Table 2.

Univariate associations between self-reported pain-related disability, factors that modify pain, and non-pain characteristics as etiologic risk factors measured categorically and incidence rate of first-onset TMD, OPPERA prospective cohort study, USA (2006–2011)

Putative risk factor	Category	N	Site-adjusted(1) TMD incidence rate (% of people per annum)	Study site-adjusted effect(2)	Site, demographic adjusted effect(3)	P-value	Imputed values for loss to follow-up(4)	P-value
Facial Graded Chronic Pain Status	2-4	20	13.37	4.40 (1.90, 10.14)	4.05 (1.74, 9.39)	<0.001	3.43 (1.48, 7.91)	0.004
	1	252	5.04	1.73 (1.23, 2.43)	1.74 (1.23, 2.45)		1.68 (1.18, 2.37)	0.003
	0 [ref]	2414	2414
Number of activities that modified facial pain last month	4-5	15	9.34	1.71 (0.42, 6.88)	3.75 (0.76, 18.24)	0.890	2.65 (0.59, 11.76)	0.200
	2-3	29	2.71	0.47 (0.08, 2.60)	0.49 (0.08, 2.69)		0.30 (0.03, 2.71)	0.280
	0-1 [ref]	42	5.44
Number of non-specific orofacial symptoms	3 or more	119	7.90	2.97 (1.96, 4.47)	2.89 (1.91, 4.35)	<0.001	2.43 (1.57, 3.74)	<0.001
	1-2	383	5.39	2.01 (1.49, 2.71)	1.98 (1.46, 2.67)		1.96 (1.44, 2.65)	<0.001
	0 [ref]	2226	2.66

⁽¹⁾Adjusted rates computed using Poisson regression controlling for study site (categorical variable, 4 levels). Estimated rate is for reference study site (University of Buffalo)

⁽²⁾Rate ratio represents relative increase in incidence rate of TMD relative to reference group. Calculated using Cox proportional hazard regression model adjusted for study site (categorical variable, 4 levels).

⁽³⁾As for footnote 2, with additional adjustment for age in years, gender (categorical, 2 levels), race/ethnicity (categorical, 2 levels) and lifetime U.S. residence (categorical, 2 levels)

⁽⁴⁾As for footnote 3, with inclusion of imputed TMD rates for subjects lost to follow-up and imputed data for values missing at baseline