Step One: Find the Right Time. Brush your dog's teeth when she's calm and relaxed. Your goal: Set a routine. Working up to brushing daily is ideal. But if her mouth is healthy, even three days a week can make a difference. Without brushing, plaque can build up, putting your dog at risk for bad breath, gum disease, and tooth decay. It can also cause painful infection. Severe infection can spread, causing life-threatening conditions.