Professional clear aligner treatment planning

A raw intraoral scan is a single continuous mesh. Before any tooth can be moved it has to become individual objects, so each crown is separated along the gingival margin and the interproximal contacts, and the missing surface below the margin is reconstructed to a plausible anatomical form. Where the scan is short of data, typically the distal of second molars or a contact closed by heavy crowding, that is flagged rather than guessed at.

Segmentation quality decides everything downstream. A crown separated too far apically overstates the interproximal enamel available and makes IPR figures optimistic. A crown separated too coronally hides the contact point that actually limits movement. A long axis is assigned to each tooth so that tipping, torque and rotation are measured against something consistent rather than against the mesh.

With the arches articulated from the bite scan, the pre-treatment record is complete: crowding measured per arch, arch form recorded, midlines related to each other and to the facial midline from your photographs, and the existing overjet and overbite noted. The setup is built on that record, and the movement table you receive is the difference between it and the planned finish.

Staging decides how much of the total movement each aligner attempts. The limits used in general aligner practice are deliberately conservative: an aligner expresses only part of what it is shaped to do, and asking for too much per stage widens that gap rather than shortening treatment. Figures commonly quoted in the aligner literature and in everyday practice sit around 0.25 mm of bodily translation per stage, roughly 1 to 2 degrees of rotation for round-rooted teeth such as canines and premolars and somewhat more for teeth with a flatter root cross-section, about 0.2 mm of extrusion, and 1 to 2 degrees of root torque. These are typical ranges rather than a promise about any particular tooth.

The limits are not uniform across the arch. A lower incisor with a short root in thin bone is staged more slowly than an upper central. Extrusion is the movement an aligner controls least well, so it is spread over more stages than an equivalent amount of tipping. Where your instructions set your own limits, the plan follows them and the stage count moves accordingly.

Stage count is an outcome of these limits and the size of the movements, not a target chosen in advance. If you give us a stage ceiling, the plan will show which movements have to be staged more slowly or left to a refinement in order to stay under it.

A smooth crown gives an aligner very little to hold. Attachments are composite features bonded to enamel that create a surface the aligner can push or pull against, and their shape follows the movement rather than the tooth. A rotation needs a surface offset from the long axis so the aligner can apply a couple. An extrusion needs an undercut the aligner can engage and lift against. Root movement needs a feature that lets the aligner deliver a moment rather than only a tipping force.

Placement matters as much as shape. An attachment set too close to the gingival margin is hard to bond cleanly and traps plaque; set too incisally it can interfere with the opposing arch. On teeth carrying anchorage, attachments are used to resist unwanted movement rather than to produce it, which is a different design problem and often a different shape.

In the aesthetic zone every attachment is a visible trade-off. If you ask for no attachments on the upper anteriors, the plan shows which movements lose control as a result and, where it is possible, redistributes the work to teeth further back or stages those movements more slowly.

Interproximal reduction is space made by removing a small thickness of interproximal enamel. It is planned contact by contact rather than as an arch total, because each contact has its own enamel thickness and its own relationship to the crowding it is meant to relieve. Conventional practice keeps individual reductions small, commonly in the range of 0.2 to 0.5 mm per contact with anterior contacts at the lower end, and keeps the total within the enamel available on both adjoining surfaces.

Distribution follows the crowding. Space made three contacts away from where a tooth needs to move will close in the wrong place, so reduction is placed at or adjacent to the crowded segment and the staging is written so the space opens as the tooth is ready to use it. Reduction is normally scheduled once the teeth have separated enough for a strip or disc to reach the contact cleanly, which is rarely at the first stage.

IPR is not always the right answer. Where the arch can accept it, expansion or controlled proclination may resolve crowding without removing enamel, and the plan says so rather than defaulting to stripping. Every reduction that survives into the approved version appears on a chart by contact, in tenths of a millimetre, against the stage it is performed, so it can be checked at the chair.

A setup that looks correct from the buccal can still be wrong in occlusion. The articulated arches are checked for interferences through the staged sequence: crowns passing through each other as they cross, a premolar that collides mid-treatment even though it clears at the finish, an upper canine that intrudes on the lower arch during a rotation. Posterior contact is reviewed at the end position and at the stages where the vertical dimension changes.

Collisions inside the arch matter as much as those between arches. Interproximal overlap between neighbouring crowns during derotation is one of the common reasons a plan looks feasible on screen and does not track in the mouth, and it is usually solved by resequencing or by moving IPR earlier rather than by asking for more force.

A revision changes what you asked it to change and preserves the case history around it. The previous version stays available, the case number does not change, and the new version carries a record of what was altered. Moving an attachment, reducing IPR at one contact, changing the finish on a single tooth or extending the staging can each be requested against that specific tooth or stage, so a revision does not become a rebuild.