Teeth are Magic Crystals.

We all know wizard teeth are full of magic.

But in fact, all teeth and bones are full of magic to varying degrees. Living animals accumulate magic in their bodies when interacting with the aether. This magic settles in the form of magicite crystals, which integrate neatly into the apatite crystals found in non-magical bones and teeth. Any creature which lives in a magically rich environment will develop a more magicitic skeleton, and grow more resistant to injury as a result.

(This is also why the cheapest form of mana potion is simply concentrated bone broth. Makes a good stew and recharges your fireballs too.)

Bones and Teeths with Special Powers

Some creatures have adapted to direct their bioaccumulation of magicite towards specific parts of their skeletons, and to shape it for more esoteric effects.

In big apex predators like wolves and lions, the magicite concentrates in the fangs. This imbues their bites with supernatural killing power. The most dramatic example of this is the smilodon's ability to bite things from several paces away.

Other examples of tissues with high magicite concentration include the horns of antelopes, the clubs of mantis shrimp, the dermal denticles of certain sharks, and the tusks of the mighty porcine unicorn.

(Larger animals and apex predators tend to accumulate more magicite, but there are exceptions to this rule.)

Magical Bird Pearls

Birds (and frogs and some other creatures) lack teeth or other bony protusions, and tend to have unenhanced skeletons. Instead, they ingest a small rock or particle of sand, and then coat it with layers of magicite. The resulting magicitic gastroliths, or mana pearls, are most commonly used simply to aid in digestion, but can also be channeled to more exotic effects.

Who can forget the fire-breath of the flamingo, the shield-penetrating honk of the celestial goose, and the psychic calls of the songbirds?

You can never quite be sure what a hawk is capable of. They ingest and store the pearls from the birds they eat as prey, and elderly hawks are on par with young wizards in terms of the diversity of their spellcasting abilities.

Teeth are the Catalyst for Verbal Spellcasting

In humans, the magicite concentrates in the teeth, but not as a weapon. Human dental magicite is the reason that song and incantation enhances spellcasting.

A child's milk teeth are essentially mundane, being apatite-based. The second set of developing adult teeth are imbued with magicite throughout the first years of a child's life. And it is only once they erupt that a child begins to display magical aptitude. Wisdom teeth are so called because they develop for longer and so accumulate a higher concentration of magicite.

People often lose their teeth as they age, and it used to be that they needed ivory dentures to maintain their magical abilities. This all changed, of course, with the discovery of arguably the most important spell of the modern wizarding era: Fauchard's Renewal

Wizards Regrow Teeth Like Sharks

Anyone who practices magic frequently, and thus cycles more aether through their body, will accumulate additional magicite. But because their teeth have already erupted and stopped growing, most of this magicite goes towards strengthening the skeleton and generally enhancing the constitution.

Fauchard's Renewal is a spell with stimulates the growth of a new set of adult teeth. It was initially used as a way to improve the quality of life of the elderly. But it was quickly discovered that when grown in the mouth of a spellcaster, this tertiary set of teeth has an incredibly high magicite-to-apatite ratio. It is thus now standard practice to apply this spell to students at the conclusion of their magical training. Practicing wizards have lost both their baby teeth and their adult teeth, and now have "wizard teeth".

Wizard teeth are powerful magical items and valuable ritual components. Some mages are thus tempted to apply the spell multiple times, harvesting teeth to enhance their power. However, this process is stressful on the body. The nutrients that would be directed towards reinforcing the bones and counteracting the effects of aging are instead directed towards growing more teeth. Those who abuse the process risk premature aging.

(Also, if you beat up a wizard and steal their teeth, you can make dentures which give you a wizard level.)