Friction â€“ Etiology & Management in SWA
INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com
One of the most common methods of translating a tooth orthodontically - sliding mechanics. Mesiodistal tooth movement - by guiding a tooth along a continuous arch wire with the use of an orthodontic bracket. Disadvantage - friction - resist the movement. www.indiandentalacademy.com
Friction is defined as a force that retards or resists the relative motion of two objects in contact, and its direction is tangential to the common boundary of the two surfaces in contact. Frictional force - 2 sliding surfaces Îą to the force - surfaces are pressed together. Ffr = u Ă— F. The value of u (the coefficient of friction) www.indiandentalacademy.com
ď ą Static Frictional forces - smallest force
needed to start a motion of solid surfaces with respect to each other. ď ą Kinetic frictional force - force needed to
resist the sliding motion of one solid object over another at a constant speed. www.indiandentalacademy.com
Several variables - directly or indirectly contribute - friction – b/w - bracket & wire; They are: Arch wire. Material. Cross-sectional shape/size. Surface texture. Stiffness.
Ligation of arch wire to bracket. Ligature wires. Elastomerics. Bracket.
Material. Slot width and depth. First order bend (in-out). Second order bend (angulation). Third order bend (torque).
Orthodontic appliance. Interbracket distance. Level of bracket slots between adjacent teeth. Forces applied for retraction. Intraoral variable.
Saliva. Plaque. Acquired pellicle. Corrosion.
Static frictional force = coefficient of static
friction x resultant normal force; Kinetic frictional force = coefficient of kinetic friction x resultant normal force. The coefficients of static and kinetic friction, generally having magnitudes between zero and one, depend upon -relative roughness of the
Prososki etal (AJO-1991) states that surface roughness influences friction most directly when dry, unlubricated sliding occurs or when only
meager lubrication is present. geometry of roughness, orientation of roughness features, and relative hardness of the two contacting surfaces. Friction tends to be highest for very rough or very smooth surfaces. www.indiandentalacademy.com
Sliding mechanics- biologic tissue response
and tooth movement - applied forces overcome the friction at the bracket-wire interface. High levels of bracket-wire friction may result in binding of the bracket little or no tooth
movement. binding of an anterior tooth under retraction loss of anchorage. The most desirable and ideal situation, - little or no friction - b/w bracket and wire. www.indiandentalacademy.com
Proffit etal considers frictional resistance in
orthodontic appliance to be multifactorial, It is α force with which the contacting
surfaces are pressed together Affected by the nature of the surface at the
interface Independent of the apparent area of contact www.indiandentalacademy.com
ďƒ˜ role of asperities (limited number of small spots at
the peak of surface irregularities) - contributing factor. ďƒ˜ These elevated areas carry the entire load between
two surfaces and may undergo plastic deformation with appropriate force. ďƒ˜ Applied load determines the true contact area. www.indiandentalacademy.com
coefficient of friction is
α shear strength of the junction &
1/ α yield strength of the material.
The interlocking of large and pointed asperities or
‘plowing’ of asperities into opposing surfaces - friction. www.indiandentalacademy.com
Arch wire: ď ą Material: Garner et al (AJO-1986) â€“ found significantly larger frictional force with beta-titanium and nitinol when compared with stainless steel. Differences in surface smoothness - account for the differences in friction.
SEM - SS
Beta - Titanium
Drescher et al - SEM study - between diverse wire materials. SS and Elgiloy - smooth surface texture, NiTi, TMA, - extensive surface roughness. Surface texture - friction magnitude in edgewise mechanics. Effective force has to increase by twofold (stainless steel) to sixfold (TMA) to overcome bracket-to-wire friction.
Tidy DC - fixed appliance in vitro to simulate
tooth movement in a previously aligned arch. Nitinol and TMA (beta-titanium) >frictional forces -2x & 5x – of SS. SS arch wires may be used in preference to nitinol or TMA arch wires to reduce the friction in sliding mechanics.
Kapila et al (AJO- 1990) greater magnitude and more frequent variation in frictional forces per unit distance of bracket travel with NiTi and ß-Ti wires than with SS or Co-Cr wires. Higher mean frictional forces - NiTi and ß-Ti wires. surface roughness of these alloys > SS or Co-Cr in SS brackets
Archwire Dimension: Tidy found that wire dimension and slot size had little effect on friction. Vaughan etal - The frictional forces with
rectangular wire than with round wire, and wire size frictional force.
Pizzoni - friction occurring in sliding mechanics
as being influenced by the bracket design, wire material and wire cross section. He concluded that round wires have lesser friction than rectangular wires, www.indiandentalacademy.com
Kapila et al(AJO 1990) -
Stainless steel, Co-Cr, and ß-Ti wires ↑ bracketwire friction with increase in wire size. Increase in size of NiTi wires - no significant effect on - friction between bracket and wire – in 0.018 inch narrow single br..
Surface properties: Ryan et al- (AJO 1997) - effects of ion
implantation on the rate of tooth movement. ion-implanted wires - > movement than their
untreated counterparts. The ion-implantation process - stress fatigue
and hardness of the material the friction. www.indiandentalacademy.com
ď ą Brackets: Drescher et al -study found narrow brackets to intensify friction by enhancing tipping movements. This implies a preference for the use of medium or wide brackets in arch-guided tooth movement, particularly in cases in which excessive mesiodistal tooth translation is required
Andreasen and Quevodo, - study to evaluate the
frictional forces in the 0.022 X 0.028” edgewise bracket system.
Multiple round and rectangular SS wires, brackets of three different widths, four bracket wire angulations.
both wet and dry conditions
Tipping the bracket &larger wires - friction, Bracket width & wet and dry conditions were
found to be insignificant
ďƒ˜ Tidy studied the effect of load, bracket width, slot
size, arch wire size, and material. ďƒ˜ The forces acting on the surface of the tooth root were simulated by a single equivalent force acting at the center of resistance of the root. The couple produced by the two-point contact with the arch wire counters the moment of this force about the arch wire.
The movable bracket was fitted with a 10 mm
power arm - weights - hung –force acting at the center of resistance of the tooth root. The length of the power arm - distance from the slot to the center of resistance of a typical canine tooth. The movable bracket was suspended from the load cell of the testing machine, while the baseplate moved downward with the crosshead on which it was mounted.
Friction α applied load and
1/ α bracket width. The friction was greatest for narrow brackets. Wide brackets and stainless steel arch wires may be
used in preference to nitinol or TMA arch wires to reduce the friction in sliding mechanics.
Kapila et al.- investigated – Frictional properties of Stainless steel (SS), cobalt-
chromium (Co-Cr), nickel-titanium (NiTi), and βtitanium (β -Ti) wires of several sizes were tested in narrow single (0.050-inch), medium twin (0.130inch) and wide twin (0.180-inch) stainless steel brackets in both 0.018 and 0.022-inch slots. frictional force - wider brackets Due to the higher force of ligation - the greater stretching of elastic ligatures on wider brackets. www.indiandentalacademy.com
Vaughan et al – Overall friction of sintered stainless steel brackets 40% to 45% < conventional cast stainless steel brackets. Pratten et al- frictional resistance of ceramic and SS brackets + SS and NiTi wire. Ceramic brackets frictional resistance than SS brackets when used in combination with either SS or NiTi arch wires.
Dickson etal- experimental polycrystalline
ceramic bracket with a SS insert and compared conventional & SS bracket. The exptl. bracket - frictional resistance and the ceramic bracket - 0˚ angulation. No sig. diff. between the two ceramic brackets at 10˚, frictional resistance than SS bracket. Stainless Steel insert slot - experimental bracket behave more like a stainless steel bracket rather than a conventional ceramic bracket. www.indiandentalacademy.com
Madhav.M and Jyothindra Kumar compared the
frictional properties and debonding characteristics of gold inserted slot Luxi™ bracket system and stainless steel inserted Clarity™ bracket system and compared them with stainless steel Gemini™ bracket. Metal inserted ceramic brackets - frictional properties as good as stainless steel brackets. Luxi™ - least kinetic friction Clarity™ bracket - highest value, of the three bracket systems evaluated for both 50 gms and 100 gms load. www.indiandentalacademy.com
Ligation. Edwards et al- ligation techniques - on the static
frictional resistance of stainless steel brackets and archwires - dry and wet conditions. No significant differences in frictional resistance
were found between conventionally tied elastomeric modules and stainless steel ligatures. Teflon-coated ligatures - lowest frictional forces. www.indiandentalacademy.com
David etal- ( AO – 95) - static frictional resistances
between Teflon- coated stainless steel and clear elastomeric ligatures –with
SS, polycrystalline ceramic and single crystal ceramic 0.022-inch slot brackets, SS and NiTi archwires, 0.018 inch and 0.016 × 0.022 inch.
Friction was measured in the dry state at bracket-
archwire angulations of 0, 5, 10, and 15 degrees. Teflon-coated SS ligatures - friction than elastomeric ligatures regardless of bracket type, archwire type, or bracket-archwire angulation. www.indiandentalacademy.com
ď ą Self ligation. SPEED ApplianceSpring-loaded, Precision, Edgewise, Energy, and Delivery, all of which describe features of the design.
Berger (AJO â€“ 1990) â†“ force - required to move rectangular steel or round braided arch wires - a standard distance self-ligation SPEED bracket < the elastomeric and the steel-tie ligated "A"-Company and American Orthodontics bracket systems.
Activa brackets -fully
programmed preadjusted brackets that were introduced in 1986- Irwin Pletcher. The arch wire -retained - resilient clip retaining groove gingival to the arch wire. The friction is < elastomeric rings and conventional brackets.
Shivapuja etal (AJO1994) –
Compared three self-ligating bracket systems to conventional SS brackets and ceramic brackets + polyurethane elastomeric and SS tie wire ligation. Self-ligating bracket systems - frictional
resistance, chairtime for arch wire removal and insertion.
Saliva. Stannard et al (AJO 1986)- compared the friction of wires under dry and wet conditions. artificial saliva - the coefficients of friction for stainless steel, beta-titanium, and nickel-titanium compared to dry conditions. Thought to occur from atomic attraction among ionic species. Water and other polar liquids - adhesion or attraction among polar materials and friction. www.indiandentalacademy.com
Baker et al – (AJO 1987)- of force necessary
to move the teeth in a saliva medium as compared to a dry medium. Kusy et al –(AO 1991) - coefficients of friction in the dry and wet (saliva) environment for stainless steel, cobalt-chromium, nickel titanium, and beta-titanium wires against either stainless steel or polycrystalline alumina brackets.
In the dry state - coefficients of friction -
stainless steel combinations beta-titanium wire combinations. In the wet state, stainless steel combinations - 0.05 over the dry state. beta titanium - 50% of the values in the dry state. Attributed to the adhesive and lubricious behavior of the saliva. www.indiandentalacademy.com
Tselepsis et al-(AJO 1994)- investigated frictional
resistance between brackets and arch wires for – arch wire, brackets, angulation, and lubrication. Lubrication significantly reduced the frictional
resistance (up to 60.5%) for both 0° and 10° bracket-to-arch wire angulation www.indiandentalacademy.com
Conclusion. Friction has been a problem for orthodontists
ever. Many efforts have been made to increase the efficiency of tooth moving mechanics by reducing or eliminating the friction, but to marginal success. Orthodontist’s dream would be to move the teeth in a frictionless system, effortlessly & efficiently. www.indiandentalacademy.com
Published on May 9, 2014
Published on May 9, 2014
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