Introductory Guide
Aim: to support the Professionist during execution and interpretation of possible electromyographic standardized analysis.
Figura 1 – Analisi elettromiografica dei muscoli temporali e masseteri.
Addresses: Well-learned Clinicians on the performance of a sEMG exam with standardized principles
A dental rehabilitation (prosthetic or conservative, surgical or orthodontic) aims at restoring a correct anatomy in order to aid an adequate function. Oral proprioception in all its declinations (periodontal, mucous, bone and articular) permits to monitor the morphology and to check the masticatory organ functionality.
From this point of view, verifying the functional adaptation to new anatomical situation can be an useful tool for the Clinician. To be able to test the proprioceptive reaction of the patient to the new oral situation can help the Dentist in order to realize the proper correction in provisional or definitive phase.
An EMG analysis with appropriate standardized procedures is able to measure, in a scientific reliable way, the alterations of muscular motor pattern caused by dental factors. In the coordination of masticatory muscles some proprioceptors register the oral morpho-functional situation and are able to operate in case of iatrogenic alterations.
In many cases, the proprioceptive perception, even if in absence of consciousness from the patient, can act alterating the muscular functionality emphasizing overload, fulcrum, anomalous torques to morphological structures. During clenching phase, performed several times a day during the swallow, the periodontal proprioception monitors how occlusal loadings are arranged.
In case of propriocetively or mechanically anomalous situations, protective nervous systems act on the muscular activation in order to protect biological structures.
Through a standardized procedure, EMG exam is able to quantify the alteration in muscular activity caused by dental proipriocesption. In figure 1, a sEMG test of Masseter and Temporal muscles. Time in abscisse, the electrical activity developed by muscles in ordinate.
The more the functional necessity of the muscle, the more numerous excited muscular fibres, the more the electrical activity developed by muscle.
Only a little part of the whole electrical activity generated in muscle reaches the skin surface.
Some technical and biological factors that spread variably this electricity in surrounding tissues exist.
One of these that influences the registration of electricity by surface electromyography is the positioning of the electrodes.
As in figure 2, the same patient, with different positioning of electrodes in the right antimere, produces different EGM registrations. For this reason, the EMG analysis has not obtained the adequate attention in functional field. When an exam gives different results from an appointment to the other it is not scientifically interesting. However, making differential calculating gives indications about the patient’s functional reaction.
Providing that absolute indications on the muscular activity in repeatable way are not possible using surface electromyograpgy, standardized protocols can be applied in order to measure the reactions to possible stimulus.
In details, making two registrations changing only one factor and measuring the effect on the muscularity can be possible. Suppose to realized a first registration in maximum voluntary clenching but without dental contact. This first registration (reference acquisition) of maximal activity is realized positioning two cotton rolls between the dental arches. Immediately after another acquisition in maximum voluntary clenching may be registered (without changing the electrodes position), altering only one factor. Indeed, removing cotton rolls teeth are in contact; the first and the second acquisition differs only in dental contact.
The software DAQ quantifies easily the difference of each muscle between the first and the second acquisition measuring mathematically which influence the dental contact has had in the activation of the masticatory muscles.
Figura 2 – Spostamento di elettrodi nell’antimero di destra causa registrazioni elettromiografiche differenti.
STARDARDITEZ INDEXES: SHORT SUMMARY
Percentage overlapping coefficient (POC) indicates, in percentage, how much the influence of dental contact is similar in the right muscles compared with the left one. An hypothetical POC of 100% shows that two muscles are influenced by dental contact in the same way. Two muscles could be both inhibited by dental contact at 50% (Impact 50%), obtaining an hypothetical POC of 100%. The 95% of subjects without muscular imbalances caused by dental origin presents POC values comprised between 80 and 90%.
Asymmetry index (Asim) compares the influence of dental contact on total activity of right antimere (right Temporals and Masseters) in respect to the left one. A negative value indicates a larger differential activity by the left antimere; vice versa a positive one. The 95% of subjects without muscular imbalances with dental origin presents Asymmetry values comprised between + 10%.
Activation index (Attiv) compares the influence of dental contact on the Temporals activity compared with Masseters one. A negative value implies a larger differential activity of Temporal muscles; vice versa positive one. The 95% of subjects without muscular imbalances with dental origin presents Activation values comprised between + 10%.
Torsion index (Torque) measures the differential activity of the right Temporal and the left Masseter compared with the opposite couple.
Indeed, in case of the prevalence of the right Temporal and the left Masseter can cause torcent forces on mandible with a right latero-deviation. In this case, the torsion index is positive. A negative one indicating torque forces on left shows a prevalence of the left Temporal and the right Masseter. The 95% of subject without muscular imbalances with dental origin presents Torque values comprised between + 10%.
Impac index represents the electrical activity that each muscle has performed during the test (clenching on teeth in contact or with provisional prosthesis or with occlusal splint…) compared with reference values on cottons, expressed in percentage. A muscle not significantly influenced by periodontal information can express values from 80 to 120% of the electricity expressed on cottons. Impact values of 50-60% indicate a non possibility to express a maximal performance. This index is very important in confirming the validity of the previous others. An excellent muscular homogeneity with normal POC, Asymmetry, Activation and Torque indexes can be consequence of several proprioceptive inhibitions with an inadequate Impact one.
TECHNICAL SUGGESTIONS FOR THE EXECUTION OF A DIFFERENTIAL EMG ANALYSIS
Figura 3
In order to obtain a differential analysis by DAQ software it is necessary doing the following acquisition:
1. Reference acquisition of maximum muscular potential (for 5 seconds), in a maximal voluntary teeth clenching with two 10mm diameter cottons rolls positioning between the second premolar and first mandibular molar as in figure 3.
2. Acquisition of the potential developed during the interested test, for example clenching in maximal intercuspidation with prosthesis, occlusal splint etc. (contraction time: 5 seconds)
3. Analysis through DAQ software; evaluating the influence of dental prioprioception (the only variable between two acquisitions) in the activation of Masseter and Temporal muscles is possible quantifying the differences between two acquisitions.
As follow, the features that two acquisitions have to satisfy in order to be analyzed in a reliable way through differential analysis DAQ software:
1. Make the test exactly in the same conditions, during the same appointment and without modifying the electrodes position, the electromyograph or something else condition, except for cotton rolls removing.
2. Make the test on a patient without any type of inflammatory pathology on teeth, support structures as periodont or alveolar bone and painless symptomatology during the teeth clenching. Painful proprioceptive phenomenon caused by chronic and non perceptible by patient lesions (periapical) can cause alterations in nervous organization of muscular coordination decreasing the effectiveness of indications from differential analysis.
3. Do not note discontinuity in raw signal that could be manifestly related with capture or technical errors (figure 4 and 5).
Figura 4
Figura 5
4. Do not show regular variation of signal that can be improbably verify in biological environment.
5. Do not present very important asymmetries during the acquisition of the same right and left muscle. In case of a marked asymmetries as in figure 7, change the electrode that less capture the electrical signal before making the exam, repositioning it better on muscular bellie and finally repeating the analysis from the start.
6. Do not verify inconstancies in raw signal caused by stimulus loss by the patient (Figure 8).
7. Ask to the patient to clench two or three times in order to obtain a more possible homogeneous performance, as in figure 9.
Figura 6
Figura 7
Figura 8
Figura 9
Technical suggestions:
1. It is advisable to positioning the cotton rolls inside the mouth’s patient but then let the patient itself to adapt them without changing significantly their position. Only his proprioception allows to position the rolls in a comfortable way in order to obtain a maximal contraction.
2. Assure that two cotton rolls have a similar hardness; soft or too much hard cotton rolls can be often find inside the packaging.
3. During the test, verify that the patient do not modify the expression contracting facial muscles; indeed, the activation of expressive muscles can increase the crosstalk effect.
DIFFERENTIAL ELECTROMIOGRAFIC TABLES INTERPRETATION: POSSIBLE PATTERNS AND RELATIVE PHYSIOLOGICAL INTERPRETATIONS
PAY ATTENTION! The following examples are hypothetical simulations, improbably verifiable in a patient! The analysis get elaborated in order to isolate complex situations that have to be observed in real analysis.
The table got from the DAQ software for the differential analysis of muscular activity allows to visualize graphically the muscular activity changes due to occlusion, in addition to provide numerically the above defined indexes. The graphical table have to be divided in two main sections (figure 10): 1. In the left section, the distribution of proprioceptive influence on the four muscles activity is graphically figured through a pie chart. It is shown as a patient photo, so the left antimere to the right and vice versa. In this figure, graphical information about POC Temp, POC Mass, Attiv, Torque and Asim can be obtained.
2. The right section shows the Impact of each muscle as a bar graph. Remember that this index represents the muscular performance obtained during the test (i.e. clenching in maximal intercuspidation on prosthesis, occlusal splint etc.). It describes the quantity of electrical activity developed by muscle during the test in percent of that developed during the reference test (maximal clenching on cotton rolls). IMPACT: Impact index shows the percent of electrical activity developed by a muscle during the test (i.e. teeth clenching or on occlusal splint) compared with the reference obtained on cotton rolls. The physiological value is comprised from 80 to 120%. In the table in figure 12, all the values are in the normal range; the influence of dental contact on right and left muscles (POC) is overlapping untill 85%. Torque effect, asymmetry or antero-posterior imbalances (Attiv) are not noticed.
Figura 10
Figura 11
Figura 13
These conditions are registered in a high muscular performance (Impact 95%).
In the table in figure 13, a general muscular coordination is performed by a low performance situation (Impact 30%) caused by a dental origin inhibition. This condition can be the result of a not enough work length in order to express similar values to maximum potential (i.e. low vertical dimension); single nociceptions (precontact/endodontic lesion/periodontal lesion etc.) can cause several inhibitions of all four muscles. So the inhibition can be “homogeneous” maintaining a good coordination but in lower performances.
ASYMMETRY:
Aymmetry index shows how the right muscles are influenced by dental contact compared with the left ones. An index greater than 0 indicates a right muscles prevalence, a negative one a left muscles one.
In this situation (figure 14), the influence of dental contact on left Temporals and Masseters is the 70% than that the left ones. In this diagram, the asymmetry value is 10%.
Altogether, Temporals are not influenced by Masseters anymore, with a consequent Activation index practically null. The right Temporal and the left Masseter perform a summary activity overlapping to homologous couple right Masseter and left Temporal, so torsion effects are not presented: Torque 1%.
Figura 14
This differential table has been verified in a situation in which the right antimere activation is greater than that developed on cotton rolls (Impact 135%). On the other hand, the left antimere has developed an activity similar than that developed with cottons. (Impact 95%).
Instead, in figure 15 the same organization of muscular activation (POC indexes; Asim, Attiv e Troque) can be occurred in case of general inhibition of total activity. Impact indexes, indeed, shoes how right muscles express their 60% of the maximal developed on cottons; the left ones the 30%. From a physiological point of view, two situations have a really different meaning, even if the equilibrium among four muscles is the same and, consequently, force with similar directions (but different intensity) were transmitted to the hard tissues. In the first situation, indeed, non significant muscular inhibitions has been shown. In the second one, muscles are inhibited, on average the 45% (average 60 and 30) of their maximum and has consequently a lower performance.
Figura 15
TORQUE
In the table in figure 16, the way in which Temporals and Masseters are under non symmetrical influences (POC 70%) but without causing asymmetry situations or antero-posterior imbalances (Asim e Attiv on average) has been noticed. How left Temporal-right Masseter couple has a greater differential than the homologous couple has to be underlined. In this situation, a torsional effect on mandible can be shown (Torque -13%). In this particular case, the effect is a consequence of a particular activation of left Temporal and right Masseter (Impact 140%). In case of figure 17, the muscular coordination can be overlapped with the previous table but it is physiologically really different. Instead, in this table torsional imbalances is verified as a consequence of an inhibition of right Temporal and left Masseter muscles, that express the 45% of their potential. Opposite muscles, indeed, maintain an average performance with an Impact of 95%.
Figura 16
Figura 17
ACTIVATION
The Activation index quantify the differential activity among Temporals and Masseters. A positive value indices a Masseter prevalence, a negative one indicates a Temporal revalence. In case shown in figure 18, how the periodontal influence is not expression of muscular inhibitions that cause asymmetries or torsional effects can be observed. But how Temporal muscles prevail on Masseters can be noted (Attiv -13%).
This value can be obtained by an inhibition on Masseter muscles (Mass Impact 45%, figure 18) or by a differential hyperactivity of Temporal muscles (Temp Impact 135%, figure 19).
Figura 18
Figura 19
BREVE SELEZIONE BIBLIOGRAFICA
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