Plaque and tartar production occur in cats just as they occur in people. Tartar deposits can invade the gum line, creating spaces that can be invaded by bacteria that cause gingivitis and other problems. Free feeding encourages plaque and tartar development because the food ingredients that contribute to these problems are present in the mouth almost all the time. Feeding once or twice a day allows the natural flow of saliva to cleanse the mouth of plaque- and tartar-forming substances throughout the day.
No proven evidence exists that plaque and tartar formation are greater in cats fed canned food as opposed to dry food. The abrasive action of dry foods, however, can be helpful in reducing the buildup of plaque and tartar. So it is a good idea to include dry food as part of the daily feeding program.