Programmed orthodontic debonding – Understanding the dynamics of the bracket-enamel interzone

• Applicant: Petra Julia Koch
• Subject Area: Biomaterials ; Dentistry, Oral Surgery
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 396127899

During orthodontic treatment with fixed multibracket appliances, the clinician temporarily bonds attachments to the enamel so that a deformed wire transfers directional forces along the tooth-root axis to the periodontal ligament, applying load into the surrounding bone. This then induces biological remodelling which is required to achieve orthodontic tooth movement. A requirement however, is that the bracket remains bonded on the enamel during the entire time of active treatment. The attachments are bonded with either a composite or a resin-modified glass-ionomer cement, creating a thin interzone between the bracket on the one side, and tooth enamel, on the other. This interzone needs to endure the orthodontically induced forces from the wire as well as intermittent additional high forces from mastication, while resisting thermal, chemical, and bacterial influences of the oral cavity. Hence, the bracket bonding material, requires on one the hand a temporarily high bond strength, and on the other hand should be easy and safe to remove at the end of an orthodontic treatment. Yet, once the teeth have reached the intended position, the multibracket appliance must be deconstructed, by debonding the brackets as gently as possible, minimizing unwanted enamel damage. Previous work has not yet systematically addressed microstructural changes taking place within different bracket-enamel interzones during the orthodontic treatment duration, which typically extends months to years. In this project, we explore a range of clinically-relevant orthodontic interzones and examine the effects of externally-applied stresses on the distributions and dynamics of mechanical deformations that affect the interzone functionality. We propose a series of ex vivo investigations of the bracket-enamel interzone using complementary high resolution imaging methods applied to a bovine-tooth model. We will combine structural, compositional, and mechanical investigational approaches to identify alterations that affect enamel and that can be attributed to orthodontic treatment. a. 2D visualisation by a variety of microscopic methods (light microscopy, polarized light microscopy, scanning electron microscopy) b. 3D visualization by micro- and nano-tomography, laboratory and synchrotron radiation micro-computed tomography (PCE-µCT) setups c. Mechanical characterization by loading the unit of tooth-bonding material-bracket in situ within both microCT methodologies described in b) above, and using digital volume correlation (DVC) as well as numerical approaches such as image-derived finite element analysis to measure and compute, respectively, the 3D deformation and strain fields within the tooth-bonding material-bracket complex. With the data accumulated, we will gain insights into the response of the interzone under load and during the debonding procedure. Our data will be used to predict component behaviour and can help optimize the clinical use of the bonding material.

• DFG Programme: Research Units
• Subproject of: FOR 2804: The Materials Science of Teeth in Function: Principles of Durable, Dynamic Dental Interphases
• International Connection: Israel, Jordan
• International Co-Applicants: Dr.-Ing. Gianluca Iori; Professor Dr. Ron Shahar