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A Radiographic Study Regarding the Negative Effects of Posts

March 1, 2005
by Dr. Roberto Cristian Cristescu and Dr. Ion Vlad Naicu


The major indication for a post is to retain the material for the core build-up of the endodontically treated teeth that present extremely damaged crowns.1,2 The preparation of the space for a post involves a risk in the theraputical phase as during this stage accidents might occur (for e.g. root perforations).3 The placement of a post also raises the risk of root fracture of that tooth4 and the risk of treatment failure,5 especially when too large a space for that post is made.6

Regarding the fracture of endodontically treated teeth, it is well described in the literature that the loss of humidity and the alteration of the physical properties of the endodontically treated teeth make them more susceptible to fracture.7-10 Still, the majority of authors, especially in the last decade, accept the theory that the risk of fracture of the endodontically treated teeth is due to the important loss of hard tooth substance (caries, traumatisms, the corect design of access cavities).11-14 It is also well known in the literature that the chance of disturbing the apical seal following the post space preparation, and that this might lead to the development of a periapical pathology.15-19

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There are two main types of posts used in the restoration of endodontically treated teeth: the cast ones and the prefabricated ones. The cast posts are more proper for the monoradicular teeth, and the prefabricated posts are mainly indicated in the posterior teeth.19

The aim of this study is to radiographically investigate, with the aid of radiology, the negative effects of those posts.

As the radiographic method is not an exact one for a proper diagnosis of a radicular fracture, even for the root perforation diagnosis, the conclusions of this study must be regarded with caution. Nevertheless, we must not forget that in endodontics, the radiographic image is usually more favourable and optimistic than the clinical reality.

MATERIALS AND METHOD

We have used a database of 8,018 periapical x-rays, from which we have selected 345 x-rays of teeth that presented endodontic posts (cast and prefabricated posts). Those images were analyzed with a software for digital image analysis (Adobe Photoshop 7.0) in order to detect the eventual root fractures that were associated with these posts.

We have considered as a possible root fracture the radiotransparent line that began somewhere at the surface of the post and was extending right until the external surface of the root. Those teeth were included in Group 1 of the study (the Posts group). We have also selected two control groups, namely the Endo Group Group 2; 46 teeth; teeth that were endodontically treated but were not presenting any post) and the Vital Group (Group 3; 47 teeth; apparently vital teeth, that presented no coronal lesion and no restoration at all).

The teeth from those two control groups were selected out of the same 345 x-rays as the ones from the Group 1, so that we were able to eliminate the differences in time of exposure or any other artifact generated by the different radiologic exposures.

For every group we have noted the following parameters:

– the presence or absence of the image of a possible root fracture;

– the presence or absence of a root perforation;

– the type of post (for Group 1: cast, prefabricated serrated posts type Dentatus; fiber posts);

– the quality of root canal filling according with the ESE criteria20 (incomplete = more than 2 mm from the radiologic apex; adequate = 0-2 mm from the radiologic apex; overfill = root canal filling material over the radiologic apex, in the periapical area);

– the presence or absence of a chronic apical periodontitis with radiologic image;

– the pathologic involvement of the furcation area.

The data was statistically analyzed using the ANOVA test (SPSS 7.5 Software Package), using a value of 0.05.

RESULTS

From the 395 teeth with posts, 135 (34.17 percent) presented images showing possible horizontal and oblique root fractures (Fig. 1),22 (5.56 percent) presented images of root perforations (Fig. 2). In Groups 2 and 3, there were no images suggesting root perforations, and the images suggesting a possible root fracture were three (6.53 percent) in Group 2 and six (12.76 percent) in Group 3. Using the ANOVA test we analyzed if there were any significant differences between the three groups regarding the number of images suggesting a possible root fracture (Fig. 3), and the result (p = 0,0000268) showed that there were significant statistical differences between the three groups. The post-hoc Tukey tests showed that there were no statistical differences between Groups 2 & 3 (p = 0,7995) (Table 1).

In Group 1 we analyzed the frequency of root fractures and perforations in correlation with the type of post (Fig.4). The results showed in Table 2 and the statistical analysis using the ANOVA (p = 0.088) test proved that there were no statistical significant differences between the cast, serrated (Dentatus type) and fiber posts in the frequency of root fractures and perforation (Table 2).

From the 135 teeth with posts that presented suggestive images for possible root fractures, 92 were restored with a crown, and 43 presented other type of coronal restoration (inlay, resin filling, amalgam filling). From the three teeth that were endodontically treated (Group 2), two were restored with a crown and the last presented a coronal filling.

From Group 1, 157 (43.25 percent) teeth were showing a healthy periapical area, meanwhile in 206 teeth (56.75 percent) we have distinguished different forms of chronic apical periodontitis (Fig. 5). In 32 teeth we were not able to correctly investigate the periapical area due to radiologic limitations (the area was not completely shown in the radiography), and therefore we didn’t include those teeth in the statistical analysis (Table 3).

Analyzing the dependence of the installation of chronic apical periodontitis in correlation with the quality of root canal filling (Fig. 6) the results showed in Group 1 (POSTS) 17 (8.29 percent) adequate root canal fillings, 181 (88.82 percent) incomplete root canal fillings and only seven (3.41 percent) overfills; for one tooth we were not able to analyze the apical area. The results are illustrated in Table 4 and Fig. 4.

The ANOVA test revealed a statistical significant correlation between incomplete root canal fillings and chronic apical periodontitis compared with adequate root canal fillings and the absence of chronic apical periodontitis (p<0.00001).

CONCLUSIONS

Frequently the literature describes the high incidence of root fractures associated with endodontically treated teeth that are restored using a post.22 There are presented high percentages of vertical root fractures, even 12.9 percent from a study group.23

On the radiographic investigation we can visualize a horizontal or oblique root fracture. In case of a vertical root fracture, we cannot distinguish the fracture line on the x-ray. The proper diagnosis of those root fractures is very complicated, involving a comprehensive and detailed anamnesis, the use of transillumination, dyes, surgical investigation procedures like reflected flaps, the inspection of the susceptible area using loupes or microscope.24 Even after the extraction of a tooth, the proper diagnosis of a root fracture needs a lot of investigation (for e.g. tooth decalcification and computer analysis).25-28

We must remember that the radiographic image of a possible root fracture (oblique or horizontal) may be in fact a lateral, secondary or accessory root canal or simply a radiographic artifact. If in literature there are studies29 that investigated the frequency and the topographic position of lateral, secondary and accessory root canals, the radiologic artifacts are very hard to correctly identify.

This is the reason we have in cluded two control groups (Groups 2 & 3), consisting of endodotically treated or vital
teeth from the same radiological images of the teeth from Group 1. We have also analyzed in Group 2 & 3 the incidence of images suggesting possible root fractures, knowing that those types of fractures might also appear in teeth without posts (even if they are vital or endodotically treated).

As the results indicate, in Groups 2 & 3 there are very few images suggesting a root fracture. In conclusion, if those lines suggesting possible root fractures from Group 1 (34.17 percent) were in fact lateral/secondary/accessory canals or simply artifacts, it will be logical to have about the same percentage in Groups 2 & 3.

The statistical analysis denied this supposition, as there are very high statistical differences between Group 1 and Groups 2 & 3 (p = 0,0000268). So, we can affirm that the endodontically treated teeth that were restored using a post presented in the radiographic investigation more often images suggesting a root fracture, compared with endodontically treated teeth or vital teeth. Very important is the high incidence of root perforations in teeth with posts (5.56 percent).

Analyzing if there is were type of post associated with a higher prevalence of root fractures, we found that teeth with cast posts presented 33.81 percent suggestive images for possible root fractures; the teeth with Dentatus-type posts have 36.11 percent images of possible root fractures. We also analyzed 12 teeth restored using a fiber post, but the low number of those teeth didn’t allow us to include them in a correct statistical analysis. However the incidence of images suggesting root fractures in those teeth restored with fiber posts was much lower (16.61 percent).

The ANOVA test revealed no statistical difference between the frequency of possible root fractures in teeth with cast posts compared with teeth with Dentatus type posts (p = 0,088). Still, the teeth with cast posts presented a very high incidence of root perforations (7.27 percent) compared with teeth with Dentatus type posts (1.87 percent). This might be explained due to the tendency to overpreparation of the root canal space for a cast post and therefore the higher risk for a root perforation.

We must also remember the importance of the coronal restoration. In this study from the 135 teeth with posts that presented possible root fractures, 92 were restored with a crown. If the tooth preparation for a post and a crown is correctly done, creating the cervical ferrule effect, the risk of root fracture will be lower. Otherwise, if a proper ferrule effect is not created, the risk of root fractures rises, and the types of vertical and oblique root fractures will appear more often.30

Different studies31-35 showed the possiblity of reinfection of the root canal during the preparation stage for a post space, especially well documentated is the importance of coronal leakage in endodontic failure. The vibrations from the rotational devices used for the preparation of the post space might alter the adhesion of the sealers to the dentine walls of a root canal (knowing that the force of adhesion of currently available sealers to the dentin walls of the root canals is quite low).

In this context we often see studies showing the correlation between teeth with posts and chronic apical periodontitis. For instance, a French study,36 showed an incidence of 28.60 percent of chronic apical periodontitis in teeth with posts, meanwhile other authors, like Saunders,32 have found values as high as 77 percent incidence of chronic apical periodontitis in teeth restored with posts.

In our study, comparing the frequency of the chronic apical periodontitis in Groups 1 & 2 we found no statistical sigificant difference (p>0.05). But if we take as a negative prognostic factor for chronic apical periodontitis the quality of root canal filling (and therefore also the quality of the endodontic treatment), then the results show us that there are indeed statistical significant differences between an adequate root canal filling and an incomplete one (p<0.00001). 88.12 percent of the teeth with chronic apical periodontitis have incomplete root canal fillings, and only 8.29 percent have adequate root canal fillings.

We have to mention here that it is possible for the teeth with incomplete root canal fillings to still have in future a good evolution of the periapical pathosis. Nevertheless, teeth with radiologic appearances of chronic apical periodontitis but adequate root canal fillings might also have a good prognosis if the root canal filling was done recently and the pathology was preexistent to the endodontic treatment.

Teeth without periapical pathosis presented in 54.14 percent of cases adequate root canal fillings, while 41.40 percent of them had incomplete root canal fillings. It is possible that these may evolve to periapical pathology. It is also true that from the 41.40 percent of teeth with post and incomplete root canal fillings, some have suffered a pulpectomy following irreversible pulpitis, and it is well known that in that pathology it is still accepted not to instrument and obturate the root canal until the radiographic apex.37

In conclusion, according to our results, we don’t think that the preparation of the root canal for a post space has any negative influence for periapical health status.

In the worst cases that preparation has negative effects on the root canal walls’ resistance (they are more prone to fracture if they remain very thick after the preparation) or it might lead to a root perforation. Therefore, it is important to prepare the root canal space for a post as soon as possible after the endodontic treatment and it is advisable that the same person who did the endodotic treatment prepare that space.

Regarding the periapical pathology, its main cause still remains the incomplete debridement, cleaning and shaping of the root canal system, followed by improper root canal filling.

For the clinical practice, it is mandatory to analyze more accurately the cases that indeed need a post, and if there is such a case, the clinician who did the endodontic treatment represents the best choice for preparing the post space, as soon as possible after the endodontic treatment.

Hopefully with the implementation on a large scale of adhesive endodontics, the use of fiberglass posts adhesively luted in a correctly prepared post space will diminish the negative effects of the posts used for the restoration of extremely damaged teeth.

At least on a theoretic level, those prefabricated posts, adhesively luted, don’t need large spaces in the root canal, they distribute the occlusal forces more uniformly, showed less microleakage and have a high degree of esthetics.3 Unfortunately there are very few long term clinical studies tto prove if those theories are right or wrong.

Dr. Roberto Cristian Cristescu, University Hospital of Dental Medicine, Bucharest.

Dr. Ion Vlad Naicu2Lecturer, Post-graduate Studies Department, Faculty of Dental Medicine, U.M.F., Carol Davila, Bucharest.

Oral Health welcomes this original article.

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