You wore braces for two years, the retainer for two months, and twenty years later your front teeth are crowding again. You're not careless — you're typical. Here's the biology and the fix.
Three forces conspire. Elastic memory: the gum fibres around each tooth (especially supracrestal fibres) stretch during treatment and keep pulling toward old positions for years. Physiological mesial drift: teeth naturally migrate slowly forward and inward across a lifetime — everyone's do, straightened or not, which narrows the front of the arch and crowds lower incisors first. Retainer abandonment: the retention message of the 1990s–2000s was "wear it for a year"; the science since says retention is lifelong. Combine all three and the classic pattern appears: lower front crowding creeping back at 30, 40 or 50.
Relapse cases are usually the best aligner cases in existence: the big movements were done decades ago; what's left is shepherding a few drifted teeth back — often a Lite case of 4–7 months, priced at the bottom of the range ($1,450 with our partner clinic versus $3,500+ for the same relapse case in the US). It's why "relapse after braces" earns the excellent tag on our candidate page, and why a large share of adult aligner patients are second-rounders (age is not the obstacle).
Relapse is progressive: the crowding you notice at year five is milder than what year fifteen delivers, and Lite cases quietly graduate into moderate ones. If your old retainer still almost fits, that's actually useful diagnostic information — mention it in your assessment. And this time, the ending is different: modern retention protocols (nightly clear retainers, often plus a bonded wire) mean round two is the last round, provided the retainer chapter is respected.
Gum-fibre elastic memory, lifelong natural forward drift of teeth, and retention that stopped decades too early. It's the standard trio — relapse is among the most common reasons adults seek orthodontic treatment.
Usually ideally — relapse cases tend to be smaller movements than the original treatment, often finishing in 4–7 months as Lite cases at the lowest price tier.
If it still seats fully, wearing it nightly can hold the current position — but a retainer is not an aligner and forcing a tight old one over drifted teeth can harm them. Get the specific advice of an assessment first; sometimes a short aligner course then fresh retainers is the safe path.
Send photos; relapse cases often qualify for the shortest, cheapest treatment tier. Honest verdict in 24 hours.