Finite element modeling of an intact and cracked mandibular second molar under quantitative percussion diagnostics loading

Quantitative percussion diagnostics (QPD) has been devised to nondestructively evaluate the mechanical integrity of human teeth and implants, the mechanical integrity of the underlying bone, and the presence of cracks, but the mechanism is not clearly understood. The purpose of this study is to better understand the dynamic behavior of a tooth under conditions consistent with QPD by focusing on physiologically accurate 3D finite element models of a human mandibular second molar with surrounding tissues. Finite element analysis (FEA) was used to study the force response of dental structures measured by the sensor in a QPD handpiece. A defect-free (intact) and a cracked tooth model containing a vertical crack involving enamel, dentin, periodontal ligament, bone, and the QPD percussion rod were used for this purpose. Different crack gap spaces were studied for comparison. The FEA model was validated with clinical QPD data for a second mandibular molar containing a vertical crack that subsequently had to be extracted. The location and size of the vertical crack was determined once the tooth was extracted. The present FEA results exhibited features consistent with those of corresponding clinical data, thus verifying the model. An examination of the relative acceleration of the crack faces with respect to each other revealed that an oscillation between the crack surfaces results in secondary peaks in the QPD energy return response compared with that of an intact tooth. The present FEA modeling can generate simulated QPD results that exhibit established distinguishing characteristics in clinical QPD data for intact and cracked second mandibular molars. The model results also give insight into how QPD detects the presence of cracks and show that the oscillation of crack surfaces can produce the multipeak QPD results for a cracked molar observed clinically.