Fracture Resistance of Occlusal Veneers made from PMMA or Polymer-Infiltrated-Ceramic

Objectives: To evaluate the influence material type, bonding technique and thermomechanical fatigue on fracture resistance of minimal-invasive occlusal-veneer-restorations made from polymethylmethacylate (PMMA) or polymer-infiltrated ceramic.
Methods: Sixty-four extracted upper premolars were prepared within enamel (non-retentive preparation) and randomly distributed to receive occlusal-veneers made either from PMMA (Telio CAD, Ivoclar Vivadent) (Group T, n=32), or from polymer-infiltrated ceramic (VITA ENAMIC, VITA Zahnfabrik) (Group E, n=32). The thickness of the veneers was 0.5 mm/0.8 mm at the fissures/cusps, respectively. Each group was divided randomly into two subgroups (n=16) bonded either by self-etch technique (s) (Multilink Primer A&B+ Multilink Automix, Ivoclar Vivadent) or by phosphoric-acid etch-and-rinse technique (t) (Total Etch + Multilink Primer A&B + Multilink Automix; Ivoclar Vivadent). Half of each subgroup was aged through thermomechanical fatigue (1.2 million cycles, 10 kg, 2.4 Hz, 0.3 mm lateral movement, and 5^○C-55^○C thermocycling). Finally, all specimens were tested for fracture resistance using compressive load. Statistical analysis was made using t-tests and Mann-Whitney-U-tests.
Results: In groups Ts and Es only 50% and 37.5% specimens survived the thermomechanical fatigue, respectively, whereas, 100% survival was found in groups Tt and Et. The mean load-to-fracture values (in Newton) of non-aged (0) and aged (1) groups were: 898±164 (Ts0), 462±391 (Ts1), 767±131 (Es0), 350±351 (Es1), 975±208 (Tt0), 1233±223 (Tt1), 1019±156 (Et0), 1321± 269 (Et1). Thermomechanical fatigue had a statistically significant influence on the fracture resistance of each material. Etch-and-rinse technique significantly increased the fracture resistance of both restorative materials compared to self-etching. The type of restorative material did not influence the fracture resistance significantly.
Conclusions: Etch-and-rinse technique seems to be an important factor to insure the durability of both restorative materials, when bonded to enamel. Fracture resistance of provisional polymer restorations manufactured with CAD/CAM is promising and seems to permit clinical application as durable long-term provisional material.