Incidence of root fractures and methods used for post removal

Discussion

Orthograde root canal re-treatment is the author’s preferred treatment approach when managing previously root-filled teeth with evidence of infected canals and apical periodontitis (Abbott 1999). This is true even if a post is present in the tooth, since the outcome of this treatment is more predictable and more successful than for retrograde/surgical treatment (Allen et al . 1989, Molven et al . 1991). However, there are instances when this approach is not followed and surgery may be recommended. Typically, this occurs when there is a very wide post in a thin root, where the tooth may not be restorable again, when a tooth has been recently restored with a post/crown and where the infection may have been present prior to this restoration being placed, and occasionally for financial reasons. These reasons for not removing a post are consistent with those reported in a recent survey of Australian and New Zealand endodontists (Castrisos & Abbott 2002). In these cases, the treatment code for post removal would not be used for billing purposes and hence these teeth were not identified by the computer search for inclusion in this study. Therefore, the sample of teeth studied is, to some extent, a biased sample in that not all teeth with posts were included and teeth that were identified as being predisposed to root fracture did not have post removal attempted. Case selection is an extremely important aspect of clinical practice that requires skill and experience combined with a thorough assessment of each individual case prior to treatment. Hence this study was essentially a study of teeth that were deemed to be suitable for post removal and further restoration. Teeth from all tooth groups and both arches were included (Table 2).

The teeth included in the first part of the study were examined prior to post removal as part of the routine endodontic examination to determine whether there were any signs or symptoms suggestive of a root fracture. They were assessed again after post removal and then at each subsequent appointment in case a root fracture had not been detected immediately post removal. The classic signs of a root fracture include looseness of the post and restoration, regular dislodgement of the restoration, and the presence of a deep narrow periodontal pocket. Many cases will have two deep narrow periodontal pockets on opposite sides of the tooth root. Tenderness to biting pressure, tenderness to percussion, and increased mobility of the tooth can also be indicative of a root fracture, but these signs could also be associated with apical periodontitis due to infected root canals. Radiographs can also help to identify root fractures either due to the presence of a fracture line or by a general widening of the periodontal ligament space along most of the root, and especially in the coronal portion, on at least one side of the tooth. In most, but not all cases, the widened ligament space will be present on both sides of the root although it may not extend all the way to the apex. The presenting signs will depend on the position and extent of the fracture or crack so there can be many variations in the signs and symptoms.
Only one of the 1600 teeth (0.06%) developed a root fracture during post removal, which indicates that root fractures are not very likely to occur with good case selection and with the techniques used in this study. This figure is slightly higher than the estimate of 0.002% reported in the survey of Australian and New Zealand endodontists (Castrisos & Abbott 2002) but it still demonstrates an extremely low risk for root fracture during post removal. These figures do not support the fears of many American endodontists (Stamos & Gutmann 1993) and the commonly stated empirical claims that root fractures are likely when posts are being removed.
Various techniques were used to remove the posts and these were similar to the techniques used by other Australian and New Zealand endodontists (Castrisos & Abbott 2002). The details recorded in the second part of the study demonstrated that the method chosen largely depended on the type of post being removed. In the sample of 234 teeth examined, cast posts/cores were the most common (65.8%) type of post removed and threequarters of these were removed from upper incisors and canines. Most of the cast posts (59.1%) were removed with an Eggler post remover. The technique generally used by the author for these cases may have included some loosening of the post by ultrasonic vibration. An ultrasonic scaler was applied to the core portion of the casting after removing the crown in order to remove any of the crown luting cement left on the surface of the core. This sufficiently loosened a few cast posts (5.8%) to remove them without any further device being applied. The Eggler device can be easily applied to anterior teeth and to most first premolar teeth, but its size prevents it from being used in most second premolars and virtually all molar teeth – fortunately, very few cast posts were used in these teeth.
When the Eggler post remover is to be used, the core must be reduced to a cube-shape with approximate dimensions of 2 mm for each side in order to allow the forcep arms of the Eggler device to be applied. This reduction was completed with a high speed bur which may produce some vibratory action along the post and this may help to break down the adhesion of the luting cement between the post and canal wall.

Many cast posts/cores (31.8%) were removed with the crown and hence did not require any form of post removal device to be used. This is likely to be an indication that the luting cement had broken down or had dissolved over time due to leakage of the restoration margins. Apart from making it easy to remove the post, the presence of leakage reinforces the need to remove the restoration and the post in order to remove the aetiologic factor causing the infection within the canal – this in turn reinforces the need for conventional re-treatment rather than periapical surgery.
The remaining 3.3% of cast posts had fractured within the canal and were removed with a combination of the Masserann kit (Micro-Méga SA, Besançon, Cedex, France) and ultrasonic vibration. In these cases, the two devices were used alternately until the post could be removed. The Masserann trepan burs were applied in a low speed handpiece used in the reverse direction (Masserann 1971) and advanced approximately 0.25–0.5 mm at a time. Ultrasonic vibration was applied subsequently to loosen the post and flush debris from the canal. The aim of this technique was to move the fulcrum point toward the apical end of the post, whilst also trying to break down the cement adhesion between the post and the dentine. Removal of some of the cement also provided space for application of the ultrasonic instrument tip and space into which the post could begin to move when being vibrated (Abbott 1996).
Preformed parallel-sided posts were removed from teeth of all tooth groups in both arches, although almost half (46.4%) of them were removed from upper incisors and canines. Lower molars (23.2%) and upper premolars (18.8%) were the next most common tooth groups with these posts. Approximately half (56.5%) of all the preformed parallel-sided posts were removed with ultrasonics alone and about a quarter (27.5%) were removed with a combination of the Masserann kit and ultrasonic vibration, using the technique outlined above. Some were removed with the crown (8.7%), and the Eggler device was used for a few (7.3%) very large parallel-sided posts. Threaded posts were simply removed with the aid of orthodontic pliers to grasp the core. One Flexipost was identified in this study and it was removed with a combination of the Masserann kit and ultrasonic vibration.
In the survey of American endodontists by Stamos & Gutmann (1993), post removal devices were not commonly used by the respondents because they were concerned about inducing root fractures and they felt the devices were dangerous or did not work. Instead, most of the respondents used haemostats (67%) or drilled the posts out with burs (62%). In view of the concerns about the dangers of post removal devices, these figures are somewhat surprising and alarming, since these two methods are considered even more dangerous and prone to complications. Removing a post with haemostats could result in extraction of the tooth, whilst drilling a post out with a bur is likely to lead to unnecessary removal of tooth structure. It is very difficult to control a high-speed bur within a confined space in such a way that it only cuts the post and not dentine. An end-cutting bur would be needed but these burs have a propensity to ‘slip’ off the surface that they are cutting and hence may gouge the root canal walls. Considerable weakening of the tooth could occur and this could ultimately lead to root fracture or render the tooth unsuitable for further restoration.

Using the techniques outlined in this study, post removal was predictable, safe, and expedient. The figure for the average time (6.5 min) was probably reduced by the number of posts that dislodged with the crowns (23.9%, designated as 0 min) and hence the mode (3 min) may be a more relevant time to consider. The time recorded included the time taken to remove the core filling material surrounding preformed posts and the time needed to reduce cast cores to fit the Eggler device. The times varied considerably and there was no particular pattern to the time required for any particular type of post. The time taken probably depended more on the type of luting cement used, the type of core filling material surrounding preformed posts, and the type of metal used for cast posts/cores. In general, when removing a post, the type of luting cement is not usually known, but resin-based cements are considered to be more difficult to remove than cements such as zinc phosphate. Composite resin cores may also be more difficult to remove than amalgam cores, and cast gold cores are usually easier to reduce than cores made with non-precious metals.

For more than 250 years, clinicians have written about the placement of posts in the roots of teeth to retain restorations.1 As early as 1728, Pierre Fauchard described the use of “tenons,” which were metal posts screwed into the roots of teeth to retain bridges.1 In the mid-1800s, wood replaced metal as the post material, and the “pivot crown,” a wooden post fitted to an artificial crown and to the canal of the root, was popular among dentists.1 Often, these wooden posts would absorb fluids and expand, frequently causing root fractures.2 In the late 19th century, the “Richmond crown,” a single-piece post-retained crown with a porcelain facing, was engineered to function as a bridge retainer.2 During the 1930s, the custom cast post-and-core was developed to replace the one-piece post crowns. This procedure required casting a post-and-core as a separate component from the crown.2 This 2-step technique improved marginal adaptation and allowed for a variation in the path of insertion of the crown