Dentinogenesis – Dentin Composition, Structure, Types and Formation

Before proceeding please make sure to subscribe and turn on the bell icon for upcoming videos. This video will be divided into two parts. In the first part of this video we will talk about the structure, the composition and types of dentin and in the second part of this video about dentinogenesis or the process of dentin formation if you haven’t watched my previous videos on developmental stages of the tooth please watch them first for a much clear concept on today’s topic. Dentin is the second mineralized tissue of the tooth lying immediately under the enamel and it makes up the bulk of a tooth. It’s harder than bone but softer than enamel. It’s made up of 70% of inorganic material that is hydroxyapatite crystals and 20% of organic material. The collagenous and non collagenous proteins contribute to its organic part with the collagenous proteins making up 90% of its organic part and the non collagenous proteins which makes up only 10% of its organic part. Also noted that the remaining 10% of dentin is made up of water. The collagenous proteins is mainly type 1 collagen with small amounts of type 3 and type 5 collagen in it. The non collagenous proteins of its organic part is made up of a wide range of proteins like dentin phosphoproteins, denin sialoproteins, dentin glycoproteins and dentin matrix protein 1 and also some other types of proteins. These non collagenous proteins fills up the space in between the collagenous proteins. Upon a closer look, the dentin is composed of tiny closely packed and fluid filled tubules occupying the entire thickness of the dentin. The cytoplasmic extension of each odontoblast lies inside each tubule with their cell bodies aligned at the inner aspect of the dentin or at the outer aspect of the pulp. The part of the dentin lying in between the tubules is called the intertubular dentin while the part of it surrounding each tubule is called peritubular Dentin. Dentin is divided into three main types, called the primary physiologic dentin, the secondary physiologic dentin and the tertiary dentin also called the reparative dentin or the reactionary dentin. The primary physiologic dentin is
further divided into the mantle dentin and the circumpulpal dentin. Let’s draw a diagram to understand the
location and the characteristics of each one of them. The mantle dentin is the first formed and the outermost layer of the dentin, lying close to the dentinoenamel junction at the crown level and the dentinocemental junction at the level of the root. This mantle dentin is relatively less mineralized when compared to other parts of dentin and it’s fibers are perpendicular to the dentinoenamel junction at the crown while parallel to the dentinocemental junction in the root. It’s thickness varies from 15 to 20 micrometers. The secondary dentin lies close to the
pulp chamber. its formation begins after the root of a tooth is completely formed and is formed slowly throughout life, with its greatest content located at the
roof and floor of pulp chamber. It has few dentinal tubules when compared to other areas of the dentin. The circumpulpal dentin is the part
of the dentin lying in between the secondary and the Mantle dentin. it forms the bulk of a tooth. Its fibers are parallel to the dentinoenamel junction. It has a maximum number of dentinal tubules and is highly mineralized when compared to other types of dentin. The tertiary dentin deposits at localized sites after any injury like carries or restorative procedures. It’s rate of deposition is directly proportional to the degree of injury at that site. Let’s move on to the next part of this
video. The dentinogenesis or the process of dentin formation occurs at the late belll stage, by the differentiated cells of the dental
papilla called the odontoblasts. The differentiation of the underlying cells
of the dental papilla into preodontoblasts occurs under the influence of the signaling molecules and growth factors released from the undifferentiated cells of
the inner enamel epithelium. As soon as the cells of the inner enamel
epithelium differentiates into preameloblasts the underlying cells of the dental papilla will stop dividing and will form two daughter cells. Out of these two daughter cells one of them will differentiate into preodontoblasts while the other one will remain
undifferentiated in the pulp of a tooth which can be activated any time by an
external stimulus . After the preameloblasts becomes the mature ameloblast and enters into its initial secretary phase, the newly differentiated odontoblasts will lay down the dentinal matrix at the end of its cytoplasmic extensions. This first layer of unmineralized dentinal matrix is called the mantle predentin. The word predentin refers to the unmineralized dentinal matrix. As soon as the predentin mineralizes, it will become the mature dentin. After this first layer of mantle dentin is formed the ameloblasts will lay down the initial layer of enamel matrix. As soon as the preodontoblasts grows into the mature odontoblasts, it moves away from the newly formed dentinal matrix or predentin and develops a cytoplasmic process called tomes fiber. Please keep in mind that tomes fiber belongs to odontoblasts while tomes process belongs to ameloblasts. And these two are not the same. At this point, the ameloblasts will be in its secretory phase and will lay down the enamel matrix for the rod and interrod enamel. The mantle predentin mineralizes to mantle dentin and the mature odontoblasts will lay down another layer of dentinal matrix called the predentin. And in this way a layer of predentin is always present between the odontoblasts and the mineralization front. If you think this video was helpful please like, subscribe, share and comment if you have any
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