The ideal angle for preparing the gingival bevel is 30° because this angle allows for optimal enamel rod exposure, enhancing the bond strength of restorative materials. A 30° bevel ensures a conservative tooth structure removal while providing a smooth, well-defined margin that facilitates better marginal adaptation and reduces microleakage. Sharper bevels (less than 30°) may cause excessive enamel prism cutting, whereas larger bevels (>30°) can remove unnecessary tooth structure, compromising tooth integrity. Thus, a 30° bevel balances mechanical retention and esthetic outcomes efficiently.

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