Purpose: to evaluate the effect of repeated heat pressing on fracture resistance and mode of failure analysis of new and reprocessed PEEK either partially or totally 3-unit FDPs.
Methods: 15 PEEK FDPs were manufactured and divided into 3 groups (n=5). Group I was pressed using new PEEK, Group II; 50% new PEEK and 50% reprocessed PEEK, and Group III; 100% reprocessed PEEK. The FDPs were vertically loaded till failure in a universal testing machine. Failed specimens were examined for mode of failure and microstructural analysis with SEM and XRD.
Results: There was a statistically significant difference between mean fracture resistance values of different PEEK conditions (P-value = 0.006, Effect size = 0.577). Pair-wise comparisons between conditions revealed no statistically significant difference between new (1719.6±315.7) and partially reprocessed PEEK (2010.4±444.4); both showed statistically significant higher mean fracture resistance than totally reprocessed PEEK (1097.2±319.5). Mode of failure analysis showed only bending in the new PEEK group bending (100%). While in the partially processed PEEK group 40% of the samples showed visible cracks at the connector area. Finally, in the totally processed PEEK group 80% showed complete fracture.
Conclusion: Totally reprocessed PEEK 3-unit FDPs had the lowest fracture resistance compared to new and partially reprocessed PEEK although all exceeded maximum occlusal forces recorded in the molar area. Incorporating reprocessed PEEK material in 3-unit FDPs increased brittleness and decreased their ability to deform and absorb stresses created during force application.