Hard tissues

Bone, or osseous tissue, is composed of osteocytes and osteoclasts embedded in a calcified matrix. Hard tissue consists of about 50% water and 50% solids. The solids are composed of cartilaginous material hardened with inorganic salts, such as calcium carbonate and phosphate of lime. 

Fairgrieve, S.I. 1993 Amino acid residue analysis of Type I collagen in human hard tissue an assessment of cribra orbitalia in an ancient skeletal samplefrom tomb 31, site 31/435-D5-2, Dakhleh Oasis, Egypt. Ph.D. dissertation, University of Toronto. 

Various in vivo studies have been performed to assess the biocompatibility of PEG/PBT copolymers upon implantation in soft and hard tissues." ... 

Pastes of calcium hydroxide with water have been used as pulp-capping materials for many years and it is the material of choice for this application (Granath, 1982). Its favourable tissue responses have been known for many years (Zander, 1939). It has a healing effect, for it induces the formation of hard tissues of reparative dentine when pulp has been exposed (Eidelman, Finn Koulourides, 1965). This action seems to be associated with its high alkalinity (pH 12-5) and consequent bactericidal and proteinlysing effect (Fisher, 1977). 

The capacity of hard tissue such as bone to generate potentials in response to mechanical stress has been known from the beginning of the nineteenth century. A piezoelectric theory to account for the electric potential observed in dry bone on deformation was proposed by Fukada and Yasuda in 1957 and subsequently explored by many others in the 1950s and 1960s as well as by Friedenberg et al. in 1971. 

R. A. Replamineform Porous Biomaterials for Hard Tissue Implants. J. BiomecL Mater. Res. Symp. 1975, 6, 23-27. f... 

In a study involving decalcified FFPE rat joint tissue sections and a variety of AR methods, Wilson et al.32 reported successful application of 0.2 M boric acid at pH 7.0 as the AR solution combining a low-temperature incubation (60°C for 17 h). The principal advantage of this AR protocol was that it minimized lifting or loss of decalcified hard tissue sections from charged slides. Their basic approach for establishing an optimal AR protocol was a test battery as described above. In a separate series of studies, based upon prior... 

Hou FJ, Lang SM, Hoshaw SJ, et al. (1998) Human vertebral body apparent and hard tissue stiffness. J Biomech 31 1009-1015... 

Nakabayashi, N. and Pashley, D.H. Hybridization of Dental Hard Tissues 1998, Chapter 2, Quintessence Publishing Co., Ltd., Tokyo, Japan. 

The hard layers are represented with a wide range of coating based on carbon, metals, ceramics, various oxides (Ti02, Si02) and nitrides (ZrN) and their combinations [14,16,24,47,136-143]. These layers can streghten the material surface, especially in materials designed for hard tissue surgery, such as... 

In contrast, through eons of evolution Nature has come up with many biopolymers that can combine important mechanical properties including strength, toughness, and elasticity. For example, sUks (Oroudjev et al. 2002), cell adhesion proteins (Law et al. 2003), and connective proteins existing in both soft and hard tissues such as muscle (Kellermayer et al. 1997 Rief, Gautel, et al. 1997 Marszalek et al. 1999 Li et al. 2000), seasheUs (Smith et al. 1999), and bone (Thompson et al. 2001)... 

H.W. Kim, H.E. Kim, J.C. Knowles, Fluor-hydroxyapatite sol-gel coating on titanium substrate for hard tissue implants, Biomaterials 25 (2004) 3351-3358. 

In addition, the presence of low concentrations of fluoride in saliva also has the effect of preventing dissolution of hydroxyapatite from enamel at low pH, an effect that has been shown to apply at values of pH as a low as 4.2 [54,55], Thus, it is the fluoride in solution that has the effect of reducing solubility, rather than the fluoride in the mineral phase [51], This effect requires extremely small amounts of fluoride, typically in the sub-ppm range [51,56], and has the effect of shifting the balance between demineralisation and remineralisation so that loss of the hard tissue is inhibited. 

Fluoride also brings about a change in composition in natural hydroxypatite, since it not only undergoes a simple exchange with hydroxyl ions but also promotes the formation of a phase containing less carbonate than the initial hydroxyapatite [65]. Fluoride is taken up more readily by demineralised enamel than by sound enamel [66], which means its availability causes a self-healing effect in the mineral phase of the hard tissue. 

The most common oral condition and dental emergency is dental caries, which is a destructive disease of the hard tissues of the teeth due to bacterial infection with Streptococcus mutans and other bacteria. It is characterized by destruction of enamel and dentine. Dental decay presents as opaque white areas of enamel with grey undertones and in more advanced cases, brownish discoloured cavitations. Dental caries is initially asymptomatic and pain does not occur until the decay impinges on the pulp, and an inflammation develops. Treatment of caries involves removal of the softened and infected hard tissues, sealing of exposed dentines and restoration of the lost tooth structure with porcelain, silver, amalgam, composite plastic, gold etc. 

Suchanek, W., and M. Yoshimnra, Processing and properties of hydroxyapatite-based biomaterials for use as hard tissue replacement implants. J. Mater. Res., 13(1), 94 (1998). 

Gel Drug delivery soft- and hard-tissue augmentation... 

K. Wada and I. Kobayashi (eds.). Biomineralization and Hard Tissue of Marine Organisms, Tokyo, Tokai University Press, 1996 (injapanese)... 

Determination of Mg in the hard tissues (shell and pearl) of shellfish by the ICP-AES method involves dissolution of the sample by hot concentrated nitric acid, hydrochloric acid and perchloric acid. However, the large excess of Ca in the matrix strongly interferes with the end analysis and causes damage to the torch. After adjusting the pH to 4.5, the Mg ions were extracted by a 0.01 M solution of 3-methyl-l-phenyl-4-trifluoroacetylpyrazol-5-one (16) in dibutyl ether and the ICP-AES analysis was carried out by direct injection of the organic solution. ... 

Another important area of materials development is related to the life sciences and concerns the development of materials to serve as replacements for body parts. There are challenges in replacing hard tissues such as hip and knee joints as well as soft tissues such as vascular tissue and ligaments. These implants will require very sophisticated composite materials if they are to model the properties of living tissues successfully. 

Katz, J. L. (1971). Hard tissue as a composite material—1. Bounds on elastic behaviour. J. Biomechanics 4, 455-73. [194]... 

The initial inflammatory reactions associated with chitosan application to hard and soft tissues need to be controlled before it can be considered for clinical application as scaffold. Further, as it takes too long for biodegradation of implanted chitosan in vivo, generally chitosan is concluded to be not suitable for the scaffold for degenerative medicine in especially dental pulp tissue surrounding hard tissue. 

Metallic biomaterials (metals such as Ti or its alloys and others) are used for the manufacture of orthopaedic implants due to their excellent biocompatibility with respect to electrical and thermal conductivity and their mechanical properties, e.g., for hard tissue replacement such as total hip and knee joints, for fracture healing aids such as bone plates and screws or dental implants. For example, Co-Cr-Mo alloys are employed for metal-on-metal hip bearings in total joint replacements. Problems with implants occur because of ion release in patients with metal implants. To control this ion release, the ultratrace determination of Co, Cr and Mo in the blood (or serum) and urine of patients with Co-Cr-Mo alloy hip implants is carried out routinely in the author s laboratory. The trace metal determination of Co, Cr and Mo in complex matrices such as urine and blood by ICP-MS is not trivial due to the low concentrations expected in the sub-ngmF1 range, the possible danger of contamination during sample collection, sample preparation and the... 

Although about 80—90 percent of the total citric acid in humans are localized in hard tissues as enamel, dentine, cementum and bones, very little is known on the biological function of citric acid in biocalcification. HA crystals are reported to be dissolved by the action of citric acid. The acid dissolves the crystals in such a way that the destruction is a preferential attack along the c-axis. It is highly probable that the HA crystallites present in mineralized tissues also do have a dislocation in the centre of the material 165). Another assumption describes that citric acid is a constituent of the aqueous phase of enamel or that citrate is bound to the surface of apatite by adsorption166). 

---