My old Lurcher boy, who will be 15 in a couple of months, has always has the worst teeth of any dog we’ve had. Our other Lurcher didn’t seem to have the same issues, despite the same dental routine and diet.
He has Plaque Off with his meals and we use Dentisept as well to reduce the build up and control the bacteria. His gums bleed easily, so I use the microfibre finger brushes, rather than a toothbrush.
About once a month, sometimes more, depending on how his teeth are, I give his teeth a gentle scrape with a dental scraper (I bought mine via Amazon). You can only do it gently though, as you don’t want to scrape the enamel itself, but it breaks up the deposits, which then come off more easily with brushing. If you give them a scrape, then a thorough clean and polish with a microfibre brush, followed by applying Dentisept it really makes a difference.
If she gets thick calculus, you can actually get that off by levering the edge and giving it a strong flick, revealing lovely pearly whites underneath. My vet showed me how to do it, but it’s basically just a case of levering/flicking it off - you just need to be find an edge to start at.
Of course that all relies on them being compliant. My boy is resigned to it after all these years and just lies with his head in my lap while I do it, but I know some dogs would really object.