| 摘要 |
<p>A rapid palatal expander comprises a double-screw jack having a cylindrical head with two diametrical holes intersecting at 90°, for receiving a driving key. Two screws having oppositely directed threads extend from the two bases of the head, and engage in two respective nut blocks connected by palatal arms to metal rings, which are cemented to the molars of the upper hemi-arches. Therefore, the nut blocks can be located proximate to the palatal mucosa on each side of the palatal suture. Two pins extend through the blocks on each side of the double screw to guide the blocks in opposite directions during rotation of the jack. The head exerts a pressure against the guide pins to prevent any undesired rotation that might reduce the current expansion degree. A longitudinal recess in the jack head intersects the entry of a hole, for introduction of a guide pin at a time in its seat with no interference by the head.</p> |
