Validating the factor structure and testing measurement invariance of modified Short-Form McGill Pain Questionnaire (Ortho-SF-MPQ) for orthodontic pain assessment

Objective: To validate the factor structure of recently modified Short-Form McGill Pain Questionnaire (Ortho-SF-MPQ) to assess orthodontic pain; and to test its Measurement Invariance (MI) across gender.

Methods: 180 orthodontic patients were enrolled in this study. 0.016 inch Super-elastic NiTi arch wire was used in 0.022″?×?0.028″ slot pre-adjusted edgewise appliance. After initial arch wire placement, pain was assessed at T1 (24 hours), T2 (day 3), and T3 (day 7) by using the Ortho-SF-MPQ which consists of seven sensory (pressure, sore, aching, tight, throbbing, pulling, miserable) and four affective (uncomfortable, strange, frustrating, annoying) descriptors. Confirmatory factor analysis (CFA) models were fitted for analysis. Multiple-groups CFA (MG-CFA) approach was used for MI testing.

Results: Data from 172 patients (85 male, 87 female) with mean age 14.2 years (SD 1.4) was analysed. CFA model fit indices value at T1 (RMSEA 0.048; CFI 0.995; TLI 0.995), T2 (RMSEA 0.051; CFI 0.998; TLI 0.997), and T3 (RMSEA 0.040; CFI 0.998; TLI 0.998) confirmed the validity of two-factor structure of Ortho-SF-MPQ in assessing orthodontic pain. MG-CFA model based non-significant scaled chi-square difference test (Satorra–Bentler method) for weak invariance (T1: χ²?=?6.566, df?=?9, p?=?0.682; T2: χ²?=?14.637, df?=?9, p?=?0.101; T3 (χ²?=?14.248, df?=?9, p?=?0.114) and strong invariance (T1: χ²?=?25.874, df?=?20, p?=?0.170; T2: χ²?=?25.052, df?=?20, p?=?0.199; T3: χ²?=?18.889, df?=?20, p?=?0.529) confirmed MI across male and female groups.

Conclusion: Two-factor structure (sensory and affective) of Ortho-SF-MPQ is structurally valid and invariant to measure pain in male and female orthodontic patents after initial arch wire placement.