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Why don't teeth regrow?

Discussion in 'Science' started by Danske, Feb 15, 2013.

  1. RobRoySyd

    RobRoySyd Member

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    Rabbits and rodents don't have molars for grinding. It's only the front incissors that have a very effective overlapping cutting action that keep growing.
    No need to keep grazing if humans had them. We'd either be visiting the dentist as regularly as we visit the barber or we'd have a Dremel tool in the bathroom beside our tooth brush.
    I think not to be overlooked here is that it's the anantomy of our mouth, teeth and tongue that enables us to make a complex range of sounds that enabled us to develop speech.
     
  2. oculi

    oculi Member

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    I dunno, birds can talk pretty well too.
     
  3. millhouse

    millhouse Chief Tiger Dentist

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    Interesting question OP.

    Mammalian species are diphydont (by and large) meaning they have two sets of teeth - deciduous "baby" teeth and permanent teeth. Some species have deciduous teeth that are not readily seen - for example rabbits deciduous teeth are frequently shed in utero.

    Some have mentioned the continued growing of teeth by some mammals eg: rats and rabbits. This certainly can be the case in some species. Rats for instance have continuously growing incisors, yet their premolar/molars are like ours and do not continually gorw. Rabbits however have continuously growing teeth throughout the mouth. Some species have teeth that continuously erupt however they are of a finite size eg: horses. These teeth continuously erupt throughout life (at varying rates) however at some point in time they are lost as they "run out".

    Evolutionarily we did not have larger jaws. The teeth we have now are as large and the jaws correspond to this. The concern over wisdom teeth no fitting in is due to diet change in the modern human. Looking in the morror you can see that your incisors (front teeth) are wine glass in shape. That is to say the teeth are narrower towards he gum. In our ancestors as we ate less "clean" food we would wear away our teeth at a much faster rate (as seen in a lot of tribal people). As the teeth wear down the width of the tooth is smaller. Our teeth are designed to have a slight migration towards the front of the mouth - this results in two things. There is enough space for the wisdom teeth to come up, as they com up later in life, and if the front teeth have not worn down and become narrower these teeth will become overcorwded and start to displace (hence the growing market inmiddle aged women's orthodontics). Our jaws and wisdom teeth are jusy fine, we just don't wear away our teeth as much as our ancestors.

    As for pain - we would most definitely deal witht he paion and discomfort of a third set of teeth erupting. As omghi said, the majority of people really suffer little whentheir secondary teeth are erupting.

    The outer surface of the crowns of our teeth is enamel - this is only created once when the tooth bud is developing in the jaw. Once made that is it, you get no more. It is a very hard material made of hydroxyapatite crystals. Enamel is partially transparent. This is why teeth naturally go an ivory colour as we age, because the less enamel we have, through wear and damage, the more dentine we see - hence teeth yellow (yes staining occurs, but a large amount is due to age related loss of enamel).

    The bulk of our teeth is made up o tissue called dentine. This is also made up of hydroxyapatite crystals, but also has other materials and is arranged in multiple tubular structures. The common name for dentine - ivory. Dentine is created throughout the life of the tooth. It is created primarily when the tooth is developing within the jaw, but secondarily throughout life as aging occurs. It can also be laid down in reponse to irritation and trauma.

    Covering the surface of the roots is cementum. Unsurprisingly this cementum is also made up of predominantly hydroxyapatite crystals, but is arranged differently to enamle and dentine. Cementum also continues to be laid down throughout life, however at a much slower rate that dentine.

    Within the dentine of the tooth lies a space that is filled with the majority of the living tissue of the tooth - the pulp (also called "the nerve"). this supplies nutrients to the Odontoblasts who lay down dentine, and also provide sensation from the tooth to the brain.

    No, teeth do not regrow. Decay is not due to them not being able to regrow fast enough. The only growth in a tooth is in the cementum or the internal pulp chamber.

    No you are incorrect. What do you think they grind their food up with? As mentioned above rats do have no continuously growing premolars/molars, yet have continuously growing incisors. Some rodents do have continuously growing premolar/molars, for example guinea pigs. Rabbits are not rodents and do have continuously growing premoalr/molars.
    ___________________
    Someone answered pretty early on. We don't need a tertiary set of teeth as we have completed our evoltionary purpose by the time the secondary set are in use. Once we have reproduced we can go on and die. This is certainly what we went on and did prior to all this medicine stuff! (and other advancements).
     
  4. Alpha2k6

    Alpha2k6 Member

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    I have not read much of this thread.

    But I have heard of several cases where adults have gotten new sets of teeth both 1 and 2 times, after the first time of loosing the babyteeth.. im sure it can be found in medical journals somewhere :)

    would be neat if possible to activate some gene to make a new set of teeth grow :)
     
  5. Luke212

    Luke212 Member

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    it does remineralise. if sometihng comes between the boundary of saliva and tooth, remineralisation is halted and demineralisation (decay) can occur.

    are you a dentist lol (tldnr)
     
  6. millhouse

    millhouse Chief Tiger Dentist

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    Yes I am, a Veterinary Dentist.

    So now you want to use a different term - remineralisation? Why didn't you say this before? This is a very different word than re-grow. Remineralisation is on a very small scale. The materials really do not build the tooth up to any great extent. If you have a paper that shows the tooth regrowing via remineralisation I would love to read it. In fact the world would love to read it.

    Did you even read the link YOU provided? Obviously it was too long, and you didn't read. Caries has is NOT caused by something getting in between "the boundary of saliva and tooth".
     
    Last edited: Feb 16, 2013
  7. rush

    rush Member

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    Do you sell flouridated schmackos?
     
  8. Luke212

    Luke212 Member

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    yes its called acid, from bacteria on the boundary. is dentistry your main job or are you mostly a vet?
     
  9. millhouse

    millhouse Chief Tiger Dentist

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    Main job.

    Luke why dont you actually use the appropriate words? If you (correctly) meant to say that acid is the cause of demineralisation in caries, then say that. Something causing decay is very vague thing to say. This is the Science sub-forum, accuracy is expected. Coming from saying teeth do regrow, to acid is the cause of decay is a long way to come. You should have just said so in the first place, and you would have been correct.

    Caries is caused by the interaction of acid and the tooth material (dentine or enamel, sometimes cementum). The acid produced by certain bacteria changes the chemical processes that occur at the interface surface of the tooth, changing the way the continuous process of mineralisation/demineralisation occurs. As the tooth material is structurally damaged, it becomes soft and will eventually be lost leading to a carious lesion. It is not "something" getting in between saliva and tooth. It is a chemical process. The tooth is still in contact with the saliva.

    No we don't use fluoridated schmakos. The fluoride provided in the water supply is more than enough in the species that are not particularly prone to caries.
     
  10. Foliage

    Foliage Member

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    http://wiki.answers.com/Q/Is_it_true_that_some_people_grow_three_sets_of_teeth

    Someone compiled a list of anecdotal responses from people who have 3 or more sets.

    lol
     
    Last edited: Feb 16, 2013
  11. OP
    OP
    Danske

    Danske Member

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    So... After all this talk, I guess I'll ask the same question again, why can't most of us regrow teeth?

    Is it just something that's been genetically programmed in us that ~2 sets is enough (bar the odd case of sharkteethitis :lol:)?
     
  12. rush

    rush Member

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    Yes, that is basically it.
     
  13. Foliage

    Foliage Member

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    Example, people with 2 sets have them fall out halfway through their life, then they can't eat and die hence no longer reproduce. A rare species of human has 3 sets of teeth, they do not die and keep reproducing, as they are alive and reproducing for longer, more of their offspring exist compared to the 2 set human.

    Over 1000 years the 2 set human becomes extinct as they are disadvantaged in comparison.

    Another example, people with 2 sets of teeth find they last their entire life time without issue, they can eat and reproduce fine. A rare species of human has 3 sets of teeth, the third set causes problems as they get infections as they try and force through too early, they hence stop eating and die. 3 set humans do not reproduce hence there are bugger all of them.

    Final example is the 2 set and 3 set humans have no advantages or disavantages, so some have them some dont.

    It all comes down to evolution, traits that make you stronger than the rest become extremely popular, traits that make you weaker are almost always killed off immediately. Traits that have no benefit what so ever (similar to noise in DNA) can be sparse or common, eg the tail bone in humans.

    Scientifically why can't we regrow them? Well our DNA isn't coded for us to do so, sometimes people do get the gene to code for them though so you get the few weird individuals that have 3-4 sets of teeth (eg link above).

    Make sense?
     
    Last edited: Feb 16, 2013
  14. The Wolf

    The Wolf Member

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    I don't beleive that the presence of absence of tertiary teeth is an evolutionary trait. I think the reason goes deeper into the fact that the pathway for it to occur cannot. (see below)

    It's not so much about DNA coding. Budding (the beggining stages of teething) is linked to a developmental stage. The differentiation of the cells that lead to tooth buds have begun their differentiation early in the childs development.
    The reason our teeth do not regrow is that our cells have 'turned off' their instruction set to be teeth. I am unaware of any differentiated cells that can go backwards in their pathways. There may be serious problems if we try and trigger the developmental stage that would lead to tooth formation in an adult
     
  15. Foliage

    Foliage Member

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    It was more of an example of evolutionary traits rather than exactly what happens as I just simply don't know enough about it to be accurate. Perhaps comparing us to a shark with unlimited regenerating teeth which would use more energy than simply 2 sets would have been better, eg we have whatever DNA that sharks have that allow for this to happen (probably a massive change).
     
  16. Dropbear

    Dropbear Member

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    because there is no evolutionary advantage in us having this ability..

    we are able to survive long enough for us to breed, and for our progeny to survive to an age where they self sufficient (around 30-40 year lifespan) with two sets of teeth. Child and Adult.

    its no real coincidence that things basically start 'breaking' on humans past about 40.
     
  17. .Radiant

    .Radiant Member

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    http://www.sciencedaily.com/releases/2013/02/130217134140.htm

    I wonder if we'll see a reintroduction of certain bacteria?
     
  18. kwchaz

    kwchaz Member

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    Seems there's more than just one question posed.
    1. Why do we not grow more teeth to replace older ones?
    2. Why do existing teeth not repair themselves?

    Question 1 has essentially been answered by the following:
    We do not possess it as part of our genetics.
    Why not?
    Because our breeding patterns do not select for it.
    Why not?
    Because we breed before any of us would die from lacking a third set of teeth. This means those who may or may not have a mutation that would result in a third set (or more, or more resistant teeth), are not being selected for, meaning there is no increase (by ratio) of such people in the resulting gene pool.

    Question 2 requires a trip down education lane.
    For what is 'a fully formed tooth', the following tissues are involved: enamel, dentine, pulp, cementum, periodontal ligaments, surrounding bone.
    The last three are not wholly related to the topic of dental caries, and so will be ignored.

    The enamel is the outermost layer of a tooth, formed whilst the tooth is still in the jaw bone (and doesn't even have a root formed yet). The cells that produce enamel die when the crown has been formed, long before a tooth erupts. When a tooth first erupts into the oral cavity, the surface of the enamel is actually not fully mature, and is highly susceptible to decay (despite being chemically more resistant to decay than dentine). This is why dentists or their auxiliary staff will recommend fissure sealants be performed on teeth, to protect them in their infancy. The enamel matures the longer it is exposed to healthy saliva.

    As we eat, or our mouths dry out during exercise, or acid produced from bacteria, or other such things, the pH in our mouths drops to quite acidic levels. At sufficient levels, acid strips the minerals ('demineralises') from enamel, causing it to weaken. Early demineralised areas appear very white ('white spot lesions'), and it is in this state that providing extra minerals and fluoride will cause them to 'remineralise' and 'rebuild'. It is ONLY when the acid attack is very superficial and no cavitation has occurred that you can do this.
    A 'cavity' is where the tooth material has literally been eaten away and has been irreversibly destroyed.

    Primarily, the main cause of dental decay is the acid produced by bacteria that colonises plaque deposits and retained food that has adhered to a tooth and has not been removed. This is why the importance of brushing thoroughly (not harder - SMARTER) and flossing daily is stressed so much.

    Acid wear from bulimia/vomiting following binge drinking/reflux produces a wholly different pattern, as does the frequent drinking of acidic drinks. The former group result in glassy, uniform loss of enamel on the palatal/lingual surfaces of teeth. The latter - particularly with people who swish their sodas :p - produces a whole mouth effect.

    Once bacteria caused demineralisation penetrates and has formed a cavity, the bacterial colony occupies the space where the destroyed tooth matter used to be, and continues producing acid which destroys further tooth matter, eventually reaching the dentine.

    Dentine is the middle layer of the tooth, is yellowish in colour (hence why some teeth are naturally more yellow than others - it isn't staining, it's the dentine shining through!), and isn't very acid resistant at all. It is the only part of the tooth where more can be produced (and it's produced by the pulp, and thus only forms deeper in the tooth, not at the surface where it's being destroyed). Once the bacteria has penetrated the stronger enamel and reaches the dentine, destruction of tooth matter is much quicker, resulting in cavities that might have small openings at the surface, but are huge inside.

    You will have all seen the commercials about dentine being composed of tubes where fluid flows inside of them, and it is rapid fluid flow which causes sensitivity. The tubes are important. :p

    When the bacteria comes close to the pulp (blood vessels, nerves), the acid produced (and other toxins) can travel in the dentinal tubes to 'affect' the pulp, without the bacteria or cavity even exposing the pulp. A pulp which has been triggered like this is likely to produce some reparative dentine, and which causes the pulp to shrink away. If you seek dental treatment early, the bacteria can all be removed, a medicament placed at the base of the cavity to soothe the pulp (and trigger further dentine formation), and that's the end of that.

    Unfortunately for many people, they don't see a dentist until it starts hurting. Then they ask 'can you just fill it?' Once the bacteria has reached the pulp, the entire canal system containing the blood vessels and nerves has become contaminated. This necessitates either sterilisation of the canal system (root canal therapy), or extraction of the infected object.

    Either way, teeth don't repair themselves following formation of a cavity because the cells responsible for formation of enamel are long dead, and the formation of dentine is not in the 'right spot'. When you have dental decay, you have an infection. If you have a white spot lesion, you have early demineralisation, and THAT you can fix at home.
     
  19. Dodge M4S

    Dodge M4S Member

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    My great grandmother lived to be 105 and she started growing a new set of teeth. I am curious as to how much times this has been recorded. You never know, maybe humans do regrow teeth but we just don't live old enough yet to need to re grow them.
     
  20. Recharge

    Recharge Member

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