Bizzy, you got this one backwards. The dry kibble contains synthetic preservatives and artificial flavor and food color additives, the canned ones don't. Canned dog food use the vacuum sealed canning method to preserve the food whereas dry dog food has to have synthetic preservatives to remain fresh in the non-airtight bag.
As far as teeth health is concerned, there is no benefit with the dry kibble over the canned. If you got an elderly dog that has weakened teeth then canned is even better in this instance. The chewing motion to break down kibble is not significant enough to count as a benefit. And no, it doesn't clean the teeth as it still gets stuck to the gumline. Healthy teeth is better provided by the proper chew toys or chew treats and appropriate dental care products - or going raw.
As far as nutritional content is concerned, canned dog food is packed with higher quality meat with lesser carbohydrate content than their kibble counterpart. And, hands down, majority of dogs find it better tasting.