As you know, mostly 5 objects take part in air polishing technology (or, in other words, air-flow):
dental unit, doctor, powder jet handpiece, powder and patient.
Let's leave the doctor and the patient alone and pay attention to the remaining objects.
In order to this technology run, it is necessary to create a water-powder-air jet. This jet is created by the unit,
the handpiece and the powder all together.
And if the influence of various powders on the air polishing process was investigated in sufficient detail, the influence of handpieces and parameters of
the dental unit remained almost beyond the scope of attention of researchers and only Pelka M, Trautmann S, Petschelt A, Lohbauer U.
Influence of air–polishing devices and abrasives on root dentin–An in vitro confocal laser scanning microscope study. Quintessence
Int. 2010;41(7):141–148. tried to draw attention to this.
And, unfortunately, no one investigated the abrasive properties of the jet itself and the dependence of the abrasive ability of the jet on
the parameters of the dental unit and handpiece. After all, it is the jet that we send to the dental deposits in order to remove them. And the abrasive
ability of the jet in our case is the capacity to remove them. Therefore, when studying the air polishing process, it is
necessary to talk about the abrasive ability of the whole water-powder-air jet, which is only partially determined by the powder used.
So, for example, we know the properties of photons - quanta of light. And differently organized photons give different results.
In one case, you organize photons into the soft light of your bedroom, and in another case, you organize photons into a laser beam that cuts metal.
Not necessary to go into the theoretical jungle here, would like to remain within the framework of conclusions for practical application, but it is usefull to give
In general terms, the essence of air polishing technology is that powder particles hit the dental deposit, chipping away small pieces from it which
are removed with water. Each particle of powder chips away its own little piece, and together they destroy the dental deposit. Chipping away these pieces or the
destruction of the dental deposit occurs due to the kinetic energy of the particles.
Kinetic energy of a particle is:
But the kinetic energy of a particle is not a determining parameter in this process. The determining parameter is
the specific kinetic energy of the particle, that is, the energy per unit contact area:
For example, if you drop a knife flat on a piece of wood from a small height, then the piece of wood will remain intact,
and if you drop the knife with its tip down from the same height, the knife will stick into this piece. In both cases,
the kinetic energy of the knife will be the same, but in the first case, the contact area of the knife with
the piece of wood is large, the kinetic energy of the knife is distributed over the entire contact area,
respectively, the energy per unit area is insignificant and does not lead to deformation of the piece of wood. In
the second case, the kinetic energy of the knife is concentrated on a small area, respectively, the energy per
unit area is significant and this causes the destruction of the piece of wood.
The mass of a particle is proportional to the cube of its size (a few words about particle size will be later),
and the contact area is proportional to the square of its size:
consequently the specific energy is proportional to the size of the particle multiplied by the square of its velocity:
We know from hydrodynamics that the square of the flow velocity in a pipe is proportional to the pressure difference between
the inlet and outlet of the pipe. The pressure at the outlet of the handpiece is always atmospheric, so the square of
the particle velocity is proportional to the pressure at the inlet to the handpiece.
This pressure is regulated at the unit:
Combining the last two dependencies, we find that the specific energy of a particle is proportional to the size of the particle
multiplied by the pressure at the inlet to the handpiece:
Thus, it follows that:
Abrasive ability of the water-powder-air jet can be altered by changing the size of the powder particles
or by changing the air pressure entering the handpiece.
Naturally, too little pressure will slow down your work, and too much pressure can damage the tooth tissues.
It should be remembered that powders from different materials interact in different ways with tooth tissues and the use of a
powder not intended for a particular procedure can cause negative consequences.
The dependence of the abrasive ability of the water-powder-air jet on the size of the powder and on the air pressure entering the handpiece can be
checked by each of you in your own dental office. For example, cleaning a coin at different jet settings.
At the same time, if you change the particle size and want to maintain the abrasive ability of the jet, then in the case of an increase in the particle size,
you should reduce the pressure, and in the case of a decrease in the particle size, you should increase the air pressure entering the handpiece.
Graphically, it can be represented as follows:
Naturally, this applies to powders made from the same material.
Moreover, the abrasive ability of the jet depend on the handpiece. Rather, it will even be more correct formulated as follows:
Every handpiece create water-powder-air jet with its own abrasive ability.
So, different handpieces create water-powder-air jet with different abrasive ability.
That is, when using the same powder and with the same air pressure at the inlet to the handpiece,
the abrasive ability of the jet will be different for different handpieces.
This is confirmed by our own research results, as well as, in particular, this conclusion can be made
based on the data presented in the above mentioned work. Pelka M, Trautmann S, Petschelt A, Lohbauer U.
Influence of air–polishing devices and abrasives on root dentin–An in vitro confocal laser scanning microscope study. Quintessence
The authors explored two handpieces, EMS Handy, EMS and Prophyflex 3, KaVo. The handpieces formed different jets:
According to the authors, Prophyflex 3 with a narrower jet (right) had more abrasive ability than the EMS Handy (left). And this is completely consistent
with our data, since it is known that a narrower jet implies higher velocities, therefore, powder particles of the right handpiece had a higher specific
energy Es and, accordingly, a higher abrasive ability.
At the same time, it is obvious that by reducing the pressure in the right handpiece, the authors would get exactly the opposite result.
In addition, it is possible that different types of dental deposits require different abrasive ability of the jet, and therefore can be
processed at different pressures of the air entering the handpiece.
Therefore, from a practical point of view, setting the air pressure entering the handpiece is one
of the most basic operations to obtain a jet of the required abrasive ability.
The air pressure entering the handpiece is one of the main parameters that determine the abrasive ability of the jet.
Set up the air pressure depending on the handpiece, the powder and the required processing.
Another factor influencing the air polishing process is the number of powder particles in the jet.
The number of powder particles in the jet determines the speed of the air polishing process.
Obviously, the more powder particles are in the jet, the faster the process takes place.
The amount of powder particles in the jet itself is determined by the flow rate of the powder.
Our research has shown that the flow rate of the powder depends on various parameters. It goes without saying that
the design of the handpiece, in particular the chamber, is the determining factor here.
The studies were carried out on a handpiece having a chamber design shown in the figure.
During the research, it was found that the flow rate of the powder depends on the amount of powder in the handpiece chamber
(what is consistent with the results Petersilka GJ, Schenck U, Flemmig TF. Powder emission rates of four air polishing devices. J Clin Periodontol. 2002;29(8):694–698.).
The more powder is in the chamber, the higher its flow rate. In this case, the maximum amount of powder that was
poured into the chamber did not close the supply and receive air holes.
Also, it was found that the flow rate of the powder depends on the spatial position of the handpiece.
The speed of the air polishing process depends on the amount of powder
in the handpiece chamber and on the spatial position of the handpiece.
However, the flow rate of powder should not be confused with the abrasive ability of the jet.
Abrasive ability is the capacity to destruction and is determined by the specific energy of the powder particles,
but the flow rate is related to the number of hits of the powder particles per unit time and is determined the amount of powder in the jet.
Although from a practical point of view, both an increase in abrasive ability and an increase in the flow rate increase the speed of the process.
But an excessive increase in the abrasive ability of the jet, in other words, in the pressure at the inlet to the handpiece,
can lead to unwanted damage to the tooth tissues.
An interesting result was obtained when studying the dependence of the powder flow rate on the air pressure at the inlet to the handpiece.
In this regard, a complete description of the experiment is given.
5 grams of powder was poured into the handpiece chamber and the time it took for the powder to leave the chamber was determined.
The handpiece was in a horizontal position and was accompanied by slight swaying from side to side. The results are shown in the graph:
Thus, it turned out that the flow rate of the powder in the pressure range of 2-4 bar did not depend on the pressure.
To verify this result,
another series of experiments was carried out. The same 5 grams of the powder was poured into the handpiece chamber,
the handpiece was turned on for one minute and it was checked how much powder left the handpiece during this time.
The results are shown in this graph:
Thus, it was confirmed that for this handpiece in the range of 2-4 bar,
the powder flow rate is independent of the air pressure at the inlet to the handpiece.
It should be noted that all studies were carried out on the powder PROFIFLUSS®-M, black currant.
Usually, clogging up of the handpieces is due to insufficient care for the
dental unit and the handpieces themselves.
Therefore, to understand why a handpiece clogs up during running, it is necessary to know how the handpiece
works and, consequently, why taking care of the dental unit and the handpieces themselves critically
affects the running of the handpieces.
It could be definitely said that powders PROFIFLUSS®
completely eliminate the possibility of handpiece clogging.
The figure shows a schematic representation of the handpiece:
The handpiece works as follows: through tube 1, air enters chamber 2 where it captures
powder 3 and through tube 4 brings the powder-air mix outward.
Parallel to this, water
is supplied through tube 5. A water-powder-air jet 6 is formed at the outlet of the handpiece.
The photo shows the nozzle of the handpiece. A powder-air mix comes out of hole 7, and water comes out of holes 8.
The powder-air mix and water do not mix inside the handpiece.
Accordingly, the air in the handpiece must be dry and clean.
The ingress of humid air with impurities
into the handpiece will cause clogging.
At the same time, checking the air quality is quite simple.
To do this, disconnect the handpiece from the handpiece hose, turn off the water supply to
this hose, bring a clean napkin to the hose and turn on the air supply. The air jet should
be directed towards the napkin:
Enough 20-30 seconds and then stop the air supply and look at the napkin.
The napkin must be clean. If there are water, oil or other stains on the
napkin, it means that the air is polluted and all the pollutions of the
air gets on the powder, as a result of which agglomerates are formed, which
clogging up the handpiece.
Check handpiece air quality regularly.
In addition, can also be said that the polluted air negativly
affect bearing life in turbine handpieces and air motors.
Also, the ingress of water into the channel 1-2-4 is possible due to a wear or
loose fit of the corresponding seals. The illustrations show seals whose wear or
loose fit can cause clogging the handpiece.
10 - hole for water, 12 - hole for powder-air mix,
9, 11 - sealing rings, 13 - sealing gasket.
Check the seals regularly.
In other hand, one should not forget about the quality of making
of the handpiece itself. The details of the handpiece,
which are responsible for its running, are small enough and it is
almost impossible to determine their defects with the naked eye.
An outwardly attractive handpiece might look like this under a microscope. Therefore:
Use only good quality handpieces.
Let's see how powders from different manufacturers look under a microscope:
And among all this huge number of particles, we cannot find two identical particles.
There are no two identical particles in nature.
But let's choose any particle from this plenty of particles and try to determine its size.
For example, like in the picture. What size has this particle? l? w? h? We live in a three-dimensional
world and we certainly cannot describe the size of a three-dimensional object with one parameter.
And of course there is no standard method for determining the particle size of a powder. In the powder industry,
for example, to determine the grain size of a powder, such concepts as fractions are used,
which are determined using sieve analysis.
The absence of a standard method for calculating the particle size of a
powder leads to the fact that each manufacturer arbitrarily assigns a
particle size to its powder.
Therefore, when using powders from different manufacturers, with the same particle size indicated on
the label, you can get water-powder-air jets of different abrasive ability.
In order to level the difference in powders
from different manufacturers, set up the correct air pressure at the inlet to the handpiece.
© VRK Lab GmbH, 2021