What should be avoided during the preparation of a molar for an onlay to ensure effective adhesion?

When preparing a molar for an onlay, ensuring the proper design of the margins is crucial for effective adhesion. A well-designed margin allows for better mechanical locking and a smooth transition between the tooth structure and the restorative material, which is essential for maximizing adhesive strength.

Proper margin design involves creating a surface that is not only contourally advantageous but also free of irregularities and allows for optimal seating of the onlay. If the margins are not designed correctly, it can hinder the bond between the onlay and the tooth, increasing the risk of microleakage, postoperative sensitivity, and ultimately failure of the restoration.

In contrast, uneven tooth surfaces, excessive occlusal reduction, and insufficient tooth structure can all present their own challenges, but they do not directly address the issue of margin design’s critical role in adhesion efficacy. Uneven surfaces can affect seating but are not inherently a margin design issue. Excessive reduction may predispose the tooth to fracture but does not compromise adhesion due to margin specifics. Insufficient tooth structure can make placement challenging yet is also a separate concern from the specific aspect of achieving effective adhesion through well-designed margins.