There are fewer choices available in rootstock for pears, compared to apples. The most widely used rootstock is a variety of quince (Cydonia oblonga), which is a different genus to pear (Pyrus).

The advantage in grafting pear onto dwarfing quince rootstock is that your tree will come to fruit much earlier (more precocious) and will have increased fruit yields for the space used.
It is also be easier to pick fruit and maintain your tree when it is smaller. 

When grafted onto a seedling D6 pear (Pyrus calleryana) rootstock, pears trees will be quite vigorous, resulting in very large trees that are slow to bear fruit.
However, the advantage is there are no compatibility issues and no need for an interstem when grafting.
 
As quince and pear are only distantly related, not all pear cultivars are compatible with quince rootstock. To guarantee success, an interstem of Beurre Hardy should be used. This is a small section of compatible scion wood grafted between the quince rootstock and the incompatible pear variety.