Dental drill

Abstract

The invention relates to a dental drill, having a main body made of Cr-Mo-N high-grade steel and a cover layer applied to the surface of the main body and comprising Zr and Hf, the average layer thickness of the cover layer being 0.5 - 3 µm.

Description

[0001] Dental drill

[0002] The invention relates to a dental drill with a highly wear-resistant and biocompatible coating.

[0003] Dental drills are primarily used to remove carious dentin. To achieve this, the dental drill must be able to work through hard dentin and must be correspondingly hard, resilient, and wear-resistant. Until now, dental drills have often been used as disposable drills. To be a sustainable, reusable product, a dental drill must have a long service life, meaning it must retain its sharpness and the integrity of its surface coating over long periods of use and through numerous thermal sterilization cycles. Furthermore, any coating should be biocompatible.

[0004] The object of the invention is therefore to provide a dental drill with a highly wear-resistant, biocompatible and durable coating.

[0005] This object is achieved by a dental drill according to patent claim 1 and a method for manufacturing according to patent claim 7. Further features, embodiments and advantages emerge from the dependent claims and the description.

[0006] One aspect of the invention relates to a dental drill comprising

[0007] (a) a base body made of stainless steel, comprising

[0008] 0.25 - 0.35 wt% C,

[0009] 14.0 - 16.0 wt% Cr,

[0010] 0.85 - 1.10 wt% Mo,

[0011] 0.30 - 0.50 wt% N,

[0012] < 1.00 wt% Mn, < 1.00 wt% Si,

[0013] < 0.03 wt% P and

[0014] < 0.025 wt% S, the remainder iron and unavoidable impurities, each impurity being < 0.03 wt%, and

[0015] (b) a covering layer applied to the surface of the base body, comprising

[0016] > 94.7 wt% Zr,

[0017] < 4.5 wt% Hf,

[0018] < 0.05 wt% C,

[0019] < 0.025 wt.% N, where the sum of Zr and Hf is > 99.2 wt.%, the sum of Fe and Cr is < 0.20 wt.%, and the average layer thickness of the covering layer is 0.5 - 3 pm.

[0020] Preferably, the stainless steel consists of the components

[0021] 0.25 - 0.35 wt% C,

[0022] 14.0 - 16.0 wt% Cr,

[0023] 0.85 - 1.10 wt% Mo,

[0024] 0.30 - 0.50 wt% N,

[0025] < 1.00 wt% Mn,

[0026] < 1.00 wt.% Si,

[0027] < 0.03 wt% P and

[0028] 0.025 wt% S, the remainder iron and unavoidable impurities, each impurity being < 0.03 wt%.

[0029] The specified weight percentages of stainless steel are based on the total mass of the stainless steel. The weight percentages of the top layer are based on the total weight of the top layer.

[0030] A further aspect of the invention relates to a method for producing a dental drill, comprising the steps of (a) applying a base body made of stainless steel, comprising

[0031] 0.25 - 0.35 wt% C,

[0032] 14.0 - 16.0 wt% Cr,

[0033] 0.85 - 1.10 wt% Mo,

[0034] 0.30 - 0.50 wt% N,

[0035] < 1.00 wt% Mn,

[0036] < 1.00 wt.% Si,

[0037] < 0.03 wt% P and

[0038] < 0.025 wt% S, the remainder iron and unavoidable impurities, each impurity accounting for < 0.03 wt%,

[0039] (b) a top layer is applied, comprising

[0040] > 94.7 wt% Zr,

[0041] < 4.5 wt% Hf,

[0042] < 0.05 wt% C,

[0043] < 0.025 wt.% N, where the sum of Zr and Hf is > 99.2 wt.%, the sum of Fe and Cr is < 0.20 wt.%, where the average layer thickness of the covering layer is 0.5 - 3 pm.

[0044] The dental drill according to the invention has a base body made of a stainless steel with a specific composition and a coating in the form of a cover layer, and the combination of the two special compositions of the base body and the cover layer, as well as the layer thickness of the cover layer, results in an extremely wear-resistant and thermally stable coating that maintains the sharpness of the drill over a long period of time and withstands a variety of thermal sterilization treatments.

[0045] For the purposes of the invention, the average layer thickness is understood to be the arithmetic mean of at least 3, preferably 5, measured layer thicknesses. For this purpose, the layer thickness is measured at at least 3, preferably 5, randomly selected locations, for example, under a microscope in a section perpendicular to the surface. The arithmetic mean of the measured layer thicknesses is then determined.

[0046] The surface hardness (also called edge hardness or boundary hardness) of the base body is defined as the Rockwell hardness, according to EN ISO 6508-1. Measurements are typically made according to ISO 6507 Part 1 / ASTM E384 (Vickers). These values ​​are then converted to Rockwell. Vickers is preferred due to the small dimensions of the parts.

[0047] The surface hardness (edge ​​hardness of the stainless steel base body) is preferably > 55 Hrc (Rockwell hardness), particularly preferably > 57 Hrc, further preferably 58 - 62 Hrc.

[0048] As stainless steel, a Cr-Mo-N steel (chromium-molybdenum-nitrogen steel) with the composition according to claim 1 is used. Preferably, the base body is made of stainless steel, comprising

[0049] 0.25 - 0.35 wt% C,

[0050] 14.5 - 15.5 wt% Cr,

[0051] 0.90 - 1.05 wt% Mo,

[0052] 0.30 - 0.50 wt% N,

[0053] 0.30 - 0.50 wt% Mn,

[0054] 0.50 - 0.70 wt% Si,

[0055] < 0.03 wt% P and

[0056] 0.025 wt% S, the remainder iron and unavoidable impurities, each impurity being < 0.03 wt%.

[0057] Preferably, the stainless steel consists of the components.

[0058] In a particularly preferred embodiment of the invention, the dental drill comprises a base body made of stainless steel, comprising 0.29 - 0.31 wt% C, 14.8 - 15.2 wt% Cr, 0.90 - 1.05 wt% Mo, 0.35 - 0.45 wt% N,

[0059] 0.35 - 0.45 wt% Mn,

[0060] 0.55 - 0.65 wt% Si,

[0061] < 0.03 wt% P and

[0062] < 0.025 wt.% S, the remainder iron and unavoidable impurities, each impurity

[0063] < 0.03 wt.%.

[0064] In the above stainless steel compositions, alloying elements commonly found in stainless steels can be added as additional components. In a preferred embodiment, the stainless steel comprises up to 0.8 wt.% Ni, more preferably up to 0.6 wt.% Ni, in particular 0.40-0.60 wt.% Ni. In a preferred embodiment, the stainless steel consists of the above-mentioned components.

[0065] In a further particularly preferred embodiment of the invention, the dental drill comprises a base body made of stainless steel, comprising

[0066] 0.25 - 0.35 wt% C,

[0067] 14.5 - 15.5 wt% Cr,

[0068] 0.90 - 1.05 wt% Mo,

[0069] 0.30 - 0.50 wt% N,

[0070] 0.30 - 0.50 wt% Mn,

[0071] 0.50 - 0.70 wt% Si,

[0072] < 0.8 wt% Ni, preferably 0.40 - 0.60 wt% Ni,

[0073] < 0.03 wt% P and

[0074] < 0.025 wt% S, the remainder iron and unavoidable impurities, each impurity being < 0.03 wt%.

[0075] In yet another particularly preferred embodiment of the invention, the dental drill comprises a base body made of stainless steel, comprising

[0076] 0.29 - 0.31 wt% C,

[0077] 14.8 - 15.2 wt% Cr,

[0078] 0.90 - 1.05 wt% Mo, 0.35 - 0.45 wt% N,

[0079] 0.35 - 0.45 wt% Mn,

[0080] 0.55 - 0.65 wt% Si,

[0081] < 0.8 wt% N i, preferably 0.40 - 0.60 wt% Ni,

[0082] < 0.03 wt% P and s= 0.025 wt% S, the remainder iron and unavoidable impurities, each impurity being < 0.03 wt%.

[0083] A cover layer is present on at least part of the surface of the base body. The cover layer is a Zr coating with the composition according to claim 1. According to the invention, the cover layer can be combined with all described base bodies, in particular also with the preferred and particularly preferred compositions of the base body. The cover layer can be applied by methods known to those skilled in the art, preferably by PVD (physical vapor deposition) coating.

[0084] In a preferred embodiment of the invention, the dental drill thus comprises

[0085] (a) a base body made of stainless steel, comprising

[0086] 0.25 - 0.35 wt% C,

[0087] 14.5 - 15.5 wt% Cr,

[0088] 0.90 - 1.05 wt% Mo,

[0089] 0.30 - 0.50 wt% N,

[0090] 0.30 - 0.50 wt% Mn,

[0091] 0.50 - 0.70 wt% Si,

[0092] < 0.8 wt% Ni, preferably 0.40 - 0.60 wt% Ni,

[0093] < 0.03 wt% P and

[0094] < 0.025 wt% S, the remainder iron and unavoidable impurities, each impurity being < 0.03 wt%, and

[0095] (b) a covering layer applied to the surface of the base body, comprising > 94.7 wt.% Zr,

[0096] < 4.5 wt% Hf,

[0097] < 0.05 wt% C,

[0098] < 0.025 wt.% N, where the sum of Zr and Hf is > 99.2 wt.%, the sum of Fe and Cr is < 0.20 wt.%, and the average layer thickness of the covering layer is 0.5 - 3 pm.

[0099] In a preferred embodiment, the cover layer is applied directly to the stainless steel base body. In other words, there is no additional layer between the cover layer and the base body.

[0100] In one embodiment of the dental drill according to the invention, the covering layer is only present on selected areas of the dental drill. Such an embodiment can be produced by applying the covering layer only to selected areas of the dental drill, preferably in all areas except for the connecting shaft of the drill. However, applying it to selected areas is often technically difficult with the conventional PVD deposition process. Therefore, it is preferred that the covering layer is applied completely, i.e. to the entire surface. If the layer is only to be applied in selected areas, the layer is then removed again in the other areas. Preferably, the coating (covering layer) is applied to the entire surface of the dental drill. It is further preferred that the covering layer is applied to the entire surface of the base body, with the exception of the connecting shaft.

[0101] According to the invention, the average layer thickness of the cover layer is 0.5 - 3 pm, preferably 1.2 - 2.6 pm, in particular 1.4 - 2.2 pm. These layer thicknesses result in a particularly wear-resistant and durable coating.

[0102] It is understood that the features mentioned above and those to be explained below can be used not only in the specified combinations, but also in other combinations or on their own, without departing from the scope of the present invention. The advantages of features or combinations of several features mentioned are merely exemplary and can be used alternatively or cumulatively. The combination of features of different embodiments of the invention or of features of different patent claims is possible, deviating from the selected references to the patent claims.

[0103] The invention is further explained below using an example. Example

[0104] A Zr covering layer of a composition according to claim 1 with an average layer thickness of 2 pm is applied to a dental drill made of Cr-Mo-N stainless steel with a composition according to claim 1 by PVD coating under usual process conditions (150 - 500 °C in high vacuum with process gas argon and nitrogen).

Claims

Claims 1 . Dental drill, comprising (a) a base body made of stainless steel, comprising 0.25 - 0.35 wt% C, 14.0 - 16.0 wt% Cr, 0.85 - 1.10 wt% Mo, 0.30 - 0.50 wt% N, < 1.00 wt% Mn, < 1.00 wt.% Si, < 0.03 wt% P and < 0.025 wt% S, the remainder iron and unavoidable impurities, each impurity being < 0.03 wt%, and (b) a covering layer applied to the surface of the base body, comprising > 94.7 wt% Zr, < 4.5 wt% Hf, < 0.05 wt% C, < 0.025 wt.% N, where the sum of Zr and Hf is > 99.2 wt.%, the sum of Fe and Cr is < 0.20 wt.%, and the average layer thickness of the covering layer is 0.5 - 3 pm.

2. Dental drill according to claim 1, characterized in that the stainless steel 0.25 - 0.35 wt% C, 14.5 - 15.5 wt% Cr, 0.90 - 1.05 wt% Mo, 0.30 - 0.50 wt% N, 0.30 - 0.50 wt% Mn, 0.50 - 0.70 wt% Si, < 0.03 wt% P and < 0.025 wt.% S, preferably additionally 0.40 - 0.60 wt.% Ni.

3. Dental drill according to claim 1 or 2, characterized in that the average layer thickness of the cover layer is 1.2 - 2.6 pm.

4. Dental drill according to one of the preceding claims, characterized in that the surface hardness of the base body is > 55 Hrc, preferably 58 - 62 Hrc.

5. Dental drill according to one of the preceding claims, characterized in that the cover layer is applied directly to the base body made of stainless steel.

6. Dental drill according to one of the preceding claims, characterized in that the dental drill consists of the base body and the cover layer.

7. A method for producing a dental drill according to any one of claims 1 to 6, comprising the steps of (a) on a stainless steel base body comprising 0.25 - 0.35 wt.% C, 14.0 - 16.0 wt% Cr, 0.85 - 1.10 wt% Mo, 0.30 - 0.50 wt% N, < 1.00 wt% Mn, < 1.00 wt.% Si, < 0.03 wt% P and < 0.025 wt% S, the remainder iron and unavoidable impurities, each impurity accounting for < 0.03 wt%, (b) a top layer is applied, comprising > 94.7 wt% Zr, < 4.5 wt% Hf, < 0.05 wt% C, < 0.025 wt.% N, where the sum of Zr and Hf is > 99.2 wt.%, the sum of Fe and Cr is < 0.20 wt.%, where the average layer thickness of the covering layer is 0.5 - 3 pm.

8. Method according to claim 7, characterized in that the cover layer is applied by PVD coating.

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