I am a dentist. PLEASE do not use a waterpik instead of brushing and flossing. I actually do NOT recommend waterpiks in the absence of gum disease or braces. Plaque is what you need to clean off your teeth every day and a waterpik does NOT remove plaque. Plaque is sticky like left over butter on your plate. You can spray the plate with water from the sink and it moves around but does not come clean. Brushing and flossing are the only ways to remove the plaque. Toothpaste is not required to remove this plaque but does have valuable fluoride to help strengthen tooth enamel and resist cavities. For young children, use just a smear of toothpaste.
Some other great tips for avoiding cavities: Brush at least twice per day. One time being the last thing before bed. Drink ONLY WATER BETWEEN MEALS. Nothing but water in a sippy cup or bottle to be carried around or left with a napping/sleeping child. For adults or children old enough to spit out the toothpaste: do not rinse with water after brushing your teeth. Use the toothpaste solution you created while brushing as a mouthwash, swishing it between the teeth for an extra minute or two after brushing. Then spit out all you can but DO NOT RINSE, eat or drink for at least 30 minutes. You get a fluoride treatment every time you brush! Hope that helps. G.