Orthodontic Materials, Bonding, and Banding Procedures
What this domain tests
Enamel etching and adhesion, bracket and band materials, light-curing discipline, and the reasons bonds fail. Expect questions on etch times, contamination, slot prescriptions, and cement cleanup.
Etching and adhesion
Prophy with fluoride-free pumice, rinse, then apply 37% phosphoric acid gel: 15–30 seconds on permanent enamel, longer (about 60 seconds) on primary or aprismatic enamel. Rinse 10–15 seconds and dry until the surface is frosty white - a glossy surface means the etch failed. Saliva or blood contamination after etching requires re-etching; contamination after primer requires reapplying primer. Self-etching primer combines etch and primer and helps in wet, hard-to-isolate areas such as second molars, at slightly lower bond strength.
Brackets and curing
- Slot sizes 0.018 and 0.022 inch; prescriptions (Roth, MBT) build in tip, torque, and in-out.
- Light-cure composite: 10–20 seconds per bracket, tip 1–2 mm away, unit output checked with a radiometer, barrier sleeves changed between patients.
- Ceramic brackets scatter light and need longer exposure.
- Clinical bond strength of roughly 6–8 MPa is adequate; clean flash before curing fully, because set flash is harder to remove without disturbing the bond.
Banding
Separators placed one week ahead (two per contact), band sized and seated with a band seater and bite stick, cemented with resin-modified glass ionomer. Floss the contacts, check occlusion, and remove all cement from the gingival sulcus - retained cement causes inflammation. Bondable molar tubes are an alternative when isolation is good.
Bonding to restorative materials
Amalgam and gold need sandblasting and a retentive design; porcelain needs sandblasting plus silane; otherwise band the tooth.
Worked example
A lower second molar bracket debonds twice in one visit. Reasoning: the failure is isolation, not adhesive. The field is wet and the bracket margin sits at or below the gingival crest. Switch to a self-etching primer, add a dry angle and HVE, consider a lingual or buccal tube or a band, and re-etch rather than adding more composite over a contaminated surface.
Traps that cost marks
Etching for 15 seconds on a primary tooth; using fluoride prophy paste before bonding; curing through ceramic at metal-bracket times; leaving cement in the sulcus after banding; and re-bonding over old composite without removing it and re-etching.