Characterisation of Machinable Structural Polymers for Full-Coverage Posterior Crowns

Objectives:
To characterise the mechanical properties of Polyetherketoneketone (PEKK) & determine if these properties are compatible with its use as a permanent full coverage posterior crown.
Methods: Samples of Pekkton^® (Cendres Metaux, Biel/Bienne, Switzerland) were subjected to the following tests: Biaxial flexural strength (BFS) using the Piston on 3 balls (n=10); Vickers Hardness (VH) 5 indentations per sample with 10kg load & 20s dwell time (n=5); Hygroscopic Expansion Change (HEC) in artificial saliva over 68 days (n=5) & Structural Strength (SS) (n=20). The data was compared to that of Lava Ultimate^® (3M ESPE, Seefeld, Germany), Vita Enamic^® (Vita Zahnfabrik, Bad Säckingen, Germany) and IPS e.Max Press^® (Ivoclar Vivadent, Schaan, Liechtenstein). Mean values & standard deviations for BFS, VH, HEC & SS tests were calculated. Data was analysed & compared using one-way ANOVA with post-hoc Tukey’s test at a level of 5% significance to determine difference between groups using statistical software SPSS v.22 (IBM Corp., USA).
Results: BFS values ranked as follows: IPS e.Max Press^® (317MPa), Pekkton^® (227MPa), Lava Ultimate^® (145MPa) and Vita Enamic^® (137MPa).
VH values ranked as follows: IPS e.Max Press^® (5063.94MPa), Vita Enamic^® (1976MPa), Lava Ultimate^® (924MPa) and Pekkton^® demonstrated the lowest value (445.06MPa).
HEC values of polymeric materials ranked as follows: Pekkton^® showed the greatest dimensional stability in HEC testing (0.14% +/- 0.14%) followed by Vita Enamic^® (0.38% +/- 0.16%) and Lava Ultimate^® (1.06% +/- 0.17%).
SS values ranked as follows: Pekkton^® showed no signs of failure at maximum load (2037N), IPS e.Max Press^® (1497N), Lava Ultimate^® (1476N) and Vita Enamic^® (1127N).
Statistical analyses revealed significant differences between each group when comparing hardness (p<0.0001). Tukey’s test demonstrated significant differences when Vita Enamic^® was compared to Lava Ultimate^® (p<0.0001) & IPS e.Max Press^® (p<0.0001) and between Lava Ultimate and IPS e.Max Press (p<0.0001).
Conclusions: Pekkton^® performs in a comparable manner to the other commercially available polymeric materials tested. A full coverage monolithic Pekkton^® crown may possess adequate mechanical and physical properties for use in the posterior region of the mouth. To ascertain this, further in vitro and in vivo trials are necessary.