## 3 Results  
The mean fracture strength for all the tested groups is summarized in Table 1. The Mean fracture resistance for LD ceramic endocrowns at 2 mm occlusal thickness was 62.55 MPa, while at 4.5 mm thickness it was reduced to 45.80 MPa. The 2 mm radicular extension for 4.5 mm occlusal thickness LD ceramic endocrowns showed the improved fracture resistance at 74.27 MPa. The PIC endocrowns displayed the least fracture resistance in comparison to other tested groups. PIC endocrowns fracture resistance for varying occlusal thickness of 2 mm, 4.5 mm and 2 mm radicular extension recorded 26.30 MPa, 21.65 MPa, and 25.66 MPa respectively. HTZ endocrowns showed moderate fracture resistance across all the groups. 2 mm occlusal thickness recorded the fracture resistance of 23.47 MPa, 4.5 mm occlusal thickness of 27.30 MPa. However, a 2 mm radicular extension showed an enhanced fracture resistance of 37.29 MPa. A One-way ANOVA (Table 2) was conducted to compare the effect of occlusal thickness and radicular extension on the fracture resistance of endocrowns fabricated from different all-ceramic materials. ANOVA analysis of variance showed that the effect of preparation design on fracture resistance was significant in LD ceramic endocrowns, F (2, 27) = 81.806, \(p\) = 0.000. Similar significant difference in fracture resistance was recorded with PIC ceramic, F (2, 27) = 30.289, \(p\) = 0.000 and Monolithic zirconia, F (2, 27) = 75.824, \(p\) = 0.000. The Shapiro-Wilk test for normality showed the p-values 0.06, 0.322 and 0.009 for LD, PIC and HTZ ceramics respectively; indicating normal distribution of data. Tukey HSD post hoc multiple comparison tests (Table 3) showed the significant difference between the majority of material fracture resistance except between 2 mm occlusal thickness and radicular extension groups from PIC ceramic with \(p\) = 0.597. The different types of failure types are presented in Table 4. The lithium silicate at with 2 mm thickness showed predominantly debonded favorable failures, while the increased thickness of 4.5 mm and radicular extension led to increased unfavorable failure with root fractures ranging from 80%-100%. Largely favorable fractured occurred \begin{table}
\begin{tabular}{c c c c c} \hline
**Group** & **Occlusal Thickness (mm)** & **N** & **Mean** & **SD** \\ \hline \multirow{3}{*}{Lithium disilicate} & 2 mm & 10 & 62.55 & 5.14 \\  & 4.5 mm & 10 & 45.80 & 5.91 \\  & Radicular extension & 10 & 74.27 & 3.67 \\ \hline \multirow{3}{*}{Polymer infiltrated ceramic} & 2 mm & 10 & 26.30 & 1.57 \\  & 4.5 mm & 10 & 21.65 & 1.41 \\  & Radicular extension & 10 & 25.66 & 2.51 \\ \hline \multirow{3}{*}{High Translucency Zirconia} & 2 mm & 10 & 23.47 & 1.45 \\  & 4.5 mm & 10 & 27.30 & 1.40 \\ \cline{1-1}  & Radicular extension & 10 & 37.29 & 4.00 \\ \hline \end{tabular}
\end{table} 
Table 1: Descriptive statistics of the mean fracture resistance at maximum load (MPa) recorded in the different groups. Figure 3: Fractured teeth specimens to evaluate the failure mode. explored the feasibility of endocrowns on premolar teeth, especially with greater occlusal thickness. The samples in the study were exposed to thermocycling and lateral occlusal loading to simulate the clinical condition [30]. The simulated lateral occlusal load is more unfavourable to resin bonding interfaces than axial loading [31]. The null hypothesis investigated was, where the endocrowns in various occlusal thickness and a radicular extension fabricated from different all-ceramic would not influence the fracture resistance. The results of the present study showed the endocrowns with radicular extension had higher mean fracture resistance; the endocrowns fabricated from LD ceramic displayed higher mean fracture resistance. Hence, both null hypotheses were rejected. Our study has shown that the LD Ceramic endocrowns with significantly higher mean fractured resistance compared to PIC ceramic and HTZ endocrowns. The normal biting force at the premolar region is recorded at 222-445 N [32].