How Invisalign Works: The Science

The micro-mechanics

Each Invisalign aligner is computer-designed to be slightly different from the one before — typically by 0.25 mm of movement per tooth per aligner. You wear each aligner for 7–14 days, then switch. The tooth feels light, constant pressure and responds by moving.

The biology

Tooth movement through bone isn't magic — it's a coordinated cell-level process:

1. Pressure applied to one side of the root via the aligner
2. Osteoclasts (bone-breaking cells) dissolve bone on the pressure side
3. Osteoblasts (bone-building cells) lay down new bone on the opposite side
4. The tooth moves forward as the bone reshapes around it

This process takes about 7–14 days per 0.25 mm, which is why aligners are changed weekly or biweekly.

Where the precision comes from

Every Invisalign case is designed in ClinCheck, Align Technology's planning software. Your orthodontist:

• Takes a 3D scan of your teeth
• Designs the final position virtually
• Breaks the total movement into 20–60 aligners
• Plans attachments (tiny tooth-coloured bumps) where extra grip is needed
• Plans IPR (interproximal reduction — 0.2–0.5 mm filed between teeth) when space is needed

The ClinCheck plan is iterated, often 3–5 revisions, before aligners are manufactured.

Attachments

Clear aligners are slippery against smooth tooth surfaces. Attachments are small composite bumps bonded to specific teeth that give the aligner something to grip. They're:

• Tooth-coloured and barely visible
• Applied in 15 minutes at the start of treatment
• Removed at the end with a polish
• Absolutely essential for rotations, extrusions, and root movements

IPR — interproximal reduction

When teeth are crowded, we sometimes need to create small amounts of space by filing 0.2–0.5 mm of enamel between specific teeth. This is:

• Painless (no nerve involvement at this depth)
• Invisible once done
• Reversible in terms of function
• Better than extracting teeth in most adult cases

Why 22 hours per day

Teeth need constant pressure to continue moving. If you wear aligners less than 22 hours, teeth start drifting back during the breaks, and you effectively fight yourself — treatment slows or stalls.

Common allowable breaks:

• Eating (1 hour per meal, max 2 hours total)
• Important meetings or dates (very occasional)
• Brushing and flossing

Why refinements are expected

After the initial set of aligners, 50–70% of cases need a second "refinement" set to perfect the result — one or two teeth that didn't track exactly as planned. This is normal, included in a good plan, and takes 2–4 months extra.

What controls speed

• Daily wear hours (22+ vs 18)
• Weekly vs biweekly aligner changes (depends on case)
• Tooth biology (younger patients move faster)
• Vibrating devices (AcceleDent, Propel) claimed to speed treatment — modest evidence

What Invisalign can't do

• Grow the jaw (only functional appliances do this, and only before puberty)
• Move teeth through dense, fused bone (ankylosed teeth)
• Fix severe skeletal bite problems alone (needs surgery)
• Correct severe impactions (usually needs braces + surgery)

Most general cosmetic and crowding cases are well within its range.

References

• Align Technology — Clinical research
• American Journal of Orthodontics and Dentofacial Orthopedics