こんにちは。
・Brush your teeth so you don't get cavities.
「虫歯にならないように歯を磨きなさい」
上記のような言い方ができます。
「歯を磨く」は brush (one's) teeth と言います。子供に言うときは Brush your teeth. で「歯を磨きなさい」になります。
「虫歯」は cavity（複数形 cavities）です。
ぜひ参考にしてください。
You should brush your teeth so that they do not rot/discolor.
You should brush your teeth so that you do not get cavities.
Depending on the age, it may be hard to explain to a child what cavities are. You can use words like rot/discolor for them to understand the negative impact caused if they do not brush their teeth. However if they are grown enough you can use cavities.
You must brush your teeth to keep them healthy and white
I have to say this to my children almost every day!
Healthy means to be in good health; free of illness and disease, and in good physical or mental condition.
If you don't brush your teeth you will get cavities.
You must brush your teeth or else you will get cavities
"If you don't brush your teeth you will get cavities." This explains to the child what will happen if they do not brush their teeth.
"You must brush your teeth or else you will get cavities." This warns the child what happens if you do not brush your teeth.
例文
"If you don't brush your teeth you will get cavities."
歯を磨かないと、歯が虫歯になるよ
歯を磨かないと、どうなるかを子供に説明しています。
例文
"You must brush your teeth or else you will get cavities."
歯を磨きなさい、そうしないと虫歯になるよ
歯を磨かないと、どうなるかを子供に警告しています
Look after your teeth and they will look after you
Explanation: Your teeth will provide you with many years of good service if you have a regular cleaning and check up routine. This sentence stresses this fact.
Example sentence:
'Look after the pennies and the pennies will look after the pounds.'
解説：定期的な歯磨きと検診を怠らないなら、あなたの歯は何年もの間良い働きをしてくれるでしょう。下記のフレーズはそれを強調しています。
例文： 'Look after the pennies and the pennies will look after the pounds.'
（1ペニーを大切にすることが、1ポンドを大切にすることに繋がります。）
→（小さなことを大切にしていると、結果的により大きなことにつながります。）
If you don't brush your teeth you will get cavities
You must brush your teeth or you will get cavities
When talking about teeth we use the term 'cavities' which means tooth decay or the teeth breaking down
So you would say 'brush your teeth so you don't get cavities' you could also use the term 'tooth decay' as this means the same as cavities
cavities'とは「虫歯」のことです。ですから、
'Brush your teeth so you don't get cavities'（虫歯にならないよう歯を磨きなさい）
と言えます。
ほかに、'tooth decay'（虫歯）も使えます。'tooth decay'は'cavities'と同じ意味です。
アメリカ合衆国 
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