IADR Abstract Archives
Local Biomechanics Regulate Mineralization and Structural Organization of Bone-Periodontal Ligament-Tooth Complex
Objectives: To map and correlate biochemical expressions at the periodontal ligament (PDL)-bone and PDL-cementum interfaces as a result of local shifts in biomechanics of the bone-periodontal ligament (PDL)–tooth complex
Methods: Hemimaxillae were harvested from 6-week-old rats and scanned at no load and loaded conditions using an in situ loading device coupled to a micro-X-ray computed tomography. The movement of the tooth relative to the alveolar socket was digitally extracted using a tether model approach. Mineral formation and resorption were captured using assays describing osteoblastic (alkaline phosphatase-ALP; bone sialoprotein-BSP) and osteoclastic (tartrate resistant acid phosphatase-TRAP) activities. The ultrastructural localization of matrix molecules was studied using a transmission electron microscope with and without immunolocalization of BSP.
Results: Rather than the traditional tension and compression, tether model indicated an increased shear strain within the distal buccal region of tooth roots. This region was characterized by TRAP+ resorption pits, suggesting an active resorption process at the respective interfaces of the complex. Higher ALP activity was observed near the crestal region of the interradicular bone compared to PDL-cementum interfaces. This indicated mineral deposition is mainly associated with interradicular bone-PDL interface. However, BSP was immunolocalized at mineral forming and resorbing sites of the complex.
Conclusions: The tether model is promising as indicated by its ability to correlate macroscale biomechanics to microscale biochemical expressions within the complex. Physiological loads from mastication contribute to strain gradients within the PDL. Natural shifts in strain gradients trigger a cascade of biochemical events, and over time, these matrix-related changes can be associated with systematic mineralization of the matrix (BSP was observed at the formation and resorption sites) at tethered ends where PDL interfaces with bone and cementum. Strain-dependent progressive mineral formation and resorption at a microscale is critical for maintenance of macroscale biomechanics of the bone-PDL-tooth fibrous joint.
Methods: Hemimaxillae were harvested from 6-week-old rats and scanned at no load and loaded conditions using an in situ loading device coupled to a micro-X-ray computed tomography. The movement of the tooth relative to the alveolar socket was digitally extracted using a tether model approach. Mineral formation and resorption were captured using assays describing osteoblastic (alkaline phosphatase-ALP; bone sialoprotein-BSP) and osteoclastic (tartrate resistant acid phosphatase-TRAP) activities. The ultrastructural localization of matrix molecules was studied using a transmission electron microscope with and without immunolocalization of BSP.
Results: Rather than the traditional tension and compression, tether model indicated an increased shear strain within the distal buccal region of tooth roots. This region was characterized by TRAP+ resorption pits, suggesting an active resorption process at the respective interfaces of the complex. Higher ALP activity was observed near the crestal region of the interradicular bone compared to PDL-cementum interfaces. This indicated mineral deposition is mainly associated with interradicular bone-PDL interface. However, BSP was immunolocalized at mineral forming and resorbing sites of the complex.
Conclusions: The tether model is promising as indicated by its ability to correlate macroscale biomechanics to microscale biochemical expressions within the complex. Physiological loads from mastication contribute to strain gradients within the PDL. Natural shifts in strain gradients trigger a cascade of biochemical events, and over time, these matrix-related changes can be associated with systematic mineralization of the matrix (BSP was observed at the formation and resorption sites) at tethered ends where PDL interfaces with bone and cementum. Strain-dependent progressive mineral formation and resorption at a microscale is critical for maintenance of macroscale biomechanics of the bone-PDL-tooth fibrous joint.
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