Pyk2 deficiency enhances bone mass during midpalatal suture expansion

Objective To determine if Pyk2 deficiency increases midpalatal suture bone mass and preserves sutural integrity after maxillary expansion. Setting and Sample Thirty‐six male Pyk2 knockout (KO) and control (WT) mice at 6 weeks of age. Materials and Methods Mice received nickel‐titanium spring expanders delivering 0 g (no intervention control), 10 or 20 g force for 14 days. High‐resolution micro‐CT was used to determine bone volume/tissue volume (BV/TV), sutural width and intermolar width. Effects on osteoclasts, chondrocytes and suture morphology were determined by histomorphometry. Results Pyk2‐KO controls (0 g) had 7% higher BV/TV compared with WT controls. Expanded Pyk2‐KO maxillae also exhibited 12% (10 g) and 18% (20 g) higher BV/TV than WT mice. Although bone loss following expansion occurred in both genotypes, BV/TV was decreased to a greater extent in WT maxillae (−10% at 10g; −22% at 20 g) compared with Pyk2‐KO maxillae (−11% only at 20 g). Expanded WT maxillae also showed a greater increase in sutural width, intermolar width and fibrous connective tissue width compared with expanded Pyk2‐KO maxillae. Moreover, osteoclast number was increased 77% (10 g) and 132% (20 g) in expanded WT maxillae, but remained unchanged in expanded Pyk2‐KO, compared to their respective controls. Cartilage area and chondrocyte number were increased to the same extent in expanded WT and Pyk2‐KO sutures. Conclusions These findings suggest that midpalatal suture expansion increases osteoclast formation in WT but not Pyk2‐KO mice, leading to higher BV/TV in expanded Pyk2‐KO maxillae. These studies suggest Pyk2‐targeted strategies may be beneficial to increase bone density and preserve sutural integrity during maxillary expansion.