Surface and bulk viscoelastic stability of solvent-stored bulk-fill resin-based composite

Halah Thanoon; Nikolaos Silikas; David C Watts

doi:10.1016/j.dental.2024.10.006

Surface and bulk viscoelastic stability of solvent-stored bulk-fill resin-based composite

Dent Mater. 2024 Oct 21:S0109-5641(24)00296-3. doi: 10.1016/j.dental.2024.10.006. Online ahead of print.

Authors

Halah Thanoon¹, Nikolaos Silikas², David C Watts³

Affiliations

¹ Division of Dentistry, School of Medical Sciences, University of Manchester, Manchester, UK; Department of Restorative Dentistry, College of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia. Electronic address: hithanoon@kau.edu.sa.
² Division of Dentistry, School of Medical Sciences, University of Manchester, Manchester, UK.
³ Division of Dentistry, School of Medical Sciences, University of Manchester, Manchester, UK; Photon Science Institute, University of Manchester, Manchester, UK. Electronic address: david.watts@manchester.ac.uk.

PMID: 39438173
DOI: 10.1016/j.dental.2024.10.006

Abstract

Objective: Investigate the effect of solvent-storage on surface hardness and bulk creep of fast photo-cured bulk-fill resin-based composite (RBC) compared to conventionally irradiated bulk-fill RBCs.

Methods: Three bulk-fill RBCs were studied: Tetric® PowerFill (fast photo-cured bulk-fill RBC) (TPF), Tetric EvoCeram® (EVO), and GrandioSO® x-tra (GSOx) (conventional). Disk-shaped specimens of clinically realistic thickness (4 mm) were prepared from each material for: Group A: surface measurements (18 mm diameter) and Group B: 4 mm diameter for bulk compressive creep measurements. Group A disks were light-cured from the upper 'occlusal' surface for either 3 s or 20 s according to the manufacturer's recommendation. Martens hardness (H_M) of both top and bottom surfaces of each specimen were measured. Group B: 4 × 4 mm cylindrical specimens were fully cured to measure bulk creep (C_B). A 20 MPa static compressive stress was applied for 2 h, followed by 2 h of unloading. Strain deformation was recorded continuously for 4 h. Both Martens and bulk creep studies were performed under the following storage conditions at 37 °C: (i) dry at 24 h post curing (baseline), and (ii) after 7 and 30 d of storage in two different media: distilled water (DW) and 75 % ethanol/water (75 % E/W).

Results: At baseline, H_M for all materials ranged from 587 to 439 N/mm² (top) and 398 to 342 N/mm² (bottom). After 30 d of solvent-storage, more pronounced H_M changes were observed, with the bottom surface being more affected. Normalised H_M for TPF decreased by 44 % after 30 d in 75 % E/W. Maximum creep strain ranged from 1.1 % to 2.1 % at baseline, and after 30 d in 75 % E/W this increased from 1.9 % to 2.9 %. Depending on the material and storage condition, the percentage creep strain recovery after 30 d ranged between 65.2 % and 80 %. Increased filler loading in the bulk-fill RBCs decreased the creep strain magnitude and increased the surface hardness.

Significance: Solvent storage decreased the Martens hardness of both upper and lower surfaces and increased the bulk creep characteristics of bulk-fill RBCs. Nevertheless, there was a similar relative stability in surface hardness and viscoelastic stability of fast-cured PowerFill compared to conventionally irradiated RBCs.

Keywords: Ageing; Bulk-fill; Creep and recovery; Martens hardness; Resin composite; Solvent-storage; Viscoelasticity.