PSI - Issue 28

Vesela Hristova et al. / Procedia Structural Integrity 28 (2020) 1002–1009 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Objelean et al. (2016). However, this system of monomers results in increased water absorption and increased polymerization shrinkage. Therefore, a new combination of UDMA (Urethane dimethacrylate) and Bis-EMA (Bisphenol A polyethethylene glycol diether dimethacrylate) has been developed to replace TEGDMA (Objelean et al. (2016). This new system of monomers is of higher molecular weight, provides lower polymerization shrinkage and better properties, but increases the viscosity of the composite. All these features of the composition of dental composites, together with the use of pre-polymerized (pre-polymers) particles, lead to an increase in their mechanical properties and biocompatibility, to a decrease of shrinkage and to an improvement of aesthetic properties (Schmidt C. and Ilie N. (2012), Objelean et al. (2016). I.P. Ichim et.al. (2007-1) have used two techniques in their study for filling of V-shaped defects on the buccal surface – placement of the whole amount of the GIC at once and incremental technique in application of the GIC and the composite material. The tests have shown that the restorative materials used are unsuitable for treatment of non carious cervical lesions because they have comparatively high modulus of elasticity E=10.2 GPa. It is stated that the optimal material for cervical restorations should be more flexible with relatively low E – about 1 Gpa. Two types of flowable composites are used in the work of May S. et.al. (2017) for treatment of V-shaped tooth defects. Fifty patients, participating in the investigations, are treated with the two composites. The results are monitored in 18 and 36 months and 95.8% success rate for 36 months is shown. Zhang Y et.al. (2016) investigate the effect of the low shrinkage Filtek TM P90 composite on the repair of the cervical defects. In the study 52 people are involved, who have at least 2 lesions of bilateral teeth recovered. One tooth is restored with Filtek TM P90 and the other bilateral tooth in the control group - with Filtek TM Z350 XT . After 1 year, the results have shown higher success rate of 94.05% in the first group comparing with 90.48% in the control group. In vitro experiments are targeted mainly to investigation microleakage of cervical lesions filled with GIC (Sahu et al. (2018), Singla et al. (2012), Gupta et al. (2012), Hakimeh et al. (2000). The information about the microleakage of obturations of V-shaped defects, made with composite restorative materials is relatively low (Poggio et al (2012), Nematollahi et al. (2017). The aim of the present paper is to study the microleakage of V-shaped defects, filled with restorative materials of different groups - auto-cured RMGIC, flowable photo-cured composite (FPC) and universal nanohybrid photo-cured composite (UPC). A total number of 36 permanent teeth (incisors, canines and premolars) were used in the study. They were chosen by the following criteria: 1) premolars with no caries, extracted for orthodontic purposes; 2) incisors and canines, extracted due to periodontal problems. After extraction, the teeth were stored in the saline until the study was conducted. Their surfaces were very well cleaned of residual biological tissue and tartar. To exclude preliminary cracks, fractures and other defects, the teeth were examined under a microscope. V-shaped defects with average sizes 2.5 mm length, 2.5 mm width and 1.3 mm depth were then made along the vestibular surface of the teeth in the area of the enamel-cement border (Dikova et al. (2020). The teeth were divided into three groups of 12 teeth in each. Restorative materials of three groups were used in the repair of the cavities – RMGIC, FPC and UPC (Table 1). Before application of the filling materials, all cavities were treated according to the instructions, given in the operating manuals. Dental auto-cured resin-modified glass-ionomer cement FUJI VIII GP (GC Corporation, Tokyo, Japan ) was used for restoration of the cavities in Group I. At first, the cavity was wiped with a cotton tuft, soaked in 3% hydrogen peroxide water, next – with a cotton tuff, soaked in 70% alcohol, and dried. GIC was applied in one portion using a back spatula and smoothed against the cavity walls. Flowable photo-cured composite with lower viscosity Estelite Flow Quick - High Flow (Tokuyama Dental Corporation inc., Japan) was applied in the cavities of Group 2 . Firstly, all of the cavities were etched with 37% orthophosphoric acid solution for 40 s, after which they were thoroughly washed with a water-air jet. The adhesive Adhese Universal (Ivoclar Vivadent AG, Liechtenstein) was applied all over the enamel and dentin surfaces of the 2. Materials and methods 2.1. Samples preparation