Effect of tooth preparation design on fracture load and fracture behavior of deciduous crowns fabricated by subtractive and additive manufacturing

Abstract Objectives This study evaluated the effects of crown material and margin design on fracture load and behavior of computer-aided design/computer-aided manufacturing (CAD-CAM) crowns for deciduous molars. Methods Three subtractive-manufacturing (SM) materials and two additive-manufacturing (AM) materials were evaluated. Crowns with knife-edge, chamfer, and deep chamfer margins were fabricated and bonded to standardized deciduous molar abutments ( n = 12/group; total = 180). Fracture load was measured under static loading, and fracture modes were classified by repairability and abutment involvement. Fracture surfaces and crack propagation were examined by scanning electron microscopy. Results Significant effects of material and material–margin interactions were observed ( p < 0.05). ESTELITE BLOCK II exhibited the highest fracture load with knife-edge margins, whereas Detax showed the highest values with deep chamfer margins. However, non-repairable abutment-involving fractures occurred in both materials with knife-edge margins. CERASMART PRIME showed lower fracture load but mainly repairable fractures. SHOFU BLOCK HC and CERASMART PRIME, unified crown–abutment fracture in ESTELITE BLOCK II, interlayer delamination in Detax, and superficial radial cracking in NextDent. Conclusions The effects of margin design on fracture load and fracture behavior were material-dependent. Among subtractive-manufacturing materials, fracture load was generally consistent with reported mechanical properties, whereas fracture behavior in additive-manufacturing materials may have been influenced by internal structure and build orientation. Material selection should consider fracture load, fracture severity, and abutment involvement. Clinical relevance Material and margin selection influence fracture resistance and failure patterns. Fracture severity and abutment involvement should be considered in addition to fracture load.