ABO Cheat Sheet 2026

The 30 highest-yield ABO facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. A couple is defined as: → Two equal and opposite non-collinear forces producing pure rotation
2. A quad helix appliance is used primarily to achieve which treatment goal? → Maxillary transverse expansion and molar derotation
3. A crossbite that shifts the mandible laterally on closure is classified as: → Functional (pseudo) crossbite
4. Which records are typically provided to a candidate in a clinical scenario for evaluation? → Photographs, radiographs, and study models/scans with history
5. What is the recommended frequency of archwire changes when using superelastic NiTi wires? → Every 6–8 weeks
6. Frontal (direct) bone resorption during tooth movement occurs when applied force is: → Light and preserves PDL vitality
7. What is the purpose of placing a step bend mesial to an upper molar tube? → To prevent the molar from tipping mesially (anti-tip bend)
8. In the ABO Written Examination, which reference domain covers the biological basis of tooth movement including periodontal ligament response to force? → Biomechanics and biology
9. A temporary anchorage device (TAD) provides what type of anchorage? → Absolute (skeletal) anchorage with minimal reactive movement
10. A cervical-pull headgear applies force in which direction relative to the maxilla? → Inferiorly and posteriorly
11. The ABO Discrepancy Index scores the tooth-size/arch-length discrepancy under which category? → Crowding
12. Which structure primarily transmits orthodontic force signals into cellular bone remodeling? → The periodontal ligament
13. During tooth movement, cells responsible for bone formation on the tension side are: → Osteoblasts
14. In the ABO Scenario-Based Component, candidates read a clinical vignette and must primarily demonstrate which competency? → Diagnosis and treatment decision-making
15. The cephalometric landmark A point (Subspinale) is defined as which point on the maxilla? → Deepest point on the curvature of the maxillary alveolar process between ANS and prosthion
16. According to standard orthodontic literature, what is the optimal light continuous force range generally cited for bodily tooth movement? → 50-100 grams
17. In reading periapical radiographs for orthodontic assessment, external apical root resorption appears as which finding? → Blunted or shortened root apices
18. The SNA angle primarily indicates the anteroposterior position of which structure? → Maxilla relative to cranial base
19. The term 'post-retention stability' in orthodontics refers to: → Long-term maintenance of corrected tooth positions after retainers are discontinued
20. Which patient is the BEST candidate for implant-supported tooth replacement after orthodontic treatment? → A 20-year-old whose jaw growth is complete with adequate bone volume
21. A radiograph shows a tooth with an inverted crown positioned high in the maxilla; this ectopic finding is termed what? → Impaction with inversion
22. Long-term stability of corrected Class III malocclusion treated with growth modification is LEAST favorable in patients with: → Vertical mandibular growth pattern and strong Class III genetics
23. A fixed lingual retainer bonded from canine to canine on the lower arch is most effective for: → Maintaining lower incisor and canine alignment long-term
24. Which growth prediction concept states that mandibular growth direction can be estimated from the cephalometric Y-axis? → Growth axis interpretation
25. Differential anchorage in extraction cases relies on the principle that: → Larger anchorage units move less than the units being retracted
26. Forsus Fatigue Resistant Device (FRD) is classified as which type of appliance? → Fixed functional appliance
27. When reading a panoramic radiograph, ectopic eruption of the maxillary canine is most often associated with which adjacent tooth resorption risk? → Lateral incisor roots
28. What is the normal value for the SNA angle in cephalometric analysis? → 82°
29. Root resorption during orthodontic treatment is most commonly detected using: → Periapical radiographs or CBCT
30. Nickel-titanium archwires are favored in early alignment because they: → Provide light, continuous force over a wide range of deflection (superelasticity)