The depth of 2/3 to 3/4 the length of the long needle corresponds to approximately which millimeters for bone contact in infiltration?

The depth of 2/3 to 3/4 the length of the long needle corresponds to approximately which millimeters for bone contact in infiltration?

• A. 20-25 mm
• B. 5-10 mm
• C. 30-40 mm
• D. 15-18 mm

Answer: (A)

The key idea is estimating how deep you need to advance a long dental needle to reach bone during infiltration. For a standard long needle, reaching bone typically requires about two-thirds to three-quarters of the needle’s length. If the needle is around 32 mm long, that depth works out to roughly 21 to 24 mm. That places the bone contact depth in the 20–25 mm range, which is why that option is the best match. Injections that are too shallow (5–10 mm or 15–18 mm) wouldn’t reach bone with a long needle, and going as deep as 30–40 mm would exceed the needle’s length for most standard setups.

The key idea is estimating how deep you need to advance a long dental needle to reach bone during infiltration. For a standard long needle, reaching bone typically requires about two-thirds to three-quarters of the needle’s length. If the needle is around 32 mm long, that depth works out to roughly 21 to 24 mm. That places the bone contact depth in the 20–25 mm range, which is why that option is the best match.

Injections that are too shallow (5–10 mm or 15–18 mm) wouldn’t reach bone with a long needle, and going as deep as 30–40 mm would exceed the needle’s length for most standard setups.