Impact of Auxiliary Features on Retention of Short Dental Crowns: An In-Vitro Analysis of Box and Groove Preparations.

BACKGROUND Several auxiliary features have been proposed to achieve sustainable retention for short-prepared dental crowns; however, achieving retention is challenging. This study aimed to assess the impact of increased total occlusal convergence and auxiliary preparation factors like box and groove on the retention form of short tooth preparations. MATERIAL AND METHODS Eighty resin machine-milled dies with a height of 3 mm and a deep chamfer margin of 1 mm were prepared to mimic the short-prepared molar. Initially, 2 teeth were prepared following the guidelines, and the total occlusal convergence was kept at 10° and 20°, respectively. Auxiliary features such as the proximal box and buccal groove were prepared on separate 20° dies. Eighty dies were prepared with 10 samples each for 10°, 20°, 20° with proximal box and 20° with buccal groove for zirconia (n=40) and metal crowns (n=40). Cementation was done with glass ionomer luting cement, and a pull-off test was conducted. Data were analyzed using one-way analysis of variance and post hoc fisher least significant difference test (P<0.05). RESULTS The highest mean was observed in the proximal box group with the metal crown (14.59), and the lowest in the group with 20° zirconia crowns (9.12). Within groups, the highest retentive values were found for the 20° taper with proximal box preparation; the lowest was for the 20° taper group. CONCLUSIONS Within the study limitations, it could be concluded that incorporating a proximal box or buccal groove in short tooth preparations with an increased total occlusal convergence improved retentive values.

Evaluation of the Milled and Three-Dimensional Digital Manufacturing, 10-Degree and 20-Degree Preparation Taper, Groove and Box Auxiliary Retentive Features, and Conventional and Resin-Based Provisional Cement Type on the Adhesive Failure Stress of 3 mm Short Provisional Crowns.

BACKGROUND This study evaluated the effects of milling (CADCAM), 3D printing, preparation taper angles (10-degree and 20-degree), auxiliary retentive features (groove and box), and provisional cement types (conventional and resin-based) on the adhesive failure stress of 3-mm short provisional crowns (PC). The research was motivated by the need to understand how digital dentistry technologies impact the retention and durability of provisional crowns. MATERIAL AND METHODS A total of 160 working models (3D-printed) and PCs [80 milled (CopraTemp)/80 printed (Asiga)] were fabricated from two 10- and 20-degree typodont master models and two 20-degree 3D-printed master models (groove and box), simulating a 3 mm high all-ceramic short PC. After provisional cementation with conventional (Kerr TempBond) and resin-based (ProviTemp) cements, 16 subgroups (n=10 each) underwent thermocycling (10 000 cycles; 5-55°C) and pull-off tests on a universal testing machine. Statistical analysis was performed using one-way ANOVA and post hoc Tukey test. RESULTS Conventional cement failed at lower stress for milled (47.68 to 73.54) and printed (48.40 to 77.91) as compared to resin cement for milled (104.2 to 137.27) and printed (184.85 to 328.84), respectively, with significant differences. Increased taper and groove decreased failure load except for the printed PC/resin cement combination. Use of proximal box preparation increased retention significantly. Except for 20-degree taper cemented with conventional cement, the differences in auxiliary retentive features for milled and printed provisional crowns were statistically significant at P≤0.05. CONCLUSIONS 3D-printed PC, resin-based cement, 10-degree taper, and proximal box preparation were associated with higher retention than milled, conventional cements, 20-degree taper, and vertical groove.