No effect of experimental occlusal interferences on pressure pain thresholds of the masseter and temporalis muscles in healthy women

Temporomandibular disorders: improving outcomes using a multidisciplinary approach

Patients with temporomandibular disorders (TMD) can become very complex. This article aims to highlight the importance of the multimodal and multidisciplinary approach in this type of patients to improve clinical outcomes. At present we have innumerable techniques and tools to approach this type of patients from a biopsychosocial model where active and adaptive type treatments are fundamental. There are various health professions that have competence in the treatment of TMD, however, although in the most complex cases should be treated simultaneously, still too many patients receive unique treatments and only from one point of view. This review exposes the treatments available from a clinical-scientific perspective and also emphasizes the importance of working in specialized units with those professionals who have competencies on the different conditions that may occur.

Occlusal interference induces oxidative stress and increases the expression of UCP3 in the masseter muscle: A rat model

OBJECTIVE

To determine whether occlusal alteration contributes to masticatory muscle damage by inducing oxidative stress.

DESIGN

Thirty Sprague-Dawley rats were randomly divided into six groups, including occlusal interference groups (3 days, 7 days, 14 days, 21 days, and removal for 3 days) and a sham group. A rat experimental model of occlusal interference was generated by a 0.6-mm unilateral bite-raise. The rats were euthanised for evaluation of histologic changes in the masseter muscles using haematoxylin-eosin staining. To further investigate the role of oxidative stress and uncoupling protein (UCP3) in the development of occlusal dysfunction-induced masseter damage, levels of UCP3 protein were measured by western blot analysis.

RESULTS

Compared with the sham group, the connective tissue of the masseter muscle was extended partially and inflammatory cells appeared following the induction of malocclusion. With respect to the oxidative stress markers, there were increases in malondialdehyde (MDA) content but decreases in superoxide dismutase (SOD) and glutathione peroxidase (GPX) activities; furthermore, the expression of UCP3 was upregulated. After eliminating the occlusal interference for 3 days, the degree of inflammation was substantially alleviated, the MDA content decreased, and SOD and GPX activities increased. The expression of UCP3 decreased.

CONCLUSIONS

Occlusal interference induces oxidative stress in the masseter muscle, regulated by UCP3. Overall, these findings have significant implications for the understanding of how occlusal dysfunction causes muscle fatigue and pain.

Quantitative sensory response of the SCM muscle on sustained low level activation simulating co-contractions during bruxing

OBJECTIVE

Bruxism is discussed as an etiological factor in the pathogenesis of orofacial and cervical pain. As the sternocleidomastoid muscle (SCM) is co-activated during clenching, our aim was to investigate, whether the muscle loading leads to peripheral or central sensitizations.

DESIGN

In twenty-one healthy female volunteers, somatosensory profiles of the SCM were recorded according to the test battery of the German Research Network on Neuropathic Pain (DFNS) prior to and after an isometric muscle exercise. QST comprised thermal and mechanical stimuli. A submaximal activation of the SCM (15% MVC) was kept for 10min in sitting position. In separate test sessions one month apart, one sham and one verum experiment were conducted in randomized order. During the muscle loading, the parameters cold detection threshold (CDT), mechanical pain sensitivity (MPS) and pressure pain treshold (PPT) were tested and experimental pain recorded by visual analogoue scales (VAS). All test sessions were performed during the follicular phase of the menstrual cycle (day 5), to avoid effects on pain perception. Data were analyzed with Repeated Measures ANOVA (SPSS 22.0) RESULTS: No significant changes were found during or after (sham) loading except for stimulus-response-function (SR, P=0.01) and PPT (P=0.02) in the sham test. No effect was observed in the verum experiment (P=0.12 up to 1.0).

CONCLUSION

Prolonged low level contraction of the SCM does not evoke painful sensitization. In contrast, submaximal muscle activation seems to have a protective effect corresponding to a training effect preventing sensitization.

ERK potentiates p38 in central sensitization induced by traumatic occlusion

This study was to investigate the role of p38 activation via ERK1/2 phosphorylation in neurons and microglia of the spinal trigeminal subnucleus caudalis (Vc) in the promotion of orofacial hyperalgesia induced by unilateral anterior crossbite (UAC) traumatic occlusion in adult rats. U0126, a p-ERK1/2 inhibitor, was injected intracisternally before UAC implant. The effects of the U0126 injection were compared to those following the injection of SB203580, a p-p38 inhibitor. Mechanical hyperalgesia was evaluated via pressure pain threshold measurements. Brain stem tissues were processed for a Western blot analysis to evaluate the activation of ERK1/2 and p38. Double immunofluorescence was also performed to observe the expression of p-ERK1/2 and p-p38 in neurons (labeled by NeuN) and microglia (labeled by OX42). The data showed that UAC caused orofacial hyperalgia ipsilaterally on d1 to d7, peaking on d3 (P<0.05). An upregulation of p-ERK1/2 was observed in the ipsilateral Vc on d1 to d3, peaking on d1. An upregulation of p-p38 was also observed on d1 to d7, peaking on d3 (P<0.05). p-ERK1/2 primarily co-localized with NeuN and, to a lesser extent, with OX42, while p-p38 co-localized with both NeuN and OX42. Pretreatment with U0126 prevented the upregulation of both p-ERK1/2 and p-p38. Similarly to an intracisternal injection of SB203580, U0126 pretreatment attenuated the UAC-induced orofacial hyperalgesia. These data indicate that UAC caused orofacial hyperalgesia by inducing central sensitization via the activation of ERK1/2 and p38 in both neurons and microglia in the Vc, potentially impacting the effects of p-ERK1/2 during p38 activation.

Botulinum neurotoxin effects on masseter muscle fibre in WNIN obese rats-Scanning electron microscope analysis

WNIN/Ob obese mutant rats are unique in comparison to similar rodent models of obesity established in the West. The present study is aimed to evaluate the masticatory function and histological changes in masseter muscle fibres treated with botulinum toxin type A (BoNT/A) in WNIN/Ob rats. Twelve WNIN/Ob obese rats and 12 lean rats at 35 days of age were taken and divided into four groups (6 rats in each group): Group-I (WNIN/Ob) and Group-II (lean) rats were injected with BoNT/A (1 unit) into right side of masseter muscle. For control left masseter of both phenotypes was injected with saline. Group-III (WNIN/Ob) and Group-IV (lean) rats were without any treatment. Growth and food intake was monitored daily for 45 days. Rats were euthanized and gross necropsy was carried out to check any abnormalities. Masseter muscles were dissected and mean muscle mass was recorded. Small portion of muscle was stored in 10% formalin for hematoxylin-eosin (H&E) staining and remaining tissue stored in gluteraldehyde for scanning electron microscopy (SEM). There is a significant decrease in the body weights and food intake of BoNT/A treated obese rats. The H&E staining of the masseter muscle in both groups showed normal morphology and orientation. The SEM analysis showed that, fibre size in BoNT/A treated masseter muscle of obese rats increased more than the saline treated side and in control rats. The increase in the muscle fibre size and transition of muscle fibre subtypes may be due to the reduced masticatory function of the masseter muscle. SCANNING 38:396-402, 2016. © 2015 Wiley Periodicals, Inc.

Dental occlusion, body posture and temporomandibular disorders: where we are now and where we are heading for

The aim of this investigation was to perform a review of the literature dealing with the issue of relationships between dental occlusion, body posture and temporomandibular disorders (TMD). A search of the available literature was performed to determine what the current evidence is regarding: (i) The physiology of the dental occlusion-body posture relationship, (ii) The relationship of these two topics with TMD and (iii) The validity of the available clinical and instrumental devices (surface electromyography, kinesiography and postural platforms) to measure the dental occlusion-body posture-TMD relationship. The available posturographic techniques and devices have not consistently found any association between body posture and dental occlusion. This outcome is most likely due to the many compensation mechanisms occurring within the neuromuscular system regulating body balance. Furthermore, the literature shows that TMD are not often related to specific occlusal conditions, and they also do not have any detectable relationships with head and body posture. The use of clinical and instrumental approaches for assessing body posture is not supported by the wide majority of the literature, mainly because of wide variations in the measurable variables of posture. In conclusion, there is no evidence for the existence of a predictable relationship between occlusal and postural features, and it is clear that the presence of TMD pain is not related with the existence of measurable occluso-postural abnormalities. Therefore, the use instruments and techniques aiming to measure purported occlusal, electromyographic, kinesiographic or posturographic abnormalities cannot be justified in the evidence-based TMD practice.