Effect of adhesion to cavity walls on the mechanical properties of resin composites

Nayif, Ma’an M.; Nakajima, Masatoshi; Aksornmuang, Juthatip; Ikeda, Masaomi; Tagami, Junji

doi:10.1016/j.dental.2007.02.008

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Volume 24, Issue 1 , Pages 83-89, January 2008

Effect of adhesion to cavity walls on the mechanical properties of resin composites

Ma’an M. Nayif
- Cariology and Operative Dentistry, Department of Restorative Science, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-Ku, Tokyo 113-8549, Japan
- Corresponding author. Tel.: +81 5803 5483; fax: +81 3 5803 0195.
Masatoshi Nakajima
- Cariology and Operative Dentistry, Department of Restorative Science, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-Ku, Tokyo 113-8549, Japan
Juthatip Aksornmuang
- Department of Prosthetic Dentistry, Faculty of Dentistry, Prince of Songkhla University, Hat Yai, Songkhla 90112, Thailand
Masaomi Ikeda
- Cariology and Operative Dentistry, Department of Restorative Science, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-Ku, Tokyo 113-8549, Japan
Junji Tagami
- Cariology and Operative Dentistry, Department of Restorative Science, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-Ku, Tokyo 113-8549, Japan
- Frontier Research on Molecular Destruction and Reconstruction of Tooth and Bone, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-Ku, Tokyo 113-8549, Japan

Received 10 August 2006; accepted 15 February 2007.

Abstract

Objectives

To evaluate the regional mechanical properties of resin composite under free and constrained conditions during polymerization.

Methods

Forty cavities (8mm diameter and 5mm depth) were fabricated in resin blocks. Half of the cavities were bonded and the other half left un-bonded. The cavities were bulk-filled with one of the following composites: flowable composite (Palfique Estelite LV, Unifil Lo Flo), and Universal composites (Clearfil AP-X, Palfique Estelite Σ), followed by photo-curing for 30s. After 24h storage, each specimen was sliced parallel to the long axis to harvest three slabs. The middle slab was serially sliced to harvest five sticks, which were trimmed to an hour-glass shape for measurement of regional ultimate tensile strength (UTS). The remaining semi-circular slabs were polished for microhardness measurement (KHN). Data were analyzed using three-way ANOVA followed by Tukey's HSD test and t-test (α=.05).

Results

The KHNs of all the resin composites were not significantly different between the bonded and unbonded groups at each cavity depth (p>0.05). The UТS of the bonded group of flowable composites was significantly lower than those of the un-bonded group at the upper regions (p<0.05), while for universal composites, there were no significant differences in UTS between the bonded and un-bonded groups (p>0.05), although Clearfil AP-X had a trend toward lower UTS under the constrained condition at the upper regions.

Significance

The UTS of resin composite decreases due to polymerization shrinkage stress when polymerized under a constrained condition, however, these effects were dependent upon regions in the cavity and the resin materials.

Keywords: Polymerization shrinkage, Resin composite, Ultimate tensile strength, Microhardness, Adhesion