after use, leaving enamelins and tuftelin in the enamel. By the end of this stage, the enamel has completed its mineralization. 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. Enamel is covered by various structures in relation to the development of tooth: Nasmyth 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 loss The high mineral content of enamel, which makes this tissue the hardest in the human body, also makes it demineralize in a process that 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 fermentable carbohydrates. Tooth cavities are caused when acids dissolve tooth enamel: Enamel is also lost through tooth wear and enamel fractures. Ca10(PO4)6(OH)2(s) + 8H+(aq) → 10Ca2+(aq) + 6HPO42−(aq) + 2H2O(l) Sugars and acids from candies, soft drinks, and 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. The critical pH for tooth enamel is generally accepted to be pH 5.5. When acids are present and the critical pH is reached, the hydroxyapatite crystallites of enamel demineralize, 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. 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