Dental handpieces that are rotatably driven by compressed air are conventionally known, such as those having an air turbine or an air motor. An example of such a conventional dental handpiece is shown in FIG. 5.
FIG. 5 is a sectional view of head section 40 of an air-turbine dental handpiece. This dental handpiece includes burr sleeve 42 for receiving and detachably holding dental treatment tool 41 therein, rotor 43 provided on the burr sleeve 42 for rotatably driving the burr sleeve 42 with compressed air, and upper and lower ball bearings 44 provided above and below the rotor 43 for rotatably supporting the burr sleeve 42. These parts are all accommodated in cartridge case 45, which is in turn housed in head housing 46. Head housing jacket 47 supporting the head housing 46 contains therein air supply passage 48a for supplying compressed air to the rotor 43 and air discharge passage 48b for discharging the compressed air supplied to the rotor 43.
The air-turbine dental handpiece discussed above has drawbacks in that, if the handpiece is operated at an air pressure that exceeds the acceptable level predetermined for each handpiece, the revolution speed of the turbine becomes too high, and the dental treatment tool may be damaged. Further, the lubricant may run out prematurely to cause wearing of the bearings, which disadvantageously reduces their service life.
In order to avoid these drawbacks, a dental unit which supplies compressed air to the handpiece is given functions to regulate the pressure of the compressed air to be supplied to the handpiece, so as to keep the air pressure in the air supply passage in the handpiece within the predetermined range. However, the pressure of the compressed air needs to be adjusted properly for each kind of dental handpiece, and such pressure adjustment requires complex operations. Thus the user may tend to use the same air pressure for different kinds of handpieces, and as a result, the above problems will occur.
In order to solve the above problems, the assignee of the present application has proposed in JP-2003-019144-A a dental handpiece having a pressure reducing member. This dental handpiece has a pressure reducing member arranged in the handpiece body section, or in the coupling (connector section) to be connected to the rear end of the handpiece body section. FIG. 6 illustrates dental handpiece 50 as the former embodiment.
The dental handpiece 50 includes grip section 51 and head section 52 provided at the distal end of the grip section 51. The head section 52 houses and rotatably supports a burr sleeve (not shown) for receiving dental treatment tool 53 therein. The grip section 51 accommodates air supply tube 54, air discharge passage 55, and water supply line 56, and pressure reducing member 60 is disposed in the intermediate part of the air supply tube 54. A flexible tube (not shown) extending from a dental unit for supplying compressed air is connected to the rear end of the grip section 51, so that the compressed air is supplied through the air supply tube 54 to the head section 52 to rotatably drive the dental treatment tool 53.
In the dental handpiece 50 discussed above, when the pressure of the compressed air supplied from the dental unit exceeds the acceptable level, the air pressure is automatically regulated by discharging the compressed air out of the air supply tube 54 through the pressure reducing member 60 into the air discharge passage 55.
The dental handpiece 50 disclosed in JP-2003-019144-A is advantageous in that the air pressure is automatically regulated. However, since the pressure reducing member 60 is disposed projecting in the intermediate part of the air supply tube 54, the grip section 51 inevitably becomes thicker, which poses problems in grippability.
In addition to the embodiment shown in FIG. 6, JP-2003-019144-A also discloses a dental handpiece having the pressure reducing member provided in the coupling. However, for providing the pressure reducing member in the coupling, relatively complex material processing is required during the production process, and thus further improvement is required.
Besides the handpieces disclosed in JP-2003-019144-A, there are other conventional dental handpieces that have a pressure reducing section integrally incorporated in the rear terminal part of the dental handpiece body. However, the above problems, such as the difficulties in making the grip section compact, and relative complexity in production process, still remain in these dental handpieces.