California Registered Dental Assistant (RDA) Written Practice Exam 2025 – Comprehensive Study Guide to Ensure Exam Success!

A 'smile line' refers to the portion of the teeth that is visible when a person smiles. This includes both the upper and lower teeth and is typically used as an aesthetic measurement in dentistry. Option A, the curve of the lips, may contribute to the appearance of a smile line, but it is not the same thing. Option B, the outline of the mouth, does not specifically refer to teeth and therefore is not a complete definition of a smile line. Option D, alignment of the teeth, is a factor that can affect the appearance of a smile line, but it is not the definition of a smile line. Only option C accurately defines a smile line.