Spatial and temporal polymerisation shrinkage evaluation of dental composites using embedded chirped fibre Bragg...

Resin-based composite materials are widely used in restorative dentistry because of their favourable aesthetic properties and ease of handling. However, polymerisation shrinkage (PS) during curing remains a major challenge, where induced contraction strains and stresses lead to marginal gap formation, interfacial debonding, secondary caries, and restoration failure. Conventional techniques for evaluating PS primarily provide global measurements and do not enable continuous spatial and temporal monitoring of strains within the material during curing. This study presents a chirped fibre Bragg grating (CFBG) optical fibre sensor as a novel distributed sensing approach for real-time monitoring of polymerisation-induced strain in resin-based dental composites. A laboratory investigation was conducted on five commercially available resin composites: (i) everX Flow, (ii) Beautifil Flow Plus F03, (iii) Luna 2, (iv) Aura Bulk Fill, and (v) G-aenial Posterior. A CFBG sensor was embedded within each specimen to continuously monitor the spatial and temporal evolution of polymerisation-induced strain during light curing. The measurements exhibited comparable temporal and spatial trends across replicate specimens, with endpoint coefficients of variation ranging from 9.34% to 15.65% and a maximum individual deviation of 17% from the mean. Comparison with conventional tensometer measurements showed similar trends in polymerisation behaviour, providing qualitative support for the CFBG sensing approach. Further, the distributed strain measurements revealed spatial variations in polymerisation behaviour along the embedded sensing region that cannot be obtained using conventional global measurement techniques. These findings demonstrate the potential of CFBG sensors as an in-situ, distributed monitoring tool for investigating polymerisation behaviour in resin-based composites and provide new insight into the spatial evolution of curing that may support future materials research and optimisation of restorative procedures.