Force System with Vertical V-Bends: A 3D In Vitro Assessment of Elastic and Rigid Rectangular Archwires
Summary
The method presented here is designed to construct and validate an in vitro 3D model capable of measuring the force system generated by different archwires with V-bends placed between two brackets. Additional objectives are to compare this force system with different types of archwires and to previous models.
Abstract
A proper understanding of the force system created by various orthodontic appliances can make treatment of patients efficient and predictable. Reducing the complicated multi-bracket appliances to a simple two-bracket system for the purpose of force system evaluation will be the first step in this direction. However, much of the orthodontic biomechanics in this regard is confined to 2D experimental studies, computer modeling/analysis or theoretical extrapolation of existing models. The objective of this protocol is to design, construct and validate an in vitro 3D model capable of measuring the forces and moments generated by an archwire with a V-bend placed between two brackets. Additional objectives are to compare the force system generated by different types of archwires among themselves and to previous models. For this purpose, a 2 x 4 appliance representing a molar and an incisor has been simulated. An orthodontic wire tester (OWT) is constructed consisting of two multi-axis force transducers or load cells (nanosensors) to which the orthodontic brackets are attached. The load cells are capable of measuring the force system in all the three planes of space. Two types of archwires, stainless-steel and beta-titanium of three different sizes (0.016 x 0.022 inch, 0.017 x 0.025 inch and 0.019 x 0.025 inch), are tested. Each wire receives a single vertical V-bend systematically placed at a specific position with a predefined angle. Similar V-bends are replicated on different archwires at 11 different locations between the molar and incisor attachments. This is the first time an attempt has been made in vitro to simulate an orthodontic appliance utilizing V-bends on different archwires.
Introduction
An important aspect of clinical orthodontic treatment is the knowledge of the force system produced by multibracket appliances. A clear understanding of the underlying biomechanical principles can help deliver predictable results and minimize potential side effects1. Recent years have seen a trend away from placing bends in archwires by building more activation with bracket position and design; however, comprehensive orthodontic treatment still requires placement of bends in archwires. Bends, when placed in different types and sizes of archwires, can create a wide variety of force systems suitable for different types of tooth movement. Although the force systems can become quite complex when multiple teeth are considered, a helpful starting point can involve a simple two-bracket system.
To date, V-bend mechanics have primarily been analyzed in the second order only, utilizing mathematical models1,2,3,4,5 and/or computer-based analysis/simulations6. This has yielded a basic understanding of the force system involved in the second order interaction of the arch wires with adjacent brackets (Figure 1). However, these methods impose certain boundary conditions in order to run simulations that might not hold true in actual clinical situations and deviations might occur. Recently, a new in vitro model involving force transducers was proposed for measuring three dimensional (3D) forces and moments created by evaluating not only second order archwire-bracket interactions but also in the third order7. However, the effect of different types of archwires on the force system at various bend positions along the incisor molar archwire span was not evaluated. Also, the study only involved evaluation of elastic orthodontic archwires, which are not the primary archwires on which tooth movement occurs. Therefore, the aim of this study was to evaluate the force system created by the placement of a V-bend at different locations in rectangular stainless steel and beta-titanium archwires in a 3D set up involving the molar and incisor brackets. Clinicians need to know the force system applied on the dentition when a specific combination of archwire bracket combination is used to fix a malocclusion.
The described technique has been developed to study the orthodontic force system in all the three planes of space, mimicking clinical reality. It is to be understood that it is extremely difficult to measure the force system clinically; therefore, such measurements have to be carried out in vitro. It is assumed that the force system created by a V-bend in the laboratory would be similar if replicated in the patient's mouth. A workflow was created to evaluate how the experimental set up has to be configured (Figure 2).
The orthodontic wire tester (OWT) is an innovative product developed by Division of Orthodontics in collaboration with the Bioengineering & Biodynamics Laboratory, UConn Health, Farmington, CT, USA (Figure 3). It is designed to accurately mimic the arrangement of the maxillary teeth within the mouth and some intra-oral conditions while providing measurements of the force system created in all the three planes of space. The major mechanical components of the OWT are a Data acquisition device (DAQ), nano Force/Torque Sensors, humidity sensors, temperature sensors, and a personal computer. The testing apparatus is placed in a glass enclosure having temperature/humidity controls. This allows for partial simulation of the intraoral environment. The DAQ serves as the interface for the three sensors: humidity sensor, force/moment sensor, thermistor and the testing apparatus with the sensors situated on a platform (Figure 3). These are linked to a software program. The software is a platform and a development environment for visual programming and is used to control different types of hardware. It was chosen to automate the orthodontic wire tester.
A series of aluminum pegs are arranged on the testing apparatus to represent the teeth of the maxillary dental arch. Two of the pegs representing the right central incisor and right first molar are connected to sensors/load cells (S1 and S2). A load cell is a mechanical device that can measure the forces and moments applied to it in all the three planes (x-y-z): Fx, Fy, and Fz; and Mx, My, and Mz. The pegs are systematically positioned to create a dental arch form. Each peg is separated from the other by a precisely recorded measurement that is calculated using average tooth widths as observed in patients undergoing orthodontic treatment. The shape chosen for the experiment is an 'ovoid' arch form created from a standardized template.
Protocol
Representative Results
Discussion
Orthodontic archwires have been studied in various ways8,9,10,11. They have also been evaluated for various mechanical properties, but they have seldom been analyzed for determining the force system they are going to create12,13,14,15. Three-point bending tests are po…
Divulgazioni
The authors have nothing to disclose.
Acknowledgements
The authors would like to acknowledge all colleagues who made this work possible, especially Drs. Aditya Chhibber and Ravindra Nanda. The authors would like to thank the Biodynamics & Bioengineering Lab at UCONN Health for the facilities provided during the development of this project.
Materials
| Force/Torque Sensors/Transducers | Nano17 F/T Sensors, ATI Industrial Automation, Apex, NC, USA | Part of the OWT | |
| CHS Series Humidity Sensor Units | TDK Corporation | Part of the OWT | |
| Temperature sensors | (Murata NTSDXH103FPB30 thermistor) Murata Manufacturing Co., Ltd | Part of the OWT | |
| LabVIEW 7.1. | Laboratory Virtual Instrumentation Engineering Workbench, Version 7.1 | Software Program | |
| Self-Ligating brackets | Empower Series, American Orthodontics. | Orthodontic Brackets | |
| Stainless steel archwires | Ultimate Wireforms, Inc. in Bristol, CT | Archwires | |
| Beta-Titanium Archwires | Ultimate Wireforms, Inc. in Bristol, CT | Archwires | |
| Data acquisition device (DAQ) | National Instruments (NI) USB 6210 | Part of the OWT | |
| Ortho Form III (Archform template) | 3M Oral Care, St. Paul, MN, USA | Ovoid arch form | |
| Weingart Plier | Hu-Friedy Mfg. Co., LLC Chicago, IL | Orthodontic Plier | |
| Light wire Plier | Hu-Friedy Mfg. Co., LLC Chicago, IL | Orthodontic Plier |
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