In the clinical situations in which the restoration of massive hard dental tissues loss is required, it is mandatory to use additional retention systems that can ensure the successful and long-term maintenance of the restoration. In the case of non-vital teeth, endodontic posts are used as additional retention systems. They can be custom cast made (metallic) or prefabricated (prefabricated metal posts or zirconia, ceramic, carbon or glass fibers posts). The use of a certain type of prefabricated endodontic post is the result of a completely and rigorously evaluation of the present clinical case.
non-vital tooth, endodontic post, post-retained endodontic restoration
În situaţiile clinice în care se impune restaurarea distrucţiilor coronare masive, este obligatorie utilizarea mijloacelor suplimentare de retenţie ce pot asigura succesul şi menţinerea restaurării pe termen lung. În cazul dinţilor devitali, ca mijloace suplimentare de retenţie se utilizează pivoturile endodontice. Acestea pot fi turnate (metalice) sau prefabricate (pivoturi metalice prefabricate sau din zirconiu, ceramică, fibre de carbon ori fibre de sticlă). Utilizarea unui tip de pivot endodontic prefabricat sau a unuia turnat este rezultatul evaluării complete şi riguroase a cazului clinic respectiv.
The coronal tissue loss involves the lack of a variable amount of hard dental substance, of different etiology, and which occurs in different degrees, from the shallow enamel crack to an important, almost complete coronary destruction when only the tooth root is present on dental arch.
The amount of residual hard dental substance plays an important role in the possibility of restoration of a tooth. From this point of view, we must first analyze whether the tooth can be restored or needs extraction. When choosing the restoration method, we must take into account multiple aspects of the clinical case, such as: the position of the tooth on the dental arch, the value of the occlusal forces, and the patient’s aesthetic expectations. Especially for young patients, it is normal to want to limit the loss of hard dental tissue as much as possible and to preserve the present state, but unfortunately this is not always possible.
In clinical situations where restoration of coronary dental tissue loss is on the borderline between direct odontal and prosthetic restorative treatment, and occlusal forces cannot be reduced or eliminated, it is mandatory to use additional retention systems that can ensure long-term obturation stability and success. In the case of non-vital teeth, endodontic posts are used as additional retention systems. Odontal restorations that use them are called armed restorations or post-retained endodontic restoration.
Special retention systems are used to improve the retention of the cavities resulting from the evolution of extensive carious processes. In situations where the loss of a hard dental substance is of traumatic etiology, the additional retention systems are, except for prosthetic methods, the solution of choice for the retention of the coronary restorative dental material. In the case of a vital tooth that has a massive loss of dental tissue, special retention systems help maintain the vitality of the dental pulp, but the use of special retention systems is also currently used in the case of endodontically treated teeth(1).
Compared to the odontal restorations in vital teeth, non-vital teeth presents specific aspects regarding coronal rehabilitation. Massive tissue damage, as well as the sacrifice of hard dental substance to obtain a proper access for endodontic instrumentation may cause difficulties in ensuring retention of restorative dental materials(2). Some authors also consider that the fracture resistance of endodontically treated teeth is significantly lower than in vital teeth. Although it is a widely held opinion, there are controversies on this topic, multiple laboratory studies have shown that fracture resistance in non-vital and vital teeth is similar.
Additional retention systems used in non-vital teeth are endodontic posts, which can be custom cast or prefabricated. The current use of prefabricated posts is associated with the coronary restoration of the dental structure using the direct method, with modern adhesive materials: composite resins or glass ionomer cement. Odontal restoration using endodontic posts is indicated in situations when the coronal non-vital tooth structure is inadequate for the proper retention of a restoration(3). The root part of the endodontic post is fixed and cemented into the prepared root canal (using curent precedures with Gates Glidden or Paeso reamers) and the supragingival portion of the posts ensures retention of the restorative material.
Custom cast posts
The custom cast posts are made in the dental technique laboratory, following an impression of the root canal preparation. The custom cast posts cast are still valuable additional retention systems due to the precision with which they can be made and due to the resistance to mechanical stresses in the oral cavity. The cast posts acts like a post-core system. Their use tends to be restricted because they have a number of disadvantages: they require an important sacrifice of hard coronal tissue, and they require time and precision to make them since the dental technique laboratory is involved. Once cemented, the treatment of possible apical lesions is almost impossible, due to their difficult removal(4).
The custom cast posts are made from metals that can be easily processed, from noble or semi-noble metals, or from silver or other special alloys (nickel-chromium, cobalt-chromium, platinum-gold-palladium, stainless steel), and will be subsequently covered with dental crown.
Prefabricated posts are widely used today, being available in a wide range of materials, shapes and sizes that can be adapted to different clinical situations. Thus, the prefabricated posts can be:
metal – stainless steel, titanium and its alloys, platinum-gold-palladium, chromium-containing alloy, surface-gold-plated copper-nickel alloy, cobalt-molybdenum alloy.
The prefabricated posts made from ceramic have the same color as the dental tissues, they are biocompatible, with a good radioopacity, but at the same time they are expensive, difficult to be cut and cannot be bent. That’s why they have a high risk of fracture under the action of occlusal forces. They are also difficult to be removed from the endodontic space when fractured. Compared to the metal posts, the prefabricated carbon fiber ones have a modulus of elasticity closer to that of the dentine, thus reducing the occlusal stress transmitted to the root(5). They are not corroded by the oral fluids and have a high wear resistance. The transfer of occlusal stress to dentine can be reduced by introducing a more elastic material, namely resin cements, which will act as force breakers(6).
Regardless of the material from which they are made, the prefabricated posts have multiple advantages: the odontal restoration is done completely inside the dental practice, without involving the dental technique laboratory, thus saving time and money. They are easy and very simple to be inserted into the prepared root canal, and can be use in almost any clinical case, including pluriradicular teeth(7). The prefabricated posts can be removed when needed, especially those fixed by screwing, easier than custom cast posts.
Despite the certain advantages of prefabricated posts, unfortunately the limitations imposed in their use must be taken into account: they do not always adapt perfectly to the endodontic preparation such as the cast ones and their coronal portion is not always sufficient to support the volume of the required dental reconstruction(8).
The principles that govern the use of endodontic posts in dental restorations in non-vital teeth are:
Minimizing the sacrifice of a hard dental substance, especially in the cervical region, in order to create the encircling effect (“ferrule effect”).
Use of adhesive techniques for both the coronal and root tissues, to increase the strength of the remaining dental structure and to improve the retention and stability over time of the post-restored tooth.
Use of the materials with dentin-like physical properties, both for core and post.
The final restoration may be done directly in the dental office or it may be a prosthetic restoration. If a direct odontal coronal restoration is made, usually a prefabricated endodontic post will be chosen. In restorations using custom cast posts, it must be associated with a microprothesis.
When choosing prefabricated endodontic post versus custom cats post for a reinforced restoration, we must assess rigorously all specific particularities of the clinical case: the quantity of remaining hard substance, the intensity of occlusal stress and the subsequent prosthetic role of the respective tooth – these aspects are always taken into account. Also, it is important to be able to obtain a proper aesthetic aspect of the restoration, especially in the frontal area.
Acknowledgements: All the authors have equal contributions for this article.
Conflict of interests: The authors declare no conflict of interests.
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