OBJECTIVES: To establish a quantitative method for objectively assessing 3-dimensional (3D) mandibular trajectories and comparing clinical evaluations with computational analyses.

METHODS: In total, 184 volunteers were recruited and grouped into control (n = 121) and temporomandibular disorder (TMD) groups (n = 63) according to the dual-axis DC/TMD checklist. 3D trajectories were generated by integrating mandibular motion and cone beam computed tomography (CBCT) records. Via digitalized data processing, the following 3 outcomes were assessed: (1) smoothness using the best-fitting polynomial curve, (2) open-closure separation by measuring the deviation between open-closure phases, and (3) condylar trajectory symmetry by comparing left and right movements. Intraclass Correlation Coefficients (ICC) were used to determine agreement between expert observations and quantitative results. Reference ranges for each parameter from the normal population were calculated. Mann‒Whitney test was used to analyze the features of the trajectories between the two groups.

RESULTS: ICC confirmed strong consistency between the parametric variations and expert observations (smoothness: 0.797; open-closure separation: 0.820; left-right symmetry: 0.920). Quantitative analyses revealed significant differences (P<0.043 for smoothness, P<0.01 for separation, and P=0.012 for symmetry) in all comparisons between movement trajectories of normal participants and those with TMD, with the latter group exhibiting greater variation and irregularities. The normal range of smoothness was calculated for condylar trajectories between 0-0.25 and 0-0.10 for incisal point trajectories. Open-closure separation normal range was computed between 0-2.28 mm for incisal point trajectory, 0-1.90 mm for left condylar trajectory, and 0-1.76 mm for right condylar trajectory. The normal range of symmetry between condylar trajectories was calculated to be between 0-4.21 mm.

CONCLUSIONS: This quantitative analysis was confirmed to be reliable and consistent with expert observations. This allowed for the discovery of substantially quantified differences in smoothness, open-closure separation, and symmetry of the motion trajectories in TMD patients versus controls.

AIM: To evaluate conditioned pain modulation (CPM) in burning mouth syndrome (BMS) patients with different pain mechanisms.

MATERIALS AND METHODS: Twenty BMS patients (52.0 ± 6.8 years, 17 women and 3 men) and age- and gender-matched 22 healthy controls were enrolled in this randomised controlled trial. The patients received an active lingual nerve block (lidocaine) and a placebo injection (saline) randomly with an interval of 1 week in a double-blinded manner. Patients evaluated their pain intensity on a 0- to 10-cm visual analogue scale (VAS) before and after each injection, with or without CPM. Based on the anaesthesia effect, BMS patients were divided into two groups with presumed different pain mechanisms; a 'central subgroup (n = 11)' with pain relief less than 1 cm and 'peripheral subgroup (n = 9)' with pain relief more than 1 cm on the VAS. Mechanical pain threshold (MPT) and wind-up ratio (WUR) were investigated at two oral mucosa regions: the region with most intense symptoms and a control region for the patient group; tongue and buccal region for the control group. CPM was induced by immersing the left hand into cold water. A moderate level of pain (around five on the VAS) was obtained by adjusting the water temperature. MPT and WUR were measured twice for all the participants with and without CPM, which was analysed and presented as relative change in MPT and WUR. Differences between groups were analysed using two-way ANOVA. Differences within group between tests were assessed by paired t-test.

RESULTS: At baseline, there were no significant group differences for MPT or WUR between BMS patients and healthy controls (p ≥ 0.156). The mean bath temperature to evoke moderate pain for the BMS group was significantly lower than that for the healthy control group (8.9°C vs. 11.9°C, p = 0.003). The CPM evoked an inhibitory modulation in 18.2%-44.4% of BMS patients, while for the healthy group, the ratio was 68.2%-81.8%. Central BMS patients had smaller CPM effects than healthy participants at the painful site and control site, which indicated a decreased CPM function (p ≤ 0.034). Peripheral BMS patients had lower CPM effects than healthy participants only at the painful site (p = 0.037).

CONCLUSIONS: The present findings documented impairment of central nociceptive inhibition processing in BMS patients which was more extensive in central BMS than peripheral BMS. These findings add to the suggestion that BMS may a heterogeneous pain condition with at least two different phenotypes.

AIMS: To investigate the effect of a lingual nerve block on spontaneous pain in patients with burning mouth syndrome (BMS) and to estimate associated somatosensory abnormalities by quantitative sensory testing (QST).

PROTOCOL AND METHODS: A standardised QST battery including cold detection threshold (CDT), warmth detection threshold (WDT), thermal sensory limen (TSL), paradoxical heat sensation (PHS), cold pain threshold (CPT), heat pain threshold (HPT), mechanical pain threshold (MPT), wind-up ratio (WUR) and pressure pain threshold (PPT) was performed at the oral mucosa of the most painful site and intraoral control site in 20 BMS patients, and at the tongue and cheek mucosa in 22 age- and gender-matched healthy controls. The effect of a lingual nerve block on spontaneous burning pain reported by the BMS patients on a 0-10 cm visual analogue scale (VAS) was investigated in a randomised double-blind crossover design using (1 mL) lidocaine (lido) or saline (sal) with an interval of 1 week. The BMS patients were grouped into 'central' and 'peripheral' mechanisms based on the effect of the lingual nerve injections. For each BMS patient, Z-scores and Loss/Gain scores were computed. Differences among groups and sites were analysed using a two-way ANOVA. Differences within group were assessed by paired t-test.

RESULTS: The 20 BMS patients were characterised on the basis of VAS changes (ΔLido-ΔSal) as a peripheral BMS subgroup (n = 9) with pain relief more than 1 cm on the VAS and a central BMS subgroup (n = 11) with pain relief less than 1 cm. BMS patients (n = 20) had lower sensitivity to thermal stimuli (i.e., CDT, WDT, TSL, CPT, HPT and PPT) and higher sensitivity to mechanical stimuli (i.e., PPT) compared with controls (p ≤ 0.007). Based on Loss/Gain coding, L1G0 (loss of thermal somatosensory function with no somatosensory gain, 55.0%) was the most frequent coding in the BMS group, which was higher than 11.4% in the control group (p < 0.001). Surprisingly, there was no significant difference between the peripheral and central BMS subgroups with regard to the Z-scores of any of the nine QST parameters (p > 0.097).

CONCLUSIONS: The results of the lingual nerve blocks demonstrated two distinct phenotypes with either peripheral or central mechanisms but no direct impact on somatosensory function. Overall, somatosensory function in BMS patients seems abnormal in the painful areas compared to matched controls with a conspicuous loss of thermosensory function.

Occlusal tactile acuity (OTA) and bite force are essential components of the sensorimotor control of oral behaviors. While these variables have been studied independently, it has not yet been revealed whethercompressive force impacts the occlusal perception mediated by the mechanoreceptive afferents in the periodontal ligament. The present study examined the effect of repetition and maximum bite force on OTA by testingnine aluminum foils of different thicknesses together with a sham test with no foil, three times each, in randomized order in 36 healthy individuals. In addition, the 40 μm foil was tested three more times at the start ofeach session to evaluate possible short-term effects. This test session was repeated with and without an interspersed maximum bite force task in between. The results demonstrated that repeated measurements increasedOTA significantly (p = 0.033); a change mainly driven by the 40 μm thickness, whereas maximum bite force testsdid not affect OTA (p = 0.097). Collectively, the results suggest that the enhanced OTA may be attributed torepetition-mediated learning and neuroplasticity within the pathways related to OTA. Furthermore, thecompressive bite force may have induced a short-term change that lasted seconds and was not detected by thesubsequent OTA measurements or may have altogether inhibited the facilitatory effect of repeated OTA. Thisunderscores the potential for future research to explore the implications of compressive force and pain on OTA inpatient populations, which could provide valuable insights into the adaptive mechanisms of the sensorimotorsystem in pathological conditions.

Background: Bruxism is a jaw-muscle activity characterized by teeth grinding and clenching. While many of its negative consequences (e.g., jaw-muscle pain, tooth fractures) are of particular interest to dentists, new insights underline the need for physicians to be knowledgeable about bruxism. In order to facilitate transfer of knowledge across disciplines, our objective was to assess what top-ranking medical journals have published on bruxism. Besides, we tested the insights described there against current science regarding the definition, assessment, epidemiology, etiology, consequences, comorbidities, and management of bruxism.

Results: In the past century, the four top-ranking medical journals have provided their readership with various bits and pieces of information on bruxism. While some of these insights have withstood the test of time, others are somewhat outdated. Further, the identified publications provide an incomplete picture of what physicians should know. The present article helps reduce this knowledge gap.

Conclusion: The role of the physician with regard to bruxism focuses mainly on its assessment and management, while insight into risk factors and comorbid conditions of bruxism is essential to high-level patient care. It is hoped that this article will contribute to improve the long-needed interdisciplinary collaboration between physicians and dentists regarding the assessment and management of bruxing patients.

The co-occurrence of bruxism, temporomandibular disorders (TMDs), and headache is common in patients. However, there is conflicting evidence regarding whether this association is simply a result of their high prevalence or whether there are indeed causal relationships. This review provides an overview of the current state of research while taking into account the controversies surrounding research methods, particularly in definitions and diagnostic standards. Bruxism-defined as repetitive jaw muscle activity during sleep or wakefulness-is not a painful disorder but may-particularly in co-occurrence with TMD-worsen pre-existing headache. It seems important to differentiate between sleep and awake bruxism because of different impact on pathophysiological processes in different primary headache disorders such as migraine and tension-type headache. Temporomandibular disorder is a heterogenous entity with both myofascial and arthrogenous types of pain in addition to nonpainful disorders. Research suggests a correlation between TMD pain and migraine, as well as between awake bruxism and tension-type headache. However, psychosocial factors may act as confounders in these relationships. Determining causality is challenging because of the limited number of experimental and clinical studies conducted on this topic. The main finding is an apparent lack of consensus on the definition and assessment criteria for bruxism. Treatment wise, it is important to differentiate all 3 conditions because treatment of one condition may have an effect on the other 2 without proving causality. For future research, it is crucial to establish greater consistency and applicability in diagnostic procedures and definitions. In addition, more experimental and clinical studies investigating the question of causality are needed.

Background: The Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) protocol recommends a 5 s and 1 kg force dynamic palpation around the lateral condylar pole of the temporomandibular joint. However, the accuracy and precision of the generated force are not known.Objective: To assess and compare the force profiles generated from dynamic palpation manually and using a palpometer, based on the forces and time recommendations suggested by the DC/TMD protocol.Methods: Nineteen healthy adults applied forces of 0.5 kg, 1.0 kg and 2.0 kg on a calibrated force sensor in a circular motion within target times of 2 s and 5 s. Participants used their right index finger for manual palpation and a calibrated palpometer for device-assisted palpation. Ten repetitions of each target force at both target times were applied. Time taken to complete each application was recorded. Repeated measures analysis of variance was used for analysis of accuracy measured as the relative difference between targeted force and actual force values and precision measured as the coefficient of variation (CV) within the 10 repeated measurements.Results: Accuracy was significantly lower (better) and precision higher (lower CV) with the palpometer than with manual palpation (p < .001). There were significant differences in accuracy and precision between the different forces but not palpation times. Most participants could not achieve the target times and tended to be faster, irrespective of the palpation method (p > .063).Conclusion: A palpometer is a more accurate and precise palpation method for dynamic force assessment compared to manual palpation; however, it remains difficult to standardize the palpation duration.

OBJECTIVES: Standardized bite training is required to prevent oral hypofunction in elderly individuals. We aimed to compare masticatory muscle activity between 24 young adults and 16 pre-elderly individuals during a biting task using a novel standardized bite device (BD).

METHODS: The BD was made of silicone rubber and included a high-force or low-force plate spring or no plate spring (dummy). The compressive stiffness of the material in each BD was measured using a texture analyzer. All participants performed a biting task 50-times at a rate of 1/s each using the three types of BDs on the right first molar. Electromyographic (EMG) activity was recorded bilaterally from the masseter and temporalis muscles. The variability of each biting training session was calculated as the coefficient of variance (CV) from the EMG activity during each biting task for each muscle. Masticatory muscle fatigue was assessed using a numerical rating scale (NRS).

RESULTS: Compressive stiffness was significantly different between each BD (P < 0.001). The CV and NRS scores were not significantly different between the groups. The EMG activities during each bite task in all muscles were not significantly different for any measurement item between the age groups. The EMG activities of high- and low-force BDs in the right temporalis (ipsilateral) muscle were significantly higher than those of the dummy BD (P < 0.001).

CONCLUSIONS: Compressive stiffness of the BD affected EMG activity only in the ipsilateral temporalis muscle, but not in the masseter or contralateral temporalis muscles, without any age effect.

Background: Despite advances in temporomandibular disorders' (TMDs) diagnosis, the diagnostic process continues to be problematic in non-specialist settings.

Objective: To complete a Delphi process to shorten the Diagnostic Criteria for TMD (DC/TMD) to a brief DC/TMD (bDC/TMD) for expedient clinical diagnosis and initial management.

Methods: An international Delphi panel was created with 23 clinicians representing major specialities, general dentistry and related fields. The process comprised a full day workshop, seven virtual meetings, six rounds of electronic discussion and finally an open consultation at a virtual international symposium.

Results: Within the physical axis (Axis 1), the self-report Symptom Questionnaire of the DC/TMD did not require shortening from 14 items for the bDC/TMD. The compulsory use of the TMD pain screener was removed reducing the total number of Axis 1 items by 18%. The DC/TMD Axis 1 10-section examination protocol (25 movements, up to 12 sets of bilateral palpations) was reduced to four sections in the bDC/TMD protocol involving three movements and three sets of palpations. Axis I then resulted in two groups of diagnoses: painful TMD (inclusive of secondary headache), and common joint-related TMD with functional implications. The psychosocial axis (Axis 2) was shortened to an ultra-brief 11 item assessment.

Conclusion: The bDC/TMD represents a substantially reduced and likely expedited method to establish (grouping) diagnoses in TMDs. This may provide greater utility for settings requiring less granular diagnoses for the implementation of initial treatment, for example non-specialist general dental practice.

Classification of temporomandibular disorders (TMD) and, indeed, all types of orofacial pains has significantly progressed in the last decade based on international consensus work and operationalized clustering of signs and symptoms. A challenging gap nevertheless continues to exist in terms of understanding the underlying pain mechanisms and link to management. Recently, a novel mechanistic descriptor 'nociplastic pain' was introduced, and diagnostic algorithms and characteristic features were proposed. This narrative and critical review aim to discuss to what extent could painful TMD conditions fit into this category. Moreover, a number of less common types of orofacial pain could possibly also reflect nociplastic pain mechanisms. A model to differentiate TMD pain mechanisms is proposed, and the implications for management are discussed. The purpose of this review is to stimulate original and novel research into mechanisms of orofacial pain and hopefully thereby improve management of the individual patient.