Bilateral molar extraction during growth is associated with impaired masticatory performance and reduced hippocampal BDNF and TrkB immunoreactivity in juvenile rats

Abstract

Background: Bilateral molar extraction during growth produces severe posterior occlusal deprivation and may impair mastication while altering oral sensorimotor input relevant to hippocampal function. Brain-derived neurotrophic factor (BDNF) and tropomyosin receptor kinase B (TrkB) contribute to hippocampal plasticity. Objective: To compare masticatory performance and hippocampal BDNF and TrkB immunoreactivity between juvenile rats with intact dentition and rats undergoing bilateral extraction of all maxillary and mandibular molars, and to explore pooled associations among these outcomes. Methods: Twenty-four juvenile male Wistar rats were enrolled; 17 reached the endpoint (control, n = 9; extraction, n = 8). Masticatory performance was measured using a granulometric masticatory performance index (MPI). BDNF and TrkB immunoreactivity in CA1, CA3, and dentate gyrus were assessed immunohistochemically. Between-group differences were analyzed using Welch t tests, 95% confidence intervals, and Hedges' g. Pooled associations were examined using Pearson correlations. Results: The extraction group showed lower MPI (0.241 ± 0.043 vs 0.566 ± 0.044), BDNF scores (3.42 ± 0.64 vs 6.74 ± 1.52), and TrkB H-scores (86.86 ± 12.76 vs 180.73 ± 22.55); all p < 0.001. Pooled MPI correlated positively with BDNF (r = 0.783) and TrkB (r = 0.899), both p < 0.001, although these associations may largely reflect between-group separation. Conclusion: Bilateral molar extraction during growth was associated with impaired food comminution and lower hippocampal BDNF and TrkB immunoreactivity. These exploratory correlations do not establish mediation, within-group biological relationships, or causality. Attrition, absence of sham controls, and unmeasured postoperative confounding limit mechanistic interpretation in this model.

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