In vitro comparison of polymerisation kinetics and the micro-mechanical properties of low and high viscosity giomers and RBC materials.
OBJECTIVE
The study aims to characterise a low and high viscosity giomer bulk fill resin restorative with established low and high viscosity resin-based composite (RBC) restoratives at simulated clinical relevant specimen depths.


METHODS
The irradiance of a light curing unit (Bluephase 20i) was measured on a laboratory-grade spectrometer at distances up to 10mm from the light tip (in 1mm increments). Polymerization kinetics (real-time decrease of CC double bond and degree of cure, DC) and micro-mechanical properties (Vickers hardness/HV; Depth of cure/DOC; Indentation modulus/E) were assessed at varying specimen depths (0.1-6mm in 100μm steps for E, DOC and HV and 0.1, 2, 4 and 6mm for DC) for a 20s irradiation.


RESULTS
One and two-way ANOVA (α=0.05) were performed. The parameter material has a significant (p<0.001) effect on DC (ηP(2)=0.839), HV (ηP(2)=0.683), and E (ηP(2)=0.536), whereas the specimen depth influenced only DC (ηP(2)=0.584) but not HV (p=0.093) or E (p=0.133). The polymerisation kinetic could be described by an exponential sum function, distinguishing between the gel and the glass phase. The hardness drop out was lower than 20%, indicated a depth of cure of 6mm for all materials.


CONCLUSIONS
The low and high viscosity giomer bulk-fill restoratives fulfil the requirements of bulk-fill placement, since under the analysed irradiation conditions an adequate depth of cure of >4mm was identified. Variation of DC with specimen depth was low, with little variation at specimen depths of <4mm. The micro-mechanical properties of the giomer materials were higher compared with the conventional RBC materials.
Department of Operative/Restorative Dentistry, Periodontology and Pedodontics, Ludwig-Maximilians-University of Munich, Goethestr. 70, 80336 Munich, Germany. Electronic address: nilie@dent.med.uni-muenchen.de.
Nicoleta
N
Ilie
Materials Science Unit, Dublin Dental University Hospital, Trinity College Dublin, Dublin, Ireland.
Garry J P
GJ
Fleming
D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry* / Q000528:radiation effects*; D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects; D055117:Curing Lights, Dental; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects*; D055119:Elastic Modulus; D005898:Glass / Q000737:chemistry; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D058105:Polymerization / Q000528:radiation effects*; D014783:Viscosity
D003188:Composite Resins; D003764:Dental Materials; C090257:Foundation composite resin; D008689:Methacrylates; C501891:Tetric EvoCeram; D017438:Bisphenol A-Glycidyl Methacrylate
Bulk fill; Giomers; Hardness; Modulus of elasticity; Polymerisation kinetics; Resin based composite