Laminated ceramics with elastic interfaces: a mechanical advantage?

OBJECTIVES

As CAD/CAM technologies improve we question whether adhesive lamination of ceramic materials could offer mechanical advantages over monolithic structures and improve clinical outcomes. The aim was to identify whether an adhesive interface (a chemically cured resin-cement) would influence the biaxial flexure strength (BFS) and slow-crack growth in a machinable dental ceramic.

METHODS

Monolithic and adhesively laminated (with a chemically cured dimethacrylate resin-cement) feldspathic ceramic discs of identical dimensions were fabricated. BFS testing was performed on the Group A monolithic specimens (n = 20), on Group B laminated specimens with the adhesive interface positioned below the neutral bending axis (n = 20) and Group C laminated specimens with the adhesive interface positioned above the neutral bending axis (n = 20). To study subcritical crack growth additional laminated specimens received controlled indentations and were exposed to thermo-mechanical fatigue. BFS data was analysed using parametric statistics (α = 0.05). Fractographic analyses were qualitatively assessed.

RESULTS

No significant differences between the mean BFS data of Groups A and B were observed (p = 0.92) but the mean BFS of Group C was slightly reduced (p < 0.01). Lamination reduced the stiffness of the structure and fractographic analysis demonstrated that energy consuming crack deflection occurred. Thermo-mechanical fatigue caused subcritical extension of radial cracks associated with indentations adjacent to the adhesive interface. Crack growth was limited to parallel to the interface and was arrested or deflected in a direction normal to the interface.

CONCLUSIONS

Ceramic lamination increased the damage tolerance of the structure and could limit or arrest subcritical crack growth at regions near the 'interlayer'.

CLINICAL SIGNIFICANCE

Lamination of a dental ceramic with a polymeric 'interlayer' could offer toughening effects which could potentially delay or arrest sub-critical crack growth at regions near the interface and thereby improve restoration longevity.