Can a Restorative Dentist repair a broken tooth?

This depends on the cause and extent of the break. If a tooth is breaking due to decay, this likely means the decay is fairly extensive and has gone untreated. A root canal could be required to save the tooth. If your tooth is broken due to some physical trauma or other accident, your dentist will likely be able to save and repair your tooth as long as there is enough tooth left to do so.