Micromechanical Imaging of Caries Affected Dentin

Dental caries are known to greatly reduce the micro-scale elastic properties of dentin. Scanning acoustic microscopy (SAM) is one of the few methods that can be used to characterize micro-scale elastic properties of materials. For soft materials, such as caries affected dentin, reflected signal amplitude is weak and high amplification settings must be used to obtain measurable signals. This received signal may be influenced by the saturation effects of system electronics at high amplifications; the accuracy of the calculated micromechanical properties is compromised if these effects are not accounted for in an appropriate manner. Objectives: To develop a methodology for characterizing the nonlinearity introduced by system electronics at high amplifications, and to quantify the elastic properties of caries affected dentin. Methods: We utilize a variety of independently characterized reference materials to develop the relationships between the Fourier amplitude and reflection coefficient (RC) at various amplification (gain) settings for a transducer with 30 MHz central frequency. These relationships are validated by comparing the predicted RC of very low acoustic impedance materials LDPE (RC = 0.12) and TPX® (RC = 0.09) with those obtained through independent measurements. The relationships are applied to obtain the RCs from 3 regions of caries affected dentin. Results: For TPX®, the discrepancy between the values predicted using the developed relationships and the theoretical values are less than 11% over a 6 dB transducer bandwidth. In the frequency range of 25.0 to 33.5 MHz, the discrepancy is <3%. Clearly, the developed relationships provide a closer prediction of unknown material whose RC lies outside the range of reference materials. Conclusion: The RCs from 3 regions of a caries affected dentin at the central frequency are found to be: 0.62-0.66 in the healthy dentin, 0.11-0.26 in the caries affected dentin. NIH/NIDCR DE014392, R13 DK069504, NIH/NIDCR S10 RR16710, K23 DE/HD00468