impression Technique↗
PubMed1989

[Mounting posterior teeth in complete dentures].

The more common techniques for analysing the alveolar ridge in full dentures were examined. Both the linear analysis and the two-dimensional one, proposed by Pound, were described. The ridge-transfer method was found to be three-dimensional, thus allowing the construction of full dentures which are more stable during each phase of mastication.

Alveolar Process↗
PubMed1989

[Evaluation of the clinical effectiveness of biofeedback EMG on muscular relaxation and painful symptomatology].

The therapeutic effectiveness of EMG biofeedback on muscular relaxation and pain symptomatology has been analysed in a group of 24 dysfunctional patients presenting consecutively at the Prosthesis Department of the Odontostomatological Clinic. A good level of muscular relaxation was achieved in 22 cases; pain symptomatology disappeared totally in 19 and reduced considerably in 3 of 24 patients examined. Therapy failed in 2 cases. The method thus presents unquestionable therapeutic value in dysfunctional patients, particularly in cases with symptomatology that is mainly due to muscular hyperactivity.

Adult↗
PubMed1987

Polyamine biosynthetic activity in normal and neoplastic human colorectal tissues.

Polyamine biosynthetic activity was assessed in various colorectal tissue samples consisting of noninvolved mucosa, benign adenomatous polyps and adenocarcinomas taken at surgery from a total of 40 patients. Ornithine decarboxylase (ODC) displayed a gradient of enzyme activity (i.e., adenocarcinoma greater than polyps greater than mucosa) which seemed to correlate positively with the neoplastic status of the tissue. In 10 of the patients, samples were obtained for all three tissue types. Five of these exhibited a clear repetition of the trends in enzyme activity seen with the mixed patient tissue sampling whereas the remainder differed by having the highest ODC activity in the polyps. In nine of the ten cases, ODC activity was substantially lower in the mucosa than in either of the neoplastic lesions. Trends in enzyme activity were the same for tissues obtained from either the colon or rectum. The ODC activity in adenocarcinomas could not be correlated with histologic differentiation, stage or site of the disease, however, in samples from female patients (all postmenopausal) the activity was elevated over normal mucosa to a greater extent (ten-fold) than in male patients (seven-fold). S-adenosylmethionine decarboxylase activity was assessed in 27 of the 40 patients and found to follow the same distribution as ODC; however, the mean value differences +/- SEM between tissues were less distinct. In general, tissue polyamine pool analysis of these same specimens reflected the levels of ornithine and S-adenosylmethionine decarboxylase activities. Overall, the data reveal an increase in polyamine biosynthetic activity in colorectal neoplasms, relative to surrounding mucosa, which may correlate with (1) progression of the neoplastic process, (2) the proportion of proliferating cells, (3) the rate of cell proliferation, or (4) a combination of two or all of these possibilities.

Adenocarcinoma↗
PubMed1986

Prediction of the shape and size of the maxillary anterior arch in edentulous patients.

The aims of the study were to examine the morphometric and angular relationships between the interincisive papilla and the maxillary anterior teeth, and to describe a clinical method derived from this analysis useful in sitting the upper front teeth. Plaster casts of upper jaws of adult patients with complete dentition, were selected. Two measurements were taken: the distance from the centre of the papilla to the most vestibular part of the labial surface of the anterior teeth; and the angles between the perpendicular to the median line and the line from the centre of the papilla to the most vestibular part of each tooth. The equation of the resulting parabola, corresponding to the upper frontal arch, can be applied to every maxillary dimension. Parabolas were divided into small, medium, and large, using the mean and standard deviations. Each curve was traced on a transparent base-plate shaped for intra-oral placement. In individuals with complete dentition the closest parabola to the maxillary frontal arch was selected and the distance between the lateral frenula measured. Statistical study demonstrated a correspondence between the interfrenulum distance and the parabolas. In edentulous patients the interfrenulum distance thus provides a curve useful in sitting the maxillary anterior arch.

Adult↗