先是希腊人，然后是罗马人，将牙膏的配方加以改进。他们添加了一些磨料如碎骨和牡蛎壳，用来清除牙齿上的污垢。

The Greeks, and then the Romans, improved the recipes for toothpaste by adding abrasives such as crushed bones and oyster shells, which were used to clean debris from teeth.

youdao

牡蛎和贻贝筏式养殖和碎壳床养殖。

Raft and cultch culture of oysters and mussels.

youdao

每一步都要踩碎不少细小的灰色的贝壳，壳已风干，内中空无一物，在脚下咭嘎地响犹如白霜或易碎的珠子。

Every step crumbled up Numbers of minute grey shells, empty and dry, that crunched under foot like hoar-frost or fragile beads.

youdao