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
Who has given root canal isthmus classification? 
Select and explain. 
A. Kim, B. Schielder, C. Krasner and Rankow, D. Vertucci
A: Kim
Answer: A: Kim 
Explanation: Kim et al Classification
Root apex cross-section
Narrow ribbon-shaped connection that contains pulp or pulpally derived tissue - ISTHMUS
According to Kim et al classification; there are 5 types:

Type I : Incomplete isthmus between 2 canals.
Type II : Well defined, complete isthmus between 2 canals.
Type III : Very short, but complete isthmus between 2 canals.
Type IV : 3 or more canals with the complete or incomplete isthmus.
Type V : 3 or more canals without any visible connection.