According to http://alpaca101.com/what-to-look-for/
"Alpacas do not have top teeth, only a hard upper palate. Ideally, the bottom teeth should meet the upper palate evenly, not protrude outward from under the palate (undershot) nor be far back on the palate"

This lady was willing to show me her teeth without being asked.
She is a "Sari" (more rare) Variety Alpaca.