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.

Dental side effects of mandibular advancement appliances - a 2-year follow-up.

BACKGROUND AND OBJECTIVES: Mandibular advancement appliances are employed in treating snoring and various forms of obstructive sleep apnea syndrome (OSAS). The splints facilitate the displacement of the mandible anteriorly and widens the pharyngeal lumen during sleep. Two-splint systems are anchored on the dental arches in the maxilla and mandible. The resulting reciprocal forces are transferred onto the teeth, leading to dental side effects when used long-term. We retrospectively examined the dental changes that occurred after patients had worn the Thornton Adjustable Positioner (TAP) for over two years. PATIENTS AND METHODS: We enrolled all patients consecutively in whom the diagnosis of OSAS was made following polysomnography in a sleep laboratory between January 2004 and December 2005 and who had been treated primarily with a TAP. We compared the patients' baseline findings with follow-up findings after more than 24 months of continuous appliance wear. RESULTS: 24/47 of the patients were still wearing the splints regularly after an average of 33 +/- 9.1 months. Overbite was highly significantly reduced (p = 0.006). We noted a reduction in the frontal overbite of more than 1 mm in ten patients (47.6%), and the overbite of one patient decreased by 4 mm. The maxillary front teeth showed significant palatal tipping and those in the mandible significant labial tipping. CONCLUSIONS: Clinically small but statistically significant dental side effects predominantly affecting the incisors' inclination occur after long-term wear of a TAP appliance. The clinical relevance of these dental changes to the patient can only be judged individually within the scope of an entire assessment.

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 degrees and 64 degrees ). 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.

Lip-to-incisor relationship and postorthodontic long-term stability of cover-bite treatment.

OBJECTIVE: To investigate the impact of a persisting high lip line and other potential relapse-inducing factors on long-term stability of orthodontic correction of retroinclined maxillary central incisors. MATERIALS AND METHODS: Thirty-one cover-bite ("Deckbiss") patients with retroinclined maxillary central incisors and a deep frontal overbite were evaluated. The maxillary central incisor inclination was determined odontometrically with study models made pretreatment, posttreatment, and at a follow-up examination (mean posttherapeutic interval: 9.0 years). The lip-to-incisor relationship, the interincisal angle, and the anteroposterior maxillary central incisor position were measured on lateral cephalograms taken after active treatment. RESULTS: The relapse tendency of the orthodontic correction of the retroinclined maxillary central incisors displayed great interindividual variability with a range of posttherapeutic inclination change of -6.75 degrees to +8.00 degrees. Multiple regression analysis revealed an increased tendency for relapse in patients with (1) a high posttherapeutic (dorsal) lip line level combined with the maxillary central incisor and lower lip contact only in the incisal crown area (P < .01) and (2) a marked therapeutically induced inclination change of the maxillary central incisors (P < .05). Interrelations between the relapse of the corrected maxillary central incisors and other evaluated parameters were not statistically significant. CONCLUSIONS: For maximum treatment stability, the elimination of an excessive overlap of the upper incisors by the lower lip should be regarded as one of the most important therapeutic objectives when treating this malocclusion.

Topographical characteristics of motor units of the lower facial musculature revealed by means of high-density surface EMG.

The objective of this study was to systematically characterize motor units (MUs) of the musculature of the lower face. MU endplate positions and principal muscle fiber orientations relative to facial landmarks were identified. This was done by the analysis of motor unit action potentials (MUAPs) in the surface electromyogram. Thirteen specially trained, healthy subjects performed selective contractions of the depressor anguli oris, depressor labii inferioris, mentalis, and orbicularis oris inferior muscles. Signals were recorded using recently developed, 0.3-mm thin and flexible high-density surface electromyography (sEMG) grids (120 channels). For each subject and each muscle and for different low contraction levels, representative MUAPs ("MU fingerprints") were extracted from the raw sEMG data according to their spatiotemporal amplitude characteristics. We then topographically characterized the lower facial MUs' endplate zones and main muscle fiber orientations on the individual faces of the subjects. These topographical MU parameters were spatially warped to correct for the different sizes and shapes of the faces of individual subjects. This electrophysiological study revealed a distribution of the lower facial MU endplates in more or less restricted, distinct clusters on the muscle often with eccentric locations. The results add substantially to the basic neurophysiologic and anatomical knowledge of the complex facial muscle system. They can also be used to establish objective guidelines for placement of conventional (surface or needle) EMG electrodes as well as for clinical investigations on neuromuscular diseases affecting the facial musculature. The localized endplate positions may also indicate optimal locations for botulinum toxin injection in the face.

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 degrees ) and anterior deep bite (> or = 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.

Case control study in the treatment of obstructive sleep-disordered breathing with an intraoral protrusive appliance.

BACKGROUND: Mandibular protrusive appliances have long been used to treat obstructive sleep apnea/hypopnea syndrome (OSAHS). Their efficacy regarding respiration during sleep varies greatly and remains difficult to predict. In this study the efficacy of a two-splint appliance on nocturnal breathing disorders, sleep profile, and daytime sleepiness were evaluated according to a specially-designed treatment process. PATIENTS AND METHODS: In this study 42 consecutive OSAHS patients who had been fitted with a mandibular protrusive appliance according to a preset treatment regimen were included in a follow-up analysis. The diagnosis and the degree of severity of OSHAS were determined by polysomnography in the sleep laboratory. The treatment regimen was established with the sleep laboratory physician. Treatment regimen included the diagnostic procedure in the sleep laboratory, each patient's dental requirements, the fabrication of the appliance used, and the titration of the mandibular protrusion. After having grown accustomed to the appliance for 24.5 +/- 7.8 days, 34 patients underwent overnight polysomnography. RESULTS: The mean apnea/hypopnea index decreased significantly from 19.6 +/- 12.8 to 3.3 +/- 7.8 events per hour to 83%; the apnea index also improved significantly, as did minimal oxygen saturation and the desaturation index. Changes in sleep profile did not reach statistical significance; the arousal index (p < 0.02) and the subjectively-assessed daytime sleepiness (p < 0.02) decreased significantly. A therapeutically-required AHI of below 5 events per hour was achieved in 88.2% of the patients. CONCLUSION: A significant improvement in the respiratory situation of the vast majority of OSAHS patients, particularly in their AHI, can be achieved when one applies the procedural steps and employs the mandibular protrusive appliance we describe herein.

Dental anomalies as a microsymptom of palatal canine displacement.

AIM: A retrospective study was performed to investigate whether palatal canine displacement is associated with other dental features permitting early clinical diagnosis of the eruption disturbance. PATIENTS AND METHODS: The study was based on the complete records of 235/8556 patients at the Department of Orthodontics, School of Dental Medicine, University of Freiburg i.Br. (mean age = 14.11 years) with at least one palatally displaced permanent canine. These patients were examined for ten different morphologic parameters, e.g. impaction and congenital absence of further teeth, hypoplastic, peg-shaped, rotated and congenitally missing upper lateral incisors, supernumerary teeth, Angle classification, and cover-bite (= "Deckbiss"). The data were compared with those of a control sample of the same size with physiologic upper canine eruption (mean-age = 10.0 years). Furthermore, in a right/left comparison the local influence of anomalies of the upper lateral incisors on palatal canine displacement was evaluated by multiple linear regression analysis. RESULTS: The statistical analyses revealed that the risk of palatal canine displacement was significantly higher in patients with hypoplasia, peg shape or congenital aplasia of upper lateral incisors, further impacted and congenitally missing teeth and cover-bite. The intergroup differences in terms of gender, rotation of upper lateral incisors and Angle classification were not statistically significant. The right/left comparison revealed a significantly higher risk of palatal canine displacement in association with an adjacent hypoplastic or peg-shaped lateral incisor and with aplasia of the contralateral upper incisor. CONCLUSION: The clinical significance of the study is that the occurrence of palatally displaced canines is often closely linked with other dental anomalies. In this context, anomalies of upper lateral incisors, aplasia or impaction of further teeth, and the anomaly of cover-bite may serve as indicators of palatal canine displacement. A retarded development of the upper lateral incisor seems to be more disturbing for physiologic canine eruption than aplasia. In patients exhibiting the stated microsymptoms, close clinical follow-up of the maxillary permanent canine eruption during the late exfoliation period is strongly recommended.

Clinical comparison of a multistranded wire and a direct-bonded polyethylene ribbon-reinforced resin composite used for lingual retention.

OBJECTIVE: The reliability of posttreatment canine-to-canine retention with resin composite retainers reinforced with plasma-treated woven polyethylene ribbons was compared to the reliability of directly bonded, multistranded wire retainers. METHOD AND MATERIALS: This prospective study was based on an assessment of 20 consecutive patients (eight women and 12 men with a mean age of 22.4 years) who required a fixed canine-to-canine retainer after undergoing orthodontic treatment. The type of retainer used was randomized for each patient. A follow-up examination was carried out once every 3 months. The length of time the retainers stayed in place without resin fracture or loosening from the teeth at one or more points was evaluated. The study's endpoint was 24 months after the retainer had been bonded. RESULTS: The ribbon-reinforced retainer remained in place for an average of 11.5 months, and the multistranded wire for a mean of 23.6 months. The difference was statistically significant. CONCLUSION: In terms of reliability for permanently fixed orthodontic retention from canine to canine, the direct-bonded multistranded wire is superior to the plasma-treated polyethylene woven ribbon and resin retainer.

Occlusal and skeletal effects of an oral appliance in the treatment of obstructive sleep apnea.

STUDY OBJECTIVE: s: Oral appliances (OAs) are considered to be a treatment option for patients with obstructive sleep apnea/hypopnea syndrome (OSAHS). Although the effectiveness of these appliances has been evaluated in a number of clinical trials, there are few follow-up studies concerning the dental and skeletal side effects that, theoretically, could be caused by OAs. We sought to examine the long-term skeletal and occlusal effects of a nocturnally worn activator in adult patients treated for OSAHS. DESIGN: We analyzed the dental casts and lateral radiographs of 34 patients (mean age, 52.9 years; SD, 9.6 years; range, 27.1 to 64.6 years) before initiating treatment and after at least 24 months of treatment (mean length of treatment, 29.6 months; range, 24.1 to 43.5 months; SD, 5.1 months). The OA was worn by each patient 6 to 8 h nightly for > 5 days per week. SETTING: Department of Orthodontics, Dental Medical School, Freiburg, Germany. MEASUREMENTS AND RESULTS: Follow-up polysomnography studies confirmed improved breathing parameters with the use of OAs. A statistically significant alteration in the occlusion was found. The anteroposterior position of the molars and the inclination of the upper and lower incisors were changed. No skeletal changes in the position of the mandible were noted. CONCLUSIONS: The data suggest that in addition to control polysomnographic examinations, regular dental follow-up visits are mandatory when lifelong OSAHS treatment with an OA is being considered for patients with obstructive sleep apnea/hypopnea.

Cephalometric analysis in patients with obstructive sleep apnea. Part II: Prognostic value in treatment with a mandibular advancement device.

BACKGROUND: The mandibular advancement device (MAD) is accepted as an additional treatment option for snoring and mild obstructive sleep disorders. Its therapeutic efficacy can only be verified through nocturnal polysomnography with the appliance in situ. The relevance of the craniofacial skeletal and soft-tissue structures as an etiological cofactor is controversial. While the lateral cephalogram of the facial skeleton is of no direct diagnostic relevance, it remains unclear to what extent cephalometric assessment can provide prognostic information to better ensure treatment success with an MAD. METHODS AND RESULTS: This study is based on the evaluation of 57 patients diagnosed polysomnographically with obstructive sleep apnea (OSA). The patients were treated primarily with a modified activator; after 6-12 weeks, control polysomnography was carried out in the sleep laboratory. The cephalometric variables were analyzed using a multivariate regression procedure with the response variable of treatment outcome. In addition to a horizontal craniofacial morphology, the downward and forward posture of the hyoid is a prognostic variable for effective therapy with an MAD.

Corrosion susceptibility of lingual wire extensions in removable appliances. An in vitro study.

MATERIAL AND METHODS: The corrosion resistance of ten different round orthodontic wires as plastic-encased extensions was evaluated in vitro. Following the production of defined test samples with free as well as with acrylic-embedded wire segments, ten samples of each product were subjected to gap provocation by deflecting the free-running wire ends with an electric drive, while 10 samples remained provocation-free. The tests were run under standardized conditions (7 days, 37 degrees C, pH 2.3, 0.1 mol NaCl/CH3CHOHCOOH), and the findings were analyzed by stereo light microscopy and scanning electron microscopy. RESULTS: The following alterations were observed on the wire surfaces: a) crevice corrosion with substantial linear surface erosion and opaque discolorations, b) localized pitting corrosion, and c) mild surface erosion with translucent discolorations. The reactions of the test samples were similar in both those that were subjected to addition mechanical loading in the electrolyte and those that were not. Cr-Ni steels were susceptible to corrosion, whereas Co-Cr alloys as well as low-nickel manganese steels had only slight visible alterations, if any, in the embedded wire sections. CONCLUSIONS: Clinically occurring discolorations in the acrylic can be attributed to corrosion processes on the embedded wire extensions. These processes can be simulated and observed in vitro. During the processing of acrylic materials now customary in the orthodontic laboratory, crevices are inevitably formed between the wire and the acrylic, furthering the corrosion process. Our results suggest that, being more resistant to crevice corrosion, Co-Cr alloys or low-nickel steels can be considered as alternatives.

A comparative study of two mandibular advancement appliances for the treatment of obstructive sleep apnoea.

Mandibular advancement appliances (MAAs) are accepted as a treatment option for snoring and mild obstructive sleep disorders. In the present clinical study two differently designed devices were examined for their effectiveness in treating obstructive sleep apnoea (OSA). The study was based on an assessment of 26 patients with a polysomnographic diagnosis of mild OSA [22 men, four women; mean body mass index 27.3 kg/m2 (SD 3.1); mean age 56.8 years (SD 5.2); mean respiratory disturbance index (RDI): 16.0 events/hour (SD 4.4)]. After insertion of the first MAA and a 6-8-week habituation period, a cardio-respiratory home-sleep study was carried out. Following a 2-3-week period with no treatment, the second appliance was inserted. The sequence of the devices was randomized. Once the patients had become accustomed to the second appliance, another somnographic registration was carried out. Daytime sleepiness, snoring, and sleep quality were assessed subjectively on a visual analogue scale. The results showed that a statistically significant improvement in the respiratory parameters was achieved with both appliances (P < 0.01). However, the activator [RDI: 5.5 events/hour, SD 3.3; apnoea index (AI): 3.4 events/hour, SD 2.1] was significantly more effective (P < 0.01) than the Silencor (RDI, 7.3 events/hour, SD 5.3; AI: 5.8 events/hour, SD 3.2). No difference was recorded in the subjective assessment of the therapeutic effects. Both appliances reduced daytime sleepiness and snoring and improved sleep quality, and both influenced the treatment outcome.

Treatment of obstructive sleep apnea with the Karwetzky oral appliance.

The aims of this retrospective study were to assess the effect of a Karwetzky mandibular protrusion appliance for treating patients with mild, moderate, and severe obstructive sleep apnea. Eighty-one of 116 patients (69.8%) suffering from obstructive sleep apnea were treated with an activator model according to Karwetzky. After 4 months (SD 4.0 months) treatment outcome was controlled by polysomnography. Therapeutic outcome depended on the severity of obstructive sleep apnea. The median apnea-hypopnea index decreased from 10.6 events/h (range 2.0-14.9) to 5.8 events/h (range 0.2-17.3, P<0.01) in the mild group, from 21.7 events/h (range 17.3-28.4) to 7.7 events/h (range 1.0-30.1, P<0.001) in the moderate group, and from 42.1 events/h (range 33.2-64.9) to 18.1 events/h (range 2.4-48.8, P<0.001) in the severe group. Sleep variables did not show consistent improvement except for a trend towards more REM sleep and slow-wave sleep. The numbers of retentive teeth did not statistically influence treatment efficacy. Comparing the pre- and post-treatment polysomnographic variables, it was found that the respiratory events rather than sleep stages were significantly reduced by the Karwetzky appliance investigated.

Therapeutic efficacy of an oral appliance in the treatment of obstructive sleep apnea: a 2-year follow-up.

The purpose of this study was to investigate the long-term efficacy of an oral appliance, the Karwetzky activator, on respiratory and sleep parameters in patients with obstructive sleep apnea (OSA). Those selected for this study were 26 patients polysomnographically diagnosed with mild-to-moderate OSA. They were initially treated successfully with this appliance, as documented by a second polysomnographic study after 6 to 12 weeks. Further polysomnographic registrations 6 to 12 months and 18 to 24 months later were performed for each patient wearing the appliance. For 21 patients (81%), therapeutic efficacy was maintained; 5 patients (19%) showed a deterioration in respiratory parameters. We corrected this by adjusting the device in 2 patients. The mean apnea-hypopnea index decreased significantly from 17.8 events per hour at the baseline registration to 4.2 events per hour (P <.001) after 6 to 12 weeks of treatment. After 6 to 12 months, the apnea-hypopnea index was 8.2 events per hour. The index remained at this level 18 to 24 months later, with 8.3 events per hour. Mean oxygen saturation was not improved with the activator, but the number of desaturations had decreased at the 6-to-12 week review. Again, the improvement declined with time, but the number of oxygen desaturations was still significantly decreased at 18 to 24 months (P <.01). Although the respiratory parameters remained statistically improved throughout the study (P <.01), sleep architecture did not change statistically. In most patients, therapeutic efficacy was maintained at the 2-year follow-up, although there was a tendency for effectiveness to fall over time. We concluded that the Karwetzky activator may be an effective treatment alternative for patients with mild-to-moderate OSA, but therapy requires diligent and regular polysomnographic follow-ups. Further long-term studies are needed to assess the continued efficacy of this oral appliance in treating OSA.

Cephalometric analysis in patients with obstructive sleep apnea. Part I: diagnostic value.

BACKGROUND: Morphological soft-tissue and skeletal anomalies of the upper extrathoracic airways are considered to be an etiological cofactor of nocturnal obstructive respiratory disorders. PATIENTS AND METHOD: In this study 106 patients with a mean age of 56.1 +/- 8.4 years and a polysomnographic diagnosis of obstructive sleep apnea (OSA) were evaluated roentgenocephalometrically for soft-tissue and skeletal anomalies. Using cluster analysis and multivariate regression analysis, 18 skeletal variables, six pharyngeal variables and five hyoid variables were evaluated as predictor variables under the criterion variable "severity of the disorder". The body mass index (BMI), as a recognized risk factor of OSA, was taken separately into account. RESULTS: No direct correlation was found between the skeletal cephalometric findings and severity of OSA. Only the position of the hyoid as an expression of a probably adaptive alteration to a changed head posture and tongue position was found to be a significant parameter correlating with the severity of OSA. CONCLUSION: Whether cephalometric radiography is of direct diagnostic relevance in the diagnosis of OSA seems questionable in the light of the results of the present study.