Bernd G. Lapatki

A surface EMG electrode for the simultaneous observation of multiple facial muscles.

With previous surface electromyography (sEMG) electrodes it has been difficult to combine small outer dimensions and secure skin attachment. We resolved this problem by developing a new skin attachment technique that yields firm electrode fixation without requiring an acrylic housing. Consequently, we could reduce the outer electrode dimensions to 4-mm diameter and only 1.5-mm thickness. In a bipolar montage, this electrode allows an inter-electrode distance of 8 mm. This improves measurement selectivity and, because of the small dimensions, makes possible the non-invasive observation of multiple facial muscles with a minimum of obstruction. Our new technique was tested on a group of 11 professional trumpeters. They were instructed to perform a series of muscle-specific facial poses and to play exercises on their instruments while EMG signals were recorded simultaneously from seven different perioral muscles. Although the skin attachment was subjected to high stress during trumpet playing, more than 98% of electrode placements yielded a secure mechanical and electrical connection. Muscle selectivity of the signals recorded during the facial poses was similar to that obtained in a previous investigation using intra-muscular fine-wire electrodes. Crosstalk in the perioral area was estimated to be lower than 25%. The availability of an unobstructive sEMG electrode for simultaneously observing multiple facial muscles opens up a wide range of applications (e.g. in speech research, psychophysiology and orthodontics).

Motor unit number estimation using high-density surface electromyography.

OBJECTIVE To present a motor unit number estimation (MUNE) technique that resolves alternation by means of high-density surface EMG. METHODS High-density surface EMG, using 120 EMG channels simultaneously, is combined with elements of the increment counting technique (ICT) and the multiple-point stimulation technique. Alternation is a major drawback in the ICT. The spatial and temporal information provided by high-density surface EMG support identification and elimination of the effects of alternation. We determined the MUNE and its reproducibility in 14 healthy subjects, using a grid of 8 x 15 small electrodes on the thenar muscles. RESULTS Mean MUNE was 271+/-103 (retest: 290+/-109), with a coefficient of variation of 22% and an intra-class correlation of 0.88. On average, 22 motor unit potentials (MUPs) were collected per subject. The representativity of this MUP sample was quantitatively assessed using the spatiotemporal information provided by high-density recordings. CONCLUSIONS MUNE values are relatively high, because we were able to detect many small MUPs. Reproducibility was similar to that of other MUNE techniques. SIGNIFICANCE Our technique allows collection of a large MUP sample non-invasively by resolving alternation to a large extent and provides insight into the representativity of this sample. The large sample size is expected to increase MUNE accuracy.

Smart Bracket for Multi-dimensional Force and Moment Measurement

Atraumatic, well-directed, and efficient tooth movement is interrelated with the therapeutic application of adequately dimensioned forces and moments in all three dimensions. The lack of appropriate monitoring tools inspired the development of an orthodontic bracket with an integrated microelectronic chip equipped with multiple piezoresistive stress sensors. Such a ‘smart bracket’ was constructed (scale of 2.5:1) and calibrated. To evaluate how accurately the integrated sensor system allowed for the quantitative determination of three-dimensional force-moment systems externally applied to the bracket, we exerted 396 different force-moment combinations with dimensions within usual therapeutic ranges (± 1.5 N and ± 15 Nmm). Comparison between the externally applied force-moment components and those reconstructed on the basis of the stress sensor signals revealed very good agreement, with standard deviations in the differences of 0.037 N and 0.985 Nmm, respectively. We conclude that our methodological approach is generally suitable for monitoring the relatively low forces and moments exerted on individual teeth with fixed orthodontic appliances.

Botulinum toxin has an increased effect when targeted toward the muscle's endplate zone: a high-density surface EMG guided study.

OBJECTIVES To compare the effect of endplate-targeted injections of a low Botulinum neurotoxin type A (BoNT-A) dose with that of injections at defined distances from the motor endplate zone. METHODS In eight healthy volunteers, the main endplate zones of the right and left extensor digitorum brevis (EDB) muscles were localized using high-density surface EMG. On the study side BoNT-A was injected at fixed distances from the endplate zone. On the control side, BoNT-A was administered into the endplate zone. Compound muscle action potential (CMAP) prior to the injection and 2, 12, and 24 weeks later were recorded. RESULTS On the control side, the mean CMAP reduction 2 weeks after BoNT-A injection was 79.3%. The difference in CMAP reduction between both EDB muscles was significantly related to the injection distance from the endplate zone. Increasing the injection distance by 1cm reduced the effect of BoNT-A by 46%. CONCLUSIONS Guided injection of a reduced BoNT-A dose into the muscles endplate zone(s) is a promising strategy for optimizing the therapeutic effectiveness of BoNT-A and for minimizing side-effects such as unwanted weakness of adjacent muscles. SIGNIFICANCE Precise endplate-targeted injections increase the effect of BoNT-A and may thus prove to reduce required dosage and treatment costs.

Optimal placement of bipolar surface EMG electrodes in the face based on single motor unit analysis

Locations of surface electromyography (sEMG) electrodes in the face are usually chosen on a macro-anatomical basis. In this study we describe optimal placement of bipolar electrodes based on a novel method and present results for lower facial muscles. We performed high-density sEMG recordings in 13 healthy participants. Raw sEMG signals were decomposed into motor unit action potentials (MUAPs). We positioned virtual electrode pairs in the interpolated monopolar MUAPs at different positions along muscle fiber direction and calculated the bipolar potentials. Electrode sites were determined where maximal bipolar amplitude was achieved and were validated. Objective guidelines for sEMG electrode placement improve the signal-to-noise ratio and may contribute to reduce cross talk, which is particularly important in the face. The method may be regarded as an important basis for improving the validity and reproducibility of sEMG in complex muscle areas.

Evidence of Potential Averaging over the Finite Surface of a Bioelectric Surface Electrode

Most bioelectric signals are not only functions of time but also exhibit a variation in spatial distribution. Surface EMG signals are often “summarized” by a large electrode. The effect of such an electrode is interpreted as averaging the potential at the surface of the skin beneath the electrode. We first introduce an electrical equivalent model to delineate this principle of averaging. Next, in a realistic finite element model of EMG generation, two outcome variables are evaluated to assess the validity of the averaging principle. One is the change in voltage distribution in the volume conductor after electrode application. The other is the change in voltage across the high impedance double layer between tissue and electrode. We found that the principle of averaging is valid, once the impedance of the double layer is sufficiently high. The simulations also revealed that skin conductivity plays a role. High-density surface EMG provided experimental evidence consistent with the simulation results. A grid with 120 small electrodes was placed over the thenar muscles of the hand. Electrical nerve stimulation assured a reproducible compound muscle response. The averaged grid response was compared with a single electrode matching the surface of the high-density electrodes. The experimental results showed relatively small errors indicating that averaging of the surface potential by the electrode is a valid principle under most practical conditions.

A retrospective cephalometric study for the quantitative assessment of relapse factors in cover-bite treatment.

Background and Aim:Cover-bite (“Deckbiss”) is regarded as a highly relapse-prone malocclusion. In this context the great significance of a high lip line (LipL) as an etiologic factor for the retroclination of the upper central incisors was recently proven within the framework of lip pressure measurements. It therefore seemed likely that a persisting high LipL after correction of cover-bite might have an equally negative impact on the stability of the treatment outcome.Materials and Methods:This issue was investigated in the present retrospective study by cephalometric analysis of the findings prior to therapy (T1), immediately after active mechanotherapy (T2), and after a mean follow-up period of 2 years (T3). The study group consisted of 40 former cover-bite patients with initial linguoversion of the upper central incisors (axial angle to anterior cranial base < 98°) and anterior deep bite (≥ 4 mm) from the records of the Department of Orthodontics, University of Freiburg i. Br., Germany.Results and Conclusions:The average relapse was ca. 20% of the total correction of the anterior linguoversion and deep bite, with the relapse tendency, however, displaying substantial interindividual variations. Multiple regression analysis revealed an increased relapse tendency in specific cases: patients with maxillary extractions, cases with a pronounced therapeutically induced change of upper central incisor inclination, and patients with a high post-therapeutic LipL or with poor compliance in the retention phase. In view of the relatively good opportunity to influence the level of the LipL therapeutically, one of the most important therapeutic objectives for cover-bite patients should be to reduce the amount by which the lower lip overlaps the upper incisors (to a maximum value of 3 mm). This can be achieved by active mechanical intrusion of the upper incisors. If the orthodontist fails to take account of this aspect when planning or performing the treatment, he has to accept an increased risk of relapse.ZusammenfassungHintergrund und Ziel:Der Deckbiss wird als sehr rezidivfreudige Anomalie angesehen. Im Zusammenhang damit konnte kürzlich im Rahmen von Lippendruckmessungen die große Bedeutung einer hohen Lippenschlusslinie (LipL) als ätiologischer Faktor für die Retroinklination der mittleren oberen Inzisivi nachgewiesen werden. Es lag daher die Vermutung nahe, dass sich eine posttherapeutisch hohe LipL ebenso negativ auf die Behandlungsstabilität nach kieferorthopädischer Korrektur des Deckbisses auswirken könnte.Material und Methoden:Dieser Fragestellung wurde in der vorliegenden retrospektiven Studie mittels kephalometrischer Auswertung der Befunde vor der Therapie (T1), direkt nach der aktivmechanischen Therapie (T2), sowie nach einer mittleren posttherapeutischen Beobachtungszeit von 2 Jahren (T3) nachgegangen. Als Untersuchungsgruppe dienten 40 ehemalige Deckbisspatienten mit initialem Steilstand der mittleren oberen Inzisivi (Achsenwinkel zur vorderen Schädelbasis < 98°) sowie frontalem Tiefbiss (≥ 4 mm) aus dem Archiv der Kieferorthopädischen Abteilung des Universitätsklinikums Freiburg i. Br.Ergebnisse und Schlussfolgerungen:Durchschnittlich rezidivierten jeweils etwa 20% des Gesamtausmaßes der Korrektur des frontalen Steilstandes und Tiefbisses, wobei jedoch die Rezidivtendenz individuell sehr unterschiedlich ausfiel. Mittels multipler Regressionsanalyse konnte nachgewiesen werden, dass die Neigung zum Rezidiv in bestimmten Fällen erhöht war: Hierzu zählten Patienten mit Extraktionen im Oberkiefer (OK), Fälle mit starker therapeutischer Inklinationsveränderung der mittleren oberen Inzisivi sowie Patienten mit hoher posttherapeutischer LipL oder mit schlechter Mitarbeit in der Retentionsphase. Im Hinblick auf die relativ gut mögliche therapeutische Einflussnahme auf die Höhe der LipL sollte es bei Deckbisspatienten als eines der wichtigsten therapeutischen Ziele angesehen werden, die Überlappung der oberen Inzisivi durch die Unterlippe (auf einen maximalen Wert von 3 mm) zu reduzieren. Dies kann durch aktiv-mechanische Intrusion der oberen Inzisivi erreicht werden. Falls der Behandler diesen Aspekt bei der Planung bzw. Durchführung der Therapie außer Acht lässt, muss er sich eines erhöhten Rezidivrisikos bewusst sein.

A Wireless Stress Mapping System for Orthodontic Brackets Using CMOS Integrated Sensors

A wireless stress mapping system for the development of “smart brackets” is presented. The system is designed for monitoring the forces and moments applied to individual teeth during orthodontic therapy which may contribute to improve treatment effectiveness. It comprises a stress mapping chip fabricated in a 0.35-μm process and a micro coil produced by gold electroplating in a photoresist mask. Twenty-four transistor-based stress sensors for measuring either in-plane shear stress or the difference of in-plane normal stresses are strategically distributed over the chip area. The sensor signals are processed by a variable-gain differential difference amplifier and digitized by a 10-bit SAR ADC, enabling a resolution down to 11 kPa at highest gain. A wireless interface conditions the energy received at 13.56 MHz and transmits the data by load modulation. With dimensions of 2 × 2.5 × 0.73 mm3 and a power consumption of 1.75 mW, the system lays the foundation for the assembly of smart brackets as innovative tools in orthodontic therapy.

Dentofacial parameters explaining variability in retroclination of the maxillary central incisors.

Background and Aim:The interrelation between retroclination of the maxillary central incisors and dentofacial parameters is a controversial subject in the literature. In contrast to comparisons between malocclusion and control groups, the objective of the present study was to identify skeletal, dentoalveolar or perioral (soft-tissue) factors which primarily determine how severely retroclination is individually manifested.Materials and Methods:For this purpose we evaluated the pretherapeutic lateral cephalograms of 83 patients with an inclination of the maxillary central incisors ranging from physiological values to very severe retroclination (inclination to anterior cranial base between 104° and 64°). A detailed analysis of the skeletal, dentoalveolar, and soft-tissue morphology was performed using lateral cephalograms taken prior to therapy. The statistical analysis included the calculation of multiple regression models for maxillary central incisor inclination and different parameters describing the lip-to-incisor relationship as dependent variables.Results:A regression model including 1) the lip-line level measured at the dorsal upper-lower lip contact point, 2) the sagittal intermaxillary relationship, and 3) the inclination of the mandibular central incisors explained 81% of the variability in maxillary central incisor inclination (p < 0.0001 for all three parameters). Statistical analysis of the morphologic base of a high dorsal lip-line level (i.e., the predominant characteristic in the retroclination cases) revealed the significance of soft-tissue, dentoalveolar, and skeletal variables (p < 0.001).Conclusions:Complementary to results of previous resting lippressure measurements, this cephalometric study suggests that a high lip-line level is the predominant causative factor for a cover- bite or Class II, Division 2 malocclusion. Therefore, we conclude that (1) lip-line measurements should be included in routine cephalometric diagnostics, and (2) that a high lip-line must be eliminated by therapeutic measures in these malocclusions to prevent a post-orthodontic relapse.ZusammenfassungHintergrund und Ziel:Die Beziehungen zwischen dem Steilstand der mittleren oberen Inzisivi und dentofazialen Parametern werden in der Literatur kontrovers diskutiert. Im Gegensatz zu Vergleichen zwischen Malokklusions- und Kontrollgruppen iden tifizierten wir in dieser Studie diejenigen skelettalen, dentoal veolären und perioralen (Weichteil-)Parameter, welche den indivi duellen Ausprägungsgrad des Steilstandes maßgeblich beein flussen.Material und Methodik:Ausgewertet wurden die prätherapeutischen fernröntgenologischen Befunde von 83 Patienten mit einer Achsenneigung der mittleren oberen Inzisivi im Bereich von physiologischen Werten bis hin zu extrem stark ausgeprägtem Steilstand, d. h. einer Inklination relativ zur vorderen Schädelbasis von 104° – 64°. Die statistische Datenanalyse beinhaltete die Kalkulation von multiplen Regressionsmodellen für die Inklination der mittleren oberen Inzisivi sowie verschiedene, die Lippen-Schneidezahn-Beziehungen charakterisierende Parameter als abhängige Variable.Ergebnisse:Mit einem Regressionsmodell, welches (1) die Höhe der Lippenschlusslinie gemessen am dorsalen Ober-/Unterlippenkontaktpunkt, (2) die sagittalen intermaxillären Beziehungen und (3) die Inklination der mittleren unteren Inzisivi einschloss, konnten 81% der Inklinationsvariabilität der mittleren oberen Inzisivi erklärt werden (p < 0,0001 für alle drei Modellparameter). Die statistische Analyse wies zudem auf eine Bedeutung von Weichteil-, dentoalveolären und skelettalen Parametern für das Zustandekommen einer hohen Lippenschlusslinie, d. h. dem dominantesten Merkmal der Fälle mit invertierten mittleren oberen Inzisivi, hin (p < 0,001).Schlussfolgerungen:Ergänzend zu den Ergebnissen von vorherigen Ruhelippendruckmessungen deutet diese kephalometrische Studie auf die überragende Bedeutung der hohen Lippenschlusslinie als kausaler Faktor für einen Deckbiss bzw. eine Angle-Klasse II/2 hin. Daraus schlussfolgern wir, dass (1) Messungen der Höhe der Lippenschlusslinie routinemäßig in die Auswertung von Fernröntgenseitenbildern (FRS) mit einbezogen werden sollten und (2) dass bei Patienten mit steilstehenden mittleren oberen Inzisivi zur Verhinderung eines Rezidivs nach kieferorthopädischer Therapie die hohe Lippenschlusslinie durch therapeutische Maßnahmen zu beseitigen ist.

An analysis of the measurement principle of smart brackets for 3D force and moment monitoring in orthodontics

Measuring the three-dimensional (3D) force-moment (F/M) systems applied for correcting tooth malposition is highly desirable for accurate spatial control of tooth movement and for reducing traumatic side effects such as irreversible root resorption. To date, suitable tools for monitoring the applied F/M system during therapy are lacking. We have previously introduced a true-scale orthodontic bracket with an integrated microelectronic stress sensor system for 3D F/M measurements on individual teeth with a perspective for clinical application. The underlying theoretical concept assumes a linear correlation between externally applied F/M systems and mechanical stresses induced within the smart bracket. However, in combined applications of F/M components the actual wire-bracket contacts may differ from those caused by separate applications of corresponding individual F/M components, thus violating the principle of linear superposition of mechanical stresses. This study systematically evaluates this aspect using finite element (FE) simulations and measurements with a real smart bracket. The FE analysis indicated that variability in the wire-bracket contacts is a major source for measurement errors. By taking the critical F/M combinations into account in the calibration of the real smart bracket, we were able to reduce the mean measurement error in five of the six F/M components to values <0.12 N and <0.04 N cm. Bucco-lingually directed forces still showed mean errors up to 0.21 N. Improving the force measurement accuracy and integrating components for telemetric energy and data transfer are the next steps towards clinical application of intelligent orthodontic appliances based on smart brackets.