Study Design Main Objectives Results: Statistical significance Clinical significance: effect size (ES)
and Minimal Important Differences (MID)		 Clinical implications
The Association between Neck Disability and Jaw Disability Cross sectional study To determine whether there was a relationship between neck disability measured using the Neck Disability Index (NDI) and jaw disability measured through the Jaw Function Scale (JFS) and the level of chronic disability of TMD based on the RDC/TMD (Chronic Pain Grade Disability Questionnaire) A strong relationship between neck disability and jaw disability was found (r = 0.82, P < 0.05). A person who has a Chronic Pain Grade Disability due to TMD grade IV will increase 19.32 points on the Neck Disability Index when compared with a person without TMD disability The obtained effect size was 0.82 (correlation coefficient) The effect size of the association (ES: 0.82) between JFS and NDI is clinical significant. These results indicate that if patients with TMD have neck disability in addition to jaw disability, physical therapy treatment needs to focus on both areas since the improvement of one could have an influence in the other.
Head and Cervical Posture in Patients with Temporomandibular Disorders (TMD) Cross sectional study The main objective of this study was to determine whether patients with myogenous and mixed TMD had different head and cervical posture measured through angles commonly used in clinical research settings (i.e. tragus-C7-horizontal, pogoniontragus-C7, eye-tragus-horizontal, and tragus-C7-shoulder), when compared to healthy individuals. Craniocervical posture measured using the eye-tragus-horizontal angle was significantly different (statistically) between patients with myogenous TMD when compared to healthy subjects (3.3°, [95% CI 0.15, 6.41] P = 0.036). This indicates a more extended position of the head (craniocervical region) in this group of patients. The calculated ES for the difference between subjects with myogenous TMD and healthy subjects in craniocervical posture (eye-tragus-horizontal angle) was 0.46 The calculated MIDs for the eye-tragus-horizontal angle were1.08° and 2.70° using 0.2 and 0.5 effect sizes respectively for the calculation [28]. The difference in the eye-tragus-horizontal angle between patients with myogenous TMD and healthy subjects was very small (3.3º) and was judged to be not clinically significant based on clinical judgment since it is very unlikely that such a small difference, as the one found in this study, would be used as a criterion for determining progression or change in posture [28]. According to the results of this study, static posture evaluation of the craniocervical system is not recommended in these patients. Clinicians should consider a more functional evaluation of the head and cervical posture in clinical settings to determine functional impairment of these subjects. Better ways to evaluate functional posture are needed.
Maximal Strength of the Cervical Flexor Muscles in Patients with Temporomandibular Disorders Cross sectional study To determine whether there was a difference in maximal cervical flexor strength in subjects with TMD (mixed and myogenous TMD) when compared to healthy subjects There was no statistically or clinically significant difference in maximal cervical flexor muscle strength among groups (P > 0.05) when adjusted by body weight. Average differences in maximal cervical flexor muscle strength between healthy and subjects with TMD ranged between 3.73 and 4.45 Newtons ([95% CI -9.9, 2.4 (Newtons)] between mixed TMD vs. healthy subjects, and [95% CI -10.3, 1.4 (Newtons) between myogenous TMD vs. Healthy subjects) The ES of the differences between Patients with TMD and healthy were between 0.25 - 0.30 The MIDs in cervical flexor strength ranged between 3.0 and 7.50 Newtons using 0.2 and 0.5 effect sizes respectively for the calculation [28]. The effect sizes reached by the differences in maximal cervical flexor muscle strength among groups were estimated to be small (ES: 0.25 - 0.30). This indicated that the differences found between healthy subjects and subjects with TMD are not clinically relevant. The results highlight that probably maximal isometric cervical flexor strength is not altered in patients with TMD. However, it is unknown if other muscular groups such as cervical extensors, rotators and lateral inclinators have reduced isometric maximal strength in these patients. In addition, it is unknown if strength measured under different condition such as rapid movements and considering patients with more severe jaw disability would be affected. Future research should look into these issues and clarify the role of maximal strength of cervical muscles in this group of patients.
Electromyographic Evaluation of the Performance of Cervical Flexor Muscles in Patients with Temporomandibular Disorders while Executing the Craniocervical Flexion Test (CCFT) Cross sectional study To determine, through electromyographic evaluation, whether patients with myogenous TMD and mixed TMD had altered muscular activity on the superficial cervical muscles (sternocleidomastoids and anterior scalenes) expressed in a higher electromyographic activity when executing the craniocervical flexion test compared to normal control subjects There were marginally no statistically significant differences (P = 0.07) in electromyographic activity in the sternocleidomastoid muscles or the anterior scalene muscles in patients with mixed and myogneous TMD subjects when compared to healthy subjects when performing the craniocervical flexion test. Mean differences in EMG activity between subjects with TMD and healthy subjects ranged from 1.6% to 12.1% MVC The effect sizes of the differences in EMG activity of the SCM and AS muscles, moderate effect sizes ranging from 0.42 - 0.82 in many of the comparisons between subjects with TMD and healthy subjects were found. The minimal important differences in EMG activity of the cervical flexor muscles while performing the CCFT ranged between 1.8 - 4.9% MVC and between 4.6 - 12% MVC using 0.2 and 0.5 effect sizes respectively for the calculation [28]. Subjects with TMD had a strong tendency to have increased EMG activity of the cervical superficial muscles when compared with healthy subjects. These results are of clinical relevance (reflected by the moderate-high effect sizes found ranging between 0.42 - 0.82) This could indicate a different strategy to activate cervical muscles to stabilize the craniocervical system when compared with pain free subjects. Clinicians and researchers should acknowledge the clinical significance of these results. Thus, exercise programs addressing these abnormal motor patterns could be of value when treating subjects with TMD. Future research should test the effectiveness of this type of program in this group of patients.
Endurance of the Cervical Flexor Muscles in Patients with Temporomandibular Disorders Cross sectional study To determine whether patients with TMD (myogenous and mixed TMD) had a reduced endurance (measured through the holding time -in seconds-) of the cervical flexor muscles at different levels of muscular contraction (25%, 50%, and 75% Maximum Voluntary Contraction) when compared to healthy subjects There was a significant difference in holding time at 25% MVC between subjects with mixed TMD when compared with subjects with myogenous TMD and healthy subjects (P < 0.05). Subjects with mixed TMD had an average of almost 8 seconds (95% CI 2.7, 12.4, seconds) of difference in holding time when compared with healthy subjects and an average of 7 seconds (95% CI 2.4, 11.8, seconds) of difference when compared with myogenous TMD. The calculated effect sizes of the differences ranged between 0.60 - 0.63 (moderate effect sizes). The MIDs in holding time ranged between 2.36 and 5.94 seconds using 0.2 and 0.5 effect sizes respectively for the calculation [28]. The effect sizes found for these differences (ES: 0.60 - 0.63) were considered clinically relevant. This implies that subjects with mixed TMD had less endurance capacity at lower level of contraction (25% MVC) than healthy subjects and subjects with myogenous TMD. These results can help guide clinicians in the assessment and prescribing more effective interventions addressing this impairment for individuals with TMD.
Fatigability of the Cervical Extensor Muscles while Doing the Neck Extensor Muscle Endurance Test (NEMET) in Patients With Temporomandibular Disorders. Cross sectional study To determine through electromyographic evaluation and through the evaluation of the holding time whether patients with myogenous and mixed TMD have greater fatigability of the cervical extensor muscles (midcervical paraspinal muscles [trapezius, capitis group, and cervicis, group]) when performing a neck extensor muscle endurance test (NEMET) when compared to healthy control subjects There were statistically significant differences in holding time and normalized median frequency drop between subjects with TMD when compared with healthy subjects (P < 0.05). Subjects with TMD presented with a reduced endurance of the cervical extensor muscles. Subjects with mixed TMD presented an average of 3.45 minutes (207 seconds) less holding time than healthy subjects (95% CI 39.8, 374.2 seconds) and subjects with myogenous TMD presented an average of 3.5 minutes (211 seconds) less holding time than healthy subjects ( 95% CI 51.6, 370.5 seconds) The calculated effect sizes of the differences ranged between 0.50 - 0.52 (moderate effect sizes) [28]. The minimally important differences in holding time ranged between 1.36 minutes (81.6 seconds) and 3.4 minutes (204 seconds) using 0.2 and 0.5 effect sizes respectively for the calculation [28]. The results obtained by this study were evaluated to be clinically important (ES: 0.51). This means that the difference in holding time found among group deserves attention. Thus, clinicians should consider these findings when managing TMD. Endurance capacity of the extensor cervical muscles could be implicated in the neck-shoulder disturbances presented in patients with TMD. These results can help guide clinicians in the assessment of fatigability of the neck extensor muscles and prescribing more effective interventions addressing this impairment for individuals with TMD.

ES = effect size; MIDs = Minimal Important Differences.