Ultrasound efficiency on the removal of posts: lengths and diameters

Objectives: This study evaluated the efficiency of ultrasound, with or without air/water cooling, for the removal of metallic posts with different lengths and diameters, using a tensile strength test. Methods: 108 maxillary canines were sectioned 13 mm from the radicular apex and, after the endodontic treatment, the roots were embedded in acrylic resin blocks. The specimens were divided into two groups: GI, the prosthetic space was prepared with #06 Largo bur coupled to a straight handpiece, mounted on a delineator device, and the specimens were subdivided into 3 subgroups, with different post lengths: GIa – 9 mm, GIb – 7 mm, GIc – 5 mm; GII, the prosthetic space was prepared in the same manner as in GI, but with Largo burs of different diameters: GIIa – 0.9 mm, GIIb – 1.3 mm, GIIc – 1.7 mm. The root canals were subsequently molded by direct technique with Duralay resin and, after casting, the metallic posts were cemented with Panavia F. Each group was again divided into two subgroups to receive ultrasonic vibration with or without air/water cooling. Ultrasound was applied perpendicularly to the long axis of the root, for 1 min at each corresponding point of the tooth surface (4 min total). Specimens were submitted to a tensile strength test on Instron machine. Results: ANOVA showed a significant difference between the length of the posts (p<0.01) and between ultrasound use with or without air/water cooling (p<0.05). There were no significant differences (p>0.05) between the different diameters tested; however, statistical analysis showed a significant difference with regard to the use of air/water cooling or not (p<0.01). Conclusions: Longer posts needed more force for removal, whereas the variation of the diameter did not influence the force necessary for removal. The use of ultrasound without cooling was more efficient for the removal of posts cemented with resin base cement.