In Depth With

Retraction and Drawback:Key differences and solutions

T

he COVID-19 pandemic has

the electric motor route, choosing the righttantly, the microbes, including bacteria andawoken a sense of urgency

air-driven handpieces can be challenging.

virus, may further contaminate the air andand concern in the dental

There has been a lot of talk about anti-

water tubes within the dental unit, and thus

world. Dental practices andretraction and anti-suck-back features but

can potentially cause cross-infection.

schools are changing the waywith little clarification about what they are

they operate by enhancing their cross-and how they work.

contamination response. Dental equipment

Should retraction occur, users can still flush
and disinfect their waterlines as needed. In

provide customers with reliable solutions

Retraction, anti-retraction
valves, and flushingto help them respond to this new normal.

Retraction is essentially related to water

One of those solutions has been to reducebeing pulled back into the system throughthe generation of aerosols during dental

the water lines. It is strictly related to fluids

Drawback, Quick Stop, and ZeroDrawback

procedures.

and debris.

Unlike retraction, a drawback is related to

manufacturers are moving quickly tosummary, the potential for cross-contamination here is quite low.

the air lines. Aerosols created during dental

Air-driven versus electricmotor handpiece

Many manufacturers, including Morita, havetreatment are drawn back into the air lines ofalready solved this problem by introducing

the handpiece and eventually into the treat-

Eliminating aerosols is nearly impossible

anti-retraction valves throughout the sys-

ment unit. When the drive air stops, the tur-with the use of air-driven handpiece andtem. Essentially, these valves use a duckbill

bine continues to spin. This creates negativeelectric contra-angle motor attachments. In

shape which blocks fluids from getting backpressure in the system and begins to draw

general, contra-angle attachments generate

into the water lines. These can be present inaerosols back into the system, kind of like a

fewer aerosols than air-driven handpieces

the treatment unit and even in the hand-vacuum. This is also known as suck-back.

since they do not rely on drive air to run thepiece itself. Usually, users can find multiple

impeller. Many practitioners like them foranti-retraction valves as fail-safes. Most

The effect is cumulative. Each time users ac-

their stable and high torque. This may be amajor manufacturers include them withintivate the drive air, the drawback forces any

good solution to reduce aerosol generation

handpieces, couplings, and the treatment

contaminates further into the handpiece,

but the costs of converting to electric motor

unit. This technology has been around for apast the coupling, and eventually into the air

driven attachments are not trivial. Also, one

while and the ISO 7494-2 standard requires

lines and the treatment unit. It is importantmust consider that electric motor handpiece

the treatment unit to include it.

to note that users cannot disinfect and flush

is heavier than the air-driven counterpart.

the airlines of the treatment unit.
One study revealed that high-speed dental

What to look for in air-driven
handpieces?

handpieces without anti-retraction valves

Many manufacturers will include a braking

may aspirate and expel debris and fluids

system to reduce the spinning motion of theAssuming that the users are not willing to go

during the dental procedures. More impor-turbine once the drive air stops. Terminol-TwinPower Turbine™ handpiece

Air-driven handpiece and electric motor handpiece

48 DENTAL ASIA SEPTEMBER / OCTOBER 2020

In Depth WithCoupling

Front view of TwinPower TurbineTM

Zero-Drawback

ogy for these types of braking systems mayIn 2015, another study was done by Quan etthem with a stopping time of approximately

vary but at Morita, it is called Quick Stop.

al. reconfirmed the results3.

0.55 seconds which is the fastest time they

A Quick Stop braking system can help

The team used a sealed environment forsystem and was faster to stop than their

reduce drawback but not eliminate it. The

drawback comparisons. They used a rubber

high torque model. This same brand also

turbine continues to rotate after the drive

stopper to create an airtight seal at the top

performed well in the drawback comparison

air stops and, like any braking system,of a cylinder so that the only way air can get

but could not eliminate it. Brands A, C, and D

manufacturers cannot force the turbine toout is through the handpiece itself. The whole

had significantly longer stopping times.

stop instantaneously. During that fraction ofhandpiece head was put in observation as

time, a drawback is still possible. Addition-drawback can occur anywhere on the area.

recorded. Brand B uses an effective braking*Videos of the tests are posted on Morita’swebsite.

ally, smaller head size creates a less inertial
force which also contributes to reducing

The vacuum, created by the drawback effect,

stopping times.

will pull water up through a centre tube. TheTakeaways

stronger the drawback the higher the water

As the field of dentistry is continuously

will rise.

evolving, it is important to understand dif-

Smaller head sizes or Quick Stop braking mechanisms will help stop the turbine

ferent phenomena that could affect dental

faster and reduce the number of possible

For handpieces, they compared newer models

practice. Understanding Zero-drawbackcontaminants from being drawn back intofrom other top tier manufacturers with Mori-feature on handpieces is paramount in ad-the system.

ta’s TwinPower Turbine™. Using the method

dressing cross-contamination issues thatabove, the TwinPower Turbine™ was the only

the practice is facing today. DA

According to one study, some manufactur-

handpiece to demonstrate a complete lackers introduced a labyrinth system to reduceof negative pressure in comparison with four

References:

drawback, but it is not enough to elimi-

other models*.

1.

Ozawa T, Nakano M, Arai T. In vitro studyof anti-suck-back ability by themselves onnate the drawback effect. Only the ZeroDrawback system was found to eliminate

Brand A performed well because of the pres-drawback.

ence of an effective braking mechanism but
still showed slight drawback.

Demonstrating Drawback
The marketing, and the research and de-

Having seen the efficacy of braking systems

velopment departments of Morita company

on the drawback, they also compared the dif-

partnered up to conduct a direct compari-

ferences between braking systems of different

son of different handpieces available in themanufacturers.

market. The team was inspired by the meth-

new high-speed air turbine handpieces. Dent
Mater J. 2010;29(6):649-654. doi:10.4012/dmj.2010-008
2.

Peng, X., Xu, X., Li, Y. et al. Transmission
routes of 2019-nCoV and controls in dental
practice. Int J Oral Sci 12, 9 (2020). https://doi.org/10.1038/s41368-020-0075-9

3.

Quan, Yingjun & Lim, Joong-Yeon & Kim,
Kyoung-Nam & Kim, Yang-Soo. (2015). A
testing methodology for suck-back behavior

odology used by Ozawa et al. in 2010 with

The test* revealed that TwinPower Turbine™

of high-speed air-turbine dental handpiece.

their in vitro study of anti-suck-back ability

performed with braking times under two

Korean Journal of Dental Materials. 42.

of new high-speed air turbine handpieces1.

seconds. Their standard head surprised

10.14815/kjdm.2015.42.1.29.

SEPTEMBER / OCTOBER 2020 DENTAL ASIA49