Osteoclast-independent bone resorption by fibroblast-like cells.
(73/1113)
To date, mesenchymal cells have only been associated with bone resorption indirectly, and it has been hypothesized that the degradation of bone is associated exclusively with specific functions of osteoclasts. Here we show, in aseptic prosthesis loosening, that aggressive fibroblasts at the bone surface actively contribute to bone resorption and that this is independent of osteoclasts. In two separate models (a severe combined immunodeficient mouse coimplantation model and a dentin pit formation assay), these cells produce signs of bone resorption that are similar to those in early osteoclastic resorption. In an animal model of aseptic prosthesis loosening (i.e. intracranially self-stimulated rats), it is shown that these fibroblasts acquire their ability to degrade bone early on in their differentiation. Upon stimulation, such fibroblasts readily release acidic components that lower the pH of their pericellular milieu. Through the use of specific inhibitors, pericellular acidification is shown to involve the action of vacuolar type ATPases. Although fibroblasts, as mesenchymal derived cells, are thought to be incapable of resorbing bone, the present study provides the first evidence to challenge this widely held belief. It is demonstrated that fibroblast-like cells, under pathological conditions, may not only enhance but also actively contribute to bone resorption. These cells should therefore be considered novel therapeutic targets in the treatment of bone destructive disorders. (+info)
The mechanical properties of human dentin: a critical review and re-evaluation of the dental literature.
(74/1113)
The past 50 years of research on the mechanical properties of human dentin are reviewed. Since the body of work in this field is highly inconsistent, it was often necessary to re-analyze prior studies, when possible, and to re-assess them within the framework of composite mechanics and dentin structure. A critical re-evaluation of the literature indicates that the magnitudes of the elastic constants of dentin must be revised considerably upward. The Young's and shear moduli lie between 20-25 GPa and 7-10 GPa, respectively. Viscoelastic behavior (time-dependent stress relaxation) measurably reduces these values at strain rates of physiological relevance; the reduced modulus (infinite relaxation time) is about 12 GPa. Furthermore, it appears as if the elastic properties are anisotropic (not the same in all directions); sonic methods detect hexagonal anisotropy, although its magnitude appears to be small. Strength data are re-interpreted within the framework of the Weibull distribution function. The large coefficients of variation cited in all strength studies can then be understood in terms of a distribution of flaws within the dentin specimens. The apparent size-effect in the tensile and shear strength data has its origins in this flaw distribution, and can be quantified by the Weibull analysis. Finally, the relatively few fracture mechanics and fatigue studies are discussed. Dentin has a fatigue limit. For stresses smaller than the normal stresses of mastication, approximately 30 MPa, a flaw-free dentin specimen apparently will not fail. However, a more conservative approach based on fatigue crack growth rates indicates that if there is a pre-existing flaw of sufficient size (approximately 0.3-1.0 mm), it can grow to catastrophic proportion with cyclic loading at stresses below 30 MPa. (+info)
Yeasts in apical periodontitis.
(75/1113)
Microbiological reports of apical periodontitis have revealed that yeasts can be isolated from approximately 5-20% of infected root canals. They occur either in pure cultures or together with bacteria. Almost all isolated yeasts belong to the genus Candida, and the predominant species is C. albicans. Pheno- and genotypic profiles of C. albicans isolates show heterogeneity comparable with those of isolates from other oral sites. C. albicans expresses several virulence factors that are capable of infecting the dentin-pulp complex, including dentinal tubules. This causes, consequentially, an inflammatory response around the root apex, which suggests a pathogenic role for this organism in apical periodontitis. Yeasts are particularly associated with persistent root canal infections that do not respond favorably to conservative root canal therapy. This may be due to the resistance of all oral Candida species against a commonly used topical medicament, calcium hydroxide. However, other antimicrobial agents may offer alternative therapeutic approaches and improve the treatment of these persistent cases of apical periodontitis. (+info)
Adhesion of 4-META/MMA-TBB resin to heated dentin: effects of pre-treatments with FeCl3 and/or HEMA.
(76/1113)
The purpose of this study was to compare the tensile bond strengths (TBSs) and failure mode of 4-META/MMA-TBB resin to 60 degrees C-heated and unheated bovine dentin, especially to investigate the influence of ferric chloride contained in citric acid pre-conditioning. In addition, the effect of HEMA priming for heated dentin was also evaluated. The TBSs to heated dentin were significantly lower than those to unheated dentin. Adhesive failures were observed in most specimens of the heated and HEMA-non primed group. HEMA application to heated dentin significantly increased the TBSs in each acid conditioning, which were also significantly higher than those of the unheated and ferric chloride-contained citric acid-conditioned group. It was clarified that heating dentin decreased the bond strength without HEMA priming even if the dentin surfaces were acid conditioned with 10-3, while HEMA priming after acid conditioning recovered the bond strength. (+info)
Effect of depth and tubule direction on ultimate tensile strength of human coronal dentin.
(77/1113)
The purpose of this study was to evaluate the effect of dentin depth and tubule direction on the ultimate tensile strength (UTS) of human dentin. Dentin slabs of 0.5-mm thickness were trimmed either from the mesial and distal (for specimens with the tubules parallel to the tensile force; parallel group) or from the occlusal and pulpal surfaces (perpendicular group) to reduce the cross-sectional area of the superficial, middle, and deep regions to 0.25 mm2, and subjected to microtensile testing. From SEM photomicrographs of the fractured specimens of the parallel group, the tubule density was investigated. For both parallel and perpendicular groups, superficial dentin showed a significantly higher UTS than deep dentin. The tubule density of superficial dentin was significantly lower than that of middle and deep dentin. When performing the microtensile bond test to deep dentin, it is possible that cohesive failure of dentin can occur at relatively low tensile stresses. (+info)
Evaluation of adhesive defects using an ultrasonic pulse-reflection technique.
(78/1113)
The purpose of this study was to examine the application of an ultrasonic pulse-reflection technique for the evaluation of adhesive defects. First, the sonic velocities in the enamel and dentin of human molars and bovine incisors were measured with a pulsar receiver attached to an ultrasonic transducer. The identification of the dentino-enamel junction and pulp-dentin interface using the ultrasonic method based on intrinsic sonic velocities showed good agreement with the actual measured thicknesses. Next, a cemented restoration with artificial faults was prepared. Half of the Au-Ag-Pd alloy plate area was cemented to the dentin slab using luting resin cement. The adhesive interface was evaluated with a high-resolution ultrasonic imaging system. Clear internal faults were evident from the ultrasonic tomogram. The findings of this study suggest that the ultrasonic pulse-reflection technique may be useful for inspecting and imaging structural defects of adhesive interfaces. (+info)
Different dental tissues as source of DNA for human identification in forensic cases.
(79/1113)
AIM: To evaluate different dental tissues (pulp, dentin, and cement) as sources of DNA for forensic analysis. METHODS: A total of 20 teeth were obtained from unidentified bodies buried at the Central Cemetary in Bogota in 1995 and exhumed in 2000. The tissues from three teeth obtained after surgery were used as controls. The pulp cavity was exposed after cutting each tooth with a high-speed handpiece. The pulp was removed and processed separately from the dentin and cement. The dentin and cement were obtained by drilling with a high-speed handpiece and placed into separate tubes. DNA was extracted from mineralized tissues after a short decalcification step with EDTA. The DNA was quantified by dot-blot hybridization with D17Z1 probe, a primate- and human-specific alpha satellite DNA for the D17Z1 locus. Polymerase chain reaction was carried out for the hypervariable control region between nucleotides 29 and 408 bp (HV2 region) of the mitochondrial DNA, followed by gel electrophoresis to evaluate the amount and efficiency of the amplification. RESULTS: The pulp yielded the strongest amplification signals. The signals for dentin and cement were very similar because of the presence of cells of the periodontal ligament in the cement. The results of the amplification of the HV2 region of the mitochondrial DNA showed that dentin and cement acted as protective factors for the cells and allowed the conservation of the DNA. CONCLUSION: Cementoblasts and odontoblasts located within the cement and dentin are surrounded by the mineral matrix of the dental structure and thus protected from any environmental degradation forces, which makes them suitable sources for the DNA analysis. (+info)
Micromechanical properties of demineralized dentin collagen with and without adhesive infiltration.
(80/1113)
In a previous study, we reported the upper limit of Young's modulus of the unprotected protein at the dentin/adhesive interface to be 2 GPa. In this study, to obtain a more exact value of the moduli of the components at the d/a interface, we used demineralized dentin collagen with and without adhesive infiltration. The prepared samples were analyzed using micro-Raman spectroscopy (micro RS) and scanning acoustic microscopy (SAM). Using an Olympus UH3 SAM (Olympus Co., Tokyo), measurements were recorded with a 400 MHz burst mode lens (120 degrees aperture angle; nominal lateral resolution, 2.5 microm). A series of calibration curves were prepared using the relationship between the ultrasonically measured elastic moduli of a set of known materials and their SAM response. Finally, both the bulk and bar wave elastic moduli were computed for a set of 13 materials, including polymers, ceramics, and metals. These provided the rationale for using extensional wave measurements of the elastic moduli as the basis for extrapolation of the 400 MHz SAM data to obtain Young's moduli for the samples: E = 1.76 +/- 0.00 GPa for the collagen alone; E = 1.84 +/- 0.65 GPa for the collagen infiltrated with adhesive; E = 3.4 +/- 1.00 GPa for the adhesive infiltrate. (+info)