Effect of Abutment Preparation Designs Influencing Retention in Short Clinical Crowns Receiving All-ceramic Complete Veneer Restoration

Aim: To evaluate the effect of seven abutment preparation designs influencing retention in short clinical crowns. Materials and methods: About 140 extracted human first mandibular premolars were collected and allocated into seven groups, each receiving experimental tooth preparations for all-ceramic complete veneer crowns, viz. group I: conventional method using medium grit diamonds only, group II: conventional method using tungsten carbide burs only, group III: conventional method using coarse grit diamonds only, group IV: conventional design with an additional axioproximal groove of 0.5 mm, group V: conventional design with an additional buccal and lingual groove of 0.5 mm, group VI: conventional design with axioproximal grooves and occlusal isthmus, and group VII: conventional design with pin holes in the buccal and lingual cervicoaxial line angles. The prepared abutments were laser scanned to receive all-ceramic restorations using a computer-aided design and computer-aided manufacturing (CAD/CAM) milling machine and were subjected to uniaxial tensile force in the universal testing machine at a 1 mm crosshead speed, until the crown dislodged from the abutment. The corresponding values were calculated, and the same process was repeated after luting with resin cement. The data were recorded and statistically analyzed. Result: The least retention in terms of tensile strength was observed in group I (conventional tooth preparation) with 52.86 ± 1.45 N/m² and 150.14 ± 1.04 N/m² before and after luting. The maximum retention was observed in group VI (tooth preparation done incorporating axioproximal grooves with occlusal isthmus) with 78.06 ± 1.81 N/m² and 187.62 ± 1.24 N/m² before and after luting. ANOVA and post hoc tests inferred a highly statistically significant difference between all the experimental groups, both before (F = 2054.9, p < 0.001) and after luting (F = 2397.35, p < 0.001). Conclusion: The abutment design incorporating the axioproximal grooves with occlusal isthmus showed the greatest retention in short abutments, followed by preparation with coarse grit diamond, both before and after luting with resin cement. Clinical significance: The modified abutment designs enhance the retention and stability of the restoration, potentially reducing the risk of dislodgment or failure in short clinical crowns. This reduces the need for crown lengthening and osteoplasty in short clinical abutments.