Common apocryphal knowledge holds that burying the tooth of a hydra will give rise to mighty warriors. It is less well known that burying the teeth of other creatures produces other effects.
1 - 2: Common Teeth
Serpent teeth: Grows small but dedicated warriors ranging from 3 and 3/4 inches to marionette-sized, depending on the size of the snake. They hate gemstones and will attempt to destroy them on sight.
Cat teeth: A small poltergeist, never seen. The corpses of ghost birds and ghost mice will be left near your sleeping area for two to four weeks.
Adult human teeth: If the person to whom the teeth belonged is alive, a small stream of blood will begin flowing from the area in which the teeth were planted within a week. Analysis would show that this is not the blood of the teeth's owner; nonetheless, the owner of the teeth will find it difficult to concentrate, like they had two cups of bottom-shelf jug wine. This lasts as long as the blood flows, about a day per tooth sown.
If the owner of the teeth is dead, the odontic farmer must take pains to irrigate the planted teeth with brackish water every third night at midnight for two weeks. This will produce a brazenhead with a circumference of one inch per tooth planted. If multiple teeth are used they must all come from the same dead person. The brazenhead will answer a number of questions equal to the number of teeth planted. It knows everything in the owner's life as well as their current afterlife situation and is compelled to answer more or less truthfully, but it doesn't want to exist and probably won't want to be very helpful. The bigger the brazenhead, the louder it is.
Children's milkteeth: If irrigated with milk and carefully tended, a handful of children's deciduous teeth -- they don't have to be from the same child -- will compact into a fist-sized bulb which will then sprout into a small shrub that produces more milkteeth as fruit. This could probably be used for some kind of scam if you put your mind to it. If you stop tending the shrub, you may come to learn that the tooth-bulb is actually the larval form of horrible little creatures. After a few weeks without milk, the instar phase of the creature will emerge from the bulb. They look like five-inch-long maggots with weasel legs and they eat bone. If they eat enough bone they'll eventually create a cocoon, molt, and emerge as winged fey creatures possessed of a malign sentience.
Hog teeth: Grows into reverse mandrakes; delicious truffles that coo and groan happily if you pick and eat them.
Cow teeth: Produces an amount of cud equal to the size of the pile of teeth sown. Literally a wad of chewed and semi-digested grasses and other plant material packed into a soggy bolus. Provides sustenance equal to an appropriate amount of trail rations for 1/2 day per tooth sown, if you can stomach chewing on it. You have to chew it continually though, if you take it out of your mouth it loses the magic.
3 - 4: Uncommon Teeth
Dog teeth: Requires a full set of 42 teeth but they don't have to be from the same dog. Six days after planting a fully-grown uncommon dog bursts forth from the earth, full of curiosity and mighty hunger. Roll on the Uncommon Dogs table.
Mongoose teeth: Plant mongoose teeth at evening and come back the next morning. The teeth will be sitting on top of the ground where you planted them. If you swallow the teeth you become immune to poison and become more agile in combat, but you are compelled to eat any scaled creatures you encounter, living or dead. These effects last an indeterminate period of time.
Spider teeth: Burying a sufficient amount (for unspecified values of "sufficient") of spiders' fangs will cause an elaborate origami sculpture the size of a lotus flower to grow from the dirt. You can't quite pin down what the origami is in the shape of. Unfolding it will reveal a blank piece of paper. The next time you sleep after unfolding the origami, you will have a fully lucid, protracted dream quest. You will not be yourself in this dream. You will be very prepared for whatever it is you do during the dream and when you awake you will possess a new skill -- roll on the Uncommon Proficiencies table. On the downside you will have an extremely difficult time distinguishing the dream from reality and vice versa, and characteristics of your dream-identity will likely haunt you; you may forget people close to you or spend the rest of your life pining over a lost love from the dream.
Stag teeth: Antlers grow from the ground. Extremely invasive, like ivy on steroids. Will deeply screw up local ecosystem if left unchecked.
Eel teeth: A clutch of land eels hatches in a week. They only live for a few days, and aside from not needing water, are identical to normal eels.
Alligator teeth: Nothing readily apparent is produced save for a slight depression in the earth where the teeth were buried. Any pressure on the depressed area will cause alligator jaws to snap shut on the object causing the pressure, with all of the force of an actual alligator bite. The jaws are actually composed of vegetable matter.
5: Magical and Monstrous Teeth
Gorgon teeth: Sowing six gorgon teeth will produce a stone ovoid about the size of an osprey's egg. It is warm to the touch. Inside is a red, glowing yolk; if poured over a petrified creature, they will depetrify. If the yolk touches non-petrified flesh, it causes horrific third-degree burns. The egg breaks much more easily than is convenient.
Theriomorph teeth: Wolfsbane grows on the spot. This is the only way to grow wolfsbane, which is not naturally occurring.
Vampire teeth: Drains all life-sustaining elements (nutrients, minerals, etc) from the surrounding soil in a 1 foot per tooth radius. Result is like you salted the earth on an extreme level; virtually nothing will grow in that spot again.
Chimera teeth: Randomly produces an outcropping of animal, vegetable, or mineral matter that acts as a carrier vector for the chimeric disease. Any creature consuming the growth will wind up fusing with some other creature due to the chimeric agents it now carries.
If mineral, it's a foot-tall irregular monolith of a random (solid) mineral, veined in a flaky, waxy prismatic substance. If collected and melted down, this substance is sovereign glue. Any creatures with mineral-based diets (rust monsters, etc.) are extremely attracted to the monolith and will attempt to eat it.
If vegetable, it's an otherworldly-looking and very attractive plant, like some flowers or a small shrub. The plant's pollen/sap/fruit can be collected and rendered into sovereign glue. Any creatures that eat vegetable matter are drawn to the plant and will find it difficult to resist eating.
If animal, it is a small and defenseless game critter, prime picking for any carnivore that may come across it. Its blood can be refined into sovereign glue.
Hag teeth: Grows curses.
Ghoul teeth: Corpse flowers sprout. Their repulsive stench is enough to drive most creatures away, but may lure carrion eaters. Prolonged exposure to the scent can cause vivid hallucinations of plague and death in humans.
6: Rare Teeth
Elemental teeth: Causes weather effects appropriate to the type of the elemental.
Wizard teeth: A random magical aberration - like a sub-sentient living spell - occurs at the site of planting. May vary from harmlessly amusing (e.g. mystery-spot-like effects: water flows uphill, strange viewing angles, etc) to extremely dangerous (e.g. localized storm of arcane energy). Even if harmless, the aberration will make it difficult to access the buried teeth. If not dispelled, the aberration grows more intense and more aware with time. If the wizard is dead, the aberration will eventually coalesce into the wizard reincarnated; if the wizard is alive, it will coalesce into the wizard's doppelganger, who will not get along with the wizard.
Outsider teeth: Terraforms the area around the planting site to match the environment from which the teeth's owner came. Area transformed corresponds linearly to quantity of teeth.
Time-displaced teeth: Five days after burying, will cause bubbles equal to the number of teeth buried to pop out and hover a couple feet over the ground. The bubbles have an elastic, rubbery consistency and are somewhat resilient; you can poke them with your finger, but pop if crushed or punctured (i.e. they'd get smashed up in a backpack or other non-rigid container). Looking into a bubble causes mild vertigo. When popped, a bubble instantly causes time to move forward or backwards in a 10-foot spherical radius around the bubble. Direction of the temporal movement is determined by the time from which the teeth's owner had come; if they were from the future time moves forward 1d6 minutes, if from the past it moves backwards 1d6 minutes.
Golem teeth: Animates one cubic foot of surrounding material per tooth buried.
Doppelganger teeth: If the doppelganger was created through arcane means (e.g. via the burying of a living wizard's teeth), a new doppelganger will grow from the earth. If the teeth's owner is living, the two doppelgangers will seek each other out and fight to the death, though they are identical in appearance and motivation.
If the doppelganger was created through alchemical means, the teeth will gradually transmute into a mixture of essential salts and ground glass over the course of a fortnight. If the essential salts are separated from the glass, they can be used to alchemically reconstitute the doppelganger.
If the owner of the teeth is a true doppelganger, the teeth will disappear and be replaced by a gold ring set with carved jade bearing a mysterious symbol. The ring permits (or enforces) entry into the dark realm from which true doppelgangers originate.