## 4 Discussion  
Fluoride release from dental materials is possible by diffusion of set ions in a wet environment. To this effect it is important to take into account the materials capacity to sustain water diffusion without having an excessively high water sorption [6]. [PERSON] et al. [7] stated that in addition to water sorption, partial removal of polymeric chains from the resin matrix of polymerized composites can also influence fluoride release capacity [9] very important because of its biocompatibility [28]. Fluoride release mostly takes place during the first week, through an acid-base reaction on the surface of the pre-reacted glass particles [9]. In the current study it was determined that the experimental gomer G released 1.87 ppm of fluoride after the first day, 0.766 ppm after a week and 0.307 ppm fluoride after 30 days. The gomer B-F03 released 3.1 ppm fluoride after the first day, 0.442 ppm after the first week and 0.242 ppm fluoride after 30 days. [PERSON] et al. found that the commercial gomer Beautiful Flow Plus F03, A2 color, released 1.0020 ppm of fluoride after the first day, 0.4140 ppm after the first week and after four weeks 0.3165 ppm of fluoride. The differences between materials may be due to the size of the samples, material batches and the sensitivity of the devices used for analyses [9]. High performance liquid chromatography (HPLC) is considered to be the most performant technique for determining the type and quantity of residual monomers released by composite resins. By HPLC technique, the non-polar compounds were eluted from the matrix of the composite resin, separating the components in the order of their hydrophobic properties. Dissolution of the monomers in the mobile phase leads to a more controlled separation [29]. Residual monomers were released from the polymeric matrix through the process of diffusion, depending on their hydrophobicity, molecular weight and flexibility of the polymer. TEGDMA is lighter and has a higher mobility when compared to the more rigid Bis-GMA molecule, and as a consequence was released in a higher amount from the matrix [30]. Depending on the storage solution, hydrophilic structures will be attracted to a watery environment, whereas an organic medium will be more accessible to hydrophobic particles. The diffusion of the storage liquid into the micro-pores of the resin matrix will lead to a progressive expansion of the pores and swelling of the polymeric matrix. The degree of swelling is also influenced by the rigidity and reticulation of the polymeric matrix. It is important that the quantity of residual monomers released to be as low as possible, ensuring a complete polymerization of the material. [PERSON] and [PERSON] stated that 85-100% percent of the residual monomer is released during the first 24 h [31]. Other literature data suggests also that a higher quantity of TEGDMA is eluted during the first 24 h after setting, and a lower quantity after one month [31]. In their study, [PERSON] et al. reported that Beautiful Bulk restorative gomer has a flexural strength of 106.0 \(\pm\) 12.7 MPa, the quantity of the inorganic filler (87 filler wt%) being reflected in the mechanical properties. ISO standard 4049 does not specify an inferior limit for the elasticity module that is in direct relation to the restoration material deformation when under the action of masticatory forces [32]. The current study found that gomer B-F00 (67.3 filler wt%) has a flexural strength of 114.83 \(\pm\) 15.45 MPa, even though the filler quantity is lower than that of a bulk fill gomer [10]. Also, the study of [PERSON] et al. [26], found that Beautiful II has a flexural strength of 115.7 MPa and the experimental gomers, 89.2-108.8 MPa. The experimental gomer (60 filler wt%), that has Bis-GMA and TEGDMA in the resin matrix, registered a value of 98.822 \(\pm\) 13.02 MPa for the flexural strength. [PERSON] and al.