A study of the Rapid Maxillary Expansion with the use of the finite element method

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Biomechanics and Remodelling for Design and Optimisation in Oral Prosthesis and Therapeutical Procedure

The purpose of dental prostheses is to restore the oral function for edentulous patients. Introducing any dental prosthesis into mouth will alter biomechanical status of the oral environment, consequently inducing bone remodelling. Despite the advantageous benefits brought by dental prostheses, the attendant clinical complications and challenges, such as pain, discomfort, tooth root resorption, and residual ridge reduction, remain to be addressed. This thesis aims to explore several different dental prostheses by understanding the biomechanics associated with the potential tissue responses and adaptation, and thereby applying the new knowledge gained from these studies to dental prosthetic design and optimisation. Within its biomechanics focus, this thesis is presented in three major clinical areas, namely prosthodontics, orthodontics and dental implantology. In prosthodontics, the oral mucosa plays a critical role in distributing occlusal forces a denture to the underlying bony structure, and its response is found in a complex, dynamic and nonlinear manner. It is discovered that interstitial fluid pressure in mocosa is the most important indicator to the potential resorption induced by prosthetic denture insertion, and based on this finding, patient-specific analysis is performed to investigate the effects caused by various types of dentures and prediction of the bone remodelling activities. In orthodontic treatments, a dynamic algorithm is developed to analyse and predict potential bone remodelling around the target tooth during orthodontic treatment, thereby providing a numerical approach for treatment planning. In dental implantology, a graded surface morphology of an implant is designed to improve osseointegration over that of a smooth uniform surface in both the short and long term. The graded surface can be optimised to achieve the best possible balance between the bone-implant contact and the peak Tresca stress for the specific clinical application need

Experimental and numerical analysis of the biomechanical characteristics of orthodontic mini-implants

Objective: Mini-implants are being utilised as anchorage units in orthodontic treatment. Nevertheless, there seem to be influencing factors that interfere with their clinical performance. The aim of this study was to experimentally and theoretically examine four different parameters, which may have an influence on the primary stability of orthodontic mini-implants. These were 1) implant type, 2) implant length, 3) implant diameter and 4) insertion angle. Material and Methods: A total of 90 mini-implants were inserted in fresh segments of bovine ribs. Implants were of two types, the Aarhus and the LOMAS mini-implant, of two lengths (7 mm and 9 mm) and of two diameters (1.5 mm and 2 mm, LOMAS only). A closed NiTi coil-spring was attached to each mini-screw. Half of the preparations were loaded with a low force of 0.5 N, the other half with a high force of 2.5 N. Mini-implant deflections during force application were non-invasively registered using a 3D laser-optical system. A subsequent finite element analysis of the applied force systems and the resulting mini-screw deflections was performed. Results: In the small force group, implant displacements showed no statistically significant difference according to the investigated parameters. In the high force group the 9mm mini-implants displaced significantly less (mean 11±8 μm) than the 7 mm long (mean 22±11 μm, p Conclusion: Implant length and implant diameter become statistically significant influencing parameters on implant stability only when a high force level is applied. Numerical results showed a good correlation to the experimental ones.Experimentelle und numerische Untersuchung des biomechanischen Verhaltens orthodontischer Mini-Implantate Seit einigen Jahren werden verstärkt orthodontische Mini-Schrauben oder Mini-Implantate zur Verankerungsverstärkung eingesetzt. Trotz zahlreicher Vorteile bestehen nach wie vor widersprüchliche Ansichten in Bezug auf Einflussfaktoren, die ihre klinischen Eigenschaften bestimmen. Ziel dieser Untersuchung war es, vier verschiedene Parameter experimentell und theoretisch zu untersuchen, die einen Einfluss auf die Stabilität der Verankerungsschrauben haben könnten. Diese waren: 1) Implantattyp, 2) Implantatlänge, 3) Implantatdurchmesser und 4) Positionierung. Zwei verschiedene Kräfte, eine geringe von 0,5 N und eine höhere von 2,5 N wurden durch eine Nickel-Titan-Zugfeder (NiTi) angelegt. Das Material bestand aus 90 Mini-Schrauben, die in frische Segmente von Rinderrippen eingesetzt wurden. Jeweils vierzig Aarhus- (American Orthodontics, Wisconsin, USA) und Lomas-Schrauben (Mondeal, Mühlheim, Deutschland) in zwei unterschiedlichen Längen (7 mm, 9 mm) und mit einem Durchmesser von 1,5 mm wurden untersucht. Die Lomas-Schrauben standen in der Länge 7 mm auch mit dem Durchmesser 2 mm zur Verfügung, um den Einfluss des Durchmessers untersuchen zu können. Die Mini-Schrauben wurden mit zwei Winkeln positioniert, jeweils eine Hälfte senkrecht, die andere Hälfte mit einer Angulation von 45° nach mesial. An den Präparaten wurden Kraft/Auslenkungs-Diagramme im Mobilitäts-Mess-System (MOMS) des Labors der Stiftungsprofessur für Oralmedizinische Technologie, mit Kräften bis 0,5 N und 2,5 N in distaler Richtung gemessen. Die NiTi-Feder wurde auf den Hals des Mini-Implantates an der einen Seite und auf dem mechanischen 3D Kraft/Drehmoment-Sensor an der anderen Seite befestigt. Die Kraftrichtung war parallel zur Knochenoberfläche und zur Horizontalen. Jede Einzelmessung wurde zweimal durchgeführt. Anschließend wurden die Präparate in einem µCT (µCT40, Scanco Medical) gescannt und die Geometrien wurden mit dem speziell für diese Aufgabe entwickelten Programm ADOR-3D rekonstruiert. Die so entwickelten Finite-Elemente(FE)-Modelle wurden im FE-System MSC.Marc/Mentat2007r1 berechnet. Die Statistik umfasste eine univariante Varianzanalyse (three-way ANOVA) zur Analyse des Einflusses der Parameter Schraubentyp, Länge, Positionierung und Kraft, einen Studentschen t-test für die Auswertung des Durchmessers und einen Altman-Bland-Test für den Vergleich der beiden Messdurchgänge und den Vergleich zwischen den experimentellen und numerischen Ergebnissen. Zusätzlich wurde ein Youden-Plot für den Vergleich der experimentellen und numerischen Ergebnisse angefertigt. Die Ergebnisse zeigten, dass sich das biomechanische Verhalten der Mini-Schrauben zwischen den zwei Kraftgruppen unterschied. Wenn eine geringe Kraft von 0,5 N angewendet wurde, wurden Auslenkungen des Schraubenkopfes von 4 bis 9 µm in Kraftrichtung gemessen, die Rotationen lagen bei 0,006° bis 0,025°. Die Ergebnisse schwankten zwischen den verschiedenen Mini-Implantaten, die Varianzanalyse zeigte jedoch keine statistisch signifikanten Unterschiede in den Auslenkungen. Bei der Anwendung der höheren Kraft von 2,5 N konnte festgestellt werden, dass die 9 mm langen Mini-Implantate eine statistisch signifikant kleinere Auslenkung (Mittelwert 10±7 μm) als die 7mm langen (Mittelwert 22±11 μm, p Zusammenfassend kann festgestellt werden, dass in klinischen Situationen, bei denen die angewandte Kraft kleiner als 1 N ist, wie zum Beispiel bei Zahnintrusionen oder indirekter Verankerung, Mini-Implantate mit kleineren Dimensionen zuverlässig eingesetzt werden können. Bei Einsatz höherer Kräfte sind entsprechende Mini-Implantat-Dimensionen entscheidend für die Primärstabilität. Jedoch sind beim klinischen Einsatz sowohl der Abstand der Zahnwurzeln als auch die anatomische Lage sorgfältig zu bedenken

Effect of chin-cup treatment on the temporomandibular joint: a systematic review

SummaryAim: To systematically search the literature and assess the available evidence for the influence of chin-cup therapy on the temporomandibular joint regarding morphological adaptations and appearance of temporomandibular disorders (TMD). Materials and methods: Electronic database searches of published and unpublished literature were performed. The following electronic databases with no language and publication date restrictions were searched: MEDLINE (via Ovid and PubMed), EMBASE (via Ovid), the Cochrane Oral Health Group's Trials Register, and CENTRAL. Unpublished literature was searched on ClinicalTrials.gov, the National Research Register, and Pro-Quest Dissertation Abstracts and Thesis database. The reference lists of all eligible studies were checked for additional studies. Two review authors performed data extraction independently and in duplicate using data collection forms. Disagreements were resolved by discussion or the involvement of an arbiter. Results: From the 209 articles identified, 55 papers were considered eligible for inclusion in the review. Following the full text reading stage, 12 studies qualified for the final review analysis. No randomized clinical trial was identified. Eight of the included studies were of prospective and four of retrospective design. All studies were assessed for their quality and graded eventually from low to medium level of evidence. Based on the reported evidence, chin-cup therapy affects the condylar growth pattern, even though two studies reported no significance changes in disc position and arthrosis configuration. Concerning the incidence of TMD, it can be concluded from the available evidence that chin-cup therapy constitutes no risk factor for TMD. Conclusion: Based on the available evidence, chin-cup therapy for Class III orthodontic anomaly seems to induce craniofacial adaptations. Nevertheless, there are insufficient or low-quality data in the orthodontic literature to allow the formulation of clear statements regarding the influence of chin-cup treatment on the temporomandibular join

Distraction Osteogenesis in the Treatment of Maxillary Hypoplasia

The aim of this chapter is to review literature reporting on the use of internal distraction osteogenesis and rigid external distraction osteogenesis and to determine the biomechanical effects of internal distractors in the treatment of maxillary hypoplasia, especially in patients with cleft lip and palate (CLP), and compare the results with non-cleft patient. The standard osteotomy used for distraction osteogenesis of the hypoplastic maxilla is LeFort I. An advancement of more than 10 mm in patients with no cleft and 6 mm in patients with CLP is beyond the limit of LeFort I osteotomy, and in such cases distraction osteogenesis for advancement of the maxilla can be used. Distraction osteogenesis (DO) is a biological process involving the formation of new bone between viable bone segments that are gradually separated by incremental traction. The external and internal usage of distraction osteogenesis in the treatment of maxillary hypoplasia in patients with cleft lip and palate is a reliable, reproducible and stable alternative method to conventional one-step LeFort I advancement techniques. Biomechanical evaluation of internal maxillary distraction osteogenesis produces mathematical results to help the surgeon and the orthodontist to understand better the therapeutic effects on the maxillofacial bones and sutures of the craniofacial system

A COMPARATIVE HISTOMORPHOLOGICAL AND MICRO CT STUDY OF THE PRIMARY STABILITY AND THE OSSEOINTEGRATION OF THE SYDNEY MINI-SCREW: AN ANIMAL STUDY USING NEW ZEALAND RABBITS

Introduction: Failure rate of orthodontic miniscrews (MSs) is 7-50%. To address this problem and to promote primary stability of the miniscrew (MS), we recently designed and developed The Sydney Mini Screw (SMS, Patent number: PCT2009014) which can be used with injectable bone graft substitutes (iBGS). The aim of this study was to assess in vivo dispersion of bone graft substitutes (BGS) and the integration of the SMS to the cortical and trabecular bone using New Zealand femur and tibia rabbit model. Method: Twenty-four MSs were randomly placed in each proximal tibia and femur of 6 New Zealand rabbits with an open surgery process. Aarhus MS was used as a control and the effect of injection of BGS was studied by implanting SMS with and without BGS injection. The dispersion and integration of the MS were studied by using micro CT (μCT) and histochemical analysis at two time points, 0 day and 8 weeks post-implantation. Results: BGS were successfully injected to the SMS and thereafter hardened in situ to fill the bone void. After 8 weeks, μCT results revealed that the iBGS were resorbed and bone tissue was formed around the MS and within its lateral exit holes. The osteointegration of the SMS samples showed similar histologic characteristics to that of Arhus controls, and initial drilling for injection of bone cements into SMS did not seem to affect adjacent bone quality. Conclusion: Results of this pilot animal study showed the high potential of SMS and the developed technique to promote the primary stability of MS. Keywords: Primary stability; orthodontic miniscrew; injectable bone graft substitute

Effects of different types of maxillary protraction on maxilla with finite element analysis

Objective: To compare two different skeletal anchorage methods with finite element analysis in the treatment of Class III patients with maxillary retrognathia. Material and Methods: Two different treatment scenarios were performed on skull model obtained from computerized tomography images of skeletal Class III patients with maxillary retrognathia and finite element analysis was performed. In the first group; mini plates were simulated on infra zygomatic crest. A unilateral 500 g protraction force was applied to the face-mask. In the second group; mini plates were simulated in infrazygomatic crest and mandibular symphysis. Then, 500g protraction force was applied with Class III elastic between the miniplates. Von Misses stresses and displacement values were evaluated comparatively. Results: In Class III elastic group, maximum Von Misses stress occurred around infra zygomatic crest and symphysis anchored with 0.078 MPa. The maxillary posterior region and paranasal regions were the areas showing the highest Von Misses tension after infra zygomatic crest and symphysis. In the face-mask group, the most common site of Von Misses stress in nasomaxillary complex and alveolar structures were infra zygomatic area where plaques were applied, followed by pterygomaxillary suture. Tensile forces are reduced especially in these two areas by spreading to surrounding structures. Conclusion: In both methods, it was determined that the amount of force transmitted to circumaxillary sutures was sufficient to induce the formation of osteogenesis in these regions.No sponso

Effective En-Masse retraction of maxillary dentition with tuberosity mini-implant anchorage: A finite element analysis

In the end of 90’s the adoption of mini-implants as anchorage allowed a paradigm change influencing even the way of thinking orthodontic mechanics. Currently, mini-screw implants or temporary anchorage devices TADs are considered versatile as it can be used clinically as an absolute source of anchorage. Recently, there has been revitalization for the en masse retraction of maxillary dentition which has various advantages over molar distalization followed by anterior retraction. Thus the entire maxillary dentition when distalized as a single unit with mini-implants as a source of anchorage using sliding mechanics would serve as a viable option in overcoming the adverse effects of distalizing appliances and provides better patient comfort. Since Modern medical imaging, modeling, and finite element (FE) analysis solutions can provide powerful tools for optimizing 3- dimensional morphology from radiographic scans and determining stress and deflection distributions for complex anatomic geometries is possible, thus the reactions of teeth and their supporting tissues on application of orthodontic forces would warrant to predict the clinical situation efficiently. Therefore the aim of the present study was to investigate effectiveness of 19 x 25-in stainless steel archwire with retraction hooks of various heights placed in a 0.022 x 0.028-in slot for en-masse retraction of maxillary dentition using tuberosity implants by finite element method

Three Dimensional Evaluation of Stress Distribution and Displacement by Miniscrew Implants Assisted Palatal Expander: A Finite Element study

AIM OF THE STUDY: The aim of the present study is to assess the stress distribution and displacement of the maxilla and teeth in an average and constricted arch width models according to different designs of RME using miniscrew implants on a 3D FE model of the skull. MATERIALS AND METHODS: Two groups of FEM models, Group-A (average maxillary arch) and Group-B (constricted maxillary arch) were constructed. The maxilla including teeth and alveolar bone were sectioned into 1mm tetrahedrons and the skull sectioned into 5mm tetrahedrons. For the FE modelling a computed tomography scan of a skull is converted to STL file using MIMICS followed by meshing the geometric model. The final constructed FE model is then imported in to ANSYS version 15.0 software. There were 4 designs of rapid maxillary expanders. In type 1- four miniscrew implants were placed 3mm lateral to mid-palatal suture. In type 2-four mini screw implants were placed beneath the alveolar ridge at the palatal slope and connected to the expander through an acrylic resin cover. In type 3-two miniscrew implants placed 3mm lateral to mid-palatal suture between canine and first premolars and connected to the expander with conventional hyrax arms soldered on the first molar (Hybrid design). In type 4-Conventional tooth borne appliance assisted by perforations using miniscrew implants in mid-palatal suture at 3 points from the incisive papilla to the last molar. Expanders were activated transversely for 0.5 mm and force of 45 newtons (N) were applied to achieve sufficient separation of two halves of the maxillary segments. Geometric nonlinear theory was applied to evaluate Von-Mises stress distribution and displacement. RESULTS: More stresses were concentrated around the miniscrew implants in type1, 3 and 2. The mean stress distribution and depth of penetration were high in the type1. Type 2 had the least stress distribution around the anchorage and showed alveolar expansion without buccal inclination. The rotation of dentoalveolar unit was larger in type 4 and type3. Type 1 and type 2 exhibited downward displacement. Type 4 and type 3 exhibited downward and backward displacement. CONCLUSIONS: Miniscrew assisted RME showed more skeletal contribution in the net expansion result compared with conventional RME. Miniscrew assisted RME has the higher probability to elucidate the sutural response. Therefore, Customizing RME design (HYBRID) for every individual patients helps us to achieve the desired results with minimum relapse. Keywords: Rapid Maxillary Expansion, Bone-borne rapid maxillary expanders, tooth-borne rapid maxillary expanders, Finite Element Modelling. AIM OF THE STUDY: The aim of the present study is to assess the stress distribution and displacement of the maxilla and teeth in an average and constricted arch width models according to different designs of RME using miniscrew implants on a 3D FE model of the skull. MATERIALS AND METHODS: Two groups of FEM models, Group-A (average maxillary arch) and Group-B (constricted maxillary arch) were constructed. The maxilla including teeth and alveolar bone were sectioned into 1mm tetrahedrons and the skull sectioned into 5mm tetrahedrons. For the FE modelling a computed tomography scan of a skull is converted to STL file using MIMICS followed by meshing the geometric model. The final constructed FE model is then imported in to ANSYS version 15.0 software. There were 4 designs of rapid maxillary expanders. In type 1- four miniscrew implants were placed 3mm lateral to mid-palatal suture. In type 2-four mini screw implants were placed beneath the alveolar ridge at the palatal slope and connected to the expander through an acrylic resin cover. In type 3-two miniscrew implants placed 3mm lateral to mid-palatal suture between canine and first premolars and connected to the expander with conventional hyrax arms soldered on the first molar (Hybrid design). In type 4-Conventional tooth borne appliance assisted by perforations using miniscrew implants in mid-palatal suture at 3 points from the incisive papilla to the last molar. Expanders were activated transversely for 0.5 mm and force of 45 newtons (N) were applied to achieve sufficient separation of two halves of the maxillary segments. Geometric nonlinear theory was applied to evaluate Von-Mises stress distribution and displacement. RESULTS: More stresses were concentrated around the miniscrew implants in type1, 3 and 2. The mean stress distribution and depth of penetration were high in the type1. Type 2 had the least stress distribution around the anchorage and showed alveolar expansion without buccal inclination. The rotation of dentoalveolar unit was larger in type 4 and type3. Type 1 and type 2 exhibited downward displacement. Type 4 and type 3 exhibited downward and backward displacement. CONCLUSIONS: Miniscrew assisted RME showed more skeletal contribution in the net expansion result compared with conventional RME. Miniscrew assisted RME has the higher probability to elucidate the sutural response. Therefore, Customizing RME design (HYBRID) for every individual patients helps us to achieve the desired results with minimum relapse