One of the keys to getting a nice proposal when doing a bridge is drawing the pontics.  This is also one of the areas most commonly overlooked.  A pontic bottom line not only needs proper dimensions, but also the right location.

If you look at this bridge example (7=10), you can visualize were you think the pontic margins should be drawn. 

Most dentists will visualize that the margins should be drawn in this position.

However, if you take a biocopy image (either a pre-op or off of a wax up), you will see that these margins are in the incorrect location.  Simply turn on the biocopy and make it transparent.

You can see that the margins of the pontic are drawn much too far lingually to get a proper proposal.  The way you correct this is to turn on the biocopy transparent and draw the margins directly through the biocopy.

This will place the margins in the correct location to mimic the biocopy pontic position for the final restorations.  If you look at the margins with the biocopy turned off and compare it again to the second figure (below) you will see the discrepancy.    

By using a transparent biocopy to draw the bottom line of your pontics, you will achieve a better proposal with very little work.  Hope this helps you all design bridges more efficiently.