Patent Description:
The process of drilling a hole into a patient's bone, for example for preparing a dental implant bed, is very sensitive with respect to the temperatures appearing at the bone of the patient during the drilling action. If the patient's bone is damaged because of too high local temperatures during the drilling action, the following implanting and healing process is significantly complicated.

To avoid a temperature-caused damage of the bone, local bone temperatures of more than <NUM> for more than <NUM> to <NUM> seconds must be avoided.

A direct temperature measurement at the patient's bone is difficult to provide. <CIT> discloses a surgical bone drill bit comprising a thermochromic material at the distal end. The color of the thermochromic material is evaluated by an optical device using an optical fibre located within a center bore of the drill body.

<CIT> describes to provide a drill bit with an integrated miniaturized temperature sensor. But it is not described in this document how to energize the rotating sensor and how to transmit the sensor's temperature information from the rotating drill bit to the non-rotating handpiece.

<CIT> discloses a temperature-sensitive optical indicator with irreversible color change for a dental bone drill bit for irreversibly indicating that the bone drill bit has been sterilized.

It is an object of the invention to provide a bone drill bit allowing the drilling person to have a temperature indication during the drilling action. This object is achieved with a bone drill bit with the features of claim <NUM>.

The bone drill bit according to the invention is preferably a dental bone drill bit, and is provided with a metal drill shaft body being provided, seen in longitudinal direction, with a drilling section defined by a distal shaft section which is provided with cutting edges and a clamping section at the proximal drill bit end provided with a clamping surface where the drill bit is clamped by clamping means of a handpiece.

The drill shaft body is provided with a passive temperature-sensitive optical indicator which is fixed to the metal drill shaft body in a thermo-conducting manner. The term 'passive' in this context means that the indicator does not provide an electrical signal which could be evaluated electrically. The term 'thermo-conducting' in this context means that no thermo-insulating layer, for example no layer comprising a substantive volumetric share of air, is provided between the optical indicator and the metal drill shaft body.

The indicator shows different colors, preferably colors visible for a human being, which indicate different temperatures. The indicator's color-change can be somehow proportional to the corresponding temperature-change. Alternatively and preferably, the color change charteristics of the indicator can be dramatic around the critical temperature in a relatively small defined temperature interval of a few Kelvin, whereas, above and below this defined and relatively small temperature interval, the indicator color does not substantially change with the drill bit body temperature.

The color-changing property of the indicator is reversible so that the drill bit can be used a couple of times for a couple of bone drilling procedures.

The drill shaft body of the bone drill bit is generally made of 'medical steel' which is basically an inert, non-corrosive and sufficiently hard steel. Medical steel generally has a relatively good and high temperature conductivity so that the heat at the distal drilling section of the drill shaft body is heat conducted relatively quickly in longitudinal direction through the drill shaft body to the proximal end section of the drill bit. The temperature-sensitive optical indicator is provided proximately of the drilling section so that the temperature information is somehow visible at the proximal end section of the bone drill bit. The temperature-sensitive optical indicator allows to relativity simply provide a visible or optically detectable indication about the temperature at the drill section of the bone drill bit.

The temperature-sensitive optical indicator is defined by a color-changing substance changing its visible-spectrum color depending on the temperature of the drill shaft body. The term 'visible-spectrum' in this context means that the color of the color-changing indicator substance is visible for a human being. As a result, the person providing the drilling action is able to see and to watch the color shift of the indicator and, therefore, is able to see if the indicator color changes to a color which indicates an exceed of the medically allowed maximum temperature at the drill section of the bone drill bit.

The temperature-sensitive optical indicator is defined by a visible indicator ring being provided around the drill shaft body. More preferably, the optical indicator is located axially between the drilling section and the clamping section of the drill shaft body. The ring-like indicator ring is visible which means that the indicator ring does not dive into the drill hole during the drilling operation and is not clamped by a clamping means. Preferably, the term 'visible' in this context means that the ring is generally visible during the drilling action for the person providing the drilling action.

Generally, the optical indicator ring is applied to the drill shaft body during the manufacturing process of the bone drill bit. Alternatively, the optical indicator ring can be provided separately, and can be manually applied to the drill shaft body by simply shifting the indicator ring over the drill shaft body. This could be done by the person providing the drilling action.

Alternatively or additionally, the temperature-sensitive optical indicator is located at the proximal end surface of the drill shaft body. Some handpieces of some manufacturers allow to see the proximal end surface of the clamped drill shaft body so that the optical indicator located at the proximal end surface is easily visible during the drilling action for a person providing the drilling action.

Preferably, a reference color area can be provided next to or directly adjacent to the temperature-sensitive optical indicator to facilitate the human detection and evaluation of the color of the optical indicator. The reference color area can have the color of the optical indicator indicating an exceeding temperature or, alternatively, can have the color of the optical indicator indicating an allowed temperature.

Preferably, the temperature-sensitive optical indicator is covered by a temperature-isolating and visually transparent protection shielding. The protection shielding thermally isolates the optical indicator so that a cooling liquid which can be present at the outside surface of the bone drill bit during the drilling action does not significantly cool down the temperature-sensitive optical indicator. Additionally, the protection shielding protects the optical indicator mechanically. The protection shielding is transparent so that the optical indicator is visible through the protection shielding.

According to a preferred embodiment, a separate heat conductor is provided within the drill shaft body. The heat conductor is at least in part axially overlapping with the drilling section and with the temperature-sensitive indicator. The temperature conductivity of the heat conductor is higher than the temperature conductivity of the drill shaft body. The heat conductor improves the conductive heat transfer from the drilling section to the temperature-sensitive optical indicator so that the temperature at the optical indicator correlates more with the temperature of the drill shaft body at the drill section and the temperature adaption delay is reduced significantly.

Preferably, the heat conductor is provided with a longitudinal conductor pin located in a central cylindrical conductor bore in the drill shaft body.

The conductor pin defines the core of the bone drill bit over a substantial length of the bone drill bit.

According to a preferred embodiment of the invention, the color-changing substance changes its color by more than <NUM> at an indicator temperature shift from <NUM> to <NUM>. The color-changing substance is provided with suitable color changing particles and can thereby be defined to show a strong color changing behavior when the temperature arrives at <NUM>.

Preferably, the drill bit is for dental applications and the maximum outside diameter of the drill shaft body is less than <NUM>. Dental bone drill bits are very compact and small in diameter so that it is very difficult to provide an electronic temperature sensor within the drill body. Providing a passive temperature-sensitive optical indicator at the outside surface of the bone drill bit avoids any mechanical weakening of the drill shaft body.

According to another concept of the invention, a handpiece with a clamping arrangement for clamping the bone drill bit according to one of claims <NUM> to <NUM> is provided. The handpiece is provided with a static, non-rotating color detection means for detecting the color of the passive temperature-sensitive indicator at the rotating bone drill bit. In other words, the color of the optical indicator is detected by a color detection means, which is a color sensor providing an electrical signal. The color detection means allows, for example, to stop or to decelerate the rotation of the bone drill bit if the optical indicator indicates a critical shaft body temperature.

Two embodiments of the invention are explained with reference to the enclosed drawings, wherein.

<FIG> and <FIG> both show a bone drill bit <NUM>;<NUM>' for dental applications. The bone drill bit <NUM> of <FIG> is provided with a drill shaft body <NUM> made out of medical steel. Seen in longitudinal direction, the bone drill bit <NUM> has a distal drill section <NUM>, a proximal clamping section <NUM> and is provided with a temperature-sensitive optical indicator <NUM> between the sections <NUM>,<NUM>. The drill shaft body <NUM> is provided with a helical flute <NUM> which defines the drill section <NUM>. The drill shaft body <NUM> is provided with a clamping surface <NUM>' at the clamping section <NUM>. The clamping surface <NUM>' can be, seen in cross section, of circular or polygonal shape. The maximum diameter d of the drill shaft body <NUM> is <NUM>,<NUM>.

The temperature-sensitive optical indicator <NUM> is provided as a visible indicator ring <NUM> being in a direct and heat-conductive connection to the drill shaft body <NUM>. The visible indicator ring <NUM> is embedded in a circular ring-like recess <NUM> and is covered with a transparent, temperature-isolating and ring-like protection shielding <NUM> completely covering the optical indicator <NUM>. The protection shielding <NUM> can be defined by a suitable transparent plastic material body <NUM>.

The optical indicator <NUM> is defined by a color changing substance <NUM> having a reversible or, not forming part of the invention, irreversible color changing behavior.

The visible-spectrum color of the color-changing substance <NUM> changes its color with at least <NUM> at a temperature shift from <NUM> to <NUM>. The color-changing substance can be any suitable thermochromatic substance, for example a substance comprising liquid crystals and/or leuco dyes.

A ring-like reference color area <NUM> is provided distally directly adjacent to the optical indicator <NUM>. If the indicator <NUM> and the reference color area <NUM> are not covered by a handpiece, the reference color area <NUM> facilitates to the person providing the drilling action to optically detect a relevant color change of the optical indicator <NUM> by comparing the colors of the optical indicator <NUM> and the reference color area <NUM>.

The drill shaft body <NUM> is provided with a central axial conductor bore <NUM> which is completely filled with a heat conductor pin <NUM> defining a heat conductor <NUM>. The heat conductor <NUM> is made of a material having a better thermal conductivity than the medical steel of the drill shaft body <NUM>. The heat conductor <NUM>, seen in longitudinal direction, substantially overlaps the drill section <NUM> and the optical indicator <NUM>. The heat conductor <NUM> can, for example, be made of copper or Tungsten.

The drill bit <NUM> is clamped and engaged in a hand piece <NUM> which is provided with a clamping means <NUM> holding and engaging the clamping section <NUM> of the drill shaft body <NUM>. The clamping means <NUM> is rotated and driven by a drill machine motor <NUM>. The drill machine handpiece <NUM> of this embodiment is also provided with a color detection means <NUM> which is a color sensor and is also provided with a light emitter illuminating the rotating optical indicator <NUM>. The color detection means <NUM> can 'see' the rotating optical indicator <NUM> so that the indicator color indicating the temperature of the drill shaft body <NUM> at the drill section <NUM> can indirectly be detected by the color detection means <NUM>. The handpiece <NUM> is also provided with a control device <NUM> which can reduce the rotational speed of the drill machine motor <NUM> if the detected temperature should exceed a maximum defined maximum temperature.

Alternatively, the handpiece could be designed to allow a person to see the optical indicator <NUM> during the drilling action so that the person providing the drilling action can see by himself if the optical indicator <NUM> indicates a critical temperature.

Claim 1:
A bone drill bit (<NUM>;<NUM>') with a metal drill shaft body (<NUM>) being provided with a drilling section (<NUM>) and a clamping section (<NUM>),
wherein the drill shaft body (<NUM>) is provided with a passive temperature-sensitive optical indicator (<NUM>;<NUM>') being in a thermo-conducting connection to the drill shaft body (<NUM>), and wherein the temperature-sensitive optical indicator (<NUM>) is defined by an indicator ring (<NUM>) being provided around the drill shaft body (<NUM>) and/or the temperature-sensitive optical indicator (<NUM>') is located at the proximal end surface (<NUM>) of the drill shaft body (<NUM>),
characterised in that the temperature-sensitive optical indicator (<NUM>; <NUM>') is defined by a color-changing substance (<NUM>) configured to reversibly change its visible-spectrum color depending on the temperature of the drill shaft body (<NUM>).