When doing a multi-unit FPD or bridge, one of the most important aspects to having a successful case completion is not only ensuring you’re following the proper dimensions for the individual preps, but making sure you have a clear path of draw and line of insertion. Here’s how you can check for such.
1. Take a buccal mirror that is used for intraoral photography and hold so you can view the occlusal surfaces of your preps.
2. Change the angulation of the mirror until you find a vantage point where you’re able to fully visualize the entirety of your finish lines on all the preps. If you can do such then you know you have a clear path of draw, if not then you need to refine the preps until such can be accomplished.
3. If you don’t have a buccal mirror then a regular exam mirror can be used. First visualize one of the prep’s finish lines and then slowly but carefully move the mirror in the same plane to attempt to visualize the other prep’s finish line.
4. Using either of the methods above, now rotate your mirror(s) to view the buccal/lingual surfaces of the preps.
5. Attempt to find the angle where both mesial and both distal tapers line up perfectly with one another.
6. Tip – Use a perio probe or the bur you’re using to prep the teeth to verify both tapers are in the same plane. Once you’d found such you know you have a line of insertion.
Hopefully putting these practices into use will help you to better understand some of the more difficult concepts relating to FPD/bridge preps.