Abstract
Greater understanding and acceptance of the new concept “bone quality”, which was proposed by the National Institutes of Health and is based on bone cells and collagen fibers, are required. The novel protein Semaphorin3A (Sema3A) is associated with osteoprotection by regulating bone cells. The aims of this study were to investigate the effects of mechanical loads on Sema3A production and bone quality based on bone cells and collagen fibers around implants in rat maxillae. Grade IV-titanium threaded implants were placed at 4 weeks post-extraction in maxillary first molars. Implants received mechanical loads (10 N, 3 Hz for 1800 cycles, 2 days/week) for 5 weeks from 3 weeks post-implant placement to minimize the effects of wound healing processes by implant placement. Bone structures, bone mineral density (BMD), Sema3A production and bone quality based on bone cells and collagen fibers were analyzed using microcomputed tomography, histomorphometry, immunohistomorphometry, polarized light microscopy and birefringence measurement system inside of the first and second thread (designated as thread A and B, respectively), as mechanical stresses are concentrated and differently distributed on the first two threads from the implant neck. Mechanical load significantly increased BMD, but not bone volume around implants. Inside thread B, but not thread A, mechanical load significantly accelerated Sema3A production with increased number of osteoblasts and osteocytes, and enhanced production of both type I and III collagen. Moreover, mechanical load also significantly induced preferential alignment of collagen fibers in the lower flank of thread B. These data demonstrate that mechanical load has different effects on Sema3A production and bone quality based on bone cells and collagen fibers between the inside threads of A and B. Mechanical load-induced Sema3A production may be differentially regulated by the type of bone structure or distinct stress distribution, resulting in control of bone quality around implants in jaw bones.
Highlights
Dental implants are constantly subject to mechanical loads such as masticatory and swallowing forces via superstructures
To investigate the net effect of mechanical load on bone around implants, mechanical repetitive load was initiated at 3 weeks post-implant placement, as implants are fully integrated into bone at 3 weeks post-implantation in rat maxillae [29]
We demonstrated that mechanical repetitive load had different effects on Sema3A production and bone quality around implants between inside threads A and B
Summary
Dental implants are constantly subject to mechanical loads such as masticatory and swallowing forces via superstructures. Mechanical stresses concentrate on the marginal bone around dental implants [1], suggesting that the maintenance of marginal bone levels for the long-term is important for successful clinical outcomes. To determine the effects of mechanical stimulation on bone around dental implants, finite element analyses have been mainly used [2,3,4]. Some studies have reported the effects on the jaw bone around implants using occlusal forces [5, 6]. Animal studies using controlledmechanical stimuli are absolutely required to clarify the net effect of mechanical loads on jaw bone reactions around implants
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