Rainer R. Miethke

Effect of variation in tooth morphology and bracket position on first and third order correction with preadjusted appliances

Major effort is put into the design of brackets to accomplish an optimal completion of orthodontic treatment with respect to 1st, 2nd, and 3rd order corrections. Because such brackets are standardized, the intraindividual variation of the teeth is not taken into consideration. The influence of vertical bracket displacement on 1st and 3rd order corrections was studied on the plaster models, including all teeth from central incisors to first molars, of 28 young persons. The facial contours were evaluated at the mesial, central, and the distal aspect of the bracket. The contours were calculated with the formula of a parabola, and the fit was found sufficient. Intertooth variation was extreme, the biggest curvature was found among the first mandibular molars. The variation was also marked between corresponding teeth. It can be concluded that the intraindividual variation in tooth morphology is larger than the variation between the different types of preadjusted appliances. Thus, if the straight wire approach should be followed, the bracket would have to be custom made. All the calculations were made with the precondition that full size wires were used. If this is not the case, the discussion concerning individual prescription is only of limited importance.

The cushion scanning technique : A method of dynamic tongue sonography and its comparison with the transducer-skin coupling scanning technique during swallowing

RATIONALE AND OBJECTIVES We describe the cushion scanning technique (CST), which solves common difficulties encountered during ultrasound investigations of swallowing. These problems arise when the transducer is held in direct contact with the submental area. Some of these problems include movements of the ultrasound transducer during swallowing and compression of the submental region, which causes abnormal swallowing patterns. METHODS To compare ultrasound images produced with the conventional hand-held transducer-skin coupling scanning technique with the CST, we studied five participants with no clinical signs of tongue dysfunction. All tongue movements were recorded by real-time B+M-mode sonography. RESULTS Images produced with the hand-held transducer were found to be unstable because the transducer moved during swallowing, thereby changing the scanning section. By contrast, the transducer and the participants head remained in a constant position throughout the CST trial. There was no obvious compression of the submental muscles. CONCLUSION The CST allows for a better intraindividual reproducibility of the swallowing pattern and for a more standardized and objective ultrasound examination than the hand-held transducer-skin coupling scanning technique.

In-vitro-Untersuchung zur Verbesserung der Haftfestigkeit von Stahlbändern beim Verwenden von Glasionomerzement

ZusammenfassungIn einer In-vitro-Studie wurde zunächst in Vorversuchen nach Überprüfung der Dosiergenauigkeit, der Homogenität der Mischung und der Wärmefreisetzung des Zementgemisches die Schwachstelle im Verbund Zahnschmelz/Glasionomerzement/Stahlband festgestellt. Diese liegt im Grenzbereich zwischen Zement und Bandmaterial. Anschließend wurde nach verschiedenen Metalloberflächenbehandlungen des Bandmaterials geprüft, ob sich die Scher- und Zugfestigkeit im Grenzbereich Stahl/Zement steigern läßt. In der verwendeten Versuchsanordnung wurden orthodontische Bänder durch massive Zylinder und/oder Stahlplatten aus dem entsprechenden Material ersetzt. Die größte Haftfestigkeit wurde bei Metalloberflächen gemessen, die mit Grobstrahlmittel aufgerauht wurden. Bei Versuchen mit unterschiedlichen Pulver-Flüssigkeits-Verhältnissen an grobgestrahlten Metallflächen erwies sich eine geringe Erhöhung des Puleeranteils als eher festigkeitssteigernd. Durch geringe Abweichungen des Pulver-Flüssigkeits-Verhältnisses von der Herstellerempfehlung nach unten wird die Festigkeit dagegen signifikant reduziert. Die vom Hersteller gelieferten Dosierhilfen erlauben allerdings eine erhebliche Variation des Pulver-Flüssigkeits-Verhältnisses. Um das Ablösen kieferorthopädischer Bänder zu verringern, sollten die Bänder von innen mit grobem Strahlmittel vorbehandelt werden. Ferner wird der untersuchte Glasionomerzement am besten in Kapseln vordosiert und bei Kühlschranktemperatur gemischt.SummaryAn in-vitro investigation was carried out with the aim of improving bond strength at the glass-ionomer cement/stainless steel interface, thus reducing loosening rates. In bovine incisors it had previously been shown that the week point is the glass-ionomer cement/stainless steel, rather than the anamel/glass-ionomer cement interface. In a simple, standardized experimental set-up permitting reproducible measurements, the semi-flexible and irregularly shaped orthodontic bands were replaced by solid stainless steel cylinders made of the same alloy, and both shear and tensile bond strength were measured. Using this set-up, five different types of surface preparation were compared in terms of their bond strength. The highest bond strength was found to be associated with a steel surface sandblasted with coarse aluminium oxide. In further experiments, the devices provided by the manufacturer for dosing powder and liquid were found to be quite inaccurate. This is particularly unfortunate, since the bonding properties of the glass-ionomer cement investigated proved to vary significantly with small variations in the powder∶liquid ratio. To reduce the rate of loosening of orthodontic bands, the cement should be mixed at refrigerator temperature, using capsules filled by the manufacturer with the optimal dosages, and then used with bands previously sandblasted with coarse aluminium oxide powder.An in-vitro investigation was carried out with the aim of improving bond strength at the glass-ionomer cement/stainless steel interface, thus reducing loosening rates. In bovine incisors it had previously been shown that the week point is the glass-ionomer cement/stainless steel, rather than the enamel/glass-ionomer cement interface. In a simple, standardized experimental set-up permitting reproducible measurements, the semi-flexible and irregularly shaped orthodontic bands were replaced by solid stainless steel cylinders made of the same alloy, and both shear and tensile bond strength were measured. Using this set-up, five different types of surface preparation were compared in terms of their bond strength. The highest bond strength was found to be associated with a steel surface sandblasted with coarse aluminium oxide. In further experiments, the devices provided by the manufacturer for dosing powder and liquid were found to be quite inaccurate. This is particularly unfortunate, since the bonding properties of the glass-ionomer cement investigated proved to vary significantly with small variations in the powder:liquid ratio. To reduce the rate of loosening of orthodontic bands, the cement should be mixed at refrigerator temperature, using capsules filled by the manufacturer with the optimal dosages, and then used with bands previously sandblasted with coarse aluminium oxide powder.

[The integration of a computer learning program for x-ray cephalometric analysis into student training].

A computer program was written for teaching undergraduate students definitions and localizations of reference points on cephalometric X-rays. The efficacy of the program as a teaching method was tested by comparing two junior/sophomore groups. While one group attended a conventional lecture for an hour, the other worked with the computer program for the same length of time. Prior to and immediately after instruction by the two methods each group marked reference points on various cephalometric tracings, which were then compared for accuracy. The result was that the students who worked with the computer marked significantly more reference points correctly than their counterparts who attended the lecture. 80% of the students belonging to the group which used the computer judged the program to be a positive educational experience. Such computer training proved to be an efficient tool for teaching students simple facts which require memorization and, equally important, the use of such educational aids. At the same time frees the instructors to dedicate more of their time to teaching more complicated and complex subject matters. A further benefit of the training program described in this article is that it can also be used to train chairside orthodontic assistants in private orthodontic practices.ZusammenfassungEin Computerprogramm, mit dem die Lage und die Namen von Bezugspunkten und strecken auf Fernröntgenseitenbildem eriernt werden können, wird hinsichtlich seines Erfolges bei Zahnmedizinstudenten der klinischen Semester geprüft und mit dem Wissenszuwachs verglichen, den eine andere Studentengruppe nach einer intensiven Vorlesung zum gleichen Thema erzielte. Die Studenten der erstgenannten Gruppe konnten nach einer Übungszeit von 60 Minuten am Computer signifikant mehr Punkte richtig makieten als die der archen nach det beschriebenen Vorlesung. Zu 80% (Medianwert) würden die Studenten, die mit dem Computerlernprogrammen et hatten, gern mit anderen Computerlernprogrammen arbeiten. Das Vermitteln von Fakontgenseiterbilden eines. Computeriernprogramms ermöglicht es, daß Lehrende Zeit gewinnen, sich auf Computerlernprogramme zu konzentrieren. Solche Lernprogramme sind auch dazu geeignet, Helferinnen in einerSummaryA computer program was written for teaching undergraduate students definitions and localizations of reference points on cephalometric X-rays. The efficacy of the program as a teaching method was tested by comparing two junior/sophmore groups. While one group attended a conventional lecture for an hour, the other worked with the computer program for the same length of time. Prior to and immediately after instruction by the two methods each group marked reference points on various cephalometric tracings, which were then compared for accuacy. The result was that the students who worked with the computer marked significantly more reference points correctly than their counterparts who attended the lecture. 80% of the students belonging to the group which used the computer judged the program to be a positive educational experience. Such computer training proved to be an efficient tool for teaching students simple facts which require memorization and, equally important, the are of such educational aids. At the same time frees the instructors to dedicate more of their time to teaching more complicated and complex subject matters. A further benefit of the training program described in this article is that it can also be used to train chairside orthodontic assistants in private orthodontic practices.