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A similar question but about teeth healing themselves is Do teeth have the capacity to heal?.
So I understand that teeth have the capacity to heal themselves to a certain degree. It appears to be that part of the reason they can't heal all of themselves is that they are not surrounded by cells. In that case why can't we grow teeth back?
If a tooth is grown in the gum, or somewhere else, it would be surrounded by cells and so should be able to grow back right?
It appears that sharks can grow their teeth back:
New teeth are continually grown in a groove in the shark's mouth and the skin acts as a “conveyor belt” to move the teeth forward into new positions.
Why can't we do this?
Unfortunately, the answer to your question isn't as well researched as other areas, I believe… let's add some complexity into this.
You're correct, teeth does "grow" in the gums. And it does start off surrounded by cells (look up: tooth bud, cap, bell stage)!
The tooth originates from an interaction between the ectomesenchyme (likely originating from the neural crest cells) and the epithelium of the mouth when it is forming while you're still an embryo in your momma's tummy.
Unlike sharks, which are homodonts (meaning, their tooth are all of one morphology), we are heterodonts (e.g. we have different shaped teeth - e.g. molars, canines, incisors, premolars). There are a couple of theories to why this occurs (look up: clone model, field model, odontogenic homeobox code - a combination of all these theories). Basically, a bunch of genes transcribe for proteins and signalling factors that create the complexity of your tooth shape and position in the mouth.
Basically, this means, our teeth are going to take longer and require more energy and effort to carve into (yes carve! lot's of the tooth shape is create by apoptosis of the regions around the "cusp" area when it is developing).
When your primary/baby teeth pop out, they serve functions such as developing speech, allowing you to eat, strengthening your jaw muscles (which in turn helps to develop your mandible and shape of the face), all this so you can have a great bite when you get older!
Luckily, sharks don't speak much underwater, so they probably don't give a poop about having properly lined up teeth. Their teeth grows everywhere. Proper bite for eating various nuts, fruits, meats and vegetables? NAH. WE JUST CHEW OFF LEGS. WE CAN ONLY SHRED STUFF. Sharks need strong ankylosed teeth (ankylosed = like an anchor? teeth are anchored into the mandible of the shark).
In contrast, humans have teeth in gomphosis (sockets), which gives our teeth some cushioning and sense of proprioception (the sense knowing how hard you're biting) when we bite on something extremely hard, to prevent us breaking our teeth - thus helping us preserve our teeth. Sharks don't have that, they just break their teeth.
Humans do finally replace their teeth, after our jaw grows enough for us to accommodate them at a genetically planned stage. This happens by tooth germs (cells) being bud off (like a flower yes :D) from the baby teeth. Note though, your 1st adult/permanent molars are already beginning to form when you're still in your momma's tummy.
I believe that the continuous creation of teeth requires more energy, but takes less time (sharks). For humans, one time creation of teeth requires less energy, but takes wayyyyy more time (and also has to be timed correctly with all our other growing bits).
TL;DR Evolutionary reasons and different functional uses of teeth between sharks and humans probably determine why we only have two sets of teeth (diphyodonts). That being said, it would be cool if we were like rats (have molars/incisors) though, which replace their teeth anytime its lost. Maybe one day we can evolve into it? Yay!
Some interesting points: You mentioned teeth "healing".
Your teeth is made up of enamel on the outside, which is NEVER replaced. It "heals" by remineralisation which is not exactly the same as growing new crystals on top of it. Kinda complex, won't go into it.
However, your teeth is always forming new dentine, which is below the enamel. In a way, your tooth really is growing back all the time. Because a new layer of dentine is deposited everyday (like… 4 micrometers). This is because the dentine producing cells, called odontoblasts, are still around. In contrast, the enamel producing cells, called ameloblasts, are removed when your tooth has developed. I THINK, the reason is to make space in your enamel so it can be fully mineralised and completely filled up by hydroxyapatite. (Too much fluoride when young can block this removal of ameloblasts and its proteins like amelogenin and enamelin = forming holes, which cavitate resulting in fluorosis).
Hopefully all that answered your question. But, it was fun for me to rant anyway. Cheers.
Because mammals had to be different, and spent way too much of their evolutionary history being tiny short lived creatures.
No seriously, mammals are outliers in this. Growing endless numbers of teeth (Polyphyodont) is the normal aka basal condition in vertebrates. Every other group of animals with teeth just keep replacing them forever. Mammals uniquely have lost this ability.
All mammals grow a fixed number of teeth, most are diphyodont growing their teeth in two distinct sets, a few mammals (elephants and kangaroo) spread their number of teeth into multiple series but the total number of teeth they produce is still fixed, they are sort of pseudo-polydont. Some whales produce a much larger number of teeth but the total number of teeth is still fixed.
Why are mammals weird, because the ancestors of all extant mammals were small short lived insectivores. If you are short lived insectivores wear is insignifiant on teeth and dislodging them is a minimal risk. Multiple sets of teeth is not a significant advantage. What is a significant advantage is tightly occluding teeth, that is teeth that fit together very tightly with multiple cusps, this shape is perfect for processing insects into digestible pieces, but it does not work well when teeth are replaced. The current thought is that mammals repurposed or lost the genes that allowed for new tooth bud formation. Many believe the genes were repurposed possibly into some of the genes that control tooth shape allowing the complex tooth structure mammals have. This is difficult to test but is supported by the fact the groups of mammals to increase the number of teeth, whales, armadillo, and some seals, also have extremely simply tooth structures and high numbers of anomalous teeth, that is teeth with seemingly no controls on their shape. Although I should note extra erroneous teeth occasionally occur in nearly every mammal line.
The exact changes have not yet been discovered and is an are with much interest. We know why pretty well even if we don't know how. Although there is some fascinating work being done by studying how reptiles continue to replace teeth throughout life. Certain basal cell lines persist in reptiles but completely differentiate in mammals during early development. Whales get around this by making a lot of new buds early on and holding on to them, but they still can't make new ones past a certain point.
Also related, why mammals have bigger nerves in their teeth.
Why Are Human Teeth So Messed Up?
Many of us have had crooked, ill-fitting teeth at some point in our lives. The reason has a lot to do with what we eat.
This article was originally published at Aeon and has been republished under Creative Commons.
W e hold in our mouths the legacy of our evolution. We rarely consider just how amazing our teeth are. They break food without themselves being broken, up to millions of times over the course of a lifetime and they do it built from the very same raw materials as the foods they are breaking. Nature is truly an inspired engineer.
B ut our teeth are, at the same time, really messed up. Think about it. Do you have impacted wisdom teeth? Are your lower front teeth crooked or out of line? Do your uppers jut out over your lowers? Nearly all of us have to say yes to at least one of these questions, unless we’ve had dental work. It’s as if our teeth are too big to fit properly in our jaws, and there isn’t enough room in the back or front for them all. It just doesn’t make sense that such an otherwise well-designed system would be so ill-fitting.
O ther animals tend to have perfectly aligned teeth. Our distant hominin ancestors did too and so do the few remaining peoples today who live a traditional hunting and gathering lifestyle. I am a dental anthropologist at the University of Arkansas, and I work with the Hadza foragers of Africa’s Great Rift Valley in Tanzania. The first thing you notice when you look into a Hadza mouth is that they’ve got a lot of teeth. Most have 20 back teeth, whereas the rest of us tend to have 16 erupted and working. Hadza also typically have a tip-to-tip bite between the upper and lower front teeth, and the edges of their lowers align to form a perfect, flawless arch. In other words, the sizes of Hadza teeth and jaws match perfectly. The same goes for our fossil forebears and for our nearest living relatives, the monkeys and apes.
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S o why don’t our teeth fit properly in the jaw? The short answer is not that our teeth are too large, but that our jaws are too small to fit them in. Let me explain. Human teeth are covered with a hard cap of enamel that forms from the inside out. The cells that make the cap move outward toward the eventual surface as the tooth forms, leaving a trail of enamel behind. If you’ve ever wondered why your teeth can’t grow or repair themselves when they break or develop cavities, it’s because the cells that make enamel die and are shed when a tooth erupts. So the sizes and shapes of our teeth are genetically preprogrammed. They cannot change in response to conditions in the mouth.
B ut the jaw is a different story. Its size depends both on genetics and environment and it grows longer with heavy use, particularly during childhood, because of the way bone responds to stress. The evolutionary biologist Daniel Lieberman at Harvard University conducted an elegant study in 2004 on hyraxes fed soft, cooked foods and tough, raw foods. Higher chewing strains resulted in more growth in the bone that anchors the teeth. He showed that the ultimate length of a jaw depends on the stress put on it during chewing.
The way the human jaw grows depends on a combination of genetics and diet. Nevit Dilmen/Wikimedia Commons
S election for jaw length is based on the growth expected, given a hard or tough diet. In this way, diet determines how well jaw length matches tooth size. It is a fine balancing act, and our species has had 200,000 years to get it right. The problem for us is that, for most of that time, our ancestors didn’t feed their children the kind of mush we feed ours today. Our teeth don’t fit because they evolved instead to match the longer jaw that would develop in a more challenging strain environment. Ours are too short because we don’t give them the workout nature expects us to.
T here’s plenty of evidence for this. The dental anthropologist Robert Corruccini at Southern Illinois University has seen the effects by comparing urban dwellers and rural peoples in and around the city of Chandigarh in northern India—soft breads and mashed lentils on the one hand, coarse millet and tough vegetables on the other. He has also seen it from one generation to the next in the Pima peoples of Arizona, following the opening of a commercial food-processing facility on the reservation. Diet makes a huge difference. I remember asking my wife not to cut our daughters’ meat into such small pieces when they were young. “Let them chew,” I begged. She replied that she’d rather pay for braces than have them choke. I lost that argument.
C rowded, crooked, misaligned, and impacted teeth are huge problems that have clear aesthetic consequences, but can also affect chewing and lead to decay. Half of us could benefit from orthodontic treatment. Those treatments often involve pulling out or carving down teeth to match tooth row with jaw length. But does this approach really make sense from an evolutionary perspective? Some clinicians think not. And one of my colleagues at Arkansas, the bioarchaeologist Jerry Rose, has joined forces with the local orthodontist Richard Roblee with this very question in mind. Their recommendation? That clinicians should focus more on growing jaws, especially for children. For adults, surgical options for stimulating bone growth are gaining momentum, too, and can lead to shorter treatment times.
A s a final thought, tooth crowding isn’t the only problem that comes from a shorter jaw. Sleep apnea is another. A smaller mouth means less space for the tongue, so it can fall back more easily into the throat during sleep, potentially blocking the airway. It should come as no surprise that appliances and even surgery to pull the jaw forward are gaining traction in treating obstructive sleep apnea.
F or better and for worse, we hold in our mouths the legacy of our evolution. We might be stuck with an oral environment that our ancestors never had to contend with, but recognizing this can help us deal with it in better ways. Think about that the next time you smile and look in a mirror.
FEFU scientists likely found way to grow new teeth for patients
A group of histologists and dentists from School of Biomedicine, Far Eastern Federal University (FEFU), teamed up with Russian and Japanese colleagues and found cells that are probably responsible for the formation of human dental tissue. Researchers propose to apply the study outcome within the development of bioengineering techniques in dentistry aimed at growing new dental tissue for patients. A related article is published in the International Journal of Applied and Fundamental Research.
FEFU scientists used human prenatal tissues to study the early stage of development of the embryonic oral cavity during the period when the teeth were set up - from the 5th to the 6th week. They have recognized several types of cells that are involved in the formation of one of the teeth rudiments -- the enamel (dental) organ. Among them, chromophobe cells with elongated spindle-shaped form have been identified which are also responsible for the development of human teeth in the first weeks of embryo formation. The data obtained can provide a fundamental basis for the development of bioengineering therapies in dentistry and gastroenterology.
'Numerous attempts to grow teeth from only the stem cells involved in the development of enamel, dentin and pulp, i.e. ameloblasts and odontoblasts, were not successful: there was no enamel on the samples, teeth were covered only by defective dentin. The absence of an easily accessible source of cells for growing dental tissue seriously restricts the development of a bioengineering approach to dental treatment. To develop technologies of tissue engineering and regenerative medicine -- promising methods of treatment in dentistry -- the cells identified by us may become the clue to the new level of quality dental treatment. Natural implants that are completely identical to human teeth will no doubt be better than titanium ones, and their lifespan can be longer than that of artificial ones, which are guaranteed for 10-15 years. Although for a successful experiment, we still have a lack of knowledge about intercellular signaling interactions during the teeth development.' said Ivan Reva, Senior Researcher of the Laboratory for Cell and Molecular Neurobiology, School of Biomedicine, FEFU.
The scientist noted that large chromophobe cells reside not only the place where the teeth of the embryo form, but also exist at the border where the multilayers squamous epithelium of the oral cavity passes into the cylindrical epithelium of the developing digestive tube. This means that the new bio-engineering approach is relevant not only for growing new dental tissue but also for growing organs for subsequent transplantation and likely will be applied in gastroenterology.
The development of new biological approaches for the teeth reconstruction with stem cells is one of the most pressing tasks in dentistry for the upcoming years. There are still a lot of questions challenging the researchers. For example, scientists have yet to figure out how in the earliest stages of human embryo development, from the seemingly homogeneous, and in fact, multilayered ectoderm, which is located in the forming oral cavity, different types and forms of teeth develop. However, it is already clear that more kinds of cells are engaged in the earliest stages of human teeth formation than it was previously supposed. Thanks to the research of FEFU scientists in cooperation with their colleagues from Russia and Japan, it also became clear that the crown of the tooth and its root have different mechanisms of formation.
This work was supported by the FEFU Scientific Foundation, within the framework of the state task 17.5740 / 2017 / 6.7.
Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.
These genes – contained in specialised cells that create teeth – mostly die off or lie dormant after our milk teeth and our adult teeth grow.
GROWING TEETH IN THE LAB
False teeth could be a thing of the past after scientists discovered a way to grow them in the laboratory.
Dental experts have found a new way to split a tooth into two fully functional teeth and then successfully implant them into the jaws of mice - a breakthrough which could help human patients in the future.
Researchers from the Riken Centre for Developmental Biology in Japan used a new technique of extracting teeth germs - the groups of cells formed early in life that will later develop into teeth.
Mice that received the teeth were able to chew and feel stimulus. However, the implanted teeth were just half the size of normal teeth.
Dr Gareth Fraser and colleagues analysed the teeth of catshark embryos, and identified the genes involved during stages of early shark tooth formation.
These genes continue to be used to grow further teeth and are found in cells called the dental lamina, which are responsible for the lifelong continuation of tooth development and regeneration in sharks.
The same genes are still present in humans - deriving from the time when humans and sharks had a common ancestor.
Dr Fraser, whose research has been published in Developmental Biology, said: 'Sharks can regenerate their teeth throughout their lives.
'The good news for us as humans is the genes that make these teeth regrow are shared by all vertebrates [creatures with skeletons] including humans.
'What it means is because we have the same genes to make teeth, we also have a regenerative program.
'We make two sets of teeth, but humans need more teeth, whether through loss or damage, so our second set are really quite valuable.
Sharks continuously regenerate their teeth through out their life with new teeth rotating forward in rows (illustrated in A). Bony fish replace teeth one by one (B) while reptiles continuously grow new teeth (C). Most mammals, however are diphyodontal, with two tooth generations (D)
'Sharks never have tooth decay, if they lose teeth they regenerate them even more rapidly.
'The point is at some level it's not so far-fetched we can use and re-utilise what nature has provided.
'At some point during adolescence, we lose the cells, they break down. There is a possibility we can re-invigorate them with future dental therapies.'
Dr Fraser said he believes that once 'a set of tweaks' is found, we will be able to regrow teeth 'when and if we need them.'
In all there are 400 genes which interact to grow a tooth.
The researchers studied the developmental stages of shark's teeth (pictured). Researchers found there are 400 genes which interact to grow a tooth, but with a 'set of tweaks' it may be possible for humans to regrow teeth when we need them
Dr Fraser said many further breakthroughs are needed to understand how to switch the network on and the work will take many years.
But he said: 'Regenerating teeth will happen.'
Rarely, humans grow additional or 'supernumerary' teeth. In one case an 11-year-old girl was reported to have 81 teeth.
In such cases, the extra teeth are a problem and must be removed.
The capacity for sharks to regrow their teeth in a conveyor-belt like fashion was first scientifically recorded in 1845 by Sir Richard Owen, the British biologist who coined the word 'dinosaur'.
He described it as 'numerous teeth ever marching slowly forward in rotary progress'.
What Happens If Your Adult Teeth Just Don't Come In?
We all like a visit from the tooth fairy, but isn't it kind of weird that we're born essentially toothless, a set of teeth grows in when we're babies, and then we lose those to make room for our comparatively giant adult teeth? The vast majority of mammals grow two sets of teeth during their lives. Our young are born toothless because mammals produce milk for their young, and mothers definitely don't want to be nursing babies with rows of sharp teeth. Losing our baby teeth — also called deciduous teeth because they fall out of our heads like autumn leaves — allows us to change our diet as we mature, and makes the most of the food-grinding capacity of our growing jaws.
So, what happens when we get our primary teeth as babies, but our adult teeth don't come in? Do we just keep our tiny baby teeth forever?
There are a few different conditions that could lead to someone not losing their primary teeth, and dentists have their ways of dealing with each, depending on whether the permanent teeth are sitting right up there waiting for the coach to put 'em in, or whether they just didn't make it to the game.
When Baby Teeth Leave the Nest
It's difficult to predict the lifespan of a baby tooth, since they're only supposed to do their job for about a decade, give or take a couple of years. That said, if a permanent tooth doesn't swoop in to take its place, a primary tooth may far outlast its life expectancy, or it could also just totally fail without warning. When a primary tooth is working way past its expiration date, a dentist will probably keep tabs on it to make sure it's healthy, but eventually it'll have to be removed and replaced.
If the permanent teeth are taking a little longer to develop than normal, or are sitting in the wings, but just aren't emerging, the dentist will usually want to wait to see what is going to happen. In the case of an ectopic tooth, a permanent tooth develops normally, but fails to erupt. In these cases, the position and angle of the tooth relative to the permanent teeth that have already erupted will help a dentist or orthodontist decide what to do. Oftentimes, an attempt is made to orthodontically drag a recalcitrant tooth into the correct position.
But having perfectly formed permanent teeth that are just kind of slow to emerge is definitely a best-case scenario. It's much harder to treat a patient who doesn't have any adult teeth to coax out.
Tooth agenesis is a congenital condition wherein a patient's mouth just didn't get directions to make some of their permanent teeth when they were born. This can range in severity from hypodontia, in which five or fewer teeth are missing, to oligodontia, when six or more permanent teeth are missing in action — this is uncommon, but often associated with genetic syndromes like Down syndrome, Van Der Woude syndrome, Reiger syndrome and ectodermal dysplasia. Anodontia is a rare recessive genetic disorder in which someone just doesn't get permanent teeth — it's also often associated with conditions like ectodermal dysplasia.
"Congenitally missing teeth are relatively uncommon," writes Jim Nickman, president of the American Academy of Pediatric Dentistry, in an email. "In the primary dentition, up to 2 percent of children will experience missing teeth, but in the permanent dentition, the range in various studies is from 0.15 percent to 16 percent. The most common missing permanent teeth are lateral incisors and premolars, and it's very common that a missing baby tooth also will not have a permanent successor."
Miracles of Modern Dentistry
So, let's say you don't have some of your permanent teeth. What can your dentist do about it?
It largely depends on what's wrong, but you can bet it's probably going to be expensive and time-consuming. In the case of a single missing tooth, your dentist might propose solutions ranging from a dental implant to some sort of fixed bridge. A treatment often used for children who are congenitally missing their incisors is to use orthodontics either to open up some space for a future implant or bridge, or shove another permanent tooth into the space to camouflage the gap.
According to Nickman, for multiple missing teeth (depending on their location), patients could end up with implants, fixed bridges or removable partial dentures. But for complete loss of teeth, the treatment would consist of removable or fixed dentures, depending on how well-developed the bone is around the missing teeth.
Sometimes a dentist will perform bone grafts to fill in a place where bone hasn't grown. But, although dentists can do all sorts of fancy patching and bridging and screwing things into your jaw, any treatment for tooth agenesis is going to have to be continually maintained. "For a young child with oligodontia or anodontia, this can be a lifelong burden requiring multiple 'temporary' partial or complete dentures until they are physically developed enough to undergo implant placement," says Nickman.
In summary, if you have all your permanent teeth in your head, take a moment to thank them for their service. Now go brush them. And don't forget to floss.
Sharks have many rows of teeth, and they fall out all the time because they have to be kept razor sharp in order to chomp their prey. Old, worn teeth are continually being replaced by new ones.
The power of laws
Some patterns are very common in nature, such as logarithmic spirals that follow the golden ratio. These patterns appear because of the very simple processes that generate them. For example, a logarithmic spiral is produced when a spiral grows faster on one side than the other.Logarithmic spiral (dashed blue curve). For this spiral, the radius grows by a factor of 1.1923 per 1 radian of angle. It is not an exact fit to the Nautilus, being off if different directions in different parts, but is a good approximate fit. Credit: Wikimedia Commons.
We can describe such patterns as following rules of growth. These rules help us understand why animals and plants are the shapes they are.
In my research I am fascinated by patterns in nature. And for many years I have searched for a pattern in how teeth grow. By looking at hundreds of teeth and measuring how they get wider as they get longer, my team and I identified a simple mathematical formula that underpins tooth shape.
This is a “power law”, in which there’s a straight-line relationship between a tooth’s width and length when you take a logarithm of these measurements. Power laws are also found in the sizes of earthquakes, extinction rates of animals and movements of the stock market.
Surprise: Chickens Can Grow Teeth
Well, better start searching the skies for flying pork—scientists have discovered a mutant chicken with a full set of crocodile-like chompers.
The mutant chick, called Talpid, also had severe limb defects and died before hatching. It was discovered 50 years ago, but no one had ever examined its mouth until now.
The researchers recently created more Talpids by tweaking the genes of normal chickens to grow teeth.
"What we discovered were teeth similar to those of crocodiles—not surprising as birds are the closest living relatives of the reptile," said Mark Ferguson of the University of Manchester.
Around 300 million years ago, the ancestor of all modern vertebrates gave rise to two lineages, the mammals and the reptiles/birds. The oldest reptiles, such as crocodiles and alligators, had cone-shaped teeth. So did the earliest birds, called archosaurs.
Then, around 80 million years ago, modern birds emerged without teeth.
"So what would you expect bird teeth to look like? You would expect them to have teeth like their ancestors and their most closely related living relative," study co-author John Fallon of the University of Wisconsin told Live Science.
Indeed, Talpid's teeth are conical, much like an archosaur's and closely resembling the teeth of a baby alligator or crocodile, Fallon said. If the chick survived, the teeth would most likely reabsorb into the mouth.
The archosaurs had mouths similar in shape to a reptile's. It turns out that developing a beak caused birds to lose their teeth.
"The reason that birds lost their teeth is that in forming a beak, the two tissues that &lsquotalk' to each other to make a tooth become separated," Fallon said. "They can't have the conversation to make a tooth. In the mutant, these tissues are brought back together."
Make more mutants
The finding made scientists curious whether healthy chickens still possessed the 80-million-year-old genetic pathway for producing teeth.
By making a few changes to the expression of certain molecules in the pathway, the researchers were able to induce tooth growth in normal developing chickens. These teeth also looked like reptilian teeth and shared many of the same genetic traits, supporting the scientists' hypothesis. None of these chickens were allowed to hatch.
This is all good news for hockey players. A direct application of this research, Ferguson said, could be re-growing teeth in people who have lost them through accident or disease.
Why didn't mammles evolve the ability to grow back adult teeth?
One of my bio professors told me that with evolution, the adaptation doesn't have to be so big and great, it just has to be good enough. I feel like this might be one of those times where the way we grow our teeth and how many times etc is just good enough for the organism to be okay.
Lasts long enough to procreate
‘Survival of the fit-enough’
Natural selection which is one of the driving forces of evolution doesn’t occur based on a need. If the ability to regrow adult teeth was a trait that appears in the early human population (or hominids for that matter) and it provided a such a selective advantage that not regrowing teeth put humans at a disadvantage then it would have become one of our adaptations. It’s the same as asking why didn’t humans evolve to fly or breath underwater. Our species adapted to survive based on traits inherited from common ancestors.
Evolution low key feels like the body trying to make the best out of the crap it’s got, like our feet not perfect for they’re job but they do the best they can
True. Simply put - because we didn't
This makes sense. Another concept to think about is what causes adaptation and evolution? The need for the next generation to be stronger than the previous in order to keep from dying out. If you think about when we need to regrow adult teeth - usually after an accident, violence, or long term neglect. These needs usually- especially long term neglect- arise after child bearing years in women. This being so the genetic need to regenerate or heal has never really had the opportunity to occur.
My immediate response would be because of lifespan and necessity.
When I think of animals that grow back teeth, I think of sharks and crocodiles, those are predators that tend to have a very long lifespan.
Mammals with similar lifespans don't need to grow teeth back. Mammal predators generally have shorter lifespans and omnivore and herbivore teeth degrade over time, but are sufficient for their lifetimes. So I guess if you consider these factors, it seems unlikely that regrowing teeth would be immensely beneficial and they sure would be costly.
This. And just as an addition: keep in mind that it's all about reproduction. Nothing that would be beneficial after you passed your genes along has evolutionary pressure (exceptions ofc in some social animals where elders teaching might play a role).
Herbivores, specifically those that eat grass, typically die of tooth loss much more frequently than they do of old age, so I wouldn't say their teeth are sufficient for their lifetimes.
In the example of humans, we kind of do. Wisdom teeth grew in as a way to replace any teeth that we had lost up to that point in life. We (generally) remove them these days because most humans haven’t lost many teeth and they cause crowding and other problems. Problems we wouldn’t have, if we lost our teeth regularly like our ancestors did.
Why is this comment so highly upvoted? The commenter shares a creative idea, but it's definitely not the reason why mammals haven't evolved to regrow adult teeth.
They also don’t use meth.. don’t use meth kids if you want to keep your teeth
Same reason we didn’t evolve to grow new arms, fly, breathe under water etc. evolution isn’t about overcoming past inconveniences, it’s more about adapting to surroundings.
Weird to think we'll be able to control how we evolve within a couple hundered years, then it will be all about overcoming our past inconveniences.
So there are some good answers but a factor I didn't see. Mammalian teeth are often far more complex in many ways. Not in our teeth are some hyper complex thing, but unlike say sharks and alligators we have like 10 different types of teeth in our mouth, and not only do those teeth each have different uses they also require specific placement in the mouth. E.g. having a canine grow back where a molar should be would be a major issue. For the animals that do this placement and style doesn't really matter so the issues that can happen just don't matter.
Note: just think of the various issues humans can and do get during our teeth getting replaced once, anything from damaging other adult teeth roots to not pushing out old ones right and causing gaping. Now imagine that happening every 5 years or so per tooth.
Grow your own TEETH - dental experts signal end of false gnashersLink copied
False teeth may become a thing of the past
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Dental experts have found a pioneering method of splitting a tooth into two fully functional teeth.
In groundbreaking tests, they were able to successfully implant "germs" which grew into new teeth with full functionality in the jaws of mice.
They hope the same method could eventually be carried out on human patients.
Current teeth replacements fail to restore full fuctionality
Researchers from the Riken Centre for Developmental Biology in Japan used a new technique of extracting teeth germs, or the groups of cells formed early in life that will later develop into teeth.
The scientists said they were easily able to split the germs into two and implant them into the mice's jaws.
The study, published in Scientific Reports of the journal Nature, showed that many current treatments of replacement fail to restore the full functionality of a tooth.
But the prospect of naturally growing new teeth in the patient's mouth would solve this problem.
The method has been successful in mice
There are currently 11million people who wear dentures in the UK.
But not all are old, with almost a million people aged 16 to 44 having false teeth.
The reasons for tooth loss are varied. While most are lost through dental disease, other reasons include the effects of drug abuse, malnutrition and genetic defects.
Experts consider teeth as a major target for regenerative medicine, with about 10 per cent of people born with some missing teeth and many others losing teeth due to accidents or disease as they age.
It is hoped it will soon be possible to regrow a missing tooth in humans
The researchers set about trying to make new teeth from a single germ. Teeth germs were removed from mice and were sliced into two with nylon thread. The experiment took about 15 days to develop the germ naturally into two teeth.
The study shows the new teeth allowed the mice to chew and feel stimulus. However, the implanted teeth were just half the size of normal teeth.
Lead researcher Takashi Tsuji said the new method could be especially useful for children who did have properly developed teeth due to conditions like cleft lip or Down syndrome.
Germs of permanent teeth or wisdom teeth could be used to develop new fully functional teeth that could then be implanted. Dr Tsuji added that they could soon consider using stem cells to grow more germs, though further tests were still needed for the process.