Dogs do lose teeth, but this generally happens in two key contexts:

1. Puppies naturally lose their baby teeth (deciduous teeth) as their adult teeth come in, usually between 3 weeks to 6 months of age. This is normal and expected in young dogs.
2. Adult dogs losing teeth is not normal and typically signals dental problems, with periodontal disease being the most common cause. This disease leads to plaque and tartar buildup, gum inflammation, and eventually bone loss around the teeth, which can cause teeth to become loose and fall out. Trauma and invasive bone tumors are other less common causes of tooth loss in adult dogs.

In summary, puppies losing teeth is normal during teething, but adult dogs losing teeth usually indicates an underlying health issue like dental disease that requires veterinary attention.