The three most important factors that determine the disposition of a case are (in order)
(1) the Periodontal condition (2) the Endodontic condition (3) the restoration. Without adequate periodontal health, the endodontic and restorative results are meaningless. Similarly, in a periodontally healthy tooth with an endo failure, the restoration of the tooth is irrelevant, since the tooth is likely not comfortable to occlusion. Lastly, where both the periodontal and endodontic conditions are favorable, the restorative treatment usually determines success. Restorative treatment options are also the area where we have the most flexibility of design. Posts are indicated for restorations when there is insufficient remaining tooth structure to retain the core.
In the vast majority of well-designed cases, a single properly placed post is adequate. There is still much misinformation about the function of the post. Post placement does NOT strengthen teeth. Posts weaken teeth due to the need to machine the post space to reasonably accommodate what is in many cases a prefabricated post. "Screw" posts (e.g./ Dentatus) cause even more stress on the root and are aptly named. Cast posts (while well fitting) have recently undergone criticism for their association with higher rates of root fracture in anterior teeth.
As an endodontist, my primary concern is producing predictable successful endodontics. However, because no treatment mode is 100% successful I believe that when endodontic treatment is performed, it should always acknowledge the possibility that retreatment may be necessary in the future. Conventional re-treatment has a reasonably good rate of success, though obviously not as high as the initial treatment. Depending on the individual case and circumstance, I tell patients that the non-surgical retreatment prognosis is about 70-80% successful. Those cases that cannot be treated successfully in that manner must be managed surgically.
When performing complex endodontic/prosthetic rehabilitating of a tooth, every effort should be made to: (1) allow for the possibility of endodontic retreatment with the least damage to the tooth and (2) minimize the possibility of the need for surgical intervention. This means preparing posts spaces in canals that have the highest rates of endodontic success. Where possible we should avoid post placement in canals where surgical retreatment may result in severe compromise of tooth structure, such as in palatal/lingual canals of posterior teeth. The exception being the palatal root of maxillary molars where the endodontic failure rate is very small. These can be posted safely because even if the post must be removed, there is generally sufficient root thickness to allow removal with minimal risk of perforation or fracture. This philosophy may conflict with some of the prosthodontic opinions that appear to favor placement of posts to minimize occlusal load or to best take advantage of remaining tooth structure.
What is particularly alarming is the tendency to use posts in situations where they are not indicated or using multiple posts when a single well placed post will suffice. When contemplating post placement, the remaining supported tooth structure must be considered. Placement of a post in an otherwise unrestored intact anterior tooth is simply malpractice. In such a case, if the endodontics fails, the tooth will require complex post removal. With the use of bonded posts, this can be very difficult. It may require enlargement of the access and further compromise of sound tooth structure. It risks fracture and in the worst case scenario when post removal is impossible - it necessitates surgery. Unfortunately, the way the fee guide is structured, there is financial incentive to place as many posts as possible. (E.g./ The fee difference for 1 vs. 3 post/cores is almost 30%!) There is great potential for abuse.
Example: Failure to locate and seal the 2nd MB canal (MB2) is the most common reason for maxillary molar retreatment. Post placement in the MB root of a crowned tooth virtually assures the need for expensive disassembly retreatment or surgery. Palatal roots should be always be used in that tooth. However, in the premolar, placement of a post in the palatal or lingual root often means surgical resection of a perfectly good buccal root. Why not post the buccal root and save the palatal root in the case of an endo failure? Decisions like these can make the difference between allowing for conventional endodontic retreatment and avoiding complicated surgery that often shortens the "good" root.
Unorthodox post use also can cause major restorative problems. Attempting to "unite" a carious root to a crown or fixed prosthesis risks loss of the abutment. Faulty margins are just that... FAULTY. No amount of repair can ensure proper seal of the crown or the canal space. Remake of the crown or prosthesis section is mandatory. Otherwise failure is inevitable. Modification of a previously prepared post space can result in strip or post perforation or fracture. Post size and adequate chamfer are other factors that must be considered in the new restoration. Post length is also important. Most studies have shown that a minimum of 5 mm of gutta percha must be left to ensure apical seal.
Post Space Preparation. If a post space is required, it is best prepared in the following way: Remove the excess gutta percha with a heat carrier. This removes most of the gross material. Follow this with a SMALL Gates Glidden drill (size 2 or 3 maximum) using a brush stroke. Do NOT force a larger Gates Glidden into the canal, it risks strip perforation. If a Parallel sided post is to be used, take the appropriate sized drill and turn it in the space using your hand only. Placing this instrument in a handpiece risks perforation. Avoid end-cutting instruments such as Peeso reamers, they are dangerous. Screw posts that have "active" threads should be avoided at all costs. If the post space is irregular or wide, consider placement of a cast post and core rather than enlarging the space to accommodate a larger prefabricated post.
Post perforation repair options. Mineral Trioxide Aggregate (MTA), sold by the trade name ProRoot (Tulsa Dentsply) has become the material of choice for attempting both nonsurgical and surgical post space perforation repairs. It is a medical grade of cement that is known in the construction trade as "Portland Cement". ProRoot MTA's water-based chemistry allows normal setting in the presence of moisture but its handling characteristics make it somewhat difficult to use. (Its very "gritty!) It also is extremely expensive. A package of 5 applications costs $500 CDN! Many clinicians have found this unacceptable and are using one package for multiple cases. (Not recommended by the manufacturer due to possible effects of storage moisture and humidity on the set properties). Unfortunately, even with this material, the post perforation is sometimes in a position that is aesthetically difficult to manage (labial surface of anterior teeth) or results in a periodontal defect that creates a chronic pocket. Furca perforations are especially difficult to repair predictably and treatment should always be presented to the patient as having a limited prognosis.
Several excellent articles have been published regarding Posts and Post placement decisions. Manning KE, Yu DC, Yu HC, Kwan EW. Factors to consider for predictable post and core build-ups of endodontically treated teeth. Part I: Basic theoretical concepts. J Can Dent Assoc. 1995 Aug;61(8):685-8, 690, 693-5 Part II: Clinical application of basic concepts. J Can Dent Assoc. 1995 Aug;61(8):696-701, 703, 705-7. Another article worth reading is : L. Stockton, C.L.B. Lavelle, M. Suzuki. Are posts mandatory for the restoration of endodontically treated teeth ? Endod Dent Traumatol 1998:14:59-63
Recent endodontic research has begun to focus on the area of access/orifice/post space seal. Initial indications suggest that this may offer greater protection for patients who may be able to afford endodontic treatment but may not be able to have a core or crown restoration placed immediately after. Flowable composites are being suggested for use over the gutta percha in canal orifices and to cover the pulpal floor of the endodontic access. The advantage of these techniques is that better coronal seal is achieved. The disadvantage is that where additional post spaces are attempted by the restoring dentist, there is much greater risk of perforation because of the presence of tooth colored composites in the access, furca and over the canal entrances. It remains to be seen whether this technique will become part of the service of the treating endodontist or whether this will be part of the responsibility of the restoring dentist.
Dentists with a particular interest in post and cores should be sure to attend the Alpha Omega Memorial/Sicher Lecture on Dec .1, 2001 in Winnipeg,Manitoba. Dr Arun Nayyar ( Prosthodontist and the originator of the "amalgam post technique") is the featured speaker. This full of CE is available to dentists at no cost ! See your Winnipeg Dental Society Calendar or call the University of Manitoba - Dept of Continuing Education for details.