There are no hard and fast rules as to the frequency of replacing a dog toothbrush. Some will say every 2 months while others will say every 4 or 6 months. It actually depends on several factors. First, the quality of the toothbrush you bought. If it is poorly made then you really cannot expect it to last that long, unless you’re going to brush your pet’s teeth only once a year. Second, the frequency of brushing will also determine the lifespan of your dog's toothbrush. If you brush your dog’s teeth every day it may not really last 2 months. If you brush your pet’s teeth once a week, then perhaps you can extend the lifespan of your doggie toothbrush to 4 or 6 months. Third, the behavior of your dog while brushing also affects toothbrush longevity. If it is known to chew on everything put into its mouth, including its toothbrush, then there’s no way the brush will last a long time. There is an easy way to tell if it’s time to replace a toothbrush, however. Look at the head of the toothbrush with the bristles pointing away from you. If you can see any bristle “peeking” on the sides of the brush head, then it’s time for a new brush.