"Well it's true, our appearance fills our confidence. but there are some diseases that destroyed not only our health but also our confidence and we think before we smile and AMELOGENESIS IMPERFECTA is one of them"

AMELOGENESIS IMPERFECTA:

Amelogenesis imperfecta is a congenital disorder characterized by abnormal formation of enamel of teeth which is not related to any systemic disorder. The disease involves only enamel of the tooth the rest of the teeth structure like dentine and pulp remain normal.

Defect causes abnormality in the structure of enamel and therefore affects their clinical appearence and funtions.

AMELO = ENAMEL( enamel is the hard , mineral-rich material that forms the protective layer of your teeth) GENESIS = GROWTH IMPERFECTA = POOR

ETIOLOGY:

Amelogenesis imperfecta accurs due to mutation of the gene related to enamel formation. These are responsible for making the proteins ( AMELX, ENAM, MMP-20, KLK-4, AMBN ) needed for normal formation of enamel. Mutation in these gene causes AMELOGENESIS IMPERFECTA.

Depending on what gene is getting mutated it effects a particular stage of enamel development. The defects in the stage of development influences the clinicl appearence of the enamel. Amelogenesis imperfecta can have different inheritance patterns depending onthe gene that is altere

AMELOGENESIS (FORMATION OF ENAMEL)

Alteration in enamel of the teeth is developmental, that's why its important to first understand the developmental stages of the teeth.

Amelogenesis is the process of formation of enamel and this formation is done by ameloblast, these ameloblasts are actually the inner enamel epithelium of the enamel organ which are called ameloblasts only when they are fully differentiated. so life cycle of ameloblasts are the functional stages of the cells of the inner enamel epithelium which the pass through during tooth development and eruption.

LIFE CYCLE OF AMELOBLAST:

The life cycle of ameloblast has six stages which are classified under three categories

PRE- SECRETORY STAGE ( in which the cells prepare themselves for secretory enamel.)

MORPHOGENIC STAGE
ORGANIZING STAGE

SECRETORY STAGE ( in which actual enamel formation accur)

3. FORMATIVE STAGE

POST- SECRETORY STAGE: (in which maturation and protection of enamel done)

4. MATURATIVE STAGE

5. PROTECTIVE STAGES

6. DESMOLYTIC STAGE

1- MORPHOGENIC STAGE : The cells of the inner enamel epithelium decide the morphology of the crown of the tooth that is to be formed hence the name morphogenic stage, in this stage the cells of the inner enamel epithelium are short columnar with alarge oval nuclei which fills the cell body the mitochondia are evenly distributed in the cytoplasm whereas the golgi bodies and centrioles are located in the proximal ends, a basement membrane is attached to these cells which separates them from the connective tissue of the dental papilla, there is a cell free zone just beneath the inner enamel epithelium in the dental papilla which has no cell

2- ORANIZING STAGE: The inner enamel epithelium cells organize themseleves to differentiate into ameloblast hence the name organizing stage, the cell increase in size and become tall columnar the nucleus shift toward the proximal ends, this shift called REVERSAL POLARITY ( Shift of ameloblast nucleus to the proximal end away from the dental papilla.). Which creates a nucleus free zone in the distal half of the ameloblasts the mitochondia shift toward the proximal end whereas golgi bodies and centrioles move to the distal end the basal membrane is still present whereas the cell free zone of dental papilla disappears as ameloblasts elongate and come in direct contact with the cell of the dental papilla so to differentiate them to odontoblast.

3-FORMATIVE STAGE: Once cell of the dental papilla differentiate into odontoblast they start deposite dentine this dentine send signal to ameloblast to form enamel hence entering formative stage and enamel organ enters the advanced BALL stage. The ameloblast elongate and develop pyramidal processes at the distal end called TOMES process. Tomes process are seprated from the cell proper by an incomplete septa called distal terminal bars. Basement membrane disintegrates in this stage . Tomes process they have a non- secratory side and a secretory side the secretory side has two parts proximal part and a distal part.Distal part produces enamel rods and proximal part produces the inter-rod. Ameloblast also undergo the reversal of nutrition that is till the organizing stage the ameloblast were getting nutrition from the dental papilla but once formarive stage begins and enamel dentine deposition starts this source of nutrition get blocked the new source of nutrition is the dental sac adjucent to the outer enamel epitelium

4- MATURATIVE STAGE : the whole thicknss of enamel is formed then ameloblast enter tthe maturative stage, two process take place in maturative stage first oragnic matter is reabsorbed from the enamel second menirals are released into it hence maturation of enamel accur about 50% of ameloblast undergo degeneration by apoptosis, in the ameloblast tomes processes disappear the cell reduce in size but are still tall columnar they re-secrete the base membrane between them and the enamel the distal surface of the ameloblast now altwrnates between being smooth and ruffled, cells have a ruffled border they are relatively in a more active state the ameloblast have numerous lysosomes shows endocytosis of enamel organic matrix and simultaneously pump out calcium for mineralization they also release bicorbonatesto maintain th ph whereas ameloblasts have smooth border they are relatively less active and only absorb some enamel proteins this process by which ameloblast alternate cyclically between having ruffled border and smooth border is called modulation and it accurs every six to eight hours. The maturative stage is about 3 times longer than formative stage.

5- PROTECTIVE STAGE : Once whole enamel is formed ane mineralized the function of ameloblast is over now this enamel needs to be protected from what from the surounding connective tissue if these enamel comes in contact with the connective tissue two things may happen either resorption of the enamel and formation and formation of developmental anomalies or it may cause deposition of cementum so this protective role is played by the ameloblast as they are already covering the enamel the ameloblast being tall columnar cells reduce in size and become cuboidal and can't be distinguished by other layer, the enamel organ itself is reduced in size and is now called REDUCED ENAMEL epithelium.

6- DESMOLYTIC STAGE: In addition to protecting the formed enamel the reduced enamel releases enzymes into the surrounding connective tissue these enzymes cause desmolysis hence the desmolytic stage and therefore helps in eruptive movements of the tooth that is why premature loss of enamel epithelium may prevent the eruptive forces of the tooth.

TYPES OF AMELOGENESIS IMPERFECTA:

There are 4 main types of amelogenesis imperfecta:

HYPOPLASTIC TYPE (type I )
HYPOMATURATION ( type II )
HYPOCALCIFIED ( type III )
HYPOMATURATION/ HYPOPLASIA / TAURODONTISM (type IV )

HYPOPLASTIC ( type I )

Defect in the formative stage lead to type I or hypoplastic amelogenesis imperfecta, about ( 60 to 70% ) cases of the anomaly are hypoplastic type where the basic defect is the inadequate deposition of enamel matrix, the mineralization is normal.In hypoplastic mutation in ENAM (which form Enamelin protein, enamel matrix protein important in crystallite elongation and is essential normal tooth development) accur, where individual were homozygous ENAM mutation of chromosome 4 they show enamel pitting with an anterior open bite, where as heterozygous presented only with the enamel pitting.

The exhibit complete absence of enamel from the crown surface or there may be very thin layer of enamel on some focal area of the crown

HYPOPLASTIC TYPE ARE SUBDIVIDED INTO 4 OTHER PATTERN .....

> THE GENERALIZED PATTERN : effect the entire dentition pin points are present on buccal surfaces of teeth later on staining of the pits may accur. the enamel present in between these pits as of

normal thickness, hardness and coloration

>LOCALIZED PATTERN : effect only some teeth in the oral cavity, large defects on the buccal middle third of the teeth are seen

>SMOOTH PATTERN: enamel exhibits a smooth surface which is thin , hard and glossy

>ROUGH PATTERN: the enamel is thin, hard and rough.

HYPOMATURATION (type II ) :

Hypomaturation amelogenesis imperfecta is characterized by adequate deposition and mineralization but inadequate muturation of crystallite. about (20 to 40%) cases of amelogenesis imperfecta are hypomaturation type the basic defect is the maturation of enamel crystal structure which result in the alteration of enamel rod and rod sheath.In this stage KALIKRIEN 4 protein secreted by KLK4 gene, it's funtion is removal of enamel matrix during maturation stage.

Divided into two pattern

PIGMENTED PATTERN : in pigmented pattern enamel has a motted and brown appearence

2- SNOW- COPPED PATTERN : in the snow copped pattern zone of opaque white enamel is seen on incisal or occlusal edges

.HYPOCALCIFICATION (type III):

Defect in calcification stage lead to type III or hypocalcification amelogenesis imperfecta associated with soft cheesy enamel that is lost rapidly and diffusely after eruption enamel can easily be removed with blunt instrument and much of the coronal or incisal enamel is lost as the teeth come into function except for the cervical portion of the tooth which are left.

HYPOMATURATION / HYPOPLASIA/ TAURODONTISM ( type IV):

Characterized by hypomaturation and hypocalcification of enamel, or let say mixture bof type I and type II is known as type IV.

TREATMENT:

Main problem people with amelogenesis imperfecta are facing is socialisation, function, and discomfort. Amelogenesis imperfecta managed by early viorous intervention, both preventively and restoratively. In primary dentition may be protected by use of preformed metal crowns on posterior teeth. the long term care involves either crowns or more frequently these days adhesive, veneers, plastic restoration.

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