Influence of metal-ceramic crown preparation geometry on adhesive stress during orthodontic headgear force application

<h2>Abstract</h2><h3>Background</h3> This study used finite element analysis to assess how crown preparation height (short, normal, long) and tapering (6°-24°) affect prosthetic crown retention under orthodontic and biting forces, measured by von Mises stress in the cement layer. <h3>Methods</h3> Models with 3 occlusocervical heights and tapering from 6° through 24° were subjected to orthodontic loads (2, 5, 10 N) and simulated bite forces (vertical or oblique 280 N). <h3>Results</h3> Under orthodontic loads, the long crown with 6° tapering showed the least stress at lower forces; a 12° taper was best at 10 N. The short crown with 6° taper consistently had the highest stress. Under vertical bite force, the long crown with 6° tapering had the least stress, whereas the normal crown with 24° tapering had the most. Under oblique bite force, the normal crown with 12° tapering had the least stress, and the long crown with 24° tapering had the most. Stress under orthodontic loads showed no consistent correlation with height or taper but increased with greater tapering under bite force. <h3>Conclusions</h3> Optimal crown design depends on force type. Long crowns performed best under vertical bite forces but worst under oblique forces. Normal crowns showed the opposite pattern. Stress distribution varies with loading conditions.