Mandíbula vs. maxilar
In Portuguese, mandíbula and maxilar both relate to the jaw, but they refer to distinct anatomical parts. Mandíbula is the lower, movable jawbone, while maxilar is the upper, fixed jawbone.
Mandíbula
B1This word specifically refers to the lower jawbone. It is the part of the jaw that moves when you talk, chew, or yawn. In common language, it is the most frequent and general word for jaw.
O boxeador recebeu um soco forte na mandíbula e caiu.
(The boxer received a strong punch to the jaw and fell.)
Ela sentiu a mandíbula estalar ao abrir a boca.
(She felt her jaw crack when she opened her mouth.)
Mastigar chiclete o dia todo pode cansar a sua mandíbula.
(Chewing gum all day can tire your jaw.)
A mandíbula de um tubarão é incrivelmente poderosa.
(A shark's jaw is incredibly powerful.)
Ele ficou de mandíbula caída quando ouviu a notícia.
(His jaw dropped when he heard the news.)
Maxilar
B2This word refers to the upper jawbone, also known as the maxilla. This bone is fixed, does not move, and holds the upper teeth. It is a more technical term than mandíbula and is often used in medical or dental contexts.
O implante dentário foi fixado diretamente no osso do maxilar.
(The dental implant was fixed directly into the upper jawbone.)
Ele precisou de uma cirurgia para realinhar o maxilar superior.
(He needed surgery to realign his upper jaw.)
Uma infecção nos dentes de cima pode se espalhar para o maxilar.
(An infection in the upper teeth can spread to the maxilla.)
A dor de sinusite às vezes irradia para a região do maxilar.
(Sinusitis pain sometimes radiates to the upper jaw region.)
O exame de raio-X mostrou uma pequena fissura no maxilar dele.
(The X-ray exam showed a small fissure in his maxilla.)
Summary
The key difference is anatomical and based on movement. Mandíbula is the movable lower jaw, used widely in everyday speech for actions like talking and chewing. Maxilar is the fixed upper jawbone, a term more common in precise medical or dental contexts. If you are talking about the part that moves or gets hit in a fight, you mean mandíbula. If you are referring to the bone structure holding the upper teeth, you mean maxilar.