Retention: treatment does not end when the appliance comes off

Relapse is the commonest complication in orthodontics, and its cause is biological before it is technical. Supracrestal periodontal fibres reorganise very slowly and retain a memory of the original position for years.

From this follows the principle patients struggle to accept: retention has no short expiry. The prevailing view is that effective retention should be maintained long-term, and in many cases indefinitely.

Saying so at the start of treatment avoids the difficult conversation at the end, when the patient discovers the appliance is finished but something has to stay.

Fixed retention consists of a wire bonded to the lingual surfaces of the anterior teeth. Its advantage is independence from compliance, which is why it prevails in the lower anterior segment, where relapse is most likely.

It does, however, have side effects that require periodic checking. The most insidious is unintended movement: if the wire debonds from a single tooth while remaining attached to the others, that tooth can move unpredictably.

The patient notices nothing, because there is no pain and no sense of looseness. Which is why checking bonded retainers cannot be left to spontaneous reporting.

The second effect is calculus accumulation. A lingual wire makes interproximal cleaning difficult, and in patients with inadequate hygiene it produces chronic gingival inflammation.

Instruction in the use of floss with a threader, or of a fine interdental brush, is as much part of delivering retention as the wire itself.

Removable retention, typically a thermoformed tray, has the advantage of simplicity and cleanliness, and holds the position of every tooth in the arch rather than the anteriors alone.

Its limitation is compliance. A patient who stops wearing it after a few months has no retention, and often does not say so.

Thermoformed material wears and distorts with use, and must be replaced periodically. A worn tray no longer retains: it maintains the sensation of wearing something without exerting the action.

The most widely adopted solution combines both: a bonded wire on the lower anteriors, where relapse is likeliest and compliance least reliable, and an upper night-time tray.

In summary: retention should be presented as part of treatment from the estimate onward, bonded wire requires scheduled checks because its faults are silent, and trays must be replaced as they wear. Relapse is not a failure of treatment: it is what happens when retention ends.