As https://dungeonfantastic.blogspot.ca/2017/02/expanded-realistic-injury-in-pyramid.html identifies, this is a new disadvantage on page 32 of Pyramid 3/100.
It can be up to 2 levels and is cumulative with Weak Bite, allowing for a total of -4 points for -4 per die to bite damage.
Neither mention this alters the Control Points in GURPS Martial Arts: Technical Grappling but this would be a useful house rule.
Missing Teeth also appears appears in PU6p23 before Missing Toes. Unlike the pyramid version it does not reduce bite damage. Instead it has these effects:
- no free grapple after bites
- extra 30 minutes per day to chew food (lowers available 'study' time)