Teeth mechanical properties

Rock Mechanical Properties. In the previous section (Figure 4-313), the wear of the bit teeth can be determined in shales by plotting the dimensionless bit torque (T, ) versus the dimensionless ROP (R,). By introducing a new parameter, namely the apparent formation strength, the bit effects can be separated from the lithology effects. 

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. 

Polymer resins were first introduced in the early 1940s as an aesthetic alternative to repair defects in anterior teeth. Some of the first resins were unfilled polymers of methyl methacrylate. Presently, these unfilled resins have been replaced by filled composite materials that limit the problems associated with polymerization volume shrinkage, abrasion or wear resistance, mechanical properties, water sorption, solubility, and thermal expansion. Polymeric composite materials generally consist of a monomer resin, a ceramic filler, a polymerization initiator or initiating system, and a coupling agent which binds the polymer... 

The primary failure modality identified clinically for restorations in posterior teeth is loss of material through abrasion. The complex nature of this failure mode in composite materials makes it difficult to correlate this phenomenon with any one mechanical property. A number of studies have suggested improvements in the system by using various mechanical properties as evidence. These studies have identified major factors such as ceramic filler loading and type of filler [186-191]. Some effects have been identified related to the... 

In anterior teeth, where aesthetics is more critical to the patient ad where the restoration can be shielded from the strongest biting forces, the composite can serve as an excellent, long lasting restorative. The current mechanical properties of the material allow excellent clinical success in these applications. 

Table 5.16 Selected Mechanical Properties of Various Calcium-Bearing Minerals Compared to Bone and Teeth...

Mechanical Properties Stress-strain, Elasticity, DuctiUty Fatigue, Fracture, Creep Viscoelasticity, Elastomers Laminates Sutures, Bone, Teeth... 

The key components in all sophisticated biological materials are the macromolecules that the cells produce and subsequently incorporate into the material. These include proteins, glycoproteins, proteoglycans, lipid assemblies and polysaccharides. Many biological materials are composed almost entirely of these assembled macromolecules. Common examples are the cuticles of many insects, the skin and tendons of vertebrates or the silk of spider webs. A very widespread adaptation is to stiffen the material by the introduction of a mineral phase. Common mineralized biological materials include the shells of mollusks, the carapaces of crustaceans, and the bones and teeth of vertebrates. Many of them are composite materials and are known to possess remarkable mechanical properties, especially when taking into account that they form at ambient temperatures and pressures, and that their mineral components are often commonplace materials with rather poor natural mechanical properties... 

Fig. 3. Comparison between the mechanical properties of different teeth. The Young s modulus (a) and the hardness (b) for two different maxillary 2nd molars and a 3rd molar.

Preliminary nanoindentation results on other teeth (premolars, incisors and canines) indicate variations in mechanical properties as large as those discussed for molars [unpubl. data]. In each case the exact distribution of mechanical properties within the enamel appears to correlate with the extent of mechanical loading experienced by the tooth during mastication. However, there appears to be an increase in the viscoelasticity (loss modulus) for the enamel of anterior teeth when compared to posterior teeth, again this may be related to their function. 

Recently, polyphase acrylic polymers have become increasingly important. They are the preferred materials for restoring anterior teeth where esthetic considerations are paramount. However, they are not satisfactory for the restoration of posterior teeth, especially in load-bearing locations where mechanical properties, such as abrasion resistance, are important (7). These materials are also used to make hip prostheses, and they are finding increasing application in orthopedics (8). 

Radiation modification of PC and PSF as plastic teeth was successfully attained by specific irradiation techniques, that is, the irradiation at elevated temperature of the Tg in inert gas atmosphere or under vacuum. The hardness and wear resistance of PC and PSF improved with a small dose of 3-5 kGy, whereas the decay of mechanical properties and coloring were scarce. By applying EB irradiation using the EB accelerator, the gradient of hardness can be formed in PC teeth. Namely, the surface area of teeth could be hardened selectively by the lower voltage of the EB accelerator. 

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 role of the fillers in composite resins is to reinforce their mechanical properties and provide a blended material whose overall properties make it suitable for the clinical repair of teeth. A limited range of materials has been used, with greater emphasis on variations in the particle size and size distribution than on chemical composition. Early materials were filed with powdered quartz, whereas modem composites are more likely to be filled with finely divided barium silicate or a radio-opaque silicate glass [8]. Filler loadings are typically of the order of 55% by volume, as they were in Bowen s original formulation [9]. 

The role of theory is to determine the conditions of h, c, tool geometry (rake angle), and work material thermo-physical-mechanical properties that give rise to serrated rather than continuous or other classifications of chips and, in the conditions of serrated chip formation, to predict such measurable features of the serration as the maximum and minimum chip thickness hi and h2, the angle 0 at which the saw teeth are inclined to the back face of the chip, the teeth face separation L, and the shear-band width . If such quantities are predicted, then the cycles of temperature and stress in the tool will also be known. 

Porous silicon particles could be utilized in a variety of consumer care applications if their cost of manufacture becomes low enough. Silica and porous silica are already widely used by the toothpaste and cosmetic industries, and porous silicon offers superior mechanical properties for teeth cleaning and very different optical properties for cosmetics. Partial thermal oxidation has been used to improve shelf life in liquid formulations and to match brown skin tones. Preliminary mouthfeel testing for oral hygiene products has been carried out, but formalized skin-feel testing and optimization is required for numerous dermatological products. Product examples discussed include multifunctional dentifrice abrasives, sunscreens, bronzers, foundation and makeup additive, and anti-aging formulations. 

These desired applications determine the main requirements to be fiilfilled in the development of glass-ceramics for dental applications. The main objective is to produce a new biomaterial, the properties of which correspond to those of natural teeth. The most important properties are mechanical properties, biochemical compatibility with the oral environment, and a degree of translucency, shade, opalescence, and fluorescence similar to that of natural teeth. An abrasion resistance similar to that of natural teeth must also be achieved. The new biomaterial must demonstrate higher chemical durability than natural teeth, to prevent it from being susceptible to decay. 

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... 

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