Xiaojing Xi,1,2,* Ruofan Jin,1,3,4,* Linfeng Yu,1 Jiali Shi,1,3,4 Chen Wang,1,3,4 Kelun Wang,1,5 Jinglu Zhang,1,3,4 Yinan Chen,1,3,4 Weina Zhou1,3,4 

1Orofacial Pain & TMD Research Unit, Institute of Stomatology, The Affiliated Stomatological Hospital of Nanjing Medical University, Nanjing, People’s Republic of China; 2Department of Stomatology, Sir Run Run Hospital, Nanjing Medical University, Nanjing, People’s Republic of China; 3State Key Laboratory Cultivation Base of Research, Prevention and Treatment for Oral Diseases, Nanjing Medical University, Nanjing, People’s Republic of China; 4Jiangsu Province Engineering Research Center of Stomatological Translational Medicine, Nanjing Medical University, Nanjing, People’s Republic of China; 5Center for Sensory–Motor Interaction (SMI), Aalborg University, Aalborg, Denmark

*These authors contributed equally to this work

Correspondence: Weina Zhou; Department of TMD & Orofacial Pain, The Affiliated Stomatological Hospital of Nanjing Medical University, 1 Shanghai Road, Nanjing, 210029, People’s Republic of China, Tel +86-25-69593026, Email weina119@126.com Yinan Chen, Department of TMD & Orofacial Pain, The Affiliated Stomatological Hospital of Nanjing Medical University, 1 Shanghai Road, Nanjing, 210029, People’s Republic of China, Tel +86-25-69593026, Email echo_chen0704@126.com

Objective: The present study aimed to preliminarily explore the temporal summation (TS) response to repetitive mechanical stimulation in patients with temporomandibular joint disorders (TMD).
Patients and Methods: Twenty patients with unilateral pain in the TMJ and 20 gender- and age-matched healthy controls were included. A modified Quantitative Sensory Testing (QST) protocol was performed including pressure pain thresholds (PPT), mechanical pain thresholds (MPT), and numerical rating scale (NRS) scores of TS effects of 10 repeated 0.5 kg, 1.0 kg pressure stimuli and pinprick stimuli were determined as wind-up ratios (WUR) on the glabrous skin of the dominant hand (extra-segmental) and bilaterally in the TMJ region (segmental). Kruskal–Wallis test and Wilcoxon test were used for data analysis.
Results: Painful TMJs had significantly lower PPT and MPT compared to controls (p ≤ 0.002) and non-painful TMJs (p ≤ 0.001). Their WUR to repetitive mechanical stimulation was higher than control TMJs (p ≤ 0.033). Non-painful TMJs showed elevated WURs to pinprick stimuli compared to controls (p = 0.018). At the hand, only MPT differed (p = 0.032).
Conclusion: Patients with unilateral TMJ pain have segmentally, but not extra-segmentally, increased sensitivity to mechanical stimuli including facilitated temporal summation mechanisms at segmental as well at extra-segmental sites.
Significance: Segmental and extra-segmental temporal summation of repetitive mechanical stimulation were tested in patients with painful TMJ and healthy individuals. The finding suggests that both peripheral and central sensitization processes are involved in patients with unilateral TMJ pain.

Keywords: temporomandibular joints, temporal summation of pain, quantitative sensory testing, painful temporomandibular disorders