Why there is cavity in the teeth

My theory is that that in the spatial space that there is no bacterium of cavity, the teeth without cavity the person would think that isn’t the need to brush the teeth but it is need, in my theory without the cavity the teeth would still fermented the cavity happens exactly in the place that the tooth is fermenting so without the cavity the teeth without brush would fermented and instead of get a hole would explode, and crack, a full lost, so the cavity make a hole where are having a lot of pressure so the hole of cavity helps keeps your teeth when you don’t brush, because without the cavity the teeth when fermented would make pressure that would break your teeth. Rute Bezerra de Menezes Gondim