Objectives: In this vitro study the effects of two different ceramic thicknesses, two different luting agents and two preparation designs on the marginal integrity of partial ceramic crowns (PCC) were investigated. Methods: Eighty extracted human molars were prepared according to the following preparation designs: A. Coverage of functional cusps/butt joint (n=40), B. Horizontal reduction of functional cusps (n=40). PCC (Vita MarkII, Cerec3 System) were fabricated and the ceramic thickness of the functional cusps was adjusted to (1): 0.5-1.0mm and (2): 1.5-2.0mm. PCC were adhesively luted to the cavities with either Excite/VariolinkII (VL) or RelyX Unicem (RX). The specimens were exposed to thermocycling and central mechanical loading (5000x8°C-55°C;30s/cycle;500000x72.5N;1.6Hz). Marginal quality was assessed by quantitative SEM analysis. Gap formation and marginal expansion  were determined along enamel, dentin, and ceramic interfaces separately, before (T1) and after (T2) TCML . Marginal degradation was defined as sum of gap formation and marginal expansion and used as test parameter. The data were statistically evaluated using the Mann Whitney U test, Wilcoxon Rank Sum test and error rates method (ERM) (p≤0.05).

Results: Marginal degradation, Median (25-75% percentiles)

Interface	TCML	Luting agent		Preparation design		Ceramic thickness
		VL	RX	A	B	1	2
Ceramic	T1	1.1(0-6.5)	0(0-0)	0(0-1.2)	0(0-3.3)	0(0-2.5)	0(0-2.9)
	T2	1.9(0-8.0)	0(0-0.5)	0(0-1.9)	0.9(0-4.8)	0(0-4.4)	0.5(0-3.2)
Enamel	T1	0(0-0)	0(0-0.8)	0(0-0)	0(0-1.3)	0(0-0)	0(0-1.3)
	T2	0(0-1.2)	0.5(0-2.6)	0(0-0.9)	0(0.2-3.6)	0(0-0.8)	0.4(0-3.9)
Dentin	T1	0(0-0.6)	0(0-0)	0(0-0)	0(0-0)	0(0-1.5)	0(0-0)
	T2	0(0-8.1)	0(0-0)	0(0-2.5)	0(0-2.1)	0(0-5.1)	0(0-0.3)

Marginal degradation using VL was significantly higher compared to RX, preparation design and ceramic thickness had no significant influence. Marginal degradation after TCML was significantly higher at the enamel interface compared to the dentin interface for VL, and vice versa for RX (ERM). Conclusions: PCC fabricated from industrially sintered feldspathic ceramics showed a low level of loss of marginal integrity. On this low level, the luting material has a higher impact on marginal adaptation than ceramic thickness or preparation design.