High Speed dental handpieces
One of the most important pieces of equipment in the dental office is a dental highspeed handpiece. Speed and torque are kings where dental handpieces are concerned, and competition is fierce between manufacturers. Because of the specialized nature, very high speeds, and extremely rigorous use of dental handpieces, the turbines that drive them must be manufactured to the highest standards. Substandard materials would result in imminent failure, and possible harm to the patient on which the equipment was being used.
A typical high speed handpiece uses air compressors to rotate a cutting bur at about 350.000 ? 400.000 rpm?s. Dental turbine, the heart of a handpiece, is the fastest spinning turbine in the world.
On the world handpiece market, today there are many different types and models of highspeed handpieces among which most well-known are manufactured by Kavo, Midwest, W&H, B&A and others. Dental turbines are located in the head of handpieces and have more or less the same basic design.
Watch the video to understand the difference and the benefits of the guiding bushing separated from chuck against the not separated one
The dental turbine
The heart and soul of the handpiece is the turbine. It performs all the work in a handpiece. The standard components are shown in the following diagram:
- Nr. 1 - At the centre of the turbine is the spindle, this is the shaft that rotates.
- Nr. 2 - Inside the spindle is the chuck, this is a hollow tube that holds the bur.
- Nr. 3 - Placed on the middle (from front to back) of the spindle (it is actually pressed in place) is the impeller. This is what catches the air causing
- the turbine to rotate.
- Nr. 4 Front bearing
- Nr. 5 Rear or back bearing
- On either side of the impeller are bearings, that allow the spindle to rotate by reducing friction.
- Nr. 6 O-Rings provide firm seating inside handpiece head while minimizing vibration.
- Nr. 7 Washer / wavy washers. Washers are usually used only on auto chuck handpieces to provide lateral tension, keeping the turbine pressed
- against the end cap to facilitate actuating the chuck.
- Nr. 8 Slinger is placed on front bearing to protect the bearing from dust and contamination.
What causes failure in dental turbines?
- Bearings (specifically the bearing cage) will generally fail first, mostly because of:
- Excessive air pressure
- Excessive temperatures during sterilization
- Side load stress
- Water from air storage tank of compressor
- Use of bent burs or a bur that is not fully seated
- Using low cost ball bearings of unknown producers
- Rapid cool downs of handpieces after sterilization with cold water. Rapid cool downs could cause warping of handpiece components and you could also introduce contaminants onto your sterilized instruments.
- Running handpieces without burs. Doing so could cause damage to the spindle/chuck assemblies.
- Irregular lubrication. The chuck must be lubricated at least once a week to keep it clean and functioning well. Debris can clog the chuck and interfere with holding the bur.
- Very important is to use correct burs. One of most common failure in dental turbines is the using of incorrect burs with les then 1,59 mm diameter. Unfortunately there are many thinner and softer burs on the market coming from low costs productions and in turn available at attractive prices. If burs are too narrow or to soft, the chuck cannot hold them well. During the rotation of 300.000 revolutions per minute or more, incorrect burs will sooner or later start to deviate and consequently cause failure of chuck mechanism.
- Another fact that causes bur eccentricity is guiding bushing (a hole into which bur is inserted) non-resistance to wear. The guiding bushing must be made of carbide or hardened steel and it must be separated from chuck (see pictures below). Many after-market producers of dental handpiece rotors combine the chuck and guiding bushing into one part because it simplifies the spindle design and thus saves costs. But this technique is not optimal for the bushing?s wear resistance. Pressures that are put on the bur during operation can create wear in the guiding bushing, giving the bur more space to move radially. Because of this radial play dentists cannot work precisely with their handpiece anymore. Increased play will also reduce bearing lifetime.
The schematic comparison between this two techniques is shown below.