Simple and Low-Cost Thermal Treatments on Direct Resin Composites for Indirect Use.

Guillermo Grazioli,Cesar Henrique Zanchi,Rafael Ratto De Moraes,Alejandro Francia,Carlos Enrique Cuevas-Suárez

doi:10.1590/0103-6440201902473

Guillermo Grazioli, Cesar Henrique Zanchi + Show 3 more

Open Access

https://doi.org/10.1590/0103-6440201902473

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Abstract

The aim of this study was to evaluate the influence of three low-cost additional thermal treatments, available in the dental office, on the mechanical, chemical and optical properties of a light-cured resin composite indicated for direct restorations but used as indirect restorative. The direct resin composite TPH3 (Dentsply) was light-polymerized using a light-emitting diode curing unit and submitted to three experimental additional thermal treatments: dry heat at 170 °C for 5 min, autoclave at 121 °C for 6 min, or microwave oven at 450 W for 3 min. The resin composite without any thermal treatment was used as negative control group. An indirect resin composite (Vita CM LC, Vita Zahnfabrik) was tested as a reference. Flexural strength, elastic modulus, microhardness, degree of C=C conversion, roughness before and after simulated toothbrush abrasion, translucency parameter and color difference (ΔE00) were evaluated. Data were analyzed at α=0.05. The indirect resin composite presented lower C=C conversion and mechanical performance. The flexural strength was significantly higher in the dry oven group compared with the control. The roughness was not different among groups before or after brushing, but the thermal treatments caused an increase in C=C conversion, microhardness, and elastic modulus without affecting the translucency parameter or showing visible color alteration (ΔE00<1.8). These results suggest that the use of additional thermal methods of polymerization represents an economical and simple alternative to enhance the mechanical and chemical properties of direct resin composites when used as indirect restoratives.

Highlights

One of the major goals in the restorative dentistry is the development of low-cost procedures with high clinical success rates and durability, low complexity and predictable results
Experimental Design In this in vitro study, a physical and chemical characterization of a light-cured resin composite indicated for direct restorations (TPH3; Dentsply, Konstanz, Germany, shade B2) was performed according to different polymerization protocols: light-activation only, light-activation followed by heating in dry oven, light-activation followed by heating in autoclave, and light-activation followed by heating in microwave oven
The results of the present study provide evidence that the additional thermal treatments tested here applied to a direct resin composite may lead to significant gains in C=C conversion and mechanical properties

Summary

Introduction

One of the major goals in the restorative dentistry is the development of low-cost procedures with high clinical success rates and durability, low complexity and predictable results. The indirect method involves the manufacture of a restoration outside the mouth using a gypsum or silicone mold obtained from an oral impression This indirect technique allows to optimize the physical-mechanical and chemical properties of the polymeric materials by performing their polymerization under controlled conditions and without the generation of polymerization stresses [4]. Indirect resin composites are light-polymerized using strobe lights, sometimes under vacuum, associated with heat generation [5] This means that special equipment is necessary and that the costs are higher. These polymerization conditions are associated with an increase in the degree of C=C conversion, which might result in improved physical and mechanical properties, color stability, and wear resistance [6,7]

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