Which factor is a source of error during probing due to tooth surface deposits?

• A. Calculus
• B. Overhangs
• C. Clinician error
• D. Gingival margin positioning

Answer: (D)

Probing depth is read from the gingival margin down to the base of the pocket, so the exact position of that margin is the reference point. When deposits are present on the tooth near the margin, they can obscure or shift where the margin actually sits. If you don’t place the probe at the true gingival margin, the distance you measure becomes unreliable because the baseline reference is off. That margin positioning error is what leads to inaccurate readings in the presence of tooth surface deposits. While deposits themselves can interfere with contact, the key factor described here is how the gingival margin’s position relative to those deposits affects the probe depth.