If you've started researching clear aligners, you've probably hit a fork in the road early on: do you treat just one row of teeth, or both? The decision sounds simple — until you realise it affects your treatment time, your final cost, and most importantly, whether your bite still works at the end of treatment.

This guide breaks down the real difference between single arch and dual arch aligners, who each option actually suits, and how to avoid the most common (and expensive) mistake people make when choosing between them.

What's the difference between single arch and dual arch aligners?

The terminology is more straightforward than it sounds. Your "arches" are simply the upper and lower rows of your teeth.

Single arch aligners treat only one row — either your upper teeth or your lower teeth, not both. You wear a series of clear trays on the arch being corrected, while the opposite arch stays untouched.

Dual arch aligners treat both rows simultaneously. You receive trays for your upper and lower teeth, and they work together throughout your treatment.

At Smileie, both options are available in daytime (20+ hours of wear per day, faster results) and nighttime (10 hours, slower but more discreet) plans. Daytime single arch starts at $937, while daytime dual arch is $1,160 — both fully inclusive of impression kit, 3D treatment plan, aligners, retainers, whitening, and free refinement.

The price difference makes single arch tempting. But cheaper isn't always smarter — and here's where most people get it wrong.

See the difference

Toggle between the two options below to see exactly which teeth get treated in each case.

When single arch aligners are genuinely the right choice

Single arch treatment makes sense in a specific set of situations. If any of the following describe you, you're likely a strong candidate:

• Only one arch has visible alignment issues. Your top teeth are crowded but your bottoms are straight, or vice versa.
• Your bite is already good. When you close your teeth together, everything lines up correctly — no overbite, underbite, crossbite, or open bite.
• The teeth not being treated are stable. They haven't shifted recently and aren't likely to shift during treatment.
• You've had previous orthodontic work on one arch and now want to correct the other.
• You're treating a relapse — a common scenario where one row of teeth has drifted years after braces or aligners, while the other row stayed put.

When these conditions are met, single arch treatment can save you money, finish faster, and produce results just as polished as full treatment. Smileie's single arch plan is also available in flexible monthly instalments from $160/month.

When dual arch aligners are the smarter call

Dual arch treatment isn't always about treating "more." It's often about treating correctly. Here's when it becomes the better — sometimes the only — option:

• Both arches have alignment issues. Even minor crowding or spacing in the untreated arch will become more noticeable once the other arch is straightened.
• Your bite is off. Overbites, underbites, crossbites, and deep bites almost always need both arches to move in coordination. Treating only one arch in these cases can make the bite worse, not better.
• You want symmetry. Faces and smiles look balanced when both arches align with each other. Treating only the upper teeth, for example, can leave a noticeable mismatch.
• You've had teeth shift after previous orthodontics. Even if the visible movement is on one arch, the underlying cause often affects both.
• You're aiming for a full smile transformation. Cosmetic upgrades tend to look incomplete when only half the work is done.

Smileie's daytime dual arch package at $1,160 includes everything needed for full treatment — or you can spread it over time with the pay-as-you-smile instalment plan at $200/month.

The one factor most people overlook: your bite

Here's the part most online aligner content skims over. Your bite — the way your upper and lower teeth meet — is the single most important consideration in this decision, and you can't fully assess it on your own.

When you straighten just one arch, the teeth in that arch shift position. If the opposite arch stays still, the way your teeth come together changes. In mild cases, this is fine. In moderate cases, it can cause:

• Premature wear on certain teeth
• Jaw discomfort or new tension
• Teeth that look straight but feel "off" when biting
• The need for refinement aligners to fix new bite issues

This is why Smileie won't let you self-prescribe. Your treatment starts with either an at-home impression kit or an in-person 3D scan, which gets reviewed by qualified dental professionals before any aligners are made. That review is where the single-vs-dual decision actually gets made, based on what your teeth and bite need.

Cost comparison: all four Smileie options

Smileie offers four core treatment plans across daytime and nighttime wear schedules. Here's the full breakdown — current sale prices included.

Every plan includes the same comprehensive package — there are no hidden add-ons or surprise fees later in treatment.

If your case is borderline and you go with single arch when you actually needed dual, you'll often need refinement aligners later — or end up commencing a second round to fix what was missed. Many people who try to save upfront spend more in the end. See the full payment plan breakdown to find what fits your budget.

How to actually figure out which one you need

You can't reliably make this call from the bathroom mirror. The proper sequence looks like this:

1. Take a candidacy assessment. Smileie's free 30-second smile assessment screens whether you're suitable for at-home aligners at all.
2. Order an impression kit ($99) or book an in-person scan. This captures the precise 3D geometry of both your arches and your bite.
3. Receive your 3D treatment plan. A licensed dental professional reviews your scans, plans the movements your teeth need, and recommends single or dual arch based on what's clinically required — not what's cheaper.
4. Review the plan before paying. You see a digital preview of your final smile and the recommended approach. If you're not happy with the plan or aren't a candidate, you don't pay for treatment — that's covered by Smileie's 100% guarantee.
5. Commence treatment knowing it's the right call. With the assessment done properly, you avoid the costly mistake of half-treating a problem that needed both arches.

Read the full step-by-step of how Smileie aligners work for more detail on the process.

Frequently asked questions