My son turned 1 today and he still has no teeth. Why?

Not unusual. Although most children start to get teeth at 6 months, some do not get their 1st tooth 'till 18 months. You should be wiping gums gently every day with soft moist cloth. At 1st b'day take your child to a pediatric dental specialist, whether teeth are present or not. Pedodontists are trained in oro-facial growth and development. Also, 1st orthodontic check-up age 7.
See below. It may take up to 18 months of age before you see tooth eruption.