Let me start by saying that if you don’t brush your dog’s teeth he could have periodontal disease and plaque that could lead to painful tooth loss.
At the beginning, I bought a toothbrush made for dogs, but as time went by I realized that I needed to look at my dog’s mouth size, her sensitivity to that particular toothbrush, how easy or hard it was to use it and much more so after a while, and this is personal preference, I realized that I liked a human toothbrush and so that is what I’ve used for the last couple of years.
By the way, Abby’s toothbrush, the one on the right side was a bit too hard/firm for her so I replaced it for a softer toothbrush that she seems to like better. Before I forget, Do Not Use human toothpaste!! Stay safe.