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。

youdao

The guide way and all gears in the headstock are hardened and precision ground.

在车头的所有齿轮经过高频淬火及精密研磨。

youdao

The only way we can continue to wear fur is if we have hardened our hearts so that we can no longer feel the pain and suffering that went into our garment.

只有这样，我们可以继续穿皮草是，如果我们有更坚定了我们的心，使我们可以不再感到痛苦和苦难，到我们的服装了。

youdao

The hotel spokesman declined to go into detail, but suggested that before the president's arrival they're hardened in some way.

WSJ: In the City's Power Suite

So it was far from the main building, and it was a result of the way that was hardened that we only lost the one local security guard.

NPR: Suicide Bomber Kills Guard At US Embassy In Turkey

Russia, of course, tends to polarize people and the battle lines on this particular issue, as on most others relating to the country, have long been drawn and have hardened and calcified over time in much the same way that the Western Front did in the First World War.

FORBES: Two Recent Examples of Russia as a Non-ideological Power