Answer: To get reliable retention!
It is impossible in approximately 70% of endodontically treated teeth, to have a root long enough for a post space to be prepared deep enough so as to make a post restoration held by cement alone reliably stay in place.

Comment - It is difficult to bond to dentine because:
i) It is an organic inorganic mix
ii) It is a wet dirty material
iii) It has a high surface energy like a non-stick pan (Prof Ralph Phillips).

The biggest single problem dentists have with post crowns - they come loose. An additional retention factor, which a thread provides, is the answer to the problem.

Answer: There are basically two groups of threaded posts:

a) Pre-Threaded Posts
With these, the thread is CUT with the THREAD CUTTER. This is a three bladed sharp cutting instrument, used by hand, and it cuts the thread in the wall of the canal 40 microns wider than the mating threaded posts. This leaves a 20 microns circumferential space around the post. The space acts first as a vent and secondly as the space for the cement.

b) Self-Threading System
Here the actual post, which is ultimately cemented into the root canal, is used to create a thread.

The choice is between these two cylindrical post systems.

A tapered threaded post acts like a wedge forced into the canal on insertion and is not recommended.

Comment - Neither of the two cylindrical threaded post systems should cause root fracture. It is the PRE-THREADING SYSTEM that research recommends, because it requires little torque to cut the thread and achieves great retention of the post.

Answer: Fracture of the root under loading is dependent on stress distribution. The larger the surface area of a post in contact with dentine, the less is the stress delivered at any point in the root.

Comment - The Kurer K4 Anchor System has the largest surface area per unit length of any threaded post because of the large number of threads per cm and hence the best stress distribution. This threaded post has three distinct advantages:

1. Mechanical retention

2. Larger surface area in contact with dentine than a non threaded post, which means larger areas to be cemented together.

3. The larger the surface area the more gentle and even is the stress distribution. Under load these threaded posts are LESS LIKELEY to fracture the root than non threaded posts.

Answer: With threaded posts the same principle of preparation applies as with non threaded posts. There is a threaded Anchor for every situation, so maximum tooth substance can be saved.

Comment:-

A. Save as much HEALTHY tooth substance as possible.

B. Leave 4mm of apical root filling undisturbed.

C. The crown should have a ferrule, cuff or collar, both as a stress distributor to the widest part of the tooth and the ideal anti rotational device.

D. Cement the post into a healthy, clean and dry, threaded preparation.

Answer: With the Kurer K4 Anchor System any cement of the dentist's choice can be used as long as it is used according to the manufacturer's instructions.

Comment - In the case of a root filling failing, it can be useful to remove a post. In many cases temporary cement can be used on a permanent basis, provided the ferrule of the crown makes unscrewing impossible.

Answer: As the thread cutter is wider than the mating anchor, a circumferential and constant space between the post and the dentine is present which allows the cement to flow around the shank without causing apical pressure.

Comment - Cement only works at optimum strength when it has a minimum film thickness. Thick cement in vents or other retention grooves has a poor shear resistance and cannot claim to substantially assist in retention. In the Kurer K4 Anchor System there is an even, minimum cement space created by the matching thread cutter. Here cement is at its optimum strength.

Answer: The anchor shanks are available in either implant quality stainless steel or titanium. The core of the Ready Core Anchor System is made from bronze with NO water absorption and optimum strength.

Comment – The stainless steel used in the anchor system for over 35 years has been extremely successful. Titanium is more flexible than stainless steel.

Answer: The thread cutter can safely prepare 100 roots. Replacement instruments and refill anchors are of course available.

Comment - The thread cutter has three sharp blades, each blade only cuts 1/3 of the total thread depth. This causes minimum stress on both dentine and the blade.

Answer: The Kurer K4 System is not technique sensitive, so long as the instructions are followed. The reamers provided are to the correct diameter so that the matching thread cutter can cut the thread. The important point is that following the clockwise turn of perhaps half a turn, the thread cutter is reversed a little before being turned in the clockwise direction again. The procedure is as simple as the use of an endodontic reamer in the root canal.

Comment - The reverse turn permits dentine debris to collect in the spaces or flutes of the thread cutter and avoids clogging. If there is any stiffness when cutting the thread the thread cutter may be removed, cleared with a bur brush and reinserted.

Answer: The Kurer Anchor System was the first cylindrical threaded post to be used in dentistry and has been highly successful since it came on to the world market in 1965.

Answer: A root restored with a post crown can last as long as the alveola bone supports the root. Equal success to that of endodontics in general should be achieved.

Answer: Secondary Caries.

Comment - Remember endodontic treatment and restoration does not change the tooth's Caries susceptibility, or the patient's oral hygiene or their diet.

When using the Kurer K4 Anchor System the clinician soon realises he is likely to achieve lasing success