Dentin mechanical properties

Cements based on phytic add set more quickly than their glass polyalkenoate or dental silicate cement cormterparts, but have similar mechanical properties (Table 8.2). They are unique among add-base cements in being impervious to acid attack at pH = 2-7. Unfortunately, they share with the dental silicate cement the disadvantage of not adhering to dentine. They do bond to enamel but this is by micromechanical attachment - the cement etches enamel - and not by molecular bonding. Lack of adhesive property is a grave weakness in a modern dental or bone... 

Bone and teeth in mammals and bony fishes all rely on calcium phosphates in the form of hydroxyapatite [Ca5(P04)30H]2, usually associated with around 5% carbonate (and referred to as carbonated apatite). The bones of the endoskeleton and the dentin and enamel of teeth have a high mineral content of carbonated apatite, and represent an extraordinary variety of structures with physical and mechanical properties exquisitely adapted to their particular function in the tissue where they are produced. We begin by discussing the formation of bone and then examine the biomineralization process leading to the hardest mineralized tissue known, the enamel of mammalian teeth. 

Table 5.14 Selected Mechanical Properties of Human Dentin and Enamel...

Mechanical Properties of Candidate Materials. The mechanical properties of enamel and dentin were presented earlier in Table 5.14. We will use these values as the basis for our material selection process. Of these properties, compressive strength is the most important. The candidate material should have a compressive strength at least that of enamel, which is about 384 MPa. 

Summary of Mechanical Properties of Bone, Dentine [3], Hydroxyapatite [3], and CBPCs. 

Whilst the use of enamel and dentine as test substrates is widespread, they are complex materials to work with due to the natural variability both within and between specimens. A number of authors have examined alternative materials, which have similar mechanical properties to enamel and dentine, to use as test substrates. Acrylic [19, 20] and synthetic hydroxyapatite [21] have been proposed as suitable materials for abrasion testing, where mechanical effects dominate. These materials have several advantages since they are available as relatively large, smooth samples and exhibit better intra- and inter-sample reproducibility than their natural counterparts. This may, therefore, give better discrimination between test products for formulation development. However, the use of natural enamel and dentine is preferred, particularly for studies that aim to understand interactions between toothpaste products and tooth hard tissues. Other methods for assessing toothpaste abrasivity to hard tissues include gravimetry [22], scanning electron microscopy [23] and laser reflection [24]. 

For all mineralized tissues, the environment in which they are tested can significantly affect their mechanical properties. For bone, tests in aqueous and in simulated physiological solutions can change the hardness and elastic modulus by 20% [16, 17]. For enamel and dentin, the difference between the dry and wet mechanical properties can be 10% [18, 19]. Earlier studies [9] found... 

Xu HHK, Smith DT, Jahanmir S, Romberg E, Kelly JR, Thompson VP, Rekow ED Indentation damage and mechanical properties of human enamel and dentin. J Dent Res 1998 77 472-480. Kodaka T, Debari K, Yamada M, Kuroiwa M Correlation between microhardness and mineral content in sound human enamel. Caries Res 1992 26 139-141. 

Early non-cavitated carious lesions only may be repaired by remineraUzation processes. However partly because of the uncertainty in outcome, and partly because results are more reliable, the method of choice for the repair of a tooth damaged by caries is surgical removal of the carious region, followed by repair with some sort of synthetic material. The act of cutting out damaged tooth material (enamel and dentine) is known to compromise the mechanical properties of the tooth [43], as shown by the results in Table 1.1. In this study, a set of 10 non-carious teeth was used per experimental set. They were mounted in dental stone and tested in compression, with the load at failure in kilograms recorded. 

The two tissues, enamel and dentine, are connected by the dentino-enamel junction, which has distinctive characteristics of its own. It unites the thin and brittle enamel layer to the thicker, tougher underlying structure of dentine. Its mechanical properties make it ideal for the function of uniting two materials with such dissimilar properties, and one of its most important functions is to prevent cracks from passing through from the enamel to the dentine [7]. This feature protects the entire tooth from mechanical failure and is important in maintaining the tooth in service for long periods of time. 

Substitutions in the HA structure are possible. Substitutions for Ca, PO4, and OH groups result in changes in the lattice parameter as well as changes in some of the properties of the crystal, such as solubility. If the OH" groups in HA are replaced by F" the anions are closer to the neighboring Ca " ions. This substitution helps to further stabilize the structure and is proposed as one of the reasons that fluoridation helps reduce tooth decay as shown by the study of the incorporation of F into HA and its effect on solubility. Biological apatites, which are the mineral phases of bone, enamel, and dentin, are usually referred to as HA. Actually, they differ from pme HA in stoichiometry, composition, and crystallinity, as well as in other physical and mechanical properties, as shown in Table 35.7. Biological apatites are usually Ca deficient and are always carbonate substituted (COs) " for (P04). For... 

Furthermore, monomers for restorative composites or composite cements should exhibit a low volume contraction during polymerization, excellent mechanical properties after polymerization, and low water solubility. The water sorption of the formed polymer should also be low. The currently used direct restorative composites, composite cements, and enamel/dentin adhesives are largely based on methaciylate chemistiy using mixtures of different methacrylates, such as crosslinking and functionalized methacrylates, which can be cured by free-radical polymerization. ... 

Huang, T.-J.G., Schilder, H. and Nathanson, D. (1992) Effects of moisture content and endodontic treatment on some mechanical properties of human dentin. J. Endodontics, 18(5), 209-215... 

Human teeth are also composed primarily of biological apatite. The outer two layers of a human tooth consist of enamel on the outside and dentine underneath that. Dentine and bones are very similar in composition and mechanical properties, but enamel is almost pure hydroxyapatite, Ca5(P04)30H. Dental enamel is the hardest part of the human body. In addition, the hardness of dental enamel is enhanced by the presence of fluoride ions in place of the hydroxides. (Thus we see... 

Measurement of mechanical properties of proteins, especially those of fibrous proteins, has been an important interdisciplinary concern in the history of protein science. In fact, the very early X-ray work by Astbury and his colleagues established the force dependent conformational transition of keratin fiber between a- and /3-forms [15]. A large body of work has since been accumulated on the measurement of mechanical parameters of fibrous structures made of keratin, collagen, dentin and other structural proteins [10, 14, 16, 17]. Measurement was done at the macroscopic level on higher order assemblies of fibrous proteins, applying established methods in materials science for the determination of, for example, static and/or dynamic elastic modulus [14],... 

The mechanical properties of the HA are similar to those of the most resistant components of the bone. HA has an elastic modulus of 40-100 GPa, dental enamel 74 GPa, the dentine 21 GPa, the compact bone 18-12 GPa. Nevertheless, dense bulk compact of HA has a mechanical resistance of the order of 100 MPa in front of to the 300 MPa of the human bone, diminishing drastically this resistance in the case of porous bulk compact. 

Several studies reported that dentin in endodontically treated teeth were more brittle than dentin in teeth with pulps [18, 19]. However, some other studies showed that the mechanical properties of endodonticed and normal dentin were comparable [20, 21]. In this study, dentin for the... 

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