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Um Yes. So um hydroxyapatite. So it's, it's part it's an inorganic component found in dental enamel and it's the outer layer of our teeth. So, enamel acts as a protective shield for our teeth and understanding the chemistry behind it is vital. So, um genetic or environmental origins can have an impact on enamel and can cause defect during its secret or maturation stage. So, if there was a disturbance in enamel matrix deposition, for example, it would cause hyperplasia which looks like pits or grooves on the enamel surface. And then if it, if there was a defect in enamel maturation, um it can cause hyper maturation. So the teeth would look opaque, not transparent. So what is hydroxyapatite? The mineral is composed of calcium and phosphate ions and it's arranged in a structure of enamel rods which extend from the dentine enamel junction to the outer surface of the enamel. Uh The chemical formula is here and it encapsulates the essence of its composition. I remember in the exam they like to ask us questions on um substitutions and the chemical formulas. So memorize those and note that the um hydroxide ion and hydroxyapatites can be replaced by fluoride or chloride as well, resulting in poor appetite or poor appetite. And the substitution plays a role in the mineral. So, solubility which is a crucial aspect of dental health and can in turn later on cause erosion and like pain. So it's quite important to know that we go into solubility later and substitutions. So definitions, um hyperplastic means a reduced quantity of enamel. Whilst hypomineralized refers to less mineralized tissue and um enamel hyperplasia. Um It's a quantitative defect and can obviously manifest as pits, grooves or irregular shaped teeth due to disturbances in the initial matrix deposition. So it's quite important to know which part affect which stage in enamel formation. Um enamel hypomineralization is a qualitative qualitative defect resulting in more opaque enamel with discolorations and a common common form of it which you'll later learn in pediatrics is molar incisor hyper mineralization which affects the first permanent molars and incisors in Children. So, um it's important to know the difference between surface and core enamel. So surface enamel is harder, it's less porous, it's less soluble and plays a crucial role in protecting the underlying structures of our teeth. And ha so here's a just um a diagram, a table for you to use for your own revision. It's because sometimes they ask questions on the differences between the enamel. Um So neogenesis and perfector. So it's an X linked disorder and can result in defects during the secretory stage leading to a thin and disorganized enamel layer. Sometimes it chips off. Um We explore the genetic aspects and environmental factors contributing to amelogenesis imperfecta. So, um and there's about there's a multiple genes specifically the ones here. So ba 83 HP 20 A in A um A B LX and those contribute to 60% of amelogenesis imperfecta cases. So make sure to know the genes um because they do ask that sometimes in the exams, um it causes defects in the D to enamel junction and can result in the enamel layer sharing really easily. So there's differences in how it shows between males and females. So if there's an affected male member of a family with X linked amelogenesis and factor, it presents as a brown mottled like hypermature enamel. So it looks quite opaque. Whereas if it was a female member, um it shows us alternating areas of normal and hypermature enamel. So it looks kind of stripy and that's because of the two X chromosomes. Um So environmental defects. Um so the environmental factors also play a role in enamel defects, infectious diseases during childhood, uh fluorosis, which um from excessive fluoride indigestion of over five parts per million, you don't find much fluorosis cases in the UK. But in other areas or um if people have been using fluoride in other, in a, in a way that you haven't advised and sometimes you can see that and the incorporation of certain substances into the mineralized matrix such as the antibiotic tetracycline. Um So that's why you can't use it during pregnancy. Um That can also contribute to enamel issues. So, yeah, and also dietary deficiencies as well. So, the enamel ph during the maturation stage. Um so the ph during this stage in enamel formation osculates between acidic and neutral and the the the the deposition of hydroxyapatite releases hydrogen ions and, and which acidifies the environment and to counteract this acidity. Um smooth ended ameloblasts express um carbonic anhydrase two which is an enzyme and produces bicarbonate ions to a neutralize the acid. And this balance um is essential for proper maturation of enamel. So the chemical composition of an enamel's mineral phase enamel rods compose of bundles of over 1000 crystallite. Lights extend from the dentine enamel junction to the enamel surface. Um hydroxyapatite is the main component. And you see the formulas here, it can be written in two forms. So make sure to memorize that um crystallite growth occurs through the epitaxial and prism pain along with the axis um which thickens the enamel, giving enamel, its unique structure of elongated hexagonal crystals. And now substitutions. So we like to ask this question. I remember it came up in mine. So um fluoride ions replace hydroxide ions resulting in the formation of flu appetites which is less soluble and contributes to caries prevention. So, um other substitutions can also occur such as carbonate ions for um hydrox hydroxide ions or phosphate ions and magnesium, magnesium ions for calcium ions. And the the both of these can destabilize the structure and sodium or lead also can also be occasionally substituted for calcium. Um So, understanding these substitutions is essential for comprehending the behavior of hydroxyapatite. Um regarding solubility at different ph levels. That's why sometimes dentists prescribe fluid varnish if um a patient has like qui acidic diet, for example. Um So acid etching. Um so it's a acid acid etching is it generates a rough surface and is a form of micromechanical retention to help bond materials like composites onto your teeth. So on deck, we use scotch bond which is 37% PPO acid. The etching pattern depends on the nature and concentration of the acid used and the orientation of the crystals. Um This rock surface enhances bonding with materials used in dental restorations. And um there's different forms of calcium phosphate minerals and in enamel, there's one called os calcium phosphate crystals and these act as a precursor to form substituted hydroxy hydroxyapatite crystallite and enamel formation. So, um when I did this, I kind of revised it as if like a like a kind of memorized this in order. So, um it involves secret ameloblasts um indicate indicating the position of the enamel space to the tomes process um which is an extension of the ameloblast to allow secretion. Um This then the assembly of amlo amylogenin secreted from the ameloblasts forms a structural framework and then calcium and phosphate ions are transported in a super super saturated solution resulting in crystal Nucleation. And to control crystal growth morphology and orientation um is specifically dictated by amelogenin nanospheres. And it's critical for the proper formation of enamel and to stop initial crystallite growth is done by degradation of the matrix. And the final maturation stage of crystal growth is also um happening at the same time as the degradation and loss of the matrix at all, all at the same time. So now I'm going to move on to some questions. Hopefully you picked it up. I've got two questions and um if you want to comment it in the comments, like the chat section, I've got the um I've got a poll as well. I can upload it on up to you. So you guys can either answer it on the chat or you can just click on the right answer on the poll and then we can see who gets it right? It's, it is anonymous s the back back. So we've got three answers so far. Um Five answers, six answers. So it looks like everyone's getting the first question right? Mm So I think the second question um seems to be a bit more varying responses. Yeah. So everyone's got basically the first question, right? Which was um yeah, so that was correct. The first one everyone's gotten right? Second one. The answer was a the first one. I get they can be a bit confusing but I think mainly remember the first one, carbonate ions substitute hydroxide ions and then the phosphate or magnesium for calcium. That's like that's common, I guess. But just remember that those in general have a destabilizing effect. Yeah. Does anyone have any questions? You can either unmute yourself now or um put anything in the chart and it can be questions about this topic, any other topics or, or just in general about your exam. Um, yeah, feel free to ask. No, no questions. Hopefully that's a good sign.