Association of salivary viscosity, intraradicular bacterial profile, and healing outcomes after nonsurgical endodontic retreatment: a prospective cohort study

Abstract This study aimed to evaluate the association between salivary viscosity, intraradicular bacterial prevalence, and healing outcomes following nonsurgical endodontic retreatment. Fifty-six patients with asymptomatic apical periodontitis associated with mandibular molars undergoing endodontic retreatment were enrolled. Salivary viscosity was measured using a digital viscometer, and intracanal bacterial species were identified using the VITEK 2 system. Clinical and cone-beam computed tomography (CBCT) assessments were performed at baseline and after 6 and 12 months. Salivary viscosity was analyzed as a continuous predictor of treatment outcomes, whereas bacterial prevalence was compared descriptively between lower and higher viscosity groups using the study-specific median. No significant differences in bacterial prevalence were observed between the lower and higher viscosity groups after false discovery rate correction (all adjusted p > 0.05). The overall 12-month treatment success rate was 88.0% (44/50). Higher salivary viscosity was independently associated with lower odds of treatment success (adjusted OR = 0.68, 95% CI: 0.43–0.90; p < 0.001). In the linear mixed-effects model, higher salivary viscosity was associated with reduced lesion volume reduction (β=−1.92, 95% CI: −3.15 to − 0.70; p = 0.003), and the significant viscosity × time interaction (β=−2.29, 95% CI: −3.42 to − 1.16; p < 0.001) indicated that this negative association became more pronounced over time. Higher salivary viscosity was independently associated with less favorable clinical and radiographic healing following endodontic retreatment, whereas bacterial prevalence did not differ significantly after correction for multiple comparisons.