Searching effectively for the evidence

Let's return to our question on dental erosion.

You want to find anything about primary teeth, so you combine all the terms in the first column with OR, so primary teeth OR primary dentition OR deciduous teeth etc.  This would retrieve results that use any of those terms.  You'd then do the same with the fluoride component, and finally the tooth erosion component. 

Once you've got a set of results for each component of your search you need to narrow it down to find evidence that is specific to your question.  To do this you'd combine the results of each component using AND, in order to retrieve any articles which are about all of the aspects of your question.  So your search in a database would look something like this.

It's never a good idea to mix ORs and ANDs in the same search, because the database will not necessarily combine your terms in the way you need.  It's advisable to do all of your OR searches first and then combine each set of results with AND as in the example above.