Calcium hydroxide is considered the best choice for direct pulp capping in young permanent teeth because it has a high pH, which provides an antibacterial effect and promotes formation of a dentin bridge by stimulating odontoblast-like cell activity. Its ability to induce hard tissue barrier formation helps preserve pulp vitality and encourages healing. Although Mineral Trioxide Aggregate (MTA) is also effective, Calcium hydroxide remains the standard due to its long history of success and ease of use. Glass ionomer cement and zinc oxide eugenol lack the bioactive properties necessary for pulp healing.

Reference: Sturdevant's Art and Science of Operative Dentistry, 7th Edition.