DHA Orthodontics exam questions

6 worked Orthodontics practice questions

Original exam-style questions from the bank, spread across the blueprint domains. They are not real or recalled exam questions. Try each one, then open the answer for the rationale and reference. None of them appear in the free mock exam, so reading them will not spoil it.

1. Question 1 · Biology of Tooth Movement and Biomechanics

   A clinician wants to retract a canine bodily rather than tip it. Approximately what moment-to-force ratio (in mm) at the bracket is needed?

   1. AAbout 5:1
   2. BAbout 1:1
   3. CAbout 10:1
   4. DAbout 20:1
   Show answer and explanation

   Correct answer: C. About 10:1

   A moment-to-force ratio of roughly 10:1 at the bracket counteracts the tipping moment and produces translation. Lower ratios produce controlled or uncontrolled tipping, and higher ratios move the root more than the crown.

   Reference: Proffit WR et al. Contemporary Orthodontics, 6th ed.

2. Question 2 · Craniofacial Growth and Development

   In which overall direction is the maxilla displaced relative to the cranial base during normal growth?

   1. ADownward and backward
   2. BUpward and forward
   3. CDownward and forward
   4. DPurely forward
   Show answer and explanation

   Correct answer: C. Downward and forward

   Growth at the circummaxillary sutures and surface remodelling move the maxilla downward and forward relative to the cranial base. Bone is added posteriorly at the sutures while the whole maxilla is carried forward.

   Reference: Proffit WR et al. Contemporary Orthodontics, 6th ed.

3. Question 3 · Interceptive Orthodontics

   An 8-year-old with a persistent thumb-sucking habit has an anterior open bite and a narrow maxilla. What is the first step in management?

   1. AHelp the child stop the habit
   2. BFixed appliances to extrude incisors
   3. CRefer for orthognathic assessment
   4. DExtract primary canines
   Show answer and explanation

   Correct answer: A. Help the child stop the habit

   Habit cessation, by encouragement or a habit-breaking appliance if needed, often allows the open bite to resolve spontaneously. Extruding incisors while the habit continues is likely to fail.

   Reference: Mitchell L. An Introduction to Orthodontics, 5th ed.

4. Question 4 · Orthodontic Appliances and Materials

   A round stainless steel wire of 0.016 inch is replaced by one of 0.032 inch of the same alloy and span. By what factor does its bending stiffness change?

   1. AIncreases 4 times
   2. BIncreases 2 times
   3. CIncreases 16 times
   4. DIncreases 8 times
   Show answer and explanation

   Correct answer: C. Increases 16 times

   For a round wire, bending stiffness varies with the fourth power of the diameter, so doubling the diameter increases stiffness by 2 to the fourth power, or 16. Strength rises with the cube of the diameter.

   Reference: Proffit WR et al. Contemporary Orthodontics, 6th ed.

5. Question 5 · Orthodontic Diagnosis and Cephalometrics

   A patient has an ANB of 2 degrees, but the perpendicular from point B to the functional occlusal plane lies 6 mm ahead of the perpendicular from point A (Wits minus 6 mm). How should this be interpreted?

   1. AClass III skeletal tendency
   2. BClass II skeletal tendency
   3. CNormal sagittal relationship
   4. DIncreased vertical dimension
   Show answer and explanation

   Correct answer: A. Class III skeletal tendency

   When BO lies well ahead of AO the Wits value is negative, indicating a Class III jaw relationship. The Wits appraisal avoids errors in ANB caused by variation in nasion position and cranial base inclination.

   Reference: Jacobson A. The Wits appraisal of jaw disharmony, Am J Orthod 1975

6. Question 6 · Orthodontic Diagnosis and Cephalometrics

   A Bolton analysis gives an anterior ratio of 80.5%. What does this indicate?

   1. AMaxillary anterior tooth-size excess
   2. BMandibular anterior tooth-size excess
   3. CMandibular anterior tooth-size deficiency
   4. DA normal anterior tooth-size ratio
   Show answer and explanation

   Correct answer: B. Mandibular anterior tooth-size excess

   The ideal anterior Bolton ratio is about 77.2%, so 80.5% means the mandibular anterior teeth are too large relative to the maxillary teeth. This makes it difficult to achieve normal overjet and overbite without reducing lower tooth width or adding maxillary tooth width.

   Reference: Bolton WA. Am J Orthod 1958; Proffit WR et al. Contemporary Orthodontics, 6th ed.