Evaluation of Polymerization Shrinkage, Microhardness, and Depth of Cure of Different Types of Bulk-Fill Composites

This study aimed to quantify polymerization shrinkage, microhardness, and depth of cure of different types of bulk-fill composites.

Six bulk-fill composites were tested: SonicFill 2 (SCF), VisCalor (VVC), Admira Fusion x-tra (AFX), Filtek Bulk Fill (FBF), Fill-Up! (FUP) and GrandioSO Heavy Flow (GHF). Sixty teeth were divided into twelve groups (n = 5) according to the composite and the irradiation level applied (standard or high). Each tooth was subjected to three scans using a micro-computed tomography device. The microhardness of the composite specimens was measured using a Vickers hardness tester. Depth of cure analysis was performed by measuring the microhardness of the composites at 0.5 mm intervals from the top surface to the bottom surface.

The highest volumetric shrinkage was found in the AFX group when polymerized at standard irradiance. After curing, the AFX group showed the highest void ratio. Increasing irradiance significantly increased volumetric shrinkage and void ratio only in the SCF group (p < 0.05). GHF achieved the maximum microhardness value of 80% at the lowest curing depth of 2.9 mm, while VVC, AFX, and SCF showed a curing depth of more than 5 mm (p < 0.05).

The high irradiance caused the most significant volumetric shrinkage and void ratio in the SCF group. Only the FUP and GHF groups were unable to achieve the desired curing depth of 4 mm.

Irradiance, material types, and thickness are important factors in the polymerization of composites.