Análise quantitativa de fluoretos nos alginatos para uso odontológico

In this study, the aim was to measure the concentration of fluoride ions in dental alginates and the quantity released from alginate molds immersed in milliQ water, 0.1N hydrochloric acid and artificial saliva. Two separate lots of each of seven brands of alginate commercially available in Brazil were analyzed: Avagel, Deguprint, Hydrogum, Orthoprint, Jeltrate, Jeltrate Plus and Jeltrate Chromatic. Fluoride was measured in each sample by direct potentiometry, using the combined fluoride-ion selective electrode. The brands with the highest fluoride concentrations were Hydrogum (7052.87 μg/g), Jeltrate Plus (6519.68 μg/g) and Orthoprint (6218.18 μg/g). Only in Hydrogum and Jeltrate were different fluoride concentrations found in lots one and two. The various materials showed differences in the amount of fluoride released from the molds into the immersion medium, the mean concentration being highest in Hydrogum and Orthoprint, in all three media. The immersion medium also influenced the release of fluoride, which was lower in saliva than in water and highest in acid. Considering that the concentrations of fluoride found in the alginates tested were high and that various sources of exposure to fluoride exist, there is a need for constant monitoring of alginates intended for dental use.

Quantitative analysis of potentially toxic metals in alginates for dental use

Alginate is one the materials most employed in practice to make dental impressions. Substances like zinc, cadmium and lead silicate, which are included in several alginate brands with the aim of improving their physical, chemical and mechanical properties, are a source of serious concern as regards their toxicity. The most serious chronic effect of oral exposure to cadmium is renal toxicity. Assimilation of lead has deleterious effects on the gastrointestinal tract, hematopoietic system, cardiovascular system, central and peripheral nervous systems, kidneys, immune system, and reproductive system. Chronic oral exposures to zinc have resulted in hypochromic and microcyte anemia in some individuals. The aim of the present study was to measure the cadmium, lead and zinc contents of seven brands of alginate for dental use on sale in Brazil. The samples were weighed and placed in the Teflon cups of a closed-system microwave oven. Aqua regia (4mL concentrated HCI:HNO3, 3:1 v/v) and hydrofluoric acid (2mL concentrated HF) were added to the samples, which were then subjected to heating. The samples were then cooled to room temperature and diluted to 25 mL in deionized water in a volumetric glass flask. The samples were diluted in duplicate and analyzed against a reagent blank. The analyses were performed in an atomic absorption flame spectrophotometer. Neither lead nor cadmium was detected. Zinc contents ranged from 0.001% to 1.36% by weight. The alginates exhibited low contents of the metals under study and gave no cause for concern regarding toxicity; even so, it is advisable to monitor potentially toxic materials continually and to analyze their plasmatic levels in the professionals working with them.

Potencial tóxico dos alginatos para uso odontológico

Alginate or irreversible hydrocolloid is one the most accepted and frequently employed impression materials in dental practice. Substances like zinc, cadmium, lead silicate and fluorides, which are included in several alginate brands with the aim of improving their physical, chemical and mechanical properties, are a source of serious concern as regards their toxicity. Some brands of alginate have been reported to contain potentially toxic fluorides and metals such as cadmium, lead and zinc silicates, either singly or combined. Consequently, special care should be taken while preparing of these materials. It is necessary to monitor potentially toxic chemicals and metals in the alginates continually to avoid contamination of dental professionals and patients. In this review, alginates used in dentistry are analyzed for potential toxicity.

Avaliação da alteração dimensional de modelos obtidos a partir de moldagens com alginato tradicional e outro com desinfetante

The present study aims at evaluating dimensional alteration of stone casts made from impressions with a standard irreversible hydrocolloid and an antimicrobial one. For this, an alginate without disinfectant (Type II Jeltrate) and other containing chlorhexidine (Type II Avagel) were used, which rose by the same regime of treatment: without disinfection; immersion; and spraying. A 1% sodium hypochlorite solution was used for 10 minutes. To obtain the impressions, a perforated impression tray was made from a standard metal model. After molding, the molds were washed in running water for 30 seconds to simulate removal of saliva. Then, with the exception of the control group, these molds were subjected to disinfection treatment. After 10 minutes they were washed again. 60 samples poured with type V special gypsum (Durone) were obtained, that were measured 3 times in a stereomicroscope (SZX12, Olympus) to record the average of dimensional alterations. The disinfection treatment did not bring significant changes in the models obtained from both alginate tested (standard p = 0.7102; with chlorhexidine p = 0.5832). The results showed a statistically significant and additional advantage of the traditional alginate on alginate with chlorhexidine, with respect to dimensional alteration (p < 0.05).

Riabilitazione protesica ed implanto-protesica di pazienti in età evolutiva affetti da Displasia Ectodermica

Introduction. Ectodermal Dysplasias are a heterogeneous group of inherited disorders characterized by dysplasia of tissues of ectodermal origin (hair, nails, teeth, skins and glands). Clinically, it may be divided into two broad categories: the X-linked hypoidrotic form and the hidrotic form. Hypohidrotic Ectodermal Dysplasia (H.E.D) is characterized by the triad oligo-anodontia, hypotricosis, hypo-anhydrosis (Christ-Siemens-Tourane syndrome). The incidence of HED is about 1/100,000. Mutation in the actodysplasin-A (EDA) and ectodysplasin-A receptor (EDAR) genes are responsible for X-linked and autosomal HED. The clinical features include sparse, fine hair, missing or conical-shaped teeth, decreased sweat and mucous glands, hypoplastic skin, and heat intolerance with exercise or increased ambient temperature. Complete or partial anodontia and malformation of teeth are the most frequent dental findings. Incisors and canines are often conical-shaped while primarily second molars, if present, are mostly affected by taurodontism. Treatment is supportive and includes protection from heat exposure, early prosthetic rehabilitation, skin, hair ear, nose and nail care, and genetic counseling for family planning. The diagnosis of HED in the neonatal and early infancy period may be difficult since sparse hair and absent teeth are normal finding at this age. In childhood the diagnosis is more easily made on the basis of history and clinical examination. Dental abnormalities are the most common complaint. Prosthetic rehabilitation has been recommended as an essential part of the management of HED because is important from functional, esthetic, and psychological standpoint. A team approach that includes input from a pediatric dentist, an orthodontist, a prosthodontist, and an oral and maxillofacial surgeon is necessary for a successful outcome. Conventional prosthodontic rehabilitation in young patient is often difficult because of the anatomical abnormalities of existing teeth and alveolar ridges. The conical shaped teeth and “knife-edge” alveolar ridges result in poor retention and instability of dentures. Moreover, denture must permit jaws expansion and a correct pattern of growth. Materials and Methods. Complete removable dentures were provided to allow for normal physiological development and a corrected masticatory function. Initial maxillary and mandibular impressions were made with smallest stock trays and irreversible hydrocolloid and then final impressions ware made with light-bodied polysulfide rubber base impression material. A base of autopolymerizing resin was constructed and a wax rim was added to the base. The patient’s vertical dimension of occlusion was established by assessing phonetic and esthetic criteria. Preliminary occlusal relations were recorded, and the mandibular cast was mounted on the articulator. Acrylic resin teeth specific for children dentures were selected and mounted. The dentures were tried in and, after proper adjustments, were inserted. The patients were monitored clinically every month to fit prostheses. Cephalometric radiographs were taken every 6 month with the prostheses in place in order to evaluate correct pattern of growth. Cephalometric measurements were realized and used to evaluate the effect of rehabilitation on craniofacial growth. Cephalometric measurements of sound patients were compared with ED patients. After two month expander screws (three-way screw in the upper denture and two-way the lower one)were inserted in each denture in order to permit the expansion of the denture and the jaws growth. Where conical teeth were present, composite crown were realized and luted to improve the esthetic and phonesis. In order to improve retention the placement of endosseous implants was carried out. TC 3D Accuitomo was performed and a resin model of mandibular bone of the patient was realized. At the age of 11 years two implants were inserted into anterior mandible in a child with anodontia. Despite a remarkable multi-dimensional atrophy of the mandibular alveolar process, the insertion of two tapered screw implants (SAMO Smiler, diameter 3.8, length 10 mm). After a submerged healing period of two-three month, the implants were exposed. Implants were connected with an expansion guide that permits mandibular growth and prosthetic retention. The amount of mandibular growth was also evaluate dusing the expansion guide. Results. Early oral rehabilitation improve oral function, phonesis and esthetic, reducing social impairment. Treated patients showed normal cephalometric measurement. Early rehabilitation is able to prevent the prognatissm of the mandibula . The number of teeth was significantly related to several changes in craniofacial morphology. Discussion. In the present study the 5,3% of ED patients showed hypodontia, the l’89,4% di oligodontia, and the 5,3% di anodontia. The cephalometric analysis supports that ED patients showed midface hypoplasia. ED groups showed an increased pogonion to nasion measurement than sound patients, indicative of class III tendency. The present study demonstrated that number of teeth was significantly correlated with deviation of cephalometric measurements from normality. Oligoanodontia is responsible for changing of cephalometric measuraments also on sagittal plane with a class III tendency. Maxillary jaw showed a retrused position related to the presence of hypodontia.

Universality class of the reversible-irreversible transition in sheared suspensions

Collections of non-Brownian particles suspended in a viscous fluid and subjected to oscillatory shear at very low Reynolds number have recently been shown to exhibit a remarkable dynamical phase transition separating reversible from irreversible behavior as the strain amplitude or volume fraction are increased. We present a simple model for this phenomenon, based on which we argue that this transition lies in the universality class of the conserved directed percolation models. This leads to predictions for the scaling behavior of a large number of experimental observables. Non-Brownian suspensions under oscillatory shear may thus constitute the first experimental realization of an inactive-active phase transition which is not in the universality class of conventional directed percolation.

Irreversible Thermal Denaturation Of Bovine Pancreatic Ribonuclease-A

The isolation and characterization of the products formed during the irreversible thermal denaturation of enzyme RNAase-A are described. RNAase-A, when maintained in aqueous solution at pH 7.0 and 70° for 2 h, gives soluble products which have been fractionated by gel filtration on Sephadex G-75 into four components. These components are designated RNAase-At1, RNAase-At2, RNAase-At3 and RNAase-At4 according to the order of their elution from Sephadex G-75. RNAase-At4 shows the same specific activity towards yeast RNA as native RNAase-A and is virtually indistinguishable from it by the physical methods employed. However, chromatography on CM-cellulose separates it into three components that show the same u.v. spectra and specific activity towards yeast RNA as native RNAase-A. RNAase-At1, RNAase-At2and RNAase-At3 are all structurally altered derivatives of RNAase-A and they exhibit low specific activity (5–10%) towards yeast RNA. In the presence of added S-protein, all these derivatives show greatly enhanced enzymic activity. RNAase-At1 and RNAase-At2 are polymers, covalently crosslinked by intermolecular disulfide bridges; whereas RNAase-At3 is a monomer. Physical studies such as 1H-n.m.r., sedimentation analysis, u.v. absorption spectra and CD spectra reveal that RNAase-At3 is a unfolded derivative of RNAase-A. However, it is seen to possess sufficient residual structure which gives rise to a low but easily detectable enzymic activity.

Invisible opportunities and irreversible trends

Small firms are always vulnerable to complex technological change that may render their existing business model obsolete. This paper emphasises the need to understand how the Internet's ubiquitous World Wide Web is impacting on their operating environments. Consideration of evolutionary theory and the absorptive capacity construct provides the foundation for discussion of how learning and discovery take place within individuals, firms and the environments that interact with. Small firms, we argue, face difficulties identifying what routines and competencies are best aligned with the seemingly invisible dominant designs that support pursuit of new enterprise in web-impacted environments. We argue that such difficulties largely relate to an inability to acquire external knowledge and the subsequent reliance on existing internal selection processes that may reinforce the known, at the expense of the unknown. The paper concludes with consideration as to how managers can overcome the expected difficulties through the development of internal routines that support the continual search, evaluation and acquisition of specific external knowledge.

Growth inhibition of human promonocytic leukaemic U937 cells by interferon gamma is irreversible and not cell cycle phase-specific.

Growth of human promonocytic leukaemic U937 cells was found arrested within 24 h upon exposure to interferon gamma (IFN-gamma). Removal of the interferon did not result in the resumption of growth, as is evident from the absence of doubling of viable cell count and(3)H-thymidine incorporation. 5-Bromo-2'-deoxyuridine-based flow cytometric analysis of the growth-arrested cells, 24 h subsequent to the removal of IFN-gamma, showed absence of DNA synthesis, confirming the irreversible nature of the growth inhibition. Propidium iodide-based flow cytometric analysis of the growth-arrested cells showed a distribution which is typical of a growth inhibition without resulting in the accumulation of cells in any specific phase of the cell cycle. These results indicated that IFN-gamma arrested growth of U937 cells in an irreversible and cell cycle phase-independent manner. These observations were in contrast to our earlier report on the reversible and cell cycle phase-specific growth inhibition of human amniotic (fetal epithelial) WISH cells by the interferon. Copyright 1999 Academic Press.

Irreversible inactivation of 3-hydroxy-3-methylglutaryl-CoA reductase by H2O2

A concentration-dependent inactivation of 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase was found on reincubation of rat liver microsomal preparations with H2O2 and at lower concentrations in the presence of KCN which inhibited the contaminating catalase. The inactivation was not affected in the presence quenchers of hydroxyl radicals and singlet oxygen and was also obtained when H2O2 was added during the reaction. HMG-CoA, but not NADPH, partially protected the enzyme from H2O2-inactivation. Even at high concentration DTT was unable to reverse this inactivation. The soluble 50 kDa-enzyme was similarly inactivated by H2O2, and the tryptic-digest of the inactivated protein indicated the presence of a disulfide-containing peptide. The results support the view that H2O2 by directly acting on the catalytic domain possibly converts an active thiol group to an inaccessible disulfide and irreversibly HMG-CoA reductase.

On the involvement of intramolecular protein disulfide in the irreversible inactivation of 3-hydroxy-3-methylglutaryl-CoA reductase by diallyl disulfide

Treatment with diallyl disulfide, a constituent of garlic oil, irreversibly inactivated microsomal and a soluble 50 kDa form of HMG-CoA reductase. No radioactivity was found to be protein-bound on treating the soluble enzyme with [35S]diallyl disulfide, indicating the absence of the mixed disulfide of the type allyl-S-S-protein. SDS-PAGE and Western blot analyses of the diallyl-disulfide-treated protein showed no traces of the dimer of the type protein-S-S-protein, but clearly indicated BME-reversible increased mobility, as expected of an intramolecular protein disulfide. The sulfhydryl groups, as measured by alkylation with iodo[2-14C]acetic acid, were found to decrease in the diallyl-disulfide-treated enzyme protein. Tryptic peptide analysis also gave support for the possible presence of disulfide-containing peptides in such a protein. It appears that diallyl disulfide inactivated HMG-CoA reductase by forming an internal protein disulfide that became inaccessible for reduction by DTT, and thereby retaining the inactive state of the enzyme.