When we adopted our dogs they were 2 years old, had not been cared for properly and already were in need of a cleaning. When we took them for their first visit we set up and appointment to have it done. IMO dogs with smaller mouths can be a bit more difficult to get into and clean, so despite brushing we always had a yearly dental cleaning. Another thing that complicated tooth care was that our dogs didn't chew on anything that wasn't a treat. No chew toys, or rope toys or dental chews. No way! They would chew bones but then they'd get in a fight over them too. And the female actually cracked a molar on a bone and had to have it extracted.
We were never perfect with brushing until later in their lives. The vet gave us a 6 week training schedule to get them used to the brushing. While they didn't learn to really LOVE having their teeth brushed, they tolerate it pretty well. Our male mini dachshund always had healthy teeth, but his sister has had awful teeth. She's had to go to regular vet cleanings, but she's also had to go to a veterinary dental specialist. She has had to have a few teeth extracted. Brushing with enzymatic tooth paste and a chlorhexidine rinse has made SO much difference in her dental health. Regardless, she still needs to go to the vet to have her teeth cleaned professionally once a year. It's around $200 to have it done.
Does that help?