1996
The present investigation conducted in a population of 258 dentally aware individuals in the age range 20 - 69 years , was initiated to elucidate the relationship between tobacco smoking and supragingival calculus , taking into account possible confounding factors such as age , gender , oral hygiene and gingival inflammation .
 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