Endodontics

Types of Posts

• Active (the post mechanically engages to the wall of canal through the use of the threads – screws) – obsolete procedure threads – screws) – obsolete procedure
• Passive (no mechanical bonding, the post relies mainly on cement to hold in canal)

Passive Cast Post-cores

An ideal „classical“ post should:

• be about 2/3 of the total root length,
• be 1/3 of its diameter,
• remain at about 4mm from the apex,
• have retention and friction along the canal walls,
• rest on a flat coronal surface (better suit the cast to the remaining root structure).

Problems: failure due to root fracture (wedge effect applied by the post on the remaining root structures) which is clinically manifested with pain or periodontal abscess. Wedge effect is a phenomenon common to all stiff posts.

Passive Pre-shaped Metal Posts

• various metal alloys (brass, steel, gold, titanium)
• smooth surface, coils, threads for cement retention
• shape: parallel, tapered, combined
• no contact between the post and root wall

Problems: metal corrosion, allergies, esthetics, no respect to anatomical shape of root.

Passive Ceramic Posts

• biocompatibility
• esthetics
• shape: parallel, tapered, combined

Problems: high stiffness produces stress concentrations, low adhesion to root dentin after thermal cycles and dynamic load tests, No respect to anatomical shape of root.

Passive Fiber Reinforced Posts

• higher survival rate among other materials
• shape: parallel, tapered, combined

Problems: no long-term data available, no respect to anatomical shape of root.

Passive Anatomical Fiber Reinforced Posts

Biomechanics of Posts

• The role of the post – whichever material is used – is to permit the rebuilding of the coronal prosthetic core, with no claims and possibilities to strengthen the remaining root structure. Nevertheless a high percentage of clinicians consider to use post-core systems as a „reinforcement“ for remaining root structure.

• Under masticatory load stiff posts cause an overload of some root areas which weakened by the endodontic treatment can risk fracture. To reduce the risk of failure the „ferrule effect“ is proposed: certain amount of remaining coronal structure should be left. In this way, the occlusal loads are distributed more uniformly along the outer root surface.

• Posts which have mechanical properties closer to the dentin reproduce better natural load transmission mechanism.

• The parallel posts provide good retention and produce uniform stress distribution along the post length. The disadvantage of such posts is that the presence of a sharp angle of the post at the apex causes the stress concentration. The parallel posts are suitable for a shorter root length.

• The tapered posts conform to the natural root shape and canal configuration. Some of the disadvantages of these posts are wedging effect, stress concentration at the coronal portion of the root and low retentive strength.

• The combined parallel and tapered posts preserve the dentin at the apex and achieve sufficient retention due to the parallel design.

The Ideal Post System Should Comply Three Conditions

• permit to rebuild coronal prosthetic core and stabilize it for long term,

• reproduce original load transmission mechanism (no stress in pulp area),

• No or minimally reduce remaining sound tissues of root and crown.