In our article last March on "Electric Motors in Dentistry" we gave you some background on how electric motors work and how to diagnose the problems they may have. In this article we are going to look at ways to improve the life and reduce the cost of repairs on electric motors and their attachments. Keep in mind that heat is the enemy and is constantly being generated, first by the electric motor, then by the gears and bearings in the contrangle and finally by the gears and bearings in the head shell. The three sources of cooling in an electric system are the water spray, the chip air or coolant air and the drive air. The drive air flows up through the motor, then the contra angle then out the back of the head shell, providing cooling along the way. The coolant air and water travel out through holes in the front of the head shell cooling the head shell and the burr as it is cutting. The goal is to maximize this cooling effect and to help the customer understand how these things work. The examples we are using will be the Adec Dental Cart and the Kavo Electrotorque Plus electric handpiece system but the principles apply to any unit out there today.
When an electric handpiece system is properly installed the system pressures should be set to the required levels. However things can change over time and not every installer pays attention to detail. As a result we see a number of handpieces and attachments which are damaged because of inadequate pressure. The drive air in the electric handpiece motor system serves 2 purposes. First, it controls the speed of the motor through a pressure sensor on the circuit board inside the controller. This is a passive function requiring only the pressure not the flow of air. The second purpose is cooling the motor and attachment while it is running. This completely dependent on an adequate flow of air, inadequate air flow can lead to motor and/or attachment failure.
This “Air Requirement” (Figure 1) list was taken from the Kavo Electrotorque installation instructions. For our purposes a Bar is roughly equal to a kg/cm2 ( that is the outer numbers on the gauge showed below) and equal to 14.5 PSI so 4.5 Bars is 65 PSI. Understanding the nomenclature is also important, what we call coolant water, Kavo calls spray water some call it handpiece water and what we call coolant air, Kavo calls spray air, some call it chip air.
First you should check the pressure coming into the dental unit, is between 70 and 80 PSI and that it will not drop more than a few pounds when you run a handpiece. If the pressure is too low adjust with the main air regulator (Figure 2), if it drops down when you run a handpiece, check the air filters (their may be more than one) and any valves that may not be open all the way, and look for any pinched or twisted tubing, restricting the air flow. If the unit has adiquate air supply then continue by checking the handpiece pressure to the electric handpiece control. Air driven handpieces require between 30 and 45 PSI and more than that will shorten
the life of the handpiece (note there are exceptions to this). The electric motor needs 65 PSI or more at the highest point in order to provide the cooling required. Some manufacturers have flow meters (Figure 3) available to measure the actual flow of air through the motor and out to the attachment. This is of corse the most reliable way to determin the air flow but they are expensive and its hard to justify the cost.
At the factory default settings, most electrics will come on at 30 psi and reach maximum RPM at 65 psi raising the handpiece pressure above 65 psi is a good way to increase cooling, but most units max out at around 65 PSI. Increasing the pressure above 65 PSI will not effect the motor rpm because once it reaches maximum it can not go any faster. This ratio of presure to RPM can be altered, in the Kavo system and maybe others, I mention this only because we have had systems come in with the complaint that “it wont go fast enough” and we find that it is not reaching full RPM untill 70-80 psi and most likely the doctors unit cannot reach that pressure. Our solution is to restore the factory settings which can simply be done by pressing the Forward/Reverse and the Up and Down arrows at the same time and hold them for about a second or 2.
Adjusting the handpiece pressure is also a simple task. Here is an example.
In this case we have an Adec cart which has very simple controls on the right hand side. Determine which handpiece the electric system is connected to and insert the Adec adjusting tool (or just a 3/32 in allen wrench) into the adjusting hole that corrisponds to that handpiece (Figure 4). Turn it clockwise to decrease the presure or CCW to raise it, with the foot control pressed as far as it can go.
Adjusting the coolant water and air flow, is not as scientific, but the rule of thumb is to keep as much water as you can without drowning the patient, and as much air as you can get without interrupting the water flow. With an attachment and burr on the motor, start by turning the coolant air clockwise till it goes off (if there is a toggle switch to control the coolant air, use that). Then with the coolant water switched on, (switch may be on the unit or on the foot control or both) first adjust the valve on the handpiece connector (if there is one) to full open then adjust the coolant water on the dental unit water until there is more than enough water (the Doctor will have to fine tune this to suit his needs).
Adjusting the coolant air can be more complicated. First turn on the coolant air and increase until it begins to reduce the water flow then back off to a strong spray, the problem is that many units, like this Adec, have one coolant air control shared by all the handpieces, so you have to compromise and find the setting that works for all the handpieces. With the water and air set at the highest usable level, the Doctor can fine tune it to suit his needs. Always try to help him to understand that he wants as much coolant water and air as he can stand because it will make his handpiece last longer, and save him money. Now that we have maximized the cooling potential lets cover a few other areas quickly.
It is hard to impress strongly enough that when an attachment or a motor (or any mechanical device) begins to make noise or act strangely, you should STOP using it and get it fixed! Continuing to use a handpiece after a bearing or a gear begins to fail only multiplies the cost of repair. It is also important to inspect for physical damage such as dents in the head shell which will often cause rapid failure as well as enough heat to injure a patient. Here is an excerpt on the subject from the Kavo manual:
A proper procedure for cleaning, lubricating and autoclaving, which is followed and checked on a routinely is essential to maintaining dental handpieces. Here are a few guidelines:
This is certainly not everything there is to say about electric handpiece maintenance but it is a start. Please call me or post any comments or questions or suggestions you may have.