Presentations at conferences are often first indicators that research is being undertaken in a particular field. For systematic reviews, these can be valuable pointers to new research and experts in the field. Some conferences publish the full-text of papers presented. Others publish just the abstracts. Conference abstracts may or may not be available as published papers.
Search these databases to find conference abstracts published in journal supplements. Additionally you may need to seek out the websites of major conferences or their host associations in your topic area.