Can teeth continue to shift?

Shifting teeth: Teeth do like to shift, mostly if your missing a tooth in front of it or below it. Sometimes when your bite is off or if you clench or grind your teeth will shift as well. Have your dentist fit you for a retainer to stop this from happening. A night gaurd may be needed if you clench or grind.

Teeth Moves: Within physiologic limit. Teeth are connected by a network of periodontal fibers that allows it to move within a limit. If the force is applied beyond what it can handle, some fibers breaks and allows teeth to move towards the direction of the force.

ALWAYS? No: Do they always shift? No. Do they usually shift when you have missing teeth, open contacts, food impaction, periodontal disease, orthodontic treatment without wearing a retainer, a malocclusion, etc? Yes. I'm not sure why you asked, but hope this answered your question.

Shifting teeth: Thing what happens if you remove a stave from a barrel. Remove a tooth and the others start to shift, especially if you clench, grind, have bone/gum damage from gum disease, or have a preexisting malocclusion. See your General Dentist for an evaluation. Consultation with a Periodontist and/or Orthodontist may be advisable.