## 3 Results  
The resultant stress distributions for the models were compared and examined. By way of these materials exhibit a brittle mechanical behavior [10], First Principal Stress was designated as analysis criterion. Figure 4 displays the first principal stress distributions for enamel, dentin and restorative shrinking and no shrinking material for class I, and, Figure 5 illustrates first principal stress distributions for enamel, dentin and restorative material for class II models following the occlusal and transversal loading in combination with shrinkage result. Additional quantitative results were detected by inspection line, defined laterally to the cavity wall. Looking at the cross section, first principal stresses were planned along the inspection patch and compared for the diverse models as previously reported [28; 29]. All the class II MO (D, E and F models in Figure 5) restorations displayed high stress concentration close to the occlusal surfaces, in comparison with class II MO (A, B and C models). However, regardless the cavity design, the models exhibited a similar stress trend along enamel-restoration interfaces. The highest stress values in the restoration, were located nearby the top corner of the dentin-enamel interface (Figure 4) and on the occlusal surfaces. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Material**} & \multicolumn{2}{c}{**Modulus of Young**} & \multirow{2}{*}{**Poisson Ratio**} & \multicolumn{1}{c}{**Linear Shrinkage**} \\  & **(GPa)** & & **(\%)** \\ \hline Dentin & 18.0 & 0.30 & – \\ \hline Enamel & 80.0 & 0.30 & – \\ \hline Food apple pulp & 3.4 & 0.1 & – \\ \hline Adhesive layer & 4.0 & 0.30 & 1.0 \\ \hline Flowable composite & 8.0 & 0.25 & 1.0 \\ \hline Glass inomer & 8.0 & 0.25 & – \\ \hline Bulk fill composite & 12.0 & 0.25 & 1.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Materials Mechanical properties: modulus of Young, Poisson ratio and linear shrinkage. Figure 3: Boundary conditions applied in the present simulation. Irrespective the cavity design, models A and B (Figures 4 and 5) exhibited a similar stress tendency along dental tissues and restoration interface as well models D and E. A different stress trend was observed in models C and F along dental enamel and restoration interface while the stress declines with depth along the dentine and restoration interface and have a tendency to zero at the cavity floor (Figures 4 and 5). For class I cavity, in Figure 4 it is evident the modification of stress distribution internally between models A and C. In model C, where no shrinking material has been replicated in the deepest 1.5 mm layer, while in model A, the highest stress was concentrated in the restoration. The same difference we found in class II (Figure 5) for internal stress distribution among model D and F. Model F, where no shrinking material has been imitated in the deepest 1.5 mm layers, while in model D, the highest stress was concentrated in the enamel. Figure 4: Global contour plots of each restorative procedure First principal stress (MPa) in a class I cavity: (**A**) Bulk-fill composite, (**B**) Flowable composite + Bulk-fill composite and (**C**) Glass-Ionomer + Bulk-fill composite. The stress trend was plotted in Figure 5 and the stress peaks in enamel tissue, dentin tissue and restoration are summarized in Table 3.  
The lowest stress magnitude in enamel was calculated in 9.0 MPa when class I design has been restored with glass-ionomer cement (no shrinking) associated with bulk-fill resin composite (Model C). However, this value increased 209% when the cavity has been prolonged to a class II and the material was the Bulk-fill resin composite (23.3 MPa). The same behavior can be observed in dentin tissue, comparing the lowest stress peak of 2.3 MPa for class I restored with glass-ionomer cement (no shrinking) associated with Bulk-fill composite with class II and the Bulk-fill composite (18.9 MPa), almost 87.93% lower stress for the first situation (Figures 6 and 7).