Dentinal crack incidence following ultrasonic vibration to intra-radicular posts

To determine the incidence of dentinal cracks on the root-face of extracted teeth containing intra-radicular posts subjected to prolonged ultrasonic vibration. Design & Setting This in-vitro experiment, conducted at the University of Manchester, UK, used post type and ultrasonic vibration as dependent variables.

Forty canine teeth were decoronated and root-filled with gutta-percha and sealer. A parallel shaped post-space of 1.4 mm diameter and 10 mm depth was prepared in each root. The teeth were grouped into morphologically similar pairs, and for each pair one tooth was randomly allocated to receive a zirconium ceramic post, the other a stainless steel post. The pairs of teeth were randomly assigned to a control or to a test group. The root-face was examined for dentine cracks or fractures with direct vision and at 20x magnification with transillumination. Samples were then stored in sterile water for one week. Ultrasonic vibration was applied continuously for 30 minutes to the top of the posts in the test groups. All samples were then re-examined for dentine cracks or fractures.

Following storage, no new cracks were evident for the control groups. Seven new cracks occurred in the test groups (following application of ultrasonic vibration), six of which were on the root-face of samples with ceramic posts. The difference in crack distribution between the two groups was significant (Fisher's Exact Test, p=0.029).

Prolonged application of ultrasonic vibration to ceramic posts increased the incidence of root-face cracks.