The influence of bracket type on the force delivery of Ni-Ti archwires

This study investigated the force delivery of an 0.014 inch nickel-titanium (Ni-Ti) archwire used in combination with a range of commercially available bracket systems, and using a model based on an 'ideal' mandibular archform. The model aimed to replicate the clinical interbracket span. The force delivery was measured at four different sites on an archwire for one batch of 10 nickel titanium archwires from one manufacturer, using one bracket/archwire combination. The four sites represented the lateral incisor, canine, second premolar and first molar positions. Force delivery was also measured for a further four different bracket designs at four different sites on the archwire using five fresh wires of the same archwire type. The wires were loaded with an M5 Nene Universal testing machine. The results demonstrate that the peak and plateau force, both of which are clinically important, are dependent on several factors of the archwire/bracket combination. The results showed that 20 per cent of the batch of 10 wires behaved differently by delivering a higher peak force. There was a statistically significant difference (P < 0.05) between the four bracket/archwire combinations for the peak forces delivered, but there was very little difference between the four bracket/archwire unloading force delivery values. The wires delivered a predictable force on the unloading curves, but self-ligating brackets may not develop sufficient strain within the wire to take full advantage of the superelastic effect of Ni-Ti wires.