What effects does sucking on a pacifier have on teething?

Depends: Apparently, it can increase the risk for "buck " teeth, or teeth that are malaligned.

During teething: During teething it is actually likely that they will chew on the pacifier and it will actually help cut the teeth, so no prob. But know too that pacifiers can cause bone malformations and tooth alignment problems if used too long, beyond age 5 especially.

Thankfully: Thankfully less than sucking on a thumb or fingers. Depends on intensity and duration. Begin encouraging cessation of pacifier use about age 3, and it should be completely discontinued by 4th b'day to prevent dents-facial distortion. Remember, 1st Examination by General Dentist or Pediatric Dental specialist by 1st b'day. 1st Examination by Orthodontic Specialist (usually free) by 7th b'day.