4520
A silica - based , fluoride - free placebo containing NaTPP , and a NaF - containing silica - based USP reference standard toothpaste were used as negative and positive control toothpastes , respectively .
 None
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: GENE 
Text: {0} 
Answer:
 None