Characterisation of machinable structural polymers in restorative dentistry

Objectives To characterise the mechanical properties of the machinable polymers Pekkton^® (Cendres-Meteaux, Biel/Bienne, Switzerland), Lava Ultimate^® (3MESPE, Seefeld, Germany), Vita Enamic^® (Ivoclar Vivadent, Schaan, Liechtenstein) and the ceramic IPS e.Max Press^® (Ivoclar Vivadent, Schaan, Liechtenstein). To determine the structural integrity of full coverage crowns fabricated from these materials. Methods The following tests were conducted: Biaxial flexural strength (BFS) using the piston on 3 balls jig (n=10); Vickers Hardness (VH) 10 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) of teeth analogues (n=20) restored with monolithic crowns from the four materials. Mean values and standard deviations for BFS, VH, HEC and SS tests were calculated and compared using one-way ANOVA with post-hoc Tukey's test at a level of 5% significance. Results BFS: IPS e.Max Press^® (317MPa±37MPa), Pekkton^® (227MPa±18MPa), Lava Ultimate^® (145MPa±18MPa) and Vita Enamic^® (137MPa±7MPa) with a significance between groups of p<0.0001. VH: IPS e.Max Press^® (5064MPa±131MPa), Vita Enamic^® (1976MPa±12MPa), Lava Ultimate^® (924MPa±27MPa) and Pekkton^® (445MPa±21MPa) with a significance between groups of p<0.0001. HEC (%vol change): Pekkton^® (0.14%±0.14%), Vita Enamic^® (0.38%±0.16%) and Lava Ultimate^® (1.06%±0.17%). SS for full-coverage crowns: Pekkton^® (2037N±49N no fracture), IPS e.Max Press^® (1497N±165N), Lava Ultimate^® (1476N±142N) and Vita Enamic^® (1127N±108N). Significance The properties investigated suggest that full coverage monolithic PEKK crowns possess adequate mechanical and physical properties for use in the posterior region of the mouth. These results must be considered alongside other data including clinical studies.