Effect of LED curing on microleakage and microhardness of Class V resin-based composite restorations

Polymerisation shrinkage is a critical limitation of dental composites and may contribute to microleakage, postoperative pain, tooth fracture, and secondary caries. It has been shown that curing methods play a significant role in polymerisation shrinkage of light-cured dental resins. The purpose of this study was to investigate the effect of a LED curing light on microleakage as well as microhardness of a dental composite.

For the microleakage test 32 Class V cavities were prepared in human premolars, conditioned with 35% phosphoric acid and treated with the bonding agent Prime & Bond NT. They were then incrementally filled with the composite Esthet-X and randomly divided into two groups of 16 each. The first group was cured by means of a Spectrum 800 set at 500 mW/cm2 for 40 seconds and the second group with the GC E-Light in standard mode. The specimens were thermo-cycled in a 0.5% basic fuchsin solution, sectioned and evaluated for dye penetration. For the microhardness test two groups of 6 specimens each were exposed using either the LED- or the Halogen curing unit. Vickers microhardness tests were performed immediately after curing as well as 24 hours later, on the top, and at the bottom surface.

At the dentine/cementum interface, significantly less microleakage (p=0.004) was found when the restorations were cured with the LED-unit. At the enamel interface no significant difference (p=0.340) in microleakage was found between curing methods. Immediately after exposure significantly harder surfaces were found at the top (p<0.001) as well as at the bottom (p<0.001), using the halogen unit (p<0.05).

Although a reduction in microleakage could be demonstrated exposing the composite restoration to an LED LCU, an effective microhardness ratio was not achieved.