Ambra Michelotti

Oral parafunctions as risk factors for diagnostic TMD subgroups.

The frequency of diurnal clenching and/or grinding and nail-biting habits was assessed in patients affected by temporomandibular disorders (TMDs) and in healthy controls in order to investigate the possible association between these oral parafunctions and different diagnostic subgroups of TMDs. The case group included 557 patients (127 men, mean age +/- SD = 34.5 +/- 15.4 years; 430 women, mean age +/- SD = 32.9 +/- 14.1 years) affected by myofascial pain or disc displacement or arthralgia/arthritis/arthrosis. The control group included 111 healthy subjects (55 men, mean age +/- SD = 37 +/- 15.2 years; 56 women, mean age +/- SD = 38.2 +/- 13.8 years). Multinomial logistic regression analysis was used to assess the association between oral parafunctions and TMDs, after adjusting for age and gender. Daytime clenching/grinding was a significant risk factor for myofascial pain (odds ratio (OR) = 4.9, 95% confidence interval (CI): 3.0-7.8) and for disc displacement (OR = 2.5, 95% CI: 1.4-4.3), nail biting was not associated to any of the subgroups investigated. Female gender was a significant risk factor for myofascial pain (OR = 3.8; 95% CI: 2.4-6.1), whereas the risk factor for developing disc displacement decreased with ageing. No association was found between gender, age and arthralgia/arthritis/arthrosis.

Guidelines and recommendations for assessment of somatosensory function in oro-facial pain conditions - a taskforce report

The goals of an international taskforce on somatosensory testing established by the Special Interest Group of Oro-facial Pain (SIG-OFP) under the International Association for the Study of Pain (IASP) were to (i) review the literature concerning assessment of somatosensory function in the oro-facial region in terms of techniques and test performance, (ii) provide guidelines for comprehensive and screening examination procedures, and (iii) give recommendations for future development of somatosensory testing specifically in the oro-facial region. Numerous qualitative and quantitative psychophysical techniques have been proposed and used in the description of oro-facial somatosensory function. The selection of technique includes time considerations because the most reliable and accurate methods require multiple repetitions of stimuli. Multiple-stimulus modalities (mechanical, thermal, electrical, chemical) have been applied to study oro-facial somatosensory function. A battery of different test stimuli is needed to obtain comprehensive information about the functional integrity of the various types of afferent nerve fibres. Based on the available literature, the German Neuropathic Pain Network test battery appears suitable for the study of somatosensory function within the oro-facial area as it is based on a wide variety of both qualitative and quantitative assessments of all cutaneous somatosensory modalities. Furthermore, these protocols have been thoroughly described and tested on multiple sites including the facial skin and intra-oral mucosa. Standardisation of both comprehensive and screening examination techniques is likely to improve the diagnostic accuracy and facilitate the understanding of neural mechanisms and somatosensory changes in different oro-facial pain conditions and may help to guide management.

The role of orthodontics in temporomandibular disorders

Temporomandibular Disorder (TMD) is the main cause of pain of non-dental origin in the oro-facial region including head, face and related structures. The aetiology and the pathophysiology of TMD is poorly understood. It is generally accepted that the aetiology is multifactorial, involving a large number of direct and indirect causal factors. Among such factors, occlusion is frequently cited as one of the major aetiological factors causing TMD. It is well known from epidemiologic studies that TMD-related signs and symptoms, particularly temporomandibular joint (TMJ) sounds, are frequently found in children and adolescents and show increased prevalence among subjects between 15 and 45 years old. Aesthetic awareness, the development of new aesthetic orthodontic techniques and the possibility of improving prosthetic rehabilitation has increased the number of adults seeking orthodontic treatment. The shift in patient age also has increased the likelihood of patients presenting with signs and symptoms of TMD. Because orthodontic treatment lasts around 2 years, orthodontic patients may complain about TMD during or after treatment and orthodontists may be blamed for causing TMD by unsatisfied patients. This hypothesis of causality has led to legal problems for dentists and orthodontists. For these reasons, the interest in the relationship between occlusal factors, orthodontic treatment and TMD has grown and many studies have been conducted. Indeed, claims that orthodontic treatment may cause or cure TMD should be supported by good evidence. Hence, the aim of this article is to critically review evidence for a possible association between malocclusion, orthodontic treatment and TMD.

Effect of Occlusal Interference on Habitual Activity of Human Masseter

It has been suggested that occlusal interference may increase habitual activity in the jaw muscles and may lead to temporomandibular disorders (TMD). We tested these hypotheses by means of a double-blind randomized crossover experiment carried out on 11 young healthy females. Strips of gold foil were glued either on a selected occlusal contact area (active interference) or on the vestibular surface of the same tooth (dummy interference) and left for 8 days each. Electromyographic masseter activity was recorded in the natural environment by portable recorders under interference-free, dummy-interference, and active-interference conditions. The active occlusal interference caused a significant reduction in the number of activity periods per hour and in their mean amplitude. The EMG activity did not change significantly during the dummy-interference condition. None of the subjects developed signs and/or symptoms of TMD throughout the whole study, and most of them adapted fairly well to the occlusal disturbance.

Mandibular rest position and electrical activity of the masticatory muscles.

STATEMENT OF PROBLEM The determination of a correct vertical dimension of occlusion is a critical procedure in clinical dentistry. PURPOSE The objectives of this study were to analyze the relation between mandibular rest position and electrical activity of masticatory muscles and to compare clinical and electromyographic rest position in subjects with different vertical facial morphologic features. MATERIAL AND METHODS Clinical rest position and electromyographic rest position were investigated in 40 subjects. Electromyographic rest position ranged from 0.4 to 12.7 mm (average 7.7 +/- 2.7 mm). Clinical rest position ranged from 0.1 to 4.4 mm (average 1.4 +/- 1.1 mm). The average difference between electromyographic rest position and clinical rest position was 6.3 +/- 2.5 mm (range 0.3 to 10.3 mm). Sixteen subjects were selected according to the Frankfort mandibular plane angle and separated in two groups having a mandibular plane angle > or = 28 degrees. RESULTS Rest position was significantly greater (p < 0.05) in the low-angle group (2 +/- 1.3 mm) than in the high angle group (0.8 +/- 0.8 mm). Electromyographic rest position did not differ between subjects with different facial morphologic features (8.1 +/- 1.7 mm low-angle group; 7.6 +/- 4.1 mm high angle group). By varying the vertical dimension millimeter by millimeter, masseter and anterior temporal electromyographic activity demonstrated a considerable decrease over an interocclusal distance of 3 to 4 mm. Further mandibular opening up to 18 mm corresponded to small changes in postural activity. CONCLUSION This study suggests that a jaw posture with a few millimeters of interocclusal distance involves a great reduction of masticatory muscle activity.

Efficacy of the Sander bite-jumping appliance in growing patients with mandibular retrusion: a randomized controlled trial

OBJECTIVES The efficacy of functional appliances remains highly debated. This randomized controlled trial investigated the skeletal and dentoalveolar effects determined by the Sander bite-jumping appliance (BJA). The null hypothesis to be tested was that the appliance would not induce supplementary mandibular growth compared to untreated controls. SETTING AND SAMPLE POPULATION This study was carried out at the Section of Orthodontics, University of Naples Federico II, Italy. Forty-six patients receiving a clinical diagnosis of skeletal and dental class II due to mandibular retrusion were either allocated to a treatment (23 patients;15 boys, 8 girls; mean age ± SD: 10.9 ± 1.3 years) or to an untreated control group (23 patients;11 boys, 12 girls; mean age ± SD: 10.5 ± 1.2 years), by using a balanced block randomization. METHODS Lateral cephalograms were taken before and after treatment and used for comparisons. Measurements were analyzed by descriptive statistics, univariate and multivariate statistical tests. RESULTS Treated individuals had a significant increase in mandibular length (6.4 ± 2.3 vs. 3.5 ± 2.5 mm; p < 0.001), overjet reduction (-5.0 ± 2.9 vs. 0.3 ± 1.2 mm; p < 0.001) and molar relationship improvement (-5.3 ± 2.4 vs. 0.1 ± 1.1 mm; p < 0.001) compared to controls. The use of the appliance did not significantly affect jaw divergence. Proclination of lower incisors was slightly greater (3.0°, p = 0.023) in treated patients than in controls. The increase in mandibular length was not significantly influenced by cervical stage (p = 0.40). CONCLUSION The BJA can effectively correct class II malocclusions by a combination of dentoalveolar and skeletal effects. The long-term stability of the correction needs to be evaluated.

JOR-CORE recommendations on rehabilitation of temporomandibular disorders

JOR-CORE recommendations on rehabilitation of temporomandibular disorders B. CAIRNS*, T. LIST , A. MICHELOTTI , R. OHRBACH & P. SVENSSON Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, BC, Canada, Department of Stomatognathic Physiology, Faculty of Odontology, Orofacial Pain Unit, Malmö University, Malmö, Sweden, Department of Oral, Dental and Maxillo-Facial Sciences, Section of Orthodontics and Clinical Gnathology University of Naples Federico II, Naples, Italy, Department of Oral Diagnostic Sciences, University at Buffalo, Buffalo, NY, USA and Department of Clinical Oral Physiology, School of Dentistry, Aarhus University, Aarhus C, Denmark

Unilateral Posterior Crossbite is Not Associated with TMJ Clicking in Young Adolescents

Unilateral posterior crossbite has been considered as a risk factor for temporomandibular joint clicking, with conflicting findings. The aim of this study was to investigate a possible association between unilateral posterior crossbite and temporomandibular disk displacement with reduction, by means of a survey carried out in young adolescents recruited from three schools. The sample included 1291 participants (708 males and 583 females) with a mean age of 12.3 yrs (range, 10.1–16.1 yrs), who underwent an orthodontic and functional examination performed by two independent examiners. Unilateral posterior crossbite was found in 157 participants (12.2%). Fifty-three participants (4.1%) were diagnosed as having disk displacement with reduction. Logistic regression analysis failed to reveal a significant association between unilateral posterior crossbite and disk displacement with reduction (odds ratio = 1.3; confidence limits = 0.6–2.9). Posterior unilateral crossbite does not appear to be a risk factor for temporomandibular joint clicking, at least in young adolescents.

Masticatory muscle activity during deliberately performed oral tasks

The aim of this study was to investigate masticatory muscle activity during deliberately performed functional and non-functional oral tasks. Electromyographic (EMG) surface activity was recorded unilaterally from the masseter, anterior temporalis and suprahyoid muscles in 11 subjects (5 men, 6 women; age = 34.6 +/- 10.8 years), who were accurately instructed to perform 30 different oral tasks under computer guidance using task markers. Data were analyzed by descriptive statistics, repeated measurements analysis of variance (ANOVA) and hierarchical cluster analysis. The maximum EMG amplitude of the masseter and anterior temporalis muscles was more often found during hard chewing tasks than during maximum clenching tasks. The relative contribution of masseter and anterior temporalis changed across the tasks examined (F 5.2; p < or = 0.001). The masseter muscle was significantly (p < or = 0.05) more active than the anterior temporalis muscle during tasks involving incisal biting, jaw protrusion, laterotrusion and jaw cupping, the difference being statistically significant (p < or = 0.05). The anterior temporalis muscle was significantly (p < or = 0.01) more active than the masseter muscle during tasks performed in intercuspal position, during tooth grinding, and during hard chewing on the working side. Based upon the relative contribution of the masseter, anterior temporalis, and suprahyoid muscles, the investigated oral tasks could be grouped into six separate clusters. The findings provided further insight into muscle- and task-specific EMG patterns during functional and non-functional oral behaviors.

Association between posterior crossbite, masticatory muscle pain, and disc displacement: a systematic review

BACKGROUND Among different malocclusions, posterior crossbite is thought to have a strong impact on the correct functioning of the masticatory system. OBJECTIVE To assess, by systematically reviewing the literature, the association between posterior crossbite and different temporomandibular disorder (TMD) diagnosis: disc displacement and masticatory muscle pain. MATERIALS AND METHODS A literature survey covering the period from January 1965 to April 2012 was performed. Two reviewers extracted the data independently and assessed the quality of the studies. RESULTS The search strategy resulted in 2919 citations, of which 43 met the inclusion criteria. The scientific and methodological quality of these studies was found to be medium-low, independently by association reported. In several studies, posterior crossbite is reported to be associated to the development of disc displacement, muscular pain, and tenderness, possibly linked to a skeletal and muscular adaptation of the stomatognathic system. However, the lack of consistency of the results reported deeply reduces the external validity of the studies, with a consequent impossibility to draw definite conclusions. CONCLUSIONS It is not possible to establish an association between posterior crossbite, muscle pain, and disc displacement because the distribution of the studies supporting or not supporting the association is similar. The consequences of posterior crossbite on the development of TMDs deserve further investigations, with high sample size, well-defined diagnostic criteria, and rigorous scientific methodologies. Finally, long-term controlled studies are needed to identify posterior crossbite as a possible risk factor for TMDs.