Bond strength of lithium disilicate to polyetheretherketone

Statement of problem. Polyetheretherketone (PEEK) is a high-performance polymer that is increasingly used in dentistry, for example, as a framework for implant-supported fixed complete dentures. One protocol calls for individual lithium disilicate crowns to be cemented on preparation-shaped retentive elements on the framework. However, the flexibility and strength of the bonded system is unclear. Purpose. The purpose of this in vitro study was to compare the flexibility and strength of bonded lithium disilicate to PEEK with the bond between lithium disilicate and zirconia. Material and methods. Fifteen PEEK (JUVORA Dental Disc), 15 zirconia (ArgenZ HT+), and 30 lithium disilicate (IPS e.max CAD) beam-shaped specimens (12.5x2x2 mm) were prepared. The ends of the PEEK beams were conditioned with 50-mu m aluminum oxide airborne-particle abrasion, followed by primer (visio.link) and light-activated polymerization. Zirconia specimens were prepared with airborne-particle abrasion and primer (Monobond Plus). Lithium disilicate specimens were etched with 4.5% hydrofluoric acid (IPS Ceramic Etching Gel) and primed (Monobond Plus). The lithium disilicate specimens were cemented (Multilink Automix) to the PEEK and zirconia specimens. Light- and chemical-activated polymerization were used. Monolithic specimens of PEEK and zirconia (25x2x2 mm) were also prepared. All specimens were stored overnight in distilled water and submitted to a 4-point bend test in a universal testing machine at 0.5 mm/min crosshead speed until fracture, and the flexural modulus and strength were calculated. Differences among groups were statistically tested by using 1-way analysis of variance followed by the Student-Newman-Keuls post hoc test (alpha=.05). Results. All bonded specimens fractured at their adhesive interface. Zirconia bonded to lithium disilicate specimens (29.7 +/- 8.8 MPa) were approximately 3 times stronger than PEEK bonded to lithium disilicate specimens (10.4 +/- 2.7 MPa) and approximately 12 times more rigid (78.5 +/- 6.7 GPa and 6.5 +/- 1.8 GPa, respectively). The flexure of monolithic PEEK was such that it did not fracture when loaded at 0.5 mm/min, while zirconia fractured at 413.9 +/- 38.5 MPa. Monolithic PEEK was approximately 37 times more flexible than monolithic zirconia (4.3 +/- 0.3 GPa and 157.2 +/- 7.2 GPa, respectively). All values were statistically significantly different except between the flexural moduli of monolithic PEEK and PEEK bonded to lithium disilicate. Conclusions. The bond strength between PEEK and lithium disilicate was significantly weaker than between zirconia and lithium disilicate. Monolithic zirconia was significantly stiffer than monolithic PEEK.