Macrophage response and surface analysis of dental cementum after treatment with high intensity focused ultrasound

Abstract

Objective: To investigate effects of HIFU on macrophage phenotype, surface micro-topography and nano-scale surface mechanical properties of dental cementum.

Materials and methods: Root discs (2 mm thickness) were cut apical to CEJ and sectioned into quadrants. HIFU setup with bowl-shaped piezo ceramic transducer submerged in a water tank was used for exposure on each specimen for 15 s, 30 s or 60 s. The specimens of the control group were left without any HIFU exposure. HIFU was generated with a continuous sinusoidal wave of 120Vpp amplitude, 250 KHZ resonance-frequency and highest ultrasonic pressure of ∼10 bar at the focus. Specimens for SEM were viewed, and micro-topography characterization performed, using AFM and Ra parameter and surface area (SA) calculated by specialized SPM surface analysis software. For nano-indentation testing, experiments were carried out using AFM. Macrophage cell isolation and culturing was performed on cementum to receive the HIFU treatment at different time periods. Raman spectroscopy were scanned to create spectra perpendicular to the cementum substrate to analyze generation of standard spectra for Raman intensity ratio of hydroxyapatite normalized to the peaks ν₁ 960 cm^-1. Data was expressed as means ± standard deviations and analyzed by one-way ANOVA in term of Ra, SA, H and E_r. Different points for fluorescence intensity ratio were analyzed by Raman using Wilcoxon rank sum test.

Results: HIFU exposure at 60 s removed the smear layer and most of cementum appeared smoothened. AFM characterisation, showed a slight decrease in the irregularity of the surface as exposure time increased. Intact macrophages can be identified in control and all experimental HIFU groups. The level of fluorescence for the control and HIFU 15 and 30 s were low as compared to HIFU 60 s.

Conclusion: If HIFU can be successfully implemented, it may be a possible alternative to current methods used in periodontal therapy to achieve smooth root surfaces.

Keywords: Dental cementum; High intensity focused ultrasound; Nanoindentation; Raman; Surface effect.