Causes Treatments Outlook Should I be worried? Your dentist may also put a small, specially-made plastic splint in place to stabilize the loose tooth. Causes of a loose tooth in adults. If you don't brush or floss on a regular basis, or if you skip regular Adult loose tooth cleanings, tartar can build up into the space underneath your gums. Hardened plaque, known as tartar, causes the gums to Adult loose tooth away from the teeth, creating gaps that can become infected.