Changes of dentinal inorganic phosphate in different areas of sound and carious human teeth.
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Adolescent↗
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Solubilization of dentin matrix collagen in situ.
The effects of the oral environment on dentin matrix collagen were studied. In the partial prostheses of 12 participants, two completely demineralized dentin specimens were mounted covered by a Dacron gauze. After an experimental period of seven weeks, the specimens were transferred to a trypsin-containing buffer for determination of the amount of denatured collagen. Subsequently, the specimens were incubated with a bacterial collagenase for assessment of the amount of collagen. After the intra-oral exposure, there was a collagen loss varying between 1 and 47 wt%. This variation might be due to differences in proteolytic activity of the colonizing microflora. After exposure to the oral environment, only about 0.5 wt% of the available collagen was trypsin-degradable. This indicates a rapid solubilization of the denatured collagen from the specimens into the oral cavity. A separate group of specimens was examined by light microscopy and transmission electron microscopy. Various degrees of breakdown could be discerned. Some experimental specimens showed loss of surface integrity and tubules heavily infected with different types of micro-organisms. The lumens of the tubules were enlarged, sometimes creating caverns as a result of the loss of the intertubular collagenous matrix.
Adult↗
Efficacy of water-soluble photoinitiator on the adhesion of composite resin to bovine teeth in all-in-one bonding system.
The self-etching primer adhesives examined in the present study were aqueous mixtures of 30 wt% 2-methacryloyloxyethyl phenyl hydrogen phosphate, 35 wt% 2-hydroxyethyl methacrylate, and photoinitiator. For the photoinitiator, camphorquinone (CQ) or 2-hydroxyl-3-(3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-N,N,N-trimethyl-1-propanaminium chloride (QTX) was used--where QTX is a unique water-soluble photoinitiator. The self-etching primer adhesive was applied directly to polished bovine dentin or enamel. Tensile bond strength of flowable composite resin to bovine teeth was measured after one-day immersion in water at 37 degrees C. The addition of QTX tended to increase tensile bond strength to dentin, whereby addition of 3 wt% of QTX produced the highest mean bond strength of approximately 10 MPa. CQ, on the other hand, did not show any efficacy in improving bond strength. For enamel bonding, there were no significant differences in bond strength between CQ and QTX. In conclusion, QTX was effective in improving the bond strength of composite resin to dentin in an all-in-one bonding system.
Acid Etching, Dental↗
Chemical interaction of phosphoric acid ester with hydroxyapatite.
Among functional monomers used in contemporary dental adhesives, 10-methacryloyloxydecyl dihydrogen phosphate (MDP) has been found to interact chemically with hydroxyapatite (HAp) most intensively and stably. This effect was thought to be the basis of the superior bonding effectiveness of MDP-based self-etch adhesives to enamel/dentin. To elucidate fully the chemical interaction and reactivity of MDP with HAp, we used (31)P CP-MAS NMR spectroscopy and powder x-ray diffraction. In an aqueous ethanol solution, Ca ions were leached from HAp to form, at short term, a MDP-calcium salt (CaMHP(2)) layered structure on the HAp surface. When MDP was allowed to interact for longer time (< 24 hrs), CaHPO(4).2H(2)O precipitated on top of this MDP-calcium salt layered structure. In conclusion, the intense chemical interaction of MDP with HAp must be ascribed to superficial dissolution of HAp induced by the MDP adsorption and subsequent deposition of MDP-calcium salt with a solubility lower than that of CaHPO(4).2H(2)O.
Adsorption↗
Peritubular dentin formation: crystal organization and the macromolecular constituents in human teeth.
Peritubular dentin (PTD) is a relatively dense mineralized tissue that surrounds the tubules of coronal tooth dentin. It is composed mainly of crystals of carbonated apatite together with a small amount of collagen. Its mode of formation has been investigated by studying the relatively dense particles isolated from a powdered preparation. Electron microscopic examination of the PTD particles, including 3-dimensional image reconstruction and electron diffraction, shows that the organization of the crystals of PTD is very similar to that of the adjacent intertubular dentin (ITD). The latter contains relatively large amounts of collagen and the carbonated apatite crystals are closely associated with the collagen matrix. The proteins present in the PTD particles are soluble after decalcification and stain with Stains All. The principal protein has higher molecular weight and a quite different amino acid composition than the phosphophoryns of the intertubular dentin. The interface between the PTD and the ITD shows structural continuity. These data show how two distinct carbonated apatite-based mineralized tissues can be organized and formed contiguously within the same organ by utilizing different sets of matrix proteins.
Adult↗
The composition of the insoluble collagenous matrix of bovine predentine.
Predentine obtained from bovine teeth by microdissection was extracted with EDTA and tris-NaCl solutions. The insoluble residue consisted mainly of collagen and resembled dentine collagen in overall amino acid composition. The residue differed in containing no detectable phosphoprotein, a much larger amount of collagen hexose and more non-collagenous glycoprotein, the neutral sugar composition of which was determined. Differences were also observed in the contents of reducible collagen cross-links. Half of the total phosphorus found in the predentine could not be accounted for solely by hydroxyapatite. The remainder was partly soluble and dialysable.
Amino Acids↗
[The state of the dental hard tissues in persons under the influence of ionizing radiation (based on the data from infrared spectroscopy)].
A total of 27 teeth were examined in those subjects having been exposed to ionizing radiation in doses between 0.5 and 2.0 Gy, together with ten teeth of essentially healthy individuals. The enamel, dentine and cement mineral and protein contents were studied versus control with the aid of infrared spectroscopy techniques. It has been ascertained that in the teeth of patients presenting with dose loads there take place changes in the organic matrix. Amide I: amide II ratio tends to diminish toward contribution of Amide I. The mineral composition of the enamel reveals practically no changes under exposure to radiation. The dentine and cement display clear-cut changes in the mineral component. There appear absorption bands that belong to more soluble forms of calcium phosphate, which fact suggests an active destructive process in underlying hard tissues of the teeth, that gets intensified under exposure to ionizing radiation.
Dental Cementum↗
Adhesives and nonshrinking dental resins of the future.
Much attention has been directed toward producing dentinal adhesives that withstand the forces involved during polymerization shrinkage of composite resins. Studies have shown that an effective dentin-adhesive bond depends on the wetting and penetration characteristics of the dentinal adhesive system and the reactivity of the treated dentinal surface. The structure of the collagen in the demineralized dentinal layer also seems to influence the behavior of the bond. Adhesive systems that do not completely denature the fibrous collagen and leave interwoven banded collagen in the demineralized layer produce superior bond strengths (greater than 20 MPa). Other research efforts seek to develop a nonshrinking high-performance polymer for use as a matrix material for dental composite resins. Spiroorthocarbonates that expand during polymerization have been developed. In combination with a three-component epoxy comonomer, matrix resins have been produced that expand during polymerization and whose mechanical properties, water sorption, solubility, and degree of polymerization are acceptable for dental use. Further developments of nonshrinking composite resins and improved dentinal adhesives will greatly increase the longevity of 21st-century composite resin restorations and should significantly ease clinical placement.
Adhesives↗
Polymethylmethacrylate-stimulated macrophages increase rat osteoclast precursor recruitment through their effect on osteoblasts in vitro.
An in vitro rat osteoclast precursor model was employed to study the role of macrophages in the osteolysis associated with aseptic loosening of cemented total joint replacements. Bone resorption at the bone-bone cement interface may involve the release of mediators by macrophages in response to phagocytosis of polymethylmethacrylate particles. Two potential pathways for the macrophage-directed bone resorption were studied. An indirect pathway was investigated in which the macrophage response to cement particles was used to stimulate rat osteosarcoma (ROS) 17/2.8 osteoblasts. Osteoblast-soluble factors then were added to osteoclast precursors. In the direct pathway, osteoclast precursors were exposed directly to macrophage-soluble factors released in response to phagocytosis of cement particles. Osteoclast precursors were identified after adherence to polished human dentin slices. Acid phosphatase-positive osteoclasts were counted using light microscopy at x200 magnification. In the indirect pathway, where the macrophage response was mediated through the rat osteosarcoma osteoblasts, a significant increase in the recruitment of osteoclast precursors was observed. In the direct pathway, when the macrophage-conditioned medium was allowed to interact directly with osteoclast precursors, the adherence of the precursors was significantly decreased. This demonstrates that the macrophage mediators released following phagocytosis of polymethylmethacrylate particles affect the release of soluble factors from osteoblasts. In turn, these osteoblast factors stimulate recruitment of osteoclast precursors to calcified tissue. Evidence from this in vitro model reveals that macrophage-soluble factors, in the absence of an osteoblast contribution, decrease the adherence of osteoclast precursors to calcified substrate. We propose that bone resorption at the aseptically loose interface of cemented arthroplasty may be mediated, at least in part, by soluble factors secreted by osteoblasts responding to macrophages that have phagocytosed particles of polymethylmethacrylate cement.
Animals↗
Influence of protecting agents on the solubility of glass ionomers.
PURPOSE: To evaluate the influence of protective agents (varnish and glaze-resin resin) on water solubility of two glass ionomer restorative cements (Chelon-Fil and Vidrion-R), with the graviometrical test (A.D.A Specification No 9). MATERIALS AND METHODS: Fifteen samples of each restorative cement were obtained and divided in one control and two experimental groups: (a) control, no protection; (b) protected with varnish; (c) protected with glaze-resin. On the two experimental groups, after the initial gelification reaction, the specimens were protected and immersed in distilled water for the period of 1 and 24 hours. RESULTS: The two glass ionomer restorative cements tested required surface protection to avoid the early solubility. Among the protective materials evaluated, the varnish was the most effective agent.
Analysis of Variance↗
The use of the D-, L- aspartic ratio in decalcified collagen from human dentin as an estimator of human age.
Among the methods dealing with the age estimation, the evaluation of the ratio of the D-, L- form of the aspartic acid in tissues with a low metabolic turnover is considered to be the most precise. We introduced demineralization of the dentin with 0.5 M EDTA adjusted to pH = 7.4. The advantage of such a procedure is that after demineralization we obtained pure insoluble protein (collagen) and soluble noncollagenous proteins in one step. In this study we analyzed insoluble collagen. The amino acids obtained after the hydrolysis were derivatized into TFA isopropyl esters and analyzed by gas chromatography on Chirasil L-Val capillary column. We analyzed human dentin from the lower canines. The correlation coefficient was 0.93 for our set of 71 persons. The result concurred with those of other scientists.
Adolescent↗
The interaction of collagenase with hydroxyapatite and related materials and enzymatic properties of the adsorbed enzyme.
The commercial collagenase from Clostridium histolyticum was adsorbed on hydroxyapatite, on bovine femur shaft and on enamel and dentin powders. The substrate specificity of the adsorbed enzyme tested, with chromophore substrate, azocoll and native collagen, differed from that obtained with the soluble enzyme. The adsorption and the substrate specificity was also dependent on the adsorbent used. A pretreatment of hydroxyapatite with chondroitin sulphate, hyaluronate and DNA lowered the adsorption of collagenase. Phosphate ion caused desorption of the enzyme from hydroxyapatite. Sodium fluoride caused partial desorption of the enzyme from hydroxyapatite and enamel and dentin powders. Colangenase adsorbed on root surfaces of teeth liberated hydroxyproline containing material.
Adsorption↗
The insoluble fraction isolated after digestion of demineralized human dentine matrix with collagenase.
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Amino Acids↗
Phosphoproteins of bovine dentin: evidence for polydispersity during tooth maturation.
The ethylenediaminetetraacetic acid extractable phosphoproteins of dentin from very young fetal calves consisted principally of a monodisperse species with an apparent molecular weight of at least 94 000 and a phosphorus content of 8.0% (w/w). In contrast, the soluble phosphoproteins extracted from mature adult animals under identical conditions ranged in molecular weight from 18000 to 94000 and contained less phosphorus. The data support the conclusion that the phosphoproteins of bovine dentin are degraded in vivo during mineralization and maturation of the tissue.
Adult↗
Mineral aspects of dentistry.
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Alkalies↗
Dentin is dissolved by high concentrations of L-ascorbic acid 2-[3,4-dihydro-2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridecyl)-2H-1-benzopyran-6-yl-hydrogen phosphate] potassium salt with or without hydrogen peroxide.
L-Ascorbic acid 2-[3,4-dihydro-2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridecyl)-2H-1-benzopyran-6-yl-hydrogen phosphate] potassium salt (EPC-K(1)) is a conjugate of vitamin C and vitamin E that is water-soluble and stable at room temperature. EPC-K(1) has been developed as a hydroxyl radical (.OH) scavenger and antioxidant. In a previous tooth whitening experiment, it was accidentally found that tooth (dentin) blocks were dissolved by EPC-K(1) with H(2)O(2). In the current study, high concentrations of EPC-K(1) (2.5, 25 mM) with 3% H(2)O(2) dissolved and caused the collapse of dentin blocks. Similar concentrations of EPC-K(1) without 3% H(2)O(2), however, dissolved the dentin blocks without collapse over a 3-week period. In these cases, a.OH-like signal was detected using an ESR spin-trapping method. The volume of calcium in solution (including the dentin block) increased on the addition of EPC-K(1) in a concentration-dependent manner. In addition, the calcium : phosphorus ratio changed from 2 : 1 in sound dentin to 1 : 2 in the collapsed dentin block. High concentrations of EPC-K(1) are therefore considered to have calcium chelating and dentin dissolving activity. The dentin dissolving activity was enhanced when EPC-K(1) was used with H(2)O(2). EPC-K(1) had no protective effect when used in tooth whitening with H(2)O(2).
Ascorbic Acid↗
Artificial caries around restorations in roots.
An artificial caries technique was used to produce caries-like lesions in the cavity walls adjacent to microfilled resin restorations with and without dentin bonding agent, and glass-ionomer cement restorations, in the roots of extracted teeth. The lesions had histological characteristics similar to those of natural lesions and to those of the lesions produced by other experimental methods. The zonal pattern of the lesions was examined by means of polarized light microscopy and microradiography, and the depth of the lesions was measured for assessment of the microleakage around the restorations. Three cavity cleaning regimes-water spray alone, 50% citric acid, and a proprietary cleaner-were compared in conjunction with the three restorative methods. Cavity cleaning with the citric acid or the proprietary cleaner, and the use of a fluoride-releasing restorative material, acted to reduce the depths of the lesions. Glass-ionomer cement restorations in cavities cleaned with citric acid showed lesions significantly shallower than those treated with other restorations. The glass-ionomer cement was soluble in the acidic environment but promoted the precipitation of minerals in the lesions. The use of a dentin bonding agent did not affect the depth of demineralization around the microfilled resin restorations.
Adhesives↗
[Adhesion mechanism of MMA/TBBO resin containing 4-META to decalcified dentin].
As a model experiment to understand the mechanism of adhesion of the 4-META-MMA/TBBO resin to dentin, 4-META-MMA/TBBO was polymerized in the presence of decalcified dentin sheet treated with citric acid (CA) aqueous solution containing ferric chloride (FC). Curing time of MMA/TBBO resin was reduced by the addition of 4-META to MMA. Addition of 4-META increased molecular weight of PMMA. PMMA polymerized inside the decalcified dentin sheet was insoluble in acetone. PMMA obtained from the monomer liquid used in commercial Super-Bond C & B was all insoluble and no soluble fraction was obtained. These results suggested that 4-META accelerated polymerization of MMA-TBBO resin in the presence of ferric ion and was effective to enhance molecular weight of PMMA. These effects seemed to be related to high bond strength of Super-Bond with dentin.
Acrylic Resins↗