The peg and core knob is the type of dental restoration required when the amount of remaining sound tooth tissue is inadequate to maintain a conventional crown. The pegs are cemented into prepared root canals, which retain core restorations, which retain the final crown.
The role of the post first is to maintain the restoration of the core and the crown, and secondly to redistribute the pressure to the root, thereby reducing the risk of coronal fractures. The post does not play any role in strengthening or supporting the teeth and can actually make it more likely to be broken at the root.
When deciding whether a tooth requires a peg and a core crown rather than a conventional crown, the following should be established:
- The presence of an adequate ferrule
- Quite long channel to retain post
- The curvature and overall anatomy of the root canal system
- The thickness of the root dentin (radiculer) is sufficient for post preparation
- Tooth recovery
The benefit of placing a post into a root canal is increasing crown retention. But there are also disadvantages, as long as the preparation for post space there is a risk of perforation, the post can also make the teeth more likely to fracture, it makes future orthograde root canal treatment much more difficult and ultimately very damaging and requires the removal of excessive tooth tissue.
More posts are needed for the anterior teeth than the posterior teeth. The main reason for this is that double-rooted teeth have large pulp chambers that can be used for core retention and therefore crowns, whereas anterior teeth are much smaller and less retentive.
When it is impossible to maintain the core on the posterior tooth and post is required, no more than one post should be used per gear, and this should be placed in the largest available channel. This is because more than one preparation for the post will involve the elimination of excessive dentine and increase the risk of fracture. A better alternative to post posterior teeth is the use of Nayyar's core restoration that extends to the entrance of the root canal.
Video Post and core
Procedures
Posts and cores are divided into two main groups: prefabricated and cast. Both of these systems use post that is placed inside the root canal of the restored tooth. Thus the teeth should be treated endodontically first. After the endodontic procedure has been completed, and the root canal (s) is filled with a peripheral gutta percha root filler, some gutta percha is removed from the channel chamber, usually with a series of endodontic files preparing and forming the root canal. The existing coronal space to the remaining gutta percha, called the post space, is now available in which to place posts. It is desirable to leave sufficient root filler in the apical area to maintain the apical seal. This procedure does not even require local anesthesia because the tooth has long died after root canal treatment and no pain is felt.
Maps Post and core
Post length
In post and core fabrication, it is desirable that the post decreases at least two-thirds of the length of the root canal (or not less than the crown height) to provide adequate retention.
It is important to leave at least 4 mm gutta percha at the top of the root canal, even at the expense of a longer post, since it is inside the apical 4 mm of the root canal of the anastomose apical delta to the outer surface of the root. If the lateral channel is not blocked with gutta percha and the cement used to place gutta percha, microleakage and microbial percolation may be greatly increased, increasing the likelihood of endodontic failure.
This is not necessarily the length of the mast in the root canal providing core retention, and thus the final crown, but longer than the post that will exist in the root structure that is around the bone . If the post is 16 mm long, but only extends 4 mm into the root structure surrounded by solid bone, the restoration will have a poor prognosis. The consideration of this crown-to-root ratio is important when evaluating the teeth for crown elongation procedures.
In the picture to the right, two extreme left and right teeth are being discussed. Both teeth in the middle have been treated endodontically, but have no post and cores.
Type
Pre-fabricated post
Post and prefabricated cores take less time to be placed, as they do not involve lab work and can be inserted immediately after the decision to use them, once endodontic therapy is completed and post space is cleared of gutta percha. After prefabricated posts are cemented correctly into the post chamber, the core material, such as dental composites, can be packed around cemented posts. Once the material has been healed or has an opportunity to be properly arranged and molded into the crown preparation, an impression can be taken for the manufacture of a prosthetic crown.
The prefabricated metal post system is being replaced by a fiber reinforced fiber reinforced composite system that offers increased resistance to untreatable dental substrate fractures such as vertical root fractures.
Cast post
If the postroom is unsuitable for prefabricated posts, poles and cast cores can be made especially for teeth. The resin pattern is generated by placing the plastic "saturation" of the heading that has been formed into the post space and the resin material, such as Duralay resin, is used to build the gear to the right dimensions. When this is done, the plastic resin/post pattern is removed from the tooth structure and attached to the former canker sores, much in the same way as is done with the wax pattern of the crown, and the cast poles of a unit and core can thus be made of gold, titanium or metal others use the lost wax technique. Where a metal post can be difficult to hide a special post made of zirconia oxide that can be made; tooth color is less than a shadow under the final restoration. Alternatively, the impression can be taken from the postroom and the dental arch using a plastic post and a polyvinyl siloxane impression material, and this is used to build a suitable post in the dental laboratory.
Materials used for posts
Submissions may be made of nonmetallic and metallic materials.
Non-Metallic
Overall, non-metallic posts indicate a lower incidence of root fracture because of their ability to withstand high stress without permanent deformation and breaking. Non-metallic postings should not be used if there is no adequate sound gear network. The sound gear network should be at least 1.5mm in a more apical fashion to the core. Non-metallic posts are also more aesthetic than metal posts as their optical properties are closer to dental tissue (except for carbon fiber posts due to darker materials). Non-metallic posts are easier to remove from gear when needed than metal posts. The direct use of non-metallic posts in the most common use but they can also be built in the laboratory.
Zirconia
Zirconia posts have high strength. However, they are fragile and have a high modulus that potentially causes root fractures. It would be difficult to delete posts if needed.
Ceramics
Ceramic post made of brittle material. This post can be too strong which can cause root fracture. It can be difficult and even impossible to remove ceramic posts.
Fiber reinforced resin
Fiber reinforced resins are non-metallic post shapes and include carbon fiber, fiberglass and ribbon-reinforced ribbon woven ribbons. These posts are more likely to fail because their fibers could be a fuss.
Carbon fiber
The carbon fiber writing shows very little deformation and is able to absorb and transfer power similar to dentin. However, this post may be dark in color which can lead to unreasonable results because the post can shine through the teeth.
Fiber glass/Fiberglass
Post glass fibers less brittle than ceramic posts. Posts that have the same fiber are the strongest. However, it is difficult to produce such material types as fiber bundles require infiltration and wetting with resins. This process can often leave the cavity on the fiber surface, leading to a weakening structure.
Metal
Traditional metal posts have been used because of good corrosion resistance and high yield strength.
Pre-fabricated metal writing
Stainless steel, titanium, titanium alloys and gold alloys are used to build prefabricated posts. This type of post is usually placed in post space and the core is built with a direct restorative core material.
There are also prefabricated posts for which cores are cast. These posts are usually made of a Type IV gold alloy (containing gold, platinum, palladium and iridium) or platinum, gold and iridium alloys, compatible with palladium and silver-free or platinum alloys, gold, palladium and silver alloys.
Move the metal post
Often metal alloys such as Type IV gold alloys are used.
Post design
There are many types of posts that are designed available for posts and cores, utilizing various combinations of the following properties:
- parallel vs. parallel vs. tapered
- smooth-sided vs jagged vs. thread
- only post vs. with the addition of a single ring circle
In the classic case one of the best designs for posts to reduce the risk of failure is the narrowest and smoothest narrow, parallel post that one can fit into post space . Utilizing the oldest post ensures that the force transmitted from the crown is distributed as much as possible from the root. Using the right diameter post ensures that as much of the natural tooth structure is left to support the post and absorb the transmitted power. A parallel post ensures the greatest retention of the post within the channel, and may be used with only a slight loss of tooth structure to the internal wall of the canal. Posts whose surface is smooth, though less powerful than a jagged or threaded surface, transmits the least power to the root structure. While both posts are smooth and serrated, as they are only located inside the post space after being cemented, the active threaded post involves the internal walls of the root canal because they are chaotic, and, while the most powerful thus far, produce such force on the fragile root structure contraindicated in most situations.
The use of headings and cores does not strengthen teeth before restoration with a crown; on the contrary, this may contribute to the weakening of the tooth structure, because the forces placed on the crown and the future prosthetic nucleus are now transmitted throughout almost all the fragile teeth and treated endodontically. This inherent weakness is taken into account when the restoration prognosis is completed and described to the patient prior to the onset of treatment. This is due to the increased risk of failure inherent in the use of post and core restorations which, when all independent failure rates of many procedures are required for dental restoration are considered shared (endodontic treatment, crown elongation (when shown), post and nucleus and prosthetic crown) patients are sometimes advised to pull teeth and place the implants.
Posts with the addition of a single ring circle increase the contact surface area between the core and involve the hard tooth network significantly, therefore the system does not require posting with at least 2/3 of the root canal depth as its indication.
Impressions
To ensure an accurate recording of the preparation and finish line, gingival retraction is necessary. Its use replaces the gingival tissue long enough to allow the impression material to flow down the margin preparation line and into the hole. The use of gingival retraction ropes is a safe method because when used properly it will not damage the gingival tissue while ensuring the recorded detail is of good quality.
The various types of gingival retraction ropes that can be used are twisted, braided and knitted. The use of all three requires pre-soaking in water or an agent that promotes hemostasis. The hemostatic agent controls gingival bleeding after preparation and before impression making.
Once the cable has been left in place for the required length of time, it is removed allowing the sulcus to be rinsed and dried to prevent the hemostatic agent from creating problems with the impression material set.
The two methods used to create impressions for posts and cores are outlined below.
Direct Techniques
- The material used with posts to create patterns for posts and cores is a self-cure acrylic resin
- The wall of the canal is lubricated before the self-healing resin is placed inside the intra-radicular portion of the duct around the post to ensure it is attached and adjusted properly with the post
- Once set, the post is deleted and checked for deficiencies. If there is a shortage that is not small enough to be managed with a candle, a remake of the impression will be required
- Once satisfied with the post, the core section is built before being refined to achieve the desired shape
- The occlusal license is assessed and the pattern is checked for the last time before it is sent to the lab for casting
Indirect Techniques
- Posts are tilted to ensure better matches within the channel as the post preparation ends at a point because the instrument used for preparation
- The post is then placed with the correct length and tested to confirm the move deny
- The occlusal tip is trimmed to parallel to the adjacent teeth and made retentive by means of a heated device. The lubricant is painted on the part lying inside the channel to help move it
- The gingival retraction as described above is completed
- Additional lightweight silicone material is sprayed inside the orifice and around the prep ensures the prep is completely sealed, before a larger additional silicone material in the stock tray is mounted on top of the prep to make the impression of full arch
- After adjusting the impression should be removed with embedded post in-situ
- Finally, an impression is made of the arch of the opponent
References
Source of the article : Wikipedia
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