Age and Functional Changes in Dentin PDF

Age and functional changes in dentin By dr: sally sakr Age and functional changes of dentin The age and functional changes of dentin are represented by: A. Changes in dentin as sclerotic dentin and dead tract. B. Formation of new dentin such as secondary and tertiary or reparative dentin....

Age and functional changes in dentin By dr: sally sakr Age and functional changes of dentin The age and functional changes of dentin are represented by: A. Changes in dentin as sclerotic dentin and dead tract. B. Formation of new dentin such as secondary and tertiary or reparative dentin.  A. Changes in dentin 1. Sclerotic or transparent dentin It is formed due to calcification of odontoblastic process and occlusion of dentinal tubules by deposition of minerals. Sclerotic dentin could be: 1. Physiologic sclerotic dentin occurs due to normal aging (in root dentin). 2. Reactive sclerotic dentin occurs due to mild stimulus (as a protective mechanism).  1. Sclerotic or transparent dentin It decreases the permeability of dentin  help to prolong pulp vitality. It appears translucent when viewed by transmitted light and are known as translucent dentine. With reflected light these areas appear dark. It is found In the root as an age change May found In the crown around dead tract  2. Dead tracts When the irritant is strong (caries or attrition), the odontoblastic processes become destroyed forming Dead tract dead tract. The tubules are empty and appear black in Tertiary dentin transmitted light and white in reflected light. They are sealed off at the pulp surface by a deposit Secondary dentin of irregular secondary dentine (tertiary dentin). Primary dentin  2. Dead tracts Each dead tract is surrounded, and isolated from the rest of the dentine, by a narrow zone of sclerosed dentin.  2. Dead tracts It appears light It appears dark under reflected light under transmitted light  2. Dead tracts Dead tract could be formed due to grinding of teeth during the ground section preparation (false dead tract). True dead tract must have tertiary dentin. True dead tract (tertiary dentin exists) False dead tract (tertiary dentin does not exist) B. Formation of new dentin 1. Regular secondary dentin: It is dentin formed after complete root formation and its formation is physiologic. Deposited by the same odontoblasts that formed primary dentin. It is formed as the pulp become reduced in size and it's formed along the surface of the pulp.  Primary dentin Secondary dentin differs from primary dentin in: 1. They have fewer dentinal tubules. 2. Less regular and has different direction. Secondary dentin Secondary dentin is separated from primary dentin by demarcation line.  2. Tertiary dentin “irregular secondary dentin” Tertiary dentin is the dentin formed in Dead tract response to various stimuli such as attrition, caries or restorative dental procedure. Tertiary dentin It is formed in localized area of the pulp. Secondary dentin Tertiary dentin is classified as either reactionary dentin or reparative dentin, Primary dentin according to the intensity of the injury.  Types of tertiary dentin 1. Reactionary dentin In case of mild stimulus, surviving odontoblasts form Reactionary reactionary (regenerative) tertiary dentin dentin. It is formed by the preexisting odontoblasts which have survived. This type of dentin has an irregular appearance with fewer tubules. 2- Reparative dentin It is formed by the newly differentiated odontoblast-like cells that replace the original odontoblasts that have been destroyed by sever stimulus. The newly differentiated odontoblast-like Reparative cells are thought to arise from deeper tertiary dentin regions of the pulp, either from the cell- rich zone or from the undifferentiated perivascular cells.  Theories of dentin sensitivi ty Theories of dentin sensitivity Three main theories have been proposed to explain dentin sensitivity: 1. Direct innervation theory. 2. Transduction theory. 3. Hydrodynamic theory. 1. Direct innervation theory: It is based on the belief that the nerves extend to the dentino- enamel junction. However, studies have not shown nerves present at this junction or in all dentinal tubules.  2. Transduction theory It is stated that the odontoblastic process is the receptor because it originates from neural crest cells and that it conducts the pain to nerve endings in the peripheral pulp and in the dentinal tubules. This theory is rejected because there are no any neurotransmitter vesicles in the odontoblastic processes or synaptic relationship between the processes and nerve endings. 3. Fluid or hydrodynamic theory (the most accepted theory) It suggests that all effective stimuli applied to dentine cause fluid movement through the dentinal tubules, and that this movement is sufficient to depolarise nerve endings in the inner parts of tubules, at the pulp-predentine junction and in the sub-odontoblastic neural plexus.  Some stimuli, such as cold, osmotic pressure and drying, would tend to cause fluid movement outwards while others, such as heat, would cause movement inwards. Movement in either direction would mechanically distort the nerve terminals and stimulate receptors in pulp. Clinical consideration  Smear layer It is a layer of debris that is formed following mechanical instrumentation of dentin and enamel “during cavity preparation”. Smear layer is composed of superficial layer and smear layer plug which occludes dentinal tubules.  Smear layer Smear layer is weak soft and irregular and contains microorganisms. Therefore, this layer has to be removed by etching in order to create a rough porous surface for bonding  Smear layer After acid etching the smear layer is removed and the dentinal tubules are opened, and demineralization of peritubular dentin occurs to allow resin bond to enters dentinal tubules and forms resin tags.  Pulp Protection in Deep Carious Lesions In the deep carious lesion, caries can reach very near or up to the pulp, so treatment of deep carious lesion requires precautions because of postoperative pulpal response. Pulp is protected by pulpal capping material either direct or indirect.  Direct pulp capping It involves the placement of biocompatible material over the site of pulp exposure to maintain vitality and promote healing. When a small mechanical exposure of pulp occurs during tooth preparation or following a trauma, an appropriate protective base should be placed in contact with the exposed pulp tissue so as to maintain the Direct pulp capping  Indirect pulp capping It is a procedure performed in a tooth with deep carious lesion adjacent to the pulp (no pulp exposure but the remaining dentin thickness is minimal). Pulp capping material (MTA) is placed to promote formation of