Orthodontic relapse: why teeth return to their original position

One of the most frustrating topics in orthodontics is relapse: the phenomenon by which teeth, after being moved to an ideal position, tend to return — partially or totally — to their pre-treatment position. Long-term studies show that significant relapse affects up to 70% of patients within 10 years of completing a conventional orthodontic treatment. Understanding why it occurs is the key to preventing it.

When a tooth is moved by an orthodontic appliance, the periodontal ligament and alveolar bone progressively remodel to adapt to the new position. But this remodelling is not instantaneous. During the months — sometimes years — following the end of active treatment, the collagen fibres of the periodontal ligament have an "elastic memory" that tends to bring the tooth back to its original position. This is why the retention phase — wearing retainers — is biologically essential at the end of any orthodontic treatment.

• Premature abandonment of retainer wear (removable plates or bonded retainer)
• Poorly fitting retainers or retainers not replaced after breakage
• Continued jaw growth in young patients (mandibular growth continues until age 25)
• Soft tissue pressure: the tongue, lips and cheeks exert permanent forces on the teeth
• Late eruption of wisdom teeth pushing the rest of the arch forward
• Untreated parafunctional habits: bruxism, thumb sucking, atypical swallowing
• Deficient initial planning: treatment not respecting the patient's muscular and functional balance

Relapse is more frequent and more pronounced after metal brace treatment than after clear aligner treatment, for several reasons. First, brace treatments are often longer, exposing the patient more to non-compliance risks for subsequent retention. Second, tooth movement with fixed appliances is often less precise in terms of three-dimensional control of the final position of each tooth — an imprecision that favours relapse. Finally, extraction treatments (removing premolars to create space) practised more frequently in conventional orthodontics have documented higher relapse rates than non-extraction treatments.

No orthodontic treatment — regardless of the appliance used — eliminates the need for a retention phase. The two main retention strategies are:

• Removable retainer: Hawley plate or thermoformed tray (essentially nocturnal after the first months)
• Bonded retainer (retaining wire): thin metal wire bonded to the inner surface of the incisors, discreet and permanent
• Combined approach: bonded for the lower arch, removable for the upper (or vice versa depending on anatomy)

The recommended retention duration has evolved: current standards recommend lifelong retention (bonded retainer) or at minimum nocturnal retention for several years. The patient must be informed of this from the beginning of treatment.

A little-known advantage of clear aligner treatments is the possibility of using the last trays of treatment as provisional retainers, before manufacturing a definitive retainer. Infinity Aligner integrates a personalised retention tray delivered with each completed treatment into its protocols, optimising patient compliance and reducing the risk of relapse during the critical months following the end of active treatment.

Orthodontic relapse is a real and documented risk, but largely preventable. It is the consequence of inadequate retention, imprecise initial planning or untreated biological factors. Require a clear retention plan from your practitioner even before starting your orthodontic treatment, and choose a system that integrates this dimension into its overall protocol.