Mechanical properties vary at different regions of enamel. The surface layer of enamel is stiffer, denser and less permeable than the rest of the enamel [ 8 ]. In spite of its hardness, enamel is extremely brittle especially when the underlying resilient dentin is lost. Enamel is translucent and varies in shade from light yellow to grey white. At the incisal edge of a recently erupted tooth, enamel appears bluish white [ 11 ]. In cervical areas, enamel reflects the yellow colour of the underlying dentin, which determines the tooth colour along with the enamel thickness and translucency.
The enamel translucency increases with age and therefore transmits the yellow colour of the underlying dentin and appears darker. Fluoride ions can penetrate the enamel from saliva and form fluorapatite crystal-rich layers at the surface, which are larger and more chemically resistant to bacterial acid dissolution [ 11 ]. Ions can penetrate enamel either from saliva, food and beverages, and then become incorporated into the interprismatic region or internally from the pulp through the DEJ and change its chemical composition [ 10 ].
In addition to small inorganic molecules, enamel is also permeable to larger molecules associated with stains and pigments. These large molecules diffuse through pores found at the prism boundaries and interprismatic enamel [ 8 ]. However, we will only consider dentin in this chapter, as the subject of this book is about calcium phosphates. Dentin is a highly organised biological structure composed of complex protein assemblies and organised mineral components, which collectively form a rigid and durable mineral-rich biocomposite [ 17 ].
Dentin is formed through the process of dentinogenesis, by odontoblasts that differentiate from ectomesenchymal cells of the dental papilla. The dental papilla primarily induces the formation of dentin until it is finally surrounded by secreted dentin, thus forming the dental pulp [ 2 ]. A complex group of synchronised biological events regulates the formation and maturation of dentin.
The main stages of dentinogenesis include the cytodifferentiation of the odontoblasts, the formation of mantle dentin, the control of mineralisation of the primary dentin organic matrix and, finally, the secretion of secondary and tertiary dentin. Primary dentin is the outermost layer of the dentin, which includes the mantle and the circumpulpal components. Secondary dentin is a layer that is secreted after the root formation. Tertiary dentin is the type of dentin that is secreted after full formation of the tooth, as a response to a stimulus, such as carious attack or wear.
Decorin and biglycan, two members of the small leucine-rich repeat SLRP family, are the PGs predominantly expressed in dentin.
The most frequently found GAGs, in turn, are chondroitin 4-sulphate and a relatively lower content of chondroitin 6-sulphate. Dentinal tubules contain cytoplasmic extensions of odontoblasts, which lie in the pulp and originally were involved in the secretion of dentin matrix.
In addition to this odontoblastic process, dentinal tubules contain dentinal fluid, which contains proteins and proteoglycans. The peritubular dentin is a highly mineralised composite material constituted of phosphorylated proteins [ 21 , 22 ], proteoglycans and glycosaminoglycans [ 22 ], which lacks collagen fibrils [ 22 , 23 ]. The intertubular dentin, on the other hand, is composed of supramolecular aggregates of collagen molecules, which are assembled into type I fibrils interconnected by noncollagenous components and water [ 24 ].
This array of organic molecules forms a hydrated organic network serving as a scaffold for the nucleation and growth of carbonated apatite mineral crystals [ 25 ]. The result of this organic—inorganic interplay is an intricate biocomposite that exhibits outstanding longevity and serves as a tough and resilient foundation for the brittle enamel, as well as a protective layer for the living pulpal soft tissue. This foundation prevents the propagation of catastrophic cracks from the brittle enamel further into the dentin [ 3 , 26 ].
Dentin and enamel are bound strongly at their common interface, which is called the dentinoenamel junction DEJ. Dentinoenamel junction is a hypermineralised area that appears like a well-defined scalloped area under the microscope. The presence and the form of this area have an important role in the structural and functional integrity of enamel and dentin.
Due to the presence of dentinal tubules, dentin is far more permeable than enamel Fig. The composition of cementum is very similar to bone. HAp minerals in cementum have a uniform small plate shape. The organic matrix is composed of collagen and noncollagenous proteins. During cementogenesis, cementum is secreted by cementoblasts and after the completion of tooth development; it covers the roots of the tooth tightly in an interlocking manner.
There are two types of cementum, which includes cellular and acellular cementum. Feature Image Source. Share this post. Share on facebook.
Share on twitter. Share on linkedin. Our Dentistry. Dental Marketing by Progressive Dental. EN ES. Contact Us. We are working hard to keep you safe! As dental erosion has become more of an issue, it is hoped that all dental practitioners develop a greater awareness of the problem and become more equipped to help manage their patients that are either at risk, or are already experiencing some level, of dental erosion. You did not finish creating your certificate.
Failure to complete ALL the steps will result in a loss of this test score, and you will not receive credit for this course. Save your progress. Table 1. Composition of Enamel and Dentin. Figure 4. Tooth surfaces after an acid challenge. These areas are susceptible to loss due to subsequent frictional forces.
Demineralization of the intertubular matrix has occurred, and some of the dentinal tubules become opened, which can lead to sensitivity.
Images courtesy of Karger. Figure 5. Daculsi, G. Method of measurement of apatite crystals in human dentin by high resolution transmission electron microscopy , Comptes Rendu Acad. Voegel, J. Buccale , 5 , — Lehman, M. Stanford, J. American Dental Assoc , 60 , — Jameson, M. Craig, R. Korostoff, E. Bowen, R. American Dental Assoc , 64 , — Carter, J. Hassan, R. Rasmussen, S. Caldwell, R. Remizov, S. Davidson, C. Pashley, D. Oral Biol , 32 7 , — Traumatol , 1 , —
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