S.E.
The reason for your dentist is instructing this is that after oral surgery, your mouth needs time to clot and heal. If you suck on anything (sippie or straw) you could pull out the clot that keeps the wound from bleeding, and prolong how long it takes to recover. Luckily, the mouth is one of the fastest things on your body to heal (after the eyes), and so 24 hours will give it enough time to form a solid clot that won't be pulled out and cause the healing process to start over. I would definately not give your son anything that requires pressure or suction for at least 24 hours...and if you can go a little longer, GREAT! Liquids are easier to swallow during this time, and won't scratch or cut the wound so are perfect while he heals.