Christoph Bourauel

Frictional forces between bracket and arch wire

Guiding a tooth along an arch wire results in a counteracting frictional force. Clinically, a mesiodistally applied force must exceed the frictional force to produce a tooth movement. A friction-testing assembly simulating three-dimensional tooth rotations was constructed to study factors affecting friction magnitude. Five wire alloys (standard stainless steel, Hi-T stainless steel, Elgiloy blue, nitinol, and TMA) in five wire sizes (0.016, 0.016 x 0.022, 0.017 x 0.025, 0.018, and 0.018 x 0.025 inch) were examined with respect to three bracket widths (2.2, 3.3, and 4.2 mm) at four levels of retarding force (0, 1, 2, and 3 N). The following factors affected friction in decreasing order: retarding force (biologic resistance), surface roughness of wire, wire size (vertical dimension), bracket width, and elastic properties of wire. The study recommends the application of 0.016 x 0.022 inch stainless steel wire combined with a medium (3.3 mm) or wide (4.2 mm) bracket for an arch-guided mechanism with an 0.018 inch slot. The effective force of this arrangement has to increase twofold to overcome the friction. For TMA wire, however, the effective force must increase sixfold, resulting in a hazardous overload of the anchorage units.

Determination of the elasticity parameters of the human periodontal ligament and the location of the center of resistance of single-rooted teeth a study of autopsy specimens and their conversion into finite element models.

Abstract.Material and Methods: The aim of this study was to determine the elasticity parameters of the human periodontal ligament by measuring three-dimensionally the initial buccolingual tooth displacements of eight singl-rooted teeth in human jaw specimens, using a noninvasive method. Subsequently the specimens were used to develop finite element models presenting the same individual geometry as the respective autopsy material. These models formed the basis for computerized movement simulations, whose characteristic was brought into line with the experimentally registered movements by adapting the elasticity parameters of the periodontal ligament. Using the individual elasticity parameters determined in this way, with which the displacement of the ocmputer models could be realistically calculated, the centers of resistance of the examined teeth were determined by simulating the effects of different force systems. Results: The nonlinear character of the initial tooth movement could be effectively simulated by using a bilinear parameter set for the elasticity of the periodontal ligament and by determining a critical expansion value for the transition from the validity range of the first Youngs modulus to the second. The mean Youngs modulus of the first phase of movement was 0.05 MPa, that of the second phase 0.28 MPa, and the critical expansion 7.5% (Poissons ratio μ = 0.3). The centers of resistance of single-rooted teeth were found to be at approximately 42% of the alveolar height from the alveolar crest to the apex, irrespective of root length and direction of loading. Conclusion: The elasticity parameters were found to be on a similar scale to those determined in previous studies on multi-rooted pig teeth.Zusammenfassung.Material und Methode: Zur Bestimmung der Elastizitätseigenschaften von menschlischem Parodontalligament wurde eine horizontale Initialbewegung einwurzeliger Zähne an acht Kieferpräparaten in einem nicht invasiven Registrierverfahren dreidimensional gemessen. Anschließend wurden Finite-Elemente-Modelle von allen untersuchten Präparaten entwickelt, die in ihrer Geometrie den Originalen entsprachen. Diese Modelle waren die Grundlage für computerberechnete Bewegungssimulationen, deren Charakteristik durch Anpassung der Elastizitätseigenschaften des Parodontalligaments mit den experimentell gemessenen Bewegungsgrößen zur Deckung gebracht wurde. Unter Verwendung der so ermittelten individuellen Elastizitätsparameter, mit denen die Auslenkungen der Computermodelle realistisch berechnet werden konnten, wurden durch Simulation der Wirkungen unterschiedlicher Kraftsysteme die Widerstandszentren der untersuchten Zähne bestimmt. Ergebnisse: Die Nichtlinearität der initialen Zahnbewegung konnte durch Verwendung eines bilinearen Parametersatzes für die Elastizität des Parodontalligaments und die Bestimmung eines Grenzdehnungswertes für den Übergang vom Geltungsbereich des ersten E-Moduls zum zweiten gut simuliert werden. Der E-Modul der ersten Phase der Bewegung betrug im Mittel 0,05 MPa, der E-Modul der zweiten Phase 0,28 MPa und die Grenzdehnung 7,5% (Poissonzahl 0,3). Die Widerstandszentren einwurzeliger Zähne lagen unabhängig von der Wurzellänge und der Belastungsrichtung bei etwa 42% der Alveolenhöhe in koronal-apikaler Richtung. Schlussfolgerung: Es konnte gezeigt werden, dass die ermittelten Elastizitätsparameter in ihrer Größenordnung denen für mehrwurzelige Schweinezähne, die in Voruntersuchungen bestimmt wurden, entsprechen.

An experimental apparatus for the simulation of three-dimensional movements in orthodontics

An apparatus for the study of three-dimensional force systems and the resulting movements during orthodontic treatment is presented. The instrument consists of two force-torque transducers which are capable of recording both forces and torques simultaneously, in all spatial directions. Each sensor has a measuring range of 15N (450 Nmm) and a resolution of 0.02 N (0.5 Nmm) and is mounted on a set of three translational and three rotational stages driven by stepping motors. Positioning accuracy is in the range of 1 micron and 0.01 degrees respectively. The apparatus is computer controlled and supported by comprehensive software.

Application of Bone Remodeling Theories in the Simulation of Orthodontic Tooth Movements

Abstract: A numerical model that calculates bone apposition and resorption around a tooth root on the basis of bone remodeling theories was developed to simulate orthodontic tooth movements. The model was used to calculate different kinds of orthodontic tooth movements, that were then compared with the expected movements based on clinical experience. For simulation of the movements the root of a canine was modeled in an idealized way in the form of an elliptical paraboloid and was processed with a finite element program. The finite element model was loaded with defined force systems. Two model assumptions were used to calculate the bone remodeling process. The mechanical loads firstly in the periodontal ligament and secondly in the alveolar bone were taken to simulate the following tooth movements: 1. mesial tipping around the center of resistance (force system at the bracket: isolated torque MY = Nmm), 2. Rotation around the long axis of the tooth (MZ = 5 Nmm), 3. uncontrolled tipping around the root tip (FX = 1 N, MZ = 5 Nmm), 4. canine retraction (FX = 1 N, MY = −9.5 Nmm, MZ = 5 Nmm), 5. and 6. extrusion/intrusion (FZ = ±0.5 N, MX = ±2.5 Nmm). Comparison with clinical experience was performed by calculating the orthodontic tooth movements based on the assumption of a fixed position of the center of resistance.It could be demonstrated that the numerical model of orthodontic bone remodeling can be used to calculate orthodontic tooth movements. However, the results are strongly dependent on the model assumptions. The model simulating the bone remodeling on the basis of the loading of the periodontal ligament delivers results that are in very good accordance with the biomechanical assumptions of the position of the center of resistance. However, marked side effects occurned with the second model, especially in the simulations of uncontrolled tipping, translation and intrusion/extrusion. Clinically, these side effects cannot be observed.Zusammenfassung: Für die Simulation orthodontischer Zahnbewegungen wurde ein numerisches Modell entwickelt, das die Knochenumbauprozesse um die Zahnwurzel auf der Grundlage sogenannter Bone-Remodeling-Theorien berechnet. Dieses Modell wurde eingesetzt, um verschiedene Arten geplanter Zahnbewegungen zu berechnen, die mit den klinisch zu erwartenden Ergebnissen verglichen wurden. Zur Simulation der Bewegung wurde die Wurzel eines Eckzahns idealisiert in Form eines elliptischen Paraboloids dargestellt und in ein Finite-Elemente-Programm eingelesen. Das Finite-Elemente-Modell wurde mit definierten Kraftsystemen belastet. In zwei Modellannahmen wurden entweder die mechanischen Belastungen 1. des paradontalen Ligaments oder 2. des Knochens verwendet, um den Knochenumbau um die Zahnwurzel bei folgenden Bewegungen zu simulieren: 1. Mesialkippung um das Widerstandszentrum (Kraftsystem am Bracket: reines Drehmoment von MY = 5 Nmm), 2. Rotation um die Zahnachse (MZ = 5 Nmm), 3. unkontrollierte Kippung um die Wurzelspitze (FX = 1 N, MZ = 5 Nmm), 4. Eckzahnretraktion (FX = 1 N, MY = −9,5 Nmm, MZ = 5 Nmm), 5. Und 6. Extrusion/Intrusion (FZ = ±0,5 N, MX = ±2,5 Nmm). Zum Vergleich mit klinischen Erfahrungen wurden die Zahnbewegungen auch aufgrund der Annahme eines festen Widerstandszentrums eines Eckzahns berechnet. Es zeigte sich, dass mit dem numerischen Modell des orthodontischen Knochenumbaus die Vorausberechnung geplanter Behandlungsschritte möglich ist. Die Ergebnisse sind jedoch stark abhängig von den Modellannahmen. Das Modell, das den Knochenumbau auf der Grundlage der Belastungen des Desmodonts simuliert, zeigte Ergebnisse, die mit den biomechanischen Annahmen über die Lage des Widerstandszentrums sehr gut übereinstimmten. Dagegen traten insbesondere bei der unkontrollierten Kippung, der Translation und der In-/Extrusion in den Simulationen mit dem zweiten Modell ausgeprägte Nebenwirkungen auf, die klinisch nicht zu beobachten sind.

Simulation of orthodontic tooth movements

Orthodontic tooth movements are based on the ability of bone to react to mechanical stresses with the apposition and resorption of alveolar bone. Currently, the underlying biophysical, biochemical, and cellular processes are the subject of numerous studies. At present, however, an analytical description of orthodontic tooth movements including all components of the processes involved seems to be impossible. It was the aim of the present study to develop a mechanics-based phenomenological model capable of describing the alveolar bone remodeling.Thus, 2 different models were developed. The first is based on the assumption that deformations of the periodontal ligament (PDL) are the key stimulus to starting orthodontic tooth movement. The second supposes that deformations of the alveolar bone are the basis of orthodontic bone remodeling. Both models were integrated into a finite element package calculating stresses, strains and deformations of tooth and tooth supporting structures and from this simulating the movement of the tooth and its alveolus through the bone. Clinically induced canine retractions in 5 patients as well as force systems were exactly measured and the tooth movements were simulated using both models.The results show that the first model allows reliable simulation of orthodontic tooth movements, whereas the second is to be rejected.ZusammenfassungKieferorthopädische Zahnbewegungen beruhen auf der Fähigkeit des Knochens, auf äußere mechanische Reize mit einem Umbau des Kieferknochens zu reagieren. Die zugrundeliegenden Vorgänge laufen auf biophysikalischer, biochemischer und zellulärer Ebene ab und sind derzeit Gegenstand zahlreicher Untersuchungen. Eine geschlossene Beschreibung aller an der Zahnbewegung beteiligten Prozesse durch ein analytisches modell erscheint aufgrund der Komplexität zur Zeit nicht möglich. Wesentliche Erkenntnisse können jedoch bereits gewonnen werden, wenn es gelingt, ein auf der Mechanik basierendes Simulationsmodell aufzustellen, das die Knochenumbauvorgänge phänomenologisch darstellt.Zur Beschreibung der orthodontischen Zahnbewegung wurden daher zwei Modelle entwickelt. Grundlage des ersten Modells ist die Annahme, daß der mechanische Schlüsselreiz in Deformationen des parodontalen Ligaments zu sehen ist. Das zweite Modell basiert auf der Hypothese, daß Deformationen der Alveolarwand zum Knochenumbau und damit zur orthodontischen Zahnbewegung beitragen. Diese Modelle wurden in ein Finite-Elemente-Programmsystem integriert, das die Berechnung von Spannungen sowie Deformationen von Zahn und Zahnhalteapparat ermöglicht und hieraus die Bewegung des Zahns durch den Knochen berechnet. Zur Verifizierung wurden bei fünf Patienten Eckzahnretraktionen sowie die klinisch eingesetzten Kraftsysteme genau vermessen und mit Hilfe beider Modelle simuliert.Die Ergebnisse zeigen, daß das erste Modell eine gute Vorhersage der orthodontischen Zahnbewegung erlaubt, während die Annahme, daß die mechanischen Deformationen der Alveolarwand den Knochenumbau mitbestimmen, die klinische Realität nicht zutreffend beschreibt.

Nickel concentration in the saliva of patients with nickel-titanium orthodontic appliances.

INTRODUCTION The purpose of this study was to examine whether nickel-titanium (Ni-Ti) archwires cause an increase of nickel concentration in the saliva of 18 orthodontic patients to estimate the possible risk of these archwires in patients who have nickel hypersensitivity. METHODS Saliva samples were collected before orthodontic treatment, after placement of the bands and brackets, 2 weeks later and before placing the Ni-Ti archwires, immediately after placing the Ni-Ti archwires, 4 weeks after placing the wires, and 8 weeks after placing the wires. RESULTS By using mass spectrometry, no statistically significant differences were found in the nickel concentrations in the samples taken without appliances, in those obtained 2 weeks after placement of the bands and brackets, and 4 and 8 weeks after placement of the archwires. Samples taken immediately after placement of the bands and brackets and the Ni-Ti archwires showed slight but significant increases in nickel concentration of 78 and 56 microg per liter, respectively, compared with the pretreatment value of 34 microg per liter. CONCLUSIONS Nickel leaching occurred after placement of the bands and brackets and after placement of the Ni-Ti archwires, associated with an increase of the nickel ion concentration in the patients saliva. This effect decreased within 10 weeks.

The Frictional Behavior of Coated Guiding Archwires

AbstractBackground: The vast range of orthodontic wires made of different alloys makes it increasingly difficult for orthodontists to judge them. Coated orthodontic wires form a group of innovative guiding archwires. Material and Methods: In the present in vitro study the frictional behavior of eight coated wires of different dimensions was investigated in archwire-guided canine retraction in the upper jaw. For this purpose five superelastic nickel titanium alloy wires (Titanol/reg; Low Force River Finish Gold and Gold 2: Forestadent®, Pforzheim Germany; Titanol® Superelastic tooth Sentalloy Ionguard™: GAC, Central Islip, NY, USA; NITI Imagination™: GAC, Central Islip, NY, USA), two β-titanium wires (TMA® Low Friction Ionguard: Ormco, Glendora, CA, USA; TMA® Low Friction Ionguard Purple: Ormco, Glendora, CA, USA) and one steel wire (Stainless steel Imagination™: GAC, Central Islip, NY, USA) were selected. The coatings were made of Teflon® or polyethylene, and by ion implantation. Three uncoated archwires (Rematitan® Lite Dimple; Dentaurum, Pforzheim, German; Titanol® Low Force River Finish: Forestadent®, Pforzheim, Germany; BioForce Sentalloy™: GAC, Central Islip, NY, USA) were used for comparison purposes. The force losses due to friction were measured using the Orthodontic Measurement and Simulation System (OMSS). Results: The results indicated that all coatings can reduce frictional losses compared with an uncoated reference wire by the same manufacturer. Measured frictional losses ranged from 48.3–6.1% with the Teflon® coatings reducing the frictional losses to less than 10% in some cases. Conclusion: An unequivocal correlation between the surface roughness and frictional forces of the wires could not be verified by scanning electron microscopy.ZusammenfassungHintergrund: Die Vielzahl an orthodontischen Drähten aus diversen Legierungen macht es die Kieferorthopäden immer schwerer, sie zu beurteilen. Eine Gruppe von neu angebotenen Führungsbögen stellen die beschichteten orthodontischen Drähte dar. Material und Methode: In der vorliegenden In-vitro-Studie wurde das Reibungsverhalten von acht beschichteten Drähten unterschiedlicher Dimension bei den bogengeführten Eckzahnretraktion im Oberkiefer untersucht. Neben fünf Nickel-Titan-Drähten (Titanol® Low Force River Finish Gold und Gold 2: Fa. Forestadent®; Titanol® Superelastic zahnfarben: Fa. Forestadent®; BioForce Sentalloy Ionguard™: Fa. GAC; NiTi Imagination™: Fa. GAC) wurden zwei β-Titan- (TMA Low Friction Iongard: Fa. Ormco; TMA Low Friction Ionguard Purple: Fa. Ormco) und ein Stahldraht (Stainless Steel Imagination™: Fa. GAC) ausgewählt. Die Beschichtungen bestanden aus Teflon®, Polyethylen oder Ionenimplantation. Als Referenz wurden drei unbeschichtete Drähte (Rematitan® Lite Dimple: Fa. Dentaurum; Titanol® Low Force River Finish: Fa. Forestadent®; BioForce Sentalloy™: Fa. GAC) in die Untersuchung einbezogen. Die Reibungsverluste wurden mit dem Orthodontischen Mess- und Simulations-System (OMSS) bestimmt. Ergebnisse: Die Ergebnisse zeigten, dass alle Beschichtungen, verglichen mit einem unbeschichteten Referenzdraht desselben Herstellers, eine Reduktion der Reibungsverluste bewirken. Die gemessenen Reibungsverluste lagen zwischen 48,3% und 6,1%, wobei bei Teflon®-Beschichtungen der Reibungsverlust zum Teil auf unter 10% sank. Schlussfolgerung: Ein eindeutiger Zusammenhang zwischen der Oberflächenrauheit und den Friktionswerten der Drähte konnte anhand von rasterelektronenmikroskopischen Aufnahmen nicht bestätigt werden.

Early Responses of Periodontal Ligament Cells to Mechanical Stimulus in vivo

Previous studies have indicated that human periodontal ligament cells undergo osteoblastic differentiation via the ERK pathway under mechanical stress in vitro. This study aimed to verify this principle in vivo. The right upper first molars of 25 anesthetized rats were loaded with constant forces of 0.1 N for up to 8 hrs. The untreated contralateral side served as a control. Paraffin-embedded sections were analyzed by immunohistochemistry for proliferating cell nuclear antigen (PCNA), runt-related transcription factor 2 (Runx2/Cbfa1), and phosphorylated extracellular signal-regulated kinases 1/2 (pERK1/2). In selected areas under tension, the proportions of Runx2-positive and pERK1/2-positive cells increased within 8 hrs of loading, whereas these proportions in selected areas under pressure were significantly lower than those in control teeth. Moreover, there were no significant changes in the number of PCNA-positive cells. Thus, mechanical stimulus up-regulates Runx2, and this regulation may be achieved via the ERK pathway.

Rare earth magnets and impaction

Aberration in the eruption process was found to be a prime etiologic factor in inducing impaction. Thus an ideal treatment approach should attempt to mimic the normal eruption modus. However, conventional traction methods have been found to be associated with gingiva inflammation, bone recession, reduced attached gingiva, periodontal pockets, exposed cementoenamel junction, and root resorption of the impacted and adjacent teeth. These side effects are the result of premature exposure of the impacted tooth to the oral cavity through a nonself-cleansing pathway and an uncontrolled force system. The present study introduces a new, magnetic attraction system, with a magnetic bracket bonded to an impacted tooth and an intraoral magnet linked to a Hawley type retainer. Vertical and horizontal magnetic brackets were designed, with the magnetic axis magnetized parallel and perpendicular to the base of the bracket, respectively. The vertical type is used for impacted incisors and canines, and the horizontal magnetic bracket is applied for impacted premolars and molars. A three-dimensional analysis of the magnetic force system, by means of the OMSS apparatus, found the small magnetic bracket combined with a large pole surface area of the intraoral magnet to exhibit the most efficient convergent guidance. For this report the magnetic eruption device was examined on one animal subject and four patients. The Nd2Fe14B magnets were coated with parylene and/or encapsulated in stainless steel housings. In deep impaction, the magnetic bracket was cold-sterilized before surgery, and the surgical mucoperiosteal flap was then sutured over the bonded magnetic bracket. Attraction was initiated 1 to 2 weeks after healing. Thus tooth emergence into the oral cavity replicated normal eruption conditioning. The system operated at an attractive force level of 0.2 to 0.5 N. Adjustment was accomplished by temporarily interposing a magnetic spacer between the two magnetic units. No side effects were observed in this restricted number of treated cases, and treatment time was reduced. The study recommends the application of magnets in the treatment of impaction on the grounds of less invasive surgical procedure, effective attractive forces at short distances, and controlled spatial guidance.

Torque expression of self-ligating brackets compared with conventional metallic, ceramic, and plastic brackets

The purpose of this research was to investigate the torque capacity of active and passive self-ligating brackets compared with metallic, ceramic, and polycarbonate edgewise brackets. Six types of orthodontic brackets were included in the study: the self-ligating Speed and Damon2, the stainless steel (SS), Ultratrimm and Discovery, the ceramic bracket, Fascination 2, and the polycarbonate bracket, Brillant. All brackets had a 0.022-inch slot size and were torqued with 0.019 x 0.025-inch SS archwires. For this purpose, the labial crown torque of an upper central incisor was measured in a simulated intraoral clinical situation using the orthodontic measurement and simulation system (OMSS). A torque of 20 degrees was applied and the correction of the misalignement was simulated experimentally with the OMSS. Each bracket/wire combination was measured five times. Maximum torquing moments and torque loss were determined. The results were analysed with one-way analysis of variance, with the bracket serving as the sole discriminating variable, and the Tukey test at the 0.05 level of significance. The ceramic bracket (Fascination 2) presented the highest torquing moment (35 Nmm) and, together with a SS bracket, the lowest torque loss (4.6 degrees). Self-ligating, polycarbonate, and selective metallic brackets demonstrated almost a 7-fold decreased moment developed during insertion of a 0.019 x 0.022-inch SS wire into a 0.022-inch slot and a 100 per cent increase in loss.