OBJECTIVE:  Compare clinical performance of metal vs. ceramic frameworks and layered vs. pressed veneer ceramic.

METHODS:  293 three-unit posterior prostheses were placed by 116 dentists.  Methods: standardized preparations, resin modified glass ionomer cement, double blinded dentist-patient and commercial laboratory (18 labs, 2 selected by each system's company).  Graded in vivo:  margin fit, esthetics, retention, gingival health, endodontic need, caries.  Graded in vitro (dies; SEM images):  breaks, surface, wear on prosthesis and opposing dentition.  Statistics:  ANOVA and Tukey-Kramer multiple comparisons (p=£0.05).

RESULTS:  Year one 99% recall; year two 98%.  Frameworks- no metal or zirconia broken by 2 years; 6 alumina broken by 1 year (18%); 9 by 2 years (26%).  Alumina significantly worse both years (p=<0.0001).  Veneer Ceramics- pressed had significantly fewer defects at 1 & 2 years (both p=<0.0001). 

Defects (surface degradation, chips, breaks, cracks, delamination, broken framework) in systems tested:

						Cumulative Defects
System	Framework	Ceramic	Fabrication	n	Defective  Prostheses	Not Replaced		Replaced
						1-yr	2-yrs
CZR Press	Zirconia	CZR Press	pressed	33	2	4	NA*	0
IPS e.max	Zirconia	e.max ZirPress	pressed	33	7	10	NA*	1
Cercon	Zirconia	CeramcoPFZ	layered	32	18	41	60	2
Everest	Zirconia	InitialZR	layered	33	14	37	59	1
Lava	Zirconia	LavaCeram	layered	32	19	68	87	2
Wol-Ceram	Alumina	Cerabien	layered	21	10	22	30	4
Wol-Ceram Exp	Alumina	Cerabien	pressed	13	9	17	24	6
Captek	Metal (AuPtPd)	Creation	layered	32	4	13	20	3
Ceramco3    (control)	Metal   (65%Au, 0%Ag)	SoftWear Enamels	layered	32	9	13	23	0
Pulse interface	Metal   (65%Au, 0%Ag)	Pulse interface	pressed	32	4	2	4	0

                                                                                                                                * Placed 1 year later

CONCLUSION:  At two years, zirconia and metal frameworks performed equally well with no breaks, and alumina had 26% breaks, indicating high risk in posterior multi-unit restorations. Pressed veneer ceramics had significantly fewer defects than layered ceramics.

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