THE EFFECT OF THE PHOTOPOLYMERIZATION METHOD ON THE QUALITY OF COMPOSITE RESIN SAMPLES

An optimal degree of conversion and minimal polymerization shrinkage a re generally antagonistic goals, as increased monomer conversion invar iably leads to elevated polymerization shrinkage values. However, both parameters are indispensable for an optimal resin composite restorati on. A number of approaches have been used to reduce the stress on the restoration cavity wall interface, such as dentine bonding agents to c ounteract polymerization shrinkage, stress-absorbing lining materials and low-intensity curing lights to control the now capacity of the mat erial during polymerization. However, the configuration of the cavity and cohesive fractures of the material and surrounding tooth tissues a re still a problem in day-to-day clinical practice. A new photopolymer ization light source, pulsed laser, ensures a higher degree of convers ion and lower polymerization shrinkage, and differentiates this techni que from standard polymerization methods and continuous-wave argon las er polymerization. The coherence and monochromacity of pulsed laser li ght set at 468 nm and the far greater intensity of laser nanopulses pr oduce a saturation effect in the depths of the composite, thus resulti ng in higher monomer conversion. The total amount of energy illuminati ng the sample surface, which is only one-fifth of that of conventional methods, and the cooling and relaxation of the material between nanop ulses may be responsible for the reduced net polymerization shrinkage.