Two patients with similar crowding can need very different treatment once you look at their periodontal health, bite, age and likely compliance. This guide follows the order of a good case assessment: diagnosis, the patient, the malocclusion and its complexity, then the decision.
1. Start with the diagnosis, not the simulation
A digital treatment simulation shows a proposed sequence of tooth movements. It shows what the software has been asked to do. It does not show whether the bone, roots and periodontium can support those movements, whether the final bite will be stable, or whether the patient’s goals are realistic.
Studies comparing planned and achieved movements have repeatedly found gaps between the two. A prospective study by Haouili and colleagues (2020) reported a mean accuracy of about 50% across the movements measured, with rotation among the least accurate. Results vary by system and protocol, but the achieved result often differs from the simulated one.
So diagnosis comes first: a clinical examination, complete records (intraoral scans, photographs, and radiographs where clinically indicated), a periodontal assessment and a written problem list. Then review the simulation against your diagnosis.
The simulation is a way to test a plan, and it should never be the plan itself.
2. Assess the patient’s goals and expectations
Find out what the patient wants before looking closely at the teeth. Some care mainly about the appearance of their front teeth. Others have a functional concern, such as wear or difficulty cleaning, or need tooth movement before restorative work. Each goal can lead to a different treatment.
Then compare the patient’s goals with your diagnosis. A patient who wants only the upper incisors aligned may also have a posterior crossbite or a skeletal discrepancy, and needs to understand what a short anterior treatment will and will not change.
At the clear aligner consultation, discuss duration, possible refinements, attachments, IPR and retention. A technically good result can still disappoint a patient who expected something different, so any gap between their goals and your clinical findings should be discussed before treatment starts.
3. Evaluate oral and periodontal health
Orthodontic tooth movement should take place in a healthy mouth. Active caries, untreated periodontal disease, symptomatic teeth and poor oral hygiene should be managed before treatment, or in some cases alongside it with close monitoring.
Review the medical and dental history. Medications that can affect bone remodeling, such as bisphosphonates, conditions that affect healing, previous orthodontic treatment, trauma and known root resorption do not automatically rule out aligners, but they change the risk and the plan.
Assess probing depths, bleeding, recession, mobility and bone levels. Patients with reduced periodontal support can often still be treated orthodontically. The European Federation of Periodontology (EFP) guideline on stage IV periodontitis includes orthodontic tooth movement as an option once the goals of periodontal therapy have been reached, with supportive periodontal care during and after treatment. With less bone support, forces generally need to be lighter and some movements are harder to control.
Note restorations, missing teeth, implants and teeth with a doubtful prognosis. Implants and ankylosed teeth will not move, and crowns can affect aligner fit and attachment bonding. Finally, consider hygiene. A patient who struggles with plaque control before treatment is likely to find it harder with aligners covering the teeth.
4. Evaluate the malocclusion
Assess the malocclusion in all three planes. No single finding makes a case suitable or unsuitable for clear aligners. What matters is the severity, the cause, the movements needed and how they will be controlled.
Crowding and spacing. Mild to moderate crowding often suits aligners when it can be resolved with modest expansion, proclination or IPR. Severe crowding raises the question of where the space will come from, including extractions. Spacing is often simple to close, but spaces from tooth-size discrepancy, missing teeth or periodontal drifting may also need a restorative plan.
Rotations. Small incisor rotations are usually manageable. Larger rotations of rounded teeth, such as canines and premolars, are harder for an aligner to grip. Kravitz and colleagues (2009) found that the accuracy of maxillary canine rotation fell significantly above 15 degrees.
Vertical problems. Deep bite and open bite correction may involve intrusion, extrusion or both, and these movements behave differently with aligners. Whether the cause is dental, skeletal or habit-related matters as much as the measurement.
Transverse problems. A dental crossbite of one or two teeth may respond well to aligners. In adults, aligner expansion is generally achieved by tipping the teeth, so a skeletal transverse problem has clear limits.
Anterior-posterior discrepancies. Small dental Class II or Class III discrepancies can sometimes be managed with distalization, elastics or IPR. Larger or skeletal discrepancies may call for growth modification, temporary anchorage, fixed appliances or surgery.
TMJ considerations. Record pain, clicking, limited opening and any large difference between centric relation and maximum intercuspation. A patient with active symptoms may need assessment before orthodontic treatment starts.
5. Understand the limits of tooth movement
Aligners move teeth by pushing on them, in small steps of around 0.25 mm per aligner in most systems. This works well for some movements and less well for others. An overview of systematic reviews by Alwafi and colleagues (2023) rated the evidence as low to moderate, but a general pattern appears.
- Buccal-lingual tipping of incisors tends to be among the more predictable movements.
- Rotations of canines and premolars are less predictable, especially as the planned rotation increases.
- Vertical movements are generally less predictable, and incisor extrusion has been reported as one of the least accurate.
- Bodily movement and root control, such as torque and root paralleling, need more force control than simple tipping.
Attachments give the aligner a surface to push against. Elastics, buttons and temporary anchorage devices extend what aligners can do. Staging, overcorrection and accurately performed IPR also affect whether the plan tracks.
For clear aligner treatment planning, the practical point is this: when a case depends on several less predictable movements, expect more refinements, more auxiliaries and a greater need for experience. The case may still be suitable, but it changes how you plan it and prepare the patient.
6. Recognize more complex cases
A complex case does not have to be turned away. It may need more experience, additional mechanics, a different appliance or a specialist opinion.
- Significant skeletal discrepancies, especially when the patient expects facial change
- Extraction cases, where root paralleling and anchorage control are demanding
- Severe deep bites or open bites, particularly skeletal or habit-related ones
- Large canine and premolar rotations, or several teeth needing extrusion
- Impacted or severely displaced teeth
- Reduced periodontal support with complex restorative or implant needs
- TMJ symptoms or a large difference between centric relation and maximum intercuspation
- Growing patients with a skeletal pattern that may benefit from growth modification
In children and adolescents, erupting teeth affect aligner fit and timing matters for skeletal problems, so an early orthodontic assessment is often useful.
When a case is beyond your experience, you can add auxiliaries, work with an experienced clinical planning team, or refer.
7. Consider patient compliance
Aligners work only when they are worn. Most protocols ask for about 20 to 22 hours a day, with aligners removed only to eat, drink anything other than water, and clean the teeth. Low wear time shows as aligners that do not seat fully, teeth that fall behind the plan and unplanned refinements. During treatment, it can be hard to tell whether the plan or the wear is the cause.
- How the patient has followed past advice, such as hygiene or retainer wear
- Their daily routine, including work, travel and eating habits
- Whether the motivation is their own
- How reliably they attend appointments
Hygiene and diet count too. Sugary or acidic drinks with aligners in place can increase the risk of caries and erosion.
Discuss compliance openly and without judgment. For some patients, a fixed appliance is the better choice, and it helps to say so early.
8. A practical clear aligner case selection checklist
Use this checklist for an initial clear aligner case assessment, before you review the simulation.
- Medical and dental history reviewed
- Intraoral scans and photographs complete, with radiographs where clinically indicated
- Problem list and treatment objectives written down
- Main concern and expected result understood
- Duration, attachments, IPR, possible refinements and retention explained
- Wear time, hygiene and appointment commitment discussed
- No active caries or untreated periodontal disease, or a plan to manage it first
- Periodontal support and bone levels assessed
- Restorations, implants, missing teeth and teeth with a doubtful prognosis noted
- Assessed in all three planes
- Skeletal component identified or ruled out
- Growth status considered for younger patients
- TMJ findings recorded
- Key movements identified and their predictability considered
- Need for attachments, auxiliaries, IPR and anchorage planned
- Case is within your experience, or a plan for added support, co-management or referral is in place
- Simulation reviewed against the diagnosis, and not the other way round
Conclusion
Good aligner treatment starts before the first aligner is designed. It starts with a diagnosis, a careful look at the patient’s goals and oral health, and a clear view of how complex the case is. The simulation then tests the plan rather than replacing it. Careful case selection will not remove every challenge, but it helps reduce avoidable complications, unplanned refinements and difficult conversations later.
