Dogs go for a ride with their teeth.

According to my estimation, your dog's small front tooth has fallen out and is now changing its teeth. If you have the opportunity to raise a puppy in the future, you can observe it carefully. They will also lose their deciduous teeth (front teeth), and it is normal to grow back now. Wait a little longer, it won't be long before it is full. Now we should be careful not to give him anything too hard, which will easily squeeze and deform his teeth. Many dogs are "fighting for teeth", which is basically caused by the owner's carelessness when changing teeth and giving back bones. The time is not long, but it can be fed normally after five months. I hope I can help you.