Tooth enamel
انسجة فم عملي / د . اسماء ثاني اسنان موصل 21 / 12 / 2015 **
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Tooth enamel is the hardest and most highly mineralized substance of the body , and with dentin, cementum , and dental pulp is one of the four major tissues which make up the tooth in vertebrates .
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A-enamel E- alveolar bone B-dentine F- periodontal ligament C-cementum G-gingiva D-pulp
Ground section
decalcified section
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Enamel's primary mineral is hydroxyapatite, which is a crystalline calcium phosphate. The large amount of minerals in enamel accounts not only for its strength but also for its brittleness. Tooth enamel ranks 5 on Mohs hardness scale and a Young's modulus of 83 GPa. Dentin, less mineralized and less brittle, 3–4 in hardness, compensates for enamel and is necessary as a support.Unlike dentin and bone, enamel does not contain collagen. Instead, it has two unique classes of proteins called amelogenins and enamelins. While the role of these proteins is not fully understood, it is believed that they aid in the development of enamel by serving as a framework support, among other functions. *
Enamel strucuture
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Head Tail
* The pits are where the Tome Process sits * The head is located coronally and the tail is located cervically * The rods are a sinusoidal shape * The head of the rod is generally less susceptible to caries* It takes 4 ameloblasts to make 1 enamel rod * Each ameloblast will contribute to 4 rods
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Gnarled enamel in cuspal and incisal enamel
*Neonatal line (A) in enamel
Scanning electron microscope
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Enamel is covered by various structures in relation to the development of tooth:
Nasmyth's membrane or enamel cuticle, structure of embryological origin is composed of keratin which gives rise to the enamel organ. Acquired pellicle, structure acquired after tooth eruption is composed of food debris, calculus, dental plaque (organic film) .*
Enamel development
*Histological slide showing a developing tooth. The mouth would be in the area of space at the top of the picture.
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Enamel formation is part of the overall process of tooth development. When the tissues of the developing tooth are seen under a microscope, different cellular aggregations can be identified, including structures known as the enamel organ, dental lamina, and dental papilla. The generally recognized stages of tooth development are the bud stage, cap stage, bell stage, and crown, or calcification, stage. Enamel formation is first seen in the crown stage.
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Tomes Processes
A visual representation of the cell junction occurs…terminal bars. *
As in all human processes, the creation of enamel is complex, but can generally be divided into two stages.
The first stage, called the secretory stage, involves proteins and an organic matrix forming a partially mineralized enamel The second stage, called the maturation stage, completes enamel mineralization
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Histologic slide showing enamel formation
*In the secretary stage, ameloblasts are polarized columnar cells. In the rough endoplasmic reticulum of these cells, enamel proteins are released into the surrounding area and contribute to what is known as the enamel matrix, which is then partially mineralized by the enzyme alkaline phosphatase. When this first layer is formed, the ameloblasts move away from the dentin, allowing for the development of Tomes’ processes at the apical pole of the cell. Enamel formation continues around the adjoining ameloblasts, resulting in a walled area, or pit, that houses a Tomes’ process, and also around the end of each Tomes’ process, resulting in a deposition of enamel matrix inside of each pit. The matrix within the pit will eventually become an enamel rod, and the walls will eventually become interrod enamel. The only distinguishing factor between the two is the orientation of the calcium phosphate crystals. *
In the maturation stage, the ameloblasts transport substances used in the formation of enamel. Histologically, the most notable aspect of this phase is that these cells become striated, or have a ruffled border. These signs demonstrate that the ameloblasts have changed their function from production, as in the secretory stage, to transportation. Proteins used for the final mineralization process compose most of the transported material. The noteworthy proteins involved are amelogenins, ameloblastins, enamelins, and tuftelins. During this process, amelogenins and ameloblastins are removed after use, leaving enamelins and tuftelin in the enamel. By the end of this stage, the enamel has completed its mineralization.
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At some point before the tooth erupts into the mouth, but after the maturation stage, the ameloblasts are broken down. Consequently, enamel, unlike many other tissues of the body, has no way to regenerate itself. After destruction of enamel from decay or injury, neither the body nor a dentist can restore the enamel tissue. Enamel can be affected further by non-pathologic processes. The discoloration of teeth over time can result from exposure to substances such as tobacco, coffee, and tea. This is partly due to material building up in the enamel, but is also an effect of the underlying dentin becoming sclerotic.As a result, tooth color gradually darkens with age. Additionally, enamel becomes less permeable to fluids, less soluble to acid, and contains less water.
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Destruction of enamel
*The high mineral content of enamel, which makes this tissue the hardest in the human body, also makes it susceptible to a demineralization process which often occurs as dental caries, otherwise known as cavities. Demineralization occurs for several reasons, but the most important cause of tooth decay is the ingestion of sugars. Tooth cavities are caused when acids dissolve tooth enamel:Ca10(PO4)6(OH)2(s) + 8H+(aq) → 10Ca2+(aq) + 6HPO42-(aq) + 2H2O(l) *
Sugars from candies, soft drinks, and even fruit juices play a significant role in tooth decay, and consequently in enamel destruction. The mouth contains a great number and variety of bacteria, and when sucrose, the most common of sugars, coats the surface of the mouth, some intraoral bacteria interact with it and form lactic acid, which decreases the pH in the mouth. Then, the hydroxylapatite crystals of enamel dematerialize, allowing for greater bacterial invasion deeper into the tooth. The most important bacterium involved with tooth decay is Streptococcus mutans, but the number and type of bacteria varies with the progress of tooth destruction.
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Furthermore, tooth morphology dictates that the most common site for the initiation of dental caries is in the deep grooves, pits, and fissures of enamel. This is expected because these locations are impossible to reach with a toothbrush and allow for bacteria to reside there. When demineralization of enamel occurs, a dentist can use a sharp instrument, such as a dental explorer, and "feel a stick" at the location of the decay. As enamel continues to become less mineralized and is unable to prevent the encroachment of bacteria, the underlying dentin becomes affected as well. When dentin, which normally supports enamel, is destroyed by a physiologic condition or by decay, enamel is unable to compensate for its brittleness and breaks away from the tooth easily.
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Systemic conditions affecting enamel
*There are many different types of Amelogenesis imperfecta. The hypo calcification type, which is the most common, is an autosomal dominant condition that results in enamel that is not completely mineralized. Consequently, enamel easily flakes off the teeth, which appear yellow because of the revealed dentin.
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. The hypoplastic type is X-linked and results in normal enamel that appears in too little quantity, having the same effect as the most common type. Chronic bilirubin encephalopathy, which can result from erythroblastosis fetalis, is a disease which has numerous effects on an infant, but it can also cause enamel hypoplasia and green staining of enamel.
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Enamel hypoplasia is broadly defined to encompass all deviations from normal enamel in its various degrees of absence. The missing enamel could be localized, forming a small pit, or it could be completely absent. Erythropoietic porphyria is a genetic disease resulting in the deposition of porphyrins throughout the body. These deposits also occur in enamel and leave an appearance described as red in color and fluorescent.
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Fluorosis leads to mottled enamel and occurs from overexposure to fluoride. Tetracycline staining leads to brown bands on the areas of developing enamel. Children up to age 8 can develop mottled enamel from taking tetracycline. As a result, tetracycline is contraindicated in pregnant women. Celiac disease, a disorder characterized by an auto-immune response to gluten, also commonly results in demineralization of the enamel.
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