Method for determining the trajectory of a machining tool, for the manufacture of a dental prosthesis pillar

Abstract

The invention relates to a method for determining the trajectory of a machining tool having several machining passes, for the manufacture of a pillar (2) of a dental prosthesis, said pillar (2) comprising a longitudinal axis (X) around which are developed a first so-called high part forming a first section (A) and having a first cross-section defining a first external surface, a second so-called low part having a second cross-section defining a second external surface, and an intermediate part forming a collar between the low part and the high part and having a personalized profile called emergence profile (20), this emergence profile (20) having a non-planar closed directrix curve and extending respectively, to form on said intermediate part, respectively towards the high part and towards the low part, a second section (B) and a third section (C). Figure to be published with the abstract: Figure 2A

Description

Title of the invention: Method for determining the trajectory of a machining tool, for the manufacture of a dental prosthesis pillar Technical field of the invention

[0001] The present invention relates to a method for determining the trajectory of a machining tool, for the manufacture of a pillar of a dental prosthesis. State of the art

[0002] When making a dental prosthesis, an abutment is used to act as an interface between the implant and the crown. Each abutment is specific to an implant and a crown, which is custom-made for the patient.

[0003] Patent application FR3031667A1 describes a method of manufacturing a dental prosthesis abutment.

[0004] The abutment comprises a lower part which is screwed into the implant and an upper part intended to receive the crown (see [Fig. 1]). Between its lower part and its upper part, the abutment comprises an intermediate part having a personalized profile, with in particular an emergence profile in the form of a collar, designed to match the curve of the dental tissues. More precisely, this intermediate part has a non-planar closed directing curve and develops, on one side towards the lower part of the abutment and on the other side towards the upper part of the abutment, by two junction zones, which are each created by projection of this directing curve.

[0005] The pillars are notably manufactured using a method which consists of obtaining generically shaped pillars from a catalog and retouching them by machining in order to conform them to the patient's anatomy. These pillars are thus acquired pre-machined, then machined by a finishing cycle in the dental office to obtain a final shape personalized to the patient's anatomy.

[0006] It is essential to precisely reproduce the geometry of the pillar's emergence profile, in order to obtain a perfectly adapted design. To machine such a pillar and obtain its personalized shape, the tool conventionally follows a helical trajectory, over the entire height of the pillar.

[0007] However, this helical trajectory often does not allow satisfactory machining of the pillar at its intermediate part, that is to say at the part which includes its emergence profile.

[0008] The aim of the invention is to propose a method for determining the trajectory of a machining tool, suitable for producing a pillar of a dental prosthesis, which ultimately allows machining to be optimized at its intermediate part, taking into account the particular shape of the emergence profile. Statement of the invention

[0009] This aim is achieved by a method for determining the trajectory of a machining tool having several machining passes, for the manufacture of a pillar of a dental prosthesis, said pillar comprising a longitudinal axis around which are developed a first part called high forming a first section and having a first cross-section defining a first external surface, a second part called low having a second cross-section defining a second external surface, and an intermediate part forming a collar between the low part and the high part and having a personalized profile called emergence profile, this emergence profile having a non-planar closed directrix curve and extending respectively, to form on said intermediate part, respectively towards the high part and towards the low part, a second section and a third section,said method consisting of creating said trajectory of the machining tool following a helix to machine the intermediate part, the helix trajectory being produced by projection of the guide curve onto said second section and the third section.

[0010] According to a particular feature, to determine the trajectory of the tool for machining a section, among said second section and said third section of the intermediate part, the method consists of: - Create generators of said section, - Create several points on the generators, - Create the helical trajectory that passes through said several points.

[0011] According to another particularity, said generators are created in: - Defining several points on the entire direction curve of the emergence profile, - Defining segments on the section between each point defined along the guide curve, - Projecting each segment obtained in order to create each generator.

[0012] According to another particularity, each machining pass is composed of several points each belonging to a distinct generator and in that, for each pass i, the coordinates of each point are defined by the following relation:

[0013] Pi(j)=Cj(tiO+j / (M*N))

[0014] In which: - Pi(j) corresponds to point j of pass i; - Cj is the generating curve on which the point P(j) of pass i is positioned; - tiO is defined by the relation tiO=i / M in which i corresponds to the pass number and M corresponds to the total number of passes to machine the section; - N corresponds to the total number of points in each pass;

[0015] According to another feature, the method comprises a step of determining the number of machining passes necessary to machine said section which consists of: - Determine the longest curve among the generating curves of the section and note L its length; - Define the maximum offset D between two passes, this offset being dependent on the desired surface condition at the end of machining; - Determine the number M of passes required for machining the section, this number M being defined by the relation M=L / D+1;

[0016] According to another feature, the method comprises a preliminary step of dividing the pillar to be obtained into four separate sections, said upper part being the first section, the lower part being the fourth section and the intermediate part being composed of the second section and the third section.

[0017] According to another particularity, for the first section and the fourth section to be machined, the trajectory followed by the machining tool follows a constant pitch helix.

[0018] According to another feature, the method comprises a step of concatenating the trajectories calculated to machine each section of the pillar.

[0019] The invention also relates to a pillar of a dental prosthesis, the pillar being obtained by the method as defined above. Brief description of the figures

[0020] Other characteristics and advantages will appear in the detailed description which follows, given with reference to the appended drawings in which: - [Fig. 1] represents in perspective and exploded view the architecture of a dental prosthesis; - Figures 2A to 2J represent the different stages of the method of the invention;

[0021] Detailed description of at least one embodiment

[0022] The invention applies to a method for determining the trajectory of a machining tool, in the field of dental prosthetics.

[0023] The method of the invention is implemented using a computer program executed by a processing unit of the machining machine or associated with it. It is stored in said processing unit on a readable memory medium. All types of media, integrated into the machine or in a separate processing unit, removable or accessible through a communication network, and conventionally used to store a computer program, may be considered.

[0024] The machining machine has four axes, including a rotary axis on which the workpiece is placed.

[0025] The method of the invention is implemented by applying an algorithm whose steps are described below.

[0026] The method is dedicated to determining the trajectory of the tool intended for machining a pillar 2 (“abutment” in English) used for producing a dental prosthesis. Such a pillar makes it possible to make the connection between the bone implant 1 and the crown 3 ([Fig.l]).

[0027] The pillar 2 extends from the bottom to the top, along a so-called longitudinal axis (X). In Figures 2A to 2J, the pillar 2 is shown horizontally, so as to be parallel to the machining direction. In the attached figures, the machining direction is indicated by the arrow FL

[0028] For machining, the tool follows a path around the longitudinal axis (X).

[0029] Conventionally, this type of pillar 2 is often obtained pre-machined, then undergoes finishing machining, for example directly in the dental office, to be personalized to the patient's anatomy.

[0030] The pillar 2 to be obtained comprises a lower part which is screwed into the implant 1 and an upper part intended to receive the crown 3. Between its lower part and its upper part, the pillar 2 comprises an intermediate part having a personalized profile, with in particular an emergence profile 20 in the form of a collar, designed to match the curve of the dental tissues. More precisely, this intermediate part has a non-planar closed directing curve and develops, on one side towards the lower part of the pillar and on the other side towards the upper part of the pillar, by two junction zones (hereinafter sections), which are each created by projection of this directing curve.

[0031] Below, the terms “upstream” and “downstream” are to be understood along the longitudinal axis (X), going from the top of the pillar to the bottom of the pillar, that is to say in the direction of machining.

[0032] The invention aims in particular to optimize the trajectory of the machining tool at the level of the intermediate part of the pillar 2, with a view to obtaining a personalized shape which best follows the shape of the emergence profile 20.

[0033] The method of the invention is based on the final shape of the pillar 2 to be obtained to define the trajectory of the machining tool.

[0034] The determination of the machining path is described below.

[0035] Division of the pillar into several juxtaposed sections

[0036] El - [Fig.2A]: The processing unit divides pillar 2 into four separate sections, following its longitudinal direction: - A first section A, of generally truncated cone shape, going from the top of the pillar to a first cross section, located upstream of the emergence profile 20. - A second section B going from said first cross section to the emergence profile 20. - A third section C going from the emergence profile 20 to a second cross section located downstream of the emergence profile 20. - A fourth section D, of truncated cone shape, going from the second cross section to a base cross section of pillar 2.

[0037] Each cross section forms a boundary between two distinct and successive sections.

[0038] Path for machining the first section A and the fourth section D

[0039] E2 - [Fig.2B]: On the first section A and the fourth section D, the method determines two helical trajectories T_A, T_D, advantageously with a constant pitch. The direction of each helix is ​​defined by the machining direction. The pitch of the helical trajectory for machining the first section A and the pitch of the trajectory for machining the fourth section D may be identical or distinct.

[0040] The method then consists of working independently on the second section B and the third section C.

[0041] The processing unit applies the same steps described below for these two sections. Path for machining the second section B

[0042] The first phase is a preparation phase for determining the trajectory of the machining tool. This preparation phase includes the following steps: - E3 - [Fig.2C]: Following the emergence profile 20, define a number N of points. This number must be sufficiently large, for example greater than 50. These points therefore belong to the direction curve of the emergence profile 20. Then, it is a question of creating N segments Si (i ranging from 1 to N), each segment Si has as its first end a point defined in the previous step (belonging to the direction curve of the emergence profile 20) and extends parallel to the longitudinal axis on the section B, that is to say up to a point present at the border between the section B and the section A. - E4 - [Fig.2D]: Project the N segments obtained so as to follow the curvature of section B and thus obtain N curves Ci which follow the generators of the pillar at the level of the second section B.

[0043] The next phase is a phase of determining the trajectory of the machining tool, from the N curves obtained during the preparation phase.

[0044] This determination phase (step E5) is implemented in the following manner, in conjunction with [Fig.2E]: - The curves generated during the preparation phase are noted Ci(t), with: • i ranging from 0 to N-1 and N being the total number of curves generated during step E4; • t being a normalized curvilinear parameter in the domain [0; 1];

[0045] It is thus understood that the term Ci(0) and the term Ci(l) respectively define the end of the curve Ci located at the level of the border with the first section A and the end of the curve Ci located at the level of the border with the third section C.

[0046] The arc length, designated L_arc, between Ci(0) and Ci(l) can be calculated by the following relation:

[0047] L_arc = Li*t in which Li corresponds to the total length of the curve Ci. - Determine the longest curve among the N generated curves and note L its length;

[0048] It is then a question of being able to determine the number of passes necessary to machine this second section B. As a reminder, a pass is formed from a 360° trajectory around the longitudinal axis (X) (axis of rotation). - Define the maximum offset D between two passes, this offset being dependent on the desired surface condition at the end of machining;

[0049] It is understood that the more passes the trajectory has, the smaller the offset D. D is a parameter predefined by the pillar manufacturing user. - Determine the number M of passes required for machining the second section B. This number M is defined by the relation M=L / D+1

[0050] This involves considering the longest curve (of length L) among the N curves generated during the preparation phase, and considering the maximum offset that one wishes to apply between two successive passes. - Calculate the points that form each pass;

[0051] Each pass consists of N points, one point per initially generated curve. Each point is denoted Pi(j) for pass i, with i ranging from 0 to Ml and j ranging from 0 to Nl.

[0052] Each point of a pass i is defined by the formula:

[0053] Pi(j)=Cj(t)

[0054] In which: - t corresponds to the coordinate taken by point Pj of pass i on curve Cj; - j identifies each point of the pass considered; each pass has N points, as many as curves generated;

[0055] We thus understand that on each pass i, the first point j=0 has the coordinate t=0 and the last point of the pass has the coordinate t=l.

[0056] In [Fig.2E], each pass is identified by the reference Pass_i, with i ranging from 0 to M-1.

[0057] More precisely, the coordinate of each new point is defined by the following relation:

[0058] Pi(j)=Cj(tiO+j / (M*N))

[0059] In which: - Pi(j) corresponds to point j of pass i; each pass thus has N points since each point belongs to one of the curves generated during the preparation phase. - Cj is the curve on which point Pi(j) of pass i is positioned; - tiO is defined by the relation ti0=i / M in which i corresponds to the number of the pass and M corresponds to the total number of passes to machine the section; - N corresponds to the number of points in each pass (one point per curve);

[0060] For each pass i, the trajectory is defined by the set of points j, each point belonging to a curve Cj. Given that, for each new point, t increases by j / (M*N), the trajectory evolves by incrementing the value of j (from 0 to Nl).

[0061] The processing unit applies the principles described above for each new pass of section B. The set of M*N points (i.e. the points defining the trajectory of all the passes) constitutes the trajectory T_B to be followed by the machining tool to machine the pillar on its second section B.

[0062] [Fig.2F] thus shows an example of trajectory T_B which can be used to machine the second section B. Path for machining the third section C

[0063] As indicated above, steps E3 to E5 are implemented in an identical manner to create the trajectory T_C of the tool on the third section C.

[0064] [Fig.2G] thus shows the creation of the segments Si on this third section C (step E3 above).

[0065] [Fig.2H] shows the projection of the segments forming the N curves Ci (step E4 above).

[0066] Step E5 of calculating the trajectory is then reproduced in an identical manner.

[0067] [Fig.21] thus shows the trajectory T_C of the tool for machining the third section C. Total trajectory

[0068] The union of the curves obtained for each section A, B, C, D forms the total primary trajectory T_tot, this must be reprojected onto the part to form the trajectory of the machining tool to machine the pillar 2 ([Fig.2J]).

[0069] Once this trajectory is completed, the processing unit is configured to send commands to the various actuators of the machining machine to machine the part according to the determined trajectory.

[0070] The method of the invention has numerous advantages, including: - It allows personalized machining of a dental prosthesis abutment; - It allows the shape of the pillar's emergence profile to be taken into account; - It is simple and reliable to implement;

Claims

Claims

1. Method for determining the trajectory of a machining tool having several machining passes, for the manufacture of a pillar (2) of a dental prosthesis, said pillar (2) comprising a longitudinal axis (X) around which are developed a first so-called high part forming a first section (A) and having a first cross-section defining a first external surface, a second so-called low part having a second cross-section defining a second external surface, and an intermediate part forming a collar between the low part and the high part and having a personalized profile called emergence profile (20), this emergence profile (20) having a non-planar closed directrix curve and extending respectively, to form on said intermediate part, respectively towards the high part and towards the low part, a second section (B) and a third section (C),said method consisting of creating said trajectory of the machining tool following a helix to machine the intermediate part, said method being characterized in that this helix trajectory is produced by projection of the guide curve onto said second section (B) and the third section (C).,

2. Method according to claim 1, characterized in that, to determine the trajectory of the tool for machining a section, among said second section (B) and said third section (C) of the intermediate part, the method consists of: - Creating generators of said section, - Creating several points on the generators, - Creating the helical trajectory which passes through said several points.

3. Method according to claim 2, characterized in that said generators are created by: - ​​Defining several points on the entire direction curve of the emergence profile (20), - Defining segments on the section between each point defined along the direction curve, - Projecting each segment obtained in order to create each generator.

4. Method according to claim 2 or 3, characterized in that each machining pass is composed of several points each belonging to a distinct generator and in that, for each pass i, the coordinates of each point are defined by the following relation: Pi(j)=Cj(tiO+j / (M*N)) In which: - Pi(j) corresponds to point j of pass i; - Cj is the generator curve on which point P(j) of pass i is positioned; - tiO is defined by the relation tiO=i / M in which i corresponds to the number of the pass and M corresponds to the total number of passes for machining the section; - N corresponds to the total number of points of each pass;

5. Method according to claim 4, characterized in that it comprises a step of determining the number of machining passes necessary to machine said section which consists of: - Determining the longest curve among the generating curves of the section and denoting L its length; - Defining the maximum offset D between two passes, this offset being dependent on the desired surface condition at the end of machining; - Determining the number M of passes necessary for machining the section, this number M being defined by the relation M=L / D+1;

6. Method according to one of claims 1 to 5, characterized in that it comprises a preliminary step of dividing the pillar to be obtained into four separate sections, said upper part being the first section (A), the lower part being the fourth section (D) and the intermediate part being composed of the second section (B) and the third section (C).

7. Method according to claim 5, characterized in that for the first section and the fourth section to be machined, the trajectory followed by the machining tool follows a constant pitch helix.

8. Method according to claim 7, characterized in that it comprises a step of concatenating the trajectories calculated to machine each section of the pillar.

9. Pillar of a dental prosthesis, characterized in that it is obtained by the method as defined in one of the preceding claims.

Images