03 January 2023

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Evaluation of residual dentin thickness after root canal preparation for post placement

Simona Chirico

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Teeth treated for extensive caries, with marked wear, or that have suffered traumatic lesions may have an insufficient residual structure to guarantee an adequate ferrule effect to support a suitable extra coronal restoration. These teeth commonly require root canal treatment, and the definitive restoration often requires the use of an intracanal post. Preparing the post pocket commonly results in the removal of far more dentin than root canal shaping alone performed during endodontic treatments, and prefabricated posts are a more conservative option than cast posts. Iatrogenic perforations can occur frequently during post housing preparation and the larger the diameter of the drills used, the greater the likelihood of perforation. Likewise, the apical position of the post can also influence the risk of perforation. However, the more apical a post is placed, the greater the retention of the restoration entrusted to it. A post should be as long as possible and provide an apical seal of at least 4 to 5 mm of intact root canal filling, but more dentin loss is to be expected as the root diameter narrows towards the apex.

Materials and methods

The study by William Ha et al. evaluated the final dentin thickness after preparation for post seating and the fit of different prefabricated posts for the most common root canal preparation systems in a model theoretical. Ten specimens per tooth type were analyzed on cone-beam computed tomography to determine the minimum residual root diameter of 5 to 13 mm from the apical foramen. The root dimensions after with 10 different shaping systems for post seating were calculated and compared with the initial root dimensions to determine the thickness of the remaining dentin. Eight types of posts were compared with root size to determine areas where there was less than 1 mm of dentin thickness.

Results

The mean shape after root canal preparation was found to be 0.57 mm in diameter at 5 mm from the apex and 0.94 mm at 13 mm from the apex. Preparation for post seating resulted in areas of less than 1 mm dentin thickness for the buccal canal of maxillary first premolars, maxillary second premolars, mandibular premolars, and the distal canal of mandibular second molars. 

Power-driven root canal preparation systems with higher taper (e.g., 6% taper) more often resulted in residual dentin less than 1mm thick in the coronal and middle third of the root compared to tapered preparation systems lower (e.g., by 4%). 

The region where, after preparation of the post housing, a thickness of less than 1 mm of residual dentin was most often found was the apical end of the root canal. However, some root canal preparation systems (mainly those with increased taper) have produced a residual dentin thickness of less than 1mm even towards the CEJ. The canals and teeth that were found to be most likely to have a remaining dentin thickness of less than 1 mm, after root canal preparation, were found in order the mandibular incisors, maxillary second premolars, maxillary first molars (mesiobuccal second canal, distobuccal canal), mandibular first molars (mesiobuccal canal, mesiolingual canal, distal canal), mandibular second molars (mesiolingual canal, mesiolingual canal, distal canal) and upper second molars (mesiobuccal canal).

The smaller posts (Endosequence Fiber Post, Brasseler USA, RelyX Fiber Post 3D, 3M, and Rebilda, VOCO) were found to fit the commonly prepared shapes best.

Conclusions

From the data of this study, it can be concluded that Endosequence Fiber Post (Brasseler USA), RelyX Fiber Post 3D (3M) and Rebilda (VOCO) are the posts that best suited the preparation forms of the root canal.

For more information: "Remaining dentinal thickness after simulated post space preparation and the fit of prefabricated posts to root canal preparation shapes."