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PubMed1975

[Studies on heat generation by drills of various abrasion grade].

By means of our own measuring method, drilling tests were performed at a test block made of silicate cement using rose-head and fissure burs as well as diamond-stones with different feed. The temperature increases only within a limited range of wear and tear, it does not increase rectilinearly but stepwise, mainly influenced by two heat values, the shearing and the friction heat. Having reached the temperature maximum, further drilling or further wear and tear only prolong drilling time. The danger of damaging the pulp is primarily dependent on the feed and less on wear and tear, as was shown by the tests with the rose head burs. Only when the feed is rising, the worn-out driller further increases a rise in temperature.

Dental High-Speed Equipment↗
PubMed2003

Transition element contained partial-stabilized cement (PSC) as a dental retrograde-filling material.

A modified silicate cement has previously been developed as a dental retrograde filling; it has great sealing ability, good biocompatibility, and anti-bacterial properties. However, its clinical application is limited by a long setting time and poor handling property. In the present study, the setting time has been shortened by raising the preparation temperature of the cement and adding transition elements into the partial-stabilized cement (PSC) to increase the rate of hydration reaction of the cement. The rate of the hydration was evaluated by micro-hardness measurement. Phase transformation and micro-structure were examined by an X-ray diffractometer and a scanning electron microscope, respectively.When the preparation temperature increased (1400 degrees C), the phase content of Ca(2)SiO(5)(C(2)S) and Ca(3)SiO(6)(C(3)S) increased but the CaO decreased. The setting time was shortened and the micro-hardness increased because the increased amplitude of vibration of the atoms about their equilibrium resting positions increased by increasing the heating temperature. When the transition elements were added to PSC, crystal defects were effectively created and monoclinic structure of C(3)S was favored to form, which would increase the hydrated reaction of PSC and shorten the setting time. Co addition is the most effective due to its ability to create more defects and stabilize the monoclinic structure. The micro-hardness of the PSC with Co 5 wt% addition was about 66 in the Vickers scale. It also exhibited an early setting within 20 min. We believe that the modified PSC will have a great potential in its application to perforation repair and retrograde filling in endodontic surgery.

Dental Cements↗
PubMed1976

pH and the cytotoxicity of fluoride in an animal cell culture system.

To investigate the mechanism for the toxicity of silicate cement as observed in a cell culture system, the effects of pH and fluoride were tested on human epithelial cells (NCTC 2544). At pH 7.3, fluoride concentrations from 15 to 25 mug/ml (0.79 to 1.3 mM) had a growth inhibitory effect. When pH of the incubation medium was lowered in the range 7.0 to 6.4, an enhanced cytoxic effect of fluoride was found, and even at 5 to 10 mug/ml growth inhibition occurred. Concomitant with the enhanced cytotoxicity of fluoride at low pH, there was an increased utilization of glucose and formation of lactate. Upon lowering the pH of the incubation medium from 7.4 to 6.7 a twofold increase in the intracellular concentration of fluoride was found.

Animals↗
PubMed1977

[Studies on the marginal leakage around various restorative materials. Part 1: Testing method and condition (author's transl)].

Standardized cavities prepared in bovine teeth were restored with 4 types of filling materials, lathe-cut amalgam, spherical amalgam, silicate cement and composite resin. Restored teeth were immersed in 4 degrees C and 60 degrees C dye solution alternately by automatic device which makes it possible to change the immersion interval and number optionally. By means of measuring the depth of dye penetration, the marginal leakage induced during the thermal change was evaluated and the effects of the immersion interval and number were investigated. Results are as follows. 1) It is possible to obtain the marginal leakage quantitatively by means of measuring the depth of dye penetration. 2) The marginal leakage around various restorations are significantly influenced by the immersion interval and number. 3) The depth of dye penetration varies with types of filling materials. 4) The optimum immersion interval and number are 2 minutes and 60-120 times to evaluate the marginal leakage around various restorative materials.

Animals↗
PubMed2003

A hybrid zinc-calcium-silicate polyalkenoate bone cement.

A novel bone cement composed of sintered zinc-calcium-silicate phosphate and hybrid polyalkenoates has been developed. Synthesis and formulation of glass fillers, monomers and polymers as well as formulation of the cement were described. The effects of sintering, polymer content, glass powder/polymer liquid (P/L) ratio and comonomer on compressive strength (CS) and curing time (CT) were investigated. The effects of P/L ratio and comonomers on shrinkage as well as exotherm were also studied. Results show that the experimental cement was 61% higher in CS, 10% lower in diametral tensile strength, 35% lower in flexural strength, 62% less in exotherm, and 68% less in shrinkage, compared to conventional polymethylmethacrylate cement. With increasing polymer content and P/L ratio in the cement formulation CS of the cement increased but CT decreased. Curing time, shrinkage and exotherm of the cement decreased with increasing P/L ratio. It appears that this novel cement may be a potential candidate for orthopedic restoration if its biological performance is good and formulation is optimized.

Biocompatible Materials↗
PubMed1982

Microstructure and strength properties of silicate and glass ionomer cements.

Microstructure characterization of silicate and glass ionomer cements has been carried out using, SEM, EDAX and ion microprobe techniques. The distribution of aluminum, calcium, fluorine, phosphorus or silicon was measured in the set cement surfaces. Cracks in the cement specimens produced by mechanical breaking, in contraction during setting, or as a result of SEM preparation were observed to occur mainly in the matrix and in the interface between matrix and particle. Powders of silicate and glass ionomer cements were separated into various fractions using sieves or cyclone separation technique. Compressive strength measurements of specimens made of powders with various size distributions have been assessed. The fractionation did not reveal any strong effect on the compressive strength properties either for the silicate or the glass ionomer cement.

Chemical Phenomena↗
PubMed2003

The caddisfly Ceraclea fulva and the freshwater sponge Ephydatia fluviatilis: a successful relationship.

The association between the aquatic phases of the caddisfly Ceraclea fulva (Trichoptera, Leptoceridae) and the freshwater sponge Ephydatia fluviatilis (Porifera, Spongillidae) has been investigated by means of scanning and transmission electron microscopy (SEM, TEM). Ceraclea fulva habitually feeds on sponges and builds its case by using the siliceous spicules of the sponge, which are arranged side by side, inter-crossed, cemented with silk, and organised in layers. In the newly hatched larva, the case is strengthened exclusively by cemented siliceous spicules, while during growth, the insect adds sponge fragments to it. The fine organisation of the sponge tissues growing on the case proves that the sponge is functional. Inter-spaced, small protrusions, derived from the outermost compact silk layer, form a series of "bridges" enhancing case/sponge adhesion. Tube-case shape varies according to the aquatic developmental phase of the insect: in the mature larva and pupa, this shelter carries larger sponge fragments dorsally. The caddisfly acts as carrier of the sponge, thus facilitating its dispersal and the colonisation of new habitats. This justifies regarding this association as a successful mutualistic relationship, and not as a unilateral parasitic behaviour on the part of the insect.

Animals↗
PubMedDate not supplied

Modification of glass ionomer cements.

Glass Ionomer cement (the term was coined by B.E. Kent) has been described as a hybrid of silicate cements and zinc polycarboxylates. Scientific efforts were devoted to improving properties to make it a fully practical material for anterior and posterior restorations and secondarily properties were modified to extend its range of application. First half of 90's witnessed modifications that replace part or most of the original formulation with alternative filler particles or matrix setting reactions to make these materials more composite like. This article focuses on the various modifications of the basic Glass ionomer cement.

Acrylic Resins↗
PubMed1979

Experimental secondary caries around amalgam, composite and glass ionomer cement fillings in human teeth.

It was the aim of this in vitro study to examine secondary caries occurring in enamel and dentin adjacent to different filling materials and after different filling methods. The materials used were: amalgam, composite and glass ionomer cement. The highest rate of secondary caries was found on the crown surface as well as root surface of teeth which were conventionally treated with amalgam and composite materials. The preliminary treatment with a copal-ether varnish (Copalite) was of insignificant value. Fluoridation of the cavity walls with a fluoride solution (Elmex-Fluid) resulted a significant cariostatic effect with amalgam- or composite fillings in enamel and in root surfaces. Zones of inhibition of demineralization could be found. The addition of 5% NaF to composite material also produced an inhibition of demineralization, manifesting itself in a reduction of the secondary caries rate and increased percentage of tight margins of the fillings. Although glass ionomer cement has adherent properties to enamel and dentin, a larger percentage of filling-margins, especially of those applied to dentin, were found to be untight. Nevertheless, the demineralizations were not very pronounced and significant zones of inhibition of demineralization were found in the cavity walls and tooth surfaces adjacent to the fillings. The amounts of fluoride released by silicate cement, glass ionomer cement and composites containing 5% NaF were compared. The glass ionomer cement showed higher values than the composite and silicate materials. After 10 days of storage in water, the dosis of fluoride released--by all materials--was 7-20 times less than on the first day.

Acrylic Resins↗
PubMed2007

Self-setting properties of a beta-dicalcium silicate reinforced calcium phosphate cement.

Beta-dicalcium silicate was used to reinforce the injectable calcium phosphate cement (iCPC) for the first time in this study. The influence of the content of beta-dicalcium silicate on the mechanical properties, setting time, rheological properties, injectability, phase evolution, microstructure, and biodegradability of iCPC was systematically investigated. The results demonstrated that the addition of 8 wt % beta-dicalcium silicate obviously enhanced the compressive strength of the CPC from 26.5 to 47.5 MPa, and did not significantly influence the biodegradability, setting time, injectability, phase evolution, and microstructure of the CPC. The beta-dicalcium silicate-reinforced iCPC with relatively high mechanical property should have potential prospects for the wider applications in surgery such as orthopedics, oral, and maxillofacial surgery.

Bone Cements↗
PubMed1991

Finishing of glass-ionomer cements.

Glass-ionomer cements offer considerable advantages in certain areas over other restorative materials. These result from their cariostatic properties, their inherent dimensional stability and their adhesive properties both to enamel and to dentine. However, because they derive from silicate cements they are prone to desiccation and require protection during the setting phase of the material. This article describes the relationship between the setting time and finishing. The effects of various types of finishing on the surface of the restorative material are also discussed.

Dental Polishing↗
PubMed1989

[Glass ionomers--types and clinical application].

With the formation of the glassionomers one wanted to combine the major qualities of the silicate cement, the composite resins and the polycarboxylate cement. The greatest advantages are bonding to tooth structure, the release of fluorides and thereby an inhibition of secondary caries, and a thermal coefficient similar to tooth structure. The glassionomers are more compatible to the pulp than the old silicates. The bonding to tooth structure is increased through pretreatment where polyacrylic acid is most recommendable. Today there are two major types of glassionomers: the water-based which contain freeze-dried acid in the glass powder, and the original, determined by the addition of an aqueous solution of polyacrylic acid to the glass powder. Certain types are delivered in premeasured capsules for mechanical blend, which decreases the sensitive handling of the material. The use of glassionomers serves a number of purposes and will properly be more widespread in the future, especially the concern of lining in combination with composite resins, the metal-reinforced to crown-buildup and the luting types, when the considerations about earlier hypersensitivity after luting of castings is clarified. The restorative types shows better promising results than composite resins in Class V restoration.

Dental Bonding↗
PubMedDate not supplied

[Restorative dentistry in a community center. 10-year report].

It is reported the results of voluntary odontological assistance in the Community Center of the Methodist Church of Vila Virginia. In a period of ten years the relation patient/dentistry student was an average of 23.08. Of the procedures, 69.9 per cent were amalgam restaurations and 30.1 per cent with silicate cement or resin. This is an important extracurricular activity for the student, in the sense that it helps improve his techniques. On the other hand, although restricted in time, this work has been important for the oral health of the community. Uniterms: voluntary extracurricular activity; amalgam, silicate or resin restaurations.

Community Dentistry↗
PubMed1995

Modeling cation/anion-water interactions in functional aluminosilicate structures.

A need for the computer simulation of hydration/dehydration processes in functional aluminosilicate structures has been noted. Full and realistic simulations of these systems can be somewhat ambitious and require the aid of interactive computer graphics to identify key structural/chemical units, both in the devising of suitable water-ion simulation potentials and in the analysis of hydrogen-bonding schemes in the subsequent simulation studies. In this article, the former is demonstrated by the assembling of a range of essential water-ion potentials. These span the range of formal charges from +4e to -2e, and are evaluated in the context of three types of structure: a porous zeolite, calcium silicate cement, and layered clay. As an example of the latter, the computer graphics output from Monte Carlo computer simulation studies of hydration/dehydration in calcium-zeolite A is presented.

Aluminum Silicates↗