You may have bone loss. You could be clenching your teeth.

Either the gap has been formed by the loss of a filling you previously had placed in the tooth or your teeth are moving or spaces are developing as your jaw changes shape as you get older. You can visit a dentist or orthodontist to evaluate spacing and crowding issues with your teeth.

Dr. Bishop

At the age of 15, the reason for your "gaps" is a simple thing called growth. You are probably in your last major growth spurt. Everything is growing, all of your bones, including your upper and lower jaws. One thing that does not increase in size with growth are your teeth. Once teeth are completely formed, they do not change size. Some young people have very crowded jaws that look like there is no way they have room for their teeth to come in, but as the jaws grow, the teeth slide into place. Others have smaller teeth that, as they grow, create spaces. All of this is part of your genetics. The old saying "Mom's teeth and Dad's jaws" is more true than you might imagine. As the world becomes smaller and people from every nationality mix and blend their genes, the differences in teeth and jaw sizes seem to become more obvious. The best way to deal with the generalized spacing is through orthodontics.