Effect of circumferential undercut placement in the root canal wall on the retention of a tapered post in large and small root canals

Abstract

Objectives. This study examined the influence of root canal space and circumferential undercut placement in the dentine wall on the retention of a prefabricated Root Keeper post. Methods. Twenty-four extracted single-rooted teeth, having narrow root canal spaces, were decoronated, treated endodontically, and then centrally embedded in resin blocks. All canal spaces were prepared with a no. 2 Peeso reamer to an 8 mm depth, and half the specimens were successively treated with a no. 3 Peeso to depths of 5 and 8 mm for the small canal group (SC) and large canal group (LC), respectively. An L-type keeper post (Aichi Steel Co.) was luted to each canal with resin cement. The assembly was thermocycled 2000 times (4–60 °C), and post retention was measured. Afterwards the dislodged post with the intact structure was sandblasted, and the canal was cleaned and slightly undercut using an inverted cone bur. Six treated posts were recemented for both grooved large canal (GLC) and grooved small canal (GSC) groups, and the repaired retentive strengths were measured. Results. Keeper posts cemented in SC (84.26±31.85 N) showed better ( p<0.05) retention than those cemented in LC (41.92±22.36 N). Interestingly, the repaired strengths of the recemented post increased in both GSC (104.29±11.89 N) and GLC (96.65±6.91 N). All posts, except for one in the GLC, failed at the keeper-post joint. Conclusions. Prefabricated Root Keeper posts had lower retentive strength in roots with a large canal space. Placement of a circumferential undercut in the root canal wall significantly enhanced the retention of the short tapered posts.