Orthodontic Assisting Knowledge
Domain overview
The Orthodontic Assisting Knowledge domain tests the vocabulary and recognition skills you need before you touch a patient: tooth identification, Angle classification, appliance parts, wire types, and instrument selection. Questions are often scenario-based-"which plier," "which tooth," "which separator"-so link each term to a chairside action.
Occlusion and measurements
- Angle Class I: the mesiobuccal cusp of the maxillary first molar sits in the buccal groove of the mandibular first molar.
- Class II: that cusp is mesial to the groove. Division 1 shows proclined maxillary incisors and increased overjet; division 2 shows retroclined central incisors, often with a deep bite.
- Class III: the cusp is distal to the groove, commonly with mandibular protrusion.
- Overjet is horizontal overlap; overbite is vertical overlap. Crossbite, open bite, crowding, spacing, and midline deviation are charted separately.
Numbering and appliances
Universal numbering runs 1–32 for permanent teeth and A–T for primary teeth. FDI uses two digits; Palmer uses quadrant brackets and 1–8. Fixed appliances include brackets, bands, arch wires (nickel-titanium, stainless steel, beta-titanium), elastomeric or steel ligatures, separators, power chain, and coil springs. Removable appliances include Hawley retainers and clear aligners; functional appliances include Twin Block and Herbst.
Instruments
Match the instrument to the task: Weingart pliers seat an arch wire; a ligature director tucks ligature tails; a band pusher seats a band; a distal end cutter cuts wire at the molar tube; a pin-and-ligature cutter removes ligatures; a Howe pliers bends wire; a bracket remover debonds.
Worked example
A separator is ordered for the maxillary right permanent first molar. Under Universal numbering that tooth is 3. Its mesial neighbor is 4 (first premolar) and its distal neighbor is 2 (second molar), so separators are placed between 3 and 4 and between 3 and 2. In FDI the same tooth is 16; a question asking for the FDI number should be answered 16, not 3.
Traps that cost marks
Do not confuse overjet with overbite. Do not assume every Class II is division 1. Do not call an elastomeric separator a permanent appliance-it is temporary. Do not use a distal end cutter intraorally without controlling the cut end. Read the tooth-numbering system stated in the question before answering.