# Evaluation of Proximal Contact Tightness and Contact Area of Posterior Composite Resin Restorations
## 1 Introduction  
The general purpose of treatments applied in restorative dentistry is to replace lost tooth tissues in accordance with their anatomical and physiological characteristics [1]. In these treatments, modern dentits have a wide range of direct and indirect restoration techniques to choose from [2]. When resin-based composites (RBC) are chosen as the materials in direct restorations, they have almost unlimited indication options, especially in small and mild lesions [3]. RBCs' can be applied in most cases, whereas the cavity boundaries change and widen due to caries lesion progression. In addition, they can be applied successfully even in more conservative or minimally invasive treatments with minimum material loss and do not need a standard cavity preparation such as amalgam or ceramic restorations [4; 5]. However, the biggest disadvantage of all RBCs' is polymerization shrinkage, which occurs after the applied RBC is cured with the light device, causing the material to lose its volume [6; 7]. Considering that there is a natural gap of 5-20 microns between teeth, this shrinkage can create a significant problem in terms of \"contact\", especially in cavities reaching the approximal sides [7]. In addition, in technically critical situations suchas cavities with deep margins or excessive tissue loss, the application stages of composite resins make it difficult to give an appropriate \"contour\" and directly affect the success of the restorations [8]. An inadequate contact or contour will lead to food impaction between the relevant teeth and indirectly to periodontal diseases and secondary caries [9]. For these reasons, it is important to create a suitable contact area between the tooth to be restored and the adjacent tooth to prevent these situations, which are the common cause of patient complaints [10]. In restorative dentistry, circumferential matrices (Tofflemire) and Ivory matrices have been used since the 1950s in the restoration of Class II cavities reaching the approximal surfaces [11; 12]. The most common reasons for choosing these matrices are their affordability, ease of application, and firm stability when adapted to the tooth [11]. However, in some cases, this practice results in the tooth's dimensions being narrower and reduced in length and width than its ideal shape [13]. In addition, as a result of the compression of the matrix bands during fixation, the slope of the bands flattens and their contact with the side teeth decreases. As a result of the fixation process applied to the healthy side, an incorrect separation can occur, and the relevant tooth comes closer to the adjacent tooth in the area to be restored [12; 14]. The narrowing of the contact area, combined with the polymerization shrinkage of the RBC, will cause an \"open contact\" problem in the restoration area. To overcome these problems, pre-anatomically shaped matrices, defined as \"Sectional Matrices\", have been developed [15]. Generally, they are used with a separation ring that separates the teeth and stabilizes the matrix coronally, supporting the formation of a suitable contact area [15; 16]. Unlike traditional matrices, these \"passively placed\" separation rings positioned in the area of the tooth to be restored will not cause a reduction in the size of the tooth. Because this passive placement is sufficient to stabilize the matrix both vertically and coronally, it prevents the formation of an incorrect contour (concave), especially in the buccal and lingual regions [16; 17]. In addition, the feet (retainer arms) of the separation ring separate the restoration area from the adjacent tooth, increasing the field of view and essentially making a separation in the right direction [17]. In this way, it is possible to create a tighter contact area between the tooth, which returns to its natural position at the end of the restoration, and the adjacent tooth. The anatomical contour of the tooth, in addition to the contact, prevents food retention and the formation of triangular dead areas [18].