Fig 1.
Schematic of how an ultrasonic scaler tip could be used to clean bacterial biofilm from dental implants in a non-touch mode using the cavitation generated around the tip.
Inset: High speed camera image of cavitation bubbles occurring around the tip of the commercially available ultrasonic scaler tested in this study.
Fig 2.
Schematic of the experimental setup for high speed imaging.
Inset: schematic of the ultrasonic scaler tip being held close to the biofilm surface for experiments. The arrow indicates the standoff distance d of the scaler tip from the biofilm that was varied in this study from 0.5 mm to 2 mm.
Fig 3.
Example of a high speed image still, showing the image analysis steps performed to calculate the area cleaned (white).
The image is taken from a video where the standoff distance between the ultrasonic scaler tip and the biofilm was 2 mm. The ultrasonic scaler used was operated at 29 kHz, with a tip vibration amplitude of 57 μm at the free end. The biofilm in this image was grown on rough (sand blasted and acid etched) titanium discs, Ra = 2 μm: (a) raw high speed image still showing the biofilm on the rough titanium surface, the black arrow shows the position of the scaler tip (b) image after the ultrasonic scaler tip was removed, (c) Image after gamma filter applied, (d) segmented image using automatic thresholding, and (e) overlay of the segmented image in blue on the raw image demonstrating that the segmentation is accurate.
Fig 4.
Total biofilm removal for the surfaces tested, removed using cavitation from an ultrasonic scaler tip at various standoff distances d, calculated using image analysis from high speed images.
The area cleaned was calculated relative to the initial amount of biofilm in each image (n = 5).
Table 1.
Representative surface roughness (Ra) of the samples tested in this study, measured using surface profilometry.
Fig 5.
High speed video stills showing biofilm being removed from a rough Ti surface using ultrasonic cavitation at a standoff distance of 0.5 mm.
Time between frames is 0.1 s (total 2 s). The cleaned area is white and the dark area is where biofilm is still attached to the surface. See S1 Video for high speed videos of all surfaces at all standoff distances.
Fig 6.
Percentage biofilm area cleaned over time for three of the surfaces tested using cavitation at three different standoff distances, calculated using image analysis.
Green: Thermanox™ rough, Orange: Thermanox™ smooth, Purple: Titanium rough.
Fig 7.
High speed image stills before and after cavitation cleaning for 2 s for various biofilm surfaces and standoff distances of the ultrasonic scaler tip.
The white arrow shows the position of the scaler tip in the images. The white area is the cleaned surface and the grey/black area is the biofilm still attached to the surface. See S1 Video for high speed videos of all surfaces at all standoff distances.
Fig 8.
Scanning electron microscopy images of the different surfaces after removal with cavitation from the ultrasonic scaler tip at different standoff distances d.
The ultrasonic scaler was operated at 29 kHz, with a tip vibration amplitude of 57 μm at the free end. Biofilm remained on the Thermanox™ rough surfaces at all distances, and individual bacteria remained on the Thermanox™ smooth surfaces at all standoff distances tested. Individual bacteria and thin biofilms remained on the rough titanium surfaces. The sand blasted and acid etched surface can be seen in the SEM images, and machining lines are visible on the smooth machined titanium surface.