This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
Which of the following does not function as a space maintainer? 
Select and explain. 
A. Lingual arch, B. Stainless steel crown, C. Class II restoration, D. Palatal expander
D: Palatal expander
Answer: D: Palatal expander 
Explanation: Lingual arch is the most effective appliance for space maintenance and minor tooth movement in lower arch.
Stainless steel crown and class II restorations, maintain the space and prevent supra-eruption and tipping of adjacent teeth.
Palatal expander is used for palatal expansion. It can increase the space in the arch, however, it cannot be used as a space maintainer.
Textbook of orthodontics, Gowrishankar 2nd edition page 521