There are different flavors of dog toothpaste available, as are gels and sprays and dog toothbrushes. It is best to clean your dog's teeth last thing at night after he drinks. This way the gel or toothpaste can mix with his saliva and break down the plaque. Used consistently, this will work well. If your dog balks at the toothbrush, use a finger brush. This attaches to your finger and you brush one or two teeth at a time in a circular motion.
This can and should be a fun experience for you both, but you must be patient as it can take some time, especially with an older dog. To begin with, just dab a little toothpaste on a finger and let him smell and taste it. With one hand lift and gently pull back his upper lip. With the other hand gently swipe all his teeth and gum with more toothpaste or gel on your finger. Praise him again and repeat this on the lower gum and teeth, and then repeat on the other side.
With gentle persistence your dog will grow to enjoy this new habit and will even expect it. Make sure you stop often and praise him. This will reassure him and soon he will let you clean his whole mouth.
Home dental hygiene is far less costly than having your veterinarian do it. It is also critical for your dog's good health. Feeding nutritional dog food will ensure he has all the vitamins and minerals he needs and an occasional beef soup bone or marrow bone (raw) will be a good treat and make him happy.