Temporomandibular disorders (TMD) comprise the most common cause of chronic facial pain conditions, and they are often associated with somatic and psychological complaints including fatigue, sleep disturbances, anxiety, and depression. For many health professionals, the subjectivity of pain experience is frequently neglected even when the clinic does not find any plausible biologic explanation for the pain. This strictly biomedical vision of pain cannot be justified scientifically. The purpose of this study is to demonstrate, by original articles from the literature and recent studies conducted in our own laboratory, the biological processes by which psychological stress can be translated into the sensation of pain and contribute to the development of TMD. The role of the hypothalamic-pituitary-adrenal axis, the serotoninergic and opioid systems in the pathogenesis of facial pain is exposed, including possible future therapeutic approaches. It is hoped that knowledge from apparently disparate fields of dentistry, integrated into a multidisciplinary clinical approach to TMD, will improve diagnosis and treatment for this condition through a clinical practice supported by scientific knowledge.

Objective: To systematically review the relationship between malocclusions and masticatory performance. In addition, we will perform a qualitative analysis of the methodological soundness of the studies. Materials and Methods: A literature survey was done by applying the Medline database (www. ncbi.nim.nih.gov) in the period from January 1965 to June 2009, using the ''Medical Subject Headings'' term malocclusion crossed with various combinations of the following terms: masticatory performance, masticatory efficiency, and chewing efficiency. The articles were separated into two main topics: (1) the influence of malocclusion treatment (orthognathic surgery) and (2) the influence of malocclusion type and severity. Results: The search strategy used identified 78 articles. After selection according to the inclusion/ exclusion criteria, 12 articles qualified for the final analysis. The research quality and methodological soundness were high in one study, medium in 10 studies, and low in one study. The most serious shortcomings comprised the clinical trials and controlled clinical trials designs with small sample sizes and inadequate description of selection criteria. Lack of method error analysis and the absence of blinding in measurements were other examples of shortcomings. Conclusions: Malocclusions cause decreased masticatory performance, especially as it relates to reduced occlusal contacts area. The influence of malocclusion treatment (orthognathic surgery) on masticatory performance is only measurable 5 years after treatment. (Angle Orthod. 2010;80:981-987.)

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Objective: To assess, by systematically reviewing the literature, the functional changes of the masticatory muscles associated with posterior crossbite in the primary and mixed dentition. Materials and Methods: A literature survey from the Medline database covering the period from January 1965 to February 2008 was performed. Randomized controlled trials, controlled clinical trials, and clinical trials that evaluated bite force, surface electromyography, and signs and symptoms of temporomandibular disorders (TMD) were included. Two reviewers extracted the data independently and assessed the quality of the studies. Results:The search strategy resulted in 494 articles, of which 8 met the inclusion criteria. Children with posterior crossbite can have reduced bite force and asymmetrical muscle function during chewing or clenching, in which the anterior temporalis is more active and the masseter less active on the crossbite side than the noncrossbite side. Moreover, there is a significant association between posterior crossbite and TMD symptomatology. Conclusion:The consequences of the functional changes for the growth and development of the stomatognathic system deserves further investigation. (Angle Orthod. 2008;79:380-386.)

The aim of this pilot study was to illustrate the feasibility of a new digital procedure to fabricate metallic orthodontic appliances. Hyrax appliances for rapid palatal expansion were produced for 3 patients using a CAD/CAM procedure without physical impressions or printed models. The work flow consisted of intraoral scanning, digital design with incorporation of a scanned prefabricated expansion screw, direct 3-dimensional metal printing via laser melting, welding of an expansion screw, insertion, and finally activation in the patients' mouths. Finite element analyses of the actual hyrax appliances were performed to ensure that the printable material used in combination with the chosen design would withstand the stress generated during activation. The results of these analyses were positive. The clinical results showed that this procedure is an efficient and viable digital way for constructing metallic orthodontic appliances. The flexibility of the digital appliance design, together with the biocompatibility and strength of the chosen material, offers a huge potential for more advanced appliance design.

It has been reported that stress can alter nociception from superficial tissues, such as skin and subcutaneous region. However, the influence of stress on an experimental deep nociception model is not understood. In this study, the temporomandibular joint (TMJ) formalin test was used to evaluate the effects of acute and chronic restraint stress on nociceptive responses in rats. Animals were initially submitted to one session of acute restraint stress (1 h) or exposed to chronic stress (40 days-1 h/day). Then, animals were killed immediately to collect blood for hormonal determinations by radioimmunoassay, or submitted to the TMJ formalin test to evaluate nociception. Rats submitted to acute restraint presented a performance similar to unstressed controls in the TMJ formalin test, whereas chronically stressed rats showed an increase in nociceptive responses. After 40 days of restraint, morphine was injected i.p. (1, 5 mg/kg or saline). The stressed rats displayed decreased morphine effects on nociception compared to unstressed controls. These findings suggest that repeated stress can produce hyperalgesia, which is, at least in part, due to alterations in the activity of opioid systems. This model may help elucidate the underlying neural mechanisms that mediate the effects of repeated stress on orofacial pain.

The aim of this study was to assess the electromyographic (EMG) activity and thickness of the masseter and anterior temporalis muscles in children with unilateral posterior crossbite (PCB). Thirty-six children (22 boys, 14 girls, and mean age of 8.8 +/- 1.1 years) were divided into the following groups: The case group with 20 PCB patients (10 on the left side, 10 on the right side); the control group with 16 normal occlusion (NOccl) subjects. EMG activity was recorded with bipolar surface electrodes at rest and during maximal clenching. The muscle thickness was measured with real-time ultrasound. Data were compared between groups and between sides. The correlation between EMG activity and muscle thickness was also evaluated. The data were analyzed using the Shapiro-Wilks test, Pearson's correlation and Spearman as appropriate, paired and unpaired t- test, and Mann-Whitney test. The results revealed that the masseter of the crossbite side was more active than that of the non-crossbite side in PCB group during maximal clenching. The comparisons of EMG activity between PCB and NOccl groups revealed some variability in the results, depending on the crossbite side. The ultrasonographic evaluation did not show statistically significant differences between groups, nor between sides in the PCB and NOccl groups. Significant correlation between EMG activity and thickness was observed only in the left masseter in the NOccl group. In conclusion, these findings showed that asymmetric muscle activity of the masticatory muscles was not related to the thickness of these muscles in children with PCB.

The subjective perception of the impact of oral health on mastication diminished after periodontal treatment. The number of teeth had considerable importance in the perception of impact on mastication in the sample studied.