Agree totally. We have had a number of long dogs - currently Whippets but last two were Greyhounds. They have long jaws and back teeth can give trouble because they don't have much to do. With the last Greyhound and now the Whippets we feed entirely raw meat at home and decent kibble & chicken wings or lamb ribs when away in the MH. All have superb white teeth, fresh breath, ............ and their poo dries white. What there is of it.Have you considered adding some raw chicken into their diet?
Either raw chicken wings or carcasses can be eaten easily by small dogs and do a great job of keeping their teeth clean and breath fresh
Our GSD has lovely white gnashers