Pre-Heating Effect on the Microhardness and Depth of Cure of Bulk-Fill Composite Resins

Abstract

OBJECTIVE: The aim of this study was to investigate the effect of preheating three bulk-fill and one conventional composite resin on the Vickers microhardness and depth of cure of these composites. METHODS: In this study, three bulk-fill composites-SDR Plus (SDR), Estelite BULK FILL Flow (EST), Admira® Fusion x-tra (AFX), and one conventional composite resin G-ænial POSTERIOR (GP) were used as the control group. The samples were obtained at room temperature (24°C) and at 55°C in T2 mode after being placed in a heating device for 10 minutes. The samples were divided into eight groups (n=10) according to the type of material and heating process that was utilized (preheated and nonheated). All samples were tested with a Vickers microhardness (VHN) tester on the bottom and top surfaces. The first measurements were obtained at baseline; the second set of measurements was performed after the samples were stored in distilled water at 37°C for 24 hours. The depth of cure was calculated using a bottom/top hardness ratio of measurements. Statistical analysis was performed utilizing the SPSS V23 and Shapiro-Wilk tests. Lastly, the Duncan test was used for multiple comparisons (p<0.05). RESULTS: While the VHN increased after the preheating procedure in bulk-fill composites, it decreased in GP. There was no difference between the baseline and the 24-hour VHN values in SDR and GP. After 24 hours, while the VHN of EST increased, the VHN of AFX decreased. There was no difference between the hardness ratios of the AFX and EST samples (p<0.001) and hardness ratios were greater than GP and SDR. CONCLUSION: When comparing the baseline and the 24-hour values, the VHN depended on the type of materials. Sufficient curing depth was obtained in all groups with a thickness of 2mm.

Evaluation of surface microhardness and gingival marginal adaptation of three different bulk‐fill flowable resin composites: A comparative study

“…7,16 The chemical composition of the matrix also play a role in enhancing the microhardness values according to previous study. 13 The composition of the resin matrix influences the viscosity of the composite. 13,17 Strong intramolecular hydrogen bonds between hydroxyl groups characterize Bis-GMA, which is the least flexible and most viscous of all dental resin monomers.…”

“…13 The composition of the resin matrix influences the viscosity of the composite. 13,17 Strong intramolecular hydrogen bonds between hydroxyl groups characterize Bis-GMA, which is the least flexible and most viscous of all dental resin monomers. Bis-GMA is a bulky and structurally rigid monomer that is very commonly incorporated into dental resin-composites and adhesives.…”

“…Bis-GMA is five times the molecular weight of methyl methacrylate and enhances toughness by extensive crosslinking. 13 UDMA is a viscous resin monomer composed of carbonyl groups and amine groups joined by hydrogen bonds. UDMA, on the other hand, has a much lower viscosity than Bis-GMA 17 as a result of poor hydrogen bonding.…”

“…These modifications make the placement of 4-5-mm-thick increments feasible. 6,10 In addition, some chemical modifications have been made in BF composites to reduce polymerization shrinkage (PS) stress, 11 such as increasing the molecular weight of the monomers in their contents, adding new stress-relieving monomers, [12][13][14][15] using of more reactive photoinitiators, and the incorporation of different types of fillers, such as prepolymer particles and fiberglass rod segments. 16 All these options are to diminish PS and minimize the negative effects of PS stress, which results in a combination of deep curing and adequate marginal adaptation.…”

“…39 Given that BF resin composites are distinguished by their enhanced depth of cure (DC). 4,13 DC of resin composites can be evaluated indirectly by surface microhardness. 16,17 The conversion degree and DC of the restorative material may have an impact on the formation of strains, which are likewise capable of compromising the integrity of the tooth-restoration interface.…”