The Influence of Bonding System Type on Strength Properties of Reconstructed Teeth with 1st Class Cavities According to Black’s Classification

The paper presents the results of strength tests of lateral teeth with 1 class cavities reconstructed with various bonding systems, i.e. selfand selective bonding systems as well as for filling with additional etching with orthophosphoric acid. In all cases a nano-hybrid, lightcured composite material was used in a layered (sandwich) cavity filling processing. The strength tests were done with the use of Instron 4465 strength machine for loadings simulating the features of proper lateral teeth occlusion. The analyses of the results were done with respect to the following quantities: ultimate force, total displacement and work to fracture. The results were compared with reference ‘healthy’ lateral teeth group. Analysis of the results proves that the type of bonding system has a significant effect on the values of individual strength parameters of the tested tooth samples. From the mechanical point of view the best results were obtained for selfand selective bonding system when comparing with additional etching procedure. However, regardless on the type of bonding system, the mechanical properties of teeth subjected to dental treatment are significantly lower than those for the ‘healthy’ teeth. Introduction Adhesion is the basic physical phenomenon that determines the success of composite crown fillings in contemporary conservative dentistry [1]. Phenomenon of adhesion consisting in the combination of surface-contact layers of two bodies in a solid or liquid phase combines with the mechanical, polarizing, diffusive and adsorptive theories of the mutual interaction of two bodies. Close contact of the contacting bodies is necessary for the formation of the adhesion phenomenon the distance between the bodies should be smaller than 1 2 Å (10 – 20 nm) – Fig. 1a. In practice, achieving such a low distance between solid bodies is difficult to achieve. Therefore, in order to obtain adhesion forces, a liquid photo polymerized material is used to wet the substrate. This material, called a bonding system, acts as an intermediate adhesive layer and provides better connection with dental fillings. The bonding systems have been developed over years. The differences between all generations of bonding systems are significant. Development of materials and techniques have changed the bonding systems themselves as well as their adhesive properties and strength [2]. In general, adhesion is determined by the value of the unitary adhesion forces or the work necessary to separate the adherent bodies, however various physical quantities are used to quantify that phenomenon between hard tissues of tooth (i.e. dentine and enamel) and dental composite filling material. The aim of the work was to determine the strength properties of reconstructed lateral tooth crowns with the use of various bonding systems. Experimental Mechanics of Solids Materials Research Forum LLC Materials Research Proceedings 12 (2019) 155-158 https://doi.org/10.21741/9781644900215-22 156 Materials and Methods Black’s scale is the most often used classification in contemporary conservative dentistry. It is based on the tooth type and the cavity location or tooth surfaces involved. Black’s scale consists of (I – VI) classes [1]. The first class cavities are located in pits or fissures of crowns, mainly in the occlusal surfaces of molars and premolars as well as in the lingual surfaces of upper incisors, and occasionally in the lingual surfaces of upper molars – Fig. 1b. Fig. 1. SEM image of adhesive layer between dentine and composite filling material (a); scheme of 1 class cavity according to Black’s classification (b) and tooth crown cavity preparation after endodontic treatment ready for final reconstruction (c) The tests were done for 15 samples lateral teeth after extraction for orthodontic reasons. All teeth were prepared for the 1 class cavities according to Black's classification. The teeth were randomly divided into three reconstructive groups (5 samples in each group): I teeth reconstructed with self-bonding system that does not require additional etching procedure, II – reconstruction with additional etching with orthophosphoric acid, III – teeth reconstructed with the use of a selective-etching bonding system – Fig. 2. All teeth-samples were prepared under a supervision of a dentist and were done with standard dental treatment procedures. A nanohybrid, light-cured composite material was used in the reconstruction of all teeth crowns, which were worked out with layered (sandwich) cavity filling processing [1, 3]. Fig. 2. Set of tooth samples with crowns reconstructed with the use of various bonding systems The tests were done with the use of Instron 4465 strength machine for loadings simulating the features of proper teeth occlusion. As there is no standardized method of strength tests of tooth crowns a compression test with a steel ball that is used instead of an opposing tooth was applied. The method was proposed and developed in [4, 5, 6]. The following quantities were registered and analyzed: ultimate force Fc , work to fracture Wc , total displacement uc . The results of the 1 Class