The history of metal posts and where we are now
Jeremy Cooper outlines the history of metal posts and shows where we are now with a case study using a state-of-the-art post.
In 1728 Pierre Fauchard used metal posts screwed into teeth to hold bridges. During the following century, people used other materials such as wooden dowels to hold teeth onto retained roots. Without proper endodontic techniques failures must have been frequent, due to apical pathology. Coupled with mechanical failures due to root fractures long term success was at best uncertain.
In the 19th century, The Richmond Crown was introduced which had a threaded tube placed in the canal, into which a screw retained crown was affixed. Later modifications led to a one piece dowel and crown being constructed. By 1930 a separate post and core was developed. This allowed the dentist to overcome the problems of differing paths of insertions of the post into the root and the overlying crown.
The cast post and core remains “a favourite” to this day. By the 1950s the science of endodontic treatment had sufficiently progressed to mean that post crowns had a more predictable and long-term outcome.
Preformed posts made from different materials have continually been produced over the past few decades. They have been made from different metals including stainless steel, titanium, titanium alloys and even gold-plated brass! Straight sided (parallel or tapered) and screw designs have been utilised. Metallic materials used for posts include carbon fibres, ceramics (including zirconia) and fibre reinforced composites.
Different core materials have been used around preformed posts and include amalgam, glass ionomers, composites and compomers. All types of cements and bonding resins have been tried with varying degrees of success.
Forty years ago it was extremely common to sever all tooth tissue above the gingival margin when constructing post crowns and simply place an anti-rotational groove or slot into the post hole to combat torsional forces.
Current opinion is that coronal tissue is retained and the ‘ferrule effect’ has proven to have a dramatic effect on reducing root fracture (Juloski et al, 2012). Furthermore, resistance to failure for teeth is greatest when the longest post is combined with the longest ferrule possible.
The almost meteoric rise in the development of post, core and cementation materials means that there is a huge dichotomy of opinion as regards what are the best materials to use. Current research is conflicting and dentists tend make decisions on “what works in their hands” or “gut feelings”. Recently the author raised this issue on GDPUK, a discussion website for dental practitioners and this variation of opinion was clearly borne out.
Anecdotally and logical thought might suggest that cast or metal preformed posts were more likely to cause root fractures when compared to fibre posts. Fibre posts certainly fracture with greater frequency at the root face, as opposed to metal posts yet surprisingly research does not definitively indicate a greater incidence of root fracture with metal posts when compared with fibre posts. Literature reviews do point out that more research is needed in this area. Certain studies may have shown bias. (Figueiredo et al, 2015)
Rebilda Post (Voco) is a glass fibre reinforced composite post. The posts are radiopaque and translucent and the glass fibres run longitudinally along the long axis of the post. As the posts contain composite they are easily bonded to composite restorative materials, for the core build up.
A 56-year-old male required the crowning of upper right central and lateral incisors. The previous crowns exhibited extensive secondary caries. Before definitive restorative work was undertaken the upper central incisor was root filled. The lateral incisor had been previously root filled and was symptom free clinically and radiographically sound. The root filling was not renewed – though there is debate whether it would be prudent to do so first, before a new restoration was provided regardless of the radiographic findings.
The crowns were taken off and caries was removed from the root surfaces of both teeth. Unfortunately, there was no coronal tissue left on either tooth so the “ferrule effect” would not be possible. Regardless of the fact that the long term prognosis would not be as good, as if there had been preserved coronal tissue, a decision was made to keep the roots.
Rebilda post system
The Rebilda post system (Voco) is a comprehensive kit that provides the operator with everything they require to provide posts for root filled teeth. Easy to follow picture instructions are provided in the box lid as an “aide de memoire”.
The GP (gutta percha) was removed from the canal, leaving 4mm GP apically undisturbed. The Rebilda Post Reamer, was used for this purpose, though a Gates Glidden bur could have been used if desired. There are four different colour coded post drills and matching posts provided in the kit. The diameter of the posts are as follows:
RED Redilda Post 10 1.0mm
GREEN Rebilda Post 12 1.2mm
BLACK Rebilda Post 15 1.5mm
YELLOW Rebilda Post 20 2.0mm
In this particular case, the Black Rebilda post 15 were chosen for both teeth. The actual process of decision making as to which size post to use is based on visual examination of the post hole aperture. Obviously if too small a post drill is chosen then one simply moves onto the next size up in the range.
Irrigation of the prepared post hole is followed by careful drying with paper points. The appropriate sized post is removed from the blister pack and tried into the post hole. The length is then adjusted accordingly with a diamond bur. Care is taken to ensure it does not produce interference with the opposing arch.
Isopropyl alcohol is then wiped over the post and dried with air from the three in one syringe. Voco Ceramic bond (primer) is then coated onto the post and after one minute is dried with compressed air.
Voco Futurabond U is then applied with the black applicator brush into the post hole. The brush is moved up and down the post hole for 20 seconds. After this, the rest of the coronal portion of the preparation is coated with the Futurabond U using the blue applicator brush.
It is optional whether to use acid etch (phosphoric acid) prior to using Futurabond U to enhance the bond strength. Suffice to say this must be carefully washed away and dried prior to bonding with the Futurabond U. The preparation is air dried and paper points are again used to dry the canal and remove excess bond. Futurabond U is a dual cured material, and should not be cured yet.
Voco Rebilda DC luting cement is then syringed into the root canal using the provided nozzle. The post is immediately placed into it. The tooth is then light cured for two-three seconds (“flash cure”) and the excess is removed, before fully curing for a further 40 seconds. If the coronal part of the post hole is wide enough, partially set Rebilda DC can easily be removed with a probe. The composite core material can then be mechanically as well as chemically “locked” into the post hole.
Composite cores were constructed on both teeth. In this case a more thixotropic material (Voco GrandioSO) was used and built around the post using a flat plastic. Other practitioners might prefer to use crown forms or moulds (e.g. Voco Rebilda Form) to help build up a core. The teeth were prepared and a dual arch impression taken. After shade taking and cementing temporary crowns an appointment was made for the fitting of the crowns.
Extract or save?
The post crown can be regarded as a “last ditch attempt” to save a tooth. The psychological effects of losing anterior teeth should not be underestimated. Conserving some tooth structure, even when subgingival is often preferable, purely based on emotion.
Before the advent of endosseous implants it could be argued that by retaining the root there would be less bone loss over time, than if it were extracted. Insertion of an implant after an extraction has been shown to help maintain bone (Greenstein and Cavallaro, 2013) and consequently facial contour.
The long-term success and predictably of the endosseous dental implant can heavily influence a practitioner on the treatment they advocate, almost as much as the accompanying economic thoughts as to whether they think the patient can and will afford it.
The “daughter test”, cited by Burke and Kelleher (2009), is a hypothetical question. A practitioner is asked to consider whether the aesthetic treatment they are proposing to a patient is one which they would carry out on his or her own daughter.
This concept could be further expanded to the “mother” or even “self” test, when one would ask: ‘What would you do in a particular clinical situation, if it were your mother or yourself?’ The present discussion may be a good example, where practitioners may be a little too keen to provide dental implants rather than post crowns.
Furthermore, in most cases a patient could have a dental implant should the post crown fail in the future.
The extraction or retention of a root and placement a post crown is a potentially complex decision. Medical history, economic and psychological factors may be obvious but decisions based on root length, size and occlusion can be more complex. As mentioned previously the ferrule effect with retained supragingival tooth structure is of paramount importance.
Fracture lines in the root surface or width of either the post hole or the remaining dentine wall will influence decisions. Similarly, if the tooth has undergone an apicectomy or a radiograph reveals signs of apical rarefaction or root resorption, these too might affect the treatment plan. Bruxism and parafunction may not just influence whether to retain the root but whether to use metal or a fibre post.
In conclusion, there are no definitive rules whether to either retain a root and restore with a post crown or alternatively extract it. Many practitioners would advocate fibre posts rather than the traditional metal post, though this is still a debatable issue.
Juloski J, Radovic I, Goracci C, Vulicevic ZR, Ferrari M (2012) Ferrule effect: a literature review. J Endod. Jan; 38(1):11-9. doi: 10.1016/j.joen.2011.09.024
Figueiredo FE, Martins-Filho PR, Faria-E-Silva AL (2015) Do metal post-retained restorations result in more root fractures than fiber post-retained restorations? A systematic review and meta-analysis. J Endod.Mar; 41(3):309-16
Greenstein G, Cavallaro J (2013) Dental implants typically help retain peri-implant vertical bone height: evidence-based analysis. Compend Contin Educ Dent. Jul-Aug; 34(7):502-11
Burke FJT and Kelleher MGD (2009) The “daughter test” in elective esthetic dentistry. J Esthet Rest Dent 21: 143–146.