Comparison of Crack Formation in Retrograde Cavities prepared with Ultrasound, Er,Cr:YSGG Laser or Bur: An ex vivo Study

Objective: The aim of this study was to compare the number of crack formation in retrograde cavities after preparation with ultrasound, Er,Cr:YSGG (erbium, chromium:yttrium, scandium, gallium and garnet) laser with different power and frequency settings and bur. Materials and methods: Root canals of 60 extracted human maxillary incisors were prepared, the apices were horizontally cut and class I retrograde cavities were prepared using an ultrasonic unit (group 1), Er,Cr:YSGG laser (group 2: 3.5 W, 30 Hz; group 3: 3.5 W, 20 Hz; group 4: 4 W, 30 Hz; group 5: 4 W 20 Hz) or high-speed bur (group 6). Cracks were examined under a stereomicroscope at a magnification of ×20, scored (0 to 3) and classified according to their location (cementum, dentin, canal wall). Scanning electron microscopy analysis was also performed. Results: Greatest number of cracks was found in the cementum, and least on the canal wall. Ultrasonics followed by bur created the greatest number of crack in the dentin. No significant differences were found when groups 2 and 4, 3 and 5, and 2 and 3 were compared at the 3 regions. A significant difference was found between groups 4 and 5 at the dentin region. Conclusion: The ultrasonic is the most aggressive root-end preparation technique. The most favorable laser setting was the one used in Group 5; and generally it was safer also than the ultrasound and the bur groups.