A review of changes in lower arch alignment from seven to fifty years.

Changes in alignment in the untreated lower arch were studied at various developmental stages: 7 to 10 years, 10 to 12 years, 12 to 15 years, 13 to 18 years, 18 to 21 years, 21 to 28 years, and 18 to 50 years. On average, crowding decreased between 7 and 12 years and increased thereafter. The maximum increase occurred in the teenage years between 13 and 18, little or no change occurred in the third decade, and small increases occurred later in life. The possible cause of these changes is discussed in relation to the deterioration in alignment reported in orthodontically treated patients after retention.