Qual seria a maneira mais segura de soltar milhares de objetos pequenos e duros de um avião típico da GA de asa alta?

Funeral homes sell gum bags for ashes. They dissolve in the ocean, releasing the ashes. You could make satchels and drop them in bundles with the teeth wrapped in kelp.

Spitballing an idea... Not sure of the legality or practicality of this, but it's an idea that came to mind.

Using a piece of 2-3" diameter PVC pipe (sized as necessary to clear the largest tooth), attach (very securely - using the appropriate PVC glue and, possibly adding some screws) it to one edge of a sturdy (heavy plastic) box. Add some eye bolts to the sides of the box.

When you reach the drop zone, attach ropes (with swivel connectors, like on a dog's leash) to the eye bolts, slide the pipe out the window/door so that it hangs into the air stream, but below the empennage, slowly pour the teeth into the other end of the box and let them slide down to the spout and out of the plane.

The pipe will guide them down far enough to clear the bottom of the plane and give you controlled output. The ropes (attached to something inside the plane prior to take off) will ensure the box doesn't go sailing out of the plane.

A nonprofit in Kenya is doing something notavelmente semelhante (link shows the distribution of pellets formed of tree seeds and fertiliser to degraded areas to encourage reforestation).

One short observation from the video suggests that the vacuum effect on the end of a flexible pipe hung out of the window of a light aircraft is sufficient to draw small objects from inside the cabin. Shark teeth might be too dense but it's worth a try.

Rig a curved PVC tube running from window to behind and below tail and have passenger pour teeth through a big funnel. You may need a fairly large diameter pipe because with this version of pipe idea, the slope of the pipe is small, making it easier for teeth to jam. Maybe the end of the pipe will even drag on ground during taxi and takeoff run or at least when you rotate for takeoff, which should be ok as long as the pipe has some flex, as the pipe doesn't have to survive multiple uses. Check what pipe does when you put the aircraft tail tiedown ring on the ground before actually flying with this idea. Also check what happens when you turn while taxiing. Operating from a grass strip would help.

Calculate CG carefully!

Maybe even bring a pressurizable (pump-up) container of water to blast teeth out if get stuck, or something like a toilet snake, or just do sufficient tests on ground ensure won't get stuck. You may want to drop teeth in steep climb to make pipe steeper.

You can crack the door on a Cessna 150 or 172 while in flight, probably can most other high wing aircraft. So just crack the door, put a PVC pipe out the door far enough so it is out in the slipstream, and pour your shark's teeth into the pipe. Further away from the tail and easier to manipulate than out the window.

Out the window should work fine, assuming they're as dense as a typical fossil. The "blowback" hazard is with low-density or fine particulate materials such as the human ashes that you hear all the horror stories about.

You can fly at a lower airspeed to further improve the clearance from the empennage.

The common technique for scattering ashes is to put them in a small cloth bag, under the wing and well away from the fuselage. Tie the bag with a slipknot, and open it by tugging on the other end of a rope run under the wing to a cockpit window.

You can further avoid risk to the airplane body by paying careful attention to the prevailing wind, and making sure the drop happens on the leeward side of the plane while crabbing. This should make the pieces move away from the plane very quickly as soon as the bag is opened.

It sounds like you're concerned that the teeth would fly around uncontrollably after being released and possibly damage the aircraft. Try changing their aerodynamic properties. The answer that mentioned marbles got me thinking that if you rolled the shark's teeth in cookie dough then the teeth would fall through the air in a more predictable fashion. I like the idea of a little ball of biodegradable cookie dough, with a crunchy shark's tooth center, falling through the sky. Then those ideas about using a pipe or just tossing out the window would be more viable. (Rolling the dough balls in powdered sugar to facilitate sliding down a pipe is optional.)

If they were marbles of the same weight, I think you could be sure would not hit tail if just poured out window, but maybe not with those teeth. Here's one solution: remove brace from side window to permit full opening. Put teeth in bag. (Optional: fill extra space in bag with sand to make heavier). Have top of bag tied shut with flaps that will open when a string pulls out a pin. Have bottom of bag securely tied to strong long rope. Throw bag out window, string comes tight first, opens top of bag, then rope comes tight and holds bag securely upside down. Or just do it with one rope, you just have a loose "bight" threaded through the rubber band that holds the bag closed, as is done with parachute shroud lines. (You could even buy a hang glider parachute deployment bag.)

Anyway after deployment the empty bag trails harmlessly way behind the tail till landing.

Better yet remove door and push bag out door. How big a bag would it take to contain all the teeth anyway?

Simpler- a strong-ish plastic bag like a trash compactor bag or heavy garbage bag. Remove door and passenger seat to accomodate huge bag with thousands of teeth. Bag is filled with teeth, bunched up on top, wrapped round with twine, then a long heavy rope is tightly tied around "bunched" point. Leave lots of excess bag material on top above "bunch" point so bag cannot slip out through twine and rope. Bag is tied to secure strong fuselage member or landing gear. To drop, do an extreme slip, or push bag out with broom or similar. Bag falls to end of rope, bottom rips open, teeth fall, empty bag trails well behind tail. (You'll use a rather long rope.)

Do tests on ground out of second-story window with same kind of bag to make sure it will consistently rip open when reaches end of rope and doesn't pull loose through rope and twine. Maybe using a bag full of same weight of gravel or sand, so you don't have to pick up all the teeth again. Of course the teeth will do a better job of ripping the bag than gravel or sand will. Make sure the bag is strong enough that the teeth won't rip the bag in the plane, and be sure the plane has an interior such that loose objects can't migrate to tailcone. Tie bag securely into place before takeoff with rope or strap that you can easily undo. Maybe better to leave passenger seat in place after all to facilitate buckling bag into place; also it will put bag in better postion for you to shove it out the missing door with one hand and avoid issue with bag clearing door sill. Make sure the bag cannot interfere with controls in any way!

A bag with a ripstop kind of "weave" (texture) would help stop minor tears and punctures from propagating before the drop, if such a thing exists in a disposable bag. You may end up needing to double-bag the teeth- do some experimenting.

Inspired by another answer Qual seria a maneira mais segura de soltar milhares de objetos pequenos e duros de um avião típico da GA de asa alta? (and now I also notice the comment suggesting to freeze the teeth in ice) : make a giant shark's tooth cookie! Mix dough and teeth together in barrel, let harden, cut away barrel, and take mister sharktoothcookie for a one-way flight in a plane with door removed.