Hmm. If all else fails, you could try using the cheat menu to create items with type 559 and frame = quality ranging from 0 to 17 until you get the right particular tooth.

This makes me want to code up an Ultima VII Item Finder that would search through the game world and report the locations of matching items. (Does such a thing not exist already?)

There's at least no need to start over, since the Temple of Discipline is reachable from many other serpent gates.
Go to Spinebreaker, then exit through the front entrance and go west, along the mountains. It's right next to it.

If you really want the tooth, then you're best off creating it, like pocococo said. It's likely that it's misplaced, and an item that small, well, you're probably never going to find it again.

If i could ask you a favor, would you mind uploading your saved game file as an attachment here in this thread? I would like to try scanning it for the missing tooth, when I get some time to.

Should be one of the GAME0x.DAT files in the Ultima VII directory. Or you could zip them all up and attach the zip.

By the way, based on some reverse-engineering I previously did for my UltimaHacks project, it seems that the serpent tooth for the Temple of Discipline should be shape 559, frame 4, quality 4.

Here is which destination corresponds to which quality/frame of tooth item:
0: Balance
1: Emotion
2: Skullcrusher
3: Spinebreaker
4: Discipline
5: Monk Isle
6: Isle of Crypts
7: Fawn
8: Great N. Forest
9: Sleeping Bull
10: Furnace
11: Mad Mage
12: Moonshade
13: Enthusiasm
14: Tolerance
15: Monitor
16: Ethicality
17: Logic