The toothbrush appears and your dog turns away. The mouth is a sensitive place, and a sore tooth or gum can make handling hurt. Before trying to get a brush into a resistant dog's mouth, ask your veterinarian about dental health and what home care is appropriate. Bad breath, bleeding gums, difficulty eating, or a sudden change in tolerance need an exam, not a stronger grip.
Begin without a brush
Let your dog approach while you hold a small amount of dog-safe toothpaste recommended by your vet. Reward a calm sniff, don't force their mouth open. Over short sessions, practice touching the side of the muzzle briefly, lifting a lip for a moment, and letting go. If they pull away, stop and make the next step easier.
Introduce the brush separately. Let your dog see it and investigate without it touching their teeth. Later, a single gentle stroke on an easy-to-reach outer tooth can be the whole session. Reward and finish. Gradually add more teeth only while your dog stays comfortable. Never use human toothpaste unless your veterinarian specifically says a product is safe for dogs.
If your dog has bitten or might bite during mouth handling, ask the clinic for a safer plan rather than attempting a home session. Your vet can also discuss other dental-care options while brushing is still a work in progress. One relaxed second today is a better start than a full forced cleaning that makes tomorrow impossible.
Sources: VCA Animal Hospitals: Successful Toothbrushing Training for Happy Dental Care. Best Friends Animal Society: How to Help Dogs Tolerate Grooming and Vet Handling.