Biaxial Flexural Strength of L/C Composites as EOP Criteria

Objective: The purpose of this study is to see if the biaxial flexural strength test of a light-cured composite can be used to validate the EOP (Energy for Optimum Polymerization) data obtained previously via Differential Scanning Calorimetry (DSC).  Methods: Renew^® hybrid composite (Bisco), VIP visible light curing unit (Bisco) and an Instron Model 4465 were used.  Test specimens of 13mm diameter and 2mm thickness were light polymerized with a 13mm light probe at 1mm distance with VIP at 500mW/cm².  The composite was placed in an SS split mold and covered with Mylar at both sides and cured.  All specimens were stored in water @ 37^ºC for 24 or 72 hrs prior to testing. [Each specimen was placed on top of three steel balls forming a triangle on the biaxial assembly base.  A special biaxial shield was placed around the specimen and head to align the head properly.]  Results: (n=20) (Units in MPa)  Analysis of the data by one way ANOVA followed by a multiple comparison using a Student-Newman-Keuls test.

Conclusions: For both 24 and 72 hr. storage, biaxial flexural strength reaches a constant after about 10sec of irradiation.  Biaxial flexural strength can be used as an indication of cure for EOP determinations.