Which muscle is primarily responsible for producing the vowels /i/ and /u/?

• A. zygomatic
• B. masseter
• C. buccinator
• D. orbicularis oris

Answer: (D)

Understanding how lip movements shape vowels is essential. The lips must achieve specific configurations for high vowels: the lips are more spread for /i/ and more rounded and protruded for /u/. The orbicularis oris is the muscle that directly encircles the mouth and can contract to close, tighten, protrude, or round the lips, giving you the precise lip posture these vowels require. That direct control over lip shape is why it’s the primary muscle for producing those vowel sounds.

Other muscles influence facial expression or jaw position but don’t determine lip shape for vowels. The zygomatics lift the corners of the mouth without changing the lip opening or rounding. The masseter moves the jaw, affecting tongue position indirectly but not the lip configuration itself. The buccinator helps keep the cheek clear of the teeth and can affect oral cavity shape during speech, but it isn’t the main driver of lip rounding or spreading for these vowels.