Polymerisation of orthodontic resins with LED and halogen curing lights

Methods: Curing was monitored using ATR-FTIR spectrometry. 4 LED and 3 halogen lights were compared using 2 adhesives (Kurasper; Kuraray, Japan, Transbond; 3M ESPE, UK). 1610cm^-1 and 1640cm^-1 peak heights were compared to calculate degree of cure (DoC%). 90% of maximum DoC (after 360s curing) was assessed as an indicator of ‘acceptable' DoC. Light intensity was measured.

Results:: LED and halogen lights produced comparable DoC over similar curing times. Mean acceptable DoC (SD) was 46.8% (1.5) for Transbond and 56.5% (0.8) for Kurasper. For Transbond, all lights achieved DoC significantly lower than the acceptable DoC after 20s and 4 lights (3 LED, 1 halogen) achieved acceptable DoC after 100s (unpaired t-test, p<0.05). For Kurasper 2 lights (1 LED, 1 halogen) achieved acceptable DoC after 20s and all lights achieved or exceeded acceptable DoC after 100s. Light intensity (range halogen: 630-1097mW/cm² / LED: 740-1504mW/cm²) did not correlate with DoC at 20s or 100s (Product moment correlation coefficient, p>0.05).

Conclusions: 20s curing may be insufficient to ensure adequate DoC. LED and halogen lights perform comparatively. Kurasper may be preferable to Transbond where light access is limited. Light intensity may not be a good predictor of curing effectiveness.