Which statement best describes parallelism in periodontal probing?

• A. The working end is perpendicular to the root surface
• B. The tip is directed toward the midline
• C. The working end is parallel to the root surface
• D. The shank is horizontal

Answer: (C)

Parallelism means the working end of the periodontal probe stays aligned parallel to the root surface as you measure. This keeps the tip in constant contact with the tooth surface, so readings reflect true sulcus depth rather than being distorted by angle or tissue. When the tip is perpendicular to the root surface, it can injure tissue and give unreliable measurements because the probe won’t stay properly seated against the surface. Directing the tip toward the midline isn’t the correct orientation for accurate probing, and the shank being simply horizontal isn’t what defines proper technique. The essential idea is that the working end runs parallel to the root surface to obtain accurate, consistent depths.