Acoustic energy affects human gingival fibroblast proliferation but leavesprotein production unchanged

Background, aims: Sonic toothbrushes are well-established in oral home care for plaque removal; however, the effects of low frequency acoustic (sonic) energy released from sonic toothbrushes to the cells of the periodontium h ave not been investigated, The purpose of this study was to evaluate the ef fects of sonic energy on human gingival fibroblast proliferation and protei n production in cell culture. Methods: Direct and indirect transfer calibration studies found the fundame ntal frequency of the Sonicare(R) sonic toothbrush to be 261 hertz (Hz) wit h amplitudes ranging from 70 to 104 decibels (dB) in the human periodontium . Using an in vitro delivery system, which coupled a signal-wave generator with a bone transducer to mimic the energy delivered by the Sonicare(R) too thbrush, the effects of signal, amplitude and duration were evaluated longi tudinally using a gingival fibroblast cell culture model. 8 strains of fibr oblasts isolated from healthy human gingiva were seeded at 30,000 cells/35 mm culture dish in minimum essential medium supplemented with 10% fetal bov ine serum. To ascertain the relationship of the amplitude and the duration of sonic stimulation to cellular proliferation, gingival fibroblasts were s ubjected 2x daily to 261 Hz sound at various amplitudes (67-97 dB) for 0, 1 5, 30, 60, and 120 s on days 1, 3, 5, 7, and 10. Results: It was found that either 30 or 120 s of sound exposure for 10 days of treatment had significant effects on cell proliferation in comparison t o control cultures. Specifically, at day 10, 87 dB at 261 Hz for 30 s 2x da iry resulted in a 25.5% increase in cell number (p<0.001), whereas 87 dB at 261 Hz for 120 s twice daily caused a 30.9% decrease in cell number (p<0.0 01) when compared to control cultures. When cells are stimulated under opti mum acoustic conditions for 10 days, there was no difference between the tr eatment and control groups for collagen (p=0.897) or noncollagen (p=0.697) protein production. Conclusions: Sonic energy has been shown to both increase and decrease cell ular proliferation depending on exposure time, however, during optimum soun d-induced conditions for cellular proliferation, sonic energy had no effect on fibroblast protein production. These data suggest that sonic energy can affect the behavior of cells in culture. Further research into the mechani sms of these changes will provide important information for manipulating ce llular behavior.