What is Teeth: Definition and 69 Discussions

A tooth (plural teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are covered by gums. Teeth are not made of bone, but rather of multiple tissues of varying density and hardness that originate from the embryonic germ layer, the ectoderm.
The general structure of teeth is similar across the vertebrates, although there is considerable variation in their form and position. The teeth of mammals have deep roots, and this pattern is also found in some fish, and in crocodilians. In most teleost fish, however, the teeth are attached to the outer surface of the bone, while in lizards they are attached to the inner surface of the jaw by one side. In cartilaginous fish, such as sharks, the teeth are attached by tough ligaments to the hoops of cartilage that form the jaw.Some animals develop only one set of teeth (monophyodonts) while others develop many sets (polyphyodonts). Sharks, for example, grow a new set of teeth every two weeks to replace worn teeth. Rodent incisors grow and wear away continually through gnawing, which helps maintain relatively constant length. The industry of the beaver is due in part to this qualification. Many rodents such as voles and guinea pigs, but not mice, as well as leporidae like rabbits, have continuously growing molars in addition to incisors. Also, tusks (in tusked mammals) grow almost throughout life.Teeth are not always attached to the jaw, as they are in mammals. In many reptiles and fish, teeth are attached to the palate or to the floor of the mouth, forming additional rows inside those on the jaws proper. Some teleosts even have teeth in the pharynx. While not true teeth in the usual sense, the dermal denticles of sharks are almost identical in structure and are likely to have the same evolutionary origin. Indeed, teeth appear to have first evolved in sharks, and are not found in the more primitive jawless fish – while lampreys do have tooth-like structures on the tongue, these are in fact, composed of keratin, not of dentine or enamel, and bear no relationship to true teeth. Though "modern" teeth-like structures with dentine and enamel have been found in late conodonts, they are now supposed to have evolved independently of later vertebrates' teeth.Living amphibians typically have small teeth, or none at all, since they commonly feed only on soft foods. In reptiles, teeth are generally simple and conical in shape, although there is some variation between species, most notably the venom-injecting fangs of snakes. The pattern of incisors, canines, premolars and molars is found only in mammals, and to varying extents, in their evolutionary ancestors. The numbers of these types of teeth vary greatly between species; zoologists use a standardised dental formula to describe the precise pattern in any given group.

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  1. FEAnalyst

    Gear teeth force from the rotation angle

    Hi, in books about machine design fundamentals, one may easily find the formulas for forces acting on the teeth of paired spur gears. They require torque as input. For example, for the tangential force: $$F=\frac{2T}{d}$$ where: ##T## - torque applied to the driven gear, ##d## - pitch diameter...
  2. S

    Any clues to the origin of this pic (cross section of teeth)

    At [01:02], this video youtu.be/qwbIu2PzCRs?t=62 shows the following picture. I'm guessing it's either Arabic or Persian. Can someone read the text and say if it gives any clues to its age and origin? If it's even of medieval vintage, it would be pretty remarkable, implying that they may have...
  3. ANSAN

    Geartrain Doubt.... How to select the number of teeth given other specifications

    Hai all, I need to get to know how a Gear pair teeth numbers are selected. Details : Power = 300KW, N1=2950, N2=816.5 , i=3.62, Helix angle = 35deg, Pressure angle = 20deg. I need to know how to select a Gear pair teeth for this input? Knowing a gear set should have common Module to transmit...
  4. T

    Why is the gear ratio reversed in a planetary gear system?

    Hello, I am confused about something. I will take the time to work it out, but right now, I am using it to remember. And I am now confused. Go here: https://www.smlease.com/entries/mechanism/gear-train-gear-ratio-torque-and-speed-calculation/ Scroll down to the section on...
  5. S

    Wood/Glass/Metal Using a hand saw with ratchet-like teeth

    I tried to saw a piece of wood with a hand saw. Its teeth have an unsymmetric, ratchet-like bias that allows you to pull the saw, but they dig into the wood and refuse to move when you push. (This is not about the blade sticking in the gap after cutting halfway -- I can't even cut a couple of...
  6. F

    What is the consequence of a very low number of teeth on a gear?

    As summarized, I've got these two gear, and another stage of 15:10. I need my gear box as small as possible, and I've never work on this scale with gear (the module is 0,9mm, so this is pretty small). I know that this question is very simple, but I did not find anything relevant on the web, so...
  7. D

    Help Calculating Forces on engaged sprocket teeth

    Hello, I am trying to analyze the forces on a chain and sprocket system. Specifically the force on each tooth that is engaged with the chain rollers on a driven sprocket. Here are a couple links on the topic, however niether of which provide a derivation or sample calcs on how they got their...
  8. EastWindBreaks

    Minimum number of teeth given the gear train ratio?

    Homework Statement Homework EquationsThe Attempt at a Solution for this class, we were not taught with contact ratio equations, nor the pressure angle is given, so for this type of problems, do we just assume that minimum number of teeth on a pinion will be 12? 3 integer factors of 180 can...
  9. 256bits

    Re-writing Human History: Uncovering 9.7 Million Year Old Teeth in Europe

    http://worldfossilsociety.org/2017/10/wfs-news-archaeology-fossil-teeth-discovery-germany-re-write-human-history/ It's just some teeth, but the researchers are scratching their head(s), over whether human history will have to be re-written. "The first paper on the find will be uploaded to...
  10. B

    Why humans need to brush their teeth

    Why do humans get cavities if the teeth are not brushed whereas animals like dogs, cats and horses don't have cavities?
  11. shintashi

    For gear teeth to linear shaft, what's the center point?

    I used to know this back when i worked with Flash animation, but I'm working on a 3D printer now and I've forgotten, when you have a set of teeth, on a linear shaft and a gear, do you base the unrolling of the gear, for the spacing, on the inside of the teeth, the outside of the teeth, or the...
  12. Eddie714

    What is the Proper Involute Profile for Worm Gear Drive Teeth Design?

    Hello i am having trouble figuring out the proper profile to use for the worm and the gear. I need to model it in solidworks and everything i am finding online is for spur gears. I need to get the worm and gear to mesh correctly so i can do some finite element analysis on it. I have calculated...
  13. kolleamm

    How are these little internal gear teeth made?

    This is a servo horn. I'd like to make my own if possible, but I have a hard time figuring out how in the world they make the teeth inside these parts. I'm not really sure what to ask in google.
  14. K

    Angular speed ratio and gear teeth ratio

    http://www.tech.plym.ac.uk/sme/mech226/gearsys/gearaccel.htm Hello, I tried to derive n=N1/N2=omega2/omega1 with using T1=T2 but it is a wrong assumption. I thought they should balance to satisfy Newton's 3rd law, but it is not. Could you explain me why.
  15. I

    Determining the number of gear teeth?

    I have a system that consists of a shaft and two selected gears. I want the shaft to be rotating at 250 RPM and to deliver an input power to the system of 850W. The input torque at the shaft is 71Nm. How can i use this information to determine how large my driving and driven gears will be...
  16. I

    Why does cold water hurt my teeth but warm water doesn't?

    Whenever I brush my teeth and I squish the water around in my mouth, I get an intense sharp pain in some of my top back teeth. I've been to the dentist several times and they say there's nothing wrong with my teeth. However whenever I drink warm water or squish warm water around in my mouth it...
  17. L

    Planetary Gears: Relationships Between Tooth Counts

    there is a relation between the no of teeth in ring gear,sun gear and plant gears are there(2R=S+P) Like that any relation between no teeth in plant and sun gears?
  18. ecoo

    Wisdom Teeth Removal - Sedation Type

    Hey guys, I'm getting my wisdom teeth removed soon. My dentist has recommended general anesthesia (put to sleep). I have some reservations about using general anesthesia, as I have heard about another type of sedation - a type they call "twilight sleep". I believe the agent used in twilight...
  19. N

    How can teeth be bent without contact forces

    Hi, so by no doubt you came here because of the bold phrase of the question. So to clear things up, this is a serious question,an no ido not believe in supranomral mind powers. This is a pragmatic question, and I am not a delusional person trying to get attention. it concerns my teeth which...
  20. Q_Goest

    What is the connection between tumors and teeth?

    A case just came out regarding a 4 month old infant who had a rare brain tumor (benign) that actually had three teeth growing in it as reported by the New England Journal of Medicine. A good layman's summary of the article can be found here...
  21. H

    Involute curve in bevel gear teeth

    Hi I have always wonder about this. I understand the concept of bevel gear, but never quite see how the involute profile would function in a bevel gear. assuming that there is a tooth(either of the driving or driven gear) located at the center between two gears ( where it has the...
  22. H

    Involute curve in bevel gear teeth

    HiI have always wonder about this. I understand the concept of bevel gear, but never quite see how the involute profile would function in a bevel gear. assuming that there is a tooth(either of the driving or driven gear) located at the center between two gears ( where it has the greatest...
  23. L

    Is Homemade Teeth Whitening Safe for Your Teeth?

    Since those white strips are so expensive, I wanted to try to make my own. My plan was to get one of those trays that fit in your mouth and you can fill with various substances to whiten teeth. But instead of buying the stuff that goes in there, I would just use my own hydrogen peroxide paste...
  24. P

    Whistle Tooth Training: Learn How to Talk with Wooden Teeth!

    Hi, I was hoping to train myself to become a whistle tooth. This is where you can talk with a sharp whistle on every "s" sound. I think this requires wooden teeth. Does anyone know anything on the subject? Thanks all!
  25. PhizKid

    Wheel attached to a spring with teeth

    Homework Statement Homework Equations F = ma Torque The Attempt at a Solution All I want to ask is for this problem is: is there friction at ALL points along the path of the wheel because it wasn't clear from the problem. Thanks
  26. T

    Teeth double reflection in mirrors

    Hello, guys! Yesterday I saw my reflection in a mirror and noticed that my teeth had two images on the mirror, and the rest of my face did not. I tried in different mirrors, and the result was the same. At first, I thought it could be the effect of two surfaces of the mirror, and in that case...
  27. A

    News Clench your teeth against Sandy , USAns

    Clench your teeth against "Sandy", USAns! Knowing all about bad weather, I advise you to have your skis ready, in order to get to work. :smile:
  28. I

    Is there a relationship between gear RPM and number of teeth?

    Hi guys, I was doing my tutorial and given the angular velocity of the first gear, we were required to calculate the angular velocity of the 8th gear given just the no. of teeth for all the gears. Now I know that there must be a faster way of calculating the angular velocity of the 8th...
  29. S

    Number of Teeth for Planetary Gear Train Question

    Hello all: I have a quick question concerning a variation of a planetary gear train I am working on. If I want a sun gear and then two planetary gears in between the sun and ring gear (like is shown in the attached picture), how do I find the number of teeth for the ring gear? Would the...
  30. R

    Calculating Gear Teeth: Finding Unknowns and PCD | Homework Help

    Homework Statement I wonder if anyone can point me in the right direction as to where to start with this problem. There are 3 gears A sun gear which is in the centre with 45 teeth, pitch 15mm and revolves at 63rpm CW This drives an arm which connects the sun gear to a planet gear, the...
  31. M

    What are the speeds of molars and premolars going down in a compression test?

    Homework Statement How to calculate for the speed of molars and premolars going down. Lower jaw is stationary or don't move. Only the upper jaw, goes down. Upper jaw and lower jaw are connected by a pivot. The jaw was attached (the upper and lower part ) in the instron machine, with a load...
  32. S

    Epicyclic gear train- finding teeth

    Homework Statement A gear ratio is req from A/D of 1:100 and that it will be necessary to redesign D so that it has 100 teeth. Determine: a)number of teeth on c b)number of teeth on planet gears. This followed on from another question. An epicyclic gear c is the annulus and is fixed. The...
  33. M

    Height/length of teeth in stator core

    Hi everyone, I'm new to this forum. I'm planning to build an alternator/generator but I can't seem to information regarding the benefits of the height/length of the teeth in the stator core as indicated by the arrow in the picture below [1]. I know the width of the teeth determine flux...
  34. R

    Find Force Applied to Tooth with Tension of 2.0 N

    The drawing below shows an elastic cord attached to two back teeth and stretched across a front tooth. The purpose of this arrangement is to apply a force to the front tooth. (The figure has been simplified by running the cord straight from the front tooth to the back teeth.) If the tension in...
  35. J

    Finding Pitch Circle & Teeth for Amplitude Movement

    How would I work out the pitch circle and number of teeth required to move the mechanism a certain amplitude? Looked over 4-5 sources for pitch circle, but cannot make sense of it..
  36. P

    Animals' Teeth: How Do They Stay Healthy Without Toothpaste?

    I was thinking how animal's teeth does not decay, as they do not brush their teeth...? if brushing is soooo crucial for healthy teeth... Are toothpastes just a whiteners with good smell or ... How did humanoids had healthy teeth without having toothpastes? Thanks for your replies. :smile:
  37. J

    Medical How do teeth sense their surface?

    I've noticed that if I allow something sugary to get into contact with my teeth, it can start hurting mildly immediately. I've thought that teeth have nerves mainly in the cores of the teeth. How can nerves, somewhere deep in the teeth, sense when sugar hits the surface of the teeth?
  38. S

    How can I determine the best design for clamping teeth for a clamping device?

    Dear All, I am designing a clamping teeth for a clamping device. The clamping device is to pulling I beam pile from the ground for recycling mounted on a hydraulic jack. I wonder how could I determine the depth of the teeth, number of teeth and the angle of teeth. As the teeth will grab into...
  39. Q

    Are wisdom teeth important to get out?

    I mean ones that arent causin irritation. What do you think?
  40. S

    How to obtain the force acting on a gear teeth

    Hi everyone. I wonder how to obtain , let say a 20T gear connect to a 40T gear compare to a 40T connect to 60T gear. (teeth size is the same) Suppose the transmitted force (at the outer of the gear) is the same, is there any different froce on the teethes in each pair (larger no. of gear...
  41. N

    Is Celebrity Sexy Teeth Just a Scam?

    You may have seen the ad for 'Celebrity Sexy Teeth'. Its been on Yahoo, ABCnews.com and many other websites. It seems to be a pretty organized scam with supposedly independent review sites that are actually their own. Here is one of those: http://www.best-teeth-whitening.com/ This one seems...
  42. C

    Number of gear teeth in two-stage reduction gears

    In a two stage reduction gearbox is it possible to have more teeth on the gear pair (helical-parallel axis) of the 2nd stage? I ran through a specification for gear sizes and I am wondering if this is ok.
  43. A

    Scissor Car Jack Purpose of Teeth

    What is the purpose of teeth in such jack ? Isn't the screw enough to provide the lift ? What will happen if these gear like teeth are not present in a scissor jack ?
  44. D

    Calculating gear teeth & ratios.

    1. This is a question that I've asked a few people and have not been able to get a solid explanation to: The crankshaft gear (A) has 14 teeth. It drives gear (B) with 21 teeth which is on a shaft & on the other end of the shaft is gear (C) with 9 teeth. The distributor is driven off gear (C)...
  45. ZapperZ

    Gorging on your Halloween candy is better for your teeth

    Just in time for all those Halloween candies that you'll be eating, here's a tip on what's best for your teeth. http://news.yahoo.com/s/livescience/20081028/sc_livescience/halloweencandytrickgorgedontnibble Zz.
  46. L

    Understanding the Relationship between Tension, Teeth, and Force

    Tension, Teeth, and Force? The drawing below shows an elastic cord attached to two back teeth and stretched across a front tooth. The purpose of this arrangement is to apply a force to the front tooth. (The figure has been simplified by running the cord straight from the front tooth to the back...
  47. T

    Optimal number of times of brushing teeth?

    How many times per day for optimal number? And when to do it each day? Why? Assume convenience is equal for all options.
  48. D

    Is a Waterpik Better Than Flossing for Braces?

    http://www.waterpik.com/oral-health-products/ (press start movie in the corner of the picture of the kid with the goofy smile) http://www.waterpik.com/oral-health/clinically-proven.html Does anyone have one of these? They're supposed to be really good for your teeth (and from those studies...
  49. K

    Vernier Calliper: Measuring Teeth Explained

    Hi all, I have a very quick question. On a vernier calliper, what are the names of the measuring teeth that define the limits of measurement? Thanks
  50. T

    Teeth damage after eating bacon and egg?

    Does your teeth feel slightly hurt after eating fried bacon and eggs? If it's not because they were too hot when you consumed them then what reasons could it be?