Dental handpiece

Abstract

A dental handpiece is disclosed including a turbine construction creating a radial in flow of air onto the impeller blades about the whole circumference of the turbine. This generates additional torque and avoids asymmetrical thrust on the impeller wheel. A pair of axially spaced air bearings support the turbine. Air supply to the bearings is controlled in such a way that the air bearings are floated before drive air is supplied to the turbine and after drive air to the turbine has been shut off. This ensures that the air bearings are always operational irrespective of the operational state of the turbine. The handpiece has an improved ergonomic shape, especially the shape and configuration of the front or drive head, which provides additional tooth clearance and a better field of view. An angled swivel connection to the umbilical cord is provided which reduces physical strain on the dentist's wrist. A self adjusting lock and key type torque connection between the dental burr and the chuck is provided which accommodates both conventional burrs and the burr of the lock and key arrangement. An auto stop arrangement for the turbine is disclosed which prevents a vacuum buildup during rundown of the turbine. The specific construction of the auto stop valve in accordance with the invention closes both the drive and exhaust air conduits.

Description

FIELD OF THE INVENTION [0001] The present invention relates to handpieces for rotating tools and particularly to turbine driven medical or dental handpieces. BACKGROUND OF THE INVENTION [0002] Numerous handpieces for rotating tools exist. Turbine driven handpieces are widely used in dental offices and medical labs around the world. Most handpieces include a handle portion, a connector at one end of the handle portion and a tool carries drive head at the other end. The connector provides a connection of the handpiece to various air, water, light and power supply conduits, generally combined in a so called umbilical cord. The drive head houses a tool rotating assembly, generally composed of a tool mount or chuck, and a motor or a turbine, rotatably mounted in the head for driving the chuck. [0003] Various different types of turbine arrangements are in use, all of which include a turbine in a turbine housing, a supply of pressurized air into the housing for driving the turbine and a se...

AI Technical Summary

Benefits of technology

[0014] It is an object of the present invention to obviate or mitigate at least one disadvantage of existing handpiece designs.

[0015] In a first aspect, the present invention provides a turbine design and method of operation, wherein drive air is evenly distributed in an annular chamber extending about the turbine chamber before the air is directed in a generally radial direction onto the turbine wheel. The results are higher torque and self-centering of the turbine, the latter being particularly important for longevity of the bearings used.

Problems solved by technology

Since conventional dental handpieces are constructed to rotate the dental drill or burr at speeds of up to 500,000 rpm, the bearings are subject to large stress.

Furthermore, asymmetrical thrust generated by drive air impinging tangentially on the turbine places additional stress on the bearings.

However, their service life is still not satisfactory.

It is easily apparent that operating the air bearings and the turbine with the same drive air causes a major disadvantage.

At shut down of the drive air, the turbine still rotates while the air pressure is no longer sufficient to fully support the spindle in the bearing sleeves.

This can result in serious damage to the bearing, which in turn limits the service life of the turbine drive unit.

Moreover, although the cylindrical air cushions may properly support the spindle in radial direction, very little support in axial direction is provided.

Although annular air cushions are provided around the thrust washers, the overall surface of these air cushions appears to be quite small considering the potentially large anal thrust force applied to the spindle upon contact of the burr with a tooth.

Furthermore, the sharp angle at the transition from the cylindrical air cushion to the annular air cushion impedes the flow of cushioning air.

The tangential air supply generates asymmetrical thrust and causes asymmetrical loading of the bearings, which increases stress and wear.

Furthermore, the torque generation of the turbine is low due to the only localized drive air supply.

Moreover, parasitic airflow (drag) is high when the drive air is supplied tangentially at the circumference of the turbine.

Only low torque transmission is possible between the chuck and the burr in such constructions, higher torque leading to slippage of the burr.

However, the use of this arrangement in an air turbine handpiece is not disclosed.

In fact, the disclosed arrangement could not be used to hold a dental burr, since the engagement between the pin and the chuck is designed for a non-rotating tool and does not easily lend itself to being used with a rotating tool.

It is a disadvantage of this prior art arrangement that the burr must be rotated in the chuck until the lock and key structures fit together.

Locating the interlocking mechanism deep in the drive head of the handpiece makes it impossible for the user to visually pre-align the lock and key structure prior to insertion of the burr.

However, since the turbine is rotating at high speed, it takes some time to gradually slow down and come to a stop.

This is undesirable, since for safety reasons, the dentist must wait until the turbine has fully stopped before removing the handpiece from a patient's mouth.

Furthermore, during this so called rundown period, the continued rotation of the turbine generates a vacuum in the turbine chamber which may lead to contaminants being sucked into the chamber.

However, the valve arrangements of these two patents shut off only the exhaust air conduit, not the drive air and chip air / water conduits.

Thus, a vacuum may still be generated and contamination may still occur.

However, the tooth clearance achievable with such a construction is limited by the length of the burr.

Furthermore, the treatment field is usually partially obstructed during use by the drive head and the neck.

However, this connection normally extends straight in extension of the handpiece, which places a fairly high twisting strain on the wrist of the user, since the straight swivel connection combined with the inherent rigidity of the umbilical cord acts as a sort of lever which exaggerates the actual downward force created by the weight of the cord.

This problem has plagued dentists for years with no solution for dental handpieces being available.

However, all of these connectors provide only a straight connection between the umbilical cord and the handpiece.

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