FR2868940A1 - Manual dental instrument incorporating a rotary roller with ceramic components for improved life and aptitude to sterilisation - Google Patents

Abstract

Manual dental instrument has at least one roller including some ceramic components (4). The roller has several rolling elements (5) that are guided by means of a cage (8). The cage is made, at least at the sides of the guidance surfaces, of ceramic or ceramic glass. The roller is driven by an electric motor able to provide rotations at up to 200,000 turns/minute (claimed).

Description

The invention relates to a dental hand instrument with a bearing

  presenting ceramic components. In such bearings there are several rolling elements which are guided and kept apart from one another by means of

a cage.

  Plastic cages according to the state of the art have certainly a longevity which is 2,000 to 5,000 cycles of sterilization, but have poor emergency operating properties. In addition, the temperature resistance of the plastic cage materials limits the sterilization process to steam sterilization at normal temperatures of 134 ° C or hot air sterilization at 180 ° C. Typical known plastic cages are attributed to elevations as a result of friction, which break off or melt causing deposits on the elements to further wear.

  From WO 90/14049 a dentist with a tool of less rolling elements of a cageless bearing is made of a ceramic material. This instrument can be sterilized and operate without bearing lubrication.

  DE 198 43 951 A1 discloses a dental handpiece in the drive system of which there is provided a bearing arrangement for mounting an engine shaft. The rolling arrangement has a plurality of rolling elements which are made of an electrically non-conductive material, in particular a ceramic material. Furthermore, the bearing rings of the bearing may be made of a ceramic material. As a material, silicon nitride is especially proposed.

  In DE 196 12 571 A1 it is proposed for non-cage bearings to have, between the ceramic rolling elements, individual rolling elements in the local temperature which damage the particle cage, which can Al promoting rolling is known a rotating hand-held instrument in which to plastic material which are soaked with a lubricant, give off lubricant and / or are made of a self-lubricating material.

  The main problem with cage-less bearings is that in the area of contact between two rolling elements, as a result of the different steering components of the rolling elements coming into contact with each other, double speeds are affected and, as a result, there is a particular risk of wear.

  The object of the invention is to further improve the longevity of a bearing of a dental hand instrument. Furthermore, it is necessary to take into account in particular the ability to sterilize the bearing and also the problem of the lubrication of the bearing.

  According to the invention, a dental hand instrument with at least one bearing having ceramic components with a plurality of rolling elements guided by means of a cage is made so that the cage is made, at least at the location of the guide surfaces, ceramic.

  Compared to the typical plastic cages used so far, the temperature resistance is increased and the wear is reduced, especially when there is a lack of lubrication or lubrication is totally omitted. The guide of the cage can take place on the inner ring or on the outer ring or by the rolling elements.

  By the use of a ceramic adapted to the application case, it is, in particular, also possible to create good sliding properties and reduce friction. Especially in the combination of ceramic / steel cage / ball or cage / raceway materials, the good friction behavior results in a greatly reduced wear in the field of cage guidance, but also in the field of guiding of the cage. balls in the cage.

  The use of a cage which is entirely made of ceramic has, moreover, the advantage that, when using bearings in a magnetic field, there is no loss of eddy current caused by the cage , as it would be the case with metal cages. As a result, the positive properties of a plastic cage are fully achieved. In addition, the production of such cages can be simpler.

  Another advantage is the resistance to sterilization of the ceramic. Ceramic is, under the given sterilization conditions, very largely chemically inert and resistant to stresses due to steam and heat.

  It is advantageously used a ceramic whose density is lower than that of the metal and, in this case in particular steel. Not only does the density enter into the calculation of the mass moment of inertia, but the geometrical formation of the cage construction also has an influence. If the volume of construction can be reduced, this can have decisive advantages. Thus, the dynamic properties during acceleration and deceleration are improved.

  If electrical insulation is sought with the aid of the bearing, that is why, according to the state of the art, for example the rolling elements or the bearing rings or the assembly can be made of ceramic, the line of air and leakage can be enlarged when using a ceramic cage, compared to a metal cage. On the other hand, the cages made of carbon-reinforced plastic have the disadvantage that they do not have good insulating properties.

  In case of stress, the ceramic has a modulus of elasticity which corresponds at least to that of steel, but which, in general, is even higher.

  Advantageously, the dental hand instrument is equipped with a cage whose ceramic coating or cage material consists of silicon nitride (Si3N4). As regards its physical and chemical properties, silicon nitride is particularly suitable for use in the dental field.

  According to an advantageous development, the ceramic used is porous at least on the surface of the cage, at the location of the guide surfaces, to absorb lubricant. This lubricant is released during operation and prevents a lack of lubrication.

  According to another advantageous development, the cage is provided, at least at the location of the guide surfaces, with a coating which is made harder than unwanted foreign materials, such as, for example, metal particles or carbon particles. of the driving electric motor, so that a deposit of particles on the guide surface can be avoided and that, because of the hardness of the ceramic, no incrustation in the surface occurs. It can therefore be here, in general, a monolayer or multilayer coating. The metal particles can be released, for example, by abrasion.

  The use of cages which contain ceramic components has, moreover, the advantage that the thermal expansion of the ceramic can be influenced by the appropriate choice of the composition of the material, so that, in case of thermal variations, the Slots for guiding the bearings and the cage guide vary in a desired manner or remain constant, therefore, in particular, that the slot does not become too large, but not too small.

  Furthermore, in particular in the case of a massive ceramic cage, there can be provided breakpoints set point that facilitate disassembly. The ceramic is, typically, susceptible to breakage and can be easily broken for disassembly.

  Advantageously, the cage has other bores which are not used to guide the rolling elements. These bores contribute to a reduction in weight and a decrease in mass inertia.

  Advantageously, the cage may be reinforced with one or more non-ceramic rings in order to oppose the centrifugal forces. This is advantageous especially in the case of a massive ceramic cage. The rings can be arranged on the outer periphery of the cage. In this case, the reinforcement rings are preferably made of metal.

  On the other hand, it may be advantageous for the reinforcement rings to be pretended, so that it is ensured that the cage is always subjected to a compression force, even at a large number of turns.

  Advantageously, the dental hand instrument is driven by a turbine and the bearing operates at at least 200,000 rpm (3,333 t / sec.). As a result, a dental handpiece with a bearing having ceramic elements can be used at existing treatment locations where compressed air is provided.

  Another advantageous embodiment of the dental hand instrument lies in the fact that the hand-held instrument has, for the drive, an electric motor and that the bearing is arranged at the engine and can operate at a number of laps up to 50,000 rpm (833 t / sec.). This allows the operation of a dentist's hand instrument when a turbine-driven handpiece can not work or is not desired.

  It is particularly advantageous for the bearing to be used for mounting drive shafts, for which they will be preferred to conventional bearings.

  Embodiments of the invention are shown in the drawing, in which: - Figure 1 illustrates a hand-held instrument in an embodiment as a turbine, - Figure 2 illustrates a dentist's hand instrument in the form of a bent part. with electric motor, - Figure 3A illustrates a bearing of the turbine of Figure 1 with a cage with guide surfaces having a coating, - Figure 3B illustrates a rolling of the turbine of Figure 1 in section along line AA of Fig. 3A; Fig. 4 illustrates a set point breakage cage and a plurality of reinforcement rings; Fig. 5 illustrates a surface cut of a porous surface cage at the guides.

  FIG. 1 illustrates a dental hand instrument 1 according to the invention in which a turbine powered by compressed air is used as a drive. The turbine is located in the head element 2 of the hand-held instrument 1, but is however not visible in the drawing. As the bearing of the turbine can be used a bearing having ceramic elements, as shown in Figures 3A, 3B.

  FIG. 2 illustrates a dental hand instrument according to the invention 3, the drive of which is carried out in the form of an electric motor. A bearing according to the invention can be used here, for example, for mounting a drive shaft in a hand-held instrument or the motor shaft in a motor.

  FIG. 3A illustrates a sectional view of a bearing 4 having ceramic elements, in which rolling balls 5 are used as rolling elements which are in contact with the inner ring 6 and the outer ring 7 of the bearing 4. The balls 5 are guided by a cage 8 which has, on the lateral guide surface 8.1 oriented towards the inner ring 6 and on the radial guide surface 8.2 oriented towards the rolling elements 5, at least on the surface, a coating 9 , 10 ceramic or glass ceramic. Moreover, the coating 9, 10 may be porous. The porosity provides lubricant absorption in the coating material, so that the lubrication of the bearing 4 is also ensured when it is not supplied with new lubricant from the outside. The bearing 4 serves to receive a shaft 11 to which the inner ring 6 is fixed.

  Figure 3B illustrates a bearing 4 having ceramic components showing in a sectional view along the line A-A of Figure 3A. The guide surface 8.3 can be seen in the circumferential direction, which also bears a coating 10. The cage 8 can also be made entirely of ceramic or glass ceramic. In this case too, an additional coating is possible, but is not essential.

  FIG. 4 illustrates a cage 12 which, in addition to the lateral rolling element guides 13, has break points 14 which, on the one hand, contribute to a reduction in the inertia torque of the bearing and, on the other hand, , are often desired in the sense of easy maintenance. In addition there are bores 14 'which cause a further reduction of the moment of inertia. In addition, the cage 12 is reinforced, on its outer periphery, reinforcing rings 15 which better protect the cage 12 against the centrifugal forces and shock stresses, as they often occur in the daily dental treatment, being Since the reinforcing rings 15 give the cage 12 greater strength and thus allow a greater number of turns of the bearing 4. For this purpose, the reinforcing rings 15 are preferably mounted under pretension. , which has the advantage that the cage 12 is, even at high revolutions, always subjected to a compressive force. This further increases the longevity of the bearing 4. The cage 12, developed with respect to the cage 8, is, on its guide surfaces 12.1, 12.2, 12.3, also provided with a porous layer 9, 10, to obtain, in this way, which concerns the lubricating properties, the same advantages as with the cage 8 illustrated in FIGS. 3a and 3b. It is possible to equip the bearing 4, which is shown in Figures 3a and 3b, alternately to the cage 8, the developed cage 12. Conversely, the cage 8 of Figures 3A, 3B may also be equipped with one or more reinforcing rings.

  FIG. 5 illustrates a sectional view of the surface of the cage 8 or 12. On the base material 16 of the cage 8, 12 is applied a porous ceramic coating 9 which is at least as deep as possible an imbibition of lubricant from the surface of this coating. The porous coating 9, 10 may be applied, in the case of cages which consist of a ceramic or non-ceramic base material, by known coating processes or, in the case of cages which are made of a ceramic base material or glass ceramic, by special processing steps in the shaping process. The size and the number of pores 17 are chosen such that, on the one hand, the lubricant can penetrate into the porous layer 9, on the other hand, the surface of the cage 8 has a hardness that is high enough to withstand the stresses during operation in the cabinet.

  The friction values of the friction partners of the bearing 4 may increase over time by metal abrasion or other dross, for example, carbon dust, and the bearing may, by improper use, be subjected to stresses which cause stress points concentrated spatially in the bearing 4 and could cause bursting materials. Also, the guide surfaces, whether made in the form of a ceramic coating or glass ceramic or solid material, must be carried out so that these stresses are supported without shortening the expected life.

Claims (12)

  1. Dental hand instrument (1, 3) with at least one bearing having ceramic components (4), the bearing (4) having a plurality of rolling elements (5) which are guided by means of a cage (8). , 12), characterized in that the cage (8, 12) is formed at least at the location of the guide surfaces (8.1-8.3, 12.1-12.3) of ceramic or glass ceramic.   2. Hand instrument dentist (1, 3) according to claim 1, characterized in that the ceramic is a silicon nitride (S13N4).   3. Dental hand instrument (1, 3) according to one of claims 1 or 2, characterized in that the ceramic has, at least at the location of the guide surfaces (8.1-8.3, 12.1-1.2. 3), a porosity that is suitable for the absorption of lubricant.   4. Dental hand instrument (1, 3) according to one of claims 1 to 3, characterized in that the guide surface (8.1-8.3, 12.1-12.3) of the cage (8, 12) has a coating (9, 10) which is harder than unwanted foreign particles, in particular metal particles or carbon particles of an electric drive motor.   5. Dental hand instrument (1, 3) according to one of claims 1 to 4, characterized in that the thermal expansion of the cage (8, 12) corresponds to the thermal expansion of the rolling elements (5) and / or bearing rings (6, 7).   6. Hand instrument dentist (1, 3) according to one of claims 1 to 5, characterized in that the cage (8, 12) has set points of rupture for destructive disassembly.   7. dental hand instrument (1, 3) according to one of claims 1 to 6, characterized in that the cage (8, 12) has other bores which serve to reduce the weight and the mass inertia.   8. Hand instrument dentist (1, 3) according to claims 1 to 7, characterized in that the cage (8, 12) is reinforced by one or more non-ceramic rings (15).   9. dental hand instrument (1, 3) according to claim 8, characterized in that the rings (15) are claimed.   10. dental hand instrument (1, 3) according to one of claims 1 to 9, characterized in that the dental hand instrument (1) has a turbine and the bearing (4) can operate at at least 200,000 rpm. (3.333 t / sec.).   11. dental hand instrument (1, 3) according to one of claims 1 to 9, characterized in that the dental hand instrument (3) has an electric motor and the bearing (4) is arranged at the engine location and can operate at rotations of up to 50,000 rpm. (833 t / sec.). 12. Hand instrument dentist (3) according to claim 10, characterized in that it comprises a drive shaft which can operate in particular at rotations of up to 200,000 rpm. (3.333 t / sec.).