The sad fact is, 10 years after completion of orthodontic treatment, only 30-50% of patients retain satisfactory teeth alignment1. After 20 years, this further drops to only 10% of patients1. While most changes to teeth alignment are due to late jaw changes between the ages of 20-30 years, tooth movement and crowding can still continue in your 50's or 60's2.
Crooked teeth can also affect your oral health - when teeth overlap, they can wear down unevenly and are harder to keep clean. Plaque and tartar build up faster, which leads to gum infections such as gingivitis and periodontitis.
1. Yu, Y. (2013). Interventions for managing relapse of the lower front teeth after orthodontic treatment (Review). Cochrane Database of Systematic Reviews.
2. Blake, M. and Bibby, K. (1998). Retention and stability: A review of the literature. American Journal of Orthodontics and Dentofacial Orthopedics, 114(3), pp.299-306.