Early radiographic response after root canal treatment in type 2 diabetes and low vitamin D status: a prospective cohort study

Type 2 diabetes mellitus (DM) and low vitamin D status (LVD) may influence periapical disease, but their relationship with early radiographic response after root canal treatment (RCT) remains uncertain. This prospective observational cohort included 473 adults classified as control ( n = 119), DM ( n = 119), LVD without DM ( n = 122), or DM with LVD ( n = 113). Participant-level treatment need was determined clinically and radiographically. Among 151 treated-tooth records from 133 participants, 132 records from 118 participants had 6-month radiographs. Participant-level treatment need was higher in the DM and DM + LVD strata than in the control and LVD strata, whereas the two diabetes strata did not differ after Holm correction. A Periapical Index (PAI) decrease of at least one category occurred in 20/26 control, 19/25 DM, 32/45 LVD, and 23/36 DM + LVD records ( p = 0.651). Complete early radiographic resolution (PAI = 1) occurred in 19/26 (73.1%), 7/25 (28.0%), 41/45 (91.1%), and 10/36 (27.8%), respectively ( p < 0.001); the two diabetes strata did not differ. In an exploratory participant-clustered analysis, each 1% higher baseline glycated haemoglobin was associated with lower odds of PAI = 1 at 6 months (odds ratio 0.44, 95% confidence interval 0.28–0.67). This association remained in analyses additionally adjusted for age and sex and when records lost to follow-up were classified as non-resolution. The independent effect of vitamin D could not be determined because supplementation was initiated after enrolment in most participants with low baseline vitamin D. Trial registration: Clinical Trials Registry-India, CTRI/2025/05/087830; registered on 28/05/2025. Recruitment began in June 2025, after registration.