Which option correctly lists the mesiodistal length, labiolingual width, and incisal-apical depth for a crescent rest?

Which option correctly lists the mesiodistal length, labiolingual width, and incisal-apical depth for a crescent rest?

• A. 2.0-2.5 mm; 1.0 mm; 1.0 mm
• B. 3.0-3.5 mm; 2.0 mm; 2.0 mm
• C. 4.0-4.5 mm; 1.0 mm; 0.5 mm
• D. 2.5-3 mm; 1.5 mm; 1.5 mm

Answer: (D)

A crescent rest needs three dimensions that define how it sits on the tooth: length along the tooth (mesiodistal), width across the tooth (labiolingual), and vertical depth from the incisal edge toward the root (incisal-apical). You want enough mesiodistal length to engage the proximal surface and share occlusal loads without overextending beyond margins; about 2.5–3 mm achieves stable contact while preserving enamel. The labiolingual width should be sufficient to give the crescent its strength without crowding or encroaching on adjacent tissues; 1.5 mm fits well for a robust, correctly contoured rest. The incisal-apical depth needs to be enough to seat the rest properly and maintain contour without reaching the pulp or harming gingival tissues; 1.5 mm provides that safe, functional depth. This combination—2.5–3 mm, 1.5 mm, and 1.5 mm—best balances retention, strength, and preservation of tooth structure, whereas other options either under- or over-dimension one or more axes, compromising function or safety.

A crescent rest needs three dimensions that define how it sits on the tooth: length along the tooth (mesiodistal), width across the tooth (labiolingual), and vertical depth from the incisal edge toward the root (incisal-apical). You want enough mesiodistal length to engage the proximal surface and share occlusal loads without overextending beyond margins; about 2.5–3 mm achieves stable contact while preserving enamel. The labiolingual width should be sufficient to give the crescent its strength without crowding or encroaching on adjacent tissues; 1.5 mm fits well for a robust, correctly contoured rest. The incisal-apical depth needs to be enough to seat the rest properly and maintain contour without reaching the pulp or harming gingival tissues; 1.5 mm provides that safe, functional depth. This combination—2.5–3 mm, 1.5 mm, and 1.5 mm—best balances retention, strength, and preservation of tooth structure, whereas other options either under- or over-dimension one or more axes, compromising function or safety.