The influence of free-radical concentration on the shear bond strength of dental composites

Abstract

The aim of this study was to evaluate the influence of the free-radical concentration on the shear bond strength between a composite resin and self-adhesive composite cement. Filtek ultimate flowable restorative composite was used for the thin layer samples, which were analyzed using electron paramagnetic resonance (EPR). Rely-X-Unicem cement was applied to the disc-shaped samples and the shear bond strength and failure modes were analysed at weekly intervals. The concentration of the free radicals dropped to 10 % after 24 h. A value for the degree of conversion equal to 74±2 % was achieved after 2 d. The shear bond values were in the range from 25.5±3.7 MPa to 9.8±4.3 MPa for four groups of samples, measured in four different time intervals. A high concentration of free radicals ensures reliable chemical bonding with a freshly applied cement in group 1, while in the samples of group 2 (7 d), group 3 (14 d) and group 4 (21 d of recombination in water), the potential of the free radicals was diminished. Keywords: composite resin, free radicals, electron paramagnetic resonance, degree of conversion, shear bond strength, adhesion properties Namen raziskave je bil prou~iti vpliv koncentracije prostih radikalov na mo~vezave med kompozitom in samostrjujo~im se kompozitnim cementom. Kompozit Filtek ultimate flowable restorative smo uporabili za pripravo vzorcev v tanki plasti za meritve koncentracije prostih radikalov z elektronsko paramagnetno resonanco (angl. EPR). Na kompozitne diske smo nanesli kompozitni cement Rely-X-Unicem in v tedenskih intervalih merili mo~vezave med obema materialoma. Koncentracija prostih radikalov se je v 24 urah zmanj{ala na 10 % za~etne koncentracije. Stopnja konverzije (DC) se je po dveh dneh ustalila pri 74±2 %. Mo~vezave med obema kompozitoma je bila v obmo~ju med 25,5±3,7 MPa in 9,8±4,3 MPa za {tiri skupine vzorcev. Visoka koncentracija prostih radikalov zagotavlja dobro kemi~no vezavo s sve`e dodanim kompozitnim cementom, medtem ko je vpliv koncentracije prostih radikalov po (7, 14 in 21) dneh rekombinacije zanemarljiv. Klju~ne besede: kompozit, prosti radikali, elektronska paramagnetna resonanca, stopnja konverzije, stri`na trdnost, adhezijske lastnosti

The Effect of Touch-Cure Polymerization on the Conversion and Hardness of Core Build-Up Resin Composites: A Laboratory Study

“…It has been postulated that surface grinding may increase the degree of conversion in resin composites by the thermal activation of residual C=C bonds [23]. The influence of this effect in the current experiment was negligible because the measurements were obtained after 3 weeks of storage at 37 • C, a period exceeding the shelf-life of free radicals available for any further polymerization [24]. The improved setting of the self-cured specimens in contact with the adhesive (SA-B group) documented by the ATR technique (2 µm analytical depth) extended into 30 µm (IIT indentation depth) as confirmed by the Martens hardness measurements.…”

Adhesion of Conventional, 3D-Printed and Milled Artificial Teeth to Resin Substrates for Complete Dentures: A Narrative Review

“…Diffusion depends on time, temperature, type of solvent and the structure and glass transition point of the polymer [33]. Because denture teeth are pre-polymerized, the chemical co-polymerization that could create an interconnected polymer network with any denture base material is difficult, since free-radical concentration is very low [34]. Moreover, the adhesion of denture base resin to denture teeth has been explained through the involvement of unreacted methyl-methacrylate groups, which in cold-cured materials cannot be proven because the remaining double bonds do not react at room temperature [35].…”