Nowadays there is no need for your dog to suffer with bleeding gums, loose teeth or any kind of disease, oral or otherwise. Various flavors of dog toothpaste is available, as are sprays, gels, finger-brushes and toothbrushes.
Never use human toothpaste as it's not good for them and they don't know how to spit!
If your dog is still a puppy, time needed to learn this new experience may be easier and quicker. With an older dog patience and plenty of praise is required. Often, depending on the trust and love between you, this may take just a few days. Under no circumstance hurry or use pressure as this will completely ruin any chance whatsoever of a successful outcome.
To begin, sit close to your dog at eye-level. Dab a little toothpaste or gel on your index finger, and with the other hand gently life and pull back your dog's upper lip exposing the teeth and gum. Run your finger quickly all the way along the gum line from the molars at the back to the front. Stop and praise him while he licks. Give him a moment to relax and repeat on the lower lip.
Again, stop and praise. Do this on the other side and allow your dog to do what he wants. If he balks, stop and leave it until tomorrow. It's a natural instinct to resist. Talking in a playful way will help him relax and when he's ready you can introduce the brush. This may also take a while. Brush in a circular motion, making sure you reach into the gum.
Clean just a couple of teeth at one time. Stop often and praise your dog while he licks. Once learned, this won't take any longer than it does for you to clean your teeth! It is a good idea to brush his teeth last thing at night as the product works best with saliva. Remove his water-dish and replace first thing in the morning. This new habit will soon be an expected treat and before you know it your dog will look forward to this quality time with you.