## 4 Discussion
An excessive taper may result in reduced retention, cement failure, and pulp devitalization, whereas an inadequate taper jeopardizes the structural durability, esthetics, and existing occlusion [31]. The present study was carried out to compare the retention of the preparation with 10\({}^{\circ}\) and 20\({}^{\circ}\) tapers. It was found that the crowns with the 20\({}^{\circ}\) taper had superior retention. The results from our study showed a higher mean pull-off retentive force (49.77 N) in group 3,i.e., milled crowns with 20-degree taper cemented with non-eugenol cement, than in group 1, i.e., milled crowns with 10-degree taper cemented with non- eugenol (43.01 N). The mean pull-off force (N) was significantly less for group 2, i.e., milled crowns with 10-degree taper and cemented with clear cement (43.57 N), than for group 4, i.e., milled crowns with 20-degree taper and cemented with clear cement (60.77 N). Comparisons between groups 5 (49.47 N) and 7(65.48 N) and between groups 6 (158.38 N) and 8 (178.74 N) also highlighted similar findings with higherentive forces for the 20-degree taper. Research carried out by [PERSON] et al. [18] evaluated the retention of full crowns prepared with three different tapers and cemented with two conventional and two adhesive resin cements. The retentive values of crowns cemented with adhesive resin and the 24\({}^{\circ}\) taper were 20% higher than those cemented with the conventional cement and the 6\({}^{\circ}\) taper. A study carried out by [PERSON] et al. reflected that that a minimum taper of 5\({}^{\circ}\) was required to corroborate the absence of undercuts during preparation. However, in clinical investigations, an average taper of 22\({}^{\circ}\) was achieved, showing no correspondence to theoretical recommendations. This study concluded that a taper of 5\({}^{\circ}\) is difficult to achieve clinically [32]. Many studies conducted in the past quote the favorability of a greater degree of taper, since it is more likely to resist lateral dislodging forces than parallel forces. Many dentists prefer making preparations with taper values over 20\({}^{\circ}\)[33; 34; 35]. Our results contradicted the results reported by [PERSON] et al. on cement lute stress. These authors found the highest stress fields in crowns cemented on abutments having 5 mm height and prepared with 30\({}^{\circ}\) taper, while the lowest stress fields were found in abutments having 5 mm height and prepared with 10\({}^{\circ}\) taper. They concluded that a lower taper of 10\({}^{\circ}\) is more biomechanically acceptable than a higher taper of 30\({}^{\circ}\)[36]. According to studies, the marginal fit and internal adaptation are better with 3D-printed temporary crowns than those prepared using the milled technique [37; 38]. The retention difference between crowns prepared with 10- and 20-degree tapers can be explained by the fact that CAD/CAM crowns, whether milled or 3D printed, have better internal adaptation and marginal fit at increased tapers, especially when crowns are cemented [39]. [PERSON] et al. concluded that the internal adaptation of the 20-degree convergence angle group exhibited statistically smaller internal spaces than those of the 6-degree convergence angle group, regardless of the computer-fixed cement space. These findings would indicate that the internal spaces are reduce as the convergence angle of abutments is increased [40]. [PERSON] et al. showed that temporary cement dissolution was significantly affected by thermal cycling for both cements used in the study, despite the fact that Temp-Bond clear cement was less affected than Temp-Bond NE conventional temporary cement. The improved marginal fit of the crown prepared with the 20-degree taper may have shielded the clear temporary cement from aging during thermal cycling, thus maintaining the physical and mechanical properties of the cement and resulting in the highest retention in comparison with the other groups [41].