Molecular Changes of Buccal Alveolar Bone After Tooth Extraction

Objectives: We previously found that tooth extraction during adolescence reduces buccal alveolar bone surface growth. This study evaluated post-extraction changes in molecular expression and histomorphometry of intracortical bone of the buccal plate.
Methods: Six 3-5 month-old domestic pigs underwent extraction of a mandibular deciduous second molar. Buccal alveolar bone was collected from extraction and contralateral non-extraction (control) sites 2-hours (n=3) or 6-weeks (n=3) after extraction. Specimens harvested from the distal-buccal region were frozen in liquid nitrogen, pulverized, and processed for RNA extraction, which was subsequently quantified for expression of sclerostin (SOST), osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) using real-time PCR with B-actin normalization. Specimens from the middle-buccal region were decalcified, sectioned, and stained with H&E, and then used to quantify histomorphometric parameters including bone volume fraction (BV/TV), trabecular thickness (TbTh), trabecular number (TbN), and trabecular separation (TbSp). Differences between extraction and control sites were compared using paired t-tests or Wilcoxon tests depending on normality of data distribution. Pearson correlation was conducted to assess the association between SOST expression and BV/TV.
Results: SOST expression was significantly lower at the extraction site compared to the control site 6 weeks after extraction (paired t-test, p=0.017). Histomorphometrically, no significant differences were found between extraction and control sites in either the 2-hour or 6-week groups, but there was a trend indicative of greater bone density at the extraction site 6 weeks after extraction. Moderate but insignificant correlation was found between SOST expression and BV/TV (Pearson correlation, r=-0.519, p=0.291).
Conclusions: Decreased SOST expression together with unchanged RANKL/OPG expression at the buccal bone of a 6-week post-extraction site suggests a likely upregulation of intracortical bone formation as reflected by a pattern of increased intracortical bone density. There may be a compensatory change intracortically in response to decreased growth at the extraction-site buccal bone surface.