The bumps on your Invisalign trays correspond to small, tooth-colored attachments bonded directly to your teeth. Officially called SmartForce attachments, they act like tiny handles that give the aligners something to grip and push against, making it possible to move teeth in ways that smooth plastic alone cannot achieve.
What the Bumps Actually Are
Each bump is a small mound of dental composite resin, the same tooth-colored filling material dentists use for cavities. It’s custom-shaped, bonded to a specific tooth, and hardened with a curing light. The bump sits on the surface of your tooth, and a matching indentation on the inside of your aligner snaps over it. That connection between bump and aligner is the whole point: it creates a precise grip that lets the aligner deliver targeted force exactly where your orthodontist needs it.
Without attachments, an aligner is essentially a smooth shell sitting over smooth teeth. It can handle simple, straightforward shifts, but it tends to slip when it tries to do anything more complex, like rotating a tooth or pulling one downward. The bumps solve that problem by giving the aligner anchor points to push against.
Why Smooth Aligners Need Extra Grip
Clear aligners work by fitting slightly differently from your current tooth position, creating gentle pressure that nudges teeth into a new arrangement. This works well for basic side-to-side movements, but teeth are not all the same shape. Canines and premolars, for instance, are relatively cylindrical. They lack the natural ridges and undercuts that an aligner could latch onto, so the plastic tends to slide right off when it tries to rotate them. Research in orthodontic biomechanics has confirmed this: the deficiency in rotations with aligners comes down to tooth anatomy. Round teeth simply don’t give the aligner enough to grab.
Attachments change the geometry. By adding a small bump to a smooth tooth surface, your orthodontist creates an artificial undercut. Now the aligner can lock onto that bump and apply a rotational or vertical force that would otherwise be impossible. Think of it like trying to turn a doorknob with greasy hands versus dry hands. The attachment is what gives the aligner traction.
Different Shapes for Different Movements
Not all bumps look the same, and that’s intentional. The shape, size, and angle of each attachment is chosen based on the specific movement that tooth needs to make.
- Rectangular (vertical): used for controlling root position, particularly on lower front teeth where space is tight.
- Rectangular (horizontal): helps with root torque on molars and provides extra retention on short teeth where the aligner might otherwise pop off.
- Ellipsoid (oval): placed on teeth with limited surface area, like unusually small lateral incisors, where a full rectangular attachment wouldn’t fit.
- Beveled toward the gumline: designed to pull posterior teeth downward (extrusion).
- Beveled toward the biting surface: placed on teeth next to one that needs to be pushed upward (intrusion), anchoring the neighbors so force is directed correctly.
- Beveled to one side: used for rotating molars when the standard software-generated rotation attachment isn’t suitable.
Your orthodontist doesn’t choose these manually for every tooth. The Invisalign software proposes attachment placement and shape based on your treatment plan, though clinicians can override or customize the recommendations.
How They’re Placed and Removed
Getting attachments placed is quick and painless. Your orthodontist uses a clear template, similar to an aligner, that has small bubble-shaped wells in the exact spots where each attachment belongs. Composite resin is pressed into these wells, the template is seated over your teeth, and a curing light hardens the resin in about 25 seconds per spot. Once the template is peeled away, the bumps remain bonded to your teeth.
After curing, any excess material (called “flash”) around the edges is carefully scraped away with a hand instrument and checked with floss between teeth. The goal is a smooth, well-defined bump with no rough edges that could irritate your cheeks or gums. Newer bonding techniques avoid using high-speed dental drills for cleanup, which reduces sensitivity.
Removal at the end of treatment is straightforward. The composite is gently polished off the tooth surface. Because the resin sits on top of your enamel rather than cutting into it, your teeth are not damaged in the process.
Comfort and Irritation
The bumps do add a slight texture you’ll notice with your tongue, especially in the first few days. Most people adjust within a week. When your aligners are in, the attachments are covered and you’re unlikely to feel them at all. When the aligners are out, during meals for example, the bumps can occasionally catch on your lips or the inside of your cheeks. This is more common with attachments on front teeth.
If an attachment has a rough edge or feels sharp, your orthodontist can smooth it down at your next visit. Orthodontic wax, the same kind used for traditional braces, can cover a particularly irritating bump in the meantime.
Staining and How to Prevent It
Because the attachments are made of composite resin, they can pick up color from the same things that stain teeth. Coffee, tea, red wine, and smoking are the most common culprits. The colored molecules from dark beverages can penetrate the surface of the composite, gradually turning a tooth-colored bump into a yellowish or brownish one. Acidic foods and drinks make this worse by weakening the enamel around the attachment, creating a more porous surface that absorbs stains more easily. Citrus fruits, soda, and energy drinks all fall into this category. Even blue-tinted mouthwash has been observed to discolor attachments.
The simplest prevention strategy: always remove your aligners before eating or drinking anything besides water, and brush your teeth before putting them back in. If you drink coffee regularly, using a straw limits contact with your teeth. Rinsing with plain water right after finishing a dark beverage helps wash away staining molecules before they settle in. A whitening toothpaste can address mild discoloration, though some formulas contain stronger chemicals that may cause sensitivity with frequent use. For stubborn stains, a professional cleaning or polishing can resurface the attachments.
The good news is that staining on attachments is temporary by definition. The bumps come off at the end of treatment, and any discoloration goes with them.
Do You Actually Need Them?
Not every Invisalign patient gets attachments, but most do. Mild cases involving small amounts of straightening may not require them. More complex treatment plans, those involving rotations, vertical movements, or significant bite correction, almost always rely on attachments to deliver enough force. The number of bumps varies widely. Some patients have just a few, while others have attachments on nearly every tooth.
If your orthodontist’s plan includes attachments, skipping them would compromise the result. The aligners are engineered around those grip points. Without them, the trays would still fit over your teeth, but they wouldn’t produce the specific forces needed to hit each planned position on schedule.