What is the normal mouth opening range?

• A. 15-20 mm
• B. 25-30 mm
• C. >40 mm (2-3 fingers)
• D. 60-70 mm

Answer: (C)

Measuring how wide the mouth opens is about the interincisal distance—how far the upper and lower front teeth separate when the mouth is opened fully. In healthy adults, this distance is typically around 40 to 50 millimeters, often described as roughly two to three finger widths. So an opening greater than about 40 millimeters fits the standard normal range.

Smaller values like 15–20 mm or 25–30 mm indicate restricted opening, which can reflect muscle tension, joint issues, or disc displacement. A very wide opening like 60–70 mm is less common and not used as the baseline “normal” range in most assessments, though some people can have unusually high mobility. Therefore, the best choice is the one describing an opening greater than about 40 mm.