Brushing teeth and tooth decay?

i think its because you don't drink soda, which is acidic on your enamel and you don't have sweets which does the same. My husband seriously hasn't brushed his teeth in over 3 years, he just rinses with listerine everyday and uses toothpicks regularly.. His dentist did say that his teeth would fall out in about 10 years if he didn't get his gingevitis taken care of, but he does eat alot of meat , spicy foods and about 1 liter bottle of soda every day for the past 5 years.