B

Highly virulent bacterial species invade dentinal tubules more aggressively, overcome pulpal defenses and cause tissue breakdown far faster than less‐virulent or commensal organisms; experimental studies show that conventional (infected) teeth develop pulp necrosis rapidly, whereas germ-free teeth or those exposed to low-virulence strains progress much more slowly or heal (Nishioka 1998, PMID 9796480; Matsui 2015, PMID 26171605).