Orthodontic Appliances and Techniques
What is examined
Fabrication and repair of removable and fixed orthodontic appliances, wire and acrylic technique, study model work, and the aligner workflow.
Removable appliances
- The Adams clasp (0.7 mm stainless steel) on first molars or primary second molars is the workhorse retainer; labial bow 0.7 mm; expansion screw 0.9–1.0 mm giving about 0.25 mm per quarter turn.
- Retention options: Hawley, thermoformed Essix (0.75–1.0 mm), and bonded lingual 3–3 retainers.
- Functional appliances such as Twin Block and activator posture the mandible; accurate bite registration and close acrylic adaptation are the technician's contribution.
Wire and fixed work
- Wire sequence: NiTi for alignment (superelastic, light forces), TMA intermediate, stainless steel for sliding mechanics and finishing.
- Fixed work involves bands, molar tubes, brackets and soldered or welded attachments; solder must flow fully, not sit in lumps.
- Archwires and auxiliaries should sit passively in the slot when the tooth is in its intended position.
Models and aligners
- Pour study models in stone, trim with a flat base and heels, and mount in occlusion. Digital models follow the same rules: scan, trim, base, export STL.
- Aligner workflow: intraoral scan, treatment planning software, printed model with offset for aligner thickness, thermoform, trim and polish.
Worked example
A Hawley retainer rocks on one side. The Adams clasp was bent on a cast poured from a poorly separated impression, leaving a bleb in the mesiobuccal undercut. Re-pour and re-bend; do not squeeze the clasp to compensate, because that work-hardens the wire and it will fracture.
Traps
- Over-tightening a clasp so the patient cannot seat the appliance.
- Polymerising acrylic against stone without a separating medium.
- Swapping upper and lower appliances on a two-appliance case.
- Delivering an aligner that has not been trimmed and polished at the gingival margin.