In-vitro investigation of frictional behavior and influence of normal forces on orthodontic materials in wet and dry states

Li, Haoyan (2021): In-vitro investigation of frictional behavior and influence of normal forces on orthodontic materials in wet and dry states. Dissertation, LMU München: Medizinische Fakultät

Abstract

This present in-vitro study investigates static and kinetic frictional forces between brackets and orthodontic archwires. To cover a wide field of parameters, which influence sliding, different environmental states and characteristics of orthodontic materials are taken into account. The study is divided into two parts: a) material study and b) simulation of the clinical situation. The material study focuses on the evaluation of the influence of the different environments as well as various orthodontic materials on frictional forces. The second part of the study targets at comparing the effect of various normal forces and ligation mechanisms on friction during the orthodontic tooth movement. The material study is conducted under (36±1) ℃ and a constant normal force (FN) of 1N in four different environmental states: 1) dry state; 2) whole human saliva; 3) deionized water and 4)artificial saliva. The fluids 2)-4) are applied to the bracket-wire combination at a rate of about 3ml/min. The study part concerning the simulation of the clinical situation is performed using artificial saliva at (36±1) ℃ and different normal forces (FN) of 1N, 1.5N, 2N, 2.5N. All other parameters are the same as in the material tests. The experimental setup consists of an Instron®4444 universal testing machine (Instron® Corp. Norwood, MA, USA), which is used to pull the archwire through the slot of the bracket and a FTD-Nano-17 - SI-25-0.25 six-axis force-torque sensor (ATI, Industrial Automation, Apex, NC, USA). This sensor records the forces opposing sliding, which are equivalent to the frictional forces. The results show that (human) saliva acts in most cases as adhesive and increases frictional forces. Active self-ligating brackets produce higher frictional forces compared to conventional and passive self-ligating brackets, especially when combined with large size wires. The measured values of stainless steel archwires present higher frictional forces compared to NiTi wires for all bracket types. The static and kinetic frictional forces increase as the archwire size and normal force increase. Thus, using the correct archwire size and moderately normal forces is important to generate appropriate friction forces during sliding therapy. Based on the results of the current in-vitro study, further investigations are needed to focus on, such as the comparison of different compositions of artificial saliva and the evaluation on which component in saliva affects friction. Also, other factors, which can have an effect on the resistance to sliding, like angulation, binding, various wire length and inter-bracket span, should be precisely compared and investigated.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Themengebiete: 600 Technik, Medizin, angewandte Wissenschaften ; 600 Technik, Medizin, angewandte Wissenschaften > 610 Medizin und Gesundheit
• Fakultäten: Medizinische Fakultät
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 13. August 2021
• 1. Bericht­erstatter:in: Wichelhaus, Andrea