The human teeth function to mechanically break down items of food by cutting and crushing them in preparation for swallowing and digesting. Humans have four types of teeth: incisors, canines, premolars, and molars, which each have a specific function. The incisors cut the food, the canines tear the food and the molars and premolars crush the food. The roots of teeth are embedded in the maxilla or the mandible and are covered by gums. Teeth are made of multiple tissues of varying density and hardness.
Dentin or dentine is a calcified tissue of the body and, along with enamel, cementum, and pulp, is one of the four major components of teeth. It is usually covered by enamel on the crown and cementum on the root and surrounds the entire pulp. By volume, 45% of dentin consists of the mineral hydroxylapatite, 33% is organic material, and 22% is water. Yellow in appearance, it greatly affects the color of a tooth due to the translucency of enamel. Dentin, which is less mineralized and less brittle than enamel, is necessary for the support of enamel. Dentin rates approximately 3 on the Mohs scale of mineral hardness. There are two main characteristics which distinguish dentin from enamel: firstly, dentin forms throughout life; secondly, dentin is sensitive.
The periodontium is the specialized tissues that both surround and support the teeth, maintaining them in the maxillary and mandibular bones. The word comes from the Greek terms περί peri-, meaning "around" and -odont, meaning "tooth". Literally taken, it means that which is "around the tooth". Periodontics is the dental specialty that relates specifically to the care and maintenance of these tissues. It provides the support necessary to maintain teeth in function. It consists of four principal components, namely:
The periodontal ligament, commonly abbreviated as the PDL, is a group of specialized connective tissue fibers that essentially attach a tooth to the alveolar bone within which it sits. It inserts into root cementum one side and onto alveolar bone on the other.
Tooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. For human teeth to have a healthy oral environment, all parts of the tooth must develop during appropriate stages of fetal development. Primary (baby) teeth start to form between the sixth and eighth week of prenatal development, and permanent teeth begin to form in the twentieth week. If teeth do not start to develop at or near these times, they will not develop at all, resulting in hypodontia or anodontia.
In embryology and prenatal development, the dental papilla is a condensation of ectomesenchymal cells called odontoblasts, seen in histologic sections of a developing tooth. It lies below a cellular aggregation known as the enamel organ. The dental papilla appears after 8–10 weeks intra uteral life. The dental papilla gives rise to the dentin and pulp of a tooth.
The dental follicle, also known as dental sac, is made up of mesenchymal cells and fibres surrounding the enamel organ and dental papilla of a developing teeth. It is a vascular fibrous sac containing the developing tooth and its odontogenic organ. The dental follicle (DF) differentiates into the periodontal ligament. In addition, it may be the precursor of other cells of the periodontium, including osteoblasts, cementoblasts and fibroblasts. They develop into the alveolar bone, the cementum with Sharpey's fibers and the periodontal ligament fibers respectively. Similar to dental papilla, the dental follicle provides nutrition to the enamel organ and dental papilla and also have an extremely rich blood supply.
The oral mucosa is the mucous membrane lining the inside of the mouth and consists of stratified squamous epithelium termed oral epithelium and an underlying connective tissue termed lamina propria. The oral cavity has sometimes been described as a mirror that reflects the health of the individual. Changes indicative of disease are seen as alterations in the oral mucosa lining the mouth, which can reveal systemic conditions, such as diabetes or vitamin deficiency, or the local effects of chronic tobacco or alcohol use. The oral mucosa tends to heal faster and with less scar formation compared to the skin. The underlying mechanism remains unknown but research suggest that extracellular vesicles might be involved.
A cementoblast is a biological cell that forms from the follicular cells around the root of a tooth, and whose biological function is cementogenesis, which is the formation of cementum. The mechanism of differentiation of the cementoblasts is controversial but circumstantial evidence suggests that an epithelium or epithelial component may cause dental sac cells to differentiate into cementoblasts, characterised by an increase in length. Other theories involve Hertwig epithelial root sheath (HERS) being involved.
The Hertwig epithelial root sheath (HERS) or epithelial root sheath is a proliferation of epithelial cells located at the cervical loop of the enamel organ in a developing tooth. Hertwig epithelial root sheath initiates the formation of dentin in the root of a tooth by causing the differentiation of odontoblasts from the dental papilla. The root sheath eventually disintegrates with the periodontal ligament, but residual pieces that do not completely disappear are seen as epithelial cell rests of Malassez (ERM). These rests can become cystic, presenting future periodontal infections.
The 'formation of Cementum' is also known as "Cementogenesis", one of the three mineralized substances of a tooth. Cementum covers the roots of teeth and serves to anchor gingival and periodontal fibers of the periodontal ligament by the fibers to the alveolar bone.
The junctional epithelium (JE) is that epithelium which lies at, and in health also defines, the base of the gingival sulcus. The probing depth of the gingival sulcus is measured by a calibrated periodontal probe. In a healthy-case scenario, the probe is gently inserted, slides by the sulcular epithelium (SE), and is stopped by the epithelial attachment (EA). However, the probing depth of the gingival sulcus may be considerably different from the true histological gingival sulcus depth.
Hypercementosis is an idiopathic, non-neoplastic condition characterized by the excessive buildup of normal cementum on the roots of one or more teeth. A thicker layer of cementum can give the tooth an enlarged appearance, which mainly occurs at the apex or apices of the tooth.
In tooth development, the hyaline layer of Hopewell-Smith is the most peripheral layer of initially unmineralized dentin that forms immediately subjacent to the cementodentinal junction (CDJ). It eventually mineralizes, but not before the rest of the dentin is already mineralized. It is 0.5-0.8 µm thick and contains enamel matrix-like protein as well as the proteins one would expect to find in dentin. It is into this hyaline layer that the initial fibers of the periodontal ligament embed themselves.
In anatomy the apical foramen is the opening at the apex of the root of a tooth, through which the nerve and blood vessels that supply the dental pulp pass. Thus it represents the junction of the pulp and the periodontal tissue.
Pulp stones are nodular, calcified masses appearing in either or both the coronal and root portion of the pulp organ in teeth. Pulp stones are not painful unless they impinge on nerves.
Tooth ankylosis is the pathological fusing of cementum or dentine of a tooth root to the alveolar bone. Ankylosis of teeth is uncommon, it more often occurs in deciduous teeth than permanent teeth.
Tooth discoloration is abnormal tooth color, hue or translucency. External discoloration is accumulation of stains on the tooth surface. Internal discoloration is due to absorption of pigment particles into tooth structure. Sometimes there are several different co-existent factors responsible for discoloration.
Hard tissue is tissue which is mineralized and has a firm intercellular matrix. The hard tissues of humans are bone, tooth enamel, dentin, and cementum. The term is in contrast to soft tissue.
