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.

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).

The importance of the level of the lip line and resting lip pressure in Class II, Division 2 malocclusion.

Many clinicians hypothesize that retroclination of the maxillary central incisors in Class II, Division 2 malocclusion is caused by increased resting lip pressure against these teeth. The purpose of this study was (1) to verify this assumption by means of simultaneous lip-pressure measurements at two different levels on the maxillary central incisor crowns, and (2) to examine factors that could possibly contribute to the increased resting lip pressure. This is the first study to prove that individuals with Class II, Division 2 malocclusion (n = 21) have the upper central incisors exposed to significantly higher lip pressure than those with Class I malocclusion (n = 21). Our statistical evaluation revealed that this is primarily attributed to a high lip line and not to a hypertonic peri-oral musculature. We concluded that orthodontic treatment of Class II, Division 2 cases should include intrusion of the maxillary incisors, to eliminate the non-physiologically high pressure exerted by the lower lip on these teeth and, consequently, to reduce the high risk of a post-orthodontic relapse.

Occlusal side effects caused by a mandibular advancement appliance in patients with obstructive sleep apnea.

Mandibular advancement appliances (MAA) have been established as an alternative treatment option for obstructive sleep apnea (OSA). Although the therapeutic effect of these devices has been proven both clinically and polysomnographically through various studies, there are very few follow-up examinations in existence concerning possible dental side effects caused by the MAA. However, if lifelong treatment of OSA is considered, these follow-up examinations are of utmost importance. This article presents 2 cases with unexpected dental side effects and occlusal alterations caused by MAA therapy.

Transcutaneous electrical nerve stimulation (TENS): its short-term and long-term effects on the masticatory muscles.

In an electromyographic study on subjects with no functional disturbances of the masticatory muscles, the duration of the post-therapeutic effects of transcutaneous electrical nerve stimulation (= TENS) on the superficial masseter and anterior temporal muscle was analyzed. The myoelectric signals were registered from 20 healthy volunteers in 3 different mandibular positions. The recordings were performed before a 20-minute TENS application with the J-4 Myomonitor and continued with a sequence of follow-up registrations with increasing interval to the initial stimulation. The EMG signals underwent computer-aided analysis and were evaluated by determining the integrated values as a parameter of muscle activity, and after Fourier transformation by 7 describing parameters of the power spectrum (e.g. mean power frequency = MPF). A detailed analysis of variance of all data was used to investigate significant changes of the parameters during the observation period. Muscular response to TENS includes a decrease in muscular activity (= reduction in integrated EMG signals) and a shift in the power spectrum to higher frequencies (increase in MPF). These changes were statistically highly significant for both analyzed muscles and for all different mandibular exercises. As these reactions to TENS are contrary to muscle fatigue, the results can be interpreted as indicating that this type of therapy stimulates a change in the biochemical and physiological muscular conditions, which leads to muscle relaxation. Electromyographically, the post-therapeutic effect lasted for 2 hours in case of normal masticatory muscle activity but for more than 7 hours in case of low muscular loading. The alterations of the integrated EMG values were more persistent than those of the parameters of the power spectrum.

In vitro investigation into the biological assessment of orthodontic wires.

The alloys used in orthodontics are subject in the moist environment of the oral cavity to various corrosion processes. If the products of the corrosion are introduced into a biological system they may cause changes. In the present investigation the corrosion rate of 23 different orthodontic wires (preformed arch wires and straight wires) made from 5 different alloys were examined in a nutrient medium by ICP-AES analysis, and the influence of the corrosion products on the cytotoxicity of a fibroblast culture was investigated using Mosmann's MTT test. The nickel-titanium wires Nitinol, Sentalloy and Original Chinese Wire and the beta-titanium alloy TMA had no effect on the rate of cell proliferation. Nor did stainless steel wires inhibit growth significantly, with the exception of Australian Wire and Wildcat Wire. The manganese-steel alloys Noninium h and Mezanium caused significant reductions in growth rate, which were attributed to the manganese ions released by the corrosion. The most severe growth inhibition was caused by the Co-Cr-Ni alloy Elgiloy, and this reaction is independent of the 4 levels of resilience. The degree of growth inhibition depended upon the concentration of corrosive cobalt and nickel ions in the eluate. In spite of the differences observed, all the orthodontic wires examined are graded under ISO-standard 10993-5 as "non-cytotoxic". The degree of toxicity was found to be determined essentially by the corrosion rate of the alloy and the cytotoxic characteristics of the resulting trace elements.

Dental age in southwest Germany. A radiographic study.

A cross-sectional study was undertaken in order to assess the dental age of healthy Southwest German boys and girls between the ages of 2 and 20 years by evaluating 1,003 panoramic radiographs. Dental age was assessed according to the method of Demirjian et al. All permanent teeth of the lower left jaw except the third molar were rated, the development of each tooth was divided into 8 defined stages. Statistical evaluation revealed a correlation between the parameters chronological age and score sum of r = 0.85 for girls and r = 0.89 for boys. The values of the score sum in relation to chronological age were distributed as in a logistic function. Two gender-specific equations for calculating dental age were devised and a marked sexual dimorphism was found. With the beginning of root formation, the girls showed accelerated development. The fact that dental age distribution in Southwest Germany is not significantly correlated to that of a French-Canadian collective underlines Demirjian's demand for regional standards of dental development to be calculated using his score system.

Contribution to the biological assessment of orthodontic acrylic materials. Measurement of their residual monomer output and cytotoxicity.

The acrylic materials used in orthodontics for the fabrication of removable appliances are subjected in the oral cavity to processes of change which influence their physical, mechanical and biological properties. It is therefore essential that every newly developed material must be judged in terms of its clinical value. In the present study, 2 orthodontic cold-cure acrylics, Orthocryl and Forestacryl, and 4 orthodontic photocure acrylics, Triad, Wil-O-Dont, Odontolux and Lux-A-Tech, were investigated and compared with 2 prosthetic acrylic materials: the cold-cure acrylic Palapress and the hot-cure acrylic Paladon. The quantity of residual monomers from methyl methacrylate (MAA) or urethane dimethacrylate (UDMA) eluted from the sample in a given time after the processing was estimated by high pressure liquid chromatography (HPLC). The cytotoxic properties of the materials were examined by Mosmann's proliferation-inhibition test with an established culture of fibroblasts (= MTT test). The hot-cure acrylic Paladon produced by far the smallest amount of eluted residual monomer and the least growth inhibition in the MTT test. The prosthetic cold-cure acrylic Palapress achieved significantly better results than the orthodontic cold-cure materials Orthocryl and Forestacryl. The photocure acrylics released less UDMA than did the cold-cure acrylics MMA. In the cell culture test, all the orthodontic materials examined were assessed as "slightly cytotoxic"; the prosthetic acrylics were graded under ISO-standard 10993-5 as "noncytotoxic". After soaking the plastic material in water for 3 days its cytotoxic properties, as exemplified by the cold-cure acrylic Forestacryl and the photocure acrylic Triad, were reduced, and during the following investigation no more inhibition of growth was observed. It was possible to confirm with the tests used that, for Triad, it is necessary to carefully remove the oxygen-inhibition layer of the photocure acrylic in order to improve the biological properties. The influence of the plastic material on fibroblast cultures was assessed, among other methods, by the quantity of residual monomers liberated. These were significantly reduced after soaking the manufactured substance in water for 3 days. Careful laboratory treatment of the photocure acrylics is necessary in order to improve their biological properties.

Potential of information technology in dental education.

The use of information technology (IT) in dentistry is far ranging. In order to produce a working document for the dental educator, this paper focuses on those methods where IT can assist in the education and competence development of dental students and dentists (e.g. e-learning, distance learning, simulations and computer-based assessment). Web pages and other information-gathering devices have become an essential part of our daily life, as they provide extensive information on all aspects of our society. This is mirrored in dental education where there are many different tools available, as listed in this report. IT offers added value to traditional teaching methods and examples are provided. In spite of the continuing debate on the learning effectiveness of e-learning applications, students request such approaches as an adjunct to the traditional delivery of learning materials. Faculty require support to enable them to effectively use the technology to the benefit of their students. This support should be provided by the institution and it is suggested that, where possible, institutions should appoint an e-learning champion with good interpersonal skills to support and encourage faculty change. From a global prospective, all students and faculty should have access to e-learning tools. This report encourages open access to e-learning material, platforms and programs. The quality of such learning materials must have well defined learning objectives and involve peer review to ensure content validity, accuracy, currency, the use of evidence-based data and the use of best practices. To ensure that the developers' intellectual rights are protected, the original content needs to be secure from unauthorized changes. Strategies and recommendations on how to improve the quality of e-learning are outlined. In the area of assessment, traditional examination schemes can be enriched by IT, whilst the Internet can provide many innovative approaches. Future trends in IT will evolve around improved uptake and access facilitated by the technology (hardware and software). The use of Web 2.0 shows considerable promise and this may have implications on a global level. For example, the one-laptop-per-child project is the best example of what Web 2.0 can do: minimal use of hardware to maximize use of the Internet structure. In essence, simple technology can overcome many of the barriers to learning. IT will always remain exciting, as it is always changing and the users, whether dental students, educators or patients are like chameleons adapting to the ever-changing landscape.

Stress, burnout and health in the clinical period of dental education.

The study examined the extent of stress, burnout and health problems experienced by fourth and fifth year dental students from the three universities of Dresden, Freiburg and Bern. The objectives of the study were to: (i) identify frequent sources of stress and to report the prevalence rates of burnout and health problems in dental students, (ii) determine the rate of students suffering from severe burnout symptoms and (iii) identify stress factors related to the burnout symptoms of emotional exhaustion and depersonalization. A total of 161 dental students from Dresden, Freiburg and Bern participated in the study. They completed the Psychosocial Stress Inventory, the Maslach Burnout Inventory and the Health Survey Questionnaire. Frequent sources of stress were limitation of leisure time, examination anxiety and the transition stress that was related to the adaptation to the demands of the clinical phase of dental education. Few differences existed between the students of the fourth and the fifth study year. Study-related stress was lowest in Bern and considerably higher in Dresden. Differences of mean levels of burnout symptoms were found only for the burnout dimension of emotional exhaustion. Students from Dresden and Freiburg were more emotionally exhausted than students from Bern, students from Dresden also reported more health problems than students from Bern or Freiburg. Ten per cent of the dental students suffered from severe emotional exhaustion, 17% complained about a severe lack of accomplishment and 28% reported severe depersonalization symptoms. Forty-four per cent of the variance of emotional exhaustion was explained by study-related factors such as lack of leisure time, examination anxiety and transition stress. The only predictor of depersonalization was a lack of social integration, accounting for 3% of the variance. A lack of social integration may be an indicator of low social competence which may cause difficulties in dealing with patients adequately and therefore result in depersonalization. The results indicate a need to identify the group of students who may have insufficient social skills for dealing adequately with the patients, and to train them accordingly.

Validation of speed of sound for the assessment of cortical bone maturity.

Bone changes its structural and physical properties during maturation. In order to validate ultrasound measurements with regard to their usefulness in assessing cortical bone maturation, speed of sound (SOS) data were compared with mechanical properties (elastic modulus, bending strength, and cortical surface hardness), density and water content. Thirty pig mandibles were selected from three different age groups. Rectangular specimens of the buccal cortical bone of the body of the mandible were prepared. SOS was measured with pulsed ultrasound at a frequency of 2 MHz in all three dimensions, bone mineral density (BMD) by quantitative computed tomography, breaking strength and apparent elastic modulus in a three-point bending test to failure, water content using the lyophilization technique, and micro-indentation hardness using a modified Vickers' technique. While SOS in all three directions, BMD, surface hardness, and bending strength increased significantly (P < 0.001), bone tissue water content decreased significantly (P < 0.001) with age. Changes in the elastic modulus were not significant. Changes in SOS in the antero-posterior and apico-occlusal directions can be partly explained by BMD. In a bucco-lingual direction the increase is inadequately explained by the physical parameters investigated, and has possibly to be attributed to structural differences. Maturation of the mandible implies changes in its architectural organization, in material composition, and in the mechanical properties of cortical bone. In vitro SOS measurements reflect different structural and physical properties that are all age dependent. It thus seems feasible that age-related changes in bone maturation could be monitored by SOS measurements.

[The influence of training on the accuracy of roentgenographic cephalometric tracings (author's transl)]. / Die Auswirkungen des Ubungseffektes auf die Genauigkeit röntgenkephalometrischer Durchzeichnungen in der Kieferorthopädie

The accuracy in landmark identification and in the determination of angular and linear measurements used in cephalometric analysis on lateral head film were statistically evaluated comparing operators with different levels of competence. The observed magnitude of methodological error was depending on - prior experience of the investigator - individual radiographic anatomical knowledge - rigour of landmark definition and - accuracy of the tracing procedure. Considering these sources of error some of the variability in the present investigation might be avoided by systematic instructions. In order to decrease the variation in landmark location the reproducibility of some points must be further improved by redefining them in their verbal assessments. From an educational point of view the correlation between individual radiographic anatomical knowledge and the magnitude of error in cephalometric analysis should be considered with particular emphasis.

[Caries occurrence and periodontal condition in 100 dental students in their clinical semester. A clinical study]. / Kariesbefall und Parodontalverhältnisse bei 100 Zahnmedizinstudenten der klinischen Semester. Eine klinische Studie.

The purpose of this study was to examine the prevalence of caries and periodontal condition of 100 randomly selected clinical dental students (73 males, 27 females) in the age range of 22-37 years (means = 26.1 +/- 3.3 years). The statistical analysis revealed the following results: DMF-T Index (Klein & Palmer 1940) = 12.61 +/- 5.41 Plaque Index (Silness & Löe 1964) = 0.37 +/- 0.23 Gingiva Index (Löe & Silness 1963) = 0.39 +/- 0.20 Periodontal pocket depth = 1.65 +/- 0.27 mm. In relation to the results of other studies, clinical dental students had a decreased DMF-T Index and were in a better state of oral health and restaurations as compared to other groups of the same age. Female students had significantly less carious teeth, plaque and gingival disease than the male students. Increasing age had a highly significant correlation to DMF-T Index. Gingiva Index and pocket depth, whereas Plaque Index was correlated to a lesser degree. Plaque was confirmed as the essential factor of gingival disease.

[On open nasal speech following operative procedures in the oro- and nasopharynx. A combined speech and cephalometric analysis (author's transl)]. / Offenes Näseln nach operative Eingriffen im Oro- und Nasopharynx. Eine kombiniert phoniatrische und röntgenkephalometrische Analyse.

A combined speech and cephalometric analysis was performed on 60 patients with class III malocclusion to evaluate the interaction between the cranio-facial skeleton and the disorder of an open nasal speech. There was an increase of durable open nasal speech after tonsillectomy but not after adenoidectomy. This predisposition to open nasal speech in class III patients appeared to be increased by the formation of the surrounding bony structures. In dependency to the cranio-facial morphology in the vertical dimension, the configuration of the bony nasopharynx and the sagittal jaw relationship were of significant importance. The cephalometric measurements confirmed the results of the speech analysis that the position and function of the soft palate are of essential significance for the development of an open nasal speech.

[Surgical methods for the correction of malocclusion Angle II/1 with postoperative prosthetic rehabilitation]. / Methode zur Operation der Angle Klasse II/1 mit postoperativer prothetischer Versorgung

The operating methods for Angle class II, 1 are described and a method developed in which a front teeth block segment in the maxilla is raised and palatally tilted. At the same time a front and lateral teeth block segment of the lower jaw is pushed forward and lowered. The method improves the profile as well as occlusion and requires only a minimum of prosthetical care.

[Muscle relaxation by transcutaneous electric nerve stimulation (TENS) in bruxism. An electromyographic study]. / Muskelentspannung durch transkutane Elektroneurostimulation (TENS) bei Bruxismus. Eine elektromyographische Studie.

In recent years transcutaneous electrical neuromuscular stimulation (TENS) has become increasingly more common in the treatment of functional diseases of the masticatory muscles and currently the practitioner can choose among a variety of stimulators. In an electromyographic study of 17 adults suffering from nocturnal bruxism and of a control group consisting of 18 adults without any functional disturbances of the masticatory muscles, the effect of this kind of neuromuscular stimulation on the temporal and masseter muscle was examined. The myoelectric signals were registered before and after TENS treatment in 3 different positions of the mandible. Each person was treated 3 times with both the Myo-Monitor (Myo-Tronics, Seattle) and the TNS SM2 MF stimulator (schwa-medico, Giessen). The different effects of continuous low frequency and intermittent high frequency muscular stimulation were studied simultaneously. Muscular activity was determined by computer aided integration of the electromyographically measured raw signals. A fourier analysis of the power spectrum yielded information on the frequency behavior of the studied muscles resulting from the TENS treatment. A statistical analysis of the results led to the following significant conclusions: 1. TENS treatment decreased the values of the registered integrated signals on all test persons, however, the treatment increased the median frequency and the mean power frequency (MPF). Since this effect is contrary to muscle fatigue, these electromyographic results can be interpreted as providing objective proof of a relaxation in the treated muscles. 2. The electromyographic changes after TENS treatment were similar when using either the Myo-Monitor or the TNS SM2 MF stimulator. In addition, the 2 different types of stimulation (high or low frequency) showed the same effects. 3. Compared to the persons in the control group, there was no significant increased muscular activity in patients with nocturnal bruxism. Following TENS treatment both groups showed the same alterations in the electromyograms. The results of the study provide further evidence that TENS treatment is an adequate supportive procedure in the treatment of nocturnal bruxism.

Speed of sound measurements in mandibular and phalangeal bone during growth.

The micromechanical and elastic properties of bone, its structural maturity and, indirectly, mineral density are important factors for the planning and assessment of orthodontic and/or jaw orthopaedic treatment. This clinical study was undertaken to evaluate age-related changes in the anterior mandibular body. The speed of sound (SOS) has demonstrated age dependency in various peripheral bones and has been proposed as an alternative method for investigating bone parameters without the use of radiation. The ultrasound transmission velocity was measured in 184 healthy subjects (93 females, 91 males; mean age 17.6 +/- 13.7 years). According to the statistical analysis, the data did not reveal any gender-related differences, but were significantly age-dependent. Different kinetics were established between the maturity of the phalanx and the anterior mandible. Further clinical investigations of age-dependent structural changes in bone maturation parameters may provide information that should be taken into account for early functional jaw orthopaedic treatment.

[The effect of prognathism surgery on the temporomandibular joint. (A clinical and radiological evaluation of temporomandibular joint changes after various methods of surgery for prognathism)]. / Der Einfluss der Progenieoperation auf das Kiefergelenk (Eine klinische und röntgenologische Bewertung der Kiefergelenk-veränderungen bei verschiedenen Progenieoperationsmethoden).

On the basis of clinical and roentgenologic examinations of progenia patients which were planned according to our occlusal concept and monitored postoperatively, we established that the condylar displacement in the roentgenogram offers an exact parameter for the extent of operative displacement of the condyles. Nevertheless, a direct conclusion concerning the clinical symptoms or freedom of complaints cannot be established on the basis of this roentgenographic analysis. The roentgenogram also showed considerable condylar alterations in patients with temporomandibular joint symptoms; greater displacement of the condyles was frequently demonstrable with temporomandibular joint complaints.

[Long term compliance with an oral protrusive appliance in patients with obstructive sleep apnoea]. / Obstruktive Schlafatmungsstörungen: Therapiecompliance mit einem intraoralen Protrusionsgerät.

BACKGROUND AND OBJECTIVE: Oral protrusive devices (OPD) are increasingly used in primary snoring and mild-to-moderate obstructive sleep disordered breathing. Due to evidence of reduced compliance with the well established standard treatment of nasal positive airway pressure (CPAP) and reports of patient preference for OPD treatment, particularly in mild cases, OPD may be considered another treatment alternative. PATIENTS AND METHODS: We contacted 192 patients suffering from obstructive sleep breathing disorder, who were treated between May 1996 and September 2001 with an OPD. The patients" use of the device was evaluated, as were any reasons for ceasing to use the device. RESULTS: 105 patients (54.4%) regularly used the appliance after a mean time of 22.7 12.3 month. 21 patients (10.9%) showed no primary compliance and stopped had using the device before the first somnographic follow-up after a mean time of 3.8 months. In this investigation 76 patients (80,2%) were classified as responders and 19 patients (20.8%) as primary non-responders. 22 responders (11.4%) demonstrated no secondary compliance after a mean of 21.9 8.8 months and the discontinued OPD treatment themselves. In 21 patients (10.9%) the nightly respiratory parameters decreased after a mean of 23.0 11.7 months; hence, those patients required CPAP. The cumulative risk using the device after four years as prescribed was 32.2%. We found a correlation between patient compliance, body-mass index and the amount of teeth in the upper and lower jaws. CONCLUSION: OPD compliance seems to be lower than frequently expected. Regular follow-up investigations are necessary to ensure adequate treatment. Poor dental status and an excess body-mass index reduce patient compliance.