Strength Of Zirconia Dentures Veneered in Press Versus Layering Technique

Objectives: The aim of this in-vitro study was to determine the fracture strength of zirconia three-unit fixed partial dentures (FPDs) with pressed or layered veneering.

Methods: Human molars were inserted pairwise in PMMA resin to create three-unit FPD situations with a gap width of 10mm. Beforehand the roots of the teeth were covered with a 0.5mm thick polyether layer to simulate periodontal mobility. All FPD cores were made of a computer aided manufactured zirconia material (Cercon Base, DeguDent, G) and divided into four test series. In one series a modified occlusal supporting core design (circular embossment) was designed. The veneering was done in different press and layering techniques (see table). All FPDs were luted to the abutment teeth with an adhesive bonding system (Syntac classic/Variolink2: Ivoclar-Vivadent, FL). After thermal cycling and mechanical loading (TCML: 6000x5°C/55°C and 1.2x10⁶x50N) fracture strengths (UTM 1446; Zwick; v=1mm/min) were determined. Failure detection was set to a 10% loss of the maximum force. Statistical analysis was performed with the Mann-Whitney U-test (p=0.05).

Results:

Type of Veneering	Veneering Manufacturer	Median Fracture Force [N] (25%/75%)
Press on	Xpress Degudent, G	987 (783/1078)
Press over		1149 (896/1268)
Layering	Cercon Ceram S Degudent, G	1227 (1115/1467)
Layering Circular embossed core		1482 (879/2692)

FPDs, which were veneered in layering technique showed marginal higher median fracture resistance than FPD with press veneering. There was no statistically significant difference between the results.

Conclusion: There was no significant difference in the fracture resistance of three-unit FPDs, which were veneered in layering or press technique. An occlusal supporting core design allowed for the improvement of the fracture resistance.