The effect of pain from orthodontic arch wire adjustment on masseter muscle electromyographic activity

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.

Predictors of the masticatory muscle activity during chewing in patients with myogenous temporomandibular disorder

OBJECTIVES

The aim of the study was to identify predictors of the masticatory muscle activity during chewing (MMA) of the masseter and temporalis anterior (TA) muscles in patients with unilateral myogenous temporomandibular disorder (mTMD).

MATERIALS AND METHODS

This observational and cross-sectional study included 109 patients diagnosed with unilateral mTMD. Surface electromyography was used to separately evaluate the MMA of the masseter and TA on the affected and unaffected sides. Also, pain intensity (with a visual analog scale), pressure pain threshold (with an algometer), active pain-free maximum mouth opening and temporomandibular joint lateral movements (with a ruler), cervical range of motions (with a goniometer), and TMD severity (with a Fonseca Anamnestic Index) were assessed. Various statistical methods were used to predict the MMA of the masseter and TA, including standard, forward, and best subsets multiple regression models.

RESULTS

While there were significant correlations between the MMA of the masseter and TA and pain intensity, pressure pain threshold values, and TMD severity, they were not found with other variables. These parameters were also predictive factors for MMA of both muscles (p < 0.05).

CONCLUSIONS

According to the present study, pain intensity, muscle and joint tenderness, and the severity of the disorder are predictive factors for MMA of the masseter and TA muscles in patients with mTMD. It is recommended that these parameters be considered when establishing clinical evaluation and treatment programs focusing on MMA in patients with mTMD.

CLINICAL RELEVANCE

The pain intensity, masticatory muscles and TMJ tenderness, and disorder severity are predictors for MMA of the masseter and TA in patients with mTMD. Pain intensity has the most significant importance.

Neuromuscular Stability of Dental Occlusion in Patients Treated with Aligners and Fixed Orthodontic Appliance: A Preliminary Electromyographical Longitudinal Case-Control Study

The aim of the present study was to evaluate if, after treatment with aligners (ALIGN) and fixed orthodontic appliance (FOA), alterations of the neuromuscular activity may occur and if differences in these changes can be detected between the two treatments. Sixteen healthy patients (7 FOA, 9 ALIGN) with class I or class II molar relation were recruited. Standardized surface electromyography (ssEMG) was used to evaluate the activity of the masticatory muscles (masseters-MM and temporalis-TM) before the beginning of the orthodontic treatment (T1), at the end (T2), and 3 months (T3) after the end of the treatment. Intragroup (within timepoints) and intergroup differences were statistically analyzed. At T1, the mean values of each ssEMG index were within the normal range in both groups. At T2, the FOA group showed larger differential recruitment of the MM than TA muscles with a value slightly over the normal range. All the indexes were normalized at T3, and no differences emerged between groups. In the FOA group, the index of MM symmetrical contraction increased significantly at T3 compared to T1 and T2. In the ALIGN group, no significant changes were observed between each timepoint. In FOA subjects, a slight alteration of the muscular activity appeared immediately after bracket removal and this alteration normalized after 3 months of rescue. In subjects treated with aligners, no significant alteration of the muscular activity was assessed.

Activation and installation of orthodontic appliances temporarily impairs mastication

OBJECTIVES

To investigate the masticatory (masticatory performance, bite force, swallowing threshold, muscle activity, and questionnaires) and nutritional (nutrient intake) impacts of the activation and/or installation of different orthodontic appliances (fixed labial, lingual appliances, and clear aligners).

MATERIALS AND METHODS

Six electronic databases and gray literature were searched (up to May 2021) for relevant studies evaluating mastication and nutrition after activation/installation of orthodontic appliances. This review followed PRISMA guidelines and was registered at PROSPERO (CRD42020199510). The risk of bias (RoB 2 and ROBINS-I) and evidence quality Grading of Recommendations Assessment, Development, and Evaluation were analyzed.

RESULTS

Of 4226 recorded and screened, 15 studies were finally included. Masticatory performance (standardized mean difference [SMD]: 1.069; 95% coefficient interval [CI]: 0.619 to 1.518) and bite force (SMD: -2.542; 95% CI: -4.867 to -0.217) reduced in the first 24 to 48 hours of fixed labial appliance installation/activation, but they were both normalized after 30 days (P > .05). The swallowing threshold remained constant (P > .05). Nutritional intake was rarely reported but showed copper (P = .002) and manganese (P = .016) reductions, with higher calorie and fat intake (P < .05). Lingual appliances impacted chewing more than labial, and clear aligner wearers reported fewer chewing problems (P < .001). Low to very low levels of evidence were found.

CONCLUSIONS

Based on low to very low levels of evidence, mastication was reduced during the first 24 to 48 hours of fixed labial appliance activation/installation, but it was transitory (up to 30 days). Due to insufficient data, the nutritional impact of orthodontic appliances was not conclusive.

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.

Low-level laser-aided orthodontic treatment of periodontally compromised patients: a randomised controlled trial

Low-level laser irradiation (LLLI) shows effects in orthodontic pain relief and periodontal inflammation control. The aim of this article is to investigate the analgesic and inflammation-modulatory effects of low-level laser irradiation among orthodontic patients with compromised periodontium. A randomised controlled trial with split-mouth design was conducted in 27 adults with treated and controlled chronic periodontitis over 6 months. One side of the dental arch underwent repeated treatment under a 940-nm diode laser (EZlase; Biolase Technology Inc.) with a beam size of 2.8 cm² for 60 seconds at 8.6 J/cm², whilst the other side received pseudo-laser treatment. Laser irradiation was applied repeatedly for 8 times during the first 6 weeks after bracket bonding and monthly thereafter until the end of orthodontic treatment. Subjective pain (assessed by visual analogue scale in pain diary and by chairside archwire activation), periodontal status (assessed by periodontal clinical parameters), cytokines in gingival crevicular fluid (interleukin 1β, prostaglandin E₂, substance P) and periodontopathic bacteria (Porphyromonas gingivalis and Treponema denticola) in supragingival plaque were assessed. The intensity of pain was lower on the laser-irradiated side at multiple follow-up visits (P < 0.05). The pain subsided 1 day earlier on the laser side, with a lower peak value during the first week after initial archwire placement (P < 0.05). The laser side exhibited a smaller reduction in bite force during the first month (mean difference = 3.17, 95% CI: 2.36-3.98, P < 0.05 at 1-week interval; mean difference = 3.09, 95% CI: 1.87-4.32, P < 0.05 at 1-month interval). A smaller increase was observed in the plaque index scores on the laser side at 1-month (mean difference = 0.19, 95% CI: 0.13-0.24, P < 0.05) and in the gingival index scores at the 3-month follow-up visit (mean difference = 0.18, 95% CI: 0.14-0.21, P < 0.05). Laser irradiation inhibited the elevation of interleukin-1β, prostaglandin E₂ and substance P levels during the first month (P < 0.05). However, no intergroup difference was detected in the bacteria levels. Low-level laser irradiation exhibits benefits in pain relief and inflammation control during the early stage of adjunctive orthodontic treatment in periodontally compromised individuals.

Centric relation-intercuspal position discrepancy and its relationship with temporomandibular disorders. A systematic review

OBJECTIVE

The objective of this study is to assess the relationship between centric relation-intercuspal position discrepancy (CR-ICP discrepancy) and temporomandibular disorders (TMDs), by systematically reviewing the literature.

MATERIALS AND METHODS

A systematic research was performed between 1960 and 2016 based on electronic databases: PubMed, Cochrane Library, Medline, Embase, Scopus, EBSCOhost, BIREME, Lilacs and Scielo, including all languages. Analytical observational clinical studies were identified. Two independent authors selected the articles. PICO format was used to analyze the studies. The Newcastle-Ottawa Scale (NOS) was used to verify the quality of the evidence.

RESULTS

Four hundred and sixty-seven potentially eligible articles were identified. Twenty studies were analyzed, being grouped according to intervention in studies in orthodontic patients (n = 3) and studies in subjects without intervention (n = 17). Quality of evidence was low, with an average score of 3.36 according to Newcastle-Ottawa Scale. In most studies, the presence of CR-ICP discrepancy is associated with the presence of muscle (pain) and joint disorders (noise, disc displacement, pain, crepitus, osteoarthritis and osteoarthrosis). However, the lack of consistency of the results reported reduces the validity of the studies making it impossible to draw any definite conclusions.

CONCLUSIONS

Because of the heterogeneity of the design and methodology and the low quality of the articles reviewed, it is not possible to establish an association between CR-ICP discrepancy and TMD. The consequence of CR-ICP discrepancy on the presence of TMD requires further research, well-defined and validated diagnostic criteria and rigorous scientific methodologies. Longitudinal studies are needed to identify CR-ICP discrepancy as a possible risk factor for the presence of TMD.

Insight into orthodontic appliance induced pain: Mechanism, duration and management

Most of the orthodontic patients experience pain during treatment and this significantly influences their attitudes and the approach towards treatment. A number of factors that influence pain response include age, gender, personal pain threshold, mood and stress level of the person, cultural differences and types of orthodontic treatment. Pain is a often overlooked subject by orthodontists, it is nevertheless important to understand the source and mechanism of the pain that occurs during treatment, as well as the methods for managing and controlling this pain. This review attempts to overview the mechanism, duration and current management strategies of orthodontic treatment.

Effect of Controlled Masticatory Exercise on Pain and Muscle Performance in Myofascial Pain Patients: A Pilot Study

The aim of this study was to test the hypothesis that strengthening masticatory muscles using a controlled chewing exercise protocol improves muscle function, as evaluated quantitatively by electromyogram, and reduces pain at rest and during function. The study included 20 patients diagnosed with myofascial pain according to the Research Diagnostic Criteria for Temporomandibular Disorders with low masseter volume increase during maximal clench. The exercise group (ten patients) was subjected to a controlled gum chewing exercise protocol for eight weeks: the control group (ten patients) received only support and encouragement. Patients were examined at the beginning and at the end of the experiment which included an electromyogram (EMG) to assess muscle performance, masticatory muscle tenderness to palpation, mouth opening range, subjective anamnestic indices to evaluate pain perception and pain relief, and chewing tests. The EMG showed that the masticatory muscle exercise did produce objective physiologic results. In the exercise group, a significant increase was found in the electric muscle activity of the masseters during maximal voluntary clench (p=0.007). The exercise group showed significant reduction in pain during rest, pain during the chewing test, and a disability score. At the end of the study, a difference between the two groups was shown in the Pain Relief Scale: significantly greater pain relief was found in the exercise group as compared to the control group (p=0.019). For all other clinical parameters, there was no difference between the two groups or interaction between time and treatment. The results of this study seem to be equivocal. Additional experiments on larger population groups with extended chewing protocols are necessary before a more substantial conclusion can be reached.

The Role of Tooth-Grinding in the Maintenance of Myofascial Face Pain: A Test of Alternate Models

OBJECTIVE

While mechanisms of myofascial face pain are poorly understood, bruxism has been implicated in the maintenance of this painful disorder. This study evaluates whether evidence of one aspect of bruxism, tooth-grinding, is positively associated with pain severity, as predicted by a psychophysiological model, or negatively associated, as predicted by an adaptation model of face pain.

PATIENTS

Participants were 51 women who met Research Diagnostic Criteria for the myofascial subtype of temporomandibular disorder.

OUTCOME MEASURES

Tooth-grinding was quantified by changes in microwear features of the molar teeth over 2 weeks. Palpated pain severity was quantified on an 11-point scale in response to palpation of the skin overlying the masseter and temporalis muscles bilaterally. Other measures included validated scales of spontaneous pain severity, stress, distress, and psychological symptoms. Association was quantified as Pearson correlation coefficients.

RESULTS

Data showed an inverse correlation (r = -0.37, P < 0.05) between palpated pain severity and the index of tooth wear, supporting the adaptation model. This correlation provided a weighted average of a strong effect (r = -0.80, P < 0.01) seen in those women reporting pain only the right side of their face with an effect that approximated zero in those reporting bilateral pain. Tooth wear measures were negatively associated with ratings of pain severity only over the right masseter.

DISCUSSION

While these data do not address the role of clenching, they cast serious doubt on the theory that myofascial face pain is maintained by tooth-grinding.

Centric slide, bite force and muscle tenderness changes over 6 months following fixed orthodontic treatment

OBJECTIVE

The postorthodontic change of the masticatory muscles was evaluated using three parameters: maximal voluntary bite force (MVBF), slide in centric (difference between maximal intercuspation and retruded contact position), and muscle sensitivity to palpation.

MATERIALS AND METHODS

MVBF was measured with a custom-made rubber tube bite force device, centric slide with a digital caliper, and sensitivity to palpation of the masseter and temporalis muscles (scale 0-3) during application of standardized digital force (10 N). Data were collected at four time points: T0, before bracket removal; T1, immediately after bracket removal; T2, after 3 months of retention; and T3, after 6 months of retention. Patients (n = 41; 22 females, 19 males; mean age 17.4 +/- 5.4 years) were examined from T0 to T1 and from T1 to T2. Of these, 28 (15 females, 13 males) were followed at T3.

RESULTS

Immediately after bracket removal (T0 to T1), MVBF increased significantly by 15%. Another significant increase (15.5%) was found 3 months posttreatment (T1-T2), and almost no increase (2%) at 6 months (T2-T3). The slide in centric remained within normal values during the three time points. A decline in sensitivity to palpation from T1 to T3 was found for both masseter and temporalis muscles.

CONCLUSIONS

Neuromuscular adaptability begins within several minutes after bracket removal. A second stage of muscular adaptation occurs within 3 months of retention. These findings suggest that muscular adjustment occurs within a short period after orthodontic treatment.

The clinical usefulness of surface electromyography in the diagnosis and treatment of temporomandibular disorders

BACKGROUND

This article presents a comprehensive review of the recent literature regarding the scientific support for the use of surface electromyography (SEMG) in diagnosing and treating temporomandibular disorders (TMDs).

TYPES OF STUDIES REVIEWED

The authors conducted a Medline search involving human studies using the key words "surface electromyography or electromyography" and "masticatory muscles or temporomandibular disorders or craniomandibular disorders." They also reviewed relevant articles regarding the clinical usefulness of SEMG based on reliability, validity, sensitivity and specificity, as well as additional references included in some of the articles.

RESULTS

The clinical use of SEMG in the diagnosis and treatment of TMD is of limited value when one considers reliability, validity, sensitivity and specificity as measurement standards. SEMG does not appear to contribute any additional information beyond what can be obtained from the patient history, clinical examination and, if needed, appropriate imaging.

CONCLUSIONS

Clinically, the determination of the presence or absence of TMD does not appear to be enhanced by the use of SEMG. However, the modality may be useful in a meticulously controlled research setting.

CLINICAL IMPLICATIONS

SEMG has limited value in the detection or management of TMD and in some instances may lead to unnecessary dental therapy as a solution for those disorders.

The influence of occlusion on jaw and neck muscle activity: a surface EMG study in healthy young adults

The electromyographic (EMG) characteristics of masseter, temporalis and sternocleidomastoid (SCM) muscles during maximum voluntary teeth clench were assessed in 27 male and 35 female healthy young adults. Subjects were divided into two groups: (i) 'complete' Angle Class I (bilateral, symmetric canine and molar Class I relationships), and (ii) 'partial' Angle Class I (one to three canine/molar Class I relationships, the remaining relationships were Class II or Class III). On average, standardized muscular symmetry ranged 80.7-87.9%. During maximum voluntary teeth clench, average co-contraction of SCM muscle was 13.7-23.5% of its maximum contraction. On average, all torque coefficients (potential lateral displacing component) were >90%, while all antero-posterior coefficients (relative activities of masseter and temporalis muscles) were >85%. The average integrated areas of the masseter and temporalis EMG potentials over time ranged 87.4-106.8 muV/muV s%. Standardized contractile muscular activities did not differ between 'complete' and 'partial' Angle Class I, and between sexes (two-way analysis of variance). A trend toward a larger intragroup variability in EMG indices was observed in the subjects with 'partial' Angle Class I than in those with 'complete' Angle Class I (significant difference for the temporalis muscle symmetry, P = 0.013, analysis of variance). In conclusion, the presence of a complete or partial Angle occlusal Class I did not seem to influence the standardized contractile activities of masseter, temporalis and SCM muscles during a maximum voluntary clench. Subjects with a 'complete' Angle Class I were somewhat a more homogenous group than subjects with 'partial' Angle Class I.

Craniofacial pain and motor function: pathogenesis, clinical correlates, and implications

Many structural, behavioral, and pharmacological interventions imply that favorable treatment effects in musculoskeletal pain states are mediated through the correction of muscle function. The common theme of these interventions is captured in the popular idea that structural or psychological factors cause muscle hyperactivity, muscle overwork, muscle fatigue, and ultimately pain. Although symptoms and signs of motor dysfunction can sometimes be explained by changes in structure, there is strong evidence that they can also be caused by pain. This new understanding has resulted in a better appreciation of the pathogenesis of symptoms and signs of the musculoskeletal pain conditions, including the sequence of events that leads to the development of motor dysfunction. With the improved understanding of the relationship between pain and motor function, including the inappropriateness of many clinical assumptions, a new literature emerges that opens the door to exciting therapeutic opportunities. Novel treatments are expected to have a profound impact on the care of musculoskeletal pain and its effect on motor function in the not-too-distant future.

The influence of orthognathic surgery on occlusal force in patients with vertical facial deformities

This study utilized bite-force measurements to determine the effect of various orthognathic surgery procedures on occlusal force generation in 42 patients with vertical facial deformities. The results showed that orthognathic surgery produced marked alterations in occlusal force levels which continued to occur up to a year after surgery. Measurements indicated that advancement of the mandible may result in weaker force levels, while bimaxillary surgery for the treatment of a "long face" brings the previously weaker bite force to a more "normal" level.

Functional characteristics of retrognathic patients before and after mandibular advancement surgery

PURPOSE

The purpose of this investigation was to compare morphologic parameters and functional performance between controls and a sample of patients with mandibular retrognathia prior to surgical correction, and to examine how oral motor function adapts after treatment.

PATIENTS AND METHODS

Twenty-four retrognathic female patients were compared with 26 female controls before and up to 3 years after mandibular advancement surgery. Measures of skeletal morphology, mandibular range of motion, maximum isometric bite force, and levels of electromyographic activity in the anterior and posterior temporalis and masseter muscles during isometric bites were made on all subjects over time. One-way analysis of variance was used to compare the controls, the patients before surgery, and the patients after surgery.

RESULTS

Surgical lengthening of the mandible averaged 7.3 mm, bringing most skeletal measures into the normal range. There were no significant differences in jaw muscle mechanical advantage between patients and controls before surgery, but surgery significantly reduced mechanical advantage of the anterior temporalis and masseter muscles. Jaw hypomobility was apparent at 6 weeks after surgery, but returned to normal values within 12 to 24 months. Before surgery the patients had maximum isometric bite forces less than half those of controls. Bite forces steadily increased after surgery, approaching normal values within 2 years. Before surgery the patients' muscle activity levels per unit of bite force were equivalent to those of controls or somewhat higher. After surgery some of the patients' muscles had significantly lower levels of muscle activity per unit of bite force than did controls.

CONCLUSION

The results of this study suggest that correction of mandibular retrognathia by mandibular advancement surgery produces some significant functional benefits.