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
Most accurate method of determination of working length in a tooth with open apex: 
Select and explain. 
A. Moisture on paperpoint, B. Electronic apex locator, C. Other digital method, D. Both 1 and 2
A: Moisture on paperpoint
Answer: A: Moisture on paperpoint 
Explanation: Advantages of apex locators

Provide objective information with high degree of accuracy.
Accurate in reading (90-98% accuracy).
Some apex locators are also available in combination with pulp tester, so can be used to test pulp vitality.

Disadvantages of apex locators

Can provide inaccurate readings in following cases:
	
Presence of pulp tissue in canal
Too wet or too dry canal
Use of narrow file
Blockage of canal
Incomplete circuit
Low battery


Chances of overestimation.
May pose problem in teeth with immature apex.
Incorrect readings in teeth with periapical radiolucencies, and necrotic pulp associated with root resorption, etc., because of lack of viable periodontal ligament.