CTB 21

flourosis is caused by what concentration of fluide

5ppm 1ppm = beneficial to reduce caries

Acid-Etching Techniques

Etching enamel surface with acid (enamel conditioning) is beneficial for adhesive dental restorative materials; by achieving two aims: - Removing plaque and other debris; - Removing a thin layer of enamel (enamel rod more than interrod) to increase the surface area for better bonding surface for adhesive materials (retention depends mainly on mechanical interlocking) . • Etched enamel appears matt and whiter;

Amelogenesis imperfecta

abnormal formation of tooth enamel, resulting in separation from the dentin beneath

transitional phase

after enamel thickness formed Decrease in height & volume of ameloblasts (morphological changes); • 50% of ameloblasts die (apoptosis) and the rest become *protective stage*

what regulates the calcium uptake

alcium-adenosinetriphosphatases (Ca-ATPase) membrane activity; calcium is actively pumped into enamel matrix; excess calcium is removed.

Linear Enamel Hypoplasia

It is a disruption to enamel formation that causes deep grooves to form on the surface of the tooth. Generally caused by poor nutrition "stressful event" during the development of the tooth. - High fever during childhood diseases (illness) can cause chronological enamel hypoplasia.

what are the 3 main functional stages of ameologenesis

Presecretory Secretory Maturation

nasmyth membrane

REE (papillary layer and ameloblasts) and basal lamina( primary enamel cuticle) form nasmyth = covers the enamel of unerupted teeth because hemidesmosomes are leaky, fluoride and other trace elements can be incorporated at surface of enamel

cyclic modulation = ruffled end

Ruffle ended - leaky junctions between ameloblasts at proximal (basal) end; tight junctions at distal (enamel) end; - selective transfer of calcium ions across ameloblast layer (pumping calcium ions into that maturing enamel).

calcium transport = where

ameloblast layer (enamel epithelium) during the secretory stage of enamel formation ruffle-ended and smooth-ended phases of the maturation stage.

step 2 ameolgenesis

enamel because fully mineralised (96%)= fully mature, organic content decreases crystals become much wider and thicker

Reduced enamel epithelium REE

papillary layer and ameloblast layer regress to form reduced enamel epithelium REE

primary enamel cuticle

is a basal laminar secreted by ameloblast After eruption, primary enamel cuticle (basal lamina) interacts with saliva and becomes acquired pellicle on the exposed crown (later with plaque adhering to it)

enamel matrix

matrix is secreted by ameloblast= matrix is then formed extracelllllarly is composed of two protein families - enamelins = role in controlling Ca and K conc - amelogenins = structure All relevant information for assembly must reside in structure of the protein Matrix disassembled during maturation phase = why concentration of pre mineralised dentine is high in organic matter

enamelins

matrix secreted first - hydrophilic proteins - Reach 10% of the matrix content; - important rollin calcium & phosphate conc and crystal nucleation = due to hydrophilic and acidic nature.

prescretory stage

morphogenetic stage = shape of the crown is established = bel stage of development -dentine is not yet mineralised, -IEE cells are short (cuboidal or low columnar) with centrally placed nuclei. histodifferenation stage: - increased length -change in polarity- then they start to prepare to produce enamel = synthesise proteins, the basal lamina is lost the cells are now ready to produce enamel nothing is produced, cells are tight junction

amelogenins roles

- Hydro*phobic* proteins; - Reach 90% of the matrix content; due to hydrophobic nature they have two roles in mineralisation: • Guide in formation of enamel crystals • Restrict growth in thickness and width of crystals, which form between them.

role of the REE

- binds to oral epithelium during eruption to prevent bleeding - fuses cervically with oral epithelium = forming junction epithelium - REE protects the unerupted crown surface from resorption by osteoclasts and from deposition of cementum.

cyclic modulation = smooth ended

- leaky junctions distally - proteins and water exit (leaving the maturing enamel); - interstitial fluid leaks into maturing enamel between ameloblasts (to neutralise the pH of enamel fluid); - trace elements are incorporated in the interstitial fluid & enter enamel fluid in enamel layer (e.g. strontium and fluoride).

rod sheath

The distal portion of Tome's process elongates as enamel thickness increases, becomes thinner as the enamel rod grows in width, gets squeezed between rod & interrod enamel, creates narrow space between them that fills with organic material and forms rod sheath. where the 3% organic material in enamel lies

Enamel Matrix - secretory phase

amlogenin and mineralised enamel ribbon are secreted from ameleoblast amelogenin forms nanospheres = which guide the formation of enamel crystals and Restrict growth in thickness and width of crystals, which form between them

Enamel hypoplasia

appears as a groove or pit in enamel surface, while enamel hypomineralisation (less mineral; abnormal maturation) appears as a smooth surface but with abnormal colour.

step 1 of amelogenesis

bell stage of tooth development once dentine is formed will send signal to IEE cells to become ameloblast = cells will become taller and begin secreting the enamel matrix = it is partially mineralised(30% mineral content) = roles enamel layer ameoloblast produce the 1st layer of enamel, they begin to move away from the dentine

enamel matrix maturation phase

clevage of amelogenin = causes collapse of nanospher and thickening of crystals ameloblast pump Ca, K and CO3 ions into matrix and remove water and degraded protein = mineralisation

Papillary layer

formed from remnants of stellate reticulum, stratum intermedium and outer enamel epithelium (with blood vessels) .

secretary

initial secretory stage - cells elongate - = tomes processes = not present = no rods are formed = rodless enamel is produced Secretory stage - ameloblasts produce tomes process, this extends into the unmineralised enamel, = distal part of tomes process = secretion from here forms the enamel rod = proximal part = inter-rod http://downloads.lww.com/wolterskluwer_vitalstream_com/imageBanks/9788184733679_Rajkumar_Sample/images/preview/figure_30.20.jpg rod sheath is formed outermost layer of enamel is being formed distal portion of Tome's process = lost = forms thin rodless enamel layer. = similar to the initial enamel layer, = ameloblast become squat again = no rods = no organic material = higher mineral content in the outer section

Abnormal Enamel

poor oral hygiene (not related to enamel formation & development): e.g. White spot lesions in enamel surface (mainly due to demineralisation in enamel surface near the gingival margin or fissures, will progress to create a cavity (caries).

febrile disease

treatment with tetracycline antibiotics which can disturb and be incorporated into mineralising tissues. For enamel it results in a band or even total brown pigmentation depending on the magnitude and the duration of the treatment (loss of enamel may also occur); environmental cause for enamel defect (another example fluoride

Molar Incisor Hypomineralisation: MIH

• Affects teeth forming in the first year of life; permanent First molars and incisors but molars more affected than incisors • Associated with opacities & loss of enamel in severe cases • Molars are fragile and caries can progress easily...Preformed metal crowns is the possible treatment option. • More common in children who have taken amoxicillin in first year of life, usually for otitis media - associated with hypomineralisation - Amoxicillin use for 20-24 months correlated with fluorosis in permanent dentition. - Inanimalmodels,amoxicillinassociatedwithinterferencewith ameloblast function and temporal sequence of amelogenesis events. - Interference believed to be at secretory phase.

maturation

• Hardening of enamel due to growth in width and thickness of pre-existing crystals. - Ruffle-ended ameloblast of maturation stage - Smooth ended ameloblast of maturation stage cells start to reduce in size= become same size as first cell 2 stages transitional phase maturation phase

direction of mineralisation of enamel

• Mineralisation increases from EDJ to surface in both primary and permanent teeth • Mineralisation increases occlusally( grinding surface) to cervically in permanent molars, and both permanent and primary incisors. no gradient in primary molars 3rd molars = thickest enamel compared to 1st = • Primary teeth are less mineralised than permanent because less time in maturation phase.

Maturation - Post Secretory Ameloblast Proteins

• Proteins used in maturation and degradation (amlogenins and non-amlogenins): - Kallikrein4 - Enamelysin • Non-amelogenins (enamelin & ameloblastine) at periphery of enamel prisms form enamel sheath • Basal lamina protein - Amelotin (also present in junctional epithelium; involved in adherence to enamel) • Produced during maturation stage

maturation phase of maturation

• Removal of water and proteins from matrix • Transport of ions required for accretion of mineral • Cyclic modulation of ameloblasts: - varies depending on ruffle ended & smooth ended borders = modulation = essential to maintaining environment that allows *accretion of mineral content (ruffle ended)* & *loss of organic matrix (smooth ended)*, through alterations in permeability of the enamel organ.