A reconstitution of the non-vital tooth

Reconstitution of the non-vital toothGérard Aboudharam demonstrates original use of a sonic system to restore a tooth and protect the previous root canal treatment.

The “adhesive” restoration of non-vital teeth with composite resins, fibre-based posts and adhesive systems constitutes true therapeutic progress.

Some of the goals of such reconstruction are:

  • Replace “lost” dental tissues
  • Protect remaining dental tissues
  • Prevent endodontic infection or reinfection.

The first goal is concerned with ensuring the retention and stabilisation of a prosthesis; this requires a tooth wall of a minimum size. In order to achieve the second goal, it is necessary to ensure that the restored tooth possesses adequate biomechanical properties.

And for the third goal, various authors have demonstrated a link between the quality of the coronal restoration of the non-vital tooth and the long-term success of the endodontic treatment (Tronstad et al, 2000) (Gillen et al, 2011). From this perspective, the essential factor relating to the restoration’s seal is its water-tightness.

Modifications of the tooth

A great deal has been written about modifications to the behaviour of the dentine brought about by loss of the pulp. Dimitriu, in his review published in 2009 (Dimitriu et al, 2009) makes this point and, in particular, describes the physical-chemical modifications of the tooth as having a very direct relationship to the loss of the pulp.

With respect to dehydration, the work of Papa (Papa et al, 1994), while dated, demonstrates a very weak variation in the moisture rates between vital teeth and teeth treated endodontically (12.35% vs. 12.10%). The modifications to collagen appear to be accompanied by a reduction in the modulus of elasticity and of the shear resistance of the dentine (Ferrari et al, 2004).

At the same time it appeared that it is, above all, the loss of dental substance and, more particularly, at the level of the marginal crests that is responsible for the reduction in the tooth’s resistance (Reeh et al, 1989) (Linn and Messer, 1994).

  • Figures 1 and 2: The first premolar shows significant decay with severely retracted pulp (pre-operative radiograph). The mesial surface of the canine is fractured. The second premolar also shows infiltration of the amalgam restoration, while the canine shows a restoration with composite resin that requires re-intervention

Post(s) and their true role

Debate still surrounds posts, particularly with respect to their benefits, risks and necessity. Various works have been published on the subject, but the hypotheses contradict one another, and none of the arguments have been accepted as definitive (Bitter and Kielbassa, 2007) (Fernandes and Dessai, 2001) (Sidoli et al, 1997) (Trope and Tronstad, 1991).

The absence of current consensus may be summarised by the following three propositions:

  1. There is no consensus on the benefits or risks of the placement of a post in a radicular space; the posts have often been considered a reinforcing element for the non-vital tooth. They are assumed to help in distributing the functional stresses to which the restored teeth are subject (Bolla et al, 2007) (Lefevre et al, 2000). In this way, they would prevent dental fractures
  2. In certain anatomical situations, the placement of a post is contraindicated; for example, curved and/or fragile roots (Abou-Rasset et al, 1982) (Déjou et al, 1989) (Raiden et al, 2001)
  3. In the case of severe decay, it may be necessary to ensure the retention of the restoration material through the use of one post, but very rarely more.

Adhesion and water-tightness

We now know that the water-tightness obtained with the “adhesive system/resin composite” combination significantly exceeds that obtained using other biomaterials: GIC (glass ionomer cements); RMGIC (resin modified glass ionomer cements); zinc phosphate cements; or carboxylates (Schwartz, 2006) (Piwowarczyk et al, 2005) (Schenke et al, 2008).

Beyond the coronal water-tightness, the intra-canal water-tightness itself may be improved with a trio comprising fibre post, adhesive and cement.

A canal has an irregular shape with undercuts. These cannot, and should not, be removed, lest the root be rendered even more fragile. Only meticulous cleaning can rid the canal of all heterogeneous substances (gutta percha, endodontic cement). This is all the more important because a simple preparation of the canal space through the use of drill bits is not sufficient to remove filling residues completely, particularly in the last third of the prepared space (Serafino et al, 2004). Such cleaning is the precondition for effective adhesion (adhesive system) and of optimal filling (cement and fibre-based post), which are conducive to a homogeneous and water-tight restoration.

  • Figures 7 and 8: After setting up the operating field, a fitting of the fibre-based post is carried out. The diameter of the post, made of glass fibres, has been selected as a function of the diameter of the canal space. The guiding principle is the avoidance of any friction. The post must be able to be inserted freely up to the end of the canal space

Role of modulus elasticity

Reduction of intra-radicular stresses among the properties considered potentially harmful to the depulped tooth, the rigidity of metal root canal posts is often cited. Even though little real proof of its harmful consequences has been produced, this is one of the arguments that has justified the use of fibre-based posts.

Over the past few years, several studies conducted on the basis of mathematic modelling have shown that a reduction in certain intra-root canal stresses may be obtained through the use of cements or other materials based on a modulus of elasticity.

Bolla (Bolla et al, 2007), in particular, demonstrated the essential role of the modulus of elasticity in the intensity of the stresses on the interface of the post and the root canal walls. A material with a high modulus of elasticity (zinc phosphate cement, for example) leads to a concentration of increased stresses in the assembly material itself, increasing the risk of its fracture, the loosening of the pin and the ensuing consequences, such as the risk of fracture of the tooth itself.

These authors have shown that the use of assembly materials with a low modulus of elasticity (cements) allows for a considerable reduction in the intensity of the inter-facial stresses, thus also reducing the risk of breakage for the assembly.

  • Figures 14, 15 and 16: The composite cement is applied with an injection tip. In this case, cement composite Nexus 3 (KerrKavo) is used. It is characterised in particular by its compatibility with all adhesive systems on the market, whether they are from the etch-and-rinse family or the auto-etching family. The injection tip is inserted to the end of the space and the space is then filled; the fibre-based post is then placed in the canal (one trick is to hold the post using self-locking pliers). Finally, the cement composite is polymerised

The difficulties

Nevertheless, difficulties remain and must be taken into account to avoid failures. The practical implementation of actions requires a willingness to modify one’s habits, apply greater rigour and take some time. Moreover, there are incompatibilities between certain adhesives and the reconstruction materials (composite resins) used. These must be understood in order to avoid failures. Moreover, light-curing of adhesives placed at the bottom of a root canal space cannot be considered efficient.

Even when using a translucent post as a vector for the light, the energy necessary to trigger the reaction is not achieved. It is thus necessary to compensate for this insufficiency by implementing systems (adhesives or composite resins) for which the priming of the polymerisation is both light- and self-curing (so-called “dual-cure” adhesives and cements).

Certain light-restoration, the marginal preparation must, in most cases, be performed before the restoration. The choice of restoration material and the indication for the use of a post necessitate the most detailed possible knowledge of the number, height and thickness of the remaining walls. This can be achieved only after the marginal preparation.

  • Figures 19-25: A new system for the insertion of composite was used in this reconstruction: the Sonicfill (KerrKavo) system. This system, which makes the universal composite much more fluid, allows it to be inserted quickly. The composite resin regains its increased viscosity after the ultrasonic vibration is stopped. The small-diameter injection cannula allows easy access to all areas of the mould and the reduced opacity of the material allows mass polymerisation. Nevertheless, in order to account for the stresses of polymerisation, the filing of the mould is carried out in three steps. The coronal core, thus reconstructed, is ready to be shaped

The shape of the post

The operating field is set up and if indicated, the space for the post is formed. The shape of the post must be adapted to the shape of the root and not vice versa. This means not using calibrated drill bits, so as not to mutilate the root in preparing a large-diameter space. Preference should be given to Largo-type drill bits not working at the height of their range.

In the case of a curved root, the space should not exceed the curvature. The space must be “clean”; cleared of any endodontic material (gutta-percha and endodontic cement). The use of smooth ultrasonic instruments with ample irrigation allows this goal to be achieved.

The post is chosen; its diameter should allow for its insertion without any friction with the walls of the space. The adhesive system is then implemented; the conditions for its implementation as defined by the manufacturer must be observed. In this situation, two- or three-step adhesives of the etch-and-rinse type using self- or dual-curing mode are particularly indicated.

Intraradicular drying after etching and rinsing is carried out with sterile paper tips. The adhesive is light-cured, the cement is injected into the space, and then the post is inserted. The matrix is prepared and adjusted. The coronal cavity is filled. Photopolymerisation is performed (1 minute for each surface of the tooth).

After curing, the matrix is placed and the preparation completed.

  • Figures 26 and 27: Old restorations on the second premolar and the canine are replaced

An original filling method

Once the post is cemented, the filling of the coronal cavity must be carried out in a rational manner. The coronal cavities of non-vital teeth are generally quite large. It is essential to avoid the porosities that can alter the mechanical properties of the reconstruction as a whole. The filling of this cavity with the Sonicfill is recommended by the manufacturer. It is one original and interesting option for implementation.

The composite resin developed for use with the Sonicfill system contains special modifiers that react to sonic energy. Sonic energy is applied through a handpiece, causing a reduction in viscosity. This increase in fluidity allows quick placement of the composite with precise adaptation to the cavity walls.

When the sonic energy is stopped, the composite resin returns to its more viscous consistency. The final polymerisation allows for a homogeneous reconstruction, the hardness of which facilitates the shaping of the preparation.

  • Figures 34 and 35: The cap is modelled with the aid of the Cerec system software. It is then machined in one block in IPS Emax CAD (Ivoclar) and finished. This cap will be assembled with self-etching and self-polymerising cement.

Clinical case

In this clinical case (Figures 1-37), a three-step system (M&R3) was used. Firstly, orthophosphoric acid is applied over the entire surface of the canal space and then rinsed. The rinsing of the orthophosphoric acid must be ample and must completely eliminate all trace of the acid. After moderate drying, paper tips remove any excess water.

The application of the chemically-polymerisable bonding resin is carried out with the aid of an endo-type microbrush with an applicator tip that is fine enough to reach the bottom of the canal space. The excess adhesive is removed with a paper tip in order to avoid leaving a layer of adhesive on the bottom of the space that is too thick.

If a post is placed for endodontic reasons, this will allow for direct and simple application of the gutta percha. The same bonding resin is applied on the post for greater wettability.

Conclusion

The adhesive restoration of non-vital teeth is not simply one method, but rather a response to questions, obstacles and failures with which dentists are confronted. It is not surprising that after having “revolutionised” the treatment of non-vital teeth, as well as the methods used in prosthetics, adhesive cementation has also contributed to the improvement of restoration methods for non-vital teeth.

This has allowed for the development of new techniques and tools. The technique proposed for this case and its indication are not universal. There are indications, limits and contraindications for adhesive restorations, as there are still numerous indications for cast metal restorations; the choice is not simple. As is frequently the case, the evaluation of the clinical situation must guide this choice.

In this context, the use of the Sonicfill system and the composite designed for it have allowed for an original and efficient implementation. It is its use in daily practice that will allow the practitioner to master it and to derive all the advantages it has to offer.


For references contact: [email protected]

This article first appeared in Endodontic Practice magazine. You can read the latest issue here.

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