Orthodontic expansion screw

1. An orthodontic expansion screw, comprising:

at least two bodies, arranged at a mutual distance which can be changed by means of a spindle, which engages both bodies, wherein the spindle has an actuating part, from which at least one threaded part proceeds, which is engaged in a threaded bore of one of the two bodies;

a straight-line guiding means, which engage both bodies and guide them along two mutually parallel guiding axes, avoiding a relative rotation of the bodies given a change in their mutual distance; and

a device for preventing or impeding an inadvertent rotation of the spindle relative to the bodies;

wherein the at least one threaded part of the spindle has at least one recess that extends in its longitudinal direction and is open in a radial direction, and that an inner surface of the threaded bore of the body in which the at least one threaded part is inserted has a projection, which is directed against the spindle and, in a position of the spindle in which the projection faces the at least one recess, the projection protrudes into the recess, whereas when the projection faces the at least one threaded part, the projection presses against the at least one threaded part;

wherein the projection is not a separately manufactured part in comparison to the body in which it is part of, but rather the projection is integrally formed from part of the body in an embossing process.

2. The expansion screw according to claim 1 , wherein the projection touches the threaded portion of the spindle in each of its positions.

3. The expansion screw according to claim 2 , wherein the projection abuts against the threaded part of the spindle under a pressure in each of its positions.

4. The expansion screw according to claim 1 , wherein the projection is convex in design.

5. The expansion screw according to claim 4 , wherein the projection is spherical in design.

6. The expansion screw according to claim 1 , wherein an extension of the protrusion is greater in the longitudinal direction of the spindle than in the circumferential direction of the spindle.

7. The expansion screw according to claim 1 , wherein an extension of the protrusion is greater in the longitudinal direction of the spindle than the pitch of the thread of the spindle.

8. The expansion screw according to claim 1 , wherein the at least one recess extends over the entire length of the at least one threaded part.

9. The expansion screw according to claim 1 , wherein the at least one recess is one of two or four recesses which are present on the at least one threaded part, which lie diametrically opposite each other in pairs.

10. The expansion screw according to claim 9 , wherein at least one threaded part is designed as a square with rounded corners, in which the thread is formed.

11. The expansion screw according to claim 10 , wherein the thread of the at least one threaded part also extends with a smaller thread depth at least partially into the at least one recess ox portion of the at least one threaded part.

12. The expansion screw according to claim 1 , wherein the at least one threaded part of the spindle comprises two threaded parts, which extend in mutually opposite directions proceeding from the actuating part, and the at least one recess comprises two recesses on each of the threaded parts lying diametrically opposite each other, wherein the two recesses on the one threaded part are offset to each other by a circumferential angle of 90° relative to the two recesses on the other threaded part around the longitudinal axis of the spindle.

13. The expansion screw according to claim 1 , wherein the device for preventing or impeding rotation acts in both rotational directions of the spindle.

14. An orthodontic expansion screw, comprising: at least two bodies, arranged at a mutual distance which can be changed by means of a spindle, which engages both bodies, wherein the spindle has an actuating part, from which at least one threaded part proceeds, which is engaged in a threaded bore of one of the two bodies;

a straight-line guiding means, which engage both bodies and guide them along two mutually parallel guiding axes, avoiding a relative rotation of the bodies given a change in their mutual distance; and a device for preventing or impeding an inadvertent rotation of the spindle relative to the bodies; wherein the at least one threaded part of the spindle has at least one flattened portion extending in its longitudinal direction, and that inner surface of the threaded bore of the body in which the at least one threaded part is inserted has a projection, which is directed against the spindle and, in positions of the spindle in which the projection does not face the at least one flattened portion, the projection presses against the at least one threaded part, whereas in positions of the spindle in which is directed against the at least one flattened portion, the projection does not touch the at least one flattened portion, or does so with less pressure than in positions in which does not face the at least one flattened portion;

wherein the projection is not a separately manufactured part in comparison to the body in which it is a part of, but rather the projection is integrally formed from part of the body in an embossing process.

15. The expansion screw according to claim 14 , wherein the projection touches the threaded portion of the spindle in each of its positions.

16. The expansion screw according to claim 15 , wherein the projection abuts against the threaded part of the spindle under a pressure in each of its positions.

17. The expansion screw according to claim 14 , wherein the projection is convex in design.

18. The expansion screw according to claim 17 , wherein the projection is spherical in design.

19. The expansion screw according to claim 14 , wherein an extension of the protrusion is greater in the longitudinal direction of the spindle than in the circumferential direction of the spindle.

20. The expansion screw according to claim 14 , wherein an extension of the protrusion is greater in the longitudinal direction of the spindle than the pitch of the thread of the spindle.

21. The expansion screw according to claim 14 , wherein the at least one flattened portion extends over the entire length of the at least one threaded part.

22. The expansion screw according to claim 14 , wherein the at least one recess flattened portion is one of two or four recesses portions which are present on the at least one threaded part, which lie diametrically opposite each other in pairs.

23. The expansion screw according to claim 22 , wherein at least one threaded part is designed as a square with rounded corners, in which the thread is formed.

24. The expansion screw according to claim 23 , wherein the thread of the at least one threaded part also extends with a smaller thread depth at least partially into the at least one flattened portion of the at least one threaded part.

25. The expansion screw according to claim 14 , wherein the at least one threaded part of the spindle comprises two threaded parts, which extend in mutually opposite directions proceeding from the actuating part, and the at least one flattened portion comprises two flattened portions on each of the threaded parts lying diametrically opposite each other, wherein the two flattened portions on the one threaded part are offset to each other by a circumferential angle of 90° relative to the two flattened portions on the other threaded part around the longitudinal axis of the spindle.

26. The expansion screw according to claim 14 , wherein the device for preventing or impeding rotation acts in both rotational directions of the spindle.