Here are a few options for you:
1) Brush your dogs teeth daily (once a week is not enough), or if he hates brushing then apply the paste directly onto his teeth.
2) Feed a dental diet such as Hill's T/D or Royal Canin Dental diet, if they aren't chewing the food then the diet itself is useless.
3) Dentastix, Greenies, CET chews, moderately soft chew toys (if you wack it on your knee and it hurts then it's too hard for your pets teeth) are all other good options for healthy teeth. If he eats the treats too fast or swallows them whole then it wont work.
Stay away from bones, sticks and hard chew toys, they will damage your dogs teeth or get lodged in their esophagus (sticks/bones).
Prevention is key as once periodontal disease sets in you cannot reverse it.