Written by Dr. Adriana Leone, DMD, founder of Wall Street Dental Spa · Medically reviewed October 2026
The hardest teeth to move with Invisalign are usually the canines, the premolars, and the molars, especially when they need to rotate or be pulled down into place. In a 2020 study published in the American Journal of Orthodontics and Dentofacial Orthopedics, rotation was the least accurate movement overall, and the lower first molar reached only 28% of its planned rotation. Round teeth with long or multiple roots give an aligner the least to grip.
Canines are generally the hardest teeth to move with Invisalign, followed by molars and premolars, with some upper lateral incisors close behind.
What these teeth share is shape. An aligner moves a tooth by pressing on its surfaces, so it works best on teeth with flat faces and clear edges.
Canines and premolars are rounded, molars are big and anchored by several roots, and small lateral incisors can be narrow enough that the plastic slips around them.
I’ve treated more than 500 Invisalign cases in Manhattan, and the teeth that ask for extra planning in my practice are the same ones the research points to.
| Tooth | Why it resists | Hardest movement | What helps |
|---|---|---|---|
| Canines (eye teeth) | Longest root in the mouth, rounded crown | Rotation and tipping | Attachments, slower staging, extra check-ins |
| Molars | Multiple roots in dense bone | Rotation and moving backward | Attachments, elastics, planned anchorage |
| Premolars | Round, cone-like crown with little grip | Rotation | Attachments, space from gentle polishing between teeth |
| Upper lateral incisors | Small, narrow crown | Rotation | Attachments, overcorrection in the plan |
| Central incisors | Flat surfaces, but short to grip vertically | Extrusion (moving down) | Attachments designed for vertical movement |
The canine has the longest root of any tooth, and a long root anchored in bone takes more force and more time to move.
The crown doesn’t help either. Canines are pointed and rounded, which means the aligner has fewer flat surfaces to push against. When a canine needs to turn, the plastic can slide around the tooth instead of rotating it.
The research reflects this. In a prospective study of 37 Invisalign patients published in the American Journal of Orthodontics and Dentofacial Orthopedics in 2009, canine rotation was significantly less accurate than rotation of every other tooth except the upper lateral incisors.
The same study found that once an upper canine needed to rotate more than 15 degrees, accuracy dropped significantly.
That 15-degree threshold is something I think about when I map out an Invisalign case digitally. A canine that needs a larger turn usually gets its rotation spread over more aligners, plus an attachment shaped to give the tray something to push against.
Lower canines are a frequent topic in Invisalign forums, and for good reason. The 2009 study found that tipping the lower canines forward or backward reached just 26.9% of the planned movement.
Molars are hard to move because they’re large, have two or three roots, and sit in thick bone at the back of the jaw.
Molars also do a lot of the anchoring in an Invisalign case. When I plan treatment, the back teeth often hold steady while the front teeth move against them. Asking a molar to move itself, especially to rotate or shift backward to create space, takes more force and more support from attachments or elastics.
A 2020 follow-up study of 38 patients found that mesial rotation of the lower first molar achieved just 28% of what the treatment plan predicted. That was the lowest figure in the study.
Premolars are a different story. They’re smaller than molars, but their crowns are round and almost cone-shaped, so rotation is their weak spot.
A 2025 systematic review of rotation with clear aligners found that upper canines and premolars remained the least reliable teeth to rotate, while incisors and molars were more predictable. The review rated its evidence as low to moderate certainty, so I read it as a consistent pattern that still needs better studies.
Yes, upper lateral incisors can be hard to move with Invisalign, mainly when they need to rotate or come down into line with the front teeth.
Some articles call the lateral incisors the hardest teeth of all, while others say molars. The research sits between those claims.
In the 2009 study, the upper lateral incisors were the one tooth whose rotation accuracy was close to the canines. They’re small and narrow, so the aligner has less surface to work with.
Central incisors are usually easier. Their flat front and back surfaces give the aligner good contact for tipping them in or out. Moving them down is the exception, because extrusion is one of the least accurate movements for aligners.
Rotation and extrusion are the hardest movements for Invisalign, and that often matters more than which tooth is involved.
Extrusion means pulling a tooth down (or up, on the lower arch) out of the gum to level it with its neighbors. Aligners are better at pushing a tooth than pulling it, since pulling means the plastic has to grip the tooth and lift it.
Here’s how two studies from the same research group compared predicted movement to what the teeth did.
| Movement | 2009 study (37 patients) | 2020 study (38 patients) |
|---|---|---|
| Overall average accuracy | 41% | 50% |
| Most accurate movement | Lingual constriction, 47.1% | Buccal-lingual crown tip, 56% |
| Least accurate movement | Extrusion, 29.6% | Rotation, 46% |
| Weakest single results | Upper central incisor extrusion, 18.3% | Lower first molar rotation, 28% |
A few things stand out to me. Accuracy improved over the decade, but the authors of the 2020 study concluded that the strengths and weaknesses of Invisalign “remained relatively the same.”
These percentages also describe a single round of aligners measured against the digital plan. They don’t mean treatment fails half the time. They’re the reason careful providers plan overcorrections and expect a few refinement aligners on harder cases.
Attachments are small, tooth-colored composite shapes bonded to specific teeth so the aligner has something to grip.
On a flat incisor, the aligner can push without much help. On a round canine or premolar, an attachment turns a smooth surface into one with an edge, which gives the plastic a point to push against when the tooth needs to rotate or move down.
I place attachments where the plan calls for them and nowhere else. A patient with mild spacing might need very few. A patient with rotated canines might need several.
I’ll be straightforward about the evidence. The 2025 review found attachments were widely used in rotation studies but that their effectiveness was inconsistent across studies. In my experience, attachments help most when they’re part of a plan that also slows the movement down, builds in overcorrection, and checks progress regularly.
They’re removed when Invisalign treatment ends, and the tooth surface is polished smooth.
Invisalign handles a wide range of cases, but a few situations call for a frank conversation during the consultation.
Some of these can still be treated with Invisalign plus attachments, elastics or a longer plan. Others are better served by braces or a referral to an orthodontist. I’d rather tell you that at the start than halfway through treatment.
For many adults with crowding, spacing or mild bite issues, Invisalign is a very good fit.
Myth: Big teeth are always the hardest. Size plays a part, but shape matters too. A small lateral incisor can be harder to rotate than a large central incisor.
Myth: If a tooth is stubborn, the aligners aren’t working. A slow tooth usually needs more time, an attachment or a plan adjustment. It’s a normal part of treatment on harder cases.
Myth: More pressure moves teeth faster. Teeth move through gradual changes in the surrounding bone. Skipping ahead to the next aligner early often leaves the stubborn teeth behind.
Myth: Wearing aligners at night is enough for difficult teeth. The teeth that resist movement are the ones that need consistent wear most. I ask patients to wear their aligners 20 to 22 hours a day.
A tooth that isn’t tracking is one that has fallen behind the aligner, so the plastic no longer sits flush against it.
You can often see it. There’s a small gap between the aligner and the edge of the tooth, usually on a canine or a lateral incisor. Here’s how I’d handle the common scenarios.
If you notice a gap on one tooth: Wear the current aligner for a few extra days and keep your wear time at 20 to 22 hours. Chewies, the small foam cylinders you bite into, can help seat the aligner. Let me know at your next check-in.
If the gap is growing with each new aligner: Stop moving ahead and call the office. We may need to go back a step, add an attachment or order refinement aligners.
If an attachment falls off: Keep wearing your aligners and call to have it rebonded. A missing attachment on a hard-to-move tooth can slow that tooth down quickly.
If you’ve been out of your aligners for a few days: Put the most recent aligner back in. If it doesn’t seat, try the previous one and call us.
Red flags
Any of these deserves a call rather than waiting for your next visit.
It depends on your treatment plan. Teeth that need to move out of the way to create space often go first, and the harder movements are frequently staged later or spread over more aligners. Your digital plan shows which teeth move in each stage, and your dentist can walk you through the order.
The 30 minute rule is an informal guideline to keep your aligners out for no more than about 30 minutes at a meal. Short breaks make it easier to reach 20 to 22 hours of daily wear. That consistency matters most for canines, premolars and molars, the teeth that are slowest to follow the aligner.
For many patients, the first week is the hardest. Your teeth feel pressure from the first aligner, your speech may adjust for a day or two, and you’re building new habits around eating and cleaning. Each new aligner can bring a day or two of pressure, which usually eases as treatment continues.
There’s no single published failure rate for Invisalign. Studies measure accuracy instead. In a 2020 study, teeth achieved an average of 50% of the movement planned for one round of aligners. That’s why providers plan overcorrections and refinement aligners, and why careful planning affects results more than the aligners alone.
Yes, lower canines are among the harder teeth to move with Invisalign. They have long roots and a rounded crown. In a 2009 study, tipping the lower canines reached only 26.9% of the planned movement. Attachments, slower staging and consistent wear help them keep pace with the rest of the arch.
If you have rotated canines, crowded premolars or a tooth that has been stubborn in past treatment, the right first step is a consultation where we scan your teeth and look at how each tooth would need to move. That scan tells us whether Invisalign alone can handle your case or whether it needs attachments, elastics or a different approach.
Wall Street Dental Spa is at 30 Wall Street, Suite 720, New York, NY 10005, in Manhattan’s Financial District. We’re open Monday to Friday, 8:00 am to 6:00 pm, and you can reach us at 646-566-3307. Your visit includes our complimentary spa services, so the consultation feels calmer than a typical dental appointment.
Dr. Adriana Leone, DMD, is the founder of Wall Street Dental Spa in Manhattan’s Financial District. A graduate of Tufts University School of Dental Medicine, she has practiced dentistry since 1999 and opened her boutique practice in 2005. Dr. Leone is recognized among America’s Top Dentists and is one of New York City’s most experienced Invisalign providers, with more than 500 cases completed. She built Wall Street Dental Spa around calm, judgment-free, wellness-focused care for busy NYC professionals.
