What Invisalign cannot fix
Clear aligners struggle with large vertical movements, severe rotation of round teeth, closing large extraction gaps, significant skeletal bite discrepancies, and any case needing substantial root movement. Fixed braces still handle these better, and some need jaw surgery regardless of the appliance.
Clear aligners have got dramatically better over twenty years and now handle a large majority of the cases that used to require brackets. That success has produced a marketing claim that outruns the evidence, and a set of cases where aligners are offered because the patient wants them rather than because they will work.
The physics is simple. A bracket bonded to a tooth lets an orthodontist apply force and, crucially, a couple — a twisting moment — precisely where they want it. An aligner is a plastic shell gripping the crown. It is excellent at tipping teeth and much weaker at moving roots, extruding teeth, and rotating anything cylindrical.
1. Large vertical movements
Pulling a tooth down into the arch (extrusion) or pushing it up (intrusion) by more than about 2mm is where aligners are weakest. A shell has very little to grip when trying to pull a tooth out of the bone. Attachments — the small tooth-coloured bumps bonded on — help, but there is a limit. Severely over-erupted or impacted teeth usually need brackets, sometimes with a chain to a surgically exposed tooth.
2. Severe rotation of round teeth
Premolars and canines are close to cylindrical. Rotating a cylinder inside a shell that grips it is mechanically awkward, and beyond roughly 20 degrees of rotation on a premolar the aligner tends to slip rather than turn the tooth. Flat-sided teeth like incisors rotate much more readily.
3. Closing large extraction spaces
Where teeth have been removed to make room, the remaining teeth must be translated bodily across the gap — root and crown together. Aligners tend to tip the crown into the space while the root lags, producing an unstable result that relapses. Cases needing more than about 4mm of space closure are usually better with fixed appliances.
4. Skeletal bite problems
In growing children, functional appliances can influence jaw growth. In adults, growth is finished.
5. Cases needing substantial root movement
Uprighting a badly tipped molar, correcting root angulation before an implant, or torquing incisor roots into the right position — all of these are bracket territory. An aligner can be designed to attempt them, and often does about 60–70% of what the digital plan predicted, which is why refinement rounds exist.
6. Anyone who will not wear them
This is the most common failure by a wide margin and the least discussed. Aligners need 20 to 22 hours a day. At 14 hours a day the treatment does not go slowly, it goes wrong — the teeth track away from the plan and the aligners stop fitting. Fixed braces work whether or not you feel like it that week.
If you are honest with yourself about compliance and the answer is uncertain, that is a clinical fact worth telling the orthodontist, not a character flaw to hide.
What aligners do genuinely well
| Case type | Aligners | Fixed braces |
|---|---|---|
| Mild to moderate crowding | Excellent | Excellent |
| Spacing / gaps | Excellent | Excellent |
| Mild relapse after old braces | Excellent | Overkill |
| Deep bite | Good | Good |
| Large rotations | Limited | Strong |
| Extraction space closure | Limited | Strong |
| Impacted canines | No | Strong |
| Skeletal discrepancy | No | No — needs surgery |
The question to ask a provider
"Would you treat this case with brackets if I had no preference?" A provider who says yes and explains why aligners are still reasonable is giving you a real answer. A provider who says aligners can do anything brackets can is selling.
It is also worth knowing whether the person treating you is an orthodontist or a general dentist who offers aligners. Both can be excellent; the training gap is three years, and it shows most in exactly the difficult cases described above.
Common questions
Can Invisalign fix an overbite?
A dental overbite — where the problem is tooth position — often yes. A skeletal overbite, where the jaws themselves are mismatched, no appliance corrects in an adult.
Is Invisalign slower than braces?
For suitable cases it is comparable, typically 12 to 18 months. For complex cases it is slower and more likely to need refinement rounds.
What happens if aligners do not achieve the plan?
A refinement round: new scans, a new series of aligners, usually included in the original fee for a set number of rounds. Check how many are included before you sign.
Are mail-order aligners the same thing?
No. Remote aligner services work without X-rays or an in-person examination, which means no one has assessed your root position or gum health. For anything beyond very mild crowding this is a meaningful risk.
