Be sure to monitor your dog for choking, though. But that's above the gumline. While these do have a mechanical cleaning action, it's nowhere near what's necessary to get everything clean. Be sure to monitor your dog for choking. The dog will try to swallow the knot and choke.
Teeth cleansing is better with flat rawhide strips anyway.
Always give rawhide under strict supervision. Safe for the dog, because they are quickly chewed down to small granules. But they don't provide much chewing exercise, or mechanical action against the tartar. They don't generally bother much with chewing. There's actually a good reason for this.