Download Document

Plasma treatment of caries: a novel
method in dentistry
R.E.J. Sladek, R. Walraven, E. Stoffels, P.J.A. Tielbeek, R.A. Koolhoven
Department of Biomedical Engineering, Eindhoven University of Technology,
P.O. Box 513, 5600 MB Eindhoven, The Netherlands
E-mail: [email protected]
Dental caries
Experiments
In dentistry dental cavities (Figure 1) as a result of caries are a major problem. Cavities in teeth can be
cleaned and/or sterilised by mechanically drilling or laser techniques. In both methods heating or
vibrations can take place and this can be painful for the patient (heating and vibrations can irritate the
nerve).
Temperature measurements
Temperature measurements will be made during plasma treatment. A thermo sensor (pt-100) is
inserted into the pulp chamber (Figure 4) and the temperature is recorded.
Also a temperature distribution model in Matlab® is made. The model is compared to the experiment.
According to Zach and Cohen, an increase in intra-pulpal temperature below 2.2 C fall within the safe
range of thermal stress.
Dental plaque experiment
Plasma treatment on dental plaque will be investigated ex-vivo by confocal microscopy (CLSM) and
vital
fluorescence techniques. Plaque is collected on enamel slabs (Figure 5). The slabs are inserted into
acrylic splints worn by participants.
Goal
Our goal is to find a less destructive (no fractures)
and less painful approach to clean dental cavities.
This may be done by use of a non-thermal
atmospheric plasma.
Figure 1: Dental cavity (left), tooth structure (right).
Why plasma?
Plasma is an efficient source of various radicals, capable of bacterial decontamination, while it operates at
room temperature and does not cause bulk destruction of the tissue.
The advantage of this novel tissue-saving treatment is that it is superficial and that the plasma can easily
penetrate the cavity, which is not possible with lasers. Also the use of plasmas is relatively cheap
compared to the use of lasers.
dual coupler
matching
network
RF amplifier
power
meter
waveform
function
generator
generator
RFsignal
Figure 4: (left) Radiograph of electrical thermistor
implanted
within the pulp chamber (Miserendino et al. 1989).
(right) Temperature measurement.
Figure 5: CLSM vital-stained 2-day-old plaque
on enamel. Thickness up to 32 m.
Magnification x500. (Netuschil et al. 1998)
Results
Using thermocouples, it has been verified that there is only little temperature increase (1 – 5 °C) in the
gas and even less in dental tissue. The modeling results are shown in Figure 7. The two-dimensional
temperature profile within the tooth has been calculated in a cylinder geometry. Thermal flux from the
plasma has been measured using a thermal probe described elsewhere. Teeth can be safely exposed to
the plasma (see Figure 9), no pain is experienced.
Applied voltage
perspex
ceramic tube
30
plasma
T ( 0C)
gas inlet
tungsten wire
22
0
Figure 3: Portable plasma needle.
Experimental set-up
RF- driven ‘plasma needle’
Tungsten wire inside a ceramic tube (Figure 2 and 3). Because of the ceramic tube, the plasma stays at the
tip of the needle. The diameter of the tunsten wire inside the perspex tube is 0.3 mm. The inner diameter
of the perspex tube is 4.0 mm. Helium flows via the gas inlet through the perspex tube to the tip of the
needle. The plasma is formed at the tip of the tungsten wire.
Experimental parameters
He (2 l/min)
13.56 MHz
26
24
gas inlet
Figure 2: A scheme of the experimental set-up.
28
Gas
RF frequency
Power dissipated in plasma
Voltage
 50 –100 mW
 200 - 400 V
100
200
Time (sec)
Figure 7: Temperature distribution
in cylinder of dentine
(rplasma=1 mm, Qin=2000 J/m2 . s).
120 mV
140 mV
160 mV
180 mV
200 mV
220 mV
240 mV
260 mV
280 mV
300 mV
Figure 8: Temperature in pulp chamber
Treatment time of 60 seconds.
Figure 9: First in vivo
experiment
Conclusions
• plasma treatment is a very promising tissue saving technique.
• plasma treatment of teeth is painless!
Plans
Bacterial viability experiments
In the near future we will investigate the efficiency of plasma-aided destruction of Escherichia coli and
bacteria present in dental plaque.