Aberrant occlusal sensitivity in adults with increased somatosensory amplification: a case-control study

OBJECTIVES

Occlusal sensitivity (OS)-the ability to detect fine objects between opposing teeth-mainly relies on the activity of mechanoreceptors located in the periodontal ligament. We tested whether somatosensory amplification (SSA)-the tendency to perceive normal somatic sensations as being intense, noxious, and disturbing, which plays a critical role in hypervigilance-affects OS.

MATERIALS AND METHODS

We measured OS in 66 adults divided into three groups based on their SSA scores (LowSSA, Intermediate - IntSSA, HighSSA) by asking them to bite on aluminum foils (8 to 72 μm thick) and a sham foil, and report whether they felt each foil. We performed 20 trials for each thickness and sham condition (each participant was tested 120 times), and compared the frequency of correct answers (%correct) among groups after adjusting for participants' trait anxiety, depression, self-reported oral behaviors, and masseter cross-sectional area.

RESULTS

%correct was affected by the interaction Foil Thickness-by-SSA (p = 0.007). When tested with the 8 μm foil, the HighSSA group had a lower %correct than the IntSSA (contrast estimate [95% CI]: -14.2 [-25.8 - -2.6]; p = 0.012) and the LowSSA groups (-19.1 [-31.5 - -6.6]; p = 0.001). Similarly, with the 24 μm foil, the HighSSA group had a lower %correct compared to the IntSSA (-12.4 [-24.8-0.1]; p = 0.048) and the LowSSA groups (-10.8 [-22.5-0.8]; p = 0.073).

CONCLUSION

Individuals with high SSA present with an aberrant occlusal sensitivity.

CLINICAL RELEVANCE

Our findings provide novel insights into the relationship between occlusal perception and psychological factors, which may influence an individual's ability to adapt to dental work.

Biological and psychological factors affecting the sensory and jaw motor responses to orthodontic tooth movement

Orthodontic tooth movement (OTM) is associated with an inflammatory response, tooth pain (i.e. orthodontic pain) and changes in dental occlusion. Clinical realms and research evidence suggest that the sensory and jaw motor responses to OTM vary significantly among individuals. While some adjust well to orthodontic procedures, others may not and can experience significant pain or not adjust to occlusal changes. This is of concern, as clinicians cannot anticipate an individual's sensorimotor response to OTM. Converging evidence shows that some psychological states and traits significantly affect the sensorimotor response to OTM and may considerably affect an individual's adaptation to orthodontic or other dental procedures. We performed a topical review to synthesize the available knowledge about the behavioural mechanisms regulating the sensorimotor response to OTM, with the intent of informing orthodontic practitioners and researchers about specific psychological states and traits that should be considered while planning orthodontic treatment. We report on studies focusing on the role of anxiety, pain catastrophising, and somatosensory amplification (i.e. bodily hypervigilance), on sensory and jaw motor responses. Psychological states and traits can significantly affect sensory and jaw motor responses and a patient's adaptation to orthodontic procedures, although large interindividual variability exists. Clinicians can use validated instruments (checklists or questionnaires) to collect information about patients' psychological traits, which can assist in identifying those individuals who may not adjust well to orthodontic procedures. The information included in this manuscript also assists researchers investigating the effect of orthodontic procedures and or/appliances on orthodontic pain.

Identification of central amygdala and trigeminal motor nucleus connectivity in humans: An ultra-high field diffusion MRI study

The neuroanatomical circuitry of jaw muscles has been mostly explored in non-human animals. A recent rodent study revealed a novel circuit from the central amygdala (CeA) to the trigeminal motor nucleus (5M), which controls biting attacks. This circuit has yet to be delineated in humans. Ultra-high diffusion-weighted imaging data from the Human Connectome Project (HCP) allow in vivo delineation of circuits identified in other species-for example, the CeA-5M pathway-in humans. We hypothesized that the CeA-5M circuit could be resolved in humans at both 7 and 3 T. We performed probabilistic tractography between the CeA and 5M in 30 healthy young adults from the HCP database. As a negative control, we performed tractography between the basolateral amygdala (BLAT) and 5M, as CeA is the only amygdalar nucleus with extensive projections to the brainstem. Connectivity strength was operationalized as the number of streamlines between each region of interest. Connectivity strength between CeA-5M and BLAT-5M within each hemisphere was compared, and CeA-5M circuit had significantly stronger connectivity than the BLAT-5M circuit, bilaterally at both 7 T (all p < .001) and 3 T (all p < .001). This study is the first to delineate the CeA-5M circuit in humans.

Development of a model to investigate the effects of prolonged ischaemia on the muscles of mastication of male Sprague Dawley rats

OBJECTIVE

The aims of this study were to develop a novel rodent model of masticatory muscle ischaemia via unilateral ligation of the external carotid artery (ECA), and to undertake a preliminary investigation to characterize its downstream effects on mechanosensitivity and cellular features of the masseter and temporalis muscles.

DESIGN

The right ECA of 18 male Sprague-Dawley rats was ligated under general anaesthesia. Mechanical detection thresholds (MDTs) at the masseter and temporalis bilaterally were measured immediately before ECA ligation and after euthanasia at 10-, 20-, and 35-days (n = 6 rats/timepoint). Tissue samples from both muscles and sides were harvested for histological analyses and for assessing changes in the expression of markers of hypoxia and muscle degeneration (Hif-1α, VegfA, and Fbxo32) via real time PCR. Data were analyzed using mixed effect models and non-parametric tests. Statistical significance was set at p < 0.05.

RESULTS

MDTs were higher in the right than left hemiface (p = 0.009) after 20 days. Histological changes indicative of muscle degeneration and fibrosis were observed in the right muscles. Hif-1α, VegfA, and Fbxo32 were more highly expressed in the masseter than temporalis muscles (all p < 0.05). Hif-1α and, VegfA did not change significantly with time in all muscles (all p > 0.05). Fbxo32 expression gradually increased in the right masseter (p = 0.024) and left temporalis (p = 0.05).

CONCLUSIONS

ECA ligation in rats induced hyposensitivity in the homolateral hemiface after 20 days accompanied by tissue degenerative changes. Our findings support the use of this model to study pathophysiologic mechanisms of masticatory muscle ischaemia in larger investigations.

Continuing professional development needs in pain management for Canadian health care professionals: A cross sectional survey

Background

Continuing professional development is an important means of improving access to effective patient care. Although pain content has increased significantly in prelicensure programs, little is known about how postlicensure health professionals advance or maintain competence in pain management.

Aims

The aim of this study was to investigate Canadian health professionals' continuing professional development needs, activities, and preferred modalities for pain management.

Methods

This study employed a cross-sectional self-report web survey.

Results

The survey response rate was 57% (230/400). Respondents were primarily nurses (48%), university educated (95%), employed in academic hospital settings (62%), and had ≥11 years postlicensure experience (70%). Most patients (>50%) cared for in an average week presented with pain. Compared to those working in nonacademic settings, clinicians in academic settings reported significantly higher acute pain assessment competence (mean 7.8/10 versus 6.9/10; P < 0.002) and greater access to pain specialist consultants (73% versus 29%; P < 0.0001). Chronic pain assessment competence was not different between groups. Top learning needs included neuropathic pain, musculoskeletal pain, and chronic pain. Recently completed and preferred learning modalities respectively were informal and work-based: reading journal articles (56%, 54%), online independent learning (44%, 53%), and attending hospital rounds (43%, 42%); 17% had not completed any pain learning activities in the past 12 months. Respondents employed in nonacademic settings and nonphysicians were more likely to use pocket cards, mobile apps, and e-mail summaries to improve pain management.

Conclusions

Canadian postlicensure health professionals require greater access to and participation in interactive and multimodal methods of continuing professional development to facilitate competency in evidence-based pain management.

Effectiveness of the Lorodent Probiotic Lozenge in Reducing Plaque and Streptococcus mutans Levels in Orthodontic Patients: A Double-Blind Randomized Control Trial

Orthodontic patients are at a significant risk for oral diseases due to increased plaque accumulation and oral bacterial dysbiosis. We aimed to determine the efficacy of the commercially available Lorodent Probiotic Complex at reducing plaque accumulation and Streptococcus mutans bacterial levels in adolescent orthodontic patients. Sixty adolescents undergoing fixed orthodontic treatment for a minimum of 6 months were recruited in a randomized, double-blind, parallel-group, placebo-controlled trial. They received either Lorodent probiotic lozenge (intervention, n = 30) or placebo lozenge (control, n = 30) orally every day for a 28-day administration period. Participants were assessed at four appointments (T1–T4) over a total of 56 days. Compliance and lozenge satisfaction were monitored. Saliva samples and supragingival plaques were collected for evaluation of S. mutans levels. Clinical assessment using a Plaque Index (PI) was used. Compliance with lozenge intake of all participants was over 90%. There was no significant change in the PI and composite PI scores in both placebo and probiotic groups at each time frame (all p &gt; 0.05) or the relative S. mutans DNA levels in the saliva and plaque between the probiotic and placebo groups. The findings of high compliance and satisfaction with the probiotic lozenges combined with the study's rigorous design offer a baseline for subsequent testing of further potential probiotics (of varying formulations, concentrations), especially in adolescents.

Impact of Stress and Trait Anxiety on the Sensory and Jaw Motor Responses to a Tonic Orofacial Nociceptive Stimulus

AIMS

To investigate how trait anxiety and stress jointly affect the sensory and jaw motor responses to a tonic orofacial nociceptive stimulus.

METHODS

Orthodontic separators were placed between the first molars in 45 adults with low (n = 14), intermediate (n = 17), and high (n = 14) trait anxiety. Tooth pain, occlusal discomfort, tooth clenching (as a jaw motor behavior), and situational stress were measured three times a day for 5 days using visual analog scales. Mixed-effects regression models were used to evaluate the sensory and motor outcome measures.

RESULTS

Pain, discomfort, and frequency of tooth-clenching trajectories were affected by trait anxiety (P = .007, P < .001, and P = .055, respectively) and stress (P < .001, P < .001, and P = .044, respectively). Individuals with high anxiety reported their highest pain (17.7 ± 2.9 mm) and discomfort (35.2 ± 4.1 mm) 24 hours earlier than those with low anxiety (pain: 15.9 ± 2.6 mm, discomfort: 28.8 ± 3.7 mm). Tooth clenching decreased progressively in response to the stimulus (P < .001).

CONCLUSION

A tonic orofacial nociceptive stimulus triggers an avoidance jaw motor behavior. Both trait anxiety and situational stress heighten the sensory response to such a stimulus, but weakly affect the motor response to it.

Short-term Effects of a First-Line Treatment Including Counseling and Self-Management Strategies on Chronic TMD Muscle Pain and Awake Bruxism in Women

AIMS

To evaluate the short-term effects of a standardized first-line noninvasive approach (FL-A) including counseling and self-management strategies on pain, masticatory muscle tenderness, and awake bruxism in women with chronic temporomandibular disorder myalgia (mTMD) and to test whether patients' trait anxiety predicted their response to treatment.

METHODS

FL-A was administered to 14 women with chronic mTMD (mean age ± SD = 33.8 ± 11.1 years; 8 with Graded Chronic Pain Scale [GCPS] grade I and 6 with grade II). Its effects on facial pain, masticatory muscle tenderness, and spontaneous awake bruxism episodes were evaluated using questionnaires, surface electromyography, and quantitative sensory testing. General linear models were used to test FL-A efficacy after 1 (T1) and 2 (T2) months.

RESULTS

FL-A reduced pain (from baseline [T0] to T2, P = .010), the frequency of awake bruxism episodes (T0 to T1, P = .024), and their intensity by about 30% (T0 to T1, P < .001). Pressure pain thresholds at the masticatory muscle locations increased significantly from T0 to T2 (P < .001). Patients' trait anxiety decreased significantly from T0 to T2 (P = .030). Trait anxiety measured at baseline was not correlated with relative changes in pain (T0 to T2, P = .248).

CONCLUSION

In the short term, FL-A reduces facial pain, masticatory muscle tenderness, and awake bruxism in women with chronic mTMD with low disability. A conservative management strategy should be prioritized for the initial management of these patients.

Sex Differences in the Temporalis Tendon-Aponeurotic Complex: An in vivo MRI Macroscopic Analysis in Children and Adolescents

The tendon-aponeurosis complex (TAC) of the temporalis dissipates forces produced during function. Abnormally reduced temporalis TACs have been found in individuals with chronic muscular temporomandibular disorders - a painful musculoskeletal condition that is more frequent in women than men. Whether there are sex differences in the temporalis TAC in healthy individuals is currently unknown. Here, we characterized and measured the temporalis TAC in healthy male and female young individuals between 5 and 15 years old to determine whether the volume of the temporalis TAC and the TAC-to-muscle ratio are different between males and females. We collected MRI studies from 90 healthy individuals, including equal numbers (15 M and 15 F) of young children (ages 5-7), children (9-11), and adolescents (13-15) and segmented the right temporalis and its TAC using software. Using general linear models, we tested the effect of sex, age, and their interaction on the volumes of the temporalis and its TAC, and the TAC-to-muscle ratio. The volumes of the temporalis and its TAC increased with age (both p < 0.001) and were not affected by sex (p = 0.252 and p = 0.179) or by the interaction sex-by-age (p = 0.079 and p = 0.095, respectively). The TAC-to-muscle ratio did not change significantly with age (p = 0.655) and was not affected by sex (0.438) or by the interaction sex-by-age (0.524). We provide, for the first time, volumetric data of the temporalis TAC in children and adolescents. The volumes of the temporalis TAC and the TAC-to-muscle ratio are not different between male and female individuals until the age of 15.

Impact of post-orthodontic dental occlusion on masticatory performance and chewing efficiency

BACKGROUND

Whether precise orthodontic detailing of occlusion impacts masticatory function is unknown. In this study, we aimed to assess the impact of post-orthodontic dental occlusion on masticatory performance and chewing efficiency.

MATERIALS AND METHODS

Fifty-four adults who completed orthodontic treatment were categorized into two groups using the American Board of Orthodontics (ABO) model grading system: one meeting ABO standards (ABO, N = 29), the other failing to meet them (non-ABO, N = 25). The electromyographic (EMG) signals of the anterior temporalis (AT) and superficial masseter muscles were recorded bilaterally during static (clenching) and dynamic (gum chewing) tests. Chewing efficiency was measured by calculating the median particle size (MPS) and broadness of particle distribution (BPD) after five chewing trials of experimental silicone food at a standardized chewing rate.

RESULTS

Participants of the ABO group had a slightly more symmetric activation of the AT muscles during clenching (P = 0.016) and chewed a gum at a slower rate (P = 0.030). During the standardized chewing test with silicone food, ABO subjects had slightly greater EMG potentials at all muscle locations than non-ABO individuals (all P < 0.05). MPS and BDP did not differ significantly between groups (all P > 0.05).

LIMITATIONS

The severity of the initial malocclusion of the study participants was not in the statistical model as a potential confounder on the outcome measures.

CONCLUSIONS

Meeting ABO standards contributes to a slightly more balanced activation of the temporalis muscles during clenching and more efficient muscle recruitment during chewing but does not improve chewing efficiency.

Evaluation of masticatory muscle response to clear aligner therapy using ambulatory electromyographic recording

INTRODUCTION

Patients undergoing clear aligner therapy (CAT) report muscle tenderness and produce wear facets on their aligner trays. However, little is known about the masticatory muscle response to clear aligners. Here, we measured the activity of the masseter during CAT using ambulatory electromyography. We also explored whether psychological traits modulate the masticatory muscle response to CAT.

METHODS

Using portable data loggers, we recorded the electromyographic (EMG) activity in the right masseter muscle of 17 healthy adults without temporomandibular disorder (16 females, 1 male; mean age ± standard deviation, 35.3 ± 17.6 years) commencing treatment with CAT over 4 weeks, under the following conditions: week 1 without aligners (baseline), week 2 with a passive aligner (dummy), week 3 with their first active aligner (active1), and week 4 with their second active aligner (active2). We used a mixed-effect model to test differences in EMG activity over the 4-weeks and a general linear model to test the effect of psychological traits on EMG activity.

RESULTS

The EMG activity of the masseter increased significantly with aligners compared with baseline. The largest relative increase in EMG activity was seen during the dummy (152%; P <0.001) and active1 (155%; P <0.001) stages. During active2, the activity of the masseter decreased significantly toward baseline levels. Participants' trait anxiety was positively associated with increases in EMG activity (P = 0.027).

CONCLUSIONS

CAT is associated with a transient increase in masticatory muscle activity, possibly because of an increase in wake-time parafunctional tooth clenching. Temporomandibular disorder-free patients adapt well to CAT as the masticatory muscle activity decreases toward baseline levels after 2 weeks.

Increased somatosensory amplification is associated with decreased pressure pain thresholds at both trigeminal and extra-trigeminal locations in healthy individuals

BACKGROUND

The diagnosis of temporomandibular disorders (TMD) is based on patient history and physical examination, and may require medical imaging. Masticatory muscle palpation is essential to make a diagnosis of TMD. However, the response of masticatory muscles to mechanical pressure stimuli depends on many physical and psychological factors.

OBJECTIVE

This study aimed at determining the impact of somatosensory amplification (SSA)-an estimate of somatic awareness and bodily hypervigilance-on pressure pain thresholds (PPTs) measured at both trigeminal and extra-trigeminal locations in healthy individuals.

METHODS

PPTs were measured at the right anterior temporalis and superficial masseter, and the thenar eminence of the right hand in one hundred healhty individuals (69F, 31M), divided in three groups based on their SSA scores: low (N = 32), intermediate (N = 34) and high (N = 34). General linear models were used to test between-group differences in PPTs including sex as a covariate. The level of significance was set at P < .05.

RESULTS

Individuals with high SSA had lower PPTs at the anterior temporalis than individuals with low (P = .006) and intermediate (P = .001) SSA. No significant between-group differences were found in PPTs measured at the masseter (P = .372). PPTs measured at the thenar eminence were significantly lower in the high than the low SSA group (P = .009). Females had lower PPTs at the masseter than males (P = .021) but not at other muscle locations (all P > .05).

CONCLUSION

Increased somatosensory amplification is associated with decreased pressure pain thresholds at both trigeminal and extra-trigeminal locations in healthy individuals. SSA could be a potential confounder while diagnosing TMD and evaluating treatment outcomes.

Music Modulates Awake Bruxism in Chronic Painful Temporomandibular Disorders

OBJECTIVE

In this experimental study, we aimed to determine whether guided music listening (GML) - a music intervention based on models of mood mediation and attention modulation - modulates masticatory muscle activity and awake bruxism in subjects with chronic painful muscular temporomandibular disorders (TMD myalgia, mTMD), a condition causing a significant burden to patients, their families, and healthcare systems.

BACKGROUND

Awake bruxism - a stress behavior characterized by clenching of the teeth - is a strong contributor to chronic mTMD. GML modulates psychological stress and motor responses and could thus reduce muscle activity in chronic musculoskeletal conditions, including mTMD.

METHODS

We recorded the electromyographic (EMG) activity in the right masseter of 14 women with chronic (>6 months) mTMD (median [IQR] = 39.5.3 [24.3] years) and 15 pain-free women (median [IQR] = 30.0 [3.5] years) during a GML session, including 3 music (stressful, relaxing, and participants' favorite music) and a no-music (pink noise) control blocks, each lasting 15 minutes. We measured the motor effort of the right masseter relative to the participants' maximum voluntary contraction (MVC), the muscular effort to maintain mandibular posture (EMG_posture ), and to produce spontaneous awake bruxism episodes (EMG_bruxism ), and the duration and frequency of spontaneous awake bruxism episodes. We tested between-group and within-group (between blocks) differences, as well as the effect of the interaction group by experimental block on these outcome measures.

RESULTS

In both groups, EMG_posture was significantly affected by the interaction group by experimental block (P < .001). Compared to pink noise [mean (95% CI); mTMD: 2.2 (1.6-2.8) %MVC; Controls: 1.1 (0.5-1.7) %MVC], EMG_posture increased during the stressful music block [contrast estimate (95% CI); mTMD: +0.8 (0.7-0.8) %MVC; Controls: +0.3 (0.3-0.4) %MVC; both P < .001], and decreased during the relaxing [mTMD: -0.4 (-0.5 to -0.4) %MVC; Controls: -0.3 (-0.4 to -0.3) %MVC; both P < .001] and favorite [mTMD: -0.5 (-0.6 to -0.5) %MVC; Controls: -0.5 (-0.5 to -0.4) %MVC; both P < .001] music blocks. EMG_posture was greater in mTMD individuals than controls during the favorite music [contrast estimate (95% CI): +1.1 (0.2-1.9) %MVC; P = .019] and the pink noise [+1.1 (0.2-2.0) %MVC; P = .014] blocks. EMG_bruxism was significantly affected by the interaction group by experimental block (P < .001). In mTMD participants, compared to the pink noise block [mean (95% CI); 23.8 (16.0-31.6) %MVC], EMG_bruxism increased during the stressful music block [contrast estimate (95% CI); +10.2 (8.6-11.8) %MVC], and decreased during the relaxing [-6.2 (-8.1 to -4.3) %MVC; P < .001] and favorite [-10.2 (-12.2 to -9.1) %MVC; P < .001] music blocks. These effects were not observed in the control group [mean (95% CI); pink noise: 19.3 (10.9-27.6); stressful: 21.2 (12.9-29.4) %MVC; relaxing: 21.6 (13.3-29.9) %MVC; favorite: 24.2 (15.8-32.7) %MVC; all P > .05]. EMG_bruxism was significantly greater in mTMD participants than controls during the stressful music block [contrast estimate (95% CI): +12.9 (1.6-24.2) %MVC; P = .026). GML did not affect the duration or the frequency of awake bruxism in either group (median [IQR], mTMD: 23.5 [96.7] s, range 1-1300 seconds; Controls: 5.5 [22.5], range 0-246 seconds; P = .108). The frequency of awake bruxism episodes was greater in the mTMD group compared to controls only during the pink noise block (median [IQR], mTMD: 5 [15.3] episodes, range 0-62 episodes; Controls: 1 [3] episode, range 0-27 episodes; P = .046). No significant between-group differences were found in either the overall time spent engaging in awake bruxism (median [IQR], mTMD: 23.5 [96.7] s, range 1-1300 seconds; Controls: 5.5 [22.5], range 0-246 seconds; P = .108), or during each block (all P > .05).

CONCLUSIONS

In subjects with chronic mTMD, relaxing music and the individual's favorite music decreased the muscular effort during spontaneous awake bruxism episodes by 26% and 44% (relative changes), respectively. In contrast, stressful music increases it by about 43%. Because of its positive effects on awake bruxism, GML with selected music could be a promising and non-invasive component of a multimodal approach for the management of chronic mTMD.

Impact of clear aligner therapy on tooth pain and masticatory muscle soreness

BACKGROUND

Clinical findings suggest that orthodontic treatment with clear aligners (clear aligner therapy/CAT) may cause masticatory muscle soreness in some patients.

OBJECTIVE

This multi-site prospective study investigated tooth pain and masticatory muscle soreness and tenderness in patients undergoing CAT and explored whether psychological traits affected these outcomes.

METHODS

Twenty-seven adults (22F, 5M; mean age ± SD=35.3 ± 17.6 years) about to start CAT were recruited at three clinics. During CAT, they reported on 100-mm visual analogue scales their tooth pain, masticatory muscle soreness and stress three times per day over 4 weeks (week 1 = baseline; week 2 = dummy aligner; week 3 = first active aligner; week 4 = second active aligner). Pressure pain thresholds (PPTs) were measured at the masseter and temporalis at baseline and after week 4. Mixed models were used to evaluate the outcome measures over time.

RESULTS

Clear aligner therapy caused mild tooth pain, which was greater with the passive than the first and second active aligners (both P < .001). Mild and clinically not relevant masticatory muscle soreness was produced by all aligners (all P < .05), with the first active aligner producing less soreness than the dummy aligner (P < .001). PPTs did not change significantly after 4 weeks. Both tooth pain and masticatory muscle soreness were affected by stress and trait anxiety, whilst muscle soreness was affected also by oral behaviours.

CONCLUSIONS

In the short term, CAT produces tooth pain and masticatory muscle soreness of limited significance. Frequent oral behaviours are related to increased masticatory muscle soreness during CAT. The medium- and long-term effects of CAT should be further explored.

Structural abnormalities in the temporalis musculo-aponeurotic complex in chronic muscular temporomandibular disorders

Some forms of chronic pain are thought to be driven and maintained by nociceptive input, which can drive plasticity within nociceptive pathways. We have previously identified abnormalities along the entire nociceptive pathway in chronic myalgic temporomandibular disorders (mTMD), including the trigeminal nerves, brainstem pathways, and in the thalamus and somatosensory cortex. These data suggest that there is a peripheral nociceptive drive in mTMD, but the source of this nociceptive activity remains unknown. Here, our aim was to determine whether structural abnormalities exist in the muscles of mastication of patients with chronic mTMD. Specifically, we tested whether the volume of the temporalis muscle and its tendon-aponeurosis complex (TAC, a structure that dissipates forces in a muscle) in mTMD patients differ compared to age- and sex-matched controls. To do so, we segmented these structures on T1-weighted structural magnetic resonance images. We found that muscle volumes in mTMD were not different to controls. However, the mTMD group had significantly smaller volumes of the bilateral temporalis TAC, and thus a smaller TAC-to-muscle volume ratio. These findings were consistent across 2 independent cohorts of 17 mTMD patients, compared to 17 age- and sex-matched controls. We propose a model where reduced TAC-to-muscle ratio could result in a predisposition to muscle tissue injury. In sum, abnormalities of the temporalis muscles in mTMD supports our hypothesis that chronic mTMD pathophysiology may be related to peripheral nociceptive barrage originating from the muscles of mastication.

Short-term effects of fixed orthodontic appliance on concentrations of mutans streptococci and persister cells in adolescents

INTRODUCTION

Orthodontic patients are at an increased risk for developing caries. Dental caries is a biofilm-mediated disease, with mutans streptococci (MS) as the primary etiologic bacterial group. It has been suggested that persister cells (PCs), a subset of cells within the biofilm, contribute to the chronic infectious nature of dental caries. PC formation can be induced by environmental stressors such as orthodontic treatment. The aim of this study was to quantify MS, aerobic and facultative anaerobe bacterial PC proportions from plaque samples during the initial stage of orthodontic treatment. This study is the first to analyze the role of PCs in a population of patients highly susceptible to caries, that is, patients undergoing orthodontic treatment.

METHODS

Plaque samples were collected from 17 participants (11 males and 6 females; age range: 11-18 years) before and 1 month after insertion of fixed orthodontic appliances. Percentages of MS and PCs were determined with selective media and a classical persister microbial assay, respectively.

RESULTS

There was a statistically significant decrease in %MS (P = 0.039) but no statistically significant difference in %PCs (P = 0.939) after 1 month of orthodontic appliance placement.

CONCLUSION

Our study illustrated the technical feasibility of analysis of PCs in plaque samples of patients during orthodontic treatment and revealed that PC formation during orthodontic treatment is highly variable across individuals.

Impact of functional orthodontic treatment on facial attractiveness of children with Class II division 1 malocclusion

Background/objectives

Whether orthodontic treatment with functional appliances improves facial aesthetics is still under debate. This study aimed to determine whether functional orthodontic treatment improves the facial attractiveness of patients with Class II division 1 malocclusion.

Materials/method

Extraoral lateral photographs of 20 children with Class I (CLI, 11.7 ± 0.8 years), and before (T1) and after treatment (T2) photographs of patients with Class II division 1 (CLII T1 and CLII T2; mean age ± SD = 11.1 ± 0.6 years) treated with functional appliances, were transformed into black silhouettes. Three panels of examiners including 30 orthodontists (39.0 ± 10.1 years), 30 dentists (40.0 ± 9.7) and 30 laypersons (39.0 ± 9.2) evaluated the attractiveness of patients’ silhouettes using a 100-mm visual analogue scale, and the sagittal position of patients’ upper lip, lower lip, and chin using a 3-point Likert scale. Two-way ANOVA and a chi-square test were used to test differences among groups. Statistically significance was set as P  &lt;  0.05.

Results

The silhouettes of CLII T2 individuals were more attractive than those of the other groups (all Ps &lt; 0.001). The upper lip, lower lip, and the chin of these individuals were judged to be normally positioned in 69.5 per cent, 74.9 per cent, and 72.3 per cent of the assessments, respectively (all Ps &lt; 0.05).

Limitations

This study did not account for the psychological profile of the examiners, which may have affected the ratings.

Conclusions/implications

Orthodontic treatment with functional appliances is associated with a superior facial profile attractiveness. Functional treatment should be considered as a treatment option to improve the facial appearance of children with Class II division 1 malocclusion.

Masseter Deoxygenation in Adults at Risk for Temporomandibular Disorders

Patients with muscular temporomandibular disorder (TMD) present with abnormal oxygenation of the jaw muscles. Nonetheless, the deoxygenation pattern of jaw muscles of healthy subjects with frequent wake-time tooth-clenching episodes, who are at greater risk for TMD, has never been investigated. This case-control study compared the deoxygenation of the masseter during standardized tasks between TMD-free individuals with frequent self-reports of wake-time clenching and those with infrequent self-reports. University students ( N = 255) filled out the Oral Behavior Checklist. Fourteen females with high versus low scores-high parafunctional (HP) group ( n = 7, ≥80th percentile of score distribution) versus low parafunctional (LP) group ( n = 7, ≤20th percentile)-completed 2 sessions during which they clenched at their maximum voluntary contraction (MVC) for 2 min and at 10% to 20% MVC for 20 min. Tissue oxygen saturation (StO₂) and changes in oxygenated hemoglobin, deoxygenated hemoglobin, and total hemoglobin of the masseter were measured via near-infrared spectroscopy and analyzed with a generalized mixed effect model. A significant interaction effect (task × study group) was found on all outcome measures, indicating that the deoxygenation pattern of the HP group differed from the LP group (all P < 0.001). MVC of the masseter induced an almost 5-times-greater reduction of StO₂ in the HP group as compared with the LP group ( P = 0.023). However, the relative increase in StO₂ at rest after the MVC was similar between groups ( P > 0.05). At the end of the prolonged MVC task (10% to 20%), the blood flow (change in total hemoglobin) was almost 6 times higher in the LP group as compared with baseline. On the contrary, it increased minimally in the HP group (all P < 0.001). Healthy individuals at risk for TMD have abnormalities in masseter deoxygenation. Future prospective studies are needed to test whether this contributes to the onset of muscular TMD.

Cervical vertebral maturation method and mandibular growth peak: a longitudinal study of diagnostic reliability

Background/objectives

The capability of the cervical vertebral maturation (CVM) method in the identification of the mandibular growth peak on an individual basis remains undetermined. The diagnostic reliability of the six-stage CVM method in the identification of the mandibular growth peak was thus investigated.

Subjects/Methods

From the files of the Oregon and Burlington Growth Studies (data obtained between early 1950s and middle 1970s), 50 subjects (26 females, 24 males) with at least seven annual lateral cephalograms taken from 9 to 16 years were identified. Cervical vertebral maturation was assessed according to the CVM code staging system, and mandibular growth was defined as annual increments in Co-Gn distance. A diagnostic reliability analysis was carried out to establish the capability of the circumpubertal CVM stages 2, 3, and 4 in the identification of the imminent mandibular growth peak.

Results

Variable durations of each of the CVM stages 2, 3, and 4 were seen. The overall diagnostic accuracy values for the CVM stages 2, 3, and 4 were 0.70, 0.76, and 0.77, respectively. These low values appeared to be due to false positive cases.

Limitations

Secular trends in conjunction with the use of a discrete staging system. In most of the Burlington Growth Study sample, the lateral head film at age 15 was missing.

Conclusions/Implications

None of the CVM stages 2, 3, and 4 reached a satisfactorily diagnostic reliability in the identification of imminent mandibular growth peak.

Evaluation of masticatory muscle activity in patients with unilateral posterior crossbite before and after rapid maxillary expansion

Objectives

The relationship between unilateral posterior crossbite (UPCB) and the possible asymmetric activation of the jaw muscles in children is still under debate. This study aimed at evaluating the jaw muscle activity of children with UPCB before and after rapid maxillary expansion (RME) by means of surface electromyography and a standardized sampling protocol.

Subjects and methods

Twenty-nine children with UPCB (UPCB-group, mean age 9.6 ± 1.6 years) and 40 UPCB-free controls (Control-group, 10.5 ± 1.1) were recruited. The activity of the left and right anterior temporalis (AT) and superficial masseter muscles (MM) was recorded during maximum voluntary clenching and a chewing task (T0). In the UPCB-group, data were collected, also, after the correction of the UPCB with RME (T1) and 6 months later (T2), without any further treatment. Electromyographic indices comparing the activity of paired muscle were computed via software to estimate the extent of asymmetric AT and MM activity. Paired and unpaired t-test or Wilcoxon-signed rank and Mann-Whitney U test, ANOVA or Friedman test and chi-squared test were used in the statistical analysis.

Results

Both groups presented with asymmetric activity of the muscles, which did not differ between groups (T0, all P > 0.05). The treatment determined a decrease in muscular activity (T1, P = 0.040), and a more asymmetric pattern of muscle activation during chewing (T1, P = 0.040), which returned similar to baseline values at T2 (all P > 0.05).

Conclusions

UPCB does not contribute to an asymmetric activation of AT and MM during functional tasks. The treatment of UPCB by RME did not determine a more symmetric activity of the assessed muscles.

Effects of clear aligners on sleep bruxism: randomized controlled trial

The possible effects on sleep bruxism (SB) of clear aligners in orthodontics are unknown. This study was conducted to analyze the effects of clear aligners on SB. Sixty subjects needing orthodontic treatment and affected by SB (33 m, 27 f, 20±;5 years) were enrolled in the study and randomly assigned to one of the following three groups: 20 were given clear aligners (CAT) (12 m, 8 f, 19±5 years), 20 occlusal splint (MOS) (9 m, 11 f, 22±5 years) and 20 a placebo splint (PMS) (12 m, 8 f, 24±3 years). All groups were followed for 6 consecutive months and monitored for SB with a portable electromyographic-electrocardiographic (EMG-ECG) device (Bruxoff®, OT Bioelettronica, Torino, Italy). MOS subjects reduced masseter contractions after 6 months of treatment (t3) (MD=-29.11, std. error 11.74, p=0.017) but increased phasic contractions related to SB after 3 months of treatment (t2) (MD=4.73, std. error 2.36, p=0.048) and tonic contractions related to SB during all the six months of treatment (t1, t2, t3) when compared to PMS. CAT subjects increased phasic contractions related to SB during the first (t1) (MD=3.94, std. error 2.27, p=0.04) and the third month (t2) of treatment (MD=4.62, std. error 2.36, p=0.046) when compared to PMS. No significant differences were found for SB index at any time for all the three groups. Although MOS and CAT affected EMG signals during sleep time differently, they did not influence the overall SB index.

Modulation of Jaw Muscle Motor Response and Wake-Time Parafunctional Tooth Clenching With Music

AIMS

To evaluate the effects of Guided Music Listening (GML) on masticatory muscles and on the amplitude of wake-time tooth clenching in individuals with higher vs lower frequency of clenching episodes.

METHODS

The electromyographic (EMG) activity of the right masseter was recorded during three 20-minute music (relaxing, stress/tension, and favorite) tasks and a control no-music task in 10 (mean age ± standard deviation [SD] = 21.4 ± 3.0 years) and 11 (22.6 ± 2.9 years) healthy volunteers with higher (HP) vs lower (LP) frequency of tooth-clenching episodes, respectively. EMG episodes greater than 10% of the maximum voluntary contraction (EMG activity of the masseter during tooth clenching) and below 10% (EMG activity during rest) were analyzed. Nonparametric tests were used to assess between-group and within-group (between-task) differences in primary outcome measures.

RESULTS

In both groups, EMG activity during rest was the greatest during the stress/tension task, and it was the lowest during the favorite task in the LP group and the relaxing task in the HP group (all P < .001). In the HP group, the amplitude of clenching episodes was significantly lower during the favorite and stress/tension tasks than during the relaxing task (all P < .05), while in the LP group, it was significantly lower during the stress/tension task than during the control task (P = .001). The experiment did not affect the frequency or duration of clenching episodes.

CONCLUSION

GML modulates masticatory muscle activity. The response to GML depends on the frequency of clenching and the type of music.

Facial attractiveness of skeletal class I and class II malocclusion as perceived by laypeople, patients and clinicians

BACKGROUND

Physical attractiveness is dependent on facial appearance. The facial profile plays a crucial role in facial attractiveness and can be improved with orthodontic treatment. The aesthetic assessment of facial appearance may be influenced by the cultural background and education of the assessor and dependent upon the experience level of dental professionals. This study aimed to evaluate how the sagittal jaw relationship in Class I and Class II individuals affects facial attractiveness, and whether the assessor's professional education and background affect the perception of facial attractiveness.

METHODS

Facial silhouettes simulating mandibular retrusion, maxillary protrusion, mandibular retrusion combined with maxillary protrusion, bimaxillary protrusion and severe bimaxillary protrusion in class I and class II patients were assessed by five groups of people with different backgrounds and education levels (i.e., 23 expert orthodontists, 21 orthodontists, 15 maxillofacial surgeons, 19 orthodontic patients and 28 laypeople).

RESULTS

Straight facial profiles were judged to be more attractive than convex profiles due to severe mandibular retrusion and to mandibular retrusion combined with maxillary protrusion (all P<0.05). Convex profiles due to a slightly retruded position of the mandible were judged less attractive by clinicians than by patients and laypeople (all P<0.05).

CONCLUSIONS

Convex facial profiles are less attractive than Class I profiles. The assessment of facial attractiveness is dependent on the assessor's education and background. Laypeople and patients are considerably less sensitive to abnormal sagittal jaw relationships than orthodontists.

Effect of somatosensory amplification and trait anxiety on experimentally induced orthodontic pain

The perception of pain varies considerably across individuals and is affected by psychological traits. This study aimed to investigate the combined effects of somatosensory amplification and trait anxiety on orthodontic pain. Five-hundred and five adults completed the State Trait Anxiety Inventory (STAI) and the Somatosensory Amplification Scale (SSAS). Individuals with combined STAI and SSAS scores below the 20th percentile (LASA group: five men and 12 women; mean age ± SD = 22.4 ± 1.3 yr) or above the 80th percentile (HASA group: 13 men and seven women; mean age ± SD = 23.7 ± 1.0 yr) were selected and filled in the Oral Behaviors Checklist (OBC). Orthodontic separators were placed for 5 d in order to induce experimental pain. Visual analog scales (VAS) were administered to collect ratings for occlusal discomfort, pain, and perceived stress. Pressure pain thresholds (PPT) were measured. A mixed regression model was used to evaluate pain and discomfort ratings over the 5-d duration of the study. At baseline, the LASA group had statistically significantly higher PPT values for the masseter muscle than did the HASA group. During the experimental procedure, the HASA group had statistically significantly higher discomfort and pain. A significant difference in pain ratings during the 5 d of the study was found for subjects in the HASA group. Higher OBC values were statistically significantly positively associated with pain. Somatosensory amplification and trait anxiety substantially affect experimentally induced orthodontic pain.

Reproducibility of the assessment of the Fränkel manoeuvre for the evaluation of sagittal skeletal discrepancies in Class II individuals

OBJECTIVES

The Fränkel manoeuvre is a procedure by which the mandible of Class II individuals is postured forward in dental Class I relationship. The evaluation of the resulting facial profile provides information concerning the components determining the sagittal discrepancy. Data concerning the reproducibility of its assessment are not available. This study aimed to evaluate the intra-observer and inter-observer reproducibility of the assessment of the manoeuvre and to assess whether the amount of clinical experience affects its reproducibility.

METHODS

Two lateral photographs, one in centric occlusion, and the other with the mandible postured forward (Fränkel manoeuvre) of 100 Angle Class II individuals aged between 9 and 13 years were evaluated by six orthodontists (T0). Each examiner was asked whether the facial profile worsen or not with the manoeuvre after being trained by an expert orthodontist. The test was repeated after 2 weeks interval (T1). Intra-observer and inter-observer agreement were evaluated by computing the Cohen's K.

RESULTS

The agreement (K values) between observations (T0 versus T1) for each examiner ranged from 0.49 to 0.72. The overall agreement was 0.65 [95% confidence interval (CI) = 0.54-0.75]. The agreement in the group with less clinical experience was 0.61 (95% CI = 0.46-0.76), while it was 0.68 (95% CI = 0.53-0.83) in the more experienced group. The amount of clinical experience did not affect intra-observer agreement (P = 0.50). The overall agreement between the examiners and the trainer was 0.74 (95% CI = 0.65-0.83) and 0.73 (95% CI = 0.64-0.83) at T0 and T1 respectively.

CONCLUSION

The assessment of the Fränkel manoeuvre is reproducible and it is not influenced by the amount of clinical experience.

Effects of muscle pain induced by glutamate injections during sustained clenching on the contraction pattern of masticatory muscles

AIMS

To evaluate the contraction pattern of masticatory muscles during sustained clenching tasks with or without experimental pain induced by glutamate injection into the masseter muscle. It was hypothesized that acute muscle pain could induce compensatory changes in the electromyographic (EMG) activity of the masticatory muscles.

METHODS

Fifteen volunteers (seven males, mean age ± SD = 29.7 ± 1.1 years; eight females, mean age ± SD = 23.5 ± 1.2 years) were recruited in a crossover experimental study. All subjects participated in two randomized 20-minute experimental sessions. Each subject was asked to clench at 25% of the maximum voluntary contraction (MVC). After 10 minutes, isotonic saline or glutamate was injected in random order into the right masseter. EMG activity (root mean square [RMS] and mean power frequency [MPF]) was assessed in the masseter and anterior temporalis muscles on both sides. Pain and fatigue were assessed by 0-10 numeric rating scales (NRS) every minute. Differences between conditions (isotonic saline vs glutamate) for all the outcome parameters were analyzed by using a mixed effect model.

RESULTS

The EMG activity of the masticatory muscles and pain and fatigue scores were not dependent on isotonic saline/glutamate injection (all P > .05). The RMS in the temporalis and masseter muscles increased with time (right masseter P = 0.001, left masseter P = .004, right temporalis P = .22, left temporalis P = .006), whereas the MPF decreased (right masseter P = .0001, left masseter P < .0001, right temporalis P = .51, left temporalis P = .0005). Scores for fatigue and pain increased during the experimental sessions (all P < .05).

CONCLUSION

Intramuscular injection of glutamate caused more pain than isotonic saline but did not affect the contraction pattern of the masticatory muscles during a sustained clenching task. This finding strongly suggests the adaptive capacity of the stomatognathic system in the presence of acute nociceptive inputs.

Social impairment of individuals suffering from different types of chronic orofacial pain

Background

The daily life of patients suffering from orofacial pain is considerably impaired as compared to healthy subjects. The aim of this study was to investigate the influence of different categories of orofacial pain on the habitual life of adult individuals.

Methods

Seven hundred eighty-one individuals with orofacial pain were recruited from an initial sample of 1,058 patients. All the individuals were allocated to groups according to their diagnosis: myofascial pain (group A, 676 subjects, 525 females and 151 males; mean age ± SD = 35.2 ± 12.6), migraine (group B, 39 subjects, 29 females and 10 males; mean age ± SD 36.0 ± 10.7), and both myofascial pain and migraine (group C, 66 subjects, 56 females and 10 males, mean age ± SD = 35.6 ± 10.8). Characteristic pain intensity (CPI), disability days (DD), disability score (DS), and graded chronic pain intensity (GCPS) were calculated according to Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) axis II. Depression and somatization (nonspecific physical symptoms) scores were also calculated.

Results

A significant association between groups and GCPS categories was found (p < 0.0001). Post hoc tests showed a significant difference between groups A and B and between A and C, but not between B and C. In group A, the most frequent GCPS score was grade II. The most frequent GCPS score in groups B and C was grade III, indicating a moderate limiting impairment. This score was more frequent in group B (41%) than in the other groups (group A = 20.6%, group C = 34.8%). GCPS grade IV was more frequent in group C (19.7%) than in the other groups. Group C had significantly higher scores for nonspecific physical symptoms than group A (p < 0.05).

Conclusions

Myofascial pain and migraine sensibly affect the common daily life of adult individuals. The comorbidity of both conditions determines a major impairment.