You're using human toothpaste
It may seem easier to squeeze out a dollop of your own toothpaste on your dog’s toothbrush, but you absolutely shouldn't do it. Many human toothpastes contain xylitol, a sugar substitute that is toxic to dogs. Even if your toothpaste doesn’t contain xylitol, dogs can swallow foaming agents, which could lead to stomach upset. As for toothpaste alternatives like baking soda, those aren’t safe bets either, since baking soda can upset the acid balance in your pet’s stomach. You should only brush your dog’s teeth with toothpaste formulated for dogs. Another great reason to use dog toothpaste? It's usually flavored with something pooches actually enjoy, like beef or chicken.
You're not praising or rewarding him.
It can take time for dogs to warm up to the idea of letting someone stick a toothbrush with toothpaste on it in their mouth. Rewarding him with extra treats and praise may help. Showing your frustration or punishing him will not. The key is to take things slow. Start off by letting him sniff the toothbrush and taste the toothpaste. Then get him used to having his mouth touched. Eventually, work your way up to actually brushing his teeth. This may take a few weeks, so you’ll have to be patient. Just remember to reward and praise him along the way. If you ever think that your dog is going to bite you, stop what you’re doing immediately and ask your veterinarian how to best care for his teeth.
You're not brushing your dog's teeth consistently.
Ideally, you should brush your dog’s teeth every day. That’s right: every day. Why is this necessary? The plaque that leads to dental disease can recolonize on the tooth surface in as little as 24 hours after a dental cleaning, so brushing every few days won’t be as effective. Remember: The key to getting your dog to accept getting his teeth brushed is to be patient and to give him plenty of rewards and praise.
You're ignoring signs of dental disease.
Brushing your dog’s teeth is a great way to keep track of his oral health. If you notice any changes like bad breath, yellow-brown tartar, inflamed gums, bleeding gums, unusual growths, pawing at the mouth, difficulty chewing or excessive drooling, you need to take him to the veterinarian. Those could all be signs of dental disease (or other oral problems) and should not be ignored.
You've never gotten his teeth professionally cleaned.
Even for the most diligent owner, brushing your adult dog’s teeth every day isn't enough to stave off dental disease. That's why your veterinarian may recommend a professional cleaning. During this procedure, your vet will remove the tartar buildup that brushing can't and may recommend dental X-rays to check for hidden signs of the disease under the gum line and in the bones.