DEVELOPMENT AND ERUPTION OF TEETH, ABNORMALITIES OF DEVELOPMENT

Introduction:

• Birth is an unmatched marvel of nature, as every big happening has a humble of beginning-So too the growth and development of a teeth.• “Study the past to know the future”. The journey of the tooth from its inception to its complete development is one such study.• The term dentition is used to describe the natural teeth in the jaw bones. There are two dentitions; the primary and the permanent dentition. A child’s primary dentition develops during the prenatal period and consists of 20 teeth which erupt and later shed or lost.• As the primary teeth are shed and the jaws grow and mature , the permanent dentition, consisting of 32 teeth, gradually erupts and replaces the primary dentition• Tooth development, or odontogenesis, takes place in many stages. Odontogenesis is a continuous process, and there is no clear-cut beginning or end point between these stagesNot all the teeth in each dentition begin to develop at the same time. The initial teeth for both dentitions develop in the anterior mandibular region, followed later by the anterior maxillary region, and then development progress posteriorly in both jaws• The primary dentition develops during both the embryonic and fetal periods. Most of the permanent dentition is formed during fetal period. Tooth development continues for years after birth, however, especially considering the formation of the permanent second and third molars. Thus, teeth have the longest developmental period of any set of organs in the body.Stomodeum or primitive oral cavity• The primitive oral cavity, or stomodeum, is lined by stratified squamous epithelium called the oral ectoderm. The oral ectoderm contacts the endoderm of the foregut to form the buccopharyngeal membrane. At about 27th day of gestation this membrane ruptures and the primitive oral cavity establishes a connection with the foregut.

Primary Epithelial Band

• After 37 days of development, a continuous band of thickened epithelium forms around the mouth in the presumptive upper and lower jaws from the fusion of separate plates of thickened epithelium.• These bands are roughly horse-shoe shaped and correspond in position to the future dental arches of the upper and lower jaws.• Each band of epithelium, called the primary epithelial band which gives rise to the dental lamina and vestibular lamina•Dental lamina

• Two or three weeks after the rupture of the buccopharyngeal membrane, when the embryo is about is about 6 weeks old, certain areas of basal cells of oral ectoderm proliferate at more rapid rate than do the cells of adjacent areas. This leads to the formation of dental lamina, which is a band of epithelium that has invaded the underlying ectomesenchyme along each of horse shoe shaped future dental arches• It serves as the primodium for ectodermal portion of decidious teeth. The permanent molars arise directly from distal extension of dental lamina. The successor of decidious teeth develop from a lingual extension of free end of dental lamina.

• Fate of dental lamina:

• The total activity extends over a period of atleast 5 years. However,the dental lamina may be still be active in the 3rd molar region after it had dissappeared elsewhere.• Remnants of dental lamina persist as epithelial pearls or islands within the jaws as well in the gingiva.Vestibular lamina

• Labial and buccal to the dental lamina in each dental arch, another epithelial thickening develops independtly and some what later. It is the vestibular lamina, also termed as lip furrow band. It subsequently hollows and forms the oral vestibule between the alveolar portion of the jaws and the lips and cheeks.

Stages of tooth development

• Initiation stage.• Bud stage.• Cap stage.• Bell stage.• Advanced bell stage.•Initiation of tooth development

• The odontogenesis is first initiated by factors resident in the first arch epithelium influencing ectomesenchyme. The bone morphogenic protein(BMP) are specifically and transiently expressed in the epithelium at sites where teeth will form.

• Odontogenesis of the primary dentition begins between the sixth and seventh week of prenatal development, during the embryonic period.• The initiation stage, involves the physiological process of induction, which is an interaction between the embryological tissues

Bud stage

• The second stage of odontogenesis is called the bud stage and occurs at the beginning of the eighth week of prenatal development for primary dentition.• This stage is named for an extensive proliferation.

• The epithelium of the dental laminae is separated from the underlying ectomesenchyme by a basement membrane.

• Simultaneous with the differentiation of each dental lamina, round or ovoid swellings arise from the basement membrane at 10 different points, corresponding to future positions of deciduous teeth. These are the primordia of the enamel organs, the tooth buds

• In the bud stage, the enamel organ consists of peripherally located low columnar cells and centrally located polygonal cells. Many cells of the tooth bud and the surrounding mesenchyme undergo mitosis.• As a result of increased mitotic activity and the migration of neural crest cells into the area the ectomesenchymal cells surrounding the tooth bud condense. The ectomesenchymal condensation immediately subjacent to enamel organ is the dental papilla.and that surrounds the tooth bud and the dental papilla is the dental sac

Cap stage

• The third stage of odontogenesis is called the cap stage and occurs for the primary dentition between the ninth and tenth week of prenatal development. This stage not only involves the proliferation stage, but various levels of differentiation (cytodifferentiation, histodifferentiation,and morphodifferentiation)

• As the tooth bud continues to proliferate, it does not expand uniformly into a larger sphere. Instead, unequal growth in different parts of the tooth bud leads to the cap stage, which is characterized by a shallow invagination on the deep surface of the bud.

Bell stage

• The fourth stage of odontogenesis is the bell stage which occurs between the eleventh and twelfth week of prenatal development. It is characterized by continuation of the ongoing process of proliferation, differentiation, and morphogenesis.

• As the invagination of the epithelium deepens and its margins continue to grow, the enamel organ assumes a bell shape. Four different types of cells are found within the enamel organ-• Inner enamel epithelium

• Outer enamel epithelium• Stratum intermedium • Stellate reticulum

• Inner enamel epithelium;

• The cells immediately adjacent to the dental papilla assume a short columnar shape and are characterized by high glycogen content. These cells are known as IEE. The IEE consists of a single layer of cells that differentiate prior to amelogenesis into tall columnar cells called ameloblasts.

• These cells are 4to 5 um in diameter and about 40um height. These elongated cells are attached to one another by junctional complexes laterally and to cells in the stratum intermedium by desmosomes.• The cells of IEE exert an organizing influence on the underlying mesenchymal cells in the dental papilla, which later differentiate into odontoblasts.

• Outer enamel epithelium.

• At the periphery of dental organ, cells assume cuboidal shape and form the external or outer enamel epithelium. At the end of the bell stage, preparatory to and during formation of enamel, the smooth surface of OEE is laid in folds. Between the folds the adjacent mesenchyme of the dental sac forms papillae that contain capillary loops and thus provide a rich nutritional supply for the intense metabolic activity of the avascular enamel organ.

• Stellate Reticulum (Enamel pulp);

• The cells in the center of dental organ synthesize and secrete glycosaminoglycans which pulls water into the dental organ. So as the fluid increases, the volume of extracellular components of dental organ increases and therefore the cells are forced apart. Cells retain connections with each other through their desmosomal contacts and they become star shaped. These cells are known as stellate reticulum.

• Before enamel formation begins,the stellate reticulum collapses, reducing the distance between the centrally situated ameloblasts and the nutrient capillaries near the OEE.

• Stratum Intermedium;

• Between the IEE and the newly differentiated stellate reticulum some epithelial cells proliferate into layer called stratum intermedium. These cells are closely attached by desmosomes and gap junctions. This layer seems to be essential for enamel formation.

• Dental Papilla;

• The dental papilla is enclosed in the invaginated portion of enamel organ. Before the IEE begins to produce enamel, the peripheral cells of mesenchymal dental papilla differentiate into odontoblasts under the organizing influence of the epithelium to form pulp and dentin.• The basement membrane that separates the enamel organ and the dental papilla just before dentin formation is called the membrana performativa.

• Dental Sac;

• Before formation of dental tissues begins, the dental sac shows a circular arrangement of fibres and resembles a capsular structure. • With the development of roots, the fibres of dental sac differentiate into periodontal ligament that become embedded in the developing cementum and alveolar bone.

Advanced Bell Stage

• During this stage,the boundary between IEE and odontoblasts outlines the future dentino-enamel junction. In addition, the cervical portion of the enamel organ gives rise to the epithelial root sheath of Hertwig.

Enamel knot, Enamel cord, Enamel niche

• During the stages of tooth development some transient structures occurs that are not necessarily present in every tooth germ or present at the same time.

• Enamel Knot: is a localized thickening in the internal dental epithelium at the center of the tooth germ.• The knot is always continuous with the enamel cord or septum, which is a strand of cells running from the knot to the external dental epithelium,that divides the dental organ into two.• These two structures determine the initial position of first cusp of the tooth during crown pattern formation.

• Enamel Niche: is an apparent structure, created because the dental lamina is a sheet rather than a single strand and often contains a concavity filled with connective tissue.

Epithelial Mesenchymal Interactions during tooth development• During the tooth development,’’messages” pass between the epithelium and mesenchyme to produce changes of increasing complexity (I.e differentiation) within the cell layers. The term induction is used to describe the effect that one cell layer has on another.

• Three main hypothesis have been put forward to explain how information leading to induction may be transferred between epithelium and mesenchyme.• 1.A chemical substance (short –range hormone) is produced by one cell layer and diffuses across the narrow intervening space to be taken up and cause induction in the other cell layer.

• 2. Induction is triggered by direct cell-to cell contact and does not involve a diffusible molecule.• 3. Induction is due to the presence of the initial extracellular matrix, a thin layer situated between the epithelium and mesenchyme and comprising the basal lamina and adjacent region. The extracellular matrix has a complex composition, consisting of collagen(mainly type 4 but possibly some type 1& 3), proteoglycans and glycoproteins.Break up dental lamina crown pattern determination• Two other important events take place during the bell stage. First, the dental lamina joining the tooth germ to the oral epithelium breaks up into discrete islands of epithelial cells, thus separating the developing tooth from oral epithelium.

• Second, the IEE folds, making it possible to recognize the shape of the future crown pattern of the tooth.• If any remnant of dental lamina persist they may form small cysts (eruption cysts) over the developing teeth and delay eruption.Vascular supply during early tooth development• Clusters of blood vessels are found ramifying around the tooth germ in the dental follicle and entering the dental papilla ( or pulp) during cap stage.• Their number in the papilla increases during histodifferentiation reaching a maximum at the onset of crown stage of tooth development.• With age, the volume of pulp tissue diminishes and the blood supply becomes progressively reduced, affecting the tissue’s viability.• The dental organ- AvascularNerve supply• Nerve fibers approach the developing tooth during the bud-cap stage of development.• Nerve fibers ramify and form a rich plexus around tooth germ. Initial innervations of the developing teeth is concerned with the sensory innervations of the future PDL and pulp.

Enamelogenesis and Dentinogenesis

• Formation of Preameloblasts : • After the formation of IEE in the bell shaped enamel organ, these inner most cells grow even more columnar or elongate as they differentiate into preameloblasts. During this differentiation, the nucleus in each cell moves away from the center of the cell to a position farthest away from the basement membrane (repolarization)

• Formation of Odontoblasts and dentin matrix:

•• After the IEE differentiates into preameloblasts, the outer cells of the dental papilla are induced by the pre ameloblasts to differentiate into odontoblasts. These cells undergo repolarization.• The odontoblasts, now begin dentinogenesis which is the apposition of dentin matrix, or predentin, on their side of basement membrane.(fig6-13)

• Thus, the odontoblast start their secretory activity some time before enamel matrix production begins. This explains why dentin layer in any location in a developing tooth is slightly thicker than the corresponding layer of enamel matrix.

Formation of ameloblasts, dentino enamel junction and enamel matrix:After the differentiation of odontoblasts from the outer cells of dental papilla and their formation of predentin, the basement between the pre ameloblasts and the odontoblasts disintegrates. This disintegration allows the preameloblasts to come into contact with the newly formed predentin. This induces the pre ameloblasts to differentiate into ameloblasts.

• Ameloblasts begins amelogenesis, or apposition of enamel matrix, laying it down on their side of now disintegrating basement membrane. The enamel matrix is secreted from Tome’s process, a tapered portion of each ameloblast that faces the disintegrating basement membrane.

• With the enamel matrix in contact with the predentin, mineralization of the disintegrating basement membrane now occurs, forming the dentino enamel junction.• The odontoblasts, unlike the ameloblasts, will leave attached cellular extensions in the length of the predentin called the odontoblastic process. Each odontoblastic process is contained in the mineralized cylinder, the dentinal tubule.

• The cell bodies of odontoblasts will remain within the pulp tissue. The cell bodies of ameloblasts will be involved in the eruption and mineralization process but will be lost after eruption.

Root development

• The process of root development takes place after the crown is completely shaped and the tooth is starting to erupt into the oral cavity. The structure responsible for root development is the cervical loop. This is the most cervical portion of enamel organ,a bilayer rim that consist of IEE and OEE.

• The cervical loop begins to grow deeper into the surrounding mesenchyme of the dental sac, to enclose more of dental papilla tissue to form Hertwig’s root sheath.• The function of this sheath or membrane is to shape the roots and induce dentin formation in root area.

• Root dentin formation:

• Root dentin forms when the outer cells of the dental papilla in the root area are induced to undergo differentiation and become odontoblasts. After the differentiation, these cells undergo dentinogenesis and begin to secrete predentin.• When root dentin formation is completed, this portion of basement membrane also disintegrates, as does the edntire HERS. After this disintegration of root sheath, its cells may become the epithelial rests of Malassez.

Cementum and pulp formation

• The apposition of cementum, or cementogenesis, in the root area also occurs when HERS disintegrates.• This disintegration of the sheath allows the undifferentiated cells of the dental sac to come into contact with the newly formed surface of root dentin. This contact of the dental sac cells with the dentin surface induces these cells to become immature cementoblasts.• The cementoblasts move to cover the root dentin area and undergo cementogenesis, laying down cementum matrix, or cementoid. Many cementoblasts become entrapped by the cementum they produce and become mature cementocytes.• As the cementoid surrounding the cementocytes becomes calcified, or matured, it is then considered cementum. As a result of the apposition of cementum over the dentin, the dentino cemental junction(DCJ) is formed.

Multirooted teeth

• Like anterior teeth, multirooted premolars and molars originate as a single root on the base of the crown. This portion on these posterior teeth is called the root trunk. The cervical cross section of the root trunk initially follows the form of the crown.• Differential growth of HERS causes the root trunk of the multirooted teeth to divide into 2 or 3 roots.• During the formation of the enamel organ on a multirooted tooth, elongation of cervical loops occurs in such a way that long, tongue like horizontal epithelial extensions or flaps develop within. Two or three extensions can be present on multirooted teeth, depending on the similar number of roots on mature tooth.Primary tooth eruption and shedding• Eruption of the primary dentition takes place in the chronological order, as does the permanent dentition later. This process involves active eruption, which is the actual vertical movement of the tooth.• After enamel apposition ceases in the crown area of each primary or permanent tooth, the ameloblasts place an acellular dental cuticle on the new enamel surface. In addition, the layers of enamel organ are compressed, forming the reduced enamel epithelium(REE)• To allow for the eruption process, the REE first fuses with the oral epithelium lining the oral cavity. Second, enzymes from the REE disintegrate the central portion of the fused tissue, leaving an epithelial tunnel for the tooth to erupt through into the surrounding oral epithel;ium of the oral cavity.• The primary tooth is then lost- exfoliated or shed- as the succedaneous permanent tooth develops lingual to it. The process consists of differentiation of osteoclasts, which absorb the alveolar bone between the two teeth, and odontoclasts which causes resorption.Permanent tooth eruption• The succedaneous permanent tooth erupts into the oral cavity in a portion lingual to the roots of the shedding or shed primary tooth.

The process of eruption for a succedaneous tooth is the same for the primary tooth. A

permanent tooth often starts to erupt before the primary tooth is fully shed.

Developmental Disturbances of Teeth

DISTURBANCES IN SIZE OF TEETH

Microdontia

The term is used to describe teeth which are smaaler than normal.outside the usual limits of variation. Three types of Microdontia are recognized:

(1) TRUE GENERALISED MICRODONTIA(2) RELARIVE GENERALISED MICRODONTIA

(3) MICRODONTIA INVOLVING A SINGLE TOOTHIn true generalized microdontia all the teeth are smaller than normal e.g.Pituatory dwarfism

Relative Generalised Microdontia Normal or slightly smaller than normal teeth are present in jaws that are somewhat larger than normal and there is an illusion of true microdontia.

Microdontia involving a single tooth is rare .It affects most often the Maxillary Lateral Incisor & Third Molar.Supernumerary teeth are frequently smaller in size.One of the most common microdontia is Peg shaped Lateral.

Macrodontia Refers to teeth that are larger than normal.

True Generalised macrodontia in which all teeth are larger than normal.e.g. Pituatory Gigantism.

Relative generalized Microdontia is common & is the presence of normal or slightly larger than normal teeth in small jaws.

Macrodontia of single tooth is rarher common condition.The tooth is normal in every respect except size.In hemihypertrophy of face teeth of involved side may be comparatively laregr than the unaffected side.

DISTURBANCS IN SHAPE OF TEETH

GEMINATION

Is an anomaly that arises from an attempt at division of a single tooth germ by an invagination ,with resultant incomplete formation of two teeth.The structure is usually one with two completely or incompletely separated crownsthat have a single root or root canal.It is in deciduous as well as permanent dentition.The term TWINNING is used to designate the production of one normal &one supernumerary tooth.

FUSIONFused teeth arise through union of two normally separated tooth germs.Depending on the stage of development of the teeth at the time of union fusionmay be either complete or incomplete.Some physical force or pressure produces contact of the developing teeth and their subsequent fusion.If this contact occurs before before calcification beigns the two teeth may be completely united to form a single large tooth. If the contact occurs when a

portion of tooth crown has completed its formation there may be union of roots only.The dentin is confluent in cases of true fusion.Fusion may occur between a normal tooth and a supernumerary tooth.

CONCRESCENCE

Is a form of fusion which occurs after root formation is completed.In this condition the teeth are united by cementum only.It is thought to arise as a result of traumatic injury or crowding of teeth with resorption of the interdental bone so that the two roots are in approximate contactand become fused by the depositionof cementum only.Diagnosis can be established by radiographic examination. Extraction of one teeth may result in the extraction of the other.

DILACERATION

Refers to an angulation or sharp bend or curve in the root or crown of a formed tooth.The condition is thought to be due to trauma during the period in which the tooth is forming with the result that the position of the calcified portion of the tooth is changed & the remainder of the tooth is formed at an angle.The curve or bend may occur anywhere along the length of the tooth sometimes along the cervical portion of the tooth.at times at the midway &sometimes at the apex.Dilacerated teeth frequently present difficult problems at the time of extraction if the operator is unaware of the condition.

TALON CUSP

Talon cusp is a supernumerary structure projecting from the dentoenameljunction to a variable distance towards the incisal edge of an anterior tooth.Studies have shown that it consists of enamel, dentine and a variable amount of pulp tissue. Hyperactivity of the enamel organ during morphodifferentiation has been attributed to its formation. Most previous reports have been made concerning the occurrence of this structure on primary and permanent teeth and mostly on the palatal aspect. Only few have been reported on the facial aspect of the teeth. When it occurs, the effects are mainly aesthetic and functional and so early detection and treatment is essential in its management to avoid complications.

BackgroundThis unusual dental anomaly showing an accessory cusp-like structure projecting from the cingulum to the cutting edge was first described by Mitchell in 1892 . It was thereafter named a Talon cusp by Mellor and Ripa due to its resemblance to an eagle's talon. Since then, this odontogenic anomaly has been given several descriptions, such as,prominent accessory cusp-like structure , exaggerated cingula additional cusp , cusp-like hyperplasia , accessory cusp and supernumerary cusp. It has been defined as a supernumerary accessory talon-shaped cusp projecting from the lingual or facial surface of the crown of a tooth and extending for at least half the distance from thecemento-enamel junction to the incisal edge . There is a wide variation in the size and shape of this anomaly. Due to this variation, and in order to have a diagnostic criteria, it has been classified into 3 types by Hattab et at:Type1: Talon - refers to a morphologically well-delineated additional cusp thatprominently projects from the palatal (or facial) surface of a primary or permanentanterior tooth and extends at least half the distance from the cemento-enamel junction to the incisal edge.

Type 2: Semi talon - refers to an additional cusp of a millimeter or more extending less than half the distance from the cemento-enamel junction to the incisal edge. It may blend with the palatal surface or stand away from the rest of the crown.

Type 3: Trace talon - an enlarged or prominent cingula and their variations, i.e. conical,bifid or tubercle-like. Radiographically, it may appear typically as a v-shaped radiopaque structure, as in true talon or semi- talon, or be tubercle-like, as in trace talon, originating from the cervical third of the root. The radiopaque v-shaped structure is superimposed over the normal image of the crown of the tooth. The point of the 'V' is inverted in mandibular cases. This appearance varies with the shape and size of the cusp, and the angle at which the radiograph is taken. It is composed of enamel, dentine and a varying amount of pulp tissue . The extent of pulp extension into the cusp is however difficult to determine because of its superimposition over the main pulp chamber. While some indicated that talon cusps contain pulp tissue , some found no evidence of pulp extension into the cusp. However, it has been suggested that large talon cusps, especially those that stand away from the tooth crown are more likely to contain

pulp tissue. A review of the literature showed that over the last two decades, increasing reports have been made of the occurrence of the condition. The reported prevalence outside Africa is between 0.06% inMexicans and 7.7% in a northern Indian population. It has also been found to be relatively common in the Chinese and Arab , and predominantly in the male population . These wide variations in prevalence could be due to individual differences in definitions of observation, from enlarged cingula to semi- or true talons . If data is taken from those who reported for treatment only, a high prevalence might be observed. Patients may seek treatment when there is a problem, usually with large cusps. No prevalence data was been found in the literature for Africans.

Aetiology

The exact aetiology is not known, but it is suggested to be a combination of genetic and environmental factors . It is thought to arise during the morphodifferentiation stage of tooth development, as a result of outfolding of the enamel organ or hyperproductivity of the dental lamina. It is suggested that disturbances during morphodifferentiation such as altered endocrine function might affect the shape and size of the tooth without impairing the function of ameloblasts and odontoblasts . There is also a suggestion of a strong genetic influence in its formation as evidenced by its occurrence in close family members. Talon cusp may occur in isolation or with other dental anomalies such as mesiodens , odontome, unerupted or impacted teeth , peg-shaped maxillary incisor, dens invaginatus , cleft lip and distorted nasal alae bilateral gemination , fusion, supernumerary teeth and enamel clefts.It has also been associated with some systemic conditions such as Mohr syndrome (oro-facial-digital II) , Sturge-Weber syndrome (encephalo-trigeminal angiomatosis, Rubinstein-Taybi syndrome, incontinentia pigmenti achromians , and Ellis-van Creveld syndrome .

Presentation

It is more common in the permanent dentition (75%) than in the primary dentition, while 92% affect the maxillary teeth . The maxillary lateral incisor is the most frequently affected in the permanent dentition while the maxillary central incisor is the most affected in the primary dentition . Most times it occurs unilaterally but bilateral cases ,including multiple talon cusps have also been reported In a particular case, talon cusps have occurred on both maxillary and mandibular teeth in the same patient . Rarely, two talon cusps may occur on a single tooth. Abbot reported a labial and a palatal talon on a

maxillary right central incisor , while another report from Nigeria presented two palatal talons on a maxillary left central incisor

Complications and Management

The complications of talon cusp are diagnostic, functional, aesthetic and pathological A large talon cusp is unaesthetic and presents clinical problems. It may present diagnostic problems if it is unerupted and resembles a compound odontome or a supernumerary tooth and so leads to unnecessary surgical procedure. Functional complications include occlusal interference, trauma to the lip and tongue, speech problems and displacement of teeth. The deep grooves which join the cusp to the tooth may also act as stagnation areas for plaque and debris, become carious and cause subsequent periapical pathology.Management will depend on individual presentation and complications. Small talon cusps are asymptomatic and need no treatment. Where there are deep developmental grooves, simple prophylactic measures such as fissure sealing and composite resin restoration can be carried out. An essential step, especially in case of occlusal interference, is to reduce the bulk of the cusp gradually and periodically and application of topical fluoride such as Duraphat ® or Acidulated Phosphate Fluoride (APF) gel to reduce sensitivity and stimulate reparative dentine formation for pulp protection, or outright total reduction of the cusp and calcium hydroxide pulpotomy. It may also become necessary sometimes, to fully reduce the cusp, extirpate the pulp and carry out root canal therapy . Orthodontic correction may become necessary when there is tooth displacement or malalignment of affected or opposing teeth.This is a report of an unusual case of talon cusp which presented on

the facialspect of a mandibular central incisor.

DENS IN DENTE(Dens Invaginatus ,Dilated composite Odontome)

Is a developmental variation which is thought to arise as a result of invagination in the surface of a tooth crown before calcification has occurred .Causes of this condition include an increased localized external pressure,focal growth retardation,&focal growth stimulation in certain areas of tooth bud.The maxillary permanent lateral incisor are most frequently involved.

Roentgenographic Examination It is recognized as a Pear shaped invagination of enamel &

dentin with a narrow constriction at the opening on the surface of the tooth & closely approximating the pulp in its depth. Food

debris may be packed in this area with resultant caries & infection of pulp,occasionally even before the tooth has completely erupted.

To prevent caries ,pulp infection,&premature loss of the toothjthe condition must be recognized early &the tooth prophylactically restored.

TAURODONTISM

The term was originated by Sir Artur keith in 1913 to describe a peculiar dental anomaly in which the body of the tooth is enlarged at the expense of the roots.The term means “BULL LIKE TEETH”

Shaw classified taurodont into

1) Hypotaurodont2) Mesotaurodont3) Hypertaurodont

Possible causes enumerated by Mangion1) Specialised or retrograde character 2) A primitive paterrn3) A mendellian recessive trait 4) An Atavistic feature 5) A Mutation resulting form Odontoblastic deficiency

Taurodont is caused by the failure of Hertwig’s epithelial sheath to invaginate at the proper horizontal level. It is observed in klinefelter syndrome (extra X chromosome in males)

C/F May affect Deciduous or Permanent teeth Teeth are invariably Molars Condition may be unilateral or bilateralR/F Frequently tend to be Rectangle in shape rather taper towards roots.the pulp chamber is extremely large with a much greater apico-occlusal height than normal.The roots are extremely short.The bifurcation may be only a few mm above the apices of the roots.

TREATMENT No special treatment.

SUPERNUMERARY ROOTS

The developmental condition is not uncommon & may involve any tooth. Teeth that are normally single rooted ,particularly the mandibular bicuspids & cuspids often have two roots.Both maxillary &mandibular molars particularly third molars , may exhibit one or more supernumerary roots.The significance in Exodontia is one of these roots may be broken off during Extraction & if unrecognized & left in the Alveolus may be a source of infection.

DEVELOPMENTAL DISTURBANCES IN NUMBER OF TEETH

ANODONTIA

True anodontia or congenital absence of teeth are of two types1)Total2)Partial

TOTAL ANODONTIA

In which all teeth are missing,may involve both the deciduous and permanent dentition.Rare condition associated with Hereditary Ectodermal Dysplasia.

TRUE PARTIAL ANODONTIA

Involves one or more teeth & is a common condition.Although any tooth may be missing ,there is a tendency for certain teeth to be missing more frequently than others.There is an increasing tendency for 3rd molars ,maxillary lateral incisors, maxillary or mandibular 2nd premolars are commonly missing often bilaterally.In severe partial anodontia ,the bilateral absence of corresponding teeth may be striking.Congenital absence of deciduous teeth are uncommon but may involve maxillary lateral incisor.Hereditary Ectodermal Dysplasia may be associated with partial Anodontia the teeth being misshapen and cone shaped.Tooth buds are extremely sensitive to radiation and may be destroyed completelyby relatively small doses.

Supernumerary Teeth

Supernumerary teeth may be encountered by the general dental practitioner as a

chance finding on a radiograph or as the cause of an impacted central incisor. They may also be found intraorally following spontaneous eruption. The most common supernumerary tooth which appears in the maxillary midline is called a mesiodens. Treatment depends on the type and position of the supernumerary tooth and on its effect on adjacent teeth.

Definition

A supernumerary tooth is one that is additional to the normal series and can be found in almost any region of the dental arch.

Etiology

The etiology of supernumerary teeth is not completely understood. Various theories exist for the different types of supernumerary. One theory suggests that the supernumerary tooth is created as a result of a dichotomy of the tooth bud.1 Another theory, well supported in the literature, is the hyperactivity theory, which suggests that supernumeraries are formed as a result of local, independent, conditioned hyperactivity of the dental lamina.1,2 Heredity may also play a role in the occurrence of this anomaly, as supernumeraries are more common in the relatives of affected children than in the general population. However, the anomaly does not follow a simple Mendelian pattern.

Prevalence

In a survey of 2,000 schoolchildren, Brook found that supernumerary teeth were present in 0.8% of primary dentitions and in 2.1% of permanent dentitions.3

Occurrence may be single or multiple, unilateral or bilateral, erupted or impacted, and in one or both jaws. Multiple supernumerary teeth are rare in individuals with no other

associated diseases or syndromes.The conditions commonly associated with an increased prevalence of supernumerary teeth include cleft lip and palate, cleidocranial dysplasia and Gardner syndrome. Supernumerary teeth associated with cleft lip and palate result from fragmentation of the dental lamina during cleft formation. The frequency of supernumerary permanent teeth in the cleft area in children with unilateral cleft lip or palate or both was found to be 22.2%.5 The frequency of supernumeraries in patients with cleidocranial dysplasia ranged from 22% in the maxillary incisor region to 5% in the molar region.6 While there is no significant sex distribution in primary supernumerary teeth, males are affected approximately twice as frequently as females in the permanent dentition.7

 

Classification

Supernumerary teeth are classified according to morphology and location In the primary dentition, morphology is usually normal or conical. There is a greater variety of forms presenting in the permanent dentition. Four different morphological types of supernumerary teeth have been described:8,9

• conical

• tuberculate

• supplemental

• odontome.

Conical

This small peg-shaped conical tooth is the supernumerary most commonly found in the permanent dentition. It develops with root formation ahead of or at an equivalent stage to

that of permanent incisors and usually presents as a mesiodens. It may occasionally be found high and inverted into the palate or in a horizontal position. In most cases, however, the long axis of the tooth is normally inclined. The conical supernumerary can result in rotation or displacement of the permanent incisor, but rarely delays eruption.

Tuberculate

The tuberculate type of supernumerary possesses more than one cusp or tubercle. It is frequently described as barrel-shaped and may be invaginated. Root formation is delayed compared to that of the permanent incisors. Tuberculate supernumeraries are often paired and are commonly located on the palatal aspect of the central incisors. They rarely erupt and are frequently associated with delayed eruption of the incisors .

Supplemental

The supplemental supernumerary refers to a duplication of teeth in the normal series and is found at the end of a tooth series The most common supplemental tooth is the permanent maxillary lateral incisor, but supplemental premolars and molars also occur. The majority of supernumeraries found in the primary dentition are of the supplemental type and seldom remain impacted.

Odontoma

Howard lists odontoma as the fourth category of supernumerary tooth. However, this category is not universally accepted. The term “odontoma” refers to any tumor of odontogenic origin. Most authorities, however, accept the view that the odontoma represents a hamartomatous malformation rather than a neoplasm. The lesion is composed of more than one type of tissue and consequently has been called a composite odontoma.Two separate types have been described: the diffuse mass of dental tissue which is totally disorganized is known as a complex composite odontoma whereas the malformation which bears some superficial anatomical similarity to a normal tooth is referred to as a compound composite odontoma.

Problems Associated with Supernumerary Teeth

Failure of Eruption

The presence of a supernumerary tooth is the most common cause for the failure of eruption of a maxillary central incisor. It may also cause retention of the primary incisor. The problem is usually noticed with the eruption of the maxillary lateral incisors together with the failure of eruption of one or both central incisors . Supernumerary teeth in other locations may also cause failure of eruption of adjacent teeth.

Displacement

The presence of a supernumerary tooth may cause displacement of a permanent tooth. The degree of displacement may vary from a mild rotation to complete displacement. Displacement of the crowns of the incisor teeth is a common feature in the majority of cases associated with delayed eruption.

Crowding

Erupted supplemental teeth most often cause crowding. A supplemental lateral incisor may cause crowding in the upper anterior region. The problem may be resolved by extracting the most displaced or deformed tooth.

Pathology

Dentigerous cyst formation is another problem that may be associated with supernumerary teeth Primosch reported an enlarged follicular sac in 30% of cases, but histological evidence of cyst formation was found in only 4 to 9% of cases.Resorption of roots adjacent to a supernumerary may occur but it is extremely rare.

Alveolar Bone Grafting

Supernumerary teeth may compromise secondary alveolar bone grafting in patients with cleft lip and palate. Erupted supernumeraries are usually removed and the socket site allowed to heal prior to bone grafting. Supernumeraries should not be extracted without consultation with the cleft team. Cooperation between the general dental practitioner and the cleft team is essential. Unerupted supernumeraries in the cleft site are generally removed at the time of bone grafting.

Implant Site Preparation

The presence of an unerupted supernumerary in a potential implant site may compromise implant placement. The supernumerary may require removal prior to implant placement. If removed at the time of implant placement, bone grafting may be required.

Asymptomatic

Occasionally, supernumerary teeth are not associated with any adverse effects and may be detected as a chance finding during radiographic examination.

Radiographic Examination

A radiographic examination is indicated if abnormal clinical signs are found. An anterior occlusal or periapical radiograph is useful to show the incisor region in detail. The bucco-lingual position of unerupted supernumeraries can be determined using the parallax radiographic principle:the horizontal tube shift method utilizes two periapical radiographs taken with different horizontal tube positions, whereas an occlusal film together with a panorex view are routinely used for vertical parallax. If the supernumerary moves in the same direction as the tube shift it lies in a palatal position, but if it moves in the opposite direction then it lies buccally. Intraoral views may give a misleading impression of the depth of the tooth. A true lateral radiograph of the incisor region assists in locating the supernumeraries that are lying deeply in the palate and enables the practitioner to decide whether a buccal rather than a palatal approach should be used to remove them.

Management of Supernumeraries

Treatment depends on the type and position of the supernumerary tooth and on its effect or potential effect on adjacent teeth. The management of a supernumerary tooth should form part of a comprehensive treatment plan and should not be considered in isolation.

Indications for Supernumerary Removal

Removal of the supernumerary tooth is recommended where:

• central incisor eruption has been delayed or inhibited;

• altered eruption or displacement of central incisors is evident;

• there is associated pathology;

• active orthodontic alignment of an incisor in close proximity to the supernumerary is envisaged;

• its presence would compromise secondary alveolar bone grafting in cleft lip and palate patients;

• the tooth is present in bone designated for implant placement;

• spontaneous eruption of the supernumerary has occurred.

Indications for Monitoring Without Supernumerary Removal

Extraction is not always the treatment of choice for supernumerary teeth. They may be monitored without removal where:

• satisfactory eruption of related teeth has occurred;

• no active orthodontic treatment is envisaged;

• there is no associated pathology;

• removal would prejudice the vitality of the related teeth.

Recommendations Following Supernumerary Removal

Three factors influence the time it takes for an impacted tooth to erupt following removal of the supernumerary:

• the type of supernumerary tooth;

• the distance the unerupted permanent tooth was displaced;

• the space available within the arch for the unerupted tooth.

Removal of a supernumerary tooth preventing permanent tooth eruption usually results in the eruption of the tooth, provided adequate space is available in the arch to accommodate it. Di Biase found 75% of incisors erupted spontaneously after removal of the supernumerary.Eruption occurred on average within 18 months, provided that the incisor was not too far displaced and that sufficient space was available.

Although the majority of authors recommend exposure of the unerupted tooth when the supernumerary is removed, Di Biase advocates conservative management without exposure.

A lower spontaneous eruption rate of 54% following supernumerary removal was reported by Witsenburg and Boering, who recommend the routine bonding of an attachment and gold chain for orthodontic traction at the time of surgery.19 However, the time and expense involved in this technique may not be justified if the rates of spontaneous incisor eruption are found to be in the region of 75 to 78%, as reported by both Di Biase and Mitchell and Bennett.

If there is adequate space in the arch for the unerupted incisor following supernumerary removal, space maintenance can be ensured by fitting a simple removable appliance. If the space is inadequate, the adjacent teeth will need to be moved distally to create space for incisor eruption. In that case, the primary canines may need to be extracted at the same time as the supernumerary tooth. Where there is adequate space and the incisor tooth fails to erupt, surgical exposure of the incisor and orthodontic traction is usually required.

DEVELOPMENTAL DISTURABNCES IN STRUCTURE OF TEETH

Amelogenesis Imperfecta

Represents a group of hereditary defects of enamel unassociated with any congenital defects of enamel unassociated with any generalized defects.It is basically an ectodermal condition since the mesodermal components are normal.Three basic types of amelogenesis Imperfecta are seen

1) Hypoplastic type2) Hypoclcific type3) Hypomaturative type

C/F

Hypoplastic –The enamel is not formed to full normal thicknessHypocalcific-The enamel is so soft that it can be removed by a prophylaxis instrumentHypomaturative –The enamel can be pierced by by an explorer pointunder firm pressure.

The crowns of teeth may or may not show discoloration.It varies from yellow to dark.In others it may have a chalky texture or cheesy consistency or be relatively hard.It may be chipped or show depressions in the base of which dentin may be formed.contact points between the teeth are often open occlusal or incisal surfaces may be abraded.

R/F

The overall shape may or maynot be normal,depending on the amount of occlusal wear.The enamel may be totally absent or when present it is a thin layerchiefly over the cusps & on the interproximal surfaces.

H/F

There is a disturbance in the differentiation or viability of the ameloblasts in the hypoplastic type,and this is reflected in defects in matrix formation up to and including total absence of matrix .In the hypocalcification types there are defects of

matrix structure and of mineral deposition.In the Hypomaturation types there are alterations in enamel rod or rod sheath structures.

TREATMENT

There is no treatment except for cosmetic appearance.

Dentinogenesis Imperfecta (Hereditary Opalescent dentin)

Shields & his co-workers have given the following classification

Type-1 Dentinogenesis Imperfecta with odontogenesis ImperfectaTpye-2 Dentinogenesis Imperfecta without odontogenesis ImperfectaType-3 Dentinogenesis Imperfecta of brandywine type

C/F

The deciduous teeth are affected more severely than permanent teeth in type1 whereas in type2 the dentitions are equally affected .both dentitions are affected in type3 .

The color of teeth may vary from gray to yellowish brown but exhibit a characteristic unusual translucent or opalescent hue.The enamel may be lost early through fracturing away ,especially on incisal & occlusal surfaces of teeth.the usual scalopping of this junction is reportedly absent .With the early of enamel the dentin undergoes rapid attrition and the occlusal surfaces are usually attrited.

R/F

Partial or total obliteration of the pulp chambers and root canals by continued formation of dentin .The roots may be short or blunted ,the cementum ,periodontal membrane ,supporting bone appear normal.The teeth of type3 are characterized as shell teeth.Enamel is normal ,dentin is extremely thin & the pulp chambers are extremely enormous . roots of the teeth are extremely short

H/F

It is purely a mesodermal disturbance.Enamel is essentially normal except for its peculiar shade, the dentin is composed of irregular tubules,often with large areas of uncalcified matrix.The tubules tend to be larger in diameter & hence less numerous.The odontoblasts have limited ability to form well-organised dentinal matrix,& they appear to degenerate easily,becoming entrapted in this matrix.

TREATMENT

Treatment is directed at prevention of enamel and dentin loss through attrition.Cast metal crowns on the posterior teeth & jacket crowns on the anterior teeth.

DENTIN DYSPLASIA (rootless teeth)

Is a rare disturbance of dentin formatin characterized by normal enamel but atypical dentin formation with abnormal pulpal mormphology.The 1st concise description of the disease was published in 1939 by Rushton .

SHIELDS & ASSOCIATES CLASSIFIED INTO

Type1- Dentin dysplasia

Type2 – Anomalous dysplasia of Dentin

Acc to Witkop Type1- Radicular denitn dysplasia Type2- Coronal dentin Dysplasia

ETIOLOGY

A Hereditary disease transmitted as an autosomal dominant characteristic.

CLINICAL FEATURES

Type1(radicular)-

Both dentitions are affected Teeth appear normal in morphologic appearance &color Amebr translucency may be present Teeth exhibit normal eruption pattern Teeth exhibit extreme mobility & are exfoliated prematurely

Type 2 (coronal)

Both dentitions are affected Deciduous teeth exhibit yellow ,brown,or bluish-grey opalescent appearance Permanent dentition is normal

R/F

Type1 In both dentitions roots are short, blunt,conicalor similarly malformed Decidous dentition pulp chambers are completely obliterated Permanent dentition shows crescent shaped pulpal remnant.

Type2

In deciduous teeth pulp chambers are completely obliterated. The permanent dentition pulp chamber is abnormally large described as a Thistle tube appearance.

TREATMENT

No treatment ,prognosis depends on occurrence of periapical lesions & upon the exfoliation of teeth due to inceased mobility.

REGIONAL ODONTODYSPLASIA(GHOST TEETH)

An unusual dental anomaly in which one or several teeth in a localized area are affected in an unusual manner..Maxillary teeth involved more than mandibular.Maot frequently involved being maxillary permanent incisor ,lateral incisor & cuspid.the deciduous & permanent are involved.C/F

The teeth affected by odontodysplasia exhibit either a delay or a total failure in eruption. Their shape is markedly altered,being generally very irregular in appearance & defective mineralization .

R/F

Marked reduction in radiodensity & teeth assume a ghost appearance.Both the enamel & dentin appear very thin & the pulp chamber is exceedingly large.

TREATMENT

Because of poor cosmetic appearance extraction with restoration using a prosthetic appliance.