At the height of Mayan civilization, body modification included a variety of alterations of the teeth. Teeth were sharpened to points, or into the letter "T" to represent the wind-glyph, and green jade was inlaid to "purify breath or express elegant speech." Other minerals inserted into teeth included iron pyrites, hematite, turquoise, quartz, serpentine, and cinnabar.
Holes in the teeth were created by spinning a drill with a bow (as in firestarting), and using powdered quartz as an abrasive.
Modified dentition was always in the visible parts of the mouth for display; there is no evidence of restorative dental work for functional purposes. (photo credit here)