Fracture strength of veneered translucent zirconium dioxide crowns with different porcelain thicknesses

Figures & data

Figure 1. An illustration showing the CAD files of the different groups with overall crown thicknesses (core/porcelain). All crowns had an equal core thickness but different porcelain thicknesses. The gradual reduction in crown thicknesses resulted in a corresponding decrease in preparation depths without changing the outer dimensions (the X-imaginary line) of any of the crowns. The red dotted line denotes the core/porcelain interface.

Table 1. Porcelain layer thicknesses in the different groups.

Groups	Thickness of porcelain layer	Thickness of zirconium dioxide core	Overall thickness of crown(preparation depth)
Group 2.5	2.5 mm^c	0.5 mm	3.0 mm
Group 2.0	2.0 mm^b	0.5 mm	2.5 mm
Group 1.0	1.0 mm^a	0.5 mm	1.5 mm
Group 0.8	0.8 mm^b	0.5 mm	1.3 mm
Group 0.5	0.5 mm^c	0.5 mm	1.0 mm
Group 0.3	0.3 mm^c	0.5 mm	0.8 mm

^a Optimal thickness according to the manufacturer’s recommendations,

^b thickness within the recommendations and

^c thickness exceeding the recommendations.

Figure 2. A custom-made knife used for the porcelain build-up, with a zirconia core mounted on the abutment die.

Figure 3. An illustration of the test set-up used for both the cyclic preload and the load to fracture. NB: The crowns were submerged in water, and a plastic foil was used to spread the load evenly over the loaded surfaces.

Table 2. Load at fracture in Newton.

Groups	Group 2.5	Group 2.0	Group 1.0	Group 0.8	Group 0.5	Group 0.3
Specimen no.
1	882	946	1402	1277	1138	1042
2	1064	1009	1355	1512	1664^ϕ	1023^ϕ
3	803	870	1727	1313	1483^ϕ	1205^ϕ
4	701	750	1256	1154	1137	1226^ϕ
5	867	1203	1430	1050	1326	1154^ϕ
6	848	805	1773	1748^ϕ	1039	1397^ϕ
7	863	969	1485	1076	1273	1086
8	903	816	1828	1297	1066	1297^ϕ
9	843	910	2118^ϕ	1639	1475	1310^ϕ
10	732	822	1030	1063	1263	1276^ϕ
Mean* Std. deviation Fracture mode (complete/cohesive)	851^a 98 0/10	910^a 131 0/10	1540^b 318.9 1/9	1313^b,c 247 1/9	1286^b,c 203.7 2/8	1202^c 123.9 7/3

* Means with the same letters in superscript (denoted a, b, c) did not show any significant difference in fracture load (p > .05). ^ϕComplete fracture mode.

Figure 4. Example of the two fracture modes: (A) Complete fracture (B) Cohesive fracture.