Perhaps you should try some spelling variations:
decrease periodontal » increased periodontal (Expand search), disease periodontal (Expand search), diseases periodontal (Expand search)
periodontal effect » periodontal effects (Expand search), periodontais effect (Expand search), periodontal defect (Expand search)
decrease will » decrease with (Expand search), decrease cell (Expand search), decrease il (Expand search)
decrease toc » decrease of (Expand search), decrease the (Expand search), decreased to (Expand search)
toc decrease » to decrease (Expand search), the decrease (Expand search), not decrease (Expand search)
decrease and » decreases and (Expand search), decrease in (Expand search), decrease of (Expand search)
and decrease » and decreases (Expand search), and decreased (Expand search), and increase (Expand search)

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (( decrease will decrease toc decrease ) OR ( decrease AND decrease periodontal effect ))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( decrease will decrease toc decrease ) OR ( decrease and decrease periodontal effect ))~".
• Adding a wildcard symbol may retrieve word variants: (( decrease will decrease toc decrease ) OR ( decrease and decrease periodontal effect ))*.