Stomatognathic adaptive motor syndrome is the correct diagnosis for temporomandibular disorders

Masticatory Function in Individuals with Temporomandibular Disorders: A Systematic Review and Meta-Analysis

The literature search was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) protocol in the PubMed, Cochrane Library, LILACS, EBSCO, Scielo, between 2012 and 2022. The methodological quality was assessed by using the Newcastle-Ottawa Study Quality Assessment Scale. Mean differences and 95% confidence intervals were calculated and combined in meta-analyses. A total of 1202 participants were included in this systematic review (690 with TMD; 512 without TMD), with 22 articles being included in the qualitative analysis. Only three studies enabled the comparative analysis of the results. Ten articles showed a high methodological quality and a low risk of bias, and twelve had a low methodological quality and an increased risk of bias. The meta-analysis showed that the differences between the intervention and control groups were not statistically significant for the percentage overlapping coefficient of the anterior temporal muscle, for the masseter, and for the torque coefficient. The parameters analyzed with the compound technique for chewing showed altered mandibular functions in individuals with TMD. With the EMG method, it was possible to suggest that TMD in adult individuals causes compensatory muscle behaviors, and several changes in the masticatory function were found.

Functional magnetic resonance imaging evaluation of masticatory muscle dysfunction in unilateral exodontia rabbits

Objective:

Occlusal alteration due to tooth loss may cause overload of masticatory muscle and promote muscle dysfunction. This study explored the feasibility of using functional magnetic resonance imaging (fMRI) to evaluate muscle dysfunction in an established unilateral exodontia animal model.

Methods:

six rabbits were extracted right maxillary molars. T2 mapping, T2* mapping and Iterative Decomposition of water and fat with Echo Asymmetry and Least Square Estimation (IDEAL-IQ) were performed one day before extraction and every 2 weeks (2th~12th week) after extraction. The T2 and T2* values and fat fraction (FF) of bilateral temporal muscle (TM), masseter muscle (MM) and medial pterygoid muscle (MPM) were measured and compared between the extraction side-and the contralateral side. Parameters of three monitoring time points (0th, sixth, 12th week) were also analyzed.

Results:

T2 values of MM on extraction side-were significantly higher than those of contralateral side-from fourth week to 12th week after extraction (p < 0.05). T2 values of MM and MPM on extraction side-and TM on contralateral side-were significantly higher in 12th week than those in 0th week (p < 0.05). And FF of bilateral MM was significantly higher in 12th week than those in 0th week (p < 0.05). T2* value showed no significant difference between extraction side-and contralateral side-and also at above three time points.

Conclusion:

T2 and T2* value and FF can be used as indicators of masticatory muscle dysfunction. fMRI is expected to be a non-invasive method for in vivo and real-time evaluation of masticatory muscle functional abnormality.

The effects of treatment timing on the management of patients with multiple facial fractures and on the self-perception of TMD recovery

OBJECTIVE

To investigate the effects of time on the orofacial functions and on the self-perception of temporomandibular disorders (TMD) recovery in a population of patients with multiple facial fractures.

METHODS

Orofacial functions and self-perception of TMD recovery was verified in patients with midface and/or lower face fractures. Patients were divided according to the time between fracture reduction and the clinical assessments: 0-1 month (Group 1), 1-3 months (Group 2), and 15 >3 months (Group 3).

RESULTS

Patients in Group 1 presented a greater compromise of swallowing and mastication when compared to patients with older fractures (p = 0.015), whereas patients in Group 3 presented a poorer TMD recovery (TMJ pain: p = 0.010 and tinnitus: p = 0.004).

CONCLUSION

Delays in functional treatments involving the myofunctional orofacial system have a negative impact on the recovery of essential orofacial functions and on TMD symptoms..

Acoustic reflex preshoot: A sign of contraction of the tensor tympani muscle?

Two tiny muscles are attached to the ossicles of the middle ear: the stapedius, whose role as a protector of the inner ear against loud noise has been widely accepted, and the tensor tympani, which remains a mystery since no valid method of detecting its contraction has yet been developed. However, tonic contraction of the tensor tympani has been associated with a number of otological conditions including fullness, tinnitus, slight hearing loss, and Menière-like findings. Our hypothesis is that an easily recognizable sign in the acoustic immittance testing that is part of almost every basic audiological evaluation indicates the contraction of the tensor tympani. During acoustic reflex assessment, a loud stimulus causes a bilateral contraction of the stapedial muscles and an increase in impedance which appears as a deflection in the tracing of the immittance test results. In the case of a contracted tensor tympani, when an intense sound is sent to provoke the acoustic reflex, the stapedius must overcome its resistance which would otherwise have the opposite effect on the footplate. This effort can be seen as a small peak or "preshoot" preceding the greater negative deflection of the impedance. We report the cases of ten patients with unilateral aural symptoms such as tinnitus, impaired noise tolerance, fullness, ear pressure and/or ear discomfort during chewing; the preshoot was present only in the symptomatic ear. If further studies confirm our hypothesis, this could give rise to new therapeutical strategies aimed at reducing contraction of the tensor tympani and balancing its function.

Monitoring of Changes in Masticatory Muscle Stiffness after Gum Chewing Using Shear Wave Elastography

This study aimed to investigate if intensive exercise affects the stiffness of the masticatory muscles measured with shear-wave elastography. The study included a cohort of healthy adults (n = 40) aged 40 ± 11 years. In each individual, the stiffness of both the masseter and temporalis muscle was examined three times: at baseline, after 10 min of intensive exercise (chewing gum), and after 10 min of relaxation. Stiffness values (median (IQR)) of both the masseter and temporalis muscle were the lowest at the baseline (11.35 (9.7–12.65) and 10.1 (9.1–10.95)), increased significantly after the exercise (12.5 (11.1–13.25) and 10.3 (10.2–10.52)) and then dropped significantly after 10 min of relaxing (11.75 (9.95–12.6) and 10.2 (9.65–11.9)). The stiffness of the temporalis muscle was significantly lower than that of the masseter muscle. The values of the stiffness of the masseters correlated significantly with the values of the stiffness of the temporalis muscles. Shear wave elastography proved to be a sensitive method for showing changes in the stiffness of the muscles involved in the mastication occurring as a response to the effort, which increased the muscle stiffness. Further research is needed to broaden knowledge on the impact of eating habits and the occurrence of parafunctions on the development of temporomandibular disorders and the condition of masticatory muscles.

Estimation of jaw-opening forces, energy expenditure and jaw-opening patterns in adults

OBJECTIVES

The aims of this study were to investigate (1) the jaw-opening forces in different stages of jaw-opening, and determine the correlation among maximum jaw-opening force, maximum jaw-opening, and parameters such as age, height, weight, and gender, (2) the energy expenditure during jaw-opening, and (3) the jaw-opening patterns in adults.

DESIGN

This was a cross-sectional study. The sample consisted of 87 participants were recruited from Dunedin, New Zealand. Jaw-opening forces were measured using an adjustable, rigid extra-oral device connected to a 1000 N load cell.

MAIN RESULTS

Outcomes were highly skewed. The median (IQR) value of maximum jaw-opening was 48 mm (8 mm). The median of maximum jaw-opening force (40.0 N) was higher than jaw-opening force at maximum jaw-opening (35.2 N) (P < 0.01). The median (IQR) of the work was 1.30 J (1.28 J), ranging from 0.38 J to 4.03 J. The median of maximum jaw-opening force and work was higher in males (54.8 N; 1.22 J) than females (33.5 N; 0.74 J) (P < 0.05). Four jaw-opening force patterns (Pattern 1, 2, 3 and 4) were fitted and generated using Origin Pro software.

CONCLUSION

A wide range of variation in jaw-opening force and work was observed, and they displayed a non-parametric, highly skewed distributions. The maximum jaw-opening force did not correspond to the maximum jaw-opening. Further studies could explore the potential association among the jaw-opening force pattern, the work of jaw-opening and TMJ diseases.

Influence of tongue exercise and orofacial myofunctional status on the electromyographic activity and pain of chronic painful TMD

Objective: To analyze the influence of tongue exercise and myofunctional status on the electromyographic activity (EMG) and pain perception in individuals with chronic painful TMDs.Methods: Twenty-four subjects diagnosed according to the DC/TMD (18-52 years old) were assessed: EMG on the masseter and anterior temporalis; myofunctional orofacial conditions underwent clinical assessment (OMES); and questionnaire for self-perception of TMD signs and symptoms (ProTMDMulti). The 50th percentile was calculated to establish a cutoff value based on OMES scores related to the functional variables of the tongue.Results: The compared groups showed no differences (p > 0.05) in self-perception of their TMD signs and symptoms or in the EMG activity during tongue exercises.Discussion: The myofunctional status of the tongue showed no impact on the painful TMD or on the activity of the masticatory muscles (captured during tongue exercise). The indication of tongue exercises in TMD cases is a safe and adequate possibility.

Dental occlusion as one cause of tinnitus

There is large support in literature linking tinnitus to dental occlusion and temporomandibular joint disorders (TMD). However, there is no model to explain such a link. This hypothesis explains how the fusimotor system of the muscles innervated by the trigeminal motor nucleus is affected by inadequacies in the occlusion of the teeth that cause changes in posture and movement of the mandible. Reptile to mammal evolution shows that stomatognathic structures underwent changes related to mastication. Among several changes, there was the appearance of a new articulation between the mandible and skull: the temporomandibular joint. The bones of the old reptile joint, quadrate-articular, have detached from the mandible and are part of the middle ear bone chain. The former becomes the incus and the latter the malleus. This bone change also carried the tensor tympani and its trigeminal motor innervation. Inadequate occlusal contacts give rise to an adapted function of the mandible and the most common compensatory muscular response is hypertonia involving all mandibular muscles, including the tensor tympani. A fundamental clinical feature that demonstrates the involvement of the trigeminal fusimotor system is the characteristic pain by palpation, but no pain on the mandibular movement. Muscle pain is always felt in the dermatome innervated by the mandibular branch of the trigeminal nerve, which carries the motor fibers, reported as tightening, similar to cramp, and has regular behavior in intensity, duration and frequency. In addition, the patient has increased musculature volume, detected by palpation of certain anatomical landmarks, but with loss of functional efficiency. The neuromotor control of the mandibular movements is poor and when asked to make lateral jaw movement touching the teeth, it is common to observe that the patient moves the lips, eyes, and even turns the head in the same direction as the movement. There is also difficulty eating hard foods and talking fast. Tongue biting while chewing is frequent, meaning that these non-physiological events surpass protective reflex circuits. The report of ear pain, tinnitus, blocked ear sensation and sudden hearing loss is common in such patients, compatible with the tonic contraction of the tensor tympani. The fusimotor system hypothesis is able to explain all events related to the symptoms and helps to establish a correct diagnosis for certain types of hearing disorders.

Effect of Breast Cancer Treatment on the Stomatognathic System

Breast cancer is the most common cancer affecting women in the world and provides functional changes in the human body. Evaluate women submitted to unilateral mastectomy, through electromyographic activity (mandibular rest, right and left laterality, protrusion, maximum voluntary contraction with and without Parafilm, habitual and non-habitual mastication) and thickness (rest and maximum voluntary contraction) of the right temporal muscle (RT), left temporal (LT), right masseter (RM) and left masseter (LM), also the molar bite force (right and left) and compare the data with healthy women. Material and Methods: 32 women were divided into two groups: unilateral mastectomy group (MG), average ± standard deviation 56.50±14.50 years (n=16) and without the disease group (CG), average ± standard deviation 56.56±14.15 years (n=16). The normalized electromyographic data, muscle thickness and maximal molar bite force were tabulated and submitted to statistical analysis (SPSS 21.0; student t test, p≤0.05). Significant statistical differences between MG and CG were found in right laterality, for RM (p=0.02); left laterality, for LT (p=0.01); chewing with peanuts, for RM (p=0.04); chewing with raisins, for LM (p=0.04) and right molar bite force (p=0.03). There was no statistically significant difference between MG and CG for muscle thickness. The results of this study suggest that women undergoing unilateral mastectomy may present functional changes, with emphasis on muscular hyperactivity, lower masticatory efficiency and lower maxillary bite force.

Can the severity of orofacial myofunctional conditions interfere with the response of analgesia promoted by active or placebo low-level laser therapy?

OBJECTIVE

To analyze the influence of orofacial myofunctional condition (OMC) on pain perception, temporomandibular disorders (TMD) severity, and the response to low-level laser therapy (LLLT) in women with painful TMD.

METHODS

Seventy-eight women, 59 with TMD, received active laser (30) or placebo (29), with 19 controls. OMC, TMD severity, pain intensity, and pressure pain threshold (PPT) were assessed at different times during the masticatory test: before treatment (LLLT dose: 780nm), during, and after 30 days.

RESULTS

No correlation was found between OMC and pain perception or TMD severity (p > 0.05). The active and placebo LLLT showed reduction of pain during chewing and better recovery levels during the rest period (p > 0.05), without differences between OMC groups.

DISCUSSION

The perception of pain and severity of TMD are not correlated with the OMC, and the response of analgesia promoted by active LLLT or placebo is not associated with OMC.

[Alteration of metabolic characteristics on the masseter muscle fiber of unilateral chewing rats and its adenosine monophosphate activated protein kinase regulatory mechanism]

OBJECTIVE

This study aims to determine the influence of unilateral chewing on metabolic characteristics of masseter muscle fibers in rats and the regulatory effect of an adenosine monophosphate activated protein kinase (AMPK) signal pathway on metabolism.

METHODS

Rats were submitted to exodontia of all the right maxillary molars and divided into 2, 4, 6, and 8 weeks groups, and corresponding control groups were set as well. Sections were stained by nicotine adenine dinucleotide tetrazolim reductase(NADH-TRase) to demonstrate the types, proportion, and density of masseter muscle fibers. AMPKα1 and p-AMPK(Thr172) levels in bilateral masseter muscles were detected by Western blot.

RESULTS

In the 2-week group, the percentage of dark fibers augmented in the ipsilateral side, whereas the percentage of intermediary fibers in the contralateral side was increased accompanied by a decrease of light fibers, compared with the control group (P<0.05). The percentage of dark fibers was increased in the bilateral sides, whereas the percentage of dark fiber in the ipsilateral sides surpassed that of the contralateral sides in the 4, 6, and 8-week groups. The percentage of intermediary fibers was decreased in the bilateral sides in the 6 and 8-week groups (P<0.05). The percentage of light fibers was reduced in the ipsilateral sides in the 8-week group, whereas no alteration was observed in contralateral sides (P>0.05). In the ipsilateral sides, p-AMPK (Thr172)/AMPKα1 levels were increased in the 2 and 4-week groups (P<0.05), whereas no change was observed in the contralateral sides in either group (P>0.05).

CONCLUSIONS

Unilateral chewing increases the oxidative metabolic ability in bilateral masseter muscle fibers especially in the non-working side accompanied with change of muscle fiber types. The improvement of aerobic metabolism ability is related to the AMPK signal pathway.
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Perturbed oral motor control due to anesthesia during intraoral manipulation of food

Sensory information from periodontal mechanoreceptors (PMRs) surrounding the roots of natural teeth is important for optimizing the positioning of food and adjustment of force vectors during precision biting. The present experiment was designed to test the hypothesis; that reduction of afferent inputs from the PMRs, by anesthesia, perturbs the oral fine motor control and related jaw movements during intraoral manipulation of morsels of food. Thirty healthy volunteers with a natural dentition were equally divided into experimental and control groups. The participants in both groups were asked to manipulate and split a spherical candy into two equal halves with the front teeth. An intervention was made by anesthetizing the upper and lower incisors of the experimental group while the control group performed the task without intervention. Performance of the split was evaluated and the jaw movement recorded. The experimental group demonstrated a significant decrease in measures of performance following local anesthesia. However, there was no significant changes in the duration or position of the jaw during movements in the experimental and control group. In conclusion, transient deprivation of sensory information from PMRs perturbs oral fine motor control during intraoral manipulation of food, however, no significant alterations in duration or positions of the jaw during movements can be observed.

Efeito do tratamento fonoaudiológico após a laserterapia de baixa intensidade em pacientes com DTM: estudo descritivo

RESUMO O aumento da dor/desconforto durante atividades como mastigar, falar e deglutir é comumente relatado por pacientes com Disfunção Temporomandibular (DTM) e a terapia fonoaudiológica miofuncional orofacial (TMO) tem sido proposta como parte do tratamento desta condição. Porém é uma modalidade que deve ser instituída quando o quadro de DTM e dor não está exacerbado a fim de não impedir ou dificultar a realização dos exercícios. Objetivo O objetivo deste estudo foi analisar o efeito da TMO no tratamento de pacientes com DTM, segundo o Research Diagnostic Criteria for temporomandibular disorders (RDC/TMD), após analgesia com laserterapia de baixa intensidade (LBI), quanto às condições miofuncionais orofaciais (CMO) e quanto à percepção dos sintomas de DTM. Método Transcorridos 30 dias após a finalização da LBI, cinco pacientes foram avaliados, com idades entre 50 e 61 anos. A aplicação do questionário ProDTMMulti para investigação da autopercepção da sintomatologia de DTM e do exame clínico AMIOFE (Avaliação Miofuncional Orofacial com Escores) para constatação das condições miofuncionais orofaciais foram realizados por fonoaudióloga experiente, antes e após a TMO. Resultados As CMO apresentaram aumento dos escores após TMO, indicando aumento do equilíbrio miofuncional orofacial. De acordo com a percepção das pacientes, após a TMO houve alívio dos sinais e sintomas de DTM. Conclusão A TMO instituída após a analgesia com LBI promoveu equilíbrio das funções orofaciais da amostra estudada e diminuição dos sinais e sintomas de DTM remanescentes, de acordo com a autopercepção dos indivíduos tratados.

Transient Hearing Loss and Objective Tinnitus Induced by Mouth Opening: A Rare Connection Between the Temporomandibular Joint and Middle Ear Space

OBJECTIVES

To describe objective tinnitus complicated with transient low-tone hearing loss coinciding with mouth opening, which was related to the connection between the mandibular fossa and middle ear space.

PATIENTS

A 41-year-old man presented with tinnitus, ear fullness, and hearing loss in the left ear on mouth opening.

MAIN OUTCOME MEASURES

Clinical case records, audiological data, and radiological analyses including computed tomography (CT) and magnetic resonance imaging.

RESULTS

Hearing thresholds on the affected side, which were evaluated with mouth opening, showed elevations of approximately 20 dB in the frequencies below 1000 Hz. Again, peak pressure on the tympanogram deviated negatively to -220 mmH2O under mouth opening without changing peak amplitude. CT showed a connection between the mandibular fossa and middle ear space, as revealed by a gas collection around the joint capsule evaluated in two phases (with and without mouth closing). Ear symptoms resolved after myringotomy.

CONCLUSIONS

Although an influence of temporomandibular disorder (TMD) on tinnitus perception has been debated, whether this association is causal or fortuitous has remained contentious. The present case showed a unique feature of tinnitus attributed to a connection between the mandibular fossa and middle ear space.

Effects of short-term training on behavioral learning and skill acquisition during intraoral fine motor task

Sensory information from the orofacial mechanoreceptors are used by the nervous system to optimize the positioning of food, determine the force levels, and force vectors involved in biting of food morsels. Moreover, practice resulting from repetition could be a key to learning and acquiring a motor skill. Hence, the aim of the experiment was to test the hypothesis that repeated splitting of a food morsel during a short-term training with an oral fine motor task would result in increased performance and optimization of jaw movements, in terms of reduction in duration of various phases of the jaw movements. Thirty healthy volunteers were asked to intraorally manipulate and split a chocolate candy, into two equal halves. The participants performed three series (with 10 trials) of the task before and after a short-term (approximately 30 min) training. The accuracy of the split and vertical jaw movement during the task were recorded. The precision of task performance improved significantly after training (22% mean deviation from ideal split after vs. 31% before; P<0.001). There was a significant decrease in the total duration of jaw movements during the task after the training (1.21 s total duration after vs. 1.56 s before; P<0.001). Further, when the jaw movements were divided into different phases, the jaw opening phase and contact phase were significantly shorter after training than before training (P=0.001, P=0.002). The results indicate that short-term training of an oral fine motor task induces behavior learning, skill acquisition and optimization of jaw movements in terms of better performance and reduction in the duration of jaw movements, during the task. The finding of the present study provides insights into how humans learn oral motor behaviors or the kind of adaptation that takes place after a successful prosthetic rehabilitation.

Reciprocal influence of masticatory apparatus, craniofacial structure and whole body homeostasis

There are evidences that the evolution into Homo erectus was partially induced by masticatory muscular dystrophy caused by a gene mutation, which in turn increased brain capacity and led to bipedalism. It is generally accepted that the morphology and function of mammalian skull are partially controlled by epigenetic mechanisms. Archeologic evidences support that the masticatory apparatus have influenced the mechanical stress distribution in hominin skull, and consequently changed craniofacial morphology and function. Even after evolution into H. erectus, alterations in food properties by civilization and cultural preferences have caused modification of human masticatory pattern and accordingly craniofacial structure. Since there are evidences that prehuman and human masticatory apparatus has been influenced the craniofacial and whole body morphology and function, this apparatus in turn might influence whole body homeostasis. Plausible reciprocal influencing mechanisms of the masticatory apparatus on the whole body homeostasis might be (1) direct mechanical influence on the craniofacial structure, (2) distortion of cerebrospinal fluid circulation, and/or (3) several neural/humoral routes. Based on these backgrounds, the hypothesis of the present study is that the morphology and function of masticatory apparatus influence the whole body homeostasis and these interactions are reciprocal. Therefore, human masticatory apparatus, at the present time, should be kept in its physiological status to maintain the whole body homeostasis. We recommend basic and clinical approaches to confirm this hypothesis.

The muscle engram: the reflex that limits conventional occlusal treatment

The engram (the masticatory "muscle memory") is shown to be a conditionable reflex whose muscle conditioning lasts less than two minutes, far shorter than previously thought. This reflex, reinforced and stored in the masticatory muscles at every swallow, adjusts masticatory muscle activity to guide the lower arch unerringly into its ICP. These muscle adjustments compensate for the continually changing intemal and external factors that affect the mandible's entry into the ICP. A simple quick experiment described in this article isolates the engram, enabling the reader to see its action clearly for the first time. It is urged that every reader perform this experiment. This experiment shows how the engram, by hiding the masticatory muscles' reaction (the hit-and-slide), limits the success of the therapist in achieving occlusion-muscle compatibility. This finding has major clinical implications. It means that, as regards the muscle aspect of treating occlusion, the dentist treating occlusion conventionally is working blind, a situation the neuromuscular school of occlusal thought seeks to correct. The controversy over occlusion continues.