Table of Contents
Guidance for separating, trimming, and finishing clear aligners and retainers thermoformed from Zendura sheet materials — consolidated from the Instructions for Use published for each material.
Trim design matters more than many clinicians expect: independent research shows the margin cut has a greater effect on appliance retention than composite attachments — see Clinical Evidence for the study.
Separating the appliance from the model#
Polyurethane fits the model intimately, and a straight vertical pull can snap teeth on plaster or 3D-printed models. De-mold progressively:
- Lift at the posterior. Slide a flat, blunt dental tool (e.g., a LeCron carver or lab knife) parallel to the model surface under the rear posterior lingual or buccal margin of the appliance.
- Break the vacuum. Gently twist the tool to break the suction seal and lift the rear edge.
- Peel forward. Flex the buccal and lingual flanges outward to clear the undercuts, then slowly peel the appliance forward from posterior to anterior.
Margin design#
Three trim approaches are in common use, in order of clinical preference:
- Straight cut 2 mm above the gingival zenith — the most retentive design. Independent testing (Cowley, Mah & O’Toole, JCO 2012) found it roughly twice as retentive as a scalloped cut without attachments, and over four times as retentive with attachments.
- Straight cut at the gingival zenith — a middle ground.
- Scalloped cut following the gingival margin — the most aesthetic, but the least retentive.
Whichever design you choose, leave at least 3 mm of gingival coverage intact to preserve the appliance’s structural rigidity and force transmission.
Trimming#
- Rough cut. Separate the formed appliance from the carrier frame with dental scissors or heavy shears.
- Precision cut. Trim to the margin line with a 1 mm carbide bur or rotary trimming wheel on a laboratory handpiece at approximately 35,000 RPM, following the intended boundary as closely as possible.
Edge finishing#
- Smooth with silicone or rubber polishers. Work at roughly 10,000 RPM with rotary silicone/rubber polishing points or a polyurethane wheel to remove micro-burrs — moderate speed avoids melting the material.
- Touch-ups. A fine nail file, emery board, or fine-grit sandpaper works for quick manual edge smoothing.
- Check the fit. The finished appliance should snap securely onto the model, sit flush against all biting surfaces, and show no air gaps along the incisal edges. Use aligner seaters (“chewies”) for a snug seat during try-in.
What to avoid#
- Never use a direct flame. Do not edge-flame Zendura materials with a micro-torch or alcohol burner: polyurethane degrades, yellows, and scorches under an open flame and can release hazardous fumes. On tri-layer materials (FLX, VIVA), direct heat also causes delamination of the layered structure.
- Skip the pumice wheel. Wet pumice slurry on rag wheels is too abrasive — it clouds and micro-scratches the high-clarity surface and can degrade the multi-layer construction. Use dry silicone polishers instead.
- Never use hot water. Hot or boiling water distorts the thermoformed appliance.
Pre-delivery sanitation#
Wash the finished appliance with a mild soap (such as a 2% Liquinox solution) and rinse well with cool water before delivering it to the patient. Patient-facing care guidance for the appliance’s lifetime of wear is in Cleaning and Disinfecting.
Authoritative fabrication documentation lives in each material’s Instructions for Use.
