INFLUENCE OF IRRADIATION EXPOSURE TIME ON THE DEPTH CURE OF RESTORATIVE RESIN COMPOSITE

A study was conducted to evaluate the degree of conversion by the hardness measurements of a commercial resin composite. The specimens were prepared according to ISO 4049 and photo-activated for 20s – 40s – 60s with  a light-emitting diodes (LEDs). To establish the optimal increment technique mono-layers 1 mm and 2 mm thick were tested. The ratio bottom-to-top was assessed for the mono-layers groups. Vickers hardness profiles were measured for mono-layer, bi-layer and tri-layer along the cross-section. The microhardness map showed difference in the mechanical characteristic of overlying resin confirmed by SEM images analysis of the fracture mechanics. Curing effectiveness of resin composite is not only dependent on the curing light unit but also from thickness of the resin composite and the duration of the exposure. The data suggest that an exposure time of 40 s or higher is required to provide composites with a homogeneous and high hardness, moreover, a 1 mm buildup multi-layering technique results in adequate curing of the bottom layer and better mechanical properties.

[1]  Alessandra Reis,et al.  Effect of exposure time on curing efficiency of polymerizing units equipped with light-emitting diodes. , 2007, Journal of oral science.

[2]  F. Rueggeberg,et al.  Correlation of bottom-to-top surface microhardness and conversion ratios for a variety of resin composite compositions. , 2004, Operative dentistry.

[3]  F. Eichmiller,et al.  Curing-light intensity and depth of cure of resin-based composites tested according to international standards. , 2002, Journal of the American Dental Association.

[4]  N. Sottos,et al.  Microcapsule induced toughening in a self-healing polymer composite , 2004 .

[5]  Olaf Althoff,et al.  Curing performance of a new-generation light-emitting diode dental curing unit. , 2004, Journal of the American Dental Association.

[6]  Jaime D N Filho,et al.  Degree of conversion and plasticization of dimethacrylate-based polymeric matrices: influence of light-curing mode. , 2008, Journal of oral science.

[7]  C. Borsellino,et al.  Effects of manufacturing procedure on unsymmetrical sandwich structures under static load conditions , 2012 .

[8]  I. E. Ruyter,et al.  Conversion in different depths of ultraviolet and visible light activated composite materials. , 1982, Acta odontologica Scandinavica.

[9]  J. W. Curtis,et al.  Factors affecting cure at depths within light-activated resin composites. , 1993, American journal of dentistry.

[10]  G. Matarrese,et al.  Performances evaluation of a bis-GMA resin based composite for dental restoration. , 2012 .

[11]  F. Rueggeberg,et al.  Polymerization depths of contemporary light-curing units using microhardness. , 2000, Journal of esthetic dentistry.

[12]  Jesús Rodríguez,et al.  Curing effectiveness of resin composites at different exposure times using LED and halogen units. , 2009, Medicina oral, patologia oral y cirugia bucal.

[13]  B. K. Moore,et al.  Depth of cure of dental resin composites: ISO 4049 depth and microhardness of types of materials and shades. , 2008, Operative dentistry.

[14]  N. Chikhi,et al.  Modification of epoxy resin with kaolin as a toughening agent , 2001 .

[15]  K. Jandt,et al.  Photoinitiator dependent composite depth of cure and Knoop hardness with halogen and LED light curing units. , 2003, Biomaterials.

[16]  Jung-Chieh Chen,et al.  Modification and compatibility of epoxy resin with hydroxyl-terminated or amine-terminated polyurethanes , 1995 .

[17]  A. Peutzfeldt,et al.  Effect of power density of curing unit, exposure duration, and light guide distance on composite depth of cure , 2005, Clinical Oral Investigations.