...he teeth from harmful bacteria and changes in temperature from hot or cold food. Directly beneath the enamel is dentin, a hard, mineral material that is similar to human bone, only stronger. Dentin surrounds and protects the pulp, or core of the tooth. Pulp contains blood vessels, hich carry oxygen and nutrients to the tooth, and nerves, hich transmit pain and temperature sensations to the brain. The outer layer of the tooth that lies belo the gum line is cementum, a bonelike substance that anchors the tooth to the jabone.The visible portion of the tooth is called the cron. Projections on the top of each cron, used primarily for cheing and grinding, are called cusps. The portion of the tooth that lies beneath the gum line is the root. The periodontal ligament anchors the tooth in place ith small elastic fibers that connect the cementum in the root to a special socket in the jabone called the alveolus.ATypes of Human Teeth Adult humans typically have 32 teeth16 in the upper ja and 16 in the loer jathat fit together and ork in concert to che food. Teeth on the right side of each ja are usually identical to the teeth on the left side and matching teeth on opposite sides are referred to as sets, or pairs. Humans are heterodontsthat is, they have teeth of different sizes and shapes that serve different functions, such as tearing and grinding. In contrast, the homodont teeth found in many animals are all the same size and shape, and perform the same function.Humans have four types of teeth, each ith a specific size, shape, and function. Adult humans have eight incisors, located at the front of the mouthfour in the upper ja and four in the loer ja. Incisors have a sharp edge that is used to cut food. On either side of the incisors are the canines, named for their resemblance to the pointy fangs of dogs. The upper canines are sometimes called eyeteeth. There are to canines in each ja, and their primary role is to tear food. Behind the canines are the bicuspids, or premolars, flat teeth ith pronounced cusps that grind and mash food. There are to sets, or four bicuspids, in each ja. Behind the bicuspids are the molars, here the most vigorous cheing occurs. There are telve molarsthree sets in each jareferred to as the first, second, and third molars. Third molars are often called isdom teeth they developed thousands of years ago hen human diets consisted of mostly ra and unprocessed foods that required the extra cheing and grinding poer of a third set of molars. Today isdom teeth are not needed for cheing and, because they can crod other teeth, are often removed.BTooth Development Humans are diphyodontthat is, they develop to sets of teeth during their lives. The first set of teeth are the deciduous teeth, 20 small teeth also knon as baby teeth or milk teeth. Deciduous teeth start developing about to months after conception. By the time a child is six years old, a second set of 32 larger teeth, called permanent teeth, start to erupt, or push out of the gums, eventually replacing the deciduous teeth.Human tooth development occurs in stages. The hard tissue of the deciduous teeth, or the dentin, forms hile the fetus is in the omb. After the child is born, tooth enamel develops in stages. Front tooth enamel, for example, is usually complete around one month after birth, hile the enamel on the second molars is not completely developed until a child is about a year and a half old. hen the enamel is fully developed the tooth erupts. Front teeth usually erupt hen a child is from 6 to 12 months of age, second molars beteen 13 and 19 months old, and canines usually erupt at 19 months or older. The final stage of tooth development is root completion, a slo process that continues until the child is more than three years old.Around the age of six, the roots of deciduous teeth sloly dissolve as the developing permanent teeth start to push them out. Deciduous teeth eventually fall out and are replaced by the erupting permanent teeth. This begins a transitional phase of tooth development that takes place over the next 15 years. As baby teeth are pushed out by permanent teeth, the entire mouth and ja transform from their childhood shape to a more pronounced, adultlike structure. From age six to age nine, a childs permanent incisors, canines, and first molars erupt. The bicuspids erupt from age 10 to age 12, and the second molars come in by age 13. The third molars, or isdom teeth, usually erupt by the age of 21.hen human teeth gro to a certain size, the root essentially closes and the teeth stop groing. Closed-rooted teeth have narro root openings that are only big enough for the periodontal ligament, blood vessels, and a nerve. CDisorders of Human Teeth The three main diseases of human teeth are tooth decay, also called dental caries gum disease, or periodontal disease and problems ith tooth alignment, called malocclusions. Human teeth problems are treated or prevented by dentists, professionals ho are specially trained to practice dentistry.Tooth decay affects approximately 90 percent of all children by the time they are 14 years old. Tooth decay begins hen bacteria are passed from mothers or caregivers to children beteen their first and second birthdays. hen these bacteria are exposed to sugars commonly found in foods, the bacteria produce harmful acids that attack tooth enamel. Left unchecked, the acid eats holes in the enamel and forms cavities of tooth decay. Most tooth decay forms in the deep grooves on the cheing surfaces of the molars, called pits and fissures. Daily tooth brushing and proper dental care help prevent and reduce tooth decay. Dentists use preventive treatments to reduce the risk of tooth decay clear plastic coatings painted on the teeth, called dental sealants, and applications of the mineral fluoride, hich fortifies tooth enamel, are to such treatments. Fluoride is also added to public ater supplies in a process called fluoridation, hich benefits more than 150 million Americans.Gum disease, or periodontal disease, is a progressive condition that orsens ith age. Gum disease occurs hen bacteria eat aay at gum tissue, causing it to pull aay from the teeth. This space beteen the tooth and gum, called a periodontal pocket, traps even more bacteria. Gum disease develops in to stages. Gingivitis, the early stage, causes red, sollen gums that bleed easily. Gingivitis can be eliminated through good oral hygiene and dental care. If not treated, gingivitis can progress to periodontitis, hen bacteria attack the bone supporting the teeth. To treat periodontitis, dentists may have to surgically cut out the infected portion of the gum so the bacteria can be removed.Malocclusionsteeth that are croded, crooked, or out of alignmentmake it more difficult to clean teeth, hich can lead to other oral health problems such as tooth decay and gum disease. Many of these disorders start to appear beteen the ages of 6 and 12, hen permanent teeth begin to erupt. Generally, malocclusions result hen ...
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