The critical apical diameter to obtain regeneration of the pulp tissue after tooth transplantation, replantation, or regenerative endodontic treatment.

Introduction: Regeneration of pulp-like tissue in the pulp chamber after tooth transplantation, replantation, or in regenerative endodontic treatment is only possible if the apical foramen is open. According to the literature, the success of regeneration decreases considerably if the foramen is smaller than 1 mm when measured on radiographs. The aim of this study was to study histologically the relation between the width of the apical foramen and regeneration of tissue in the pulp chamber after autotransplantation.

Methods: Fifteen single-rooted mature teeth of 3 adult beagle dogs were used. All experimental teeth were extracted and underwent apicoectomy. The teeth were photographed from the apical side, and the width of the foramen was calculated. The foramen width ranged from 0.24-1.09 mm. All teeth were replanted in infraocclusion. The observation period was 90 days after transplantation.

Results: The 10 teeth with the smallest apical diameter, ranging between 0.24 and 0.53 mm, showed vital tissue in at least one third of the pulp chamber. The 6 most successful teeth showing vital tissue in the entire pulp chamber had an apical diameter between 0.32 and 0.65 mm, and 80% of the experimental teeth with a diameter varying between 1.09 and 0.31 mm showed vital tissue in at least one third of the pulp chamber 90 days after transplantation.

Conclusions: The size of the apical foramen seems not to be the all decisive factor for successful revascularization and ingrowth of new tissue after transplantation. The minimum width of the apical foramen has not been determined, but a size smaller than 1 mm does not prevent revascularization and ingrowth of vital tissue. In this animal study an apical foramen of 0.32 mm did not prevent ingrowth of new tissue in two-thirds of the pulp chamber 90 days after transplantation.