Presadam is very right. The carb value in kibble doesn't help but isn't as much of a problem as the texture/substance of the food versus the teeth being used for the job. Carnassial molars (those really big ones almost to the back of the mouth) are designed for shearing like scissors. Particular food easily gets stuck around these teeth. Meat and bone is easily sliced and broken while keeping surfaces abraded. (similar to what our ancestors did by chewing on green twigs) Some dogs (and people) have a genetic hardness or "cleanliness" to their teeth, as well as those prone to buildup and periodontal/gingival disease. Give your dogs more bones to chew on, check their teeth frequently and you won't have this continuous problem. They also sell tooth brushes and fluoride wipes.