Use the MeSH Database, an online vocabulary look-up aid, to build searches in PubMed. You can find a link to the MeSH Database at the bottom of PubMed's basic search screen.
For instance, if you want to search cancer of the jaw, finding the MeSH term will help you narrow down your results. The actual MeSH term is "Jaw Neoplasms" and it is further subdivided into additional catagories. Your term may fall under MULTIPLE categories, as in the example below.
You can also use additional subheadings or quantifiers to group together those citations about a particular aspect of a subject.
Check off the terms you want to search and send them to the PubMed search builder. Click Search PubMed to complete the search.
Then use Limits to refine your search even further.