The Hollow Tube Theory in Endodontics: Historical Origins, Experimental Refutation and Contemporary Clinical Legacies

Abstract

The hollow tube theory occupies an unusual position in endodontic history. Formulated from early implant experiments in the 1930s, it proposed that an unfilled, non-vital root canal could sustain periapical inflammation because tissue fluids entering and stagnating within an open tubular space became irritating when they diffused back into adjacent tissues. Although subsequent experiments failed to confirm that an empty sterile tube was intrinsically pathogenic, the theory helped consolidate an enduring clinical emphasis on complete obturation and the ‘hermetic seal’. This critical narrative review reconstructs the theory’s intellectual origins, evaluates the evidence that displaced it, and examines its continued influence on contemporary reasoning about disinfection, leakage, obturation, treatment outcome and regenerative endodontics. Literature was selected through live searches of PubMed/MEDLINE, Directory of Open Access Journals, Semantic Scholar and accessible scholarly records, supplemented by citation chaining and verification against DOI and journal records. The evidence indicates that the theory was refuted as a causal biological explanation: empty or sterile tubes generally permitted connective-tissue repair or ingrowth, whereas infected necrotic canals reproducibly induced apical disease. Modern histobacteriology and molecular microbiology further show that persistent disease is usually related to residual or secondary intraradicular infection, with less frequent contributions from extraradicular infection, foreign-body reactions or lesion-specific factors. Nevertheless, the hollow tube concept survives indirectly whenever radiographic density, laboratory leakage or the elimination of every visible void is treated as a biological endpoint rather than a technical surrogate. Contemporary clinical studies do not establish consistent superiority of one obturation technique or material when adequate infection control, apical containment and coronal restoration are achieved. Regenerative procedures provide the clearest conceptual inversion: a disinfected canal deliberately left without conventional obturation can support tissue ingrowth when an appropriate scaffold and coronal barrier are provided. The historical lesson is therefore not that obturation is dispensable, but that its biological purpose must be defined by microbial control, ecological exclusion and prevention of reinfection rather than by fear of an empty space itself.