What are attachments on clear aligners for?

What an attachment is

An attachment is a small bump of tooth-colored composite resin, the same family of material used for white fillings, bonded to the outside surface of a selected tooth for the duration of aligner treatment. Each one is shaped and placed according to the digital plan, usually with a thin template that holds the resin in the exact position while it is cured with a light. The aligner is made with a matching recess, so when the tray is seated the plastic wraps around the bump.

Attachments are temporary. They sit on the enamel surface rather than being cut into the tooth, and they come off at the end of treatment. When the plan is finished, the resin is removed and the enamel is polished.

Why a smooth tray needs something to push against

A clear aligner moves teeth by being made slightly "ahead" of where the teeth are, so that the plastic presses on them until they catch up. Each tray in the series moves teeth a small step, and the trays only work if they are worn for most of the day as prescribed.

That pressure works well for some movements and poorly for others. A tooth is roughly cone-shaped and sits in bone, and a smooth tray squeezing a smooth crown tends to do one thing reliably: tip it. Movements that need more control run into trouble.

• Tipping a tooth sideways usually works with the tray alone, because the plastic can press on one side of the crown.
• Rotating a tooth, especially a rounded tooth such as a canine or premolar, is hard for a smooth tray, because the plastic slides around the curve instead of turning it. An attachment gives the tray an edge to push on.
• Moving the root, not just the crown, requires a force on the crown that also levers the root in the right direction. A bump placed in the right spot lets the tray apply that leverage.
• Pulling a tooth down or up into line (extrusion or intrusion) is among the hardest movements for plastic alone, because a smooth tray has little to hold when it tries to lift a smooth tooth. A bump shaped for that movement gives the tray something to grip.
• Keeping the back teeth still while front teeth move (anchorage) may also call for attachments on the teeth that are not supposed to move.

In other words, the bump is not there because the tooth is more crooked. It is there because the planned movement for that tooth is one that plastic alone does poorly.

What changes the answer for you

Two people can start aligners with similar-looking smiles and finish with very different numbers of attachments. What usually decides it:

• The movements the plan asks for. Mild crowding that resolves with tipping may need few attachments. Rotated canines, a tooth that has to be pulled down into line, or a plan that moves roots to straighten the bite will usually need more.
• Where the moving teeth sit. Attachments on premolars and molars are rarely noticed. Attachments on the upper front teeth are more visible, and the dentist weighs that against how much the attachment helps.
• Whether the tooth is a restored surface. Resin bonds differently to a crown or veneer than to natural enamel. Bonding to ceramic needs a different preparation, and the dentist may choose to place the attachment on a neighboring natural tooth instead, or to accept slower movement.
• Attachment design. Some plans use conventional shapes placed by the clinician; others use shapes generated by planning software and described as optimized for a specific movement. A review finds that these optimized designs may help in some cases, but their advantage over conventional shapes has not been consistently shown.

If you had a consultation and the plan lists the attachments, you can ask the dentist to point to each one and say which movement it serves. A clear aligner consultation usually covers this as part of the review of the digital setup.

What the evidence says

A systematic review of clinical trials found that attachments generally improve the results of clear aligner treatment, with the most consistent benefit for tilting the roots of front teeth (torque), rotating teeth, moving teeth along the arch and keeping the back teeth still as anchorage. The same review noted that some findings were contradictory or did not reach statistical significance, that the evidence on intrusion was thin, and that the included trials carried a medium risk of bias. It is positive but not conclusive evidence.

A more recent review of rotational movements in adults put numbers on the limitation. Across the included studies, the accuracy of planned rotations averaged roughly two thirds of what was planned, with a wide range between studies, and canines and premolars were the least predictable teeth. Attachments and interproximal reduction (slimming the sides of some teeth very slightly to make room) were commonly used, but their benefit was not consistent across studies.

The practical reading for a patient is this: attachments make difficult movements more likely to happen as planned, but they do not guarantee it. Some teeth may not finish moving as planned even with attachments in place, and the dentist may then order additional aligners, often called a refinement set. Ask at the consultation how refinements are handled in your plan. If the dentist recommends an attachment on a front tooth, it is usually because the alternative is a movement that may not finish.

Living with attachments

How they look

Under the aligner, attachments are usually hard to see at a conversational distance because the resin is matched to the tooth and the plastic covers it. Without the aligner in, you can see and feel small bumps on the teeth that carry them. Attachments can be noticed more on the upper front teeth, which is why their placement there is a judgment call.

Staining and cleaning

Composite resin can pick up stain from coffee, tea, red wine and similar foods and drinks, and attachments are no exception. Laboratory studies find that the type of resin and how thoroughly it is cured affect how much it discolors and wears. In practice, you can limit staining by rinsing after dark drinks, brushing before the aligner goes back in, and cleaning carefully around the base of each bump, where plaque can build up. Keeping the aligner itself clean matters just as much, because a stained tray shows the attachments more.

Wear over time

Attachments are not static. A study that scanned attachments repeatedly during treatment found that they wear down with brushing, eating, biting forces and the repeated pulling of aligners on and off throughout the day. As a bump loses height, the tray grips it less, which can reduce the force on that tooth. This is one reason the dentist looks at the attachments at each visit and may replace one that has worn or chipped.

If one comes off

Attachments sometimes come loose (debond), for example when the aligner is pried off awkwardly or something hard is bitten. This is not an emergency. In most cases, you keep wearing the aligners on schedule so the other teeth stay on track, and you tell the office so they can decide whether and when the attachment should be replaced. The answer depends on which tooth it is and which stage of the plan you are in. Ask the office at the start of treatment what they would like you to do if an attachment comes off, and whether they want you to keep the piece.

Removal at the end

When the last aligner has done its work, the attachments are removed with fine dental burs and the enamel is then polished smooth. Laboratory studies show that attachment removal can leave very small amounts of enamel loss and small specks of resin behind, and that careful, multi-step polishing done under magnification gives the best balance between the two. The surface afterward usually looks and feels like the rest of the tooth, and the dentist checks it before fitting the retainer. Retainers follow aligner treatment in the same way they follow braces, because teeth tend to drift back without them.

The next step

If you are considering aligners, ask at the consultation how many attachments the proposed plan uses, which teeth carry them, what movement each one is for, and whether any sit on front teeth. If you have a crown, veneer or bonding on a tooth that would need an attachment, mention it. Loul Dental Studio lists clear aligners and retainers among its services; you can request an appointment online or call (805) 565-5111 during office hours. For help deciding between aligners and braces in the first place, see which questions decide the fit.