Teeth, tooth rows. Groups of teeth, anatomotopografy. Physiological and pathological types of bite
ANATOMY OF THE TEETH
By the structure the teeth are most close to the bone tissue, but exceed its hardness and durability. Three parts are distinguished in the tooth. The part which protrudes over the alveolus is called the crown. The part of the tooth hidden in the alveolus is called the root; the root is usually longer than crown almost twice. The border between the crown and root is called the neck.
The substance of the tooth basically consists of dentine, having bone-like structure and covered with enamel in the crown part and with cementum- in the root one. There is a cavity inside the tooth filled by a friable connecting tissue rich in vessels and nerves. This connecting tissue is called the pulp. In the crown part the size of this cavity is bigger, it is called the pulp chamber. The chamber becomes narrowed towards the root, getting a character of the canal. The pulp chamber repeats partly the external form of the tooth.
The following surfaces are distinguished in the crown of each tooth:
1. External, or vestibular(Latin: vestibulum – a threshold – a part of the mouth between the teeth and lips), participating in formation of the convex side of the dental arch. At the frontal teeth it is turned aside lips and consequently it is called labial, and at the lateral – aside cheeks and is called buccal
2. Internal, ororal, turned aside the palate, is called palatal on the upper teeth, and lingual – on the lower ones.
3) Surfaces of the teeth contact are called aproximal. The side turned forward is called medial, and turned backward–distal .
4) The surface participating in chewing or nibbling of food, is called masticatory (occlusal)at the lateral teeth and cutting edge – at the anterior ones.
The teeth contributing to grinding of food, have a wide masticatory surface with 3-5 tubers; these are big molars which were called masticatory teeth, or molars. The small molars contributing to crushing of food, are supplied with two tubers. These teeth are called premolars. The teeth, which role in chewing is reduced only to gripping and nibbling of food, have a masticatory surface in the form of a narrow edge, thanks to that they received the name of incisors. The teeth called canines have a narrow cutting edge in the form of a triangle.
During human life the teeth erupt twice. The first teeth are called decidious (milk) teeth. They erupt 20 iumber and, from 6-7 years of age, are replaced by permanent ones. Permanent teeth are 32 iumber, 16 on each jaw: 4 incisors, 2 canines, 4 premolars, 6 molars, of which the last two are referred to as wisdom teeth. The teeth are paired organs and located symmetrically in the jaw.
For marking teeth the dental formula is used. There are two variants of the widespread dental formulas. The standard formula is accepted on the territory of Ukraine consisting in figure marking of each tooth rendering its serial position in a dentition in relation to the midline. The right side is separated from the left one by a vertical line, and the upper dentition from the lower – by horizontal line:
8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 8
8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 8
In the WHO (World health organization) formula each tooth is marked by double figure. The second figure, as well as in the previous case, means a serial number of the tooth from the midline. The first figure means the angle of the maxillodental system.
1 – the right upper angle of constant bite.
2 – the left upper angle of constant bite.
3 – the left lower angle of constant bite.
4 – the right lower angle of constant bite.
5 – the right upper angle of milk bite.
6 – the left upper angle of milk bite.
7 – the left lower angle of milk bite.
8 – the right lower angle of milk bite.
So, for example, the formula presented above, would look in the WHO variant:
18 17 16 15 14 13 12 11 21 22 23 24 25 26 27 28
48 47 46 45 44 43 42 41 31 32 33 34 35 36 37 38
Separate teeth by their structure differ from each other by a number of peculiarities which should be known by dental technicians for correct modeling, selection and anatomic statement of a denture.
The shape of the teeth.
Incisors.All incisors have crowns of chisel-like shape. The labial surface of the upper incisors is slightly convex in the longitudinal direction and a little more in the transversal one. The palatal surface is closer to the cutting edge, flat or concave, and aside the neck is thickened and forms the convexity sometimes much expressed and called dental tubercle.
Roots of the upper incisors are massive enough and straight. Distinctive signs between the upper incisors of the right and left side are clearly marked. The medial half of the labial surface is more convex than distal; the medial angle of the cutting edge is straight, and distal – is rounded off. The upper lateral incisors differ from central ones by smaller size.
The lower incisors have the same shape as upper ones, but are considerably narrower. According to it their roots are also less flattened from the sides. The size of the lower lateral incisors is more than the central ones. The cutting edges of the lower central incisors are straight, and distal angles are a little rounded off in the lateral incisors.
Canines are the most powerful teeth of all group of the anterior teeth. They are located on the border between the anterior and lateral teeth and experience the masticatory pressure directed at different planes. Their roots are more massive and longer than in other anterior teeth. The labial surface of the canines is sharply convex, especially closer to the neck, and divided by the longitudinal protuberance going from the angle top at the cutting edge into two facets: medial and distal. The medial facet is narrower than distal and more convex in the transversal than in the longitudinal direction. The lingual surface is also convex and divided by the longitudinal protuberance into two slopes: medial and distal. The cutting edge of the canine is of triangular form, and the medial side is shorter than the distal; the top of the triangle is referred to the cutting tuber.Signs of the right or left side of the canines are clearly marked and determined by the cutting edge and facets on the labial side.
The lower canines are similar to the upper ones, but they are of less size, unlike the upper incisors their lingual surface is flat or slightly concave therefore their dental tubercle is expressed less distinctly.
The upper premolars are convex, both by labial and palatal sides in the longitudinal and even more in the transversal direction. The buccal surface of the first premolar is wider and higher than the lingual one and consequently the buccal tuber stands out above the crown level more than the lingual one. The masticatory surface has a quadrangular form, and the lateral side is wider than internal, and angles are slightly rounded off. There are two tubercles on the masticatory surface divided by a transversal sulcus. In the first premolar the sulcus is not symmetrical, and is closer to the palatal tuber that’s why the buccal tuber is bigger on the masticatory surface than on the lingual.
The second premolar differs from the first one by equally expressed tubers.The lower premolars differ from the upper ones both in the shape and size. Their crown in a cross-section looks like the outline of a circle. The lingual tuber of the first lower premolar is poorly developed, buccal one is rounded off and inclined aside the oral cavity. Facets on the buccal side are well expressed, and medial facet is narrower than distal one that allows to distinguish easily the teeth of the right and left side.
The second lower premolars are larger than the first ones, their tubers are equally developed, and the form of the masticatory surface comes nearer to a square.
The premolars have one root, except for the first upper one which in most cases has two roots – buccal and palatal. Sometimes two roots may be in the second upper premolar.
The upper molars have massive crowns of diamond shape, and medially- buccal and distal- palatal angles are sharp, and opposite to them are blunt. Their palatal surface is more convex than buccal. On the buccal surface there are two convexities located in the longitudinal direction (according to two buccal tubers on the masticatory surface), and one transverse convex is located about the middle of the tooth, a little closer to the neck.
On the masticatory surface there are four tubers, the largest is medially-palatal. The palatal tubers are rounded off, and buccal are pointed and turned aside.
The second upper molars are similar in the shape to the first ones, but a little smaller. The upper molars have three roots: two buccal and one palatal.
The lower molars have a cubiform. Their buccal surface is convex both in the longitudinal and transversal direction and is more convex than lingual. The greatest convex is located in the lower third of the tooth (close to the neck).
There are five tubers on the masticatory surface of the first lower molar: three buccal and two lingual. The buccal tubers are rounded off, and lingual ones are sharper. The largest tuber is medially-buccal.
The second lower molar is a little smaller than the first one, and also has four tubers of almost identical size.
The lower molars have two roots: medial and distal. Wisdom teeth are of irregular shape and sometimes are absent. The amount of their roots is variable.
ANATOMY OF DENTAL ARCHES.
Dental arches are teeth and alveolar processes divided by bone septums into separate cells. A conditional line made through certain surfaces of the teeth, alveolar processes, or bone sockets is also called a dental arch. According to this we distinguish: basal dental arch (passes through the tooth neck), occlusal (passes through the occlusal surfaces and cutting edges of the teeth), vestibular dental arch (through equators of the teeth on the vestibular surface), oral dental arch (through equators of the teeth on the oral surface).
Sagittal compensatory curve.A number of occlusal surfaces of the masticatory teeth and their arrangement in the dentition form the curve having sagittal direction and calling occlusal curve Speie, named by the author who has described this phenomenon for the first time.
This curve on the mandible is concave, and on the contrary, on the maxilla it is convex from top to bottom. Uniqueness of this curve consists in pushing forward the mandible before contact of the incisors with cutting edges (anterior occlusion), at least two contacts of the masticatory teeth (on the right and left) are kept. That is there always will be triangle contact. This feature of the curve is called Bonwill triangle. This curve is a part of the conditional circle which centre is in the eye-socket. The circle radius as well as Speie curve is approximately 60 – 70 mm. Expressiveness of this curve depends on a degree of overlapping of the anterior teeth. The more frontal overlapping, the more sharply the dental arch is bent in the sagittal direction. The Speie curve is more flat, the smaller is the angle between a tangent to it and a horizontal plane.
Occlusal curve.It begins at the medially – buccal tuber ofthe first premolar and ends at the distal tuber of the third molar of the mandible. This curve is caused by a deviation of roots to the lateral sides. Accordingly crowns on the maxilla disperse fanlikely, and roots converge in one point. This phenomenon gives additional lateral stability to a dentition. Besides, each tooth gets additional fixation from its neighbour.
Transversal (cross-section) compensatory curves.Simultaneously with presence of the sagittal occlusal curve on each masticatory tooth there are also tubers arranged on the curve in the transversal direction. These curves are called transversal compensatory curves as they provide contacts of dental tubers in lateral movements of the mandible. They are formed as a result of different levels of the buccal and palatal tubers, both on the maxilla and mandible. Such position accounts for inclination of the masticatory tooth crowns towards inside on the mandible, and towards outside – on the maxilla.
Thus, sagittal curvature of the dental arches gives the masticatory teeth stability in the anteroposterior direction, and the inclination of crownsof these teeth in the buccal-palatal direction creates conditions for their stability in the lateral direction. It should be noted that stability of the dental arches is also supported by thickenings (counterforce) of the maxillary bones, by internal and external oblique lines on the mandible, and the thickening going to the zygomatic arch – on the maxilla.
Teeth (singular, tooth) are structures found in the jaws (or mouths) of many vertebrates that are used to tear, scrape, and chew food. Some animals, particularly carnivores, also use teeth for hunting or defense. The roots of teeth are covered by gums.
Teeth are among the most distinctive (and long-lasting) features of mammal species. Paleontologists use teeth to identify fossil species and determine their relationships. The shape of an animal’s teeth is related to its diet. For example, plant matter is hard to digest, so herbivores have many molars for chewing. Carnivores, on the other hand, need canines to kill and tear meat.
Humans are diphyodont, meaning that they develop two sets of teeth. The first set (the “baby,” “milk,” “primary” or “deciduous” set) normally starts to appear at about six months of age, although some babies are born with one or more visible teeth, known as Neonatal teeth. Normal tooth eruption at about six months is known as teething and can be quite painful for an infant.
Some animals develop only one set of teeth (monophyodont) while others develop many sets (polyphyodont). Sharks, for example, grow a new set of teeth every two weeks to replace worn teeth. Rodent incisors grow and wear away continually through gnawing, maintaining relatively constant length. Some rodent species, such as the sibling vole and the guinea pig, have continuously growing molars in addition to incisors.
Anatomy
Dental anatomy is a field of anatomy dedicated to the study of tooth structures. The development, appearance, and classification of teeth fall within its purview, though dental occlusion, or contact among teeth, does not. Dental anatomy is also a taxonomical science as it is concerned with the naming of teeth and their structures. This information serves a practical purpose for dentists, enabling them to easily identify teeth and structures during treatment.
The anatomic crown of a tooth is the area covered in enamel above the cementoenamel junction (CEJ). The majority of the crown is composed of dentin with the pulp chamber in the center. The crown is within bone before eruption. After eruption, it is almost always visible. The anatomic root is found below the cementoenamel junction and is covered with cementum. As with the crown, dentin composes most of the root, which normally have pulp canals. A tooth may have multiple roots or just one root. Canines and most premolars, except for maxillary (upper) first premolars, usually have one root. Maxillary first premolars and mandibular molars usually have two roots. Maxillary molars usually have three roots. Additional roots are referred to as supernumerary roots.
Humans usually have 20 primary teeth (also called deciduous, baby, or milk teeth) and 32 permanent teeth. Among primary teeth, 10 are found in the maxilla and the other 10 in the mandible. Teeth are classified as incisors, canines, and molars. In the primary set of teeth, there are two types of incisors, centrals and laterals, and two types of molars, first and second. All primary teeth are replaced with permanent counterparts except for molars, which are replaced by permanent premolars. Among permanent teeth, 16 are found in the maxilla with the other 16 in the mandible. The maxillary teeth are the maxillary central incisor, maxillary lateral incisor, maxillary canine, maxillary first premolar, maxillary second premolar, maxillary first molar, maxillary second molar, and maxillary third molar. The mandibular teeth are the mandibular central incisor, mandibular lateral incisor, mandibular canine, mandibular first premolar, mandibular second premolar, mandibular first molar, mandibular second molar, and mandibular third molar. Third molars are commonly called “wisdom teeth” and may never erupt into the mouth or form at all. If any additional teeth form, for example, fourth and fifth molars, which are rare, they are referred to as supernumerary teeth.
Most teeth have identifiable features that distinguish them from others. There are several different notation systems to refer to a specific tooth. The three most commons systems are the FDI World Dental Federatiootation, the universal numbering system, and Palmer notation method.
Enamel
Enamel is the hardest and most highly mineralized substance of the body and is one of the four major tissues which make up the tooth, along with dentin, cementum, and dental pulp. It is normally visible and must be supported by underlying dentin. Ninety-six percent of enamel consists of mineral, with water and organic material composing the rest. The normal color of enamel varies from light yellow to grayish white. At the edges of teeth where there is no dentin underlying the enamel, the color sometimes has a slightly blue tone. Since enamel is semitranslucent, the color of dentin and any restorative dental material underneath the enamel strongly affects the appearance of a tooth. Enamel varies in thickness over the surface of the tooth and is often thickest at the cusp, up to 2.5 mm, and thinnest at its border, which is seen clinically as the cementoenamel junction (CEJ).
Enamel’s primary mineral is hydroxyapatite, which is a crystalline calcium phosphate. The large amount of minerals in enamel accounts not only for its strength but also for its brittleness. Dentin, which is less mineralized and less brittle, compensates for enamel and is necessary as a support. Unlike dentin and bone, enamel does not contain collagen. Instead, it has two unique classes of proteins called amelogenins and enamelins. While the role of these proteins is not fully understood, it is believed that they aid in the development of enamel by serving as framework support among other functions.
Dentin
Dentin is the substance between enamel or cementum and the pulp chamber. It is secreted by the odontoblasts of the dental pulp. The formation of dentin is known as dentinogenesis. The porous, yellow-hued material is made up of 70% inorganic materials, 20% organic materials, and 10% water by weight. Because it is softer than enamel, it decays more rapidly and is subject to severe cavities if not properly treated, but dentin still acts as a protective layer and supports the crown of the tooth.
Dentin is a mineralized connective tissue with an organic matrix of collagenous proteins. Dentin has microscopic channels, called dentinal tubules, which radiate outward through the dentin from the pulp cavity to the exterior cementum or enamel border. The diameter of these tubules range from 2.5 μm near the pulp, to 1.2 μm in the midportion, and 900 nm near the dentino-enamel junction. Although they may have tiny side-branches, the tubules do not intersect with each other. Their length is dictated by the radius of the tooth. The three dimensional configuration of the dentinal tubules is genetically determined.
Cementum
Cementum is a specialized bony substance covering the root of a tooth. It is approximately 45% inorganic material (mainly hydroxyapatite), 33% organic material (mainly collagen) and 22% water. Cementum is excreted by cementoblasts within the root of the tooth and is thickest at the root apex. Its coloration is yellowish and it is softer than either dentin or enamel. The principal role of cementum is to serve as a medium by which the periodontal ligaments can attach to the tooth for stability. At the cementoenamel junction, the cementum is acellular due to its lack of cellular components, and this acellular type covers at least ⅔ of the root. The more permeable form of cementum, cellular cementum, covers about ⅓ of the root apex.
Pulp
The dental pulp is the central part of the tooth filled with soft connective tissue. This tissue contains blood vessels and nerves that enter the tooth from a hole at the apex of the root. Along the border between the dentin and the pulp are odontoblasts, which initiate the formation of dentin. Other cells in the pulp include fibroblasts, preodontoblasts, macrophages and T lymphocytes. The pulp is commonly called “the nerve” of the tooth.
Radiograph of lower right third, second, and first molars in different stages of development.
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.
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.
The tooth bud (sometimes called the tooth germ) is an aggregation of cells that eventually forms a tooth. It 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 a tooth’s root shape. 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.
Eruption
Tooth eruption in humans is a process in tooth development in which the teeth enter the mouth and become visible. Current research indicates that the periodontal ligaments play an important role in tooth eruption. Primary teeth erupt into the mouth from around six months until two years of age. These teeth are the only ones in the mouth until a person is about six years old. At that time, the first permanent tooth erupts. This stage, during which a person has a combination of primary and permanent teeth, is known as the mixed stage. The mixed stage lasts until the last primary tooth is lost and the remaining permanent teeth erupt into the mouth.
There have been many theories about the cause of tooth eruption. One theory proposes that the developing root of a tooth pushes it into the mouth. Another, known as the cushioned hammock theory, resulted from microscopic study of teeth, which was thought to show a ligament around the root. It was later discovered that the “ligament” was merely an artifact created in the process of preparing the slide. Currently, the most widely held belief is that the periodontal ligaments provide the main impetus for the process.
Histologic slide of tooth erupting into the mouth.
A: tooth
B: gingiva
C: bone
D: periodontal ligaments
The periodontium is the supporting structure of a tooth, helping to attach the tooth to surrounding tissues and to allow sensations of touch and pressure. It consists of the cementum, periodontal ligaments, alveolar bone, and gingiva. Of these, cementum is the only one that is a part of a tooth. Periodontal ligaments connect the alveolar bone to the cementum. Alveolar bone surrounds the roots of teeth to provide support and creates what is commonly called an alveolus, or “socket”. Lying over the bone is the gingiva, which is readily visible in the mouth.
Periodontal ligaments
The periodontal ligament is a specialized connective tissue that attaches the cementum of a tooth to the alveolar bone. This tissue covers the root of the tooth within the bone. Each ligament has a width of 0.15 – 0.38 mm, but this size decreases over time. The functions of the periodontal ligaments include attachment of the tooth to the bone, support for the tooth, formation and resorption of bone during tooth movement, sensation, and eruption. The cells of the periodontal ligaments include osteoblasts, osteoclasts, fibroblasts, macrophages, cementoblasts, and epithelial cell rests of Malassez. Consisting of mostly Type I and III collagen, the fibers are grouped in bundles and named according to their location. The groups of fibers are named alveolar crest, horizontal, oblique, periapical, and interradicular fibers. The nerve supply generally enters from the bone apical to the tooth and forms a network around the tooth toward the crest of the gingiva. When pressure is exerted on a tooth, such as during chewing or biting, the tooth moves slightly in its socket and stretches the periodontal ligaments. The nerve fibers can then send the information to the central nervous system for interpretation.
Alveolar bone
The alveolar bone is the bone of the jaw which forms the alveolus around teeth. Like any other bone in the human body, alveolar bone is modified throughout life. Osteoblasts create bone and osteoclasts destroy it, especially if force is placed on a tooth. As is the case when movement of teeth is attempted through orthodontics, an area of bone under compressive force from a tooth moving toward it has a high osteoclast level, resulting in bone resorption. An area of bone receiving tension from periodontal ligaments attached to a tooth moving away from it has a high number of osteoblasts, resulting in bone formation.
The gingiva (“gums”) is the mucosal tissue that overlays the jaws. There are three different types of epithelium associated with the gingiva: gingival, junctional, and sulcular epithelium. These three types form from a mass of epithelial cells known as the epithelial cuff between the tooth and the mouth. The gingival epithelium is not associated directly with tooth attachment and is visible in the mouth. The junctional epithelium, composed of the basal lamina and hemidesmosomes, forms an attachment to the tooth. The sulcular epithelium is nonkeratinized stratified squamous tissue on the gingiva which touches but is not attached to the tooth. This leaves a small potential space between the gingiva and tooth which can collect bacteria, plaque, and calculus.
The Role Of Saliva In Oral And General Health
Saliva plays an important role in oral health. Saliva monitors, regulates and maintains the integrity of the oral hard and soft tissues, protects oral tissues against disease and plays an important role in the preservation of oral homeostasis.
Saliva is important to the general health. Saliva protects the oral and para-oral tissues against immunologic injury and bacterial, fungal and viral infections, buffers harmful oral and oesophageal acids, guards against gastroesophageal reflux disease, lubricates the delicate oral mucous membranes, contributes to speech, osculation and taste, to the ingestion, preparation, swallowing and digestion of foods, facilitates oral and oesophageal clearance and enhances the feeling of general wellness.
The importance in stimulating and maintaining salivary flow serves to protect against disease processes. The presence of salivary dysfunction is indicative of both oral and systemic diseases. Persistent dry mouth is a very common symptom and is generally caused by systemic conditions. Saliva is increasingly used as a diagnostic fluid. Simple salivary tests now exist which indicate the presence of both oral and systemic diseases. Dentists should be encouraged to perform salivary tests for oral diseases and be aware of other salivary tests for systemic conditions.
Patients with reduced salivation should be counselled to explain the causes of the symptoms and the nature of the disease, provided with information on available treatments and an integrated treatment plan including dietary advice, adequate fluid intake, maintaining meticulous oral hygiene and frequent dental visits, use of fluorides, saliva stimulants such as sugarless gum, substitutes and coating agents, avoidance of harmful habits (alcohol, tobacco and drugs) and undergoing investigation to exclude possible systemic diseases.
Greater awareness at institutional, practice and public levels concerning diagnosis and problems of dry mouth and the role of saliva in maintaining health should be encouraged.
Crown – the visible part of a tooth.
Dentin – the hard but porous tissue located under both the enamel and cementum of the tooth. Dentin is harder than bone.
Enamel – the tough, shiny, white outer surface of the tooth.
Gums – the soft tissue that surrounds the base of the teeth.
Nerves – nerves transmit signals (conveying messages like hot, cold, or pain) to and from the brain.
Periodontal membrane/ligament – the fleshy tissue between tooth and the tooth socket; it holds the tooth in place. The fibers of the periodontal membrane are embedded within the cementum.
Pulp – the soft center of the tooth. The pulp contains blood vessels and nerves; it nourishes the dentin.
Root – the anchor of a tooth that extends into the jawbone. The number of roots ranges from one to four.
Roots
Some teeth have a single root while others have multiple roots. The following chart will show you how many roots each type of tooth has. The root numbers indicated here are general guidelines. It should be noted that considerable individual variation exists and almost anything is possible in exceptional cases.
INCISORS CANINES PREMOLARS MOLARS
MAXILLARY 1 ROOT 1 ROOT 2,1 ROOTS 3 ROOTS
MANDIBULAR 1 ROOT 1 ROOT 1 ROOT 2 ROOTS
Teeth that have two roots are said to be bifurcated. Teeth that have three roots are said to be trifurcated. Maxillary first premolars are usually bifurcated while the maxillary second premolar usually has just one root. It is important to understand the number and position of roots since this will influence things like root canal treatments and how you will exert your force when doing extractions.
The position of the roots varies by tooth. The maxillary first premolar with two roots will have one root positioned towards the facial and the second towards the lingual. Maxillary molars have three roots, two roots on the facial and one on the lingual. The mandibular molars have two roots, one root positioned on the mesial and one on the distal.
In the primary dentition the root numbers and locations are identical to the adult teeth. The only differences are that the primary roots are smaller and in the case of the primary molars, the roots are more widely spread apart.
Inside of each root is a small canal through which the nerves and vessel pass. This canal is called the root canal. The normal setup is to have one canal is each root. The exception to this is the mandibular molars where the mesial root contains two canals rather than one. In this case the mesial root will have one facial canal and one lingual canal. The other exception is the maxillary first molar. About 80% of the time the mesial buccal root will contain two canals. These canals are usually called MB1 and MB2 (MB stands for mesial buccal).
View Angles of Teeth
In discussing the shape and location of teeth and their roots it is helpful to know which angle you are viewing the tooth from. The view angles are described as if you were sitting looking at the tooth from the angle named. In a facial view, for example, you see the teeth as if you were glued to the persons face. In a lingual view you see the tooth as one sitting on the patients tongue. The other views are mesial, distal and occlusal or incisal.
At certain times it is helpful to make sections through the teeth and their roots to better see their shape or location. The three sections that we use are horizontal, facio-lingual, mesio-distal. A horizontal section is the same as a cross section. In this type section you are cutting through the tooth separating the top from the bottom. To remember the other two sections it is helpful to think of the name coming from the orientation of the cutting instrument. In other words, in a facio-lingual section the handle of the cutting instrument is towards the facial and the tip towards the lingual. In a mesio-distal section the handle is towards the mesial and the tip towards the distal.
Cross Sectional View
When making a facio-lingual or mesio-distal section you can see a lengthwise outline of where the nerve and vessels run inside the tooth. As discussed before, the narrow path inside the root is called the root canal. The soft tissues enter the tooth at the apex. This is usually a very narrow constriction. The nerve will then continue up into the inside of the crown where it expands somewhat in its width. The expanded area inside the crown is called the pulp chamber. The walls of the pulp chamber are giveames by the surface that they lie closest to. So a pulp chamber will have a facial, lingual, mesial and distal wall. In addition the top of the chamber is called the roof and the base of the chamber, if there is one, is called the floor. Teeth with a single root canal will not have a floor to the chamber. Teeth with multiple root canals have a pulpal floor.
In the roof of the pulp chamber it is common to encounter small projection towards the surface of the tooth. These are usually located below cusps or other projections on the surface of the tooth. These small extensions are called pulp horns and can become a problem especially if you slip while drilling on a tooth. Usually it is a pulp horn into which your drill drops.
The pulp chamber of a tooth is a dynamic environment. In addition to having a constant blood flow and nervous signals, there is also a constant repair mechanism taking place. Inside the pulp chamber small cells exist called odontoblasts. These cells are responsible for producing new dentin. When a tooth is subject to irritation the odontoblasts become active and begin to produce new dentin in the area of irritation. The original dentin laid down when the tooth is formed is called primary dentin. Dentin laid down after that time is called secondary dentin. This phenomenon takes place very slowly and because of that, sometimes the tooth cannot lay dowew dentin as fast as the decay is progressing. When this occurs the decay may eventually enter the pulpal chamber of the tooth and kill it. However, if the decay moves slowly or the irritation is not too acute, the tooth will lay down layer after layer of dentin until there is a barrier of adequate thickness. This isolates the odontoblasts and other soft tissues from the irritation. This is part of what goes on when a new filling is placed. When a tooth is drilled on and a new filling is placed the tooth is irritated, both by the drilling and the new filling. The tooth will initially be tender and possibly cold sensitive but with time inflammation in the pulp chamber will decrease and the tooth will build a layer of insulative dentin between the pulpal chamber and the new filling.
Pulpal Damage
Sometimes a tooth will be subjected to so much stress that the pulpal tissues will begin to break down. This can result from decay entering the tooth, deep fillings, crowns, overuse-like those that clench their teeth), orthodontics or other traumas -like having the tooth bumped or knocked out. Diagnosis of pulpal damage involves several tests or questions. First, we usually start by asking the patient about their symptoms. A patient who reports pain with stimulation in a tooth that quickly resolves usually has pulpal trauma but not full breakdown of the pulpal tissue. This is common following restorative work or during orthodontics. This is often call reversible pulpitus. When a person reports pain with stimulation that does not resolve quickly, it indicates additional damage to the pulpal structures. This may or may not be reversible. When a person reports spontaneous pain (“it wakes me up at night”) or pain lasting a long duration, this usually indicates permanent damage or irreversible pulpitus.
You can also test the amount of damage to the pulpal tissues by placing cold on the tooth. A healthy tooth will respond quickly, usually within 3-5 seconds, and recover quickly, in about the same amount of time. A hyper sensitive tooth usually has reversible damage. A prolonged recovery time indicates additional damage, possibly irreversible. No response to cold indicates that the nerve is no longer functional and that the damage is irreversible.
A second way to test the tooth is by tapping on it. This is called a percussion test. When there is swelling within the pulpal chamber it can cause inflammation of the periodontal ligament (PDL- the ligament that surrounds the roots and connects them to the bone). Tapping on the tooth elicits a painful response as the PDL at the apex of the tooth is compressed.
A third way to determine pulpal vitality is with a radiograph. (Radiographs are commonly but incorrectly called x-rays). When a tooth is irreversibly damaged it will often show a widening of the PDL space around the apex. This is caused by necrotic (dead) tissue being discharged out of the apex of the tooth into the adjacent PDL space. It is more likely that this will be visible if the pulpal tissue has been dead for a while.
Treatment of a tooth with irreversible pulpitus involves doing a root canal treatment (RCT). This treatment involves scrubbing out all of the tissues from the inside of the root canals using metal files and chemicals, such as household bleach. When all of the tissue is removed the chamber is then refilled using an inert rubber material called gutta percha and a sealer paste that fills in around the gutta percha. This fills the chamber preventing re-infection. A well done treatment removes all tissue and completely fills the root canal spaces to the apex without extruding beyond the
confines of the root.
Root Canal Therapy
Bone Support
The bone that supports the teeth is called the alveolar bone. The depressions in the alveolar bone that cradles the teeth are called the alveolar socket or alveolus. The tooth is not actually in direct contact with the bone. Instead, the tooth is held in place by a short ligament called the periodontal ligament or PDL for short. This ligament connects from the bone to the cementum covering the root of the tooth. Essentially teeth hang in a sling made up of the PDL and are allowed to move freely in any direction though the amount of movement is small. When a tooth is extracted we are essentially tearing the ligament that connects the tooth to the bone.
The PDL becomes very important when we are performing orthodontics. When pressure is applied to a tooth in any direction it stretches the ligament on the side where the pressure is coming from and compresses the ligament on the side away from the pressure. Contained in the bone are cells that are capable of making new bone (osteoblasts), or those that break down existing bone (osteoclasts). These cells become active in response to pressure. When you pull on bone, as in a stretched PDL, osteoblasts will begin laying dowew bone in response. When bone is not pulled on, as is the case in a compressed PDL, osteoclasts will begin to break down the bone in the area. So during orthodontic treatment, through the actions of osteoclasts and osteoblasts, the tooth essentially floats through the bone to its new location.
Soft Tissue Supports
Covering the alveolar bone and lining all the inside of your mouth is a tissue broadly referred to as oral mucosa. The environment in the human mouth is a harsh one (especially in some mouths). The linings of the mouth have adapted to this environment by being rich in keratin, a substance that strengthens the surface, and by shedding off the outermost layers on a regular basis. This is the same mechanism that the body uses to deal with other harsh environments, such as the lining of the digestive tract or the skin. The linings of the mouth are turned over approximately every week to ten days. Certain areas in the mouth are subject to greater stress than others. These contain greater amounts of keratin. This can be noted visually by the color changes in the tissue. The areas that receive the greatest stress are the roof of the mouth (palate) and the gums (gingiva) immediately surrounding the teeth. If you look in your mouth you will see that these areas are much pinker than other areas such as the linings of the cheeks.
Now we will focus on the structure of the gingiva. The gingiva that is positioned immediately around the neck of the tooth is called the unattached gingiva (also called the marginal or free gingiva). Part of the unattached gingiva is a pyramid like projection that reaches up and fills in the space between the teeth. This is called the inter-dental papilla. The unattached gingiva receives this name because it does not connect directly into the tooth or root but is rather a projection from the structures below. You can demonstrate this tissue in your own mouth by placing a piece of floss around your tooth and slowly moving it apically. You will see that the floss moves, with little or no resistance, beneath the gum line. The floss is now sitting in a space called the sulcus. This is a trough like depression that circles each of your teeth between the gums and the tooth. The sulcus is important because it is here that pockets of bacteria first
collect and begin the process of gum disease, (we will talk
about later on).
In a healthy mouth the sulcus will be less than 3.5 mm in depth all around the tooth. At the bottom of the sulcus is where the PDL begins it’s attachment to the root of the tooth. As mentioned before, the PDL is a fiber network that connects the tooth to the bone. There are other fibers that bind the gingiva to the bone. Where these fibers attach to the gingiva you can see small depressions in the gingiva. These “dimples” in the gingiva give it a fine “orange peel” appearance called stippling. When gum disease is present sometimes the fibers binding down the gums are damaged and the stippled appearance of the gums is lost.
The PDL marks the boundary between the unattached gingival and the attached gingiva. The attached gingiva is attached directly to the bone. The unattached gingiva and the attached gingiva together form a band of tissue collectively referred to as the gingiva which is from 3-6 mm wide.
Where the gingiva ends the alveolar mucosa begins. The junction between the two is seen by a color change. The gingiva is a lighter pink and the alveolar mucosa is a deeper red. The muccogingival junction forms the boundary between the gingiva and the mucosa.
Perhaps the most common disease of the mouth is periodontal disease, sometimes called gum disease. This is caused because bacteria are able to establish a colony on the teeth and from there can attack the gums surrounding the teeth. The gingiva immediately surrounding the necks of the teeth is most prone to this attack. Early episodes of gum disease are called gingivitis. This is when the upper most level of the gums and the linings of the sulcus become infected and inflamed. The clinical evidence of this is not difficult to detect since the gingiva takes on a deeper color, becoming red rather than pink and the gingiva bleeds easily when touched. As the disease progresses, you will see the redness in the unattached gingiva increasing and the papilla becoming inflamed and puffy. Also, you will notice that stippling in the gums is lost as the bacteria attack and destroy the fibers that bind the gingiva to the bone.
In later stages the PDL itself is attacked and destroyed. This will lead to the sulcus depth increasing. When sulcular depth reaches 3.5-5.5 mm it is considered to be a case of moderate gum disease. Sulcular depth greater than 5.5 mm is considered an advanced case of gum disease. Good home care, early detection, and regular professional cleanings are the most effective way to prevent or control the disease. Once the PDL is destroyed it is difficult, if not impossible, to regenerate.
Factors of Periodontal Disease
There a several factors that predispose a person to get periodontal disease. One is the care that a person gives their mouth. The bacteria that cause the disease are facultative anaerobes. This means that they act differently in the presence of oxygen than they do in the absence of oxygen. They are relatively innocuous when oxygen is present, but when sealed up in a sulcus by a layer of plaque the oxygen quickly becomes depleted and the bacteria become much more aggressive in their behavior. Under these conditions damage is caused by the bacteria. Regular brushing and flossing break this layer of plaque and allow oxygen to enter these areas keeping the bacteria in check.
A second factor is the anatomy of the site. Multi-rooted teeth are much more likely to become infected than single rooted teeth. The space between the roots makes a nice place for the bacteria to hide away and cause damage. Periodontal disease is directly related to the number of roots that a tooth has.
A third factor is genetics. Certain people have been shown to possess genes that make them susceptible to periodontal disease. Some of these genes caow be tested for. A positive response would make one become much more aggressive in diagnosing and treating this problem.
A fourth factor is disease. Certain diseases, like diabetes, can make a person more susceptible to periodontal disease. In the case of diabetes this is caused by poor vascularity. Other diseases can weaken the immune system, making it harder for the body to fight off infection. Many diseases, such as cancer, are treated with medications that can dry out the mouth. This side effect can lead to periodontal disease and decay.
A fifth factor involves early childhood contacts. The bacteria that cause the disease are acquired from those with whom you have close contact. Not all bacteria are created equal. Some strains are much more dangerous than others. A newborn child does not have it’s own bacterial colonies. These are transferred, especially from the child’s mother. A mother with known periodontal disease should consider precautions such as using an anti-microbial mouthwash during the child’s first few months of life so that bacteria can come from another less virulent source.
The sixth factor is related to certain unhealthy behaviors. Smoking causes a huge increase in the chances of periodontal disease. Alcohol and drug abuse also have a negative affect.
What Are the Different Types of Teeth?
Every tooth has a specific job or function (use the dental arch in this section to locate and identify each type of tooth):
Incisors— the sharp, chisel-shaped front teeth (four upper, four lower) used for cutting food.
Canines— sometimes called cuspids, these teeth are shaped like points (cusps) and are used for tearing food.
Premolars— these teeth have two pointed cusps on their biting surface and are sometimes referred to as bicuspids. The premolars are for crushing and tearing.
Molars— used for grinding, these teeth have several cusps on the biting surface
What is occlusion or bite?
Occlusion is how your teeth come together when you close your jaw. Your occlusion is influenced by three primary components: teeth, nerves and muscles, and bones. Another factor, which can affect the way your teeth come together, is your posture.Take note of the fact that when you tilt your head back and bite, your teeth will hit differently than when you tilt your head forward. The same rule applies when you are lying down on your side. Your lower jaw will shift to one side. We now need to define ideal occlusion or bite. I’m going to attempt to explain this by describing some functional terms.
Centric Occlusion:
Centric Occlusion is the term used to define the habitual position of closure. In other words, the position your teeth are in when you repeatedly bite. In an ideal centric occlusion all the teeth are in proper contact.The teeth are not in cross bite, there is no under bite or over bite.
Canine Guidance:
Now let’s try and explain how an individual with an ideal bite functions. Starting at centric occlusion and keeping the teeth in contact as much as possible, we slide the lower jaw to one side. In an ideal occlusion, when the lower jaw is shifted to one side, the posterior teeth should not touch. What happens is that the lower canine or eye tooth is riding up on the upper canine. This is called Canine Guidance or canine protected occlusion. Canine protected occlusion is an important concept.
