A post abutment is used to rebuild root canal-treated teeth whose natural crown has been severely destroyed, so that they can subsequently be restored with a crown and thus preserved. If the natural crown of a tooth is largely destroyed, there is sometimes not enough remaining tooth substance to attach an artificial crown to it. The basic prerequisite for a post build-up is a root canal-treated tooth in whose root the post is anchored. The shape of a post build-up fabricated indirectly in the dental laboratory or materials used to cover a directly placed post make it possible to build up an artificial tooth stump, which in turn can be prepared (milled) to receive a partial or full crown. In this way, the severely destroyed tooth can be preserved. The new crown can also be used to anchor a bridge.
Indications (areas of application)
- Physiologically loaded anterior teeth with vertical dentin walls less than 2 mm.
- Anterior teeth under increased load with vertical dentin walls over 2 mm.
- Physiologically loaded posterior teeth with a preserved enamel wall – these can be restored with a partial or full crown.
- Physiologically loaded posterior teeth with preserved dentin walls even below 2 mm – to be restored with a full crown.
- Posterior teeth under increased load with a preserved enamel wall or a three-surface cavity – to be restored with a partial or full crown.
- Under increased load standing posterior teeth with preserved dentin walls even below 2 mm – to be restored with a full crown.
- Almost complete loss of the clinical tooth crown: cast post build-up.
Contraindications
- Insufficient (inadequate) root filling – This should be renewed before restoration with a post build-up, if necessary.
- Allergy to components – e.g. metal alloys or composite-based luting material.
- Low substance loss in endodontically restored anterior teeth – These can be adhesively stabilized and restored with a composite filling (plastic filling).
- Minor substance loss in endodontically treated posterior teeth – These can be stabilized with an inlay or a partial crown using adhesive cementation technology.
Before the procedure
Before making a post buildup, it must be clinically and radiographically clarified that the tooth is asymptomatic, shows no apical signs of inflammation (bone dissolution at the root apex), and that the root filling is sufficient (wall-standing and extending to the root apex). In multirooted teeth, the radiograph must first be used to decide whether only one or multiple posts should be placed and in which root the post or posts should be placed.
The procedures
First, the root filling is removed to the desired post length using special drills that are matched to the posts used in the subsequent procedure. The depth of the drill hole or the length of the root post should be at least equal to the length of the subsequent clinical crown. As a rule of thumb, the root post should be about 2/3 of the root length. However, at least 4 millimeters of the root canal filling material must be retained apically (towards the root). Care must also be taken to ensure that the already severely reduced tooth structure is not further weakened by the preparation for the post. For stability reasons, the preparation margin of the future crown must be placed at least 2 to 3 millimeters apical (rootward) of the base of the post abutting the residual tooth structure. I. Direct procedure
In the direct procedure, a prefabricated root post is inserted by the dentist into the prepared root canal, with either adhesive (micromechanically anchored with resin) or conventional cementation. The post protrudes above the level of the destroyed tooth and thus provides a retention surface (surface for chemical or mechanical anchorage) on which the core build-up material – e.g. acrylic – is held. The artificial tooth stump built up in this way can be prepared (milled) to accept a laboratory-produced crown, similar to a natural tooth. Materials that can be considered for a direct post are:
- Metal posts
- Glass- and quartz-fiber-reinforced composite posts (plastic posts)
- Zirconia ceramic root posts
Since a root post is subjected to shear forces under tooth loading, posts with dentin-like modulus of elasticity (with behavior similar to the dentin in tension and elongation) are useful – this is the case, for example, with fiber-reinforced composites. In addition to smooth, passively cemented posts, there are also active posts that have a thread. When using these posts, the primary hold achieved in the root canal is greater, but the risk of root fracture (breakage) is significantly increased compared to the non-active post systems. Therefore, passive posts without a thread are to be preferred. II. Indirect procedure In this case, a prefabricated plastic post is inserted after the root filling has been removed. The only purpose of this is to transfer the post dimensions to the dental laboratory. An impression of the tooth or jaw to be restored is taken over the post. The pin remains in the impression material. In the dental laboratory, a post abutment is modeled in wax or plastic and then cast in metal. The post abutment is fixed in the root canal by the dentist using cement. If necessary, the tooth is prepared again and another impression is taken, on the basis of which the crown is fabricated in the laboratory. In both direct and indirect fabrication, the fabrication of the post build-up is therefore followed by the fabrication of a crown in the laboratory to definitively restore the tooth.
Possible complications
- Perforation (piercing) of the root wall.
- Weakening of the tooth structure with increased risk of fracture as a result.
- Longitudinal splitting of the root
Due to the existing risks and advances in adhesive cementation techniques of composites and ceramic restorations, only large coronal defects (loss of substance of the clinical tooth crown) with low dentin wall thicknesses are increasingly restored with post abutments today.