B

Reasoning: In a typical endosseous dental implant, the visible top portion is the crown, which is secured to an underlying abutment screw; this screw passes through the separate abutment that seats on the fixture (implant body) embedded in bone. This top-to-bottom order exactly matches option B (1 = crown, 2 = abutment screw, 3 = abutment, 4 = fixture) [Sim et al., 2017, PMID 29065610; Laney et al., 1986, PMID 3945114].