Ultrasound Induces DMP-1 Isoform Expression in Human Tooth Slice Culture

Objective: As odontoblasts may respond to trauma by upregulating their secretory activity, this study aimed to examine the effects of Low Intensity Pulsed Ultrasound (LIPUS) on Odontoblasts, by the expression of Dentine Matrix Protein-1 and secretion of predentine.

Methods: Extracted premolars were collected from adolescent patients (11-14 years old) as part of their orthodontic treatment, with the inclusion criteria of open apex and sound condition. Teeth were sectioned using a sterile diamond wafer blade with PBS as the coolant into 600 µm thick slices. Tooth slices were cultured in 6-well plates with 4 ml culture media at 37ºC, 5% CO2 for 5 days with medium changes every two days. LIPUS was applied to test slices for 5, 10, 15 or 20 min/day. Control slices received a sham transducer for the same time periods. Following culture, tooth slices were snap frozen in liquid nitrogen for RNA extraction and subsequent RT-PCR for DMP-1 expression. A second group of tooth slices were fixed for histological examination and histomorphometric measurement of predentine thickness and odontoblast cell number.

Results: Histomorphometric analysis showed significant increase in predentine thickness in LIPUS treatment groups compared to that of controls (p-value < 0.0005). Moreover, mean odontoblast cell counts were significantly higher in the LIPUS treatment groups 5, 10 and 15 minutes(p-value < 0.0005, p < 0.0005 and p = 0.005 respectively)except for the 20 minutes LIPUS group where there was no significant difference (p-value = 0.053). RT-PCR identified the presence of an inducible DMP-1 isoform in both the 5 and 10 minute LIPUS treatment groups.

Conclusion: These results suggest that LIPUS may increase secretion of predentine in the tooth slice organ culture system and induce the expression of DMP-1, indicating a stimulatory effect on human ondontoblasts. LIPUS may provide a novel method for stimulating dentine repair following trauma.