In addition to the classification I mentioned in the first post about Dental Screws in Prosthodontics and Dental Implant Prosthodontics, here is the second classification of Dental Screws that may be inserted in the oral cavity.
Classification based on methods of machining the internal thread.
There are two ways of machining the internal thread. The internal thread may be cut in the internal surface of a tube, and the external thread fits this precisely. Alternatively, the internal thread may be cut in the internal surface of a metal part of the prosthetic component of dental implants.
Internal thread cut. on the internal surface of a tube.
1. High precision and clamping ability.
2. Sufficient strength to withstand the friction generated by frequent insertion and removal of the external thread.
3. It is tough because the tube itself is surrounded by a metal structure.
1. It tends to be bulky because of the thickness of the tube.
2. It may not be possible to fit it exactly where required.
3. Increased tooth substance must be removed to provide space.
Internal threads cut into the metal structure design.
1. The versatility allows one to cut the thread in the exact position desired.
2. Minimal space is required.
3. Less tooth substance need be removed.
1. The clamping of the threads is relatively poor because of the variable degree of engagement of the external and internal threads.
2. Frequent insertion and removal of a screw may damage the thread of the male or female components, making subsequent clamping impossible.
3. A tap fractured in the process of cutting internal threads may be difficult to remove.
Space permitting, the advantages of employing tubes with internal threads normally outweigh the drawbacks
Matsuo E, (1981): Screw Retained Dental Prosthesis, Quintessence Publishing Ed. 1.