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

The surface topography of 100 clinically used archwires of stainless steel, beta-, or nickel-titanium were investigated that had contacted either cera mic 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 ce ramic or stainless steel brackets. A control group consisted of two sets: 3 0 unused wires comprised of five round and rectangular wires of each alloy, and four wires that were ligated and immediately removed from patients' mo uths. After ultrasonic cleaning, each wire was inspected under an optical a nd/or a scanning electron microscope. Notches were categorized with regard to frequency, patterns, and severity, and mapped as a function of wire aspe ct (lingual, facial, and occlusal/gingival) and anatomical regions (molar, premolar, canine, and incisor). From these data the average severity of not ch patterns and a notching index were derived. Although no recognizable def ect 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 damag ed on their facial aspect. With regard to anatomical regions, notching was prevalent in the anterior regions and sparse in the molar regions. The notc h activity and the severity were nearly three times greater from ceramic br ackets than from stainless steel brackets. Over one-third of all notches do cumented 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 number s of 1. From these tabulations a theory of notch formation was proposed in which vertical movement from tooth or wire during mastication caused fretti ng wear, and horizontal movement during orthodontic procedures such as spac e closure, tipping, or bodily movement caused sliding wear.