Years ago, when a child in her daughter’s class lost her first tooth and got $20 from the Tooth Fairy, Linda Jerrett was angry. “All the parents were,” recalled Jerrett, whose daughter is now 20. Still, as for how she determines how much cash the imaginary sprite will swap for baby teeth (she also has a 7- and a 13-year-old), Jerrett said “social pressure” remains a guiding factor. “In my town it’s generally five bucks a tooth,” said said. That’s almost $3 more than the 2011 national per-tooth average of $2.10, according to insurer Delta Dental.