Question

An 8-year-old patient has a combined mesiodistal width of 19.5 mm for the four mandibular incisorsUsing the Tanaka-Johnston analysis, what is the predicted width of the unerupted mandibular canine and premolars on one side?

• A. 20.5 mm
• B. 20.25 mm
• C. 20.75 mm
• D. 20 mm

Hint:

For Tanaka–Johnston analysis: Mandibular arch = (Sum of lower incisors ÷ 2) + 10.5 Maxillary arch = (Sum of lower incisors ÷ 2) + 11

Answer 1

The Correct Option is B

To solve this problem, we use the Tanaka-Johnston analysis, a commonly used method in orthodontics to predict the size of unerupted teeth. The analysis involves using the mesiodistal width of mandibular incisors to estimate the mesiodistal width of the canines and premolars.

Given: 

• Combined mesiodistal width of the four mandibular incisors = 19.5 mm.

According to the Tanaka-Johnston analysis, the estimation for one side of the dental arch is calculated as follows:

1. The formula used is: \(Y = 0.5 \times \text{(sum of the mesiodistal widths of mandibular incisors)} + 10.5\)
2. Plugging the values we have: \(Y = 0.5 \times 19.5 + 10.5\)
3. Calculating this gives: \(Y = 9.75 + 10.5 = 20.25 \text{ mm}\)

Therefore, the predicted width of the unerupted mandibular canine and premolars on one side is 20.25 mm.

Conclusion: The correct answer is 20.25 mm, matching the prediction using Tanaka-Johnston analysis.