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Objectives: To determine the incidence of dentinal cracks on the root-face of extracted teeth containing intra-radicular posts subjected to prolonged ultrasonic vibration. This in-vitro experiment used post type and ultrasonic vibration as dependant variables. Methods: Forty canine teeth were decoronated and canals prepared using rotary nickel-titanium files (GT-Rotary). Canals were then obturated using root canal sealer (AH-Plus) and gutta-percha. A post-space of 1.4mm diameter, 10mm depth was prepared in each. The teeth were grouped into morphologically similar pairs, for each pair one tooth was randomly allocated to receive a zirconium ceramic post (CosmoPost), the other a stainless steel post (ParaPost XP). Self-cure, resin-based cement (ParaPost Cement) was used to cement all the posts. The pairs of teeth were randomly assigned either to a 'control' or 'test' group. The root-face was examined for dentine cracks or fractures with direct vision and at 20x magnification, in strong lighting, with digital imaging transillumination (DiFOTI) and quantitative light-induced fluorescence (QLF). Control groups were stored in sterile water. Ultrasonic vibration was applied continuously (for a period of 30 minutes) to the top of the posts in the 'test' groups. All samples were then re-examined. Results: Following application of ultrasonic vibration, seven further dentine cracks were evident. No new cracks were evident for the control groups. Seven new cracks occurred in the test groups, one was on the root-face of a sample with a stainless steel post, the rest 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). Conclusions: Prolonged application of ultrasonic vibration to ceramic posts increases incidence of root-face cracks. |