1. Field of the Invention
The present invention relates to an orthodontic bracket which, in particular, enables to secure a proper pressing-down force to an archwire supported in an archwire slot for correcting irregular rows of teeth or twisted teeth.
2. Description of the Related Art
U.S. Pat. No. 5,108,285 discloses a self-ligation bracket as an orthodontic bracket. This self-ligation bracket is a PASSIVE TYPE bracket where an opening of an archwire slot is closed with a rotating clip for the archwire not to get out from the archwire slot.
The PASSIVE TYPE bracket is that the clip serves as a cap to form a through-hole of the archwire. In contrast, an ACTIVE TYPE bracket is that the clip bends itself to press down the archwire to a bottom of the slot.
In this PASSIVE TYPE bracket, thickness of the clip is made large to increase rigidity so that the archwire slot is closed with the clip of high rigidity to avoid the archwire from getting out of the slot.
According to this PASSIVE TYPE bracket, when setting a thin and round archwire (0.014 or 0.016 inch diameter) used at an initial stage of the treatment in an archwire slot of 0.018 inch size, even if closing the opening of the archwire slot with the clip, the clip does not come into contact with the thin and round archwire.
Therefore, since the archwire can be slid in the interior of the archwire slot, a friction free condition can be obtained which is required to the thin archwire used at the initial stage of the treatment.
On the other hand, if setting a comparatively thick and square archwire (0.016 inchxc3x970.022 inch or 0.017 inchxc3x970.025 inch) used at the second and final stage of the treatment in the archwire slot of 0.018 inch size, and closing the opening of the archwire slot with the clip, the clip comes into contact with the archwire.
However, since the clip has the high rigidity, the archwire is firmly urged by the clip and is made tight within the slot, so that the archwire cannot be slid in the interior of the archwire slot. Further, the clip of high rigidity cannot be expected to be bent, and for example, even if a tooth is strongly twisted as a rotation control, the clip itself cannot be expected to press down the wire into the slot.
For solving such inconveniences, it may be assumed that the clip is made small in thickness. By making the clip thin, it is possible that flexibility of the clip is increased, and the pressing force of the archwire by the clip is made small although the archwire comes into contact with the clip, so that the archwire is made slid within the slot.
However, if making the clip thin, there is a problem that when adding the strong rotation to the clip from the archwire, the clip opens unexpectedly by pushing-up force.
The invention has been established in view of the above mentioned problems, and it is an object of the invention to offer such an orthodontic bracket enabling the archwire to slide within the archwire slot even when the clip comes into contact with the archwire, and enabling to cause the clip to bent so as to press down the archwire toward the bottom of the slot even when the strong rotation is added.
For accomplishing the object of the invention, the invention as set forth in a first aspect is an orthodontic bracket comprising:
a base firmly attachable directly or indirectly to teeth surfaces;
a bracket main body disposed on one side of the base;
a groove-shaped archwire slot formed along a mesiodistal direction in the bracket main body, for holding an archwire therein;
a clip having a substantially belt shape and being curved substantially in a U-shape for covering at least one part of an opposite side to the base in the archwire slot, the clip having a catching end portion provided at an upper part thereof and a sliding-rotation supporter provided at a lower part thereof;
a cover portion supported by the bracket main body, under which the catching end portion gets into and engages with; and
a guide portion formed in at least one of the bracket main body and the base and along a tooth axial direction crossing with the archwire slot, for guiding the clip in a guiding direction, the guide portion having a front side part, a bump portion and an inner side part, which are provided in order in the guiding direction, at a ceiling face thereof,
wherein when the sliding-rotation supporter slides on the ceiling face and gets over the bump portion of the ceiling face from the front side part to reach the inner side part of the ceiling face, the clip enables to press down the archwire toward a bottom of the archwire slot.
Herein, the orthodontic bracket according to the invention includes an embodiment that the bracket main body is secured to the face-shaped base attachable to the teeth surfaces, or an embodiment that the bracket main body is welded, via the base, to a band attached to the teeth surfaces.
In the thus structured orthodontic bracket, when the sliding-rotation supporter of the clip gets over the bump portion of the ceiling face from the front side part to reach the inner side part of the ceiling face, the orthodontic bracket is structured so that the catching end portion of the clip gets into under the cover portion of the bracket.
Therefore, even if the strong rotation is effected to the clip from the archwire, the catching end portion of the clip is prevented from getting out of the cover portion and opening.
In the orthodontic bracket as set forth in a second aspect, according to the orthodontic bracket of the first aspect, it is preferable that the ceiling face inclines so that the inner side part of the ceiling face comes nearer to the base than the front side part of the ceiling face.
The orthodontic bracket is structured so that, by tilting the ceiling face, it is brought nearer to the base toward the inner side part in the guiding direction. Therefore, the more the sliding-rotation supporter of the clip is pressed toward the inner side part in the guiding direction, the more the clip presses down the archwire to the bottom of the archwire slot.
In the orthodontic bracket as set forth in a third aspect, according to the orthodontic bracket of the second aspect, it is preferable that the ceiling face has a stepwise portion. Therefore, when the sliding-rotation supporter pressed toward the inner side part in the guiding direction gets over the stepwise portion, the sliding-rotation supporter has less possibility to return to an initial position, thereby to securely maintain a condition where the archwire is pressed down to the bottom of the archwire slot.
In the orthodontic bracket as set forth in a fourth aspect, according to the orthodontic bracket of the first aspect, it is preferable that when the sliding-rotation supporter is positioned at a front of the bump portion, the clip enables to rotate with respect to the bracket main body.
By arranging the sliding-rotation supporter in the front of the bump portion, the clip can be rotated with respect to the bracket main body. Therefore, the archwire can be easily detachably attached to the archwire slot, and this kind of self-ligation brackets can be reduced in size.
In the orthodontic bracket as set forth in a fifth aspect, according to the orthodontic bracket of the fourth aspect, it is preferable that the clip has a curved portion, and when the clip rotates with respect to the bracket main body, the curved portion comes into contact with an edge of the base and controls a rotation of the clip.
By controlling the rotation of the clip with the edge of the base, the clip does not get out of the bracket main body. Therefore, the archwire can be more easily detachably attached to the archwire slot.
In the orthodontic bracket as set forth in a sixth aspect, according to the orthodontic bracket of the first aspect, it is preferable that the clip has a releasing recess at an upper part thereof.
Herein, as the releasing recess, a concave or a through-hole may be exemplified. Therefore, if an operator hooks it at his fingers, nails or the distal end of the instrument, the catching end portion and the covering portion can be engaged more securely or released more easily, and the clip can be rotated with respect to the bracket main body.
In the orthodontic bracket as set forth in a seventh aspect, according to the orthodontic bracket of the first aspect, it is preferable that the bracket main body has a tube, and the clip is arranged to follow an outer circumference of the tube.
In the orthodontic bracket as set forth in an eighth aspect, according to the orthodontic bracket of the first aspect, it is preferable that the clip has a tab at an upper part thereof and the cover portion has a groove for holding the tab of the clip therein.
In this invention, with respect to the tab held in the groove formed in the cover portion, if the operator hooks the tab at his fingers, nails or the distal end of the instrument to press down the tab, the catching end portion and the covering portion can be engaged more securely or released more easily.