Saturday, February 09, 2013

In Vitro Comparison of Mechanical Properties and Degree of Cure of Bulk-Fill Composites

Journal of Esthetic and Restorative Dentistry

Volume 25, Issue 1, pages 72–76, February 2013

P. Czasch, N. Ilie Clinical Oral Investigations [Epub ahead of print]

Abstract
Objective
To compare mechanical properties and degree of conversion of two bulk-fill flowable composite resins (Venus Bulk Fill, Heraeus Kulzer; SureFil SDR Flow, Dentsply Caulk, Milford, DE, USA).
Materials and Methods
The degree of conversion, Vickers hardness, and indentation modulus of Venus Bulk Fill and SureFil SDR Flow (SDR) were measured as a function of depth and polymerization time. Flexural strength and modulus of elasticity also were evaluated. The degree of conversion of the composite resins was evaluated at 0.1-, 2-, 4-, and 6-mm (the latter in bulk or in 2-mm increments) depths when light-activated for 10, 20, or 40 seconds using an Elipar Freelight 2 (3M ESPE) light emitting (LED) curing device. The 6-mm bulk-filled specimens were used for determination of hardness and indentation modulus. Flexural strength and modulus of elasticity were determined in a three-point bending test. The size of the fillers in each composite resin was assessed with field emission scanning electron microscope (FE-SEM).
Results
Increased polymerization time increased the degree of conversion of 4- and 6-mm bulk increments for both composite resins. However, no improvement was noticed when the 6-mm bulk increments were polymerized for at least 20 seconds for Venus Bulk Fill and 40 seconds for SDR, compared to incrementally polymerized increments. When composite resins were compared, Venus Bulk Fill outperformed SDR, having a degree of conversion of approximately 5% higher for all irradiation times and depths. The most significant finding regarding hardness was that both composite resins reached a hardness value of 80% of the surface hardness at the depth of 6 mm. SDR had higher values for hardness and indentation modulus, and higher macromechanical properties values (flexural strength and modulus of elasticity) than Venus Bulk Fill. FE-SEM images showed SDR to have smaller particle fillers than Venus Bulk Fill.
Conclusions
SDR had better mechanical properties despite a lower degree of conversion than Venus Bulk Fill. Also, polymerization time of 20 seconds for 4-mm bulk placed increments of either material seems appropriate.
Commentary
Results of this study revealed better properties for SDR than for Venus Bulk Fill. That was true despite its lower degree of conversion. It is worth noting that the study was performed in a laboratory setting with the light-curing unit very close to the material. That is unlikely to occur clinically, which may result in different properties and degree of conversion. According to the results of the present study, recommended irradiation times should suffice in providing adequate properties to the materials tested. Relevant properties are not compromised if the bulk-fill flowable composite resins are light-activated for at least 20 seconds when used in 4-mm increments.

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