Customer Service: 1-800-331-7993
September 30, 2014
Welcome back! In previous Practice Tips #3 (previously known as Tech Tips) we discussed the basics of dental units and the required operating pressure (80 psi air, 40 psi water). After a few technical calls from dentists lately, we thought it would be a good topic to revisit.
As discussed before, insufficient air pressure can lead to a myriad of problems. In most systems, air is also used to prevent handpiece function. Air flows through the handpiece holder (see below for a holder or go to our holders & bars for more variety) pushing down on a diaphragm to keep the handpiece from running when it's in the holder. For this system to work, the main air pressure needs to be higher than your drive air, so that it can keep the drive air from forcing its way through the system. This is another reason your main pressure needs to be quite high (typically 80 psi).
If you have a cuspidor, air pressure can be used to activate the water to rinse the bowl and fill the cup. For systems with a timer (the bowl rinse or cup filler will run for a time and then automatically shut off), an air reservoir is typically used to provide the timing. When activated (usually via a pilot valve- #10-10), air flows into the reservoir which gradually drains as it flows into a block to turn the water on. Once the reservoir is emptied of air, the pressure is released on the water valve and the water then shuts off. The timer adjustment simply controls how long it takes for the air to empty from the reservoir.
Since water is denser than air, air pressure needs to be at least twice your water pressure for the air activated functions to work more efficiently. Otherwise, the greater density of water can allow it to “force” its way through the lines.
Your foot control, also, operates under standard regulated line pressure. The foot control is the first point at which your drive air pressure is stepped down. By having a solid 80 psi inlet pressure, you have plenty of range to control the outlet pressure. If the pressure came in at only 40 psi (for example), you’d have much more difficulty getting a full 40 psi to your handpiece when you need that much power.
Your foot control may also have air operated accessories, such as a water on/off toggle. You need ample air pressure at this toggle for the same reason as you need high air pressure inside the unit. Of course, you can’t have 80 psi in the operatories unless you have enough pressure coming out of your compressor, which should be set to cycle at 90-100 psi (to support the inevitable loss of pressure as it travels). The regulators (#05-54) in the operatories can only step the air pressure down, so you need to be sure the pressure coming into the room is in excess of 80 psi. Adequate air pressure is the first step in keeping your units running well.
We can't tell you how many calls we get that could be quickly diagnosed in-house had the doctor simply checked the gauges first, so don't forget to check yours when experiencing issues with any dental unit component. Please give us a call at 800-331-7993 with any questions.
Thanks for reading and see you next month!
August 29, 2014
There are 2 basic types of attachments used with slow-speed motors: nosecones and contra angles.
A nosecone is a straight attachment that will accept a slow-speed bur or a shaft-driven angle (contra angle or prophy angle). Nosecones are unique and come with different gear ratios. The default is a 1:1 ratio – the nosecone will operate at the same speed as the motor. 4:1 is a common gear reduction, the nosecone will spin at ¼ the speed of the motor. Some nosecones (primarily those designed for use with electric motors) will also have speed increasing gears, so they will operate at a 1:5 gear ratio (for example), or 5 times the output speed of the motor.
Nosecones are standardized so they all will accept the same diameter bur or shaft driven attachment. Nosecones also incorporate a pin of some sort to prevent rotation of any shaft driven attachment placed on the nosecone. All shaft driven attachments have a groove that slides over this pin.
As nosecones can accept a slow-speed bur, all you may need to perform a particular procedure may be a motor and nosecone (and bur, of course).
The other type of attachment, a contra angle, will work with gear driven attachments only (most commonly some sort of head). They will not accept a bur, so further attachments are required. As the name implies, a contra angle provides an angle for the next attachment which can improve intra-oral access.
Both Midwest and E-type contra angles accept the same type of gear driven heads. The heads incorporate a drive shaft with a gear at the end that seats into the contra angle meshing with the internal drive shaft causing the head to spin. The drive gear has pointed teeth making it easier to seat the two halves together. The head also has square “teeth” under a threaded collar that mesh with the square “teeth” on the outside of the contra angle. These teeth hold the head onto the contra angle and prevent the entire head from spinning (so only the drive shaft spins). It is these teeth that one must count to determine compatibility between a head and contra angle. Heads and contra angles come with either 12 or 14 locking teeth.
Star systems do not normally use a contra angle attachment. Instead, they use a straight attachment which accepts a Star-specific head. Star heads have an elbow incorporated at the end to provide the angle normally provided by a contra angle attachment as used by other systems.
American Dental Accessories, Inc. also has an after-market contra angle that will work with a Star-type motor. This angle will allow you to use standard heads with your Star system (which can save money over the more costly Star-specific heads).
Regardless of system, a contra angle (or angle attachment) will require a 3rd attachment for use with a rotary instrument and will not be a complete set-up for a given procedure (as a motor and nosecone alone can be).
Finally, there are heads. As mentioned above, heads will have both drive teeth and attachment teeth (or drive teeth and a threaded elbow). The number of attachment teeth will determine compatibility with a particular contra angle. The head will accept the rotary instrument with which one will perform a given procedure. The most common head is a latch head which will accept a latch (or RA, for “Right Angle”) bur. RA burs have a groove at the end into which the latch of the head will secure holding the bur in. Some heads also accept standard friction grip burs, exactly as used in a high-speed handpiece.
Other heads are designed only to accept prophy cups. Prophy cups can come with either a threaded “screw on” shaft or that simply “snap on” a knob designed for this purpose. Some are also attached to a standard latch-type shaft so they’ll work in a standard latch head.
The flexibility afforded by the various head configurations allows for a tremendous range of applications for a slow-speed set-up. This flexibility can allow for great value with a slow-speed system.
June 29, 2014
The turbine is the heart of the high-speed handpiece and bearings are the heart of the turbine.
Bearings are the most common failure point of a turbine and are often the primary differentiator between one turbine and another.
Way back in Tech Tips #22, “High-speed Handpiece Design,” we covered all of the components that make up a complete bearing assembly. For ease of reference, we’ve included the diagram of a bearing assembly below. For further explanation of the components, check out Tech Tips #22.
Today, we’re going to look at some of the different bearing materials and designs on the market.
Many turbines use stainless steel bearings that require lubrication. The balls, inner ring, outer ring, and shield are all made of stainless steel. The ball cage will be made of a polymer (there are a few more variations within this broad category and different types of polymers for the cage, but all these permutations require lubrication).
Stainless steel bearings have been in use for decades and are a proven design with good performance and good reliability. They are manufactured in large quantities for dental turbines and many other industries so cost is comparatively low. As these turbines incorporate metal bearings in metal housings, they require lubrication. Most handpiece lubricants on the market are designed to withstand the rigors of sterilization, but these turbines should still be lubricated every time they are used (see our handpiece maintenance products here). Lubrication after using and before sterilization is generally adequate, but consult the manufacturer of your turbine and lubricant to determine if post sterilization lubrication is required as well.
Many turbines currently on the market are advertised as “lube free.” There are 2 primary methods of manufacturing lube free bearings:
LTL bearings are still the same basic stainless steel design so they share many of the features of standard stainless bearings. The greasing and sealing process adds to the cost (and they aren’t manufactured in quantities like the standard bearings), so they will add to the cost of the turbine or handpiece that uses them. The sealing process, also, prevents debris from getting into the center of the bearing assembly and on the actual steel balls, so maintenance is a little easier. Nonetheless, these bearings (or, more accurately, turbines that incorporate these bearings) still need to be cleaned after every use and before sterilization.
Last of all, there are ceramic bearings. Ceramic bearings are actually made of a ceramic silicon nitride, so they have a very smooth low-friction surface. The low-friction surface removes the need for lubrication and also minimized heat build-up during use. They, also, withstand high temperatures very well, so they withstand repeated sterilization better than stainless steel bearings.
Both LTL and ceramic bearings will run at higher rpm than stainless bearings and are better able to handle higher air pressure (they typically require in excess of 40 psi drive air pressure). The higher rpm can help these turbines cut faster so some practitioners feel they perform better (naturally, this is subjective).
In summary, the materials and techniques used to manufacture lube free bearings are more costly than standard stainless bearings, so these bearings (or the turbines that incorporate them) often cost twice as much as turbines that need to be lubricated. It’s up to the practitioner if the advantages are worth the expense.