Sir, an interesting case is presented of a 34-year-old gentleman referred into the restorative department at The Royal London Dental Hospital. He presented with chronic periapical periodontitis around the previously root filled and post crowned 11, the crown was loose but could not easily be removed with finger pressure.

At assessment there was a discussion of what material the post was made out of as it appears relatively radiolucent (Fig. 1a). Upon removing the crown to begin re-root canal treatment it was discovered that the post was in fact a plastic burn-out post (Fig. 1b) and the core was largely a zinc oxide-eugenol-based material. This type of post is, of course, designed to be used to create an intra oral wax/resin post and core which can then be cast by a technician. The patient recalled that the post and crown had been made in London within the last 6 months and to his knowledge was meant to be permanent.

Figure 1
figure 1

(a) radiolucent post and (b) plastic burn-out post

Full size image

The post may have been designed to temporarily support the crown, allowing easier access for re-root canal treatment. Alternatively, the dentist who placed it may have been unaware of the purpose of the different post materials provided in a direct post kit, perhaps mistaking it for a composite-fibre post. It is important that a clinician is aware of the materials and the manufacturers intended use for them.

In this case the use of this post may have contributed to the leakage which resulted in the failure of this patient's initial endodontic treatment and was defiantly the cause of his crown becoming mobile.