One of the four major tissues of the human body that makes up the tooth in animals is tooth enamel. It is the hardest part of human body. It covers the crown and forms the visible part of the tooth. It is a very hard structure and the colour may vary from white to off-white. It is a highly mineralized structure and it aims at the protection of the tooth to avoid the degradation of the tooth by the acids other minerals or substances present in food. In some cases, the enamel is not formed; this leads to the visibility of the dentin.
According to most researchers, the formation of tooth enamel in animals is similar to that of humans. Whereas the distribution of minerals is different in monkeys, pigs, humans, and dogs. Let us learn more about the hardest part of our body.
Enamel does not consist of blood or nerve supply within it. The enamel’s hardness enables the teeth to withstand the blunt and heavy masticatory forces. Enamel is so hard because it is primarily composed of inorganic materials such as about 95% to 98% of calcium and phosphate ions that form the structure of strong hydroxyapatite crystals. But these are not pure crystals, because they're carbonated and they contain trace minerals such as lead, strontium, magnesium, and fluoride. These factors make “biological hydroxyapatite” more soluble than pure hydroxyapatite.
Approximately one % to twenty of enamel is formed by the usage of organic materials, particularly with the enamel-specific proteins called enamelins, which have a high affinity for binding hydroxyapatite crystals. Water makes up the rest of the enamel, accounting for about four % of its composition.
The inorganic, organic, and water components of enamel are highly organized: many carbonated hydroxyapatite crystals are arranged in long, thin structures, these structures are called rods that are four micrometres to eight micrometres in diameter. It is estimated that the amount of rods during a tooth ranges from five million within the lower lateral incisor to twelve million within the upper first molar. In general, rods extend at right angles from the junction of dento enamel to the tooth surface. Surrounding each rod is a rod sheath that is made up of a protein matrix of enamelins. The area that is present in between the rods is named interrod cement or interrod enamel. Thus enamel is the hardest tissue in human body.
Where the crystals don't form between the rods then space occurs. Typically these spaces are called pores, they contribute to enamel’s permeability, which allows the movement of fluid and diffusion to occur, but they also cause variations in density and hardness in the tooth, which can create spots that are more susceptible to demineralization or the loss of calcium and phosphate ions when oral pH becomes too acidic and drops below the level of 5.5. In demineralization, the crystalline structure shrinks in size, while pores get enlarged.
Enamel teeth are formed by epithelial cells called ameloblasts. Just before a tooth erupts from the gums, the ameloblasts are broken down, removing enamel’s ability to regenerate or repair itself. This means that when the enamel is broken by decay or injury, it can't be restored beyond the traditional course of remineralization. When a tooth erupts, it's also not fully mineralized. To completely mineralize the tooth, calcium, phosphorus, and fluoride ions are taken up from saliva to add a layer of 10 micrometres to 100 micrometres of enamel over time.
There are conditions that can affect the enamel formation and thus increases the risk of caries. These include the genetic disease amelogenesis imperfecta, during which enamel isn't completely mineralized and flakes off easily, exposing softer dentin to cariogenic bacteria. Other conditions are linked with increased enamel demineralization, like esophageal reflux disease (GERD) and disorder.
Structure of Hardest Part of Teeth
The basic unit of enamel is known as an enamel rod. Measuring four to eight micrometre in diameter, formerly an enamel rod is known as an enamel prism, it is a tightly packed mass of hydroxyapatite crystals in an organized pattern. When observing the cross-section, the enamel is best compared to a keyhole, with the highest, or head, oriented towards the crown of the tooth, and therefore the bottom, or tail, oriented toward the root of the tooth.
The arrangement of these crystals within each of the enamel rods is highly complex. Both ameloblasts are the cells that initiate enamel formation and Tomes' processes affect the pattern of the crystals. Enamel crystals present in the head of the enamel rod are oriented parallel to the long axis of the rod. When found within the tail of the enamel rod, the orientation of the crystals diverges slightly for about 65 degrees from the long axis.
The arrangement of enamel rods is understood more clearly compared to their internal structure. Enamel rods are found in rows alongside the tooth, and within each row, the long axis of the enamel rod is usually perpendicular to the underlying dentin. In permanent teeth, the enamel rods are present near the cementoenamel junction (CEJ) that tilt slightly towards the root of the tooth. Understanding enamel orientation is very important in restorative dentistry because enamel unsupported by the underlying dentin is prone to fracture.
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Microstructure of enamel
Nanostructure of enamel
There are Several Clinical Significances Some of Them Include:
Hypoplasia Enamel: If the formation of enamel happens with lesser quality than that of the normal one then this leads to the condition called hypoplasia enamel. It appears as a white spot, pits, grooves, thin and chipped part of the enamel. In some severe cases, the enamel will not develop completely.
Bulimia: It can cause the erosion of the enamel that ultimately leads to the decay of the tooth. Due to the source of acids such as vomiting or binge eating can lead to decay. Frequent vomiting can erode the enamel and form cavities.
Enamel plays a major role to protect the health of the teeth. It protects us daily from wear and tear of the outer layer present on the teeth. It also helps to feel the extreme temperature conditions such as extreme hot or cold when we eat or drink. It also avoids the acids or chemicals that can damage the teeth.