Method for designing a connector
A method for designing a connector between a first and a second element of a dental restoration, such as a connector between coping and coping, or coping and pontic, or pontic and pontic of a bridge, which is characterized by the steps of computing a (first) model of the first element and a (second) model of the second element, defining a connecting straight line between the first model and the second model, computing edge curves (γ 0, γ4 ) on the first model and the second model, whereby the edge curves are defined by origins of surface normal vectors of the models, which satisfy boundary conditions relative to the connecting line, computing offset curves (γ 1, γ3 ) on the first model and the second model from the first edge curves, and connecting the first edge curves and the offset curves of the first model and of the second model and computing the connector on the basis of the course of the connection between the curves.
1. A CAD/CAM method for designing a connector between one first and one second element of a dental restoration, where for generating data required for the production of the connector, the connector is designed comprising the steps of:
computing a first model of the first element and a second model of the second element;
defining a connecting straight line between the first model and the second model;
computing edge curves (γ 0 , γ 4 ) on the first model and the second model, respectively, the edge curves being defined by the origins of surface normal vectors of the models, which satisfy boundary conditions relative to the connecting line;
computing offset curves (γ 1 , γ 3 ) on the first model and the second model, respectively, from the edge curves; and
connecting the edge curves and the offset curves of the first model and the second model, and computing the connector on the basis of the path of the connection between the curves.
2. The method of claim 1 , additionally comprising specifying a third curve (γ 2 ), pierced by the connecting straight line, between the first model and the second model, wherein the connector has a course aligned to the connections between the first edge curves, the offset curves, and the third curve.
3. The method of claim 2 , wherein the third curve (γ 2 ) possesses a circular shape, having a center which is passed by a second centroid-connecting straight line, which extends between the centroids of the edge curves or of the surfaces enclosed by the edge curves.
4. The method of claim 3 , wherein the third curve is pierced by the second centroid-connecting straight line, said second centroid-connecting straight line extending between the centroids of the edge curves or of the surfaces enclosed by the edge curves, whereby a third curve is pierced by the second centroid-connecting straight line in the middle between the centroids.
5. The method of claim 4 , wherein the third curve is located in a plane, which is defined by vectors that originate in centers of additional third centroid-connecting straight lines, which extend between centroids of equal segments of the edge curves or of surface regions of the surfaces of the first and second model enclosed by the edge curves.
6. The method of claim 5 , wherein each edge curve is subdivided into three equal segments, and from each segment centroid originates one of the third centroid-connecting straight lines.
7. The method of claim 3 , wherein the radius of the third curve substantially corresponds to one half of the sum of average radii of the edge curves of the first and second models.
8. The method of claim 2 , wherein the third curve (γ 2 ) possesses a geometry different from that of a circle.
9. The method of claim 8 , wherein the third curve possesses polygonal geometry.
10. The method of claim 1 , wherein as boundary condition for the position of the origin of the surface normal vector defining the edge curve (γ 0 , γ 4 ), one specifies an angle α between the connecting straight line and the surface normal vector.
11. The method of claim 1 , wherein as boundary condition for the position of the origin of the surface normal vector defining the edge curve (γ 0 , γ 4 ), one specifies a facing distance to be maintained relative to a preparation margin of at least one of the first and second elements.
12. The method of claim 1 , wherein as boundary condition for the position of the origin of the surface normal vector defining the edge curve (γ 0 , γ 4 ), one specifies an angle α between the surface normal vector and the connecting straight line as well as an angle β, which extends between the connecting straight line and a line extending between the origin of the surface normal vector and a characteristic point of the first or second model, whereby (α+β): 2≈φ with 30°≦φ90°.
13. The method of claim 12 , wherein 70°≦φ≦90°.
14. The method of claim 12 , wherein the characteristic point is the centroid.
15. The method of claim 1 , wherein the connecting straight line between the first and the second model passes through at least one of their centroids, pseudo-rotation axes, and principal axes of inertia.
16. The method of claim 1 , wherein at least one element is a pontic, and data for position and size of the pontic for the dental restoration to be produced are retrieved from a data library and subsequently, a connecting straight line is specified.
17. The method of claim 1 , including the steps of:
scanning a physical model of a stump,
computing a three-dimensional model from the measured point distribution acquired by the scanning,
computing from the three-dimensional model, a three-dimensional model of a coping as the first or second model,
parameterizing the three-dimensional coping model in a two-dimensional parameter space, in which each point corresponds to an X, Y, Z coordinate and a normal vector in the three-dimensional space of the coping, and
determining the first edge curve from the parameterized two-dimensional space.
18. The method of claim 1 , including the steps of:
computing a three-dimensional model as the first or second model of a pontic selected from a library,
parameterizing the three-dimensional model in a two-dimensional parameter space, in which each point corresponds to one X, Y, Z coordinate and one normal vector in the three-dimensional space, and
determining the edge curve from the parameterized two-dimensional space.
19. The method of claim 18 , wherein rounding radii between the connector and the first or second element are computed from the course of the edge curve and the offset curve computed therefrom.
20. The method of claim 1 , for producing a pontic and taking into account the shape of the gingiva such that the gingiva side of the pontic maintains a minimum distance to the gingiva.
21. A CAD/CAM method for designing a connector between one first and one second element of a dental restoration, where for generating data required for the production of the connector, the connector is designed comprising the steps of:
computing a first model of the first element and a second model of the second element;
defining a connecting straight line between the first model and the second model;
computing edge curves (y 0 , y 4 ) on the first model and the second model, respectively, the edge curves being defined by the origins of surface normal vectors of the models, which satisfy boundary conditions relative to the connecting line;
computing offset curves (y 1 , y 3 ) on the first model and the second model, respectively, from the edge curves; and
connecting the edge curves and the offset curves of the first model and the second model, and computing the connector on the basis of the path of the connection between the curves,
wherein as boundary condition for the position of the origin of the surface normal vector defining the edge curve (y 0 , y 4 ), one specifies an angle α between the surface normal vector and the connecting straight line as well as an angle β, which extends between the connecting straight line and a line extending between the origin of the surface normal vector and a characteristic point of the first or second model, whereby (α+β): 2=φ with 30°φ≦90.