Christian Sander

Periodontal Ligament Hydrostatic Pressure with Areas of Root Resorption after Application of a Continuous Torque Moment

OBJECTIVE To evaluate the risk of root resorption, individual finite element models (FEMs) of extracted human maxillary first premolars were created, and the distribution of the hydrostatic pressure in the periodontal ligament (PDL) of these models was simulated. MATERIALS AND METHODS A continuous lingual torque of 3 Nmm and 6 Nmm respectively was applied in vivo to the aforementioned teeth. After extraction, FEMs of these double-rooted teeth were created based on high-resolution microcomputed tomographics (micro CT, voxel size: 35 microns). This high volumetric resolution made the recognition of very small resorption lacunae possible. Scanning electron micrographs of the root surfaces were created as well. This enabled the investigation of advantages and disadvantages of the different imaging techniques from the viewpoint of the examination of root resorption. Using the FEMs, the same loading conditions as applied in vivo were simulated. RESULTS The results of clinical examination and simulations were compared using the identical roots of the teeth. The regions that showed increased hydrostatic pressure (>0.0047 MPa) correlated well with the locations of root resorption for each tooth. Increased torque resulted in increased high-pressure areas and increased magnitudes of hydrostatic pressure, correlating with the experiments. CONCLUSION If hydrostatic pressure exceeds typical human capillary blood pressure in the PDL, the risk of root resorption increases.

Soft-tissue changes after maxillomandibular advancement surgery assessed with cone-beam computed tomography

INTRODUCTION The purpose of this study was to quantify anteroposterior and transverse facial soft-tissue changes with respect to underlying skeletal movements after maxillomandibular advancements by using cone-beam computed tomography. METHODS Thirty white patients were treated by maxillomandibular advancements after LeFort I osteotomies and bilateral sagittal split osteotomies. The patients were scanned by using cone-beam computed tomography within 1 week before the surgery, within 1 week after the surgery, and a minimum of 8 weeks postsurgery. We measured the differences between the first and last images and calculated ratios for anteroposterior and transverse soft-to-hard tissue movements. Changes in the greatest interalar width were also measured. RESULTS There was a statistically significant difference in the greatest interalar width change between patients receiving maxillary advancements greater than 4 mm and those having advancements less than or equal to 4 mm (P <0.023). Mean ratios of anteroposterior soft-to-hard tissue movements were 84.9% +/- 38.0% in the malar region, 96.1% +/- 15.5% in the chin, and 101.1% +/- 27.3% in the subcommissural region. Mean ratios of transverse soft-to-hard tissue movements were 39.4% +/- 19.7% in the malar region and 82.5% +/- 56.7% in the subcommissural region. CONCLUSIONS The amount of maxillary advancement most likely plays a role in the postsurgical increase in interalar width. In addition, facial soft tissues appear to respond more to anterior movement of the jaws than to an increase in transverse dimensions after maxillomandibular advancements.

Influence of different modeling strategies for the periodontal ligament on finite element simulation results

INTRODUCTION The finite element method is a promising tool to investigate the material properties and the structural response of the periodontal ligament (PDL). To obtain realistic and reproducible results during finite element simulations of the PDL, suitable bio-fidelic finite element meshes of the geometry are essential. METHODS In this study, 4 independent coworkers generated altogether 17 volume meshes (3-dimensional) based on the same high-resolution computed-tomography image data set of a tooth obtained in vivo to compare the influence of the different model generation techniques on the predicted response to loading for low orthodontic forces. RESULTS It was shown that the thickness of the PDL has a significant effect on initial tooth mobility but only a remarkably moderate effect on the observed stress distribution in the PDL. Both the tooth and the bone can be considered effectively rigid when exploring the response of the PDL under low loads. The effect of geometric nonlinearities could be neglected for the applied force system. CONCLUSIONS Most importantly, this study highlights the sensitivity of the finite element simulation results for accurate geometric reconstruction of the PDL.

Correspondences of hydrostatic pressure in periodontal ligament with regions of root resorption: A clinical and a finite element study of the same human teeth

INTRODUCTION The main objectives of this study were to generate individual finite element models of extracted human upper first premolars, and to simulate the distribution of the hydrostatic pressure in the periodontal ligament (PDL) of these models for evaluation of the risk of root resorption. METHODS The individual extracted teeth were from a previous in vivo study that investigated root resorption after application of continuous intrusive forces. The results of experimental examination and simulations were compared on these identical tooth roots. The applied force system was 0.5N and 1.0N of intrusive force. RESULTS The simulated results during intrusion of 0.5N showed regions near the apical thirds of the roots with hydrostatic pressure over the human capillary blood pressure. These regions correlated with the electron microscopies of previous studies performed in Brazil with the identical teeth. An increased force of 1.0N resulted in increased areas and magnitudes of the hydrostatic pressure. CONCLUSIONS The key parameter indicating beginning root resorption used in this study was an increased value for hydrostatic pressure in the PDL.

Initial results regarding force exertion during rapid maxillary expansion in children.

Aim and Method:We developed a method to measure the forces occurring during rapid maxillary expansion and carried out the University of Ulm rapid maxillary expansion method, similar to that of Chatellier & Chateau, in ten patients.Results:The forces occurring on the maxilla increased up to 120 N. There was considerable variation in force level from patient to patient. After “rupture” of the midpalatal suture, the forces decreased. The remaining forces seemed to be the result from stress on soft tissue and bone.ZusammenfassungZiel und Methodik:Zur Messung der bei der Gaumennahterweiterung entstehenden Kräfte wurde ein spezielles Messverfahren entwickelt. Mit Hilfe dieses Messverfahrens wurde bei zehn Patienten eine Gaumennahterweiterung nach der Ulmer Methode durchgeführt; diese ist vergleichbar mit der Methode von Chatellier & Chateau.Ergebnisse:Die hierbei auf den Oberkiefer wirkenden Kräfte stiegen auf bis zu 120 N an. Das Kraftniveau schwankte von Patient zu Patient deutlich. Nach erfolgter Erweiterung der Gaumennaht fielen die Kräfte ab. Es blieb eine Restspannung übrig, die vermutlich auf die noch bestehenden Spannungen durch die Weichteile und die Knochen zu begründen sind.

In-vitro results of rapid maxillary expansion on adults compared with finite element simulations

This study was mainly performed to investigate the effects of high maxillary expansion forces on the skull with fresh and thiel-fixed human skulls. The maxillary suture was not weakened except in one experiment. This study compares the strain measured on the zygomatic process of the skull with the results of a finite element model generated for this purpose. An increasing transversal force was applied on the alveolar process (teeth) until rupture. Strain on the zygomatic process, maxilla displacement and the expanding forces were registered. The results of this study show linear material behaviour of the skull before rupture. The highest stress during the experiments and FE simulation was observed on the alveolar process. Conclusions of this study are the necessity of the existence of appropriate models and that female specimens seem to rupture at a lower force than male ones. Both male and female specimens show a similar linear behaviour in the force/strain curve within each gender group. The probability of maxillary suture opening in adults during ultra-rapid maxillary expansion with tooth anchorage is very low. Complications and unwanted rupture could occur.

Contactless measurement of canine retraction by digital macrophotogrammetry during hybrid retractor application.

Abstract.A new contactless method for measuring tooth movements is presented. Digital macrophotogrammetry (DMP) enables the orthodontist to obtain information on the three-dimensional movement of a tooth at each session. Analysis of the DMP images provides information on the translation and toration of a tooth during treatment. It is conceivable that the introduction of DMP will make an important contribution to quality assurance.DMP application during canine retraction with the Hybrid Retractor® has pave the way for the orthodontic appliance to be correctly adjusted at each session.Despite intra- and interindividual differences during canine movement, for which the anisotropy of the bone seems to be basically responsible, a movement velocity of ca 1.2 mm is to be expected over the entire treatment period.The preconditions for the three-dimensional orientation and description of canine movement are:1. The markers on the brackets and attachments must be clearly visible throughout the treatment.2. The teeth to which the scaling frame is fixed should not move during treatment.3. Four measuring points should be visible on each bracket.4. The control points on the frame must be positioned three-dimensionally, and it must be possible to determine their position with sufficient accuracy in advance.In vitro calibration of the photogrammetry presented here yielded a resolution of 1 μm for translation and of better than 1/10° for rotation around the three spatial axes under optimal conditions.Zusammenfassung.Ein neues berührungsloses Verfahren zur Vermessung der Zahnbewegung wird vorgestellt. Die digitale Makrophotogrammetrie (DMP) ermöglicht dem Anwender, bei jeder Sitzung eine Information über die dreidimensionale Bewegung eines Zahnes zu gewinnen. Durch die Auswertung der DMP-Bilder entstehen somit Informationen über die Translation und Rotation eines Zahnes während der Behandlung. Es ist denkbar, dass durch Einführung der DMP ein wichtiger Beitrag zur Qualitätskontrolle geliefert wird.Die Anwendung der DMP bei der Retraktion des Eckzahnes mittels des Hybrid-Retraktors® eröffnete die Möglichkeit zur Korrektur der Behandlungsapparatur bei jeder Behandlungssitzung.Trotz intra- und interindividueller Unterschiede bei der Bewegung des Eckzahnes, für die im Wesentlichen die Anisotropie des Knochens verantwortlich zu sein scheint, kann über den gesamten Behandlungszeitraum mit einer Bewegungsgeschwindigkeit von ca. 1,2 mm pro Monat gerechnet werden.Die Voraussetzungen für die dreidimensionale Orientierung und Beschreibung der Eckzahnbewegung sind folgende:1. Die Markierungspunkte auf den Brackets und Attachments müssen während der gesamten Behandlung deutlich sichtbar sein.2. Die Zähne, auf denen der Passrahmen befestigt wird, sollten sich während der Behandlung nicht bewegen.3. Auf jedem Bracket sollten vier Messpunkte sichtbar sein.4. Die Passpunkte auf dem Rahmen müssen dreidimensional angeordnet sein, ihre Lage muss mit ausreichender Genauigkeit vorherbestimmt werden können.Eine in vitro durchgeführte Eichung der hier dargestellten Photogrammetrie ergab eine Auflösung von 1 μm bei der Translation und eine Auflösung von besser als 1/10° bei der Rotation um die drei Raumachsen unter optimalsten Bedingungen.

Development and biomechanical investigation of a new compound palatal arch.

Abstract.Background and Aim:There are many advantages in using a transpalatal arch in orthodontic treatment. In addition to the active movement of individual teeth, such an arch can be used to provide additional anchorage. The aim of this study was to further develop and improve both the clinical and the biomechanical properties of the conventional transpalatal arch.Material and Methods:Currently available compound material components form an established part of orthodontic therapy. The Compound palatal arch® broadens the scope of this treatment system. The biomechanical effects of the newly developed Compound palatal arch® were verified by comparing them with those of commercially available conventional transpalatal arches. The recently developed Compound palatal arch® is made of one compound element: nickel-titanium/stainless steel. The specific dimensions and design of the nickel-titanium element are aimed at exploiting its superelasticity, even during active molar movement. The biomechanical investigation was carried out using sixcomponent measuring sensors to register the forces and moments in the three spatial dimensions (x, y and z) at 37 °C. The following appliances were investigated: Goshgarian transpalatal arch, quad-helix appliance, Arndt memory expander®, and Compound palatal arch®.Results:Transpalatal arches could not be inserted without the arch being under tension. This is particularly important when the arch is being used for anchorage purposes. The Goshgarian arch had to be classified as problematic for the movement of single teeth as the load/deflection rate was high. However, this can be utilized for anchorage purposes. The clinical advantage of a quad-helix appliance is the option for asymmetric tooth movement.Conclusions:This study showed that the quad-helix was effective for both unilateral and bilateral derotation as well as for transversal tooth movement. However, expansions should be confined to ≤ 4 mm, and derotations to < 10°, as forces and moments are otherwise not within the physiologic range. The Arndt memory expander® displayed no advantages over either the quad-helix appliance or the Goshgarian transpalatal arch. Nor did it display any superelastic properties. The linear relationship, the relatively high forces and moments, and the lack of clinical adjustability cast doubts on the benefits of this appliance. The newly developed Compound palatal arch® showed substantial advantages in molar derotation compared with conventional transpalatal arches. Superelastic properties were achieved through the design and positioning of the nickel-titanium element. Expansion with the Compound palatal arch® was comparable with that with conventional transpalatal arches. The clinical advantage is in the fact that this appliance can be reactivated and that dental asymmetries can be treated.Zusammenfassung.Hintergrund und Ziel:In der Anwendung von Transpalatinalbögen ergeben sich viele Vorteile in der orthodontischen Therapie. Neben der aktiven Bewegung von Einzelzähnen werden Palatinalbögen ebenfalls als Verankerungselemente verwendet. Ziel dieser Studie war die Weiterentwicklung und Verbesserung konventioneller Transpalatinalbögen sowohl klinisch als auch biomechanisch.Material und Methode:Bereits entwickelte Compound-Behandlungselemente sind etablierte Behandlungsmaterialien in der orthodontischen Therapie. Der Compound-Palatinalbogen® erweitert dieses Behandlungssystem. Zur Verifizierung der biomechanischen Effekte wurde der neu entwickelte Compound-Palatinalbogen® mit konventionellen, auf dem Markt befindlichen Palatinalbögen verglichen. Der neu entwickelte Compound-Palatinalbogen® besteht aus einem Compound-Element: NiTi-Stahl. Durch die spezifische Größe und den Einbau des NiTi-Elementes soll die Superelastizität auch bei aktiven Zahnbewegungen am Molaren nutzbar gemacht werden. Die biomechanische Untersuchung erfolgte mit Sechs-Komponenten-Messsensoren zur Darstellung der Kräfte und Momente in drei Ebenen des Raumes (x, y, z) bei 37 °C. Folgende Bögen wurden untersucht: Goshgarian, Quadhelix, Arndt-Memory-Expander®, Compound-Palatinalbogen®.Ergebnisse:Es zeigte sich, dass ein spannungsfreies Einsetzen von Palatinalbögen nicht möglich ist—insbesondere bei Anwendung von Transpalatinalbögen in der Verankerung ein klinisch zu beachtender Effekt. Der Goshgarian-Bogen war für die Bewegung von Einzelzähnen als problematisch einzustufen, da die Last-/Biegerate groß war. Dies kann jedoch in der Verankerung genutzt werden. Der Vorteil von Quadhelices liegt klinisch in der Lösung von asymmetrischen Zahnbewegungen.Schlussfolgerungen:Diese Studie zeigt, dass sich Quadhelices gut für die ein-/beidseitige Derotation und Transversalbewegung eignen. Es sollte jedoch nicht mehr als 4 mm expandiert und < 10° Derotation eingebogen werden, da sonst die Kräfte und Momente in unphysiologische Bereiche kommen. Für den Arndt- Memory-Expander® konnten keine Vorteile gegenüber der Quadhelix und dem Goshgarian-Bogen festgestellt werden. Es zeigten sich keine superelastischen Eigenschaften. Das lineare Verhalten, die relativ hohen Kräfte und Momente und die fehlende klinische Nachjustage machen die Indikation dieser Apparatur fraglich. Der neu entwickelte Compound-Palatinalbogen® zeigte wesentliche Vorteile in der Derotation von Molaren gegenüber den konventionellen Palatinalbögen. Durch die Konstruktion und Anordnung des NiTi-Elementes konnte ein superelastisches Verhalten erzielt werden. In der Expansion war der Compound-Palatinalbogen® vergleichbar mit den konventionellen Palatinalbögen. Der klinische Vorteil liegt in der Nachaktivierbarkeit und der möglichen Behandlung von Asymmetrien.

Use of a modified expander during rapid maxillary expansion in adults: an in vitro and finite element study.

PURPOSE This preliminary study was performed to evaluate a proposed maxillary expansion treatment method for adults with fused intermaxillary sutures. MATERIALS AND METHODS This study was performed in three Thiel-fixed skulls from older female cadavers with a microimplant-supported expansion screw. This modified expansion screw was mounted on the palatine process with microimplants and activated every 15 to 20 seconds with an activation key until the intermaxillary suture ruptured. A strain gauge was bonded to the expansion screw and calibrated so it could be used as a force sensor device. Rupture of the intermaxillary suture was indicated by a sudden drop in the registered force, through visible opening of the suture, and via computed tomographic data. Finite element simulations were performed, which led to the experimental testing. RESULTS Rupture of the intermaxillary suture was achieved in all three experiments with the microimplant-supported screw. The strain measurement on one of the expansion screws resulted in an expansion force of 86 N. Finite element simulations showed a high tensile stress concentration exerted by the microimplant-supported expansion screw on the intermaxillary suture. CONCLUSION The applied expansion force led to high tensile stress concentrations, mainly on the intermaxillary sutures, resulting in the opening of fused intermaxillary sutures. This method may help adults to be treated by an orthodontist, thereby avoiding surgical intervention.

A downloadable meshed human canine tooth model with PDL and bone for finite element simulations

OBJECTIVE The aim of this study is to relieve scientists from the complex and time-consuming task of model generation by providing a model of a canine tooth and its periradicular tissues for Finite Element Method (FEM) simulations. METHODS This was achieved with diverse commercial software, based on a micro-computed tomography of the specimen. RESULTS The Finite Element (FE) Model consists of enamel, dentin, nerve (innervation), periodontal ligament (PDL), and the surrounding cortical bone with trabecular structure. The area and volume meshes are of a very high quality in order to represent the model in a detailed form. Material properties are to be set individually by every user. The tooth model is provided for Abaqus, Ansys, HyperMesh, Nastran and as STL files, in an ASCII format for free download. SIGNIFICANCE This can help reduce the cost and effort of generating a tooth model for some research institutions, and may encourage other research groups to provide their high quality models for other researchers. By providing FE models, research results, especially FEM simulations, could be easily verified by others.