Why Pure Plastic Isn't Always Enough
A plain Invisalign tray is a single sheet of thermoformed plastic shaped to a slightly different position than the tooth currently sits in; the mismatch between the tray's shape and the tooth's actual position is what generates movement. On flat, easily gripped tooth surfaces, that mismatch alone is often enough to produce reliable movement. But some tooth movements need more than gentle, evenly distributed pressure against a smooth crown — they need something for the plastic to actively grip, push against or pull on, and a smooth tooth surface does not give the tray anything to hold onto for those movements.
SmartForce attachments solve that grip problem. They are small, tooth-coloured shapes bonded directly onto the enamel of a specific tooth using dental composite, the same tooth-coloured filling material used for fillings and minor cosmetic bonding elsewhere in the mouth. Once bonded, the attachment becomes a raised, three-dimensional feature that the aligner tray is manufactured to snap onto and lock around, rather than simply lying flat against a smooth crown. That combination — a small composite shape on the tooth and a matching recess built into the aligner plastic — is what lets an otherwise passive removable tray apply a directional, targeted push instead of a general one.
Not every tooth in a treatment plan receives an attachment, and not every patient's plan uses them at all; the treating dentist decides where attachments are placed and how many are needed based on the specific movements the case requires. Simple corrections on teeth that are already well-aligned may not need any attachment. More demanding movements — the kind that would otherwise be difficult for a smooth aligner tray to grip reliably — are where attachments tend to concentrate.
How Attachments Facilitate Complex Tooth Rotations
The clinical purpose of a SmartForce attachment is to direct extrusion and rotation forces — the two categories of tooth movement a flat aligner surface struggles to generate on its own. Rotation means turning a tooth around its own vertical axis, common for teeth that have grown in twisted relative to the rest of the arch. Extrusion means drawing a tooth further out of the bone toward the biting surface, needed when a tooth sits shorter than its neighbours. Both movements require the aligner to apply force from more than one direction at once, and a smooth tooth crown does not give the plastic anywhere to catch hold for that kind of multi-directional push.
An attachment changes that by giving the aligner a physical feature to interact with instead of a bare surface. The Invisalign aligner is manufactured with a precisely shaped hollow built into the tray at the exact location of the attachment, and the tray snaps onto the attachment much as a socket snaps onto a shaped peg. As the patient progresses from one tray in the sequence to the next, each tray's attachment-recess is positioned slightly differently from the last, so the interaction between the attachment and the plastic incrementally pulls, tips or twists the tooth in the planned direction. This is the same underlying biological mechanism described in the orthodontic literature on periodontal ligament remodelling under sustained force: however the force is generated — by an archwire or by an aligner tray gripping an attachment — the periodontal ligament and surrounding bone respond to it the same way, resorbing on the compression side and rebuilding on the tension side (Li et al., 2021).
Attachment shape is not one-size-fits-all. Different shapes — rectangular, bevelled, elliptical — are used depending on whether the movement needed is primarily rotation, extrusion, or a more complex combination of tipping and root movement, and the treatment-planning software used to design an Invisalign sequence selects the shape and placement based on the specific correction that tooth needs. This is also why attachments tend to appear more often in cases involving larger tooth rotations, tipping corrections, or root movements — the categories of movement that provider surveys and systematic reviews identify as the more biomechanically demanding end of clear aligner therapy.
Maintenance, Cleaning, and Dealing with Dislodged Buttons
Because attachments are raised composite orthodontic appliances bonded onto the tooth surface, they create small ledges where plaque and food particles can collect more easily than on the smooth enamel around them, similar in principle to how a bracket base on a metal brace creates a catch-point for debris. Routine care focuses on that margin:
- Brush thoroughly around each attachment, not just across the tooth surface
- Use interdental brushes or floss at the point where the composite meets the enamel
- Clean the aligner tray itself with a soft toothbrush and lukewarm water, not hot water, since heat can distort the tray's shape
- Avoid hot food and drink while trays are in place, for the same reason
An attachment occasionally comes loose from the tooth before treatment is finished, since the bond, while designed to hold for the duration of a treatment stage, is not indestructible and can be dislodged by biting something hard or by repeated friction from removing and reseating the tray. A dislodged attachment on its own is not a dental emergency, but it does change how well the current and following trays fit, since the tray was manufactured assuming the attachment's shape would be present. Treatment providers generally ask patients to contact the clinic to have the attachment rebonded or reshaped rather than continuing to wear the trays as though nothing changed.
Attachment Removal Process at Treatment Completion
When active tooth movement is complete, attachments are no longer needed and are removed as part of finishing treatment. The clinician grinds the composite away from the tooth surface, generally using a slow-speed handpiece or a polishing instrument, and then polishes the underlying enamel to restore a smooth surface and remove any fine scratches left by the removal instrument. Because attachments are bonded only to the enamel surface itself rather than into the tooth structure, removing them does not involve drilling into the tooth or affect its structural integrity.
The choice of removal instrument affects how the enamel surface looks and feels afterward. A 2025 in-vitro study comparing several one-step composite-removal tools found that a white stone bur left significantly more surface roughness and measurably greater enamel loss (0.115 +/- 0.054 mm depth) than aluminium-oxide-based polishing tools, which left surface roughness close to the tooth's pre-attachment baseline (Nguyen and Nguyen, 2025). That finding does not mean attachment removal causes permanent enamel damage as a rule — the same study found that gentler instruments preserved enamel integrity well — but it does show the outcome depends on the specific technique and instrument used, which is why removal is carried out by a trained clinician rather than something a patient does at home.
After the attachments are removed and the enamel is polished, the dentist typically checks tooth position, may take new digital scans or impressions, and moves the patient into a retention phase — usually a retainer — to hold the corrected position while the periodontal ligament and surrounding bone finish stabilising around the teeth's new alignment.