We brush our dogs' teeth every day with an enzymatic toothpaste, but still take them in for a thorough cleaning every 3 to 5 years to make sure it's clean under the gum. Once you see that dark staining, it's a good indication that they need to have a cleaning done, filip. Dogs get gum disease just like people do, so you should definitely have Pedro's teeth evaluated by a vet.
And I'll second that request for pics!
Welcome to the board!