Bilayered composite restoration: the effect of layer thickness on fracture behavior

Figures & data

Table 1. The commercial composites used.

Material (code)	Manufacturer (Lot No.)	Composition
Essentia, universal shade (PFC)	GC Corp, Tokyo, Japan (1804122)	UDMA, BisEMA, BisGMA, TEGDMA, Bis-MEPP, Prepolymerized silica and barium glass 81 wt%
everX Flow, bulk shade (FRC)	GC Corp, Tokyo, Japan (1810282G)	Bis-EMA, TEGDMA, UDMA, Short glass fiber (200–300 µm and Ø7 μm), Barium glass 70 wt%

Bis-GMA: bisphenol-A-glycidyl dimethacrylate; TEGDMA: triethylene glycol dimethacrylate; UDMA: urethane dimethacrylate; Bis-MEPP: bis (p-methacryloxy (ethoxy)1-2 phenyl)-propane; Bis-EMA: ethoxylated bisphenol-A-dimethacrylate; wt%: weight percentage.

Figure 1. Representation of the process of scanning, designing and milling abutment models with different thicknesses used in this study.

Figure 2. Schematic drawing of a bilayered core-crown restoration and the compression load test setup.

Figure 3. Linear regression (n = 48) between different thicknesses of the overlaying PFC and measured load-bearing capacity (N) of tested restorations.

Figure 4. Percentage and photographs of various fracture patterns of the crown specimens. (A) Catastrophic crushing of particulate filler composite; (B) delamination of particulate filler composite from the fiber reinforced core; (C) cracking fracture in plain fiber reinforced composite.

Table 2. Mean fracture load values (N) and standard deviations (SD) of tested restorations with different surface PFC thicknesses.

Thickness of surface PFC
0 mm	3989.8 (334)^a
0.5 mm	3202.1 (335)^b
1 mm	2888.8 (348)^bc
1.5 mm	2696.5 (278)^c
2 mm	2032.2 (465)^d
Only PFC	1907.7 (179)^d

The same superscript letters represent non-statistically significant differences (p > .05) among the groups.