10483
There is a clearly defined and substantial role for free radicals or reactive oxygen species ( ROS ) in periodontitis , but little research has been performed in this area.
 None
Locate the role in the text that participated in the event based on the event type and return it in the event list. 
 Option: Event type: RNA,cell type,protein,cell line,DNA, Arguments type: . 
Text: {0} 
Answer:
 None