Dietmar Kubein-Meesenburg

Masticatory musculature under altered occlusal relationships--a model study with experimental animals.

In a study with experimental animals, the occlusal relationships of male Wistar rats were altered by the bilateral extraction of lateral teeth; the bolus function was eliminated by feeding a soft diet. Both steps led to relief of strain on the temporomandibular joint and thus also in the muscular system itself. The masticatory muscles adapted to the new experimental conditions. We observed a reduction in muscle dry weight and a shift in muscle fiber composition in favour of the IIb fibers, which indicates that less masticatory strength was required. Adaptation thus occurred equally on the macroscopic and microscopic levels.

Influence of thermoplastic appliance thickness on the magnitude of force delivered to a maxillary central incisor during tipping.

INTRODUCTION The aim of the study was to quantify the forces delivered by thermoplastic appliances made of 2 materials with 2 thicknesses to a maxillary central incisor during tipping. METHODS Two materials were tested, each in 2 thicknesses: Erkodur (Erkodent Erich Kopp GmbH, Pfalzgrafenweiler, Germany) 1.0 and 0.8 mm, and Biolon (Dreve Dentamid GmbH, Unna, Germany), 1.0 and 0.75 mm. For each material, 5 appliances were produced. To measure the forces applied, an isolated measuring tooth, part of a standardized resin model, was deflected in 0.05 degrees steps from 0 degrees to 0.42 degrees in the vestibular and palatine directions, after placing the respective appliance on the model. For statistical analysis, the force components Fx/tipping and Fz/intrusion at a displacement of +/- 0.151 mm from the incisor edge were selected. Means and standard deviations were calculated. The Wilcoxon 2-sample test for group pairings was used. RESULTS The norms for the mean Fx forces ranged from 1.62 (SD, 0.41) to 5.35 N (SD, 0.63). The mean Fz forces were between 0.07 (SD, 0.13) and -2.47 N (SD, 0.34). The highest intrusive forces were measured during vestibular displacement of the measuring tooth. The forces delivered by the thick appliances were overall significantly higher (P <0.0001) than those of the thin materials. The forces delivered by the Biolon appliances were generally significantly higher (P <0.0001) than those for the Erkodur materials. CONCLUSIONS The forces applied were mostly too high when compared with those stated in the literature as ideal. In addition to thickness, the thermoforming process influences the magnitude of the force delivered by a thermoformed appliance.

Changes in the shape of the mandible by orthodontic surgical technics with stable fixation of the segments

Es wird uber eine Methode berichtet, mit der nach sagittaler Spaltung des aufsteigenden Astes, nach Segmentverlagerung und anschliesender Miniplattenosteosynthese Form- und Lageveranderungen des Unterkiefers erzeilt werden konnen. Eine starre intermaxillare Immobilisation in der postoperativen Phase nach sagittaler Spaltung ist bei diesem Verfahren nicht erforderlich. Fur den Patienten ist dies ein entscheidender Vorteil. Die Art des Vorgehens ermoglicht auserdem eine achsengerechte Einstellung der proximalen Segmente und damit der Kiefergelenke. Im Anschlus daran wird die Position der Kondylen kontrolliert. Schon intraoperativ ist damit die Indikation fur eine evtl. Korrektur der Osteosynthese zu stellen und kann im Bedarfsfall sofort durchgefuhrt werden.

Initial Forces and Moments Delivered by Removable Thermoplastic Appliances during Rotation of an Upper Central Incisor

OBJECTIVE To determine the forces and moments delivered to a maxillary central incisor during rotation by three different thermoplastic appliances with identical thickness. MATERIALS AND METHODS Five identical appliances were manufactured from each of three materials (Ideal Clear 1.0 mm, Erkodur 1.0 mm, Biolon 1.0 mm). An upper central incisor fixed in a measuring device was rotated around its central axis in 0.5-degree steps to +/-2.5 degrees, +/-5 degrees, and +/-7.5 degrees (equivalent to an activation of +/-0.17 mm, +/-0.34 mm, and +/-0.51 mm of the incisor edge) in the clockwise and anticlockwise directions with the respective appliance fixed in place. For statistical analysis, the moments Tz (rotation) and forces Fz (intrusion) were tested. Means and standard deviations for Tz and median and 25% and 75% quantiles for Fz were calculated. An analysis of variance (ANOVA) was performed. RESULTS The minimal moment was determined at a rotation of -0.17 mm (-7.3 Nmm, +/-0.8), and the maximal moment at a deflection of -0.51 mm (-71.8 Nmm. +/-2.5) was recorded. The minimal value for Fz was measured at an activation of -0.17 mm (0.0 N), and the highest intrusive forces were evaluated for a rotation of -0.51 mm (-5.8 N). The particular material sometimes had a significant (P < .05) influence on the forces delivered and the moments. CONCLUSIONS During rotation with aligners, an intrusive force can also be observed. The direction of rotation, and the materials used all exert an influence on the force delivery properties of the appliance.

Morphology of the Interphalangeal Joint Surface and Its Functional Relevance

PURPOSE To study and to clarify the curvature morphology of the articular surfaces of the proximal interphalangeal (PIP) joint and to relate joint morphology and joint kinematics. METHODS The radii and centers of curvature of 40 PIP joints were determined by sagittal and transverse intersections of highly precise replicas that were prepared by dental methods. RESULTS The PIP joint is proved to be a nonconforming joint: the articular surface of the proximal end of the middle phalanx has lesser curvatures than the condyles of the proximal phalanx. In intersections through the apex of the radial and ulnar condyles, the measured differences of the radii between the articular surfaces of the PIP joint were sagittally about 30% and transversely about 49% of the respective radii of the condyles. Incongruity of the joint results in 2 morphologically given axes for extension respective to flexion: (1) an axis given by the articular surfaces of both condyles of the proximal phalanx; and (2) a second axis given by the articular surface of the proximal end of the middle phalanx. Both articulating surfaces have 2 contact points in the transverse plane, one each, central to the apex of radial and ulnar condyles, respectively. In the middle of the joint, in the intercondylar groove, a small joint cavity was present in 37 of 40 joints. CONCLUSIONS The physiological incongruity of the 2 articular surfaces of the PIP joint was defined quantitatively. This allows the derivation of a theoretical model for PIP joint function that explains the kinematics and mechanical stability of the joint as well as the lubrication and nutrition of the cartilaginous structures.

How do spinal segments move

PURPOSE To study and clarify the kinematics of spinal segments following cyclic torques causing axial rotation (T(z) (t)), lateral-flexion (T(x) (t)), flexion/extension (T(y) (t)). METHODS A 6D--Measurement of location, alignment, and migration of the instantaneous helical axis (IHA) as a function of rotational angle in cervical, thoracic, and lumbar segments subjected to axially directed preloads. RESULTS IHA retained an almost constant alignment, but migrated along distinct centrodes. THORACIC SEGMENTS: IHA was almost parallel to T(z) (t), T(x) (t), or T(y) (t), stationary for T(x) (t) or T(y) (t), and migrating for T(z) (t) along dorsally opened bows. IHA locations hardly depended on the position or size of axial preload. LUMBAR SEGMENTS: IHA was also almost parallel to T(z) (t), T(x) (t), or T(y) (t). In axial rotation IHA-migration along wide, ventrally or dorsally bent bows depending on segmental flexional/extensional status. Distances covered: 20-60mm. In lateral-flexion: IHA-migration to the left/right joint and vice versa. In flexion/extension IHA-migration from the facets to the centre of the disc. CERVICAL SEGMENTS: In flexion/flexion IHA was almost stationary for and parallel to T(y) (t). In axial rotation or lateral-flexion IHA intersected T(z) (t)/T(x) (t) under approximately -30 degrees /+30 degrees. CONCLUSIONS Generally joints alternate in guidance. Lumbar segments: in axial rotation and lateral-flexion parametrical control of IHA-position and IHA-migration by axial preload position. Cervical segments: kinematical coupling between axial rotation and lateral-flexion. The IHA-migration guided by the joints should be taken into account in the design of non-fusion implants. FE-calculations of spinal mechanics and kinematics should be based on detailed data of curvature morphology of the articulating surfaces of the joint facets.

Initial forces generated by three types of thermoplastic appliances on an upper central incisor during tipping.

The force properties of thermoformed appliances have not been systematically investigated. Therefore, the aim of the present study was to quantify the forces delivered by thermoplastic appliances manufactured from three different materials, with the same thickness, on a central upper incisor, during tipping. Five identical appliances were manufactured from three different materials all with a thickness of 1.0 mm (Ideal Clear, Erkodur, and Biolon). For measuring the forces, an isolated measuring tooth, as part of a standardized resin model incorporated in a newly developed measuring device, was tipped in nine 2.7 arc minute (0.04629 degree) steps, from 0 to 0.416 degrees in the vestibular and palatal directions around a rotational axis through the virtual apex, after positioning an appliance on the model. For statistical analysis, the force components Fx/tipping and Fz/intrusion at a displacement of +/-0.151 mm from the incisor edge were determined. Means and standard deviations (SDs) were calculated. The Kruskal-Wallis test for overall effects and the Wilcoxon two-sample test for individual group pairings were used (P < 0.05 significance level). The mean Fx forces ranged from -2.82 N (SD 0.62) to 5.42 N (SD 0.56). The mean Fz forces were between -0.14 N (SD 0.52) and -2.3 N (SD 0.43). The highest intrusive forces were measured during vestibular displacement of the measuring tooth. The forces delivered by the Biolon appliance were found to be much greater (P < 0.01) than those of the other materials. The forces delivered by the materials investigated were mostly higher than those stated in the literature.

Impulse debracketing compared to conventional debonding.

OBJECTIVE To evaluate impulse debonding compared to three conventional methods for bracket removal in relation to the damage caused to the enamel surface. MATERIALS AND METHODS Ninety-six osteotomed third molars were randomly assigned to two study groups (n = 48) for bracket bonding with either a composite adhesive system (CAS) or a glass-ionomeric cement (GIC). These two groups were then each randomly divided into four subgroups (n = 12) according to the method of debonding using (1) bracket removal pliers, (2) a side-cutter, (3) a lift-off debracketing instrument, or (4) an air pressure pulse device. Following debonding and corresponding postprocessing with either a finishing bur (CAS) or ultrasound (GIC), the enamel surfaces were assessed for damage, adhesive residues, and the need for postprocessing using scanning electron microscopy and the Adhesive Remnant Index, and the surfaces were compared in terms of mode of removal and type of adhesive using Fishers exact test (alpha = 5%). RESULTS No significant differences were found between the two different types of adhesives (CAS, GIC) in terms of the amount of damage to the enamel. Portions of enamel damage were found for impulse debonding/0%<bracket removal pliers/4%<lift-off debracketing instrument/17%<side-cutter/21%. The highest Adhesive Remnant Index grades were seen for impulse debonding. GIC residues after postprocessing using ultrasound were seen in 79%, compared to 48% after rotational postprocessing of CAS residues. CONCLUSIONS Impulse debonding provides a good alternative to conventional debonding methods, as the adhesion is usually separated at the bracket-adhesive interface, thereby avoiding enamel damage, independent of the adhesive used.

Detection and size differentiation of simulated tooth root defects using flat-panel volume computerized tomography (fpVCT)

OBJECTIVE Our aim was to evaluate the capacity of flat-panel volume computerized tomography (fpVCT) to enable the observer to detect and differentiate 3 different sizes of simulated tooth root defects in radiographs. STUDY DESIGN Three simulated tooth root defects of different sizes and a defect-free area (160 sites in total) were randomly distributed on the buccal and lingual surface of 20 mandibular premolar roots of Sus scrofa domestica with round burs. For the imaging of the specimens, an fpVCT prototype was used. Findings were evaluated by 3 observers. RESULTS Cavity 0 (no lesion) was correctly identified in 53%, cavity 1 in 69%, cavity 2 in 96%, and cavity 3 in 89%. Altogether, the simulated cavities were classified in a correct manner in 77%. The values were compared using receiver operating characteristic curves. The area under the curve (AUC) for cavity 0 versus the pooled results for cavities 1-3 was found to be 0.72. The AUC for the pooled results for 0-2 (no pathologic impact) versus cavity 3 (potential pathologic impact) was 0.94. There was no significant dependence of the results on the observer (P = .37). Results with P < .05 were considered to be significant. CONCLUSIONS Flat-panel volume computerized tomography, which is currently used only as a research tool, has a high potential in detection and differentiation at an early stage of external root resorption cavities with pathologic relevance..

Bedeutung und Technik der kiefergelenkpositionierung bei der sagittalen Spaltung des Unterkiefers

ZusammenfassungDie stabile Fixation der Segmente bei kieferorthopädischen Operationen bietet den vorteil, daß auf langzeitige starre intermaxilläre Immobilisation verzichtet werden kann. Die Vorteile erstrecken sich auch auf eine signifikante Reduktion der stationären Behandlungszeit und eine deutliche Abkürzung des gesamten Krankheitsverlaufes. Platten- oder Schraubenverbindungen von Osteotomiesegmenten haben jedoch den Nachteil, daß sie postoperativ nur sehr schwierig oder gar nicht mehr zu korrigieren sind. Daher ist eine Voraussetzung für die Anwendung stabiler Osteosyntheseverfahren im Unterkiefer und auch bei bimaxillären Eingriffen die exakte Übertragung der präoperativen Kondylusposition auf die postoperative Situation. Die vorgestellte Technik, die sich seit Jahren in der engen Zusammenarbeit zwischen Kieferorthopädie und Kieferchirurgie bewährt hat, erscheint uns die notwendige Voraussetzung für eine moderne Behandlung dentofazialer Anomalien.SummaryThe rigid fixation of segments in orthognatic surgery offers the advantage of avoiding long-term rigid intermaxillary immobilisation and reducing in-hospital treatment time and the entire clinical course. Nevertheless, it is difficult or even impossible to correct postoperatively osteotomy segments. Therefore the exact transfer of the preoperative position of the condyle to the postoperative situation is essential for the use of this technique and its use in bimaxillary surgery. The presented technique, which has been successful in the cooperation of orthodontics and orthognatic surgery for many years, is a prerequisite for an up to date treatment of dentofacial anomalies.