Issue 10.4

Virtual Journal of Orthodontics

Virtual Journal of Orthodontics

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Please, if you find these pages useful, consider making a donation of €5, €20, €50, or whatever you can, to sustain Virtual Journal of Orthodontics.

Thanks,Gabriele FloriaVJO Founder

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Dir. Resp. Dr. Gabriele FloriaDDS Spec. Orthod.Viale Gramsci 73 50121 Firenze Italy fax +390553909014

All rights reserved. Iscrizione CCIAA n° 31515/98 © 1996 ISSN-1128-6547 NLM U. ID: 100963616 OCoLC: 40578647

The first on-line, paperless orthodontic journal since 1996

AUTHORS:

1. Dr. Anitha. A (B. D. S, M. D. S.) Ph. D Scholar and Assistant Pro-fessor Department of Orthodontics and Dentofacial Orthopae-dics. A. J. Institute of Dental Sciences, Rajiv Gandhi University of Health Sciences, Mangalore - 575004, Karnataka, India.

2. Dr. Akhter Husain (B. D. S, M. D. S., Diplomat, Indian Board of Orthodontics.) Ph. D Scholar, Professor and Head Department of Orthodontics and Dentofacial Orthopaedics. Yenepoya Dental College, Yenepoya University, Mangalore - 575018, Karnataka, India.

3. Dr. Raghuvir Ballambat (B. E, M. E, Ph. D) Director of Research Department of Mechanical Engineering Manipal Institute of Technology, Manipal University - 576104, Karnataka, India.

4. Dr. Raghavendra Kini (B. D. S, M. D. S) Senior Professor Depart-ment of Oral Medicine and Radiology, A. J. Institute of Dental Sciences, Rajiv Gandhi University of Health Sciences, Mangalo-re - 575004, Karnataka, India.

5. Dr. Nillan Shetty (B. D. S, M. D. S) Senior Professor Department of Orthodontics and Dentofacial Orthopaedics, A. J. Institute of Dental Sciences, Rajiv Gandhi University of Health Sciences, Mangalore - 575004, Karnataka, India.

6. Dr. Rohan Mascarenhas (B. D. S, M. D. S., Diplomat, Indian Board of Orthodontics.) Ph. D Scholar and Senior Professor. De-partment of Orthodontics and Dentofacial Orthopaedics. Yene-poya Dental College, Yenepoya University, Mangalore - 575018, Karnataka, India.

7. Dr. Rohan Rai (B. D. S, M. D. S) Professor and Head Depart-ment of Orthodontics and Dentofacial Orthopaedics, A. J. Institu-te of Dental Sciences, Rajiv Gandhi University of Health Scien-ces, Mangalore - 575004, Karnataka, India.

Address of Correspondence:

Dr. Anitha. A (B. D. S, M. D. S.) Ph. D Scholar and Assistant ProfessorDepartment of Orthodontics and Dento-facial Orthopaedics. A. J. Institute of Dental Sciences, Rajiv Gandhi Univer-sity of Health Sciences, Mangalore - 575004, Karnataka, India. Phone No: +91-7259191971; +91-8242458403; Email: anitha_4485@yahoo.in Fax: 0824-2224968; 0824-2225541

TRIBOLOGY: A NEW FRONTIER IN ORTHODONTICS

Abstract:

Tribology is the science and engineering of interacting surfaces in relative motion. It includes the study and application of principles of friction, lubrication and wear. Friction is a force that retards or re-sists the relative motion of two objects in contact. In Orthodontics, friction is a clini-cal challenge which is generated by an archwire and bracket and is influenced

by interaction of many variables like the bracket composition, bracket width, inter-bracket distance, slot size, arch wire, sec-ond order angulation, degree of torsion, ligation, and wet and dry environment. The ability to quantify and control friction will lead to less anchorage loss, more predictable tooth movement, and the use of ideal force levels to overcome fric-tion and optimize physiological tooth movement.

An understanding of this mechanism is im-perative as this insight enables the Ortho-dontist appropriate utilization of orthodon-tic biomechanical principles, as well as how it pertains to the orthodontic appli-ances.

Keywords: Tribology, Friction, Nanotribol-ogy, Biotribology, Archwire-Bracket inter-face.

Introduction:

The word “Tribology” is from the Greek word tribein, meaning to rub. Tribology is the science and engineering of interacting surfaces in relative motion. It includes the study and application of the principles of friction, lubrication and wear1,2 (Fig.1).

Figure 1: Components of Tribology

Leonardo da Vinci who is considered as the Father of Modern Tribology is credited with formulating some of the first funda-mentals of friction and also apparently sketched designs for anti-friction bearings.

Friction:

Friction is a force that retards or resists the relative motion of two objects in contact. Friction is the product of coefficient of fric-tion and normal force. As the two surfaces in contact slide against each other, two components of total force arises. The fric-tional force component (F) and the normal force (N) perpendicular to the contacting surface and to the frictional force compo-nent (Fig 2).3

Figure 2: Relationship between friction and contact sur-face area.3

Frictional force is directly proportional to the normal force such that, F = μN where,

- μ = Coefficient of friction i.e. sur-face roughness of material.

- N = Normal force i.e. the force acting perpendicular to the object.

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Lubrication:

Lubrication is the process or technique em-ployed to reduce wear of one or both sur-faces in close proximity and moving rela-tive to each other, by interposing a sub-stance called lubricant between the sur-faces to carry the load between the oppos-ing surfaces. The interposed lubricant film can be a solid (ex: graphite), a solid/liquid dispersion, a liquid/liquid dispersion (ex: grease) or exceptionally, gas.4

Wear:

Wear is erosion or sideways displacement of material from its "derivative" and origi-nal position on a solid surface performed by the action of another surface. Some commonly referred to wear mechanisms include:

- Adhesive wear

- Abrasive wear

- Surface fatigue

- Fretting wear

- Erosive wear

What is Nanotribology?

Nanotribology can be defined as the in-vestigations of interfacial processes, on scales ranging in the molecular and atomic scale, occurring during adhesion, friction, scratching, wear, nano-indentation, and thin-film lubrication at sliding surfaces.5 The need for Nanotribology can be summa-rized as follows:

- For advanced health care: to modify surfaces in order to create struc-tures that control interaction between mate-rials and biological systems.

- For energy conversion and stor-age: nanoscale carbide coatings, self-assembled layers for friction control, mate-rials performances at nano- and MEMS scale as a function of aging. For in-situ lu-brication study and control.

- Microcraft space exploration and Industrialization: to make self repairing ma-terials and self-replicating, biomemmetic materials and nanoscale devices which can sustain any need for movement of slid-ing surfaces for long periods under severe conditions.

What is Biotribology?

In the human body many tissues move in relation to one another, and the body has to allow for that movement or

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the tissue will split and break down. It is a multidisciplinary field of research involving biology, orthopaedics, biomaterials, sci-ence and tribology and thus a study of fric-tion, wear and lubrication of biological systems.6 Presently its significance lies in the following fields:

- Making hip replacements last.

- Maintaining the blood flow with the help of LVAD device.

- Ocular tribology

- Dental tribology

Role of Tribology in Orthodontics:

In Orthodontics, Tribology plays a very im-portant role in the performance, reliability, efficiency and optimization of the orthodon-tic systems. Studies of the myriad of pa-rameters, such as bracket composition, bracket width, interbracket distance, slot size, arch wire type, arch wire size, second order angulation, degree of torsion, liga-tion, and wet or dry environment, have helped our understanding by identifying trends or patterns of friction.7,8 The ortho-dontic literature notes numerous variables that affect the levels of friction at the bracket-archwire interface. In addition, ex-perimental protocol and design often af-

fect the outcome of in vitro frictional studies.9,10 The nature of friction in ortho-dontics is multi-factorial, derived from both a multitude of mechanical or biological fac-tors. Numerous variables have been as-sessed using a variety of model systems with nearly equally varying results.

Methods to evaluate the Tribological char-acteristics of the existing Orthodontic sys-tems:

- Pin on Disc Tribometer: It con-sists of a stationary "pin" under an applied load in contact with a rotating disc. The pin can have any shape to simulate a spe-cific contact, but spherical tips are often used to simplify the contact geometry.11

Coefficient of friction is determined by the ratio of the frictional force to the loading force on the pin. The pin on disc test has proved useful in providing a simple wear and friction test for low friction coatings.

- A Universal Friction Tester12 can also be used to draw conclusions on ideal requirements for improving the effective-ness of Orthodontic systems.

- Finite element analysis (FEA) is a computer based numerical technique for calculating the strength and behavior of materials. Until the early 1970’s FEA was limited to aeronautics, automotive, de-

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fense and nuclear research. However, the present day computers are now able to handle FEA for different applications. In Or-thodontics FEM13 has been used for study-ing stress distribution in the teeth, perio-dontal ligament and in the Orthodontic ap-pliances. Orthodontic bracket systems and appliances have been modeled and stud-ied to understand how the materials would act under various biological conditions.

- A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning it with a focused beam of electrons. The electrons interact with electrons in the sam-ple, producing various signals that can be detected and which contains information about the sample's surface topography and composition.14 This principle can be used to study the surface roughness and surface changes of the given materials.

Conclusion:

Friction is not likely to be eliminated from materials, thus the best remedy is to con-trol friction by achieving two clinical objec-tives: maximizing both the efficiency and the reproducibility of the orthodontic appli-ances. Efficiency refers to the fraction of force delivered with respect to the force ap-plied, while reproducibility refers to the abil-

ity of the clinician to activate the orthodon-tic appliance so that it behaves in a predict-able manner. Therefore, the clinician should be aware of the characteristics of the orthodontic appliance that contribute to friction during sliding mechanics and the extent of the amount of force expected to be lost to friction. This will help allow effi-cient reproducible results to be achieved.

References:

1. David T. Biographical Memoirs of Fellows of Royal Society, 2005;54:425.

2. Dowson. D. History of Tribology, Longman Group Ltd., London, 1979.

3. Emile R, Lorne K, Robert K. A fundamental review of variables associated with low velocity frictional dynamics. Semin Orthod, 2003:9(4):223-225.

4. Beinkowski, Keith. Coolants and Lubri-cants, The truth. Manufacturing Engineering. March, 2003.

5. Richie K, Sahil S. Friction on the nanoscale: new physical mechanisms. Materials Letters, 1999;38:360-66.

6. Anne J. Biotribology: The Tribology of living tissues. Lubrication and Technology, 2003:33-38.

7. Emile R. Friction: An overview. Semin Or-thod, 2003;9(4):217-90.

8. Kusy RP, Whitley JQ. Friction between differ-ent wire-bracket configurations and materials. Semin Orthod 1997;3:166-177.

9. Drescher D, Bourauel C, Schumacher HA. Frictional forces between bracket and arch wire. Am J Orthod Dentofac Orthop 1989;96:397-404.

10. Wichelhaus A, Geserick M, Hibst R, Sander FG. The effect of surface treatment and clinical use on

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friction in NiTi orthodontic wires. Dent Mater 2005;21:938-945.

11. Surowska B, Walczak M, Bienia J. Applica-tion of the sol-gel coatings in dental prosthetics. Achievements in Mechanical and Material Engineering (Conf. proceed.)2012.

12. Drescher D, Bourauel C, Schumacher HA. Frictional forces between bracket and arch wire. Am J Orthod Dentofac Orthop 1989;96:397-404.

13. Kojima Y, Fukui H. Numeric simulations of en-masse space closure with sliding mechanics. Am J of Dentofac Orthop 2010;138(6)702-04.

14. Doshi UH, Bhad-Patil WA. Static frictional force and surface roughness of various bracket and wire combinations. Am J of Dentofac Orthop 2011;139(1)74-9.

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