In Dr. William Cheung’s May JADA article, "A Review of the Management of Endodontically Treated Teeth: Post, Core and the Final Restoration," I believe he is correct in stating that screw-type posts offer more retention, but not necessarily that the additional stress is dangerous. He just makes this short mention of screw-type posts as if they are all alike.
It is true that older, original screw-type posts did exert excessive pressure that sometimes did fracture roots. But we cannot categorize all screw-type posts together, because there is one that is significantly different than any others I have ever seen.
The screw-type post of which I speak is the ParaPost XT (Coltène/Whaledent, Cuyahoga Falls, Ohio). I also will state that I have used this particular brand of screw-type post thousands of times over the years and have never caused a fractured root, not even once.
There are two reasons I see for this. First, some thinking has been done by the manufacturer in designing the threads so that they are not at the bottom of the post, which is the area that might exert the most pressure on the most vulnerable portion of the root, which is close to the apex. This is the less important reason, in my opinion, because we often have to cut some of the post away, since it is too long, and the screw is then at the bottom of the post anyway.
The important distinction is that there is very little difference between the post of any particular size and the bur used to make the post hole. And, if you closely examine the threads of the post, you will note that they are very small and protrude only very slightly. In other words, it is not like screwing a screw into wood, where plenty of torque is needed to forcefully embed the screws into the wood. By the time the post hole is drilled, the diameter of the post for that size of bur is just slightly greater than the hole.
I also believe in using the final bur several times, with water irrigation between times. This ensures that the hole is the maximum size. In the event that the post is shortened, be sure that the end of the cut portion is slightly rounded. This is necessary because the cutting by a separating disk does leave a little bit of flash, the tip will, therefore, be wider than the rest of the post. This we do not want, so, using the same separating disk, turn the end of the post around the flat blade of the rotating separating disk until all flash is removed.
You will then note that the post screws into place very easily. This does not exert excessive stress on the root and, as I have said, has never caused a fracture in a root in my hands. For cementation, I acid etch the canal and use a dual-cure resin. If you are looking for superior retention of a post, this is it, in my opinion. They just do not become loose, and they do not cause a fracture of the root. What else is more important than that?
I believe that these screw posts are indicated when maximum retentiveness is needed, such as when the entire tooth is fractured off at the gum line. If there is sufficient tooth structure remaining, I use a fiber post. In cases where there isn’t room for the hand screwdriver to be used without pressing onto the tooth structure, then this usually indicates that there is sufficient coronal tooth structure remaining, and the screw post is not needed anyway.
I respect the opinion of endodontists who uniformly, as far as I know, advise the use of passive posts to prevent root fractures. But we can understand this because they are responsible for the endodontics, and not the restoration. If a post comes loose and a crown or bridge abutment is loose, it is the responsibility of the restorative dentist. But I, as a restorative dentist, also do not wish to have the roots fractured. Since I am responsible for the final restoration and its retention, I am happy to be able to place a post that has superior retention and will not fracture the root, if used in the manner described above.
