Once plaque has hardened into calculus (tartar), brushing can't remove it. If you think you might brush too hard, hold your toothbrush the same way you hold a pen.
如果你认为刷牙可能太用力，握你的牙刷就想握一支笔一样。
In contrast, the KEY III is suitable for the treatment of soft tissue and hard tissue (enamel and bone), and in periodontology for gentle calculus removal.
相反，KEYIII则适用于治疗软组织和硬组织(牙釉质和牙骨质)，在牙周病学中可轻柔地去除结石。
The hard, rough stains are calculus.
又粗又硬的着色的地方就是齿石。
If you study hard, you won't fail your calculus test.
如果你用功点，你的微积分就不会不及格。
If you study hard, you won't fail your calculus test.
如果你用功点，你的微积分就不会不及格。
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