Fig 1.

In the nested case control study, sleep quality worsened over time in the lead-up to first-onset TMD (n=220), but remained stable for matched controls (n=193). The four time periods on the horizontal axis refer to: the first quarter (i.e. 3 months) after enrollment; intermediate quarters fall between the first and penultimate quarters; the penultimate quarter immediately preceded the final quarter; and the final quarter (i.e. the 3 months prior to the follow-up visit at which presence or absence of TMD was determined). Estimates are adjusted means calculated from a generalized estimating equation regression model in which the numeric rating scale of sleep quality (range 0–10, higher scores denote worse sleep quality) was the dependent variable. Predictor variables were follow-up period (4 categories), incident TMD case classification (2 categories) and their 2-way interaction. Error bars represent ± 1 standard error (se) of the adjusted mean. Estimates are adjusted for study site, sex, age in years and race/ethnicity.

The * symbol signifies a statistically significant difference (P <0.05) compared to the first quarter in the same study group.