First you have to understand basics of QlikView, like data management, basics of Set Analysis and how QlikView work.
QlikView load datadistinctly, when the data source have two identical row then QlikView load single row only due its default behavior, rather than both row, if you need both row then you have useno distinctor other mechanism in load.
When you filtered data with the selection of a dimension and you want to calculate something beyond this selected dimension value then you need Set Analysis.
For example there is dimension in your data set say Year, and you chose Year : 2009 and you want to calculate sales value of year 2008 or 2009 then you need to use of Set Analysis.
In your case, suppose you selected Dental then you have to wright.