Post Crown:

Post Crown:

A crown, replacing the natural crown, which is retained on the stump of the tooth root from which the pulp has been removed and treated by root canal filling. The post or pin integral with the crown and sealed in the treated root canal with suitable cement.


Historical Background
Various methods of restoring pulpless teeth have been reported for more than 200 years:
1-In 1747, Pierre Fauchard described the process by which roots of maxillary anterior teeth were used for the restoration of single teeth and the replacement Post was fabricated of gold or silver and held in the root canal space with a heat-softened called “mastic.”
2-Porcelain crowns were described in the early 1800s.
3-In 1849, Tomes written post length and diameter conform closely to today’s principles in fabricating posts.

Indications
1. Endodontic treated teeth.
2. Realignment of mal-posed tooth.
3. As a bridge retainer (short span bridge).
4. Tooth with short clinical crown.

contra indication:
1. Periodontal problem.
2. Mal-occlusal.
3. Unsufficient length and width of the root.
4. Internal or external root resorption.
5. The silver cone technique fill canal.

Types of post crown:
1. One unit post-crown: the post, core and crown are in one peace.
2. Two units post-crown: the post and core are in one peace and crown is the second peace.
3. Three units post-crown: The post or the dowel in one peace, the core is the second peace which inserted in the post part, and the third peace is the crown.

Parts of post crown:
1. The post (dowel): It is the part which inserted into the prepared part of the treated root canal system it should be 2 / 3 of the total root length.
2. The core: It is the coronal part of the restoration which is attached to full metal or any other types other restorations.
3. The crown or any other final restoration.


THE PROPER LENGTH FOR THE POST:
A wide range of recommendations have been made regarding post length, which includes the following:
1-The post should be longer than the crown.
2-The post should be one and one-third the crown length the post should be half the root length.
3-The post should be two-thirds the root length.
4-The post should be terminated halfway between the crestal bone and root apex.
5-The post should be as long as possible without disturbing the apical.














6- The recent study established a relationship between post length and alveolar bone level .When teeth have little bone support; stresses increase dramatically and are concentrated in the dentin near the post apex.
7-To minimize stress in the dentin and in the post, the post should extend more than 4 mm apical to the bone crest.
8-Basically, it is important to leave at least 5 mm of gutta percha at the apex of the root canal, because it is within the apical 5 mm of the root canal that 95% of lateral accessory canals split off from the main canal and anastomose with the exterior surface of the root. Should these lateral canals not be blocked with the gutta percha and the cement used to place the gutta percha, the chances of microleakage and percolation of microbes is drastically increased, thereby increasing the likelihood of an endodontic failure.







THE PROPER FOR THE POST DIAMETER:
1-Post diameter is to not exceed one-third the root Diameter.
2-Each millimeter of increase (beyond one-third the root diameter) causes a six fold increase in the potential for root fracture).
3-Instruments used to prepare posts should be related in size to root dimensions to avoid excessive post diameters that lead to root perforation.
4-Safe instrument diameters to use are 0.6 to 0.7 mm for small teeth such as mandibular incisors and 1 to 1.2 mm for large diameter roots such as the maxillary central incisor.
5-Molar posts longer than 7 mm have an increased chance of perforations and therefore should be avoided even when using instruments of an appropriate diameter.






Crown preparation:
1-We should remove any undercut in the post-crown preparation as unsupported enamel, previous filling, cement base and any weak part of the tooth which may fracture later on when applied the force of occlusion.
2- About 2-3 mm sound tooth structure leaving only supra-gingival.
3-The type of the finishing line depend on the type of the crown and metal which will used as in case of jacket crown a butt shoulder is all around.
4-The bevel placed around the occlusal external surface of the periphery of the preparation; this will provide a good collar around the occlusal surface periphery of the preparation which will help in holding the tooth structure together and preventing the fracture of the remaining tooth structure canal and the key way preparation will place in the other canal.


Root canal preparation:
1-The pesso reamers or pesso burs which are available in different sizes.
2- we selection size depend on the final size of the filled root canal.
3-The pesso reamers or pesso burs has a blunt non cutting end which will follow the area of less resistance through gutta-percha with attention in order not to perforate the root.
4-We taken radiograph in order to determine the length, width, shape of the root canal in addition to the type and the quality of the filling material specially in the apical third of the root canal.
5-The pesso bur is removed up to 2\3 of the gutta-percha of the root canal length leaving 3-5 mm filling at the apex of the root canal to get the maximum retention and support for the post and to prevent the dislodgment of the apical gutta-percha filling material.
6-On the other side this if happen will lead to the leakage followed by failure of the case The canal sides is made parallel to each other with slight flaring toward the outside.
7- With short root teeth a pin hole can used to increase the retention of the post ,which placed parallel to the post canal preparation , a key way shape is done about 1 mm width and 4 mm extended into the root canal wall using a flat ended fissure bur ,this key way will act as a guide during the insertion of the final post and also it will prevent the rotation of the final restoration specially in the teeth with rounded cross section of the canal.
8-For the multi-rooted posterior teeth we should place the post in the largest canal which is the palatal canal in the upper molar teeth and the distal canal of the lower molar teeth for the maxillary premolar we place the post in the buccal canal.
9-Multi-post sometimes avoided because it weaken the tooth and it will not be parallel to each other.





Anti-rotation:
1. Pins
2. Key way shape.
3. Post surface texture: Post with rough surface is more retentive than post with smooth surface.
4. The orifice of the root canal shape is triangular shape for incisors and elliptical shape for upper canine.

The retention of the post-crown depend on:
1-The longer length of the post is the more retention
2-The wider post diameter is the more retentive.
3-The parallel sided inside wall preparation is more retentive than tapered preparation.

Mechanico-Anatomical Aspect of Posts:
1-Maxillary Centrals favorable for posts (Anti-rotational required).
2-Maxillary Laterals tapered post only indicated.
3-Maxillary cuspid Ideal for posts tapered post and sided parallel (Anti-rotational required).
4-Maxillary first Premolars is not advisable to mechanically widen the canal (use smallest post) U-shaped parallel can be used.
5-Maxillary first Premolars is favorable for posts sided parallel is most indicated and tapered post are least indicated.
6-Maxillary 1st and 2nd Molar, palatal root is favorable for posts sided parallel is most indicated, it is unadvisable for the buccal roots
7-Maxillary 3rd Molar has unpredictable root study carefully before.
8-Mandibular Centrals only the smallest tapered post (Anti-rotational required).
9-Mandibular Laterals the same as centrals with better accommodation.
10-Mandibular Cuspid one of the most suitable for posts prime indication for tapered post. (Anti-rotational required).
11-Mandibular first Premolars much more suitable for posts, sided parallel is most indicated.
12-Mandibular 2nd Premolars is more stronger favorable for posts (Anti-rotational is not required).
13-Mandibular 1st and 2nd Molar, the distal root is favorable for posts, be careful of sided parallel or not because of perforation tendency.
14-Mandibular 3rd Molar has unpredictable root study carefully before.