Tooth wear and tertiary crowding: a 13-year cohort study in Amazon Indigenous populations.

Background: Tooth wear is an important mechanism for reducing dental dimensions and, consequently, dental crowding. The objective of this cohort study was to examine the relation of tooth wear, adjusted for covariates (age, tooth loss, arch perimeter and intercanine width), on tertiary crowding in Amazon Indigenous populations.

Methods: A sample of 40 Indigenous people in permanent dentition at T0 (baseline) and after 13 years (T1) were evaluated. The sample included 16 males and 24 females belonging to two villages, Arara (n = 22, mean ages 16.6 and 29.9 years) and Assurini do Xingu (n = 18, mean ages 16.0 and 29.6 years). Clinical, intraoral photograph and dental cast evaluations were performed at both times. The anterior crowding was measured using Little's Irregularity Index (LI) and modeled through a multilevel linear regression with the predictor variables: village, tooth wear (T1-T0), age (T0), tooth loss (T1-T0), changes in intercanine width (T1-T0) and changes in arch perimeter (T1-T0).

Results: A slight increase was observed (< 1 mm) in anterior dental crowding and a decrease in arch perimeter < 1.5 mm, while tooth wear increased between 0.65 and 0.99 units. The contextual variable (village) had no significant association with LI. In the upper arch, tooth loss was the only variable that showed an inverse association with LI (β=-0.41, p < 0.05). In the lower arch, the increase in dental crowding was inversely associated with tooth wear (β=-1.30, p < 0.05) and changes in arch perimeter (β=-0.31, p < 0.05). The other variables did not show significant associations.

Conclusion: After 13 years, dental crowding and tooth wear increased, while the arch dimensions tended to decrease. The changes in long-term dental crowding seem to have distinct etiological components for each dental arch. In the mandible, the changes in incisor alignment were associated with increased tooth wear and decreased dental arch dimensions. Whereas in the maxilla, only tooth loss caused alterations in tooth alignment. It is suggested that the effect of increased tooth wear on the etiology of tertiary crowding is of small magnitude and restricted to the lower dental arch.