# Evaluation of Proximal Contact Tightness and Contact Area of Posterior Composite Resin Restorations
## 4 Discussion  
In this study, different matrix systems and techniques used to create approximal contacts in Class II posterior RBC restorations were tested. For this purpose, a novel in vitro device was designed to measure the approximal contact tightness of Class II RBC restorations. To ensure the validity of this model, techniques similar to those applied by [PERSON] et al. in a randomized clinical trial and an in vitro experiment were used [20,21]. Although the tested hypothesis was that the contact tightness obtained would be equal for all groups, in light of the findings, this hypothesis (h0) was rejected because there were statistically significant differences between the groups. In general, it is known that contour and approximal contact are the most important factors in preventing food impaction, tooth migration, periodontal complications, and caries [14,22]. While pre-shaped (contoured) matrix bands contribute to a better anatomical contour of approximal restorations, it is known that the flat matrix bands used in traditional matrices are insufficient to create contact [18,23]. In this in vitro study, Class II restorations were implanted with a traditional technique (environmental matrix system and wooden wedge), a modified sectional matrix (sectional matrix ring, band, and wooden wedge), and a modern sectional matrix system (separation ring, anatomical band, and wedge). The degree of contact and contact tightness obtained by applying composite resin restorations to Class II approximal cavities were compared. A tighter contact and better histogram results were obtained in the PM matrix with an anatomical matrix band and the OM matrix groups using a traditional wedge compared to the traditional ivory matrix (Group IM). This result is supported by the results of the studies conducted by [PERSON] et al., [PERSON] et al., and [PERSON] et al. [24, 25, 26]. However, when the effect of fixing the anatomical matrix band with an anatomical wedge or a wooden (traditional) wedge was examined, the contour obtained with the \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Matrix Type** & \multicolumn{4}{c}{**Cavity Design**} \\ \hline  & **Class II (OM)** & **Class II (OD)** & **Class II (MOD)** & & \\  & **Mesial** & **Distal** & **Mesial** & **Mesial** & **\(p\)** \\ \hline
**Palodent Plus** & 96.692  & 81.142  & 91.852 & 84.423 & 0.147 \\
**(PM)** & (7.11) & (3.47) & (8.25) & (5.67) & \\
**OmniMatrix** & 102.041  & 102.748 & 95.741 & 88.892 & \\
**(OM)** & (6.20) & (9.41) & (8.81) & (9.96) & \\
**Ivory Matrix** & 111.913  & 110.948 & 101.265 & 92.046  & 0.236 \\
**(IM)** & (25.06) & (16.95) & (15.08 & (11.17) & \\
**Control** & 109.355 & 102.411 & 109.355 & 102.411 & \\
**(18.29)** & (15.81) & (18.29) & (15.81) & \\ \hline \hline \(p\)** & 0.068 & 0.047  & 0.095 & 0.247 & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Histogram results from the study (pixel density). anatomical wedge was found to be closer to the natural form of the dental tissue. In addition, in restorations where an anatomical wedge was used, extrusion and irregularities at the interface occurred less often. In this study, both contact tightness and contour values were better in the sectional matrix group, where anatomical bands and wedges were used, than in the other groups. It can be claimed that when there is less protrusion and irregularity at the interface, smoothing and polishing with sandpaper causes less material loss. Studies in the literature are consistent with the results of this research [27; 28; 29; 30]. There are also studies showing that finishing and polishing processes performed on approximal surfaces with interface sanding may cause changes in the surface of composite restorations and affect the contact and contour [31; 32]. In this study, immediately after the RBCs' were made, dry sanding and polishing were carried out for 40 s with composite interface sandpapers with four different grain thicknesses.