Influence of ceramic and stainless steel brackets on the notching of archwires during clinical treatment

Abstract

The surface topography of 100 clinically used archwires of stainless steel, beta-, or nickel-titanium were investigated that had contacted either ceramic or stainless steel brackets. One group consisted of two sets: 60 wires with no treatment records accessed to bias analyses, and 40 wires for which extensive clinical records were available, half of which were used with ceramic or stainless steel brackets. A control group consisted of two sets: 30 unused wires comprised of five round and rectangular wires of each alloy, and four wires that were ligated and immediately removed from patients' mouths. After ultrasonic cleaning, each wire was inspected under an optical and/or a scanning electron microscope. Notches were categorized with regard to frequency, patterns, and severity, and mapped as a function of wire aspect (lingual, facial, and occlusal/gingival) and anatomical regions (molar, premolar, canine, and incisor). From these data the average severity of notch patterns and a notching index were derived. Although no recognizable defect patterns were observed in the control group, seven basic patterns were recognized for each wire cross-sectional shape in the clinically used wires. These wires appeared most damaged on their lingual aspect and least damaged on their facial aspect. With regard to anatomical regions, notching was prevalent in the anterior regions and sparse in the molar regions. The notch activity and the severity were nearly three times greater from ceramic brackets than from stainless steel brackets. Over one-third of all notches documented in ceramic bracket cases had severity numbers of 3 and penetrated at least one-quarter of each wire's dimension, However, over two-thirds of all notches documented in stainless steel bracket cases had severity numbers of 1. From these tabulations a theory of notch formation was proposed in which vertical movement from tooth or wire during mastication caused fretting wear, and horizontal movement during orthodontic procedures such as space closure, tipping, or bodily movement caused sliding wear.

Evaluation of frictional forces between ceramic brackets and archwires of different alloys compared with metal brackets

“…1,25,26 The composition of the slot is perhaps the most important factor, since the coefficient of friction, which is specific for each pair of materials, depends on it. 6 The present study shows results similar to those of other investigators, who point to SS brackets as the ones producing the lowest frictional forces. 1,3,20,27 This is attributable to the physical properties of the metal, which provide a low coefficient of friction and allow a good surface finish.…”

“…2 Despite manufacturers' efforts to improve their qualities by incorporating metal slots, dulling the slot edges, and glazing their surfaces, the physical properties of ceramic brackets are still inferior. 3,4 Up to 60% of the force applied for dental movement can be lost as the result of ceramic bracket resistance to sliding, [5][6][7][8] leading to a longer treatment period.…”

“…9,11,12 When there is no clearance, and deflections and damage to the wire are introduced, resistance to sliding is the result of classic friction plus elastic deformation (binding) and plastic deformation (notching), 9,12 which is three times higher in ceramic brackets. 6 The aim of this study was to evaluate, in vitro, frictional forces produced by one metal bracket and three types of ceramic brackets: monocrystalline, polycrystalline, and polycrystalline with metal slots, combined with wires of different alloys.…”

Three-dimensional relationship between the critical contact angle and the torque angle

“…2 The angle at which the clearance between the archwire and the bracket first disappears is defined as the critical contact angle ( c ). 3 If the angulation between the archwire and the bracket slot is less than the critical contact angle in the passive configuration, only classic friction is important, because binding 4,5 and notching 6 are nonexistent (Fig 1, A). Several investigators have studied the causes and effects of resistance to sliding in the passive configuration as a function of wire alloy, bracket material, surface modification and roughness, and wet and dry states.…”

Frictional Properties of Self-Ligating Brackets and Low-Friction Ligatures

“…Friction is defined as "the force tangential to common boundary of two bodies in contact that resist the motion of one relative to the other. The amount of friction is proportional to the force with which the two surfaces are pressed together and dependent on the nature of the surfaces in contact (Articolo et al, 2000). The application of force has to overcome the friction to allow tooth movement.…”