Bones are in a consistent cycle of being rebuilt and remade throughout your life. It is for this reason, that if you break a bone, it will heal over time. This is due to the cells that make up the bone and help regenerate it when there is breakage. This is helped by the bone marrow in your bones, something which is absent in teeth.
Conversely, teeth do not have such properties and are not a tissue which repairs itself. As a result, when your tooth breaks it does not heal itself in the way bones do. Additionally, a tooth is made up of four key properties: dentin, cementum, pulp and enamel. Enamel is the strongest part of the body and can withstand a great deal of pressure, which helps hugely with eating and the daily wear and tear inflicted on it.