Influence of composite restorative materials and light-curing units on diametrical tensile strength

Abstract

The aim of this study was to evaluate the diametrical tensile strength (DTS) of three light-curing photo-activated composites with two different light curing units (LCU). Three types of dental restorative composites were used in this study: micro filled A110 (3M Espe); P60 (3M Espe) for posterior restorations, and micro-hybrid Charisma (Heraeus-Kulzer). The two LCUs were: halogen light (HAL) (Degulux, Degussa) and blue light emitting diode (LED) (Ultrablue, DMC). Resin composite specimens were inserted incrementally into a Teflon split mold measuring 3 mm in depth and 6 mm in internal diameter, and cured using either LCU (n = 10). Specimens were placed into a dark bottle containing distilled water at 37 degrees C for 7 days. DTS tests were performed in a Universal Testing Machine (0.5 mm/min). Data were submitted to two-way ANOVA and Tukey's test. Results were (MPa): A110/HAL: 276.50 +/- 62.94a; A110/LED: 306.01 +/- 65.16a; P60/HAL: 568.29 +/- 60.77b and P60/LED: 543.01 +/- 83.65b; Charisma/HAL: 430.94 +/- 67.28c; Charisma/LED: 435.52 +/- 105.12c. Results suggested that no significant difference in DTS was obtained with LCUs for the same composite. However, resin composite restorative materials presented different DTS.

Diametral tensile strength of composite resins submitted to different activation techniques

“…An important milestone in the history of modern restorative dentistry was the development of light-cured composite resins for direct procedures 1,7,9,14 . Improvements in composite resin mechanical properties and light curing devices have permitted their use in posterior teeth with greater reliability than was the case some years ago 1,3,7,9 .…”

“…Specifically, addition of heat may improve physical diametral tensile properties 13,15 , compressive and flexural strengths 15 , wear resistance, hardness 13 , and polymerization conversion 6,8 . Achieving adequate depth of cure of radiation-activated polymers is important to ensure optimal mechanical properties of the restoration 1,4,[13][14]16 . Thus, the physical properties of the resin are enhanced and the effects of polymerization shrinkage are minimized 10 .…”

“…On the other hand, there are problems related to the chemistry of cured composite, particularly to the degree of conversion and cross-linking density 2,11,16 . It may be influenced by many factors including chemical structure of the monomers, light illumination time and intensity needed to activate polymerization, and filler composition 1,14,16 . Investigation into the effect of post-curing on the properties of dental materials would be beneficial for the development of restorative dental materials.…”

“…Filler content, filler particle size and distribution of the filler particles all highly influence the physical and mechanical properties of the composite materials 2,4,11,14,16 . Manufacturers have increased the filler content and reduced the average filler particle size to produce resin-based composite materials for Class II posterior restorations, which need adequate strength and wear resistance to withstand masticatory forces to which they are subjected 9,14,16 .…”

“…Manufacturers have increased the filler content and reduced the average filler particle size to produce resin-based composite materials for Class II posterior restorations, which need adequate strength and wear resistance to withstand masticatory forces to which they are subjected 9,14,16 . These posterior resin-based composites have basically the same chemistry and physical characteristics, however the cure conditions still are the most important difference between them.…”