Non-invasive ultrasonic device to evaluate demineralized dentine lesions

Objective:

The purpose of this study was to compare the acoustic characteristics of sound, demineralized and remineralized dentine specimens by using an ultrasonic device measuring microhardness.

Methods:

10 freshly extracted human molars were cut roughly parallel to buccal surface using a water-cooled saw to expose sound dentine surfaces, and embedded into acrylic polymer. The specimens were measured micro-Vickers hardness (VHN) and acoustic characteristics (Acoustic Mineral Density index, AMD index) by using an ultrasonic device (Ha-Ichigou, Tauzar Research Institute, Koriyama). To make demineralized lesions, the 6 dentine specimens were soaked into acidic gel (pH=5.0) for 3 days. After measuring AMD index, the 6 demineralized specimens were placed into remineralization solution containing 1.5mM Ca, 0.9mM phosphate and 10 ppm F-(pH=7.0). AMD index was measured after 4, 8 and 24 days of remineralization process. The data were analyzed statistically with Dunnett's multiple comparison test.

Results:

The AMD index of sound dentine (1496±180) indicated the statistically significant correlation with microhardness (56±6 VHN). Average AMD index of 6 sound dentine specimens and the specimens demineralized for 3 days were 1600±47 and 1146±66, respectively, and the specimens remineralized for 4, 8, 24 days were 1204±15, 1287±33, 1646±34 respectively. The AMD indexes were significantly different compared between each sequential measurement.

Conclusion:

Because the mineral distributions of dentin were reported the high correlation with microhardness in vitro, the highly correlation of the AMD index and VHN suggested that the AMD index would be represent the state of mineral distributions of various dentine conditions. The ultrasonic device developed in this study opened the new research field evaluating the mineral distribution in demineralized dentine lesions with non-invasive and non-destructive means.