| 摘要 |
<p>A sand-glass is provided at least on the front with a cover depicting a face. The cover has a tooth-shaped recess arranged at a height above the base of the sand glass such that the recess is only covered by sand when all the sand has run through the sand-glass. The sand-glass is particularly suitable for indicating to children the course and end of the minimum duration for brushing of the teeth.</p> |
