dental anatomy dental anatomy dental anatomy is a field of anatomy dedicated to the study of human tooth structures. the development, appearance, and classification of teeth fall within its purview. (the function of teeth as they contact one another falls elsewhere, under dental occlusion.) tooth formation begins before birth, and the teeth's eventual morphology is dictated during this time. dental anatomy is also a taxonomical science: it is concerned with the naming of teeth and the structures of which they are made, this information serving a practical purpose in dental treatment. for the general description and information on human teeth, see teeth (human). for other uses, see tooth (disambiguation). usually, there are 20 primary ("baby") teeth and 32 permanent teeth, the last four being third molars or "wisdom teeth", each of which may or may not grow in. among primary teeth, 10 usually are found in the maxilla (upper jaw) and the other 10 in the mandible (lower jaw). among permanent teeth, 16 are found in the maxilla and the other 16 in the mandible. each tooth has specific distinguishing features. growing of tooth main article: tooth development radiograph of lower right (from left to right) third, second, and first molars in different stages of development. panoramic x-ray radiography of the teeth of a 64-year-old male. dental work performed mostly in uk/europe in last half of 20th century tooth development is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. although many diverse species have teeth, non-human tooth development is largely the same as in humans. for human teeth to have a healthy oral environment, enamel, dentin, cementum, and the periodontium must all develop during appropriate stages of fetal development. primary (baby) teeth start to form between the sixth and eighth weeks in utero, and permanent teeth begin to form in the twentieth week in utero. if teeth do not start to develop at or near these times, they will not develop at all. a significant amount of research has focused on determining the processes that initiate tooth development. it is widely accepted that there is a factor within the tissues of the first branchial arch that is necessary for the development of teeth. the tooth bud (sometimes called the tooth germ) is an aggregation of cells that eventually forms a tooth and is organized into three parts: the enamel organ, the dental papilla and the dental follicle. the enamel organ is composed of the outer enamel epithelium, inner enamel epithelium, stellate reticulum and stratum intermedium. these cells give rise to ameloblasts, which produce enamel and the reduced enamel epithelium. the growth of cervical loop cells into the deeper tissues forms hertwig's epithelial root sheath, which determines the root shape of the tooth. the dental papilla contains cells that develop into odontoblasts, which are dentin-forming cells. additionally, the junction between the dental papilla and inner enamel epithelium determines the crown shape of a tooth. the dental follicle gives rise to three important entities: cementoblasts, osteoblasts, and fibroblasts. cementoblasts form the cementum of a tooth. osteoblasts give rise to the alveolar bone around the roots of teeth. fibroblasts develop the periodontal ligaments which connect teeth to the alveolar bone through cementum. tooth development is commonly divided into the following stages: the bud stage, the cap, the bell, and finally maturation. the staging of tooth development is an attempt to categorize changes that take place along a continuum; frequently it is difficult to decide what stage should be assigned to a particular developing tooth. this determination is further complicated by the varying appearance of different histologic sections of the same developing tooth, which can appear to be different stages. identification nomenclature teeth are named by their sets and also arch, class, type, and side. teeth can belong to one of two sets of teeth: primary ("baby") teeth or permanent teeth. often, "deciduous" may be used in place of "primary", and "adult" may be used for "permanent". "succedaneous" refers to those teeth of the permanent dentition that replace primary teeth (incisors, canines, and premolars of the permanent dentition). succedaneous would refer to these teeth as a group. further, the name depends upon which arch the tooth is found in. the term, "maxillary", is given to teeth in the upper jaw and "mandibular" to those in the lower jaw. there are four classes of teeth: incisors, canines, premolars, and molars. premolars are found only in permanent teeth; there are no premolars in deciduous teeth. within each class, teeth may be classified into different traits. incisors are divided further into central and lateral incisors. among premolars and molars, there are first and second premolars, and first, second, and third molars. the side of the mouth in which a tooth is found may also be included in the name. for example, a specific name for a tooth may be "permanent maxillary left lateral incisor." numbering systems comparison of alphanumeric notation, palmer notation, iso 3950 (fdi) notation, universal numbering system, and paleoanthropology notation main article: dental notation there are several different dental notation systems for associating information to a specific tooth. the three most commons systems are the fdi world dental federation notation, universal numbering system (dental), and palmer notation method. the fdi system is used worldwide, and the universal is used widely in the united states. although the palmer notation was supposedly superseded by the fdi world dental federation notation, it overwhelmingly continues to be the preferred method used by dental students and practitioners in the united kingdom. it was originally termed the "zsigmondy system" after the austrian dentist adolf zsigmondy who developed the idea in 1861, using a zsigmondy cross to record quadrants of tooth positions. the palmer notation consists of a symbol (┘└ ┐┌) designating in which quadrant the tooth is found (from the dentist's perceptive) and a number indicating the position from the midline. permanent teeth are numbered 1 to 8, and primary teeth are indicated by a letter a to e. the universal numbering system uses a unique letter or number for each tooth. the uppercase letters a through t are used for primary teeth and the numbers 1 - 32 are used for permanent teeth. the tooth designated "1" is the right maxillary third molar and the count continues along the upper teeth to the left side. then the count begins at the left mandibular third molar, designated number 17, and continues along the bottom teeth to the right side. the fdi system uses a two-digit numbering system in which the first number represents a tooth's quadrant and the second number represents the number of the tooth from the midline of the face. for permanent teeth, the upper right teeth begin with the number, "1". the upper left teeth begin with the number, "2". the lower left teeth begin with the number, "3". the lower right teeth begin with the number, "4". for primary teeth, the sequence of numbers goes 5, 6, 7, and 8 for the teeth in the upper right, upper left, lower left, and lower right respectively. as a result, any given tooth has three different ways to identify it, depending on which notation system is used. the permanent right maxillary central incisor is identified by the number "8" in the universal system. in the fdi system, the same tooth is identified by the number "11". the palmer system uses the number and symbol, 1┘, to identify the tooth. further confusion may result if a number is given on a tooth without assuming (or specifying) a common notation method. since the number, "12", may signify the permanent left maxillary first premolar in the universal system or the permanent right maxillary lateral incisor in the fdi system, the notation being used must be clear to prevent confusion. in 1891 victor haderup devised a variant of eight tooth quadrant system in which plus (+) and minus (-) were used to differentiate between upper and lower quadrants, and between right and left quadrants (e.g., +1 = upper right central incisor; 1- = lower left central incisor). primary teeth were numbered as upper right (05+ to 01+), lower left (-01 to -05). this system is still used in denmark. anatomic landmarks crown and root the tooth is attached to the surrounding gingival tissue and alveolar bone (c) by fibrous attachments. the gingival fibers (h) run from the cementum (b) into the gingiva immediately apical to the junctional epithelial attachment and the periodontal ligament fibers (i), (j) and (k) run from the cementum into the adjacent cortex of the alveolar bone. the term "crown" of a tooth can be used in two ways. the term "anatomic crown" of a tooth refers to the area above the cementoenamel junction (cej) or "neck" of the tooth. it is completely covered in enamel. the term "clinical crown" often is convenient in referring to any part of the tooth visible in the mouth, but as a rule the unqualified term "crown" refers to the anatomic crown. the bulk of the crown is composed of dentine, with the pulp chamber within. the crown is enclosed within bone before the tooth erupts, but after eruption the crown is almost always visible in an anatomically normal and clinically healthy mouth. the anatomic root is found below the cementoenamel junction and is covered with cementum, whereas the clinical root is any part of a tooth not visible in the mouth. similarly, the anatomic root is assumed in most circumstances. dentin composes most of the root, which normally has pulp canals. the roots of teeth may be single in number (single-rooted teeth) or multiple. canines and most premolars, except for maxillary first premolars, usually have one root. maxillary first premolars and mandibular molars usually have two roots. maxillary molars usually have three roots. the tooth is supported in bone by an attachment apparatus, known as the periodontium, which interacts with the root. surfaces main article: glossary of dentistry surfaces that are nearest the cheeks or lips are referred to as either buccal (when found on posterior teeth nearest the cheeks) or labial (when found on anterior teeth nearest the lips). those nearest the tongue are known as lingual. lingual surfaces can also be described as palatal when found on maxillary teeth beside the hard palate. surfaces that aid in chewing are known as occlusal on posterior teeth and incisal on anterior teeth. surfaces nearest the junction of the crown and root are referred to as cervical, and those closest to the apex of the root are referred to as apical. the tissue surrounding apex is called periapical. mesial signifies a surface closer to the median line of the face, which is located on a vertical axis between the eyes, down the nose, and between the contact of the central incisors. surfaces further away from the median line are described as distal. cusp a cusp is an elevation on an occlusal surface of posterior teeth and canines. it contributes to a significant portion of the tooth's surface. canines have one cusp. maxillary premolars and the mandibular first premolars usually have two cusps. mandibular second premolars frequently have three cusps--- one buccal and two lingual. maxillary molars have two buccal cusps and two lingual cusps. a fifth cusp that may form on the maxillary first molar is known as the cusp of carabelli. mandibular molars may have five or four cusps. cingulum a cingulum is a convexity mesiodistally resembling a girdle, encircling the lingual surface at the cervical third, found on the lingual surface of anterior teeth. it is frequently identifiable as an inverted v-shaped ridge, and its appearance is comparable to a girdle. all anterior teeth are formed from four centers of development, referred to as lobes. three are located on the facial side of the tooth, and one on the lingual side. the cingulum forms from this lingual lobe of development. the majority of a lingual surface's cervical third is made up of the cingulum. on lower incisors, a cingulum usually is poorly developed or absent. maxillary canines have a large, well-developed cingulum, whereas the cingulum of mandibular canines is smoother and rounded. ridges ridges are any linear, flat elevations on teeth, and they are named according to their location. the buccal ridge runs cervico-occlusally in approximately the center of the buccal surface