Perhaps you should try some spelling variations:
decrease periodontal » increased periodontal (Expand search), disease periodontal (Expand search), diseases periodontal (Expand search)
periodontal defect » periodontal defects (Expand search), periodontal desfecho (Expand search), periodontal effects (Expand search)
decrease during » increase during (Expand search), increases during (Expand search), increased during (Expand search)
during decrease » during increased (Expand search), during depressed (Expand search), during disease (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)
decrease to » decreased to (Expand search), decrease toc (Expand search), decrease the (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 to decrease during decrease ) OR ( decrease AND decrease periodontal defect ))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( decrease to decrease during decrease ) OR ( decrease and decrease periodontal defect ))~".
• Adding a wildcard symbol may retrieve word variants: (( decrease to decrease during decrease ) OR ( decrease and decrease periodontal defect ))*.