To simulate in a laboratory setting longitudinal cracking in root filled premolar teeth, using cyclic mechanical fatigue.
Mesial-occlusal-distal (MOD) cavities were prepared in twenty root filled, single-rooted, mandibular premolars restored with fibre posts and resin composites. The samples were randomly divided into two groups based on the loading approaches: static loading with a crosshead speed of 0.5 mm/min and step-stress cyclic loading (1 Hz) with increasing amplitude. The loads and numbers of cycles to failure were recorded. Micro-CT was also used to identify the fracture modes. Statistical analysis was performed using T-student test. The level of significance was set at 0.05 RESULTS: The mean fracture loads for the static-loading and cyclic-loading groups were 769±171 N and 720±92 N, respectively. There was no significant difference between the two groups (p>0.05). The proportions of longitudinal, cuspal and mixed-mode fractures under cyclic loading were 50, 20 and 30%, respectively. Longitudinal fractures occurred with larger numbers of cycles and higher average loads per cycle compared with the other fractures. Static loading produced only cuspal fractures.
Longitudinally-cracked premolar teeth with root fillings were successfully produced using the step-stress cyclic loading method. This provides a more clinically-representative methodology for studying cracked teeth in a laboratory setting..

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