Evaluation of bulk-fill composites in clinically relevant conditions of polymerisation

Abstract

Svrha rada bila je analizirati savojnu čvrstoću (FS) i modul elastičnosti (FM) bulk-fill kompozitnih materijala s naglaskom na klinički relevantne uvjete polimerizacije. Rezultati uzoraka debljine 4 mm uspoređeni su s rezultatima uzoraka debljine 2 mm pripremljenim prema ISO-standardu. Spomenuta svojstva ispitana su i u slučaju ubrzanog starenja materijala. Ispitano je pet bulk-fill kompozitnih materijala, od čega su dva posebno namijenjena za kratkotrajnu polimerizaciju visokim intenzitetom svjetlosti. Izrađeni su uzorci oblika kvadra u dimenzijama: 16 x 2 x 4 mm i 16 x 2 x 2 mm. Rabljena su tri polimerizacijska protokola: (I) ISO: 2-mm uzorci polimerizirani 6 x 20 s (1.000 mW/cm2, obostrano); (II) 10s: 4-mm uzorci polimerizirani 3 x 10 s (1.073 mW/cm2, jednostrano); (III) 3s: 4-mm uzorci polimerizirani 3 x 3 s (2.589 mW/cm2, jednostrano). Definirana su tri vremena mjerenja, odnosno mehanička su svojstva testirana nakon: jednog dana, termocikliranja (10.000 ciklusa) i termocikliranja (10.000 ciklusa) nakon kojeg je slijedilo 7 dana u apsolutnom alkoholu. FS izmjerena je testom naprezanja u tri točke (Inspekt Duo 5kN-M, Hegewald&Peschke, Nossen, Njemačka), dok je FM izračunat. FM bio je značajno viši kod uzoraka polimeriziranih prema ISO-protokolu nego kod uzoraka debljine 4 mm. Razlike vrijednosti savojne čvrstoće za sve polimerizacijske protokole izjednačene su nakon termocikliranja i uranjanja u apsolutni alkohol. Svi testirani materijali zadovoljili su zahtjev ISO 4049 savojne čvrstoće (80 MPa) za sve metode polimerizacije i sve uvjete starenja. Kratkotrajnom polimerizacijom postignute su gotovo optimalne vrijednosti savojne čvrstoće materijala kao one pripremljene ISO-protokolom.The purpose of this study was to analyse the flexural strength (FS) and flexural modulus (FM) of bulk-fill composite materials, with an emphasis on clinically relevant polymerisation conditions. Specimens 4-mm-thick were compared with 2-mm-thick specimens prepared according to the ISO standard. Said properties were also tested under the accelerated ageing conditions. Five bulk-fill composite materials were tested, two of which are specifically designed for rapid polymerisation with high light intensity. Cuboid-shaped specimens were made, measuring: 16 x 2 x 4 mm and 16 x 2 x 2 mm. Three polymerisation protocols were used: (I) ISO: 2-mm-thick specimens polymerised 6 x 20s (1,000 mW/cm2, double-sided); (II) 10s: 4-mm-thick specimens polymerised 3 x 10s (1,073 mW/cm2, one-sided); (III) 3s: 4-mm-thick specimens polymerised 3 x 3s (2,589 mW/cm2, one-sided). Three measurement times were defined, that is, the mechanical properties were tested after: one day; thermocycling (10,000 cycles); and thermocycling (10,000 cycles) followed by 7 days in absolute alcohol. The FS was measured by a three-point bending test (Inspekt Duo 5kN-M, Hegewald&Peschke, Nossen, Germany), while the FM was calculated. The FM was significantly higher in specimens polymerised according to the ISO protocol than in 4-mm-thick specimens. The differences in flexural strength values for all polymerisation protocols were equalised after thermocycling and immersion in absolute alcohol. All tested materials met the ISO 4049 flexural strength requirement (80 MPa) for all polymerisation methods and ageing conditions. Rapid polymerisation achieved almost optimal values of the FS of tested materials, similar to those prepared under the ISO protocol