During transillumination, which finding allows light to pass through the ENTIRE tooth without interruption?

Correct answer: B. A craze line

• A. A vertical root fracture blocks light and, being subgingival, is usually diagnosed instead by an isolated deep narrow probing defect.
• B. CORRECT. A CRAZE LINE is confined to enamel and does not extend into dentine. Because there is no full-thickness discontinuity, light passes right through and the tooth transilluminates EVENLY. Craze lines are extremely common, particularly in older patients, and are of no clinical significance beyond occasional aesthetic concern.
• C. A fractured cusp likewise interrupts light transmission at the fracture line.
• D. A true crack extends into dentine and BLOCKS light transmission — the segment beyond the crack stays dark while the near segment glows. That abrupt interruption is the diagnostic sign.

Note: The rule: light PASSES through a craze line, light STOPS at a crack. Combine transillumination with a bite test (Tooth Slooth) and methylene blue dye for a definitive diagnosis.